U.S. patent application number 09/991655 was filed with the patent office on 2002-08-15 for multiple channel scanning device using oversampling and image processing to increase throughput.
This patent application is currently assigned to SAIC. Invention is credited to Drobot, Adam Thomas, Green, Albert Myron, Phillips, Edward Alan, White, Robert Courtney, Wyeth, Newell Convers.
Application Number | 20020110077 09/991655 |
Document ID | / |
Family ID | 22213410 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020110077 |
Kind Code |
A1 |
Drobot, Adam Thomas ; et
al. |
August 15, 2002 |
Multiple channel scanning device using oversampling and image
processing to increase throughput
Abstract
A multiple channel scanning device has a scanning head with
multiple columns of apertures that emit light which is projected to
a small spot on the surface of a recorded medium. Light returned
from the medium reenters the apertures and is conducted to
detectors. In a preferred embodiment, the scanning head is rapidly
oscillated (may be on the order of 100 kHz rate), in a direction
parallel to the columns. The medium is moved in a direction
perpendicular to the columns so that the same recorded regions pass
beneath successive columns of apertures. The data from the
detectors is image-processed to improve the quality of data reading
using the successive readings of the same data regions. This allows
errors to be corrected and throughput to be improved.
Inventors: |
Drobot, Adam Thomas;
(Annandale, VA) ; Green, Albert Myron;
(Alexandria, VA) ; Phillips, Edward Alan; (Great
Falls, VA) ; White, Robert Courtney; (Fairfax,
VA) ; Wyeth, Newell Convers; (Oakton, VA) |
Correspondence
Address: |
BANNER & WITCOFF
1001 G STREET N W
SUITE 1100
WASHINGTON
DC
20001
US
|
Assignee: |
SAIC
San Diego
CA
|
Family ID: |
22213410 |
Appl. No.: |
09/991655 |
Filed: |
November 26, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09991655 |
Nov 26, 2001 |
|
|
|
09088780 |
Jun 2, 1998 |
|
|
|
Current U.S.
Class: |
369/112.27 ;
369/118; G9B/7.018; G9B/7.109 |
Current CPC
Class: |
G11B 7/124 20130101;
G11B 7/005 20130101 |
Class at
Publication: |
369/112.27 ;
369/118 |
International
Class: |
G11B 007/135 |
Claims
What is claimed is:
1. A scanning device for scanning a target surface having data
written thereon, said data being arranged in adjacent data cells on
said target surface, each of said cells having one of a set of
possible configurations representing data, comprising: a read/write
head with at least one reading laser source connected to emit light
from an array of output apertures and receive light through an
array of input apertures; an image processor; said read/write head
and said target surface being supported to move relative to each
other to scan said target surface; said array of output apertures
being arranged such that multiple ones of said output apertures
scans substantially a same cell of said surface; said read/write
head including detectors to produce detection signals, each
corresponding to a respective one of said multiple ones and
connected to said image processor; said image processor being
configured to generate an estimate of a configuration of said same
cell and to generate a signal stream representing said
estimate.
2. A device as in claim 1, wherein said output apertures are
coaxial with said input apertures.
3. A device as in claim 1, wherein said read/write head includes a
optoelectronic chip having light guides formed therein, each of
said light guides being connected to a one of said output
apertures.
4. A device as in claim 1, wherein said optoelectronic chip
includes at least one optical switch to modulate an output of one
of said reading laser source and a writing laser source.
5. A device as in claim 4, wherein said at least one optical switch
modulates said laser source by selectively directing said output
between a write output aperture and another direction leading
ultimately to dissipation of energy of said writing laser source,
whereby said writing laser source is enabled to operate in a
continuous manner while writing.
6. A device as in claim 1, wherein said read/write head further
comprises multiple reading laser sources, each connected to an
array of light guides interconnected to split a laser output of
said each of said multiple reading laser sources into multiple
paths, each connected to a one of said output apertures.
7. A device as in claim 6, wherein said array of light guides are
interconnected with respective optical switches controlled by a
controller programmed to cause said laser output to be shared among
multiple ones of said output apertures by shunting said laser
output to a first fraction of said multiple ones at a first time
and shunting said laser output to second fraction of said multiple
ones at a second time.
