U.S. patent application number 14/468296 was filed with the patent office on 2014-12-11 for servo feedback control based on designated scanning servo beam in scanning beam display systems with light-emitting screens.
The applicant listed for this patent is Prysm, Inc.. Invention is credited to Roger A. Hajjar.
Application Number | 20140362300 14/468296 |
Document ID | / |
Family ID | 42108442 |
Filed Date | 2014-12-11 |
United States Patent
Application |
20140362300 |
Kind Code |
A1 |
Hajjar; Roger A. |
December 11, 2014 |
Servo Feedback Control Based on Designated Scanning Servo Beam in
Scanning Beam Display Systems with Light-Emitting Screens
Abstract
Scanning beam display systems that scan one servo beam and an
excitation beam onto a screen that emits visible light under
excitation of the light of the excitation beam and control optical
alignment of the excitation beam based on positioning of the servo
beam on the screen via a feedback control.
Inventors: |
Hajjar; Roger A.; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Prysm, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
42108442 |
Appl. No.: |
14/468296 |
Filed: |
August 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14052513 |
Oct 11, 2013 |
8814364 |
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14468296 |
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12643623 |
Dec 21, 2009 |
8556430 |
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14052513 |
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PCT/US2008/068679 |
Jun 27, 2008 |
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12643623 |
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11769580 |
Jun 27, 2007 |
7878657 |
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PCT/US2008/068679 |
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Current U.S.
Class: |
348/744 |
Current CPC
Class: |
G01J 3/513 20130101;
G02B 26/105 20130101; G03B 21/60 20130101; G02B 26/123 20130101;
G02B 26/127 20130101; G02B 26/101 20130101; G02B 26/12 20130101;
G03B 21/567 20130101; G01J 3/506 20130101; H04N 9/3135
20130101 |
Class at
Publication: |
348/744 |
International
Class: |
H04N 9/31 20060101
H04N009/31; G02B 26/12 20060101 G02B026/12; G01J 3/50 20060101
G01J003/50; G02B 26/10 20060101 G02B026/10 |
Claims
1. A scanning beam display system, comprising: an excitation light
source to produce at least one excitation beam having optical
pulses that carry image information; a servo light source to
produce at least one servo beam at a servo beam wavelength that is
invisible; a beam scanning module to receive the excitation beam
and the servo beam and to scan the excitation beam and the servo
beam; a light-emitting screen positioned to receive the scanning
excitation beam and the servo beam and comprising a light-emitting
area which comprises (1) parallel light-emitting stripes which
absorb light of the excitation beam to emit visible light to
produce images carried by the scanning excitation beam, and (2)
stripe dividers parallel to and spatially interleaved with the
light-emitting stripes with each stripe divider being located
between two adjacent stripes, each stripe divider being optically
reflective; an optical servo sensor positioned to receive light of
the servo beam scanning on the screen including light reflected by
the stripe dividers and to produce a monitor signal indicative of
positioning of the servo beam on the screen; and a control unit
operable to, in response to the positioning of the servo beam on
the screen in the monitor signal, adjust timing of the optical
pulses carried by the scanning excitation beam based on a relation
between the servo beam and the excitation beam to control the
spatial alignment of spatial positions of the optical pulses in the
excitation beam on the screen.
Description
PRIORITY CLAIM AND RELATED PATENT APPLICATION
[0001] This patent document is a continuation of and claims
priority to U.S. patent application Ser. No. 14/052,513 entitled
"Servo Feedback Control Based on Designated Scanning Servo Beam in
Scanning Beam Display Systems with Light-Emitting Screens" filed
Oct. 11, 2013, which is a continuation of U.S. patent application
Ser. No. 12/643,623 entitled "Servo Feedback Control Based on
Invisible Scanning Servo Beam in Scanning Beam Display Systems with
Light-Emitting Screens" filed Dec. 21, 2009, and is a continuation
of and claims priority to International Application No.
PCT/US2008/068679 entitled "Servo Feedback Control Based on
Designated Scanning Servo Beam in Scanning Beam Display Systems
with Light-Emitting Screens" and filed Jun. 27, 2008, which
designates U.S. and claims priority from U.S. patent application
Ser. No. 11/769,580 entitled "Servo Feedback Control Based on
Invisible Scanning Servo Beam in Scanning Beam Display Systems with
Light-Emitting Screens" and filed on Jun. 27, 2007. The disclosures
of these applications are incorporated by reference as part of the
specification of this document.
BACKGROUND
[0002] This patent application relates to scanning-beam display
systems.
[0003] In a scanning-beam display system, an optical beam can be
scanned over a screen to form images on the screen. Many display
systems such as laser display systems use a polygon scanner with
multiple reflective facets to provide horizontal scanning and a
vertical scanning mirror such as a galvo-driven mirror to provide
vertical scanning. In operation, one facet of the polygon scanner
scans one horizontal line as the polygon scanner spins to change
the orientation and position of the facet and the next facet scans
the next horizontal line. The horizontal scanning and the vertical
scanning are synchronized to each other to project images on the
screen.
SUMMARY
[0004] This patent application describes, among others,
implementations of display systems and devices based on scanning
light on a light-emitting screen under optical excitation. The
described display systems use light-emitting screens under optical
excitation and at least one excitation optical beam to excite one
or more light-emitting materials on a screen which emit light to
form images. Servo control mechanisms for such display systems are
described based on a designated servo beam that is scanned over the
screen by the same scanning module that scans the image-carrying
excitation optical beam. This designated servo beam is used to
provide servo feedback control over the scanning excitation beam to
ensure proper optical alignment and accurate delivery of optical
pulses in the excitation beam during normal display operation. In
some implementations, multiple lasers can be used to simultaneously
scan multiple excitation laser beams on the screen. For example,
the multiple laser beams can illuminate one screen segment at a
time and sequentially scan multiple screen segments to complete a
full screen.
[0005] In one implementation, a scanning beam display system
includes a light module to direct and scan at least one excitation
beam having optical pulses that carry image information and at
least one servo beam at a servo beam wavelength different from a
wavelength of the excitation beam; a screen positioned to receive
the scanning excitation beam and the servo beam and comprising a
light-emitting layer of parallel light-emitting stripes which
absorb light of the excitation beam to emit visible light to
produce images carried by the scanning excitation beam, the screen
configured to reflect light of the servo beam towards the light
module to produce servo feedback light; and an optical servo sensor
module positioned to receive the servo feedback light and to
produce a servo feedback signal indicative of positioning of the
servo beam on the screen. The light module is responsive to the
positioning of the servo beam on the screen in the servo feedback
signal to adjust timing of the optical pulses carried by the
scanning excitation beam to control the spatial alignment of
spatial positions of the optical pulses in the excitation beam on
the screen.
[0006] As an example, the screen in the above system can include
servo feedback marks that have facets facing the excitation light
source that are specularly reflective to light of the servo beam,
and areas outside the servo feedback marks that are diffusively
reflective to light of the servo beam. In this example, the system
includes a Fresnel lens located between the screen and the light
module to direct the scanning servo beam and excitation beam to be
at a substantially normal incidence to the screen. The Fresnel lens
has an optic axis symmetrically in a center of the Fresnel lens to
be parallel to and offset from an optic axis of the light module to
direct light of the servo beam that is specularly reflected by a
servo feedback mark into the optical servo sensor while light of
the servo beam that is diffusely reflected by the screen outside a
servo feedback mark is spread by the Frensnel lens over an area
greater than the optical servo sensor to direct a fraction of
diffusely reflected light of the servo beam into the optical servo
sensor.
[0007] In another implementation, a method for controlling a
scanning beam display system includes scanning one or more
excitation beams modulated with optical pulses to carry images on a
screen to excite parallel light-emitting strips to emit visible
light which forms the images; scanning a servo beam at an optical
wavelength different from an optical wavelength of the one or more
excitation beams, on the screen; detecting light of the servo beam
from the screen to obtain a servo signal indicative of positioning
of the servo beam on the screen; and, in response to the
positioning of the servo beam on the screen, controlling the one or
more scanning excitation beams to control the spatial alignment of
spatial positions of the optical pulses in each excitation beam on
the screen.
[0008] In another implementation, a scanning beam display system,
includes an excitation light source to produce at least one
excitation beam having optical pulses that carry image information;
a servo light source to produce at least one servo beam at a servo
beam wavelength that is invisible; a beam scanning module to
receive the excitation beam and the servo beam and to scan the
excitation beam and the servo beam; and a light-emitting screen
positioned to receive the scanning excitation beam and the servo
beam. The screen includes a light-emitting area which comprises (1)
parallel light-emitting stripes which absorb light of the
excitation beam to emit visible light to produce images carried by
the scanning excitation beam, and (2) stripe dividers parallel to
and spatially interleaved with the light-emitting stripes with each
stripe divider being located between two adjacent stripes. Each
stripe divider is optically reflective. An optical servo sensor is
positioned to receive light of the servo beam scanning on the
screen including light reflected by the stripe dividers and to
produce a monitor signal indicative of positioning of the servo
beam on the screen. This system includes a control unit operable
to, in response to the positioning of the servo beam on the screen,
adjust timing of the optical pulses carried by the scanning
excitation beam in response to the monitor signal based on a
relation between the servo beam and the excitation beam to control
the spatial alignment of spatial positions of the optical pulses in
the excitation beam on the screen.
[0009] In another implementation, a scanning beam display system
includes a light-emitting screen comprising a light-emitting area
which comprises (1) parallel light-emitting stripes which absorb
excitation light to emit visible light, and (2) optically
reflective stripe dividers parallel to and spatially interleaved
with the light-emitting stripes with each stripe divider being
located between two adjacent stripes. Excitation lasers are
provided to produce excitation laser beams of the excitation light
and at least one servo light source fixed in position relative to
the excitation lasers is provided to produce at least one servo
beam at a servo beam wavelength that is invisible. This system also
includes a beam scanning module to receive the excitation laser
beams and the servo beam and to scan the excitation laser beams and
the servo beam; at least one first optical servo sensor positioned
to receive light of the servo beam reflected from the screen to
produce a first monitor signal indicative of positioning of the
servo beam on the screen; at least one second optical servo sensor
positioned to receive light of the excitation laser beams reflected
from the screen to produce a second monitor signal indicative of
positioning of each excitation laser beam on the screen; and a
control unit operable to, in response to the first and the second
monitor signals, adjust timing of the optical pulses carried by
each excitation laser beam based on a relation between the servo
beam and each excitation laser beam to control the spatial
alignment of spatial positions of the optical pulses in the
excitation beam on the screen.
[0010] In yet another implementation, a method for controlling a
scanning beam display system includes scanning at least one
excitation beam modulated with optical pulses on a screen with
parallel light-emitting stripes in a beam scanning direction
perpendicular to the light-emitting stripes to excite the
fluorescent strips to emit visible light which forms images. The
screen comprises stripe dividers parallel to and spatially
interleaved with the light-emitting stripes with each stripe
divider being located between two adjacent stripes and each stripe
divider is optically reflective. This method also includes:
scanning a servo beam, which is invisible, along with the
excitation beam on the screen; detecting light of the scanning
servo beam from the screen including light produced by the stripe
dividers to obtain a monitor signal indicative of positioning of
the servo beam on the screen; and, in response to the positioning
of the servo beam on the screen, adjusting timing of the optical
pulses carried by the scanning excitation beam based on a relation
between the servo beam and the excitation beam to control the
spatial alignment of spatial positions of the optical pulses in the
excitation beam on the screen.
[0011] These and other examples and implementations are described
in detail in the drawings, the detailed description and the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows an example scanning laser display system having
a light-emitting screen made of laser-excitable light-emitting
materials (e.g., phosphors) emitting colored lights under
excitation of a scanning laser beam that carries the image
information to be displayed.
[0013] FIGS. 2A and 2B show one example screen structure with
parallel light-emitting stripes and the structure of color pixels
on the screen in FIG. 1.
[0014] FIG. 3 shows an example implementation of the laser display
system in FIG. 1 in a pre-objective scanning configuration having
multiple lasers that direct multiple laser beams on the screen.
[0015] FIG. 4 shows an example implementation of a post-objective
scanning beam display system based on the laser display system in
FIG. 1.
[0016] FIG. 5 shows one example for simultaneously scanning
consecutive scan lines with multiple excitation laser beams and an
invisible servo beam.
[0017] FIG. 5A shows a map of beam positions on the screen produced
by a laser array of thirty-six excitation lasers and one IR servo
laser when a vertical galvo scanner and a horizontal polygon
scanner are at their respective null positions.
[0018] FIG. 6 shows one example of a scanning display system using
a servo feedback control based on a scanning servo beam.
[0019] FIG. 7 shows an example of a servo detector for detecting
the servo feedback light in FIG. 6.
[0020] FIGS. 8 and 9 show two screen examples for the servo control
based on a scanning servo beam.
[0021] FIG. 10 shows optical power of servo light having optical
signals corresponding to stripe dividers on the screen.
[0022] FIG. 11 shows an example of a screen having peripheral
reference mark regions that include servo reference marks that
produce feedback light for various servo control functions.