8. A device as in claim 7, wherein said first fraction of said
multiple ones is equal to a single one of said output
apertures.
9. A device as in claim 1, wherein: said read/write head further
comprises multiple reading laser sources, each connected to an
array of light guides interconnected to split a laser output of
said each of said multiple reading laser sources into multiple
paths defined by said light guides, each path being connected to a
one of said output apertures; and said array of light guides are
interconnected with respective optical switches controlled by a
controller programmed to cause said laser output to be shared among
multiple ones of said output apertures by shunting a percentage of
said laser output to a first fraction of said multiple ones at a
first time and shunting a second fraction of said laser output to
second fraction of said multiple ones at a second time.
10. A scanning device for scanning a target surface having data
written thereon, said data being arranged in columns of adjacent
data cells on said target surface, each of said columns of data
cells having one of a set of possible configurations representing
data, comprising: a read/write head with an array of input
apertures arranged in successive columns such that each of said
columns receives light from a same one of said columns of data
cells; at least one detector connected to detect light received by
said array of input apertures; said detector generating a signal
indicating an estimate of a one of said possible configurations by
combining information derived from light received by all of said
successive columns.
11. A device as in claim 10, wherein said detector combines said
information by detecting light from each of said columns and
synthesizing an improved estimate of said one of said possible
configurations from a combination of signals generated thereby.
12. A scanning device for scanning a target surface having data
written thereon, said data being arranged in columns of adjacent
data cells on said target surface, each of said columns of data
cells having one of a set of possible configurations representing
data, comprising: a scanning head with an array of input apertures
arranged in successive columns such that each of said columns
receives light from a same one of said columns of data cells and
each; at least one detector connected to detect light received by
said array of input apertures; said detector generating a signal
indicating an estimate of a one of said possible configurations by
combining information derived from light received by all of said
successive columns.
13. A device as in claim 12, wherein said scanning head includes at
least one laser connected to conduct light to said array of input
apertures, whereby said array of input apertures functions as an
array of output apertures from which light is emitted.
14. A device as in claim 13, further comprising an imaging optical
element positioned between said scanning head and said target
surface to image light emitted from said output apertures onto said
target surface, said light from said same one of said columns of
data cells being light emitted from said array of output apertures,
returned from said target surface, and imaged by said imaging
optical element back onto said input apertures.
15. A device as in claim 14, wherein at least one detector is an
array of detectors, each being respective of one of said array of
input apertures and said scanning head includes a light guide
leading from each of said input apertures of said array of input
apertures to said respective detector.
16. A method of reading data from a recorded surface having
successive columns of data cells, said successive columns
comprising at least one row of said data cells, comprising the
steps of: moving said recorded surface such that light from a first
output aperture is focused onto a first of said successive columns;
receiving light returned from said recorded surface responsively to
said first step of moving; detecting light returned from said
recorded surface and storing a first result thereof; moving said
recorded surface such that light from a second output aperture is
focused onto said first of said successive columns; receiving light
returned from said recorded surface responsively to said second
step of moving; detecting light returned to said first input
aperture and storing a second result thereof, calculating data
represented by said first of said respective columns responsively
to a computed combination of said first and second results.
17. A method as in claim 16, wherein: said first step of receiving
includes receiving light at a first input aperture corresponding to
said first output aperture; and said second step of receiving
includes receiving light at a second input aperture corresponding
to said second output aperture.
18. A method of reading data from a recorded surface having
successive columns of data cells, said successive columns
comprising at least one row of said data cells, comprising the
steps of: moving said recorded surface such that light from a first
output aperture is focused onto a first of said successive columns;
receiving light returned from said recorded surface responsively to
said first step of moving; detecting light returned from said
recorded surface and storing a first result thereof; moving said
recorded surface such that light from a second output aperture is
focused onto said first of said successive columns; receiving light
returned from said recorded surface responsively to said second
step of moving; detecting light returned to said first input
aperture and storing a second result thereof, calculating data
represented by said first of said respective columns responsively
to a computed combination of said first and second results.
19. A method as in claim 18, wherein: said first step of receiving
includes receiving light at a first input aperture corresponding to
said first output aperture; and said second step of receiving
includes receiving light at a second input aperture corresponding
to said second output aperture.
20. A scanning device for scanning a medium with data written
thereon, said data being arranged in columns of adjacent data cells
on said target surface, each of said columns of data cells having
one of a set of possible configurations representing data,
comprising: a scanning head with an array of input apertures
arranged in successive columns such that each of said columns
receives light from a same one of said columns of data cells; at
least one detector connected to detect light received by said array
of input apertures; said detector generating a signal indicating an
estimate of a one of said possible configurations by combining
information derived from light received by all of said successive
columns; a frame connected to said scanning head; said medium being
attachable to said frame such that said medium is movable relative
to said read/write head, whereby said media moves in a first
direction relative to said read/write head; an oscillating motor
connected between said frame and said read/write head to oscillate
said scanning head relative to said medium, whereby a spacing of
said input apertures may exceed a spacing of said adjacent cells
while permitting light returned from substantially all of said
adjacent cells to be detected by said at least one detector.
21. A device as in claim 20, wherein said medium is moved
continuously in said first direction at a constant speed.
22. A device as in claim 20, wherein a direction of an oscillation
of said read/write head has a component substantially perpendicular
to said first direction.
23. A device as in claim 22, wherein said scanning head includes at
least one laser connected to conduct light to said array of input
apertures, whereby said array of input apertures functions as an
array of output apertures from which light is emitted.
24. A device as in claim 23, further comprising an imaging optical
element positioned between said scanning head and said target
surface to image light emitted from said output apertures onto said
target surface, said light from said same one of said columns of
data cells being light emitted from said array of output apertures,
returned from said target surface, and imaged by said imaging
optical element back onto said input apertures.
25. A device as in claim 24, wherein at least one detector is an
array of detectors, each being respective of one of said array of
input apertures and said scanning head includes a light guide
leading from each of said input apertures of said array of input
apertures to said respective detector.
Description
BACKGROUND OF THE INVENTION
[0001] Various optical scanners are known for such applications as
data storage, bar code reading, image scanning (surface definition,
surface characterization, robotic vision), and lidar (light
detection and ranging). Referring to FIG. 1, a prior art scanner 50
generates a moving spot of light 60 on a planar target surface 10
by focusing a collimated beam of light 20 through a focusing lens
40. If the assembly is for reading information, reflected light
from the constant intensity spot 60 is gathered by focusing lens 40
and returned toward a detector 32. To write information, the
light-source is modulated. To cause the light spot 60 to move
relative to the surface 10, either the surface 10 is moved or the
scanner 50 is moved. Alternatively, the optical path could have an
acousto-optical beam deflector, a rotating prism-shaped mirror, or
a lens driven galvanometrically or by piezoelectric positioners.
Scanners also fall into two functional groups, raster and vector.
Both types generally use the same types of beam deflection
techniques.
[0002] Higher-speed raster scanners use either spinning
prism-shaped (polygonal cross-sectioned) mirrors or multifaceted
spinning holograms (hologons). Performance parameters for these
conventional beam deflection techniques are listed in Table 1. The
discrete optics in these devices are generally attended by high
costs for mass manufacture, assembly, and alignment.
1TABLE 1 Performance of Conventional Beam Deflectors for Optical
Scanning. Polygonal Galvano-Driven Hologons Acousto-Optic Parameter
Mirrors Mirrors (Transmission) Deflectors Wavefront .lambda./8 at
0.55 .lambda./8 at 0.55 .mu.m .lambda./6 at 0.55 .mu.m .lambda./2
at 0.55 .mu.m Distortion .mu.m Area resolution 25,000 (scan 25,000
(scan 25,000 (scan 1,000 (scan lens (spot-widths/sec lens limited)
lens limited) lens limited) limited) Cross-axis error 1 0 arc sec
1-2 arc sec 10 arc sec 0 (uncorrected) (uncorrected) Speed (spot 1
.times. 10.sup.8 2 .times. 10.sup.6 2 .times. 10.sup.7 2.8 .times.