[0023] FIG. 12 shows a start of line reference mark in a peripheral
reference mark region to provide a reference for the beginning of
the active fluorescent area on the screen.
[0024] FIGS. 13 and 14 show optical power of servo light having
optical signals corresponding to stripe dividers, the start of line
reference mark and end of line reference mark on the screen
[0025] FIGS. 15, 16 and 17 show examples of a use of a sampling
clock signal to measure position data of stripe dividers on the
screen using servo feedback light from the excitation beam or the
servo beam.
[0026] FIG. 18A shows an example of a vertical beam position
reference mark for the screen in FIG. 11.
[0027] FIGS. 18B and 18C show a servo feedback control circuit and
its operation in using the vertical beam position reference mark in
FIG. 18A to control the vertical beam position on the screen.
[0028] FIG. 19 shows an example of the screen in FIG. 11 having the
start of line reference mark and the vertical beam position
reference marks.
[0029] FIG. 20 shows an operation of the servo control based on the
servo beam that is scanned with the excitation beam.
[0030] FIGS. 21, 22 and 23 show examples of screen designs that
have IR servo feedback marks that do not affect the transmission
amount of excitation beams while having a property of diffuse or
specular reflection for at least the servo beams.
[0031] FIG. 24 shows an example of the screen design to have
specularly reflective IR feedback marks and diffusively reflective
areas outside the IR feedback marks on the screen.
[0032] FIG. 25 shows an example of a system based on the design in
FIG. 24.
[0033] FIG. 26 shows an example of a system that combines IR servo
feedback and visible light servo feedback.
[0034] FIGS. 27A-D, 28, 29 and 30 illustrate aspects of the system
in FIG. 26.
[0035] FIG. 31 shows a system implementation of the system in FIG.
26.
DETAILED DESCRIPTION
[0036] Examples of scanning beam display systems in this
application use screens with light-emitting materials or
fluorescent materials to emit light under optical excitation to
produce images, including laser video display systems. Various
examples of screen designs with light-emitting or fluorescent
materials can be used. In one implementation, for example, three
different color phosphors that are optically excitable by the laser
beam to respectively produce light in red, green, and blue colors
suitable for forming color images may be formed on the screen as
pixel dots or repetitive red, green and blue phosphor stripes in
parallel.
[0037] Phosphor materials are one type of fluorescent materials.
Various described systems, devices and features in the examples
that use phosphors as the fluorescent materials are applicable to
displays with screens made of other optically excitable,
light-emitting, non-phosphor fluorescent materials. For example,
quantum dot materials emit light under proper optical excitation
and thus can be used as the fluorescent materials for systems and
devices in this application. More specifically, semiconductor
compounds such as, among others, CdSe and PbS, can be fabricated in
form of particles with a diameter on the order of the exciton Bohr
radius of the compounds as quantum dot materials to emit light. To
produce light of different colors, different quantum dot materials
with different energy band gap structures may be used to emit
different colors under the same excitation light. Some quantum dots
are between 2 and 10 nanometers in size and include approximately
tens of atoms such between 10 to 50 atoms. Quantum dots may be
dispersed and mixed in various materials to form liquid solutions,
powders, jelly-like matrix materials and solids (e.g., solid
solutions). Quantum dot films or film stripes may be formed on a
substrate as a screen for a system or device in this application.
In one implementation, for example, three different quantum dot
materials can be designed and engineered to be optically excited by
the scanning laser beam as the optical pump to produce light in
red, green, and blue colors suitable for forming color images. Such
quantum dots may be formed on the screen as pixel dots arranged in
parallel lines (e.g., repetitive sequential red pixel dot line,
green pixel dot line and blue pixel dot line).
[0038] Examples of scanning beam display systems described here use
at least one scanning laser beam to excite color light-emitting
materials deposited on a screen to produce color images. The
scanning laser beam is modulated to carry images in red, green and
blue colors or in other visible colors and is controlled in such a
way that the laser beam excites the color light-emitting materials
in red, green and blue colors with images in red, green and blue
colors, respectively. Hence, the scanning laser beam carries the
images but does not directly produce the visible light seen by a
viewer. Instead, the color light-emitting fluorescent materials on
the screen absorb the energy of the scanning laser beam and emit
visible light in red, green and blue or other colors to generate
actual color images seen by the viewer.
[0039] Laser excitation of the fluorescent materials using one or
more laser beams with energy sufficient to cause the fluorescent
materials to emit light or to luminesce is one of various forms of
optical excitation. In other implementations, the optical
excitation may be generated by a non-laser light source that is
sufficiently energetic to excite the fluorescent materials used in
the screen. Examples of non-laser excitation light sources include
various light-emitting diodes (LEDs), light lamps and other light
sources that produce light at a wavelength or a spectral band to
excite a fluorescent material that converts the light of a higher
energy into light of lower energy in the visible range. The
excitation optical beam that excites a fluorescent material on the
screen can be at a frequency or in a spectral range that is higher
in frequency than the frequency of the emitted visible light by the
fluorescent material. Accordingly, the excitation optical beam may
be in the violet spectral range and the ultra violet (UV) spectral
range, e.g., wavelengths under 420 nm. In the examples described
below, Violet or a UV laser beam is used as an example of the
excitation light for a phosphor material or other fluorescent
material and may be light at other wavelength.
[0040] FIG. 1 illustrates an example of a laser-based display
system using a screen having color phosphor stripes. Alternatively,
color pixilated light-emitting areas may also be used to define the
image pixels on the screen. The system includes a laser module 110
to produce and project at least one scanning laser beam 120 onto a
screen 101. The screen 101 has parallel color phosphor stripes in
the vertical direction and two adjacent phosphor stripes are made
of different phosphor materials that emit light in different
colors. In the illustrated example, red phosphor absorbs the laser
light to emit light in red, green phosphor absorbs the laser light
to emit light in green and blue phosphor absorbs the laser light to
emit light in blue. Adjacent three color phosphor stripes are in
three different colors. One particular spatial color sequence of
the stripes is shown in FIG. 1 as red, green and blue. Other color
sequences may also be used. The laser beam 120 is at the wavelength
within the optical absorption bandwidth of the color phosphors and
is usually at a wavelength shorter than the visible blue and the
green and red colors for the color images. As an example, the color
phosphors may be phosphors that absorb UV light in the spectral
range below 420 nm to produce desired red, green and blue light.
The laser module 110 can include one or more lasers such as UV
diode lasers to produce the beam 120, a beam scanning mechanism to
scan the beam 120 horizontally and vertically to render one image
frame at a time on the screen 101, and a signal modulation
mechanism to modulate the beam 120 to carry the information for
image channels for red, green and blue colors. Such display systems
may be configured as rear scanning systems where the viewer and the
laser module 110 are on the opposite sides of the screen 101.
Alternatively, such display systems may be configured as front
scanning systems where the viewer and laser module 110 are on the
same side of the screen 101.
[0041] Examples of implementations of various features, modules and
components in the scanning laser display system in FIG. 1 are
described in U.S. patent application Ser. No. 10/578,038 entitled
"Display Systems and Devices Having Screens With Optical
Fluorescent Materials" and filed on May 2, 2006 (U.S. Patent
Publication No. 2008-0291140, PCT Patent Application No.
PCT/US2007/004004 entitled "Servo-Assisted Scanning Beam Display
Systems Using Fluorescent Screens" and filed on Feb. 15, 2007 (PCT
Publication No. WO 2007/095329), PCT Patent Application No.
PCT/US2007/068286 entitled "Phosphor Compositions For Scanning Beam
Displays" and filed on May 4, 2007 (PCT Publication No. WO
2007/131195), PCT Patent Application No. PCT/US2007/68989 entitled
"Multilayered Fluorescent Screens for Scanning Beam Display
Systems" and filed on May 15, 2007 (PCT Publication No. WO
2007/134329), and PCT Patent Application No. PCT/US2006/041584
entitled "Optical Designs for Scanning Beam Display Systems Using
Fluorescent Screens" and filed on Oct. 25, 2006 (PCT Publication
No. WO 2007/050662). The disclosures of the above-referenced patent
applications are incorporated by reference in their entirety as
part of the specification of this application.
[0042] FIG. 2A shows an exemplary design of the screen 101 in FIG.
1. The screen 101 may include a rear substrate 201 which is
transparent to the scanning laser beam 120 and faces the laser
module 110 to receive the scanning laser beam 120. A second front
substrate 202, is fixed relative to the rear substrate 201 and
faces the viewer in a rear scanning configuration. A color phosphor
stripe layer 203 is placed between the substrates 201 and 202 and
includes phosphor stripes. The color phosphor stripes for emitting
red, green and blue colors are represented by "R", "G" and "B,"
respectively. The front substrate 202 is transparent to the red,
green and blue colors emitted by the phosphor stripes. The
substrates 201 and 202 may be made of various materials, including
glass or plastic panels. The rear substrate 201 can be a thin film
layer and is configured to recycle the visible energy toward the
viewer. Each color pixel includes portions of three adjacent color
phosphor stripes in the horizontal direction and its vertical
dimension is defined by the beam spread of the laser beam 120 in
the vertical direction. As such, each color pixel includes three
subpixels of three different colors (e.g., the red, green and
blue). The laser module 110 scans the laser beam 120 one horizontal
line at a time, e.g., from left to right and from top to bottom to
fill the screen 101. The relative alignment of the laser module 110
and the screen 101 can be monitored and controlled to ensure proper
alignment between the laser beam 120 and each pixel position on the
screen 101. In one implementation, the laser module 110 can be
controlled to be fixed in position relative to the screen 101 so
that the scanning of the beam 120 can be controlled in a
predetermined manner to ensure proper alignment between the laser
beam 120 and each pixel position on the screen 101.
[0043] In FIG. 2A, the scanning laser beam 120 is directed at the
green phosphor stripe within a pixel to produce green light for
that pixel. FIG. 2B further shows the operation of the screen 101
in a view along the direction B-B perpendicular to the surface of
the screen 101. Since each color stripe is longitudinal in shape,
the cross section of the beam 120 may be shaped to be elongated
along the direction of the stripe to maximize the fill factor of
the beam within each color stripe for a pixel. This may be achieved
by using a beam shaping optical element in the laser module 110. A
laser source that is used to produce a scanning laser beam that
excites a phosphor material on the screen may be a single mode
laser or a multimode laser. The laser may also be a single mode
along the direction perpendicular to the elongated direction
phosphor stripes to have a beam spread that is confined by and is
smaller than the width of each phosphor stripe. Along the elongated
direction of the phosphor stripes, this laser beam may have
multiple modes to spread over a larger area than the beam spread in
the direction across the phosphor stripe. This use of a laser beam
with a single mode in one direction to have a small beam footprint
on the screen and multiple modes in the perpendicular direction to
have a larger footprint on the screen allows the beam to be shaped
to fit the elongated color subpixel on the screen and to provide
sufficient laser power in the beam via the multimodes to ensure
sufficient brightness of the screen.
[0044] Referring now to FIG. 3, an example implementation of the
laser module 110 in FIG. 1 is illustrated. A laser array 310 with
multiple lasers is used to generate multiple laser beams 312 to
simultaneously scan the screen 101 for enhanced display brightness.
A signal modulation controller 320 is provided to control and
modulate the lasers in the laser array 310 so that the laser beams
312 are modulated to carry the image to be displayed on the screen
101. The signal modulation controller 320 can include a digital
image processor that generates digital image signals for the three
different color channels and laser driver circuits that produce
laser control signals carrying the digital image signals. The laser
control signals are then applied to modulate the lasers, e.g., the
currents for laser diodes, in the laser array 310.
[0045] The beam scanning can be achieved by using a scanning mirror
340 such as a galvo mirror for the vertical scanning and a
multi-facet polygon scanner 350 for the horizontal scanning. A scan
lens 360 can be used to project the scanning beams form the polygon
scanner 350 onto the screen 101. The scan lens 360 is designed to
image each laser in the laser array 310 onto the screen 101. Each
of the different reflective facets of the polygon scanner 350
simultaneously scans N horizontal lines where N is the number of
lasers. In the illustrated example, the laser beams are first
directed to the galvo mirror 340 and then from the galvo mirror 340
to the polygon scanner 350. The output scanning beams 120 are then
projected onto the screen 101. A relay optics module 330 is placed
in the optical path of the laser beams 312 to modify the spatial
property of the laser beams 312 and to produce a closely packed
bundle of beams 332 for scanning by the galvo mirror 340 and the
polygon scanner 350 as the scanning beams 120 projected onto the
screen 101 to excite the phosphors and to generate the images by
colored light emitted by the phosphors. A relay optics module 370
is inserted between the scanners 340 and 350 to image the
reflective surface of the reflector in the vertical scanner 340
into a respective reflecting facet of the polygon scanner 350 in
order to prevent beam walk across the thin facet of the polygon
scanner 350 in the vertical direction.
[0046] The laser beams 120 are scanned spatially across the screen
101 to hit different color pixels at different times. Accordingly,
each of the modulated beams 120 carries the image signals for the
red, green and blue colors for each pixel at different times and
for different pixels at different times. Hence, the beams 120 are
coded with image information for different pixels at different
times by the signal modulation controller 320. The beam scanning
thus maps the time-domain coded image signals in the beams 120 onto
the spatial pixels on the screen 101. For example, the modulated
laser beams 120 can have each color pixel time equally divided into
three sequential time slots for the three color subpixels for the
three different color channels. The modulation of the beams 120 may
use pulse modulation techniques to produce desired grey scales in
each color, a proper color combination in each pixel, and desired
image brightness.
[0047] In one implementation, the multiple beams 120 are directed
onto the screen 101 at different and adjacent vertical positions
with two adjacent beams being spaced from each other on the screen
101 by one horizontal line of the screen 101 along the vertical
direction. For a given position of the galvo mirror 340 and a given
position of the polygon scanner 350, the beams 120 may not be
aligned with each other along the vertical direction on the screen
101 and may be at different positions on the screen 101 along the
horizontal direction. The beams 120 can only cover one portion of
the screen 101.
[0048] In one implementation, at an angular position of the galvo
mirror 340, the spinning of the polygon scanner 350 causes the
beams 120 from N lasers in the laser array 310 to scan one screen
segment of N adjacent horizontal lines on the screen 101. The galvo
mirror 340 tilts linearly to change its tiling angle at a given
rate along a vertical direction from the top towards the bottom
during the scanning by the polygon until the entire screen 101 is
scanned to produce a full screen display. At the end of the galvo
vertical angular scan range, the galvo retraces to its top position
and the cycle is repeated in synchronization with the refresh rate
of the display.
[0049] In another implementation, for a given position of the galvo
mirror 340 and a given position of the polygon scanner 350, the
beams 120 may not be aligned with each other along the vertical
direction on the screen 101 and may be at different positions on
the screen 101 along the horizontal direction. The beams 120 can
only cover one portion of the screen 101. At a fixed angular
position of the galvo mirror 340, the spinning of the polygon
scanner 350 causes the beams 120 from N lasers in the laser array
310 to scan one screen segment of N adjacent horizontal lines on
the screen 101. At the end of each horizontal scan over one screen
segment, the galvo mirror 340 is adjusted to a different fixed
angular position so that the vertical positions of all N beams 120
are adjusted to scan the next adjacent screen segment of N
horizontal lines. This process iterates until the entire screen 101
is scanned to produce a full screen display.
[0050] In the above example of a scanning beam display system shown
in FIG. 3, the scan lens 360 is located downstream from the beam
scanning devices 340 and 350 and focuses the one or more scanning
excitation beams 120 onto the screen 101. This optical
configuration is referred to as a "pre-objective" scanning system.
In such a pre-objective design, a scanning beam directed into the
scan lens 360 is scanned along two orthogonal directions.
Therefore, the scan lens 360 is designed to focus the scanning beam
onto the screen 101 along two orthogonal directions. In order to
achieve the proper focusing in both orthogonal directions, the scan
lens 360 can be complex and, often, are made of multiples lens
elements. In one implementation, for example, the scan lens 360 can
be a two-dimensional f-theta lens that is designed to have a linear
relation between the location of the focal spot on the screen and
the input scan angle (theta) when the input beam is scanned around
each of two orthogonal axes perpendicular to the optic axis of the
scan lens. The two-dimensional scan lens 360 such as a f-theta lens
in the pre-objective configuration can exhibit optical distortions
along the two orthogonal scanning directions which cause beam
positions on the screen 101 to trace a curved line. The scan lens
360 can be designed with multiple lens elements to reduce the bow
distortions and can be expensive to fabricate.
[0051] To avoid the above distortion issues associated with a
two-dimensional scan lens in a pre-objective scanning beam system,
a post-objective scanning beam display system can be implemented to
replace the two-dimensional scan lens 360 with a simpler, less
expensive 1-dimensional scan lens. U.S. patent application Ser. No.
11/742,014 entitled "POST-OBJECTIVE SCANNING BEAM SYSTEMS" and
filed on Apr. 30, 2007 (U.S. Patent Publication No. 2008-0247020
describes examples of post-objective scanning beam systems suitable
for use with phosphor screens described in this application and is
incorporated by reference as part of the specification of this
application.
[0052] FIG. 4 shows an example implementation of a post-objective
scanning beam display system based on the system design in FIG. 1.
A laser array 310 with multiple lasers is used to generate multiple
laser beams 312 to simultaneously scan a screen 101 for enhanced
display brightness. A signal modulation controller 320 is provided
to control and modulate the lasers in the laser array 310 so that
the laser beams 312 are modulated to carry the image to be
displayed on the screen 101. The beam scanning is based on a
two-scanner design with a horizontal scanner such as a polygon
scanner 350 and a vertical scanner such as a galvanometer scanner
340. Each of the different reflective facets of the polygon scanner
350 simultaneously scans N horizontal lines where N is the number
of lasers. A relay optics module 330 reduces the spacing of laser
beams 312 to form a compact set of laser beams 332 that spread
within the facet dimension of the polygon scanner 350 for the
horizontal scanning Downstream from the polygon scanner 350, there
is a 1-D horizontal scan lens 380 followed by a vertical scanner
340 (e.g., a galvo mirror) that receives each horizontally scanned
beam 332 from the polygon scanner 350 through the 1-D scan lens 380
and provides the vertical scan on each horizontally scanned beam
332 at the end of each horizontal scan prior to the next horizontal
scan by the next facet of the polygon scanner 350. The vertical
scanner 340 directs the 2-D scanning beams 390 to the screen
101.
[0053] Under this optical design of the horizontal and vertical
scanning, the 1-D scan lens 380 is placed downstream from the
polygon scanner 140 and upstream from the vertical scanner 340 to
focus each horizontal scanned beam on the screen 101 and minimizes
the horizontal bow distortion to displayed images on the screen 101
within an acceptable range, thus producing a visually "straight"
horizontal scan line on the screen 101. Such a 1-D scan lens 380
capable of producing a straight horizontal scan line is relatively
simpler and less expensive than a 2-D scan lens of similar
performance. Downstream from the scan lens 380, the vertical
scanner 340 is a flat reflector and simply reflects the beam to the
screen 101 and scans vertically to place each horizontally scanned
beam at different vertical positions on the screen 101 for scanning
different horizontal lines. The dimension of the reflector on the
vertical scanner 340 along the horizontal direction is sufficiently
large to cover the spatial extent of each scanning beam coming from
the polygon scanner 350 and the scan lens 380. The system in FIG. 4
is a post-objective design because the 1-D scan lens 380 is
upstream from the vertical scanner 340. In this particular example,
there is no lens or other focusing element downstream from the
vertical scanner 340.
[0054] Notably, in the post-objective system in FIG. 4, the
distance from the scan lens to a location on the screen 101 for a
particular beam varies with the vertical scanning position of the
vertical scanner 340. Therefore, when the 1-D scan lens 380 is
designed to have a fixed focal distance along the straight
horizontal line across the center of the elongated 1-D scan lens,
the focal properties of each beam must change with the vertical
scanning position of the vertical scanner 380 to maintain
consistent beam focusing on the screen 101. In this regard, a
dynamic focusing mechanism can be implemented to adjust convergence
of the beam going into the 1-D scan lens 380 based on the vertical
scanning position of the vertical scanner 340.
[0055] For example, in the optical path of the one or more laser
beams from the lasers to the polygon scanner 350, a stationary lens
and a dynamic refocus lens can be used as the dynamic focusing
mechanism. Each beam is focused by the dynamic focus lens at a
location upstream from the stationary lens. When the focal point of
the lens coincides with the focal point of the lens, the output
light from the lens is collimated. Depending on the direction and
amount of the deviation between the focal points of the lenses, the
output light from the collimator lens toward the polygon scanner
350 can be either divergent or convergent. Hence, as the relative
positions of the two lenses along their optic axis are adjusted,
the focus of the scanned light on the screen 101 can be adjusted. A
refocusing lens actuator can be used to adjust the relative
position between the lenses in response to a control signal. In
this particular example, the refocusing lens actuator is used to
adjust the convergence of the beam directed into the 1-D scan lens
380 along the optical path from the polygon scanner 350 in
synchronization with the vertical scanning of the vertical scanner
340. The vertical scanner 340 in FIG. 4 scans at a much smaller
rate than the scan rate of the first horizontal scanner 350 and
thus a focusing variation caused by the vertical scanning on the
screen 101 varies with time at the slower vertical scanning rate.
This allows a focusing adjustment mechanism to be implemented in
the system of FIG. 1 with the lower limit of a response speed at
the slower vertical scanning rate rather than the high horizontal
scanning rate.
[0056] The beams 120 on the screen 101 are located at different and
adjacent vertical positions with two adjacent beams being spaced
from each other on the screen 101 by one horizontal line of the
screen 101 along the vertical direction. For a given position of
the galvo mirror 540 and a given position of the polygon scanner
550, the beams 120 may not be aligned with each other along the
vertical direction on the screen 101 and may be at different
positions on the screen 101 along the horizontal direction. The
beams 120 can cover one portion of the screen 101.
[0057] FIG. 5 illustrates the above simultaneous scanning of one
screen segment with multiple scanning laser beams 120 at a time.
Visually, the beams 120 behaves like a paint brush to "paint" one
thick horizontal stroke across the screen 101 at a time to cover
one screen segment between the start edge and the end edge of the
image area of the screen 101 and then subsequently to "paint"
another thick horizontal stroke to cover an adjacent vertically
shifted screen segment. Assuming the laser array 310 has N=36
lasers, a 1080-line progressive scan of the screen 101 would
require scanning 30 vertical screen segments for a full scan.
Hence, this configuration in an effect divides the screen 101 along
the vertical direction into multiple screen segments so that the N
scanning beams scan one screen segment at a time with each scanning
beam scanning only one line in the screen segment and different
beams scanning different sequential lines in that screen segment.
After one screen segment is scanned, the N scanning beams are moved
at the same time to scan the next adjacent screen segment.
[0058] In the above design with multiple laser beams, each scanning
laser beam 120 scans only a number of lines across the entire
screen along the vertical direction that is equal to the number of
screen segments. Hence, the polygon scanner 550 for the horizontal
scanning can operate at slower speeds than scanning speeds required
for a single beam design where the single beam scans every line of
the entire screen. For a given number of total horizontal lines on
the screen (e.g., 1080 lines in HDTV), the number of screen
segments decreases as the number of the lasers increases. Hence,
with 36 lasers, the galvo mirror and the polygon scanner scan 30
lines per frame while a total of 108 lines per frame are scanned
when there are only 10 lasers. Therefore, the use of the multiple
lasers can increase the image brightness which is approximately
proportional to the number of lasers used, and, at the same time,
can also advantageously reduce the speed of the scanning
system.
[0059] A scanning display system described in this specification
can be calibrated during the manufacture process so that the laser
beam on-off timing and position of the laser beam relative to the
fluorescent stripes in the screen 101 are known and are controlled
within a permissible tolerance margin in order for the system to
properly operate with specified image quality. However, the screen
101 and components in the laser module 101 of the system can change
over time due to various factors, such as scanning device jitter,
changes in temperature or humidity, changes in orientation of the
system relative to gravity, settling due to vibration, aging and
others. Such changes can affect the positioning of the laser source
relative to the screen 101 over time and thus the factory-set
alignment can be altered due to such changes. Notably, such changes
can produce visible and, often undesirable, effects on the
displayed images. For example, a laser pulse in the scanning
excitation beam 120 may hit a subpixel that is adjacent to an
intended target subpixel for that laser pulse due to a misalignment
of the scanning beam 120 relative to the screen along the
horizontal scanning direction. When this occurs, the coloring of
the displayed image is changed from the intended coloring of the
image. Hence, a red pixel in the intended image may be displayed as
a green pixel on the screen. For another example, a laser pulse in
the scanning excitation beam 120 may hit both the intended target
subpixel and an adjacent subpixel next to the intended target
subpixel due to a misalignment of the scanning beam 120 relative to
the screen along the horizontal scanning direction. When this
occurs, the coloring of the displayed image is changed from the
intended coloring of the image and the image resolution
deteriorates. The visible effects of these changes can increase as
the screen display resolution increases because a smaller pixel
means a smaller tolerance for a change in position. In addition, as
the size of the screen increases, the effect of a change that can
affect the alignment can be more pronounced because a large moment
arm in scanning each excitation beam 120 associated with a large
screen means that an angular error can lead to a large position
error on the screen. For example, if the laser beam position on the
screen for a known beam angle changes over time, the result is a
color shift in the image. This effect can be noticeable and thus
undesirable to the viewer.
[0060] Implementations of various alignment mechanisms are provided
in this specification to maintain proper alignment of the scanning
beam 120 on the desired sub-pixel to achieved desired image
quality. These alignment mechanisms include reference marks on the
screen, both in the fluorescent area and in one or more peripheral
area outside the fluorescent area, emitted visible light in red,
green and blue colors by the phosphor stripes to provide feedback
light that is caused by the excitation beam 120 and represents the
position and other properties of the scanning beam on the screen.