10.sup.7 widths/sec) Bandwidth 0.3-20 .mu.m 0.3-20 .mu.m
Monochromatic monochromatic Scan efficiency 80-1 00% 65-90% 90%
60-80% (from The Photonics Design and Applications Handbook 1993,
Laurin Publishing Co., Inc., p. H-449)
[0003] The performance parameters listed in Table 1 assume
different levels of importance depending on the optical scanning
application. For raster scanning to cover extended surface areas,
the emphasis is on speed, area resolution, and scan efficiency.
Wide bandwidth is needed if the surface is to be color-scanned. For
applications requiring vector scanning of precise paths at high
resolution, the optical system typically uses a monochromatic,
focused spot of light that is scanned at high speed with low
wavefront distortion and low cross-axis error. Optical data storage
has been a prime application of this type of optical scanning.
[0004] In optical data storage media, information is stored as an
array of approximately wavelength-size dots (cells) in which some
optical property has been set at one of two or more values to
represent digital information. Commercial read/write heads scan the
media with a diffraction-limited spot, typically produced by
focusing a collimated laser beam with a fast objective lens system
as shown in FIG. 1. A fast objective lens, one with a high
numerical aperture, achieves a small spot size by reducing
Fraunhofer-type diffraction. The spot is scanned by moving an
assembly of optical components (turning mirror, objective lens,
position actuators) over the optical medium, either along a radius
of a disc spinning under the spot or across the width of a tape
moving past the head. The assembly moves in one dimension along the
direction of the collimated laser beam. As the disk spins or the
tape feeds, the line of bit-cells must be followed by the spot with
sufficient precision to avoid missing any bit cells. The fine
tracking is achieved by servo mechanisms moving the objective lens
relative to the head assembly. An auto-focus servo system is also
necessary to maintain the diffraction limited spot size because the
medium motion inevitably causes some change in the lens/medium
separation with time. Proper focus adjustment is possible because
the medium is flat and smooth. Such a surface reflects incident
light in well-defined directions like a mirror. Light reflected
from the medium is collected by focusing optics and sent back along
the collimated beam path for detection.
[0005] Scanning by several spots simultaneously is used to achieve
high data rates through parallelism in one known system called the
CREO.RTM. optical tape system.
[0006] The reading of optically stored data is a prime application
example of this type of optical scanning. Commercial read/write
heads for optical data storage systems scan with a
diffraction-limited light spot, typically produced by focusing a
collimated laser beam with a fast objective lens system as shown in
FIG. 1. The spot is scanned by moving an assembly of optical
components (turning mirror, objective lens, position actuators)
over the optical storage medium, either along a radius of a disc
spinning under the spot or across the width of a tape moving
through the head. The assembly moves in one dimension along the
direction of the collimated laser beam. Light reflected from the
storage medium is collected by the focusing optics and sent back
along the collimated beam path. It is diverted out of the source
path by a beam splitter 31 for routing to a detector 32. However,
because of the collimated beam optical design of this system, light
entering the return path from areas outside the scanning spot can
propagate some distance back toward the detector before the angular
displacement is transformed into sufficient spatial displacement to
be caught by an aperture stop. This extraneous light is more of a
problem in a multiple spot system in which several areas of the
scanned surface are illuminated at once, and crosstalk between
adjacent and nearby spots is likely. The use of discrete optical
components in such devices to eliminate this effect, poses great
difficulty and cost for mass-manufacture because of the requirement
of precise optical alignment of components.
[0007] One scanning device that avoids reliance on discrete optical
elements to achieve scanning is described in U.S. Pat. No.
4,234,788. In this scanner, an optical fiber is supported rigidly
at one end in a cantilevered fashion. The supported end of the
fiber is optically coupled to a light emitting diode or photo diode
for transmitting or receiving light signals, respectively. The
fiber is free to bend when a force is exerted on it. The fiber can
thus be made to scan when light from the light-emitting diode
emanates from the tip of the fiber as the fiber is forced back and
forth repeatedly. To make the fiber wiggle back and forth an
alternating electric field, generally perpendicular to the axis of
the fiber, is generated. The fiber is coated with a metallic film.