The feedback light can be measured by using one or more optical
servo sensors to produce one or more feedback servo signals and
such feedback servo signals are used to generate a location map for
red, green and blue sub-pixels on the screen. A servo control in
the laser module 110 processes this feedback servo signal to
extract the information on the beam positioning and other
properties of the beam on the screen and, in response, adjust the
direction and other properties of the scanning beam 120 to ensure
the proper operation of the display system.
[0061] For example, a feedback servo control system can be provided
to use peripheral servo reference marks positioned outside the
display area unobservable by the viewer to provide control over
various beam properties, such as the horizontal positioning along
the horizontal scanning direction perpendicular to the fluorescent
stripes, the vertical positioning along the longitudinal direction
of the fluorescent stripes, the beam focusing on the screen for
control of image color (e.g., color saturation) and image
sharpness, and the beam power on the screen for control of image
brightness and uniformity of the image brightness across the
screen. For another example, a screen calibration procedure can be
performed at the startup of the display system to measure the beam
position information as a calibration map so having the exact
positions of sub-pixels on the screen in the time domain. This
calibration map is then used by the laser module 110 to control the
timing and positioning of the scanning beam 120 to achieve the
desired color purity. For yet another example, a dynamic servo
control system can be provided to regularly update the calibration
map during the normal operation of the display system by using
servo reference marks in the fluorescent area of the screen to
provide the feedback light without affecting the viewing experience
of a viewer. Examples for using servo light produced by phosphor
stripe dividers from the excitation light and feedback light from
other reference marks for servo control and screen calibration are
described in the incorporated-by-reference PCT Patent Application
No. PCT/US2007/004004 entitled "Servo-Assisted Scanning Beam
Display Systems Using Fluorescent Screens" (PCT Publication No. WO
2007/095329).
[0062] The display systems in this application provide servo
control mechanisms based on a designated servo beam that is scanned
over the screen by the same scanning module that scans the
image-carrying excitation optical beam. This designated servo beam
is used to provide servo feedback control over the scanning
excitation beam to ensure proper optical alignment and accurate
delivery of optical pulses in the excitation beam during normal
display operation. This designated servo beam has an optical
wavelength different from that of the excitation beam. As an
example, this designated servo beam can be an IR servo beam that
may be invisible to human. The examples below use an IR servo beam
130 to illustrate features and operations of this designated servo
beam.
[0063] Referring to FIG. 1, the laser module 110 produces an
invisible servo beam 130 such as an IR beam as an example of the
designated servo beam. The laser module 110 scans the servo beam
130 on to the screen 101 along with the excitation beam 120.
Different from the excitation beam 120, the servo beam 130 is not
modulated to carry image data. The servo beam 130 can be a CW beam.
The stripe dividers on the screen 101 can be made reflective to the
light of the servo beam 130 and to produce feedback light 132 by
reflection. The servo beam 130 has a known spatial relation with
the excitation beam 120. Therefore, the positioning of the servo
beam 130 can be used to determine the positioning of the excitation
beam 120. This relationship between the servo beam 130 and the
excitation beam 120 can be determined by using reference servo
marks such as a start of line (SOL) mark in a non-viewing area of
the screen 101. The laser module 101 receives and detects the
feedback light 132 to obtain positioning information of the servo
beam 130 on the screen 101 and uses this positioning information to
control alignment of the excitation beam 120 on the screen.
[0064] The servo beam 130 is invisible to human and thus does not
produce any noticeable visual artifact on the screen 101 during the
normal operation of the system when images are produced on the
screen 101. For example, the servo beam 130 can have a wavelength
in a range from 780 nm to 820 nm. For safety concerns, the screen
101 can be made to have a filter that blocks the invisible servo
beam 130 from exiting the screen 101 on the viewer side. In this
regard, a cutoff absorbing filter with a bandpass transmission
range only in the visible spectral range (e.g., from 420 nm to 680
nm) may be used to block the servo beam 130 and excitation beam
120. The servo control of the excitation beam 120 based on the
servo beam 130 can be performed dynamically during the normal
operation of the system. This servo design avoids manipulation of
the image-producing excitation beam 120 during the normal display
mode for servo operations and thus avoids any visual artifacts that
may be caused by the servo-related manipulation of the
image-producing excitation beam 120.
[0065] In addition, the scattered or reflected excitation light by
the screen 101 may also be used for servo control operations during
a period when the system does not show images, e.g., during the
startup period of the system or when the excitation beam 120 is
outside the active display area of the screen 101. In such a case,
the scattered or reflected excitation light, labeled as light 122,
can be used as servo feedback light for servo control of, e.g., the
horizontal alignment or the vertical alignment of each laser beam
120.
[0066] In the examples of the systems in FIGS. 3 and 4, the servo
beam 130 is directed along with the one or more excitation beams
120 through the same optical path that includes the relay optics
module 330A or 330B, the beam scanners 340 and 350, and the scan
lens 360 or 380. Referring to FIG. 5, the servo beam 130 is scanned
along with the scanning excitation beams 120 one screen segment at
a time along the vertical direction of the screen. The servo beam
130 is invisible and can be overlapped with a scanning path of one
excitation beam 120 or along its own scanning path that is
different from a path of any of the excitation beams 120. The
spatial relation between the servo beam 130 and each excitation
beam 120 is known and fixed so that the positioning of the servo
beam 130 on the screen 101 can be used to infer positioning of each
excitation beam 120.
[0067] A light source for generating the servo beam 130 and a light
source for generating an excitation beam 120 can be semiconductor
lasers in a light source module which can be an array of lasers and
at least one of the lasers in the laser array can be a servo laser
that produces the servo beam 130. In one implementation, the
location of the servo laser is known relative to each excitation
laser in the laser array in the laser module 110. The servo beam
130 and each excitation beam 120 are directed through the same
relay optics, the same beam scanners and the same projection lens
and are projected on the screen 101. Therefore, the positioning of
the servo beam 130 on the screen 101 has a known relation with the
positioning of each excitation beam 120 on the screen. This
relation between the servo beam 130 and each excitation beam 120
can be used to control the excitation beam 120 based on measured
positioning of the servo beam 130. The relative position relation
between the servo beam 130 and each excitation beam 120 can be
measured using the servo feedback, e.g., during a calibration
process that may be separately performed or performed during the
power-up period of the system. The measured relative position
relation is used for the servo feedback control.
[0068] FIG. 5A shows a map of beam positions on the screen produced
by a laser array of thirty-six excitation lasers and one IR servo
laser when a vertical galvo scanner and a horizontal polygon
scanner are at their respective null positions in a prototype
pre-objective scanning display system. The thirty-six excitation
lasers are arranged in a 4.times.9 laser array and the IR servo
laser is placed in the center of the laser array. The laser beams
occupy an area of about 20 mm.times.25 mm on the screen. In this
example, the vertical spacing is one half of a pixel between two
vertically adjacent excitation lasers and the horizontal spacing
between two adjacent excitation lasers is 3.54 pixels. Because the
excitation lasers are spatially staggered along both horizontal and
vertical directions, each scan in one screen segment produces
thirty-six horizontal lines on the screen occupying thirty-six
pixels along the vertical direction. In operation, these
thirty-seven laser beams are scanned together based on the scanning
shown in FIG. 5 to scan one screen segment at a time to
sequentially scan different screen segments at different vertical
positions to scan the entire screen. Because the IR servo laser is
fixed in position with respect to each and every one of the
thirty-six excitation lasers, the positioning of the servo beam 130
produced by the IR servo laser on the screen 101 has a known
relation with respect to each beam spot of an excitation beam 120
from each of the thirty-six excitation lasers.
[0069] FIG. 6 illustrates a scanning beam display system based on a
servo control using the invisible servo beam 130. A display
processor and controller 640 can be used to provide control
functions and control intelligence based on servo detector signals
from radiation servo detectors 620 that detect servo feedback light
132 from the screen 101. A single detector 620 may be sufficient
and two or more servo detectors 620 can be used to improve the
servo detection sensitivity.
[0070] Similarly, one or more radiation servo detectors 630 may
also be used to collect excitation servo light 122 produced by
scattering or reflecting the excitation beam 120 at the screen to
provide additional feedback signals to the processor and controller
640 for the servo control. This use of the servo light 122 for
feedback control can be an optional feature that is used in
combination with the IR servo feedback control. In some system
implementations, the IR servo feedback alone without the feedback
based on the feedback light 122 shown in FIG. 6 can be sufficient
to align the excitation beam 120 to the proper phosphor stripes on
the screen 101. Examples for using the servo light 122 produced by
phosphor stripe dividers for servo control are described in the
incorporated-by-reference PCT Patent Application No.
PCT/US2007/004004 entitled "Servo-Assisted Scanning Beam Display
Systems Using Fluorescent Screens" (PCT Publication No. WO
2007/095329).
[0071] In FIG. 6, a scanning projection module 610 is provided to
scan and project the excitation and servo beams 120 and 130 onto
the screen 101. The module 610 can be in a post-objective
configuration or a pre-objective configuration. As illustrated, the
image data is fed to the display processor and controller 640 which
produces an image data signal carrying the image data to the signal
modulator controller 520 for the excitation lasers 510. The servo
laser which is among the excitation lasers in the array 510 is not
modulated to carry image data. The signal modulation controller 520
can include laser driver circuits that produce laser modulation
signals carrying image signals with image data assigned to
different lasers 510, respectively. The laser control signals are
then applied to modulate the lasers in the laser array 510, e.g.,
the currents for laser diodes to produce the laser beams 512. The
display processor and controller 640 also produces laser control
signals to the lasers in the laser array 510 to adjust the laser
orientation to change the vertical beam position on the screen 101
or the DC power level of each laser. The display processor and
controller 5930 further produces scanning control signals to the
scanning projection module 610 to control and synchronize the
horizontal polygon scanner and the vertical scanner.
[0072] FIG. 7 shows one example of the servo detector design where
a servo detector 620 detects the servo feedback light 132. The
servo detector 620 can be a detector designed to be sensitive to
light of the servo beam wavelength for the invisible servo beam 130
and less sensitive to other light such as the visible light and the
excitation light. An optical filter 710 can be used to filter the
light from the screen 101 to selectively transmit the servo
feedback light 132 while blocking light at other wavelengths, such
as the excitation light and visible light. Such a filter allows a
wider range of optical detectors to be used as the servo detector.
FIG. 7 also shows an example of an optional servo detector 630 for
detecting the servo feedback light 122 at the excitation
wavelength. The servo detector 620 can be a detector designed to be
sensitive to light of the excitation wavelength of the excitation
beam 120 and less sensitive to light at wavelengths of the servo
beam 130 and the visible light emitted by the screen 101. An
optical filter 720 can be used to filter the light from the screen
101 to selectively transmit the excitation servo feedback light 122
while blocking light at other wavelengths. The servo detector
signals 721 and 722 from the servo detectors 620 and 630,
respectively, are directed to the processor and controller 640 for
servo control operations.
[0073] FIGS. 8 and 9 show two exemplary screen designs for the
screen 101 for providing the feedback light 122 and 132. In FIG. 8,
each strip divider 810 is made optically reflective to the servo
and excitation beams so the reflection can be used as the feedback
light 132. The strip divider 810 can also be made reflective and
opaque to light to optically isolate adjacent light-emitting
stripes to enhance contrast and to reduce cross talk. The
light-emitting stripes such phosphor stripes emitting red, green
and blue light are less reflective to the servo and excitation
beams than the stripe dividers 810 so that the feedback light 132
exhibits a spike every time the servo or excitation beams 130 pass
through a stripe divider 810. An absorbent black layer 820 can be
coated on each stripe divider on the viewer side to reduce glare of
ambient light to the viewer. FIG. 9 shows another screen design
where a reflective servo reference mark 910 is formed on the
excitation side of each strip divider 901, e.g., a reflective
stripe coating.
[0074] In each horizontal scan, the beam 120 or 130 scans across
the light-emitting stripes and the reflections produced by the
stripe dividers can be used to indicate horizontal positions of the
stripe dividers, spacing between two adjacent stripe dividers and
horizontal positions of the horizontally scanned beam 120 or 130.
Therefore, reflections from the stripe dividers can be used for
servo control of the horizontal alignment between the beam 120 and
the light-emitting strips.
[0075] FIG. 10 shows operation of the stripe dividers as alignment
reference marks. As the servo beam 120 or 130 is scanned
horizontally across the screen 101 and the light at the servo beam
shows a low power when the servo beam 130 is at a light-emitting
stripe and a high power when the servo beam is at a stripe divider.
When the beam spot of the servo beam 130 on the screen 101 is less
than the width of one subpixel, the power of the servo light shows
a periodic pattern in each horizontal scan where the high power
peak corresponds to a stripe divider. This pattern can be used to
measure the position of the stripe dividers or the width of each
stripe divider based on clock cycles of a clocking signal in the
processor and controller 640. This measured information is used to
update a positioning map of each excitation beam 120 in the
horizontal scan. When the beam spot of the servo beam 130 is
greater than one width of the subpixel but is less than one color
pixel made up by three adjacent subpixels, the power of the servo
light 132 still shows a periodic pattern in each horizontal scan
where the high power peak corresponds to one color pixel and thus
can be used for servo control.
[0076] In addition to the stripe dividers as alignment reference
marks on the screen 101, additional alignment reference marks can
be implemented to determine the relative position of the beam and
the screen and other parameters of the excitation beam on the
screen. For example, during a horizontal scan of the excitation and
servo beams across the light-emitting stripes, a start of line mark
can be provided for the system to determine the beginning of the
active light-emitting display area of the screen 101 so that the
signal modulation controller of the system can properly control the
timing in delivering optical pulses to targeted pixels. An end of
line mark can also be provided for the system to determine the end
of the active light-emitting display area of the screen 101 during
a horizontal scan. For another example, a vertical alignment
referenced mark can be provided for the system to determine whether
the scanning beams are pointed to a proper vertical location on the
screen. Other examples for reference marks may be one or more
reference marks for measuring the beam spot size on the screen and
one or more reference marks on the screen to measure the optical
power of the excitation beam 120. Such reference marks can be
placed a region outside the active fluorescent area of the screen
101, e.g., in one or more peripheral regions of the active
fluorescent screen area and are used for both excitation and servo
beams.
[0077] FIG. 11 illustrates one example of a fluorescent screen 101
having peripheral reference mark regions. The screen 101 includes a
central active light-emitting display area 1100 with parallel
fluorescent stripes for displaying images, two stripe peripheral
reference mark regions 1110 and 1120 that are parallel to the
fluorescent stripes. Each peripheral reference mark region can be
used to provide various reference marks for the screen 101. In some
implementations, only the left peripheral reference mark region
1110 is provided without the second region 1120 when the horizontal
scan across the fluorescent stripes is directed from the left to
the right of the area 1100.
[0078] Such a peripheral reference mark region on the screen 101
allows the scanning display system to monitor certain operating
parameters of the system. A reference mark in the peripheral
reference mark region can be used for a servo control operation
based on the servo feedback light 132 generated from the servo beam
130. When the servo feedback light 122 generated from the
excitation beam 120 is also used for a servo control operation, a
reference mark in the peripheral reference mark region can be used
for servo control operation based on the servo feedback light 122.
A reference mark in the peripheral reference mark region can be
used to measure both the excitation beam 120 and the servo beam 130
for a servo control operation in some implementations. The
description on various examples of reference marks below may
specifically refer to the excitation beam 120 and similar functions
can be used in connection with the servo beam 130.
[0079] Notably, a reference mark in the peripheral reference mark
region is outside the active display area 1100 of the screen 101
and thus a corresponding servo feedback control function can be
performed outside the duration during the display operation when
the excitation beam is scanning through the active fluorescent
display area 2600 to display image. Therefore, a dynamic servo
operation can be implemented without interfering with the display
of the images to the viewer. In this regard, each scan can include
a continuous mode period when an excitation beam sans through the
peripheral referenced mark region for the dynamic servo sensing and
control and a display mode period when the modulation of the
excitation beam is turned on to produce image-carrying optical
pulses as the excitation beam scans through the active fluorescent
display area 1100. The servo beam 130 is not modulated to carry
image data and thus can be a continuous beam with a constant beam
power when incident onto the screen 101. The power of the reflected
servo light in the feedback light 132 is modulated by the reference
marks and stripe dividers and other screen pattern on the screen
101. The modulated power of the reflected servo light can be used
to measure the location of the servo beam 130 on the screen
101.
[0080] FIG. 12 shows an example of a start of line (SOL) reference
mark 1210 in the left peripheral region 1110 in the screen 101. The
SOL reference mark 1210 can be an optically reflective, diffusive
or fluorescent stripe parallel to the fluorescent stripes in the
active light-emitting region 1100 of the screen 101. The SOL
reference mark 1210 is fixed at a position with a known distance
from the first fluorescent stripe in the region 1100. SOL patterns
may be a single reflective stripe in some implementations and may
include multiple vertical lines with uniform or variable spacing in
other implementations. Multiple lines are selected for redundancy,
increasing the signal to noise ratio, accuracy of position (time)
measurement, and providing missing pulse detection.
[0081] In operation, the scanning excitation beam 120 is scanned
from the left to the right in the screen 101 by first scanning
through the peripheral reference mark region 1110 and then through
the active region 1100. When the beam 120 is in the peripheral
reference mark region 1110, the signal modulation controller in the
laser module 110 of the system sets the beam 120 in a mode that
ensures adequate sampling of information without crosstalk (e.g.
one beam at a time during one frame) When the scanning excitation
beam 120 scans through the SOL reference mark 1210, the light
reflected, scattered or emitted by the SOL reference mark 1210 due
to the illumination by the excitation beam 1210 can be measured at
an SOL optical detector located near the SOL reference mark 1210.
The presence of this signal indicates the location of the beam 120.
The SOL optical detector can be fixed at a location in the region
1110 on the screen 101 or off the screen 101. Therefore, the SOL
reference mark 1210 can be used to allow for periodic alignment
adjustment during the lifetime of the system.
[0082] When the pulse from the SOL 1210 detected is detected for a
given excitation beam, the laser can be controlled to, after the
delay representing the time for scanning the beam from the SOL 1210
to the left edge of the active display area 1100, operate in the
image mode and carry optical pulses with imaging data. The system
then recalls a previously measured value for the delay from SOL
pulse to beginning of the image area 1100. This process can be
implemented in each horizontal scan to ensure that each horizontal
line starts the image area properly and optical pulses in each
horizontal scan are aligned to the light-emitting stripes. The
correction is made prior to painting the image for that line in the
area 1100 on the screen 101, so there is no time lag in displaying
the images caused by the servo control. This allows for both high
frequency (up to line scan rate) and low frequency errors to be
corrected.
[0083] The servo beam 130 can be used to provide a positioning
reference for each excitation beam 120 for controlling both the
timing for beginning image-carrying pulses before the excitation
beam enters the active light-emitting area 1100 and during the
normal display when the excitation beam 120 scans in the active
light-emitting region 1100. FIG. 13 illustrates the detected signal
power of the light at the servo beam wavelength in the feedback
light 132 to show optical signals indicative of positions of the
SOL mark and stripe dividers on the screen 101. The optical peaks
in the feedback light shown in FIGS. 13 and 14 are idealized as
sharp square wave signals and are likely to have tailing and
leading profiles shown in FIGS. 15-16. Such a pulse signal with
trailing and leading profiles can be converted into square wave
like pulse signals by edge detection.
[0084] Similar to the SOL mark 1210, an end-of-line (EOL) reference
mark can be implemented on the opposite side of the screen 101,
e.g., in the peripheral reference mark region 1120 in FIG. 11. The
SOL mark is used to ensure the proper alignment of the laser beam
with the beginning of the image area. This does not ensure the
proper alignment during the entire horizontal scan because the
position errors can be present across the screen. Implementing the
EOL reference mark and an end-of-line optical detector in the
region 1120 can be used to provide a linear, two point correction
of laser beam position across the image area. FIG. 14 illustrates
the detected signal power of the light at the servo beam wavelength
in the feedback light 132 to show optical signals indicative of
positions of the SOL mark, stripe dividers and EOL mark on the
screen 101
[0085] When both SOL and EOL marks are implemented, the laser is
turned on continuously in a continuous wave (CW) mode prior to
reaching the EOL sensor area. Once the EOL signal is detected, the
laser can be returned to image mode and timing (or scan speed)
correction calculations are made based on the time difference
between the SOL and EOL pulses. These corrections are applied to
the next one or more lines. Multiple lines of SOL to EOL time
measurements can be averaged to reduce noise.
[0086] Based on the stripe divider and SOL/EOL peripheral reference
marks, the positioning of the servo beam 130 on the screen 101 can
be measured. Because the servo beam 130 has a fixed relation with
each excitation beam 120, which can be measured at the SOL
reference mark or EOL reference mark, any error in the positioning
of the servo beam 130 suggests a corresponding error in each
excitation beam 120. Therefore, the positioning information of the
servo beam 130 can be used in the servo control to control the
servo beam 130 and each excitation beam 120 to reduce an alignment
error of the excitation beam.
[0087] The present servo control operates to place each optical
pulse in the excitation beam 120 near or at the center of a target
light-emitting stripe to excite the light-emitting material in that
stripe without spilling over to an adjacent light-emitting stripe.
The servo control can be designed to achieve such alignment control
by controlling the timing of each optical pulse in order to place
the pulse at a desired position on the screen 101 during a
horizontal scan. Accordingly, the servo control, i.e., the
processor and controller 640, needs to "know" horizontal positions
of the light-emitting stripes in each horizontal line before each
horizontal scan in order to control the timing of optical pulses
during the scan. This information on horizontal positions of the
light-emitting stripes in each horizontal line constitutes a
two-dimensional position "map" of the active display area or
light-emitting area of the screen 101 of (x, y) coordinates where x
is the horizontal position of each stripe divider (or equivalently,
the horizontal position of the center of each stripe) and y is the
vertical position or ID number of a horizontal scan. This position
map of the screen 101 can be measured at the factory and may change
in time due to changes in the system components due to temperature,
aging and other factors. For example, thermal expansion effects,
and distortions in the optical imaging system will need
corresponding adjustments in the precise timing to activate each
color in a pixel. If the laser actuation does not properly
correspond to the timing where the beam is directed at the central
portion of a sub-pixel or stripe for the intended phosphor, the
beam 120 will either partially or completely activate the wrong
color phosphor. In addition, this position map of the screen 101
can vary from one system to another due to the component and device
tolerances during the manufacturing.
[0088] Therefore, it is desirable to update the position map of the
screen 101 and to use the updated position map for controlling the
timing of pulses of the excitation beam 120 in each horizontal scan
during the normal display. The position map of the screen 101 can
be obtained using the feedback light 122 and 132 in a calibration
scanning when the system is not in the normal display mode, e.g.,
during the start-up phase of the system. In addition, the servo
feedback light 132 can be used in real time video display to
monitor and measure changes in an existing position map of the
screen 101 when the system is operating in the normal display mode
to produce images on the screen 101. This mode of the servo control
is referred to as dynamic servo. The dynamic monitoring of the
screen 101 can be useful when the system operates for an extended
period time without a downtime because the screen 101 may undergo
changes that can lead to significant changes to the position map of
the screen 101 that is updated during the start-up phase of the
system.
[0089] The position map of the screen 101 can be stored in the
memory of the laser module 110 and reused for an interval of time
if the effects that are being compensated for do not change
significantly. In one implementation, when the display system is
turned on, the display system can be configured to, as a default,
set the timing of the laser pulses of the scanning laser beam based
on the data in the stored position map. The servo control can
operate to provide the real-time monitoring using the servo
feedback light 132 and to control the pulse timing during the
operation.
[0090] In another implementation, when the display system is turned
on, the display system can be configured to, as a default, to
perform a calibration using the excitation beam 120 and the servo
beam 130 to scan through the entire screen 101. The measured
position data are used to update the position map of the screen
101. After this initial calibration during the start-up phase, the
system can be switched into the normal display mode and,
subsequently during the normal display operation, only the servo
beam 130 is used to monitor the screen 101 and the data on the
screen 101 obtained from the servo beam 130 can be used to
dynamically update the position map and thus to control the timing
of pulses in the beam 120 in each horizontal scan.
[0091] The calibration of the position map of the screen 101 can be
obtained by operating each scanning beam 120 or 130 in a continuous
wave (CW) mode for one frame during which the scanning laser beams
120 and 130 simultaneously scan through the entire screen, one
segment at a time as shown in FIG. 5, when multiple laser beams 120
are used. If a single laser is used to produce one excitation beam
120, the single scanning beam 120 is set in the CW mode to scan the
entire screen 101, one line at a time, along with the servo beam
130. The feedback light 122 and 132 from the servo reference marks
on the stripe dividers is used to measure the laser position on the
screen 101 by using the servo detectors 620 and 630.
[0092] The servo detector signals from the servo detectors 620 and
630 can be sent through an electronic "peak" detector that creates
an electronic pulse whenever a servo signal is at its highest
relative amplitude. The time between these pulses can be measured
by a sampling clock in a digital circuit or microcontroller that is
used by the processor and controller 640 to process and generate an
error signal for controlling timing of optical pulses in each
excitation beam 120 in a horizontal scan.
[0093] In one implementation, the time between two adjacent pulses
from the electronic peak detector can be used to determine the
spacing of the two locations that produce the two adjacent
electronic pulses based on the scan speed of the scanning beam 120
or 130 on the screen 101. This spacing can be used to determine the
subpixel width and subpixel position.
[0094] In another implementation, servo measurements and
corrections are based on relative time measurements. Depending on
the beam scan rate and the frequency of the sampling clock, there
are some nominal number of clocks for each sub-pixel. Due to
optical distortions, screen defects or combination of the
distortions and defects, the number of clock cycles between two
adjacent pulses for any given sub-pixel may vary from the nominal
number of clock cycles. This variation in clock cycles can be
encoded and stored in memory for each sub-pixel. Alternatively, a
correction value can be calculated and used for some number N of
adjacent sub-pixels because changes usually do not occur with
significant changes between adjacent sub-pixels.