A charge is stored on the film, especially near the tip, by
formiing a capacitance with a metallized plate oriented
perpendicularly to the fiber axis (optically at least partly
transparent). The stored charge makes the fiber responsive to the
electric field.
[0008] A drawback of this device is the limit on the speeds with
which the fiber can be made to oscillate. The device requires a
series of elements to move the fiber: an external field-generating
structure, a DC voltage source to place charge on the fiber
coating, and an AC source to generate the external field. Another
drawback of this prior art mechanism is the inherent problem of
stress fractures in the fiber optics. Bending the fiber repeatedly
places serious demands on the materials. Problems can arise due to
changes in optical properties, changes in the mechanical properties
causing unpredictable variation in the alignment of the plane
followed by the bending fiber, the amplitude of vibration, the
natural frequency of vibrations, and structural failure. Still
another limitation is imposed by the need to place a conductor
between the fiber tip and the optical medium to form the
capacitance. This places another optical element between the fiber
tip and the scanned surface and makes it impossible to sweep the
tip very close to the scanned surface as may be desired for certain
optical configurations.
[0009] Another prior art scanning device is described in U.S. Pat.
No. 5,422,469. This patent specification describes a number of
different devices to oscillate the end of an optical light guide or
optical fiber. One embodiment employs a piezo-electric bimorph
connected to the free end of a device to which the free end of an
optical fiber and a focusing lens are attached. Reflected light is
directed back through the fiber to a beam splitter which directs
the reflected light out of the bidirectional (outgoing/return) path
at some point along the fiber remote from the source of light. The
above embodiment uses a simpler prime mover, a piezo-electric
bimorph. However, the need for a focusing lens attached to the end
of the fiber, by increasing the mass, imposes difficult practical
requirements for high speed oscillation of the fiber. In addition,
to achieve very small projected spot size requires a high numerical
aperture at the output end of the focusing optics. It is difficult
to achieve this with the conventional optics contemplated by the
'469 disclosure. Furthermore, the reciprocation of the fiber as
described in the '469 patent requires a multiple-element device.
Friction between the motor and the fiber can cause changes in the
optical properties of the fiber, and mechanical changes in the
motor, the fiber, or the interface, that result in changes (which
may be unpredictable) in the amplitude of oscillation or the
resonant frequency of the motor-fiber combination (which might
generate, or be susceptible to, undesired harmonics). Also, the
process of assembly of such a combination of a motor and a fiber
presents problems. Ideally, for high frequency operation, the
device would be very small.
[0010] Common to all storage/retrieval devices is the need for
greater and greater data rates. Increases in speed have been
achieved by increasing the speed of scanning. However, there are
practical limits, particularly with regard to the writing
operation, relating to physical properties inherent in the optical
media.
[0011] Also common to the applications of optical scanning
technology is the need for great precision in the focus of the
scanning light source and the return signal.
SUMMARY OF THE INVENTION
[0012] A multiple channel scanning device has a scanning head with
multiple columns of apertures that emit light which is imaged by a
lens onto the surface of a recorded medium. Light returned from the
medium is imaged back onto the apertures and conducted to
detectors. In a preferred embodiment, the scanning head is rapidly
oscillated (may be on the order of 100 kHz rate), in a direction
parallel to the columns. The medium is moved in a direction
perpendicular to the columns so that the same recorded regions pass
beneath successive columns of apertures. The data from the
detectors is image-processed to improve the quality of data-reading
using the successive readings from the same data regions. This
allows errors to be corrected and throughput to be improved. An
alternative embodiment, scan spots are swept over nearly the same,
or the same, regions to achieve oversampling.
[0013] According to an embodiment, the invention provides a
scanning device for scanning a target surface with data written on
it. The data is arranged in adjacent data cells on the target
surface. Each of the cells has one of a set of possible
configurations representing data. For example, a cell could be
highly reflective to represent a "1" and less reflective to
represent a "0." The scanning device has a read/write head, with at
least one laser source, that transmits light to an array of output
apertures from which light is emitted. The light returned from the
surface is received through an array of input apertures. The
read/write head and the target surface are mutually supported to
move relative to each other to scan the target surface. The array
of output apertures is arranged such that some scan substantially
the same cells of the target surface. The read/write head includes
detectors that detect the returned light and send resulting signals
to an image processor. The image processor generates an estimate of
a configuration of each cell from the redundant or quasi redundant
data and generates a signal stream representing the estimate. In a
variation, the output apertures are coaxial with the input
apertures. In another variation, the read/write head has an
optoelectronic chip with internal light guides formed in it, each
of the light guides being connected to one of the output apertures.
In still another variation, the optoelectronic chip has at least
one optical switch to modulate an output of either a reading laser
source or a writing laser source to allow the scanning device to
write data as well as read it. The light sources of the invention,
for writing purposes, are, preferably, modulated by optical
switches that selectively direct the output between a write output
aperture and another direction leading ultimately to dissipation of
energy of the writing laser source. This way, the writing laser
source can operate continuously during writing. Multiple reading
laser sources may be connected to an array of light guides
interconnected to split light from the multiple reading laser
sources into multiple paths, each connected to a one of the output
apertures. The array of light guides may be interconnected with
respective optical switches controlled by a controller programmed
to cause the laser output to be shared among multiple output
apertures by alternately shunting the laser output to a first
fraction of the output apertures and shunting the laser output to
second fraction of the output apertures. The fractions could
constitute just a single aperture.
[0014] According to another embodiment, the invention provides a
scanning device for scanning a target surface with data written on
it. The data is arranged in columns of adjacent data cells on the
target surface. Each of the columns of data cells has one of a set
of possible configurations representing data as discussed above.
The device has a read/write head with an array of input apertures
arranged in successive columns such that each of the columns
receives light from the same one of the columns of data cells.
There is at least one detector connected to detect light received
by the array of input apertures. The detector generating a signal
indicates an estimate of one of the possible configurations by
combining information derived from light received by all of the
successive columns. In a variation, the detector combines the
information by detecting light from each of the columns and
synthesizing an improved estimate of the one of the possible
configurations from the combination of signals generated.
[0015] According to still another embodiment the invention provides
a scanning device for scanning a target surface that has data
written thereon, the data is arranged in columns of adjacent data
cells on the target surface. Each of the columns of data cells has
one of a set of possible configurations representing data. The
device has a scanning head with an array of input apertures
arranged in successive columns so each of the columns receives
light returned from the columns of data cells passing under it.
Also at least one detector is connected to detect light received by
the array of input apertures. The detector generates a signal
indicating an estimate of one of the possible configurations by
combining information derived from light received by all of the
successive columns. In a variation, the scanning head has at least
one laser connected to conduct light so that it is emitted from the
array of input apertures. In this way, the array of input apertures
functions as an array of output apertures from which light is
emitted. In another variation, an imaging optical element
positioned between the scanning head and the target surface images
light emitted from the output apertures onto the target surface.
The light from the same one of the columns of data cells is light
emitted from the array of output apertures, returned from the
target surface, and imaged by the imaging optical element back onto
the input apertures. In another variation, there is an array of
output apertures, each being respective of one of the array of
input apertures. Also, the scanning head includes a light guide
leading from each of the input apertures to the respective
detector.
[0016] According to still another embodiment, the invention
provides a method of reading data from a recorded surface that has
successive columns of data cells. The successive columns have at
least one row of the data cells. The method has the following
steps: Moving the recorded surface such that light from a first
output aperture is focused onto a first of the successive columns.