[0095] FIG. 15 shows one example of the detected reflected feedback
light as a function of the scan time for a portion of one
horizontal scan, the respective output of the peak detector and the
sampling clock signal. A nominal subpixel with a width
corresponding to 9 clock cycles of the sampling clock and an
adjacent short subpixel corresponding to 8 clock cycles are
illustrated. In some implementations, the width of a subpixel may
correspond to 10-20 clock cycles. The clock cycle of the sampling
clock signal of the digital circuit or microcontroller for the
servo control dictates the spatial resolution of the error signal.
As an example for techniques to improve this spatial resolution,
averaging over many frames can be utilized to effectively increase
the spatial resolution of the error signal.
[0096] FIG. 16 shows one example of the detected reflected feedback
light as a function of the scan time for a portion of one
horizontal scan, the respective output of the peak detector and the
sampling clock signal where a nominal subpixel corresponding to a
width of 9 clock cycles and an adjacent long subpixel a
corresponding to a width of 10 clock cycles re illustrated.
[0097] During calibration, contaminants such as dust on the screen,
screen defects, or some other factors may cause missing of an
optical pulse in the reflected feedback light that would have been
generated by a servo reference mark between two adjacent subpixels
on the screen 101. FIG. 17 illustrates an example where a pulse is
missing. A missing pulse can be determined if a pulse is not
sampled or detected within the nominal number of clock cycles for a
subpixel within the maximum expected deviation from the nominal
number of clocks for a subpixel. If a pulse is missed, the nominal
value of clock cycles for a subpixel can be assumed for that
missing sub-pixel and the next sub-pixel can contain the timing
correction for both sub-pixels. The timing correction can be
averaged over both sub-pixels to improve the detection accuracy.
This method may be extended for any number of consecutive missed
pulses.
[0098] The above use of the sampling clock signal to measure the
position map of the screen 101 can be used with detection with the
excitation servo feedback light 122 or the servo feedback light 132
from the screen 101. Because the excitation beam or beams 120 scan
all horizontal lines in the screen 101 during a calibration scan in
a CW mode, the position data from the excitation servo feedback
light 122 can provide data for each and every subpixel of the
screen 101. The position data obtained from the servo beam 130 and
its corresponding feedback light 132, however, only covers one
horizontal scan line per screen segment as shown in FIG. 5. The
position data measured from the servo beam 130 for one screen
segment can be used as a representative scan for all horizontal
lines in that screen segment is used to update position data for
all lines in that screen segment. Two or more servo beams 130 may
be used to increase the number of lines measured in each screen
segment.
[0099] Vertical position of each laser can be monitored and
adjusted by using an actuator, a vertical scanner, an adjustable
lens in the optical path of each laser beam or a combination of
these and other mechanisms. Vertical reference marks can be
provided on the screen to allow for a vertical servo feedback from
the screen to the laser module. One or more reflective, fluorescent
or transmissive vertical reference marks can be provided adjacent
to the image area of the screen 101 to measure the vertical
position of each excitation beam 120. Referring to FIG. 11, such
vertical reference marks can be placed in a peripheral reference
mark region. One or more vertical mark optical detectors can be
used to measure the reflected, fluorescent or transmitted light
from a vertical reference mark when illuminated by the beam 120 or
130. The output of each vertical mark optical detector is processed
and the information on the beam vertical position is used to
control an actuator to adjust the vertical beam position on the
screen 101.
[0100] FIG. 18A shows an example of a vertical reference mark 2810.
The mark 2810 includes is a pair of identical triangle reference
marks 2811 and 2812 that are separated and spaced from each other
in both vertical and horizontal directions to maintain an overlap
along the horizontal direction. Each triangle reference mark 2811
or 2812 is oriented to create a variation in the area along the
vertical direction so that the beam 120 partially overlaps with
each mark when scanning through the mark along the horizontal
direction. As the vertical position of the beam 120 changes, the
overlapping area on the mark with the beam 120 changes in size. The
relative positions of the two marks 2811 and 2812 defines a
predetermined vertical beam position and the scanning beam along a
horizontal line across this predetermined vertical position scans
through the equal areas as indicated by the shadowed areas in the
two marks 2811 and 2812. When the beam position is above this
predetermined vertical beam position, the beam sees a bigger mark
area in the first mark 2811 than the mark area in the second mark
2812 and this difference in the mark areas seen by the beam
increases as the beam position moves further up along the vertical
direction. Conversely, when the beam position is below this
predetermined vertical beam position, the beam sees a bigger mark
area in the second mark 2812 than the mark area in the first mark
2811 and this difference in the mark areas seen by the beam
increases as the beam position moves further down along the
vertical direction.
[0101] The feedback light from each triangle mark is integrated
over the mark and the integrated signals of the two marks are
compared to produce a differential signal. The sign of the
differential signal indicated the direction of the offset from the
predetermined vertical beam position and the magnitude of the
differential signal indicates the amount of the offset. The
excitation beam is at the proper vertical position when the
integrated light from each triangle is equal, i.e., the
differential signal is zero.
[0102] FIG. 18B shows a portion of the signal processing circuit as
part of the vertical beam position servo feedback control in the
laser module 110 for the vertical reference mark in FIG. 18A. A PIN
diode preamplifier 2910 receives and amplifies the differential
signal for the two reflected signals from the two marks 2811 and
2812 and directs the amplified differential signal to an integrator
2920. An analog-to-digital converter 2930 is provided to convert
the differential signal into a digital signal. A digital processor
2940 processes the differential signal to determine the amount and
direction of the adjustment in the vertical beam position and
accordingly produces a vertical actuator control signal. This
control signal is converted into an analog control signal by a
digital to analog converter 2950 and is applied to a vertical
actuator controller 2960 which adjusts the actuator. FIG. 18C
further shows generation of the differential signal by using a
single optical detector.
[0103] FIG. 19 shows an example of the screen in FIG. 11 having the
start of line (SOL) reference mark and the vertical beam position
reference marks. Multiple vertical beam position reference marks
can be placed at different vertical positions to provide vertical
position sensing of the excitation beams 120 in all screen
segments. The example in FIG. 19 shows the SOL reference mark is
located between the vertical beam position reference marks and the
screen display area so that, in a horizontal scan beginning from
the left to the right, the excitation beam 120 or the servo beam
130 hits the SOL reference mark after the vertical beam position
reference marks. In another implementation for a horizontal scan
beginning from the left to the right, the SOL reference mark is
located between the vertical beam position reference marks and the
screen display area to ensure that the excitation beam 120 or the
servo beam 130 hits the SOL reference mark before the vertical beam
position reference marks. In addition, separate from the vertical
beam position reference marks for the excitation beams 120,
multiple vertical beam position reference marks can be placed at
different vertical positions, e.g., one vertical reference mark for
the servo beam 130 to provide vertical position sensing of the
servo beam 130 in each screen segment. These vertical reference
marks are presented by the numeral "1910" in FIG. 19. The
combination of the SOL reference 1210, the vertical reference marks
1910 and the periodic pattern in the strip structure of the
light-emitting area 1110 provides positioning information of the
invisible servo beam 130, positioning information of the excitation
beams 120 and the horizontal parameters of the pixels on the screen
101 for servo control in a scanning display system.
[0104] FIG. 20 shows an example of the operation of a servo control
using the servo beam 130 during the normal display mode when each
excitation beam 120 is used for carrying optical pulses for
producing images on the screen 101 and is not used for servo
control. The servo beam 130 is a CW beam and is scanned over one
horizontal line per screen segment with the scanning modulated
excitation Laser beams 120. The servo feedback light 132 is
detected by the one or more servo detectors 620 to measure an
alignment error of the servo beam 130 on the screen 101 during the
normal display. The alignment of each excitation laser beam 120 is
adjusted based on the measured alignment error of the servo beam
130 to reduce the alignment error of the excitation laser beam 120.
In other implementations, the red, green and blue light emitted by
the screen 101 or a portion of back-reflected excitation light of
the scanning excitation beam 120 can be used to provide a
calibration mechanism to calibrate the measurements obtained via
the servo beam 130.
[0105] In the above examples for using the invisible IR servo beam
130 to provide the feedback light 132 to the laser module 110, the
parallel phosphor stripes and the stripe dividers on the screen 101
are used to produce back-reflected feedback light 132 by reflection
of the servo beam 132 at the stripe dividers. Alternatively, the
screen 101 can be designed to include IR feedback marks that are
configured to produce desired feedback light 132. The IR feedback
marks can be registered with a special spatial relationship with
respect to the stripe dividers or the phosphor stripes, e.g., a
servo feedback mark is aligned in position with a light-emitting
stripe or a division (a divider) between two adjacent parallel
light-emitting stripes in the screen. In the examples described
below, such position registration is not required and it is
sufficient that the IR feedback marks have a fixed and known
spatial relationship with respect to the stripe dividers or the
phosphor stripes so that there is a fixed and known mapping of the
positions of the IR feedback marks and the positions of the
phosphor stripes and stripe dividers.
[0106] FIG. 21 shows an example design for the light-emitting
screen 101 that includes IR feedback marks on the excitation side
of the phosphor layer. This screen 101 includes a phosphor stripe
layer 2110 with parallel phosphor stripes emitting red, green and
blue light under excitation of the excitation beam 120, a back
panel 2112 on the excitation side of the phosphor layer 2110 facing
the excitation beam 120 and the IR servo beam 130, and a front
panel 2111 on the viewer side of the phosphor layer 2110. In this
example, IR feedback marks 2120 are formed on the back surface of
the back panel to provide the IR feedback light 132 by reflecting
or scattering the IR servo beam 130. In other implementations, the
IR feedback marks 2120 may be placed at other positions and can be
located on either the excitation side or the viewer side of the
phosphor layer 2110.
[0107] The IR feedback marks 2120 are designed to provide position
registration of the servo beam 130 on the screen and can be
implemented in various configurations. For example, the IR feedback
marks 2120 can be periodic parallel stripes that are parallel to
the parallel phosphor stripes in the phosphor layer 2110. An IR
feedback mark 2120 can be placed at any position relative to a
stripe divider or a phosphor stripe in the phosphor layer 2110
along the horizontal direction, including a position horizontally
displaced from a stripe divider or the center of a phosphor stripe.
The width of each of the IR feedback marks 2120 can be equal to the
width of the beam spot of the IR servo beam 130 on the screen 101
when the detection for the IR servo feedback light 132 is based on
a peak detector. IR feedback marks 2120 with a width wider than the
width of the beam spot of the IR servo beam 130 on the screen 101
can be used if the detection for the IR servo feedback light 132 is
based on the position of each IR feedback mark 2120 with respect to
a position reference such as the SOL mark. The width of the IR
feedback marks 2120 may be less than the width of each phosphor
stripe, e.g., one half of the width of a phosphor stripe. The
spacing between two adjacent IR feedback marks 2120 can be greater
than the spacing between two adjacent phosphor stripes. For
example, the IR mark spacing can be 25 mm and the phosphor stripe
spacing can be 1.5 mm.
[0108] The IR feedback marks 2120 can be made to be optically
different from the areas surrounding and between the IR feedback
marks 2120 to allow for optical detection of the IR feedback marks
2120 to register the positions of the IR feedback marks 2120 on the
screen while maintaining the substantially the same optical
transmission for the excitation beam 120 as the areas surrounding
and between the IR feedback marks 2120. Therefore, the presence of
the IR feedback marks 2120 does not optically interfere with the
optical transmission of the excitation beam 120 by optically
imprinting the shapes of the marks 2120 on the excitation beam 120
that reaches the phosphor layer of the screen 101. In this regard,
the IR feedback marks 2120 can be implemented in various
configurations. For example, each IR feedback mark 2120 can be made
to have a smooth surface facing the excitation side and optically
specularly reflective to light and the areas surrounding and
between the IR feedback marks 2120 are configured to exhibit
optically diffused reflection which spreads in different
directions. The specularly reflective IR feedback marks 2120 and
the diffusively reflective areas surrounding and between the marks
2120 have the same optical transmission characteristics. Different
from the above design of having specularly reflective marks 2120 in
a diffusive background, the IR feedback marks 2120 can also be made
diffusively reflective to light and the areas surrounding and
between the marks 2120 are made specularly reflective. As another
example, the IR feedback marks 2120 can have a transmissivity or
reflectivity at the wavelength of the excitation beam 120 that is
significantly different from the wavelength of the servo beam and
servo wavelengths. For example, the IR feedback marks 2120 can be
configured to be optically transparent to light of the excitation
beam 120 and optically reflective to light of the servo beam 130 so
that the IR feedback marks 2120 are optically "invisible" to the
excitation beam 120 and reflect the servo beam 130 to produce the
IR servo feedback light 132.
[0109] FIGS. 22 and 23 show examples of screen layout
configurations with vertical reference marks 1910 for measuring the
vertical positions of the IR servo beam 130. In FIG. 22, the
vertical reference marks 1910 are located on the edge of the
screen, preferable outside the main display area of the screen. In
FIG. 23, the vertical reference marks 1910 are placed at the edges
and in the middle of the screen and may be made to have the same
optical transmission characteristics for light of the excitation
beam 120.
[0110] FIG. 24 shows a specific example of a screen design with
specularly reflective IR feedback marks and optically diffusive
areas surrounding and between the IR feedback marks. In this
example, an IR feedback mark is formed by a film stripe that has a
smooth surface to produce a specular reflection 2430 of the
incident IR servo light 130. The screen area between two IR
feedback marks is formed by a film layer with a roughened surface
that diffuses light in reflecting the incident IR servo light 130
to produce the diffused reflection 2440 that spreads in different
directions forming a diffused reflection cone. The two regions 2410
and 2420 have approximately the same optical transmission for light
of the excitation beam 120.
[0111] The above screen design for IR servo feedback can use the
different optical behaviors of the specular reflection and the
diffusive reflection of the IR servo beam 130 from the screen in
the optical far field from the screen to facilitate the servo
detection as shown in the example in FIG. 25.
[0112] FIG. 25 shows an exemplary scanning beam display system 2500
that provides an IR servo feedback based on the screen design in
FIG. 24. The laser module 110 projects and scans both the IR servo
beam 130 and the excitation beam 120 onto the screen 101 with IR
feedback marks. The laser module 110 has a symmetric optic axis
2501 around which the beam scanning is performed. The screen 101
has a construction as shown in FIG. 21 or 22 based on the design in
FIG. 24. An optical telecentric lens 2510 such as a Fresnel lens
layer is provided in to couple the incident scanning beams 120 and
130 from the laser module 110 onto the screen 101 in a
substantially normal incidence to the screen 101. The telecentric
lens 2510 is configured to have its symmetric optic axis 2502 to be
parallel to the optic axis 2501 of the laser module 110 with an
offset 2503. As illustrated, the Fresnel lens 2510 is placed in
front of the back surface of the screen 101 with an air gap
2520.
[0113] The IR servo detection is provided by using an IR servo
detector 2530 located along an optical path of the returned
specular reflection 2430 of the incident IR servo light 130 from
the IR feedback marks on the screen 101. The location of the IR
servo detector 2530 is determined by the offset 2503 for receiving
the returned specular reflection 2430 of the incident IR servo
light 130 from each IR feedback mark on the screen 101. Returned IR
light in a direction different from the specular reflection
direction at each IR feedback mark is directed by the Fresnel lens
2510 to miss the IR servo detector 2530 when the deviation from the
specular reflection exceeds a range beyond the aperture of the IR
servo detector 2530. Under this design, only a very small fraction
of the returned IR servo light in the diffused reflection 2440 from
an area between IR feedback marks is received by the IR servo
detector 2530 and the majority of the returned IR servo light in
the diffused reflection 2440 is not collected by the IR servo
detector 2530. In contrast, the light in the returned specular
reflection 2430 of the incident IR servo light 130 from each IR
feedback mark on the screen 101 is substantially collected by the
IR servo detector 2530. Based on this difference, the detector
signals from the IR servo detector 2530 can be used to determine a
hit by the scanning IR servo beam 130 on an IR feedback mark.
[0114] The light of the excitation beam 120 can also be reflected
back by the specular and diffusive regions on the screen 101.
Hence, the specularly reflected light at the excitation wavelength
is directed back to the same location at the IR servo detector
2530. A wavelength selective optical beam splitter can be used to
split the collected light at the servo wavelength and the collected
light at the excitation wavelength into two separate signals for
separate optical detectors, the IR servo detector 2530 to receive
the IR servo light and another servo detector to receive the
feedback light at the excitation wavelength.
[0115] The scanning IR servo beam 130 can be a CW beam. As such,
each hit at an IR feedback mark on the screen produces an optical
pulse at the IR servo detector 2530. In each horizontal scan, the
IR servo detector 2530 detects a sequence of optical pulses that
correspond to the different IR feedback marks on the screen,
respectively. The detector output of the IR servo detector 2530 is
similar to the detector outputs shown in FIGS. 13-17 obtained by
using phosphor strip dividers as IR feedback marks except that the
pulse separation in the detector output of the IR servo detector
2530 in time is greater and corresponds to the IR feedback mark
spacing. Similarly, SOL or EOL signals can be used to determine the
horizontal location of the scanning IR servo beam 130 and vertical
reference marks can be used to determine the vertical position of
the scanning IR servo beam 130.
[0116] In the system examples in FIGS. 1, 6 and 7, the excitation
servo feedback light 122 can be used in combination with the servo
feedback based on invisible servo beam 130. In such systems with
combination servo controls, the positioning measurements from both
the IR servo light feedback and the excitation light servo feedback
can be used to calibrate with respect to each other. For example,
such a display system can be operated to perform a calibration
using the excitation beam 120 and the IR servo beam 130 to scan
through the entire screen 101 to measure the position maps of the
screen 101 and to use the position map obtained from the excitation
beam 120 to calibrate the position map obtained from the IR servo
beam 130. Based on this calibration, during the normal operation of
the system, the feedback from the IR servo beam 130 can be used,
without the feedback based on the excitation light servo feedback,
to monitor the screen 101 and to control the timing of pulses in
the beam 120 in each horizontal scan.
[0117] In some implementations, the screen 101 can be designed to
utilize as much the excitation light for producing the visible
light by reducing any optical loss of the excitation light from the
excitation beam 120. For example, the screen can be designed to
eliminate any optical reflection back to the laser module 110 by
using, e.g., an optical layer on the excitation side of the
phosphor layer to transmit light of the excitation beam into the
phosphor layer and recycle any excitation light from the phosphor
layer back into the phosphor layer. Under such a design, it can be
difficult to use light from the excitation beam 120 to produce the
servo beam 122. The following sections describe system designs that
use visible light emitted by the phosphor layer in the screen 101
to produce a visible servo beam and to provide a second feedback
mechanism in addition to the invisible IR servo feedback.
[0118] FIG. 26 shows an example of a scanning beam display system
2600 that provides the servo feedback based on the IR servo beam
130 and a second servo feedback based on detection of emitted
visible light from the phosphor layer in the screen. In this
system, an off-screen optical servo sensing unit 2610 is used to
detect the red, green and blue light emitted from the screen 101.
The servo sensing unit 2610 can be located at a location where the
emitted visible light from the screen 101 can be detected, e.g., at
the viewer side of the screen 101 or at the excitation side of the
screen 101 as shown, and the location of the servo sending unit
2610 can be selected based on the screen design and the system
layout. Three optical detectors PD1, PD2 and PD3 are provided in
the sensing unit 2610 to detect the red, green and blue fluorescent
light, respectively. Each optical detector is designed to receive
light from a part of or the entire screen 101. A bandpass optical
filter can be placed in front of each optical detector to select a
designated color while rejecting light of other colors. This
sensing unit 2610 generates a servo feedback signal 2612 to the
laser module 110 for controlling the system operation.
[0119] One way to correct the horizontal misalignment in the
display systems in FIG. 26 is to program the display processor in
the laser module 110 to control the timing of the optical pulses
based on the position error detected in the feedback signal 2612.
For example, the laser module 110 can delay the modulated image
signal carried by the modulated laser beam 120 by one sub color
pixel time slot if the green detector has an output and red and
blue detectors have no output or by two sub color pixel time slots
if the blue detector has an output and red and green detectors have
no output. This correction of a spatial alignment error by a time
delay may be achieved digitally within the display processor. No
physical adjustment in the optical scanning and imaging units in
the laser module 110 is needed. Alternatively, you mean the
controller unit in the laser module 110 may be adjusted to
physically shift the position of the excitation beam 120 on the
screen 101 so that the laser position on the screen 101 is adjusted
horizontally to the left or right by one sub pixel in response to
the error detected by the servo sensing unit 2610. The optical
alignment by physically adjusting the scanning laser beam 120 and
the electronic or digital alignment by controlling the timing of
optical pulses can be combined to control the proper horizontal
alignment.
[0120] A test pattern can be used to check the horizontal alignment
in the display system 2600 in FIG. 26. For example, a frame of one
of the red, green and blue colors may be used as a test pattern to
test the alignment. FIG. 27A shows a test pattern for the color
pixel embedded with the detectors in the servo sensing unit 2610
and the corresponding outputs of the three detectors PD1, PD2 and
PD3 when the horizontal alignment is proper without an error. FIGS.
27B, 27C and 27D show three different responses generated by the
three detectors PD1, PD2 and PD3 when there is a misalignment in
the horizontal direction. The detector responses are fed to the
laser module 110 and are used to either use the time-delay
technique or the adjustment of the beam imaging optics to correct
the horizontal misalignment.
[0121] Hence, the servo feedback control based on sensing the
screen-emitted visible light in FIG. 26 is operated in during a
designated calibration operation of the system 2600 when the system
2600 is not displaying images for the viewer. This type of feedback
control is "static" because the system is operated out of its
normal display mode and is operated with test patterns for
measuring the alignment conditions of the screen 101. For example,
such a static servo feedback algorithm can be performed once at the
power-on of the display system or at the factory initial map
generation before the system begins the normal display of the
images on the screen 101 and the display system can be controlled
to perform the initial clock calibration to align the laser pulses
to the sub-pixel center positions. Different from the static servo
control, a dynamic servo control can also be implemented during the
normal display operation mode of the system. For example, the
dynamic servo feedback algorithm is performed continuously during
the normal operation of the display system. This dynamic servo
feedback keeps the pulses timed to the subpixel center position
against variations in temperature, screen motion, screen warping,
system aging and other factors that can change the alignment
between the laser and the screen. The dynamic servo control is
performed when the video data is displayed on the screen and is
designed in a way that it is not apparent to the viewer. This
dynamic control is provided by the invisible servo control in the
system 2600 in FIG. 26.
[0122] FIG. 28 illustrates an example of an optical servo design
using a visible light servo optical sensor 4501 placed away from a
fluorescent screen 101 on the viewer side of the screen 101 in the
scanning beam display system 2600. The optical sensor 4501 may be
configured and positioned to have a field of view of the entire
screen 101. A collection lens may be used between the screen 101
and the sensor 4501 to facilitate collection of the fluorescent
light from the screen 101. The optical sensor 4501 can include at
least one optical detector to detect fluorescent light at a
selected color, e.g., green from different colors (e.g., red, green
and blue) emitted by the screen 101. Depending on the specific
techniques used in the servo control, a single detector for a
single color may be sufficient for the servo control in some
implementations and, in other implementations, two or more optical
detectors for detecting two or more colors of the fluorescent light
from the screen 101 may be needed. Additional detectors may be used
to provide detection redundancy for the servo control. Referring to
the reference marks for generating reference signals, detection of
such reference signals and control functions based on the reference
signals from reference marks, the servo control can be combined
with the control functions of the reference marks for the system.
In an example described below, the start of line reference mark
outside the screen area having the fluorescent stripes can be used
as a timing reference for static servo control of the timing of
optical pulses of the scanning beam.
[0123] In the example in FIG. 28, the optical sensor 4501 includes
three servo optical detectors 4510, 4520 and 4530 (e.g.,
photodiodes) that detect, respectively, three different colors
emitted by the screen 101. The photodiodes 4510, 4520 and 4530 are
arranged in three groupings and each group is filtered by a red
filter 4511, a green filter 4521 or a blue filter 4531 so that
three photodiodes 4510, 4520 and 4530 receive, respectively, three
different colors. Each filter may be implemented in various
configurations, such as a film which makes a photodiode sensitive
only to one of the red, green and blue colors from the viewing
screen.
[0124] The detector circuit for each color group can include a
preamplifier (preamp) 4540, a signal integrator (e.g., a charge
integrator) 4541, and an A/D converter 4540 to digitize the red,
green or blue detector signal for processing in a digital servo
circuit 4550 which may be a microcomputer or microprocessor. The
red, green and blue light intensities of the fluorescent light
emitted from the screen 101 can be measured and the measured
results are sent to the digital servo circuit 4550. The digital
servo circuit 4550 can generate and use a reset signal 4552 to
reset the integrators 4541 to control the integration operation of
the detectors. Using these signals, the digital servo circuit 4550
can determine whether there is an error in the alignment of a
scanning laser beam on the screen 101 and, based on the detected
error, determines whether the laser clock is to be advanced or
delayed in time in order to center the laser pulses on the
subpixels on the screen 101.
[0125] The static servo control operations described here are
performed when the display system is not in the normal operation
for displaying images on the screen. Hence, the regular frame
scanning in both directions using the galvo vertical scanner and
the polygon horizontal scanner during the normal operation can be
avoided. The vertical scanning by the galvo scanner can be used to
direct a scanning laser beam at a desired vertical position and
fixed at that position to perform repetitive horizontal scans with
different time delays in the laser pulse timing to obtain the
desired error signal indicating the laser timing error in the
horizontal scan. In addition, a special laser pulse pattern (e.g.,
FIGS. 27A-D and 29) that does not carry image signals can be used
during the static servo operation to generate the error signal.