Receiving light returned from the recorded surface responsively to
the first step of moving. Detecting light returned from the
recorded surface and storing a first result thereof Moving the
recorded surface such that light from a second output aperture is
focused onto the first of the successive columns. Receiving light
returned from the recorded surface responsively to the second step
of moving. Detecting light returned to the first input aperture and
storing a second result thereof Calculating data represented by the
first of the respective columns responsively to a computed
combination of the first and second results. In a variation of the
method, in the first step of receiving, light is received at a
first input aperture corresponding to the first output aperture. In
addition, in the second step of receiving, light is received at a
second input aperture corresponding to the second output
aperture.
[0017] According to still another embodiment, the invention
provides a method of reading data from a recorded surface with
successive columns of data cells. The successive columns comprise
at least one row of the data cells. The method has the following
steps: Moving the recorded surface such that light from a first
output aperture is focused onto a first of the successive columns.
Receiving light returned from the recorded surface responsively to
the first step of moving. Detecting light returned from the
recorded surface and storing a first result thereof Moving the
recorded surface such that light from a second output aperture is
focused onto the first of the successive columns. Receiving light
returned from the recorded surface responsively to the second step
of moving. Detecting light returned to the first input aperture and
storing a second result thereof Calculating data represented by the
first of the respective columns responsively to a computed
combination of the first and second results. In a variation of the
method, in the first step of receiving, light is received at a
first input aperture corresponding to the first output aperture. In
addition, in the second step of receiving, light is received at a
second input aperture corresponding to the second output
aperture.
[0018] According to another embodiment, the invention provides a
scanning device for scanning a medium with data written on it. The
data is arranged in columns of adjacent data cells on the target
surface. Each of the columns of data cells has one of a set of
possible configurations representing data. The scanning device has
a scanning head with an array of input apertures arranged in
successive columns such that each of the columns receives light
from the same one of the columns of data cells. In addition, at
least one detector is connected to detect light received by the
array of input apertures. The detector generates a signal
indicating an estimate of a one of the possible configurations by
combining information derived from light received by all of the
successive columns. There is a frame connected to the scanning
head. The medium is attachable to the frame such that the medium is
movable relative to the read/write head. As a result, the media
moves in a first direction relative to the read/write head. An
oscillating motor connected between the frame and the read/write
head oscillates the scanning head relative to the medium. As a
result, a spacing of the input apertures may exceed a spacing of
the adjacent cells while still permitting light returned from
substantially all of the adjacent cells to be detected by the
detector. In a variation, the medium is moved continuously in the
first direction at a constant speed. In another variation, the
direction of an oscillation of the read/write head has a component
substantially perpendicular to the first direction. In still
another variation, the scanning head includes at least one laser
connected to conduct light so that it is emitted from array of
input apertures. As a result, the array of input apertures
functions as an array of output apertures from which light is
emitted. In still another variation there is an imaging optical
element (e.g., a lens system) positioned between the scanning head
and the target surface to image light emitted from the output
apertures onto the target. The light from the same one of the
columns of data cells is emitted and returned from the array of
output apertures. This light is imaged by the same imaging optical
element back onto the input apertures. In another variation, there
is an array of detectors, each being respective of one of the input
apertures. The scanning head includes a light guide leading from
each of the input apertures to the respective detector.
[0019] The invention provides an essential component in an
optoelectronic chip designed to direct the flow of light and
modulate the light output in a multi-channel optical scanning head.
The invention leads to a reliable, robust, manufacturable, low-cost
component for optical scanning devices used for optical data
storage, bar code readers, image scanning for digitization or
xerography, laser beam printers, inspection systems, densitometers,
and 3-dimensional scanning (surface definition, surface
characterization, robotic vision). Speed and accuracy are enhanced
through the use of image processing techniques applied to redundant
and partly redundant data.
BRIEF DESCRIPTION OF THE DRAWING
[0020] In the drawing,
[0021] FIG. 1 is a ray trace diagram showing a scanning device
according to the prior art.
[0022] FIG. 2 is an illustration of an optoelectronic chip with
integral waveguides, beam switches, a laser source, and beam dumps
to allow the generation of a modulated signal using one laser
source through multiple channels simultaneously.
[0023] FIGS. 3, 4, and 5 illustrate the light flow taken by an
optoelectronic switch in three respective modes.