[0126] In the static servo control, the laser pulse pattern for a
laser can be chosen to generate a signal that is proportional to
the position error of the laser pulses on the screen 101. In one
implementation where multiple lasers are used, each laser is pulsed
one at a time across the screen 101 and the remaining lasers are
turned off This mode of operation allows the timing for each laser
to be measured and corrected independently during a static servo
control process.
[0127] FIGS. 29 and 30 illustrate one example technique for
generating the error signal for implementing the static servo
control. FIG. 29 shows an example of a test optical pulse pattern
modulated onto a scanning laser beam that has a periodic pulse
pattern of laser pulses. The pulse width in time of this test pulse
pattern corresponds to a spatial width on the screen that is
greater than the width (d) of the border between two adjacent
subpixels and less than twice of the width (D) of a subpixel (one
fluorescent stripe). For example, the pulse width in time of this
pulse pattern corresponds to a spatial width equal to the width (D)
of a subpixel. The repetition time of the pulse pattern corresponds
to a spatial separation of two adjacent laser pulses on the screen
that is equal to the width (3D) of one color pixel (three
successive fluorescent stripes).
[0128] In operation, the timing of the laser pulse pattern in FIG.
29 is adjusted so that each laser pulse partially overlaps with one
subpixel and an adjacent subpixel to excite light of different
colors in the two adjacent subpixels. Hence, a laser pulse
overlapping with two adjacent subpixels (e.g., a red subpixel and a
green subpixel) has a red excitation portion that overlaps with the
red subpixel to produce red light and a green excitation portion
that overlaps with the adjacent green subpixel to produce green
light. The relative power levels of the emitted red light and the
emitted green light are used to determine whether the center of the
laser pulse is at the center of the border between two adjacent
subpixels and the position offset between the center of the laser
pulse and the center of the border. Based on the position offset,
the servo control adjusts the timing of the laser pulse pattern to
reduce the offset and to align the center of the laser pulse at the
center of the border. Upon completion of this alignment, the servo
control advances or delays the timing of the laser pulse pattern to
shift each laser pulse by one half of the subpixel width to place
the center of the laser pulse to the center of either of the two
adjacent subpixels. This completes the alignment between a laser
and a color pixel. During the above process, the vertical scanner
is fixed to direct the laser under alignment to a fixed vertical
position and the horizontal polygon scanner scans the laser beam
repetitively along the same horizontal line to generate the error
signal.
[0129] The above process uses the relative power levels of the
emitted red light and the emitted green light to determine position
offset between the center of the laser pulse and the center of the
border between two adjacent subpixels. One way to implement this
technique is to use a differential signal based on the difference
in the amounts of light emitted by the two different phosphor
materials. A number of factors in the servo detection in FIG. 28
can affect the implementation. For example, different fluorescent
materials for emitting different colors may have different emission
efficiencies at a given excitation wavelength so that, under the
same scanning excitation beam, two adjacent subpixels can emit
light in two different colors (e.g., green and red) with different
power levels. As another example, the color filters 4511, 4521 and
4531 for transmitting red, green and blue colors may have different
transmission values. As yet another example, the optical detectors
4510, 4520, and 4530 may have different detector efficiencies at
the three different colors and thus for the same amount of light
entered into the detectors at different colors, the detector
outputs may be different. Now consider the condition where the
center of a laser pulse is aligned to the center of the border
between two adjacent subpixels and thus the laser pulse is equally
spit between the two adjacent subpixels. Due to the above and other
factors, the servo optical detectors corresponding to the emission
colors of the two adjacent subpixels may produce two detector
outputs of two different signal levels when the laser pulse is
equally spit between the two adjacent subpixels. Hence, for a given
display system, the servo detector signals can be calibrated to
account for the above and other factors to accurately represent the
position offset of the laser pulse. The calibration can be achieved
via the hardware design, software in the digital signal processing
in the servo digital circuit 4550 in FIG. 28, or a combination of
both the hardware design and signal processing software. In the
following sections, it is assumed that the proper calibration is
implemented so that the calibrated detector outputs from two
different servo optical detectors are equal when the laser pulse is
equally spit between the two adjacent subpixels.
[0130] Therefore, under a proper alignment condition, each of the
laser pulses has one half of the pulse over a green subpixel, and
the remaining one half of the same pulse over an adjacent red
subpixel. This pulse pattern generates equal amounts of red and
green light on the servo detectors when the alignment is proper.
Therefore, the difference in the detector output voltage between
the red detector and the green detector is an error signal that
indicates whether the alignment is proper. When the alignment is
proper, the differential signal between the red and green detectors
is zero; and, when the alignment is off from the proper alignment,
the difference is either a positive value or a negative value
indicating the direction of the offset in alignment. This use of a
differential signal between two color channels can be used to
negate the importance of measuring the absolute amplitude of the
light emanated from the viewing screen phosphor. Alternatively, the
difference between two different color channels, the blue and red
detectors or the green and blue detectors, may also be used to
indicate the alignment error. In some implementations, because the
blue light is closest to the incident excitation laser light
wavelength, it can be more practical to use the difference between
the green and red detectors for the servo control. An optical
sensor for detecting light from the reference mark, which is
separate from the optical sensor 4501 for detecting the fluorescent
feedback light from the screen in FIG. 28, is used to generate the
detection signal and is connected to the digital servo circuit
4550.
[0131] In the static servo control, the start of the timing scan
can be corrected first using the test pulse pattern in the scanning
laser beam. The timing is corrected for the first group of adjacent
pixels along the horizontal scan (e.g., 5 pixels), then the next
group of adjacent pixels of the same size, e.g., the next 5 group,
then the next 5 group, until the entire scan has been corrected for
a given laser. Here, the number of 5 pixels is chosen as an example
for illustration. Such grouping can be used to reduce the amount of
time needed for the servo control and to increase the
signal-to-noise ratio of the error signal when the signals
generated from different pixels in one group are integrated. In
practice, the number of pixels for each of the groups can be
selected based on specific requirements of the display system. For
example, the severity of the initial timing error may be considered
where a small timing error may permit a large number of successive
pixels to be in a group for the servo control and a large timing
error may require a smaller number of successive pixels to be
grouped together for the servo control. In each measurement, the
timing error of the scanning beam can be corrected to one clock
cycle of the digital clock of the digital servo circuit 4550. In
FIG. 45, digital servo circuit 4550 is a micro-controller which is
designed to have timing control for each individual laser and is
used to correct the timing of the laser pulse for each pixel.
[0132] Notably, various phosphors can exhibit persistence in
fluorescent emission. This property of phosphors can cause the
phosphor to produce light after the laser pulse has moved to the
next pixel. Referring to FIG. 28, the signal integrator 4541 can be
connected at the output of the preamp 4540 for each servo detector
to offset this effect of the phosphor. The integrator 4541 can be
used to effectively "sum" all the light for a given preamp 4540
over multiple pixels while the reset line for the integrator is low
to set the integrator in the integration mode. When the
micro-controller initiates an A/D sample, the summed light for a
given color is sampled. The reset line 4552 for each integrator
4541 then goes high until the integrator voltage is set back to
zero to reset the integrator 4541 and is subsequently released back
to low to restart a new integration period during which the
integrator 4541 starts summing the light again.
[0133] FIG. 30 illustrates how the error signal varies as the laser
timing is varied from its nominal position directly centered
between the red and green subpixels using the laser pulse pattern
in FIG. 29. When the error voltage of a differential signal based
on the laser pulse pattern in FIG. 29 is equal to zero as shown in
FIG. 30, there are equal amounts of Red and Green light on the red
and green servo detectors, and the timing of the laser pulses is
directly over the borders between two adjacent sub-pixels. In this
manner, the error signal at each sample represents the laser timing
error only for the period after the previous reset pulse. Using
this scheme, a corrected laser timing map can be generated for each
laser on every horizontal sweep until the entire screen timing is
corrected for each laser. The vertical scanner is used to change
the vertical position of the horizontal scanning beam from each
laser.
[0134] The above technique for generating the static servo error
signal uses a border between the two adjacent subpixels as an
alignment reference to align the laser pulse in a laser pulse
pattern. Alternatively, the center of each subpixel may be directly
used as an alignment reference to center the laser pulses directly
over the subpixels without using the borders between two adjacent
subpixels. Under this alternative method, the output from a single
color servo optical detector is sufficient to generate the error
signal for the servo control. An alignment reference mark, such as
the start of line (SOL) peripheral alignment reference mark in FIG.
12 and a separate SOL optical detector that detects the feedback
light from the SOL mark, can be used to provide a timing reference
and assist the alignment. Referring to FIG. 45, the SOL optical
detector is connected to direct its output to the digital servo
circuit 4550.
[0135] This alternative static servo technique can be implemented
as the follows. A test pulse pattern that has at least one pulse
corresponding to one subpixel within a pixel used to modulate the
scanning laser beam where the pulse width corresponds to one
subpixel width (D) or less. In a horizontal scan, the laser timing
is adjusted on the first group of subpixels of the scan after the
SOL signal is detected by the SOL optical detector. Based on the
timing reference from the SOL signal, the laser timing of the laser
pulse pattern is adjusted to maximize the detected optical power of
one of the three colors emitted by the fluorescent screen, e.g.,
the Green light (or Red, or Blue). The adjustment can be achieved
by pulsing the laser once per pixel and adjusting the laser timing.
When the Green light is maximized on the first 5 pixels, the next
five green subpixels are pulsed. The timing is advanced by one
clock cycle during one horizontal scan, then delayed by one clock
cycle on subsequent laser horizontal scans at the same vertical
position on the screen. The timing that produces the maximum Green
light is chosen as the correct laser timing. If the output signal
from advancing the clock cycle is equal to the output signal form
delaying the clock cycle, then the laser timing is proper and is
left unchanged. The next 5 pixels are then illuminated with the
advanced and delayed laser clock cycles, and the timing that
produces the maximum Green light is chosen for this group of 5
pixels. This operation is repeated across the horizontal length of
the screen until the end of the screen is reached. This method can
also produce a laser clock that is corrected for each laser as the
beam from the laser sweeps horizontally across the screen.
[0136] The above static servo control operations are performed when
the display system is not in the normal operation and thus a test
pulse pattern (e.g., FIG. 29) that does not carry image signals can
be used. The dynamic servo correction is performed by using the
invisible IR servo feedback during normal operation and viewing of
images on the screen.
[0137] On a given horizontal scan, all the lasers can be advanced
in phase by one clock cycle of the digital circuit 4550. This
operation causes all the laser beams to shift in their positions on
the screen by a scanning distance over the one clock cycle and this
shift is small when the scanning distance is small (e.g., less than
one tenth of the subpixel width). Accordingly, the amplitude of the
emitted color light from a subpixel (e.g., the green detector) is
slightly changed. On the next frame, all the lasers are delayed in
phase by one clock cycle. If the nominal laser pulse position is
initially correct, the amplitudes of the delayed and advanced scans
of the two different and successive image frames should be equal
for any color chosen to be measured and observed. When the
amplitudes of the delayed and advanced scans of two different
frames are different, there is a laser timing error and a
correction can be applied to the laser timing to reduce the
difference in subsequent image frames while the error signal is
being monitored and the correction is updated based on the newly
generated error signal. The sign of the difference indicates the
direction of the offset in the laser timing error so that the servo
control can apply the correction to negate the offset. Similar to
the second static servo control method described above, the output
from a single color servo optical detector is sufficient to
generate the error signal for the dynamic servo control.
[0138] FIG. 31 shows a more detailed example of a scanning beam
system based on both the dynamic invisible servo feedback and the
visible light static servo feedback. An IR servo detector 620 is
provided on the excitation side of the screen 101 to detect the IR
servo light 132 reflected from the screen 101 while visible light
servo detectors 3110 are placed on the viewer side of the screen
101 to detect screen-emitted visible light 3120 to provide visible
light servo detector signals that are fed into the display
processor and controller 640. The visible light static servo
feedback is used to calibrate the position map of the dynamic IR
servo feedback during a calibration run of the system and the
calibrated dynamic IR servo feedback is used during normal
operation of the system to correct beam alignment errors.
[0139] While this patent application contains many specifics, these
should not be construed as limitations on the scope of an invention
or of what may be claimed, but rather as descriptions of features
specific to particular embodiments of the invention. Certain
features that are described in this patent application in the
context of separate embodiments can also be implemented in
combination in a single embodiment. Conversely, various features
that are described in the context of a single embodiment can also
be implemented in multiple embodiments separately or in any
suitable subcombination. Moreover, although features may be
described above as acting in certain combinations and even
initially claimed as such, one or more features from a claimed
combination can in some cases be excised from the combination, and
the claimed combination may be directed to a subcombination or a
variation of a subcombination.
[0140] Only a few implementations are disclosed. However,
variations and enhancements of the described implementations and
other implementations can be made based on what is described and
illustrated in this patent application.
* * * * *