[0024] FIG. 6 shows an embodiment similar to that of FIG. 2 except
that a backup laser is included with a crossover to the backup
laser to supply the multiple channel light guide network.
[0025] FIG. 7 is an illustration of a group of lasers formed in an
optoelectronic chip interconnected by combiners to combine the
energy of the lasers into one source.
[0026] FIG. 8 is a ray trace diagram showing a multiple channel
scanning head according an embodiment of the invention, where the
imaging optics are fixed and the scanning head is oscillated by a
MEMS motor to scan a region of a target surface.
[0027] FIG. 9 is a ray trace diagram showing a multiple channel
scanning head according an embodiment of the invention, where the
imaging optics and scanning head are fixedly interconnected and
oscillated as a unit by a MEMS motor to scan a region of a target
surface.
[0028] FIG. 10 is a ray trace diagram showing a multiple channel
scanning head according an embodiment of the invention, where the
imaging optics are oscillated as a unit by a MEMS motor to scan a
region of a target surface.
[0029] FIG. 11 illustrates a scanning head with fiber-optic light
guides and multiple detectors for purposes of describing the
scanning of a region simultaneously by multiple channels.
[0030] FIG. 12 illustrates a scanning head similar to the
embodiment of FIG. 11 except that the light source employed
combines the power of multiple individual light sources to produce
light of sufficient intensity to write on the media. Alternatively,
the additional light sources may serve as backup sources in case of
failure of one source.
[0031] FIG. 13 illustrates an embodiment of a multiple channel
scanning head where multiple columns of input apertures scan an
identical region and image processing techniques are applied to the
redundant data to enhance accuracy and increase throughput.
[0032] FIG. 14 is a simplified isometric rendering illustrating the
embodiment of FIG. 13 with only one column of ray traces
showing.
[0033] FIG. 15 illustrates the use of an image processing computer
to process the data from multiple channels of redundant data for
the embodiments of FIGS. 13 and 14.
[0034] FIGS. 16-19 illustrate different ways of oversampling the
scanned surface with variations of an embodiment of the
invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0035] Referring to FIG. 2, an optical scanning optoelectronic chip
616 has single laser source 606 that supplies light to multiple
output apertures 601. Light emitted by laser 606 is guided by light
guides 617 to various rail taps 605a-605c. Light from laser 606 is
output, ultimately, through four output apertures 601 and applied
to a scanned surface 10 at regions A, B, C, and D respectively. An
optical switch 609 allows light from the laser to be directed to a
beam dump 602 for dissipation and absorption of light energy.
Switching optical switch to a bypass position, in effect, modulates
the output of light from the output apertures 601. Note that
although in the embodiment shown, light is directed at the scanned
region without any focusing optics, focusing optics may be used
between the chip 616 and the target 10. Also note that although the
chip 616 has an on-board laser, the laser could be a separate
device and light applied to the light guide network through an
input aperture.
[0036] The purpose of the optoelectronic chip in this system is to
control the distribution of light from the laser sources to the
optics that produce the scan and to direct the light signals
returning from the scanned surface into the set of photo detectors.
The integrated design allows the reduction of size, moving mass,
component count, and manufacturing cost, compared to scanning
systems with multiple discrete optics components. The
optoelectronic chip design allows very accurate positioning of the
light apertures by lithography without requiring monolithic,
multiple output laser arrays. Parallel, integrated read/write
channels with multiplexing have low cost per channel in a compact,
robust configuration. Electro-optic switching is required to
achieve the required data rates. The most cost effective technology
available today is a polymer waveguide optoelectronic chip made
using Photonic Large Scale Integration (PLSI).
[0037] The basic element of the PLSI chip is a one channel to two
channel splitter, which can direct light from one input into one of
two outputs, or split the intensity between the two outputs. This
has been achieved easily by implementing waveguide structures
containing non-linear optical polymeric material that has an index
of refraction controlled by planar metal electrodes. This basic
design allows for the fabrication of electro-optic switches and
optical rail taps (directional couplers). Many such devices have
been fabricated using simple, multi layer metal and polymer films
photo lithographically defined with batch methods commonly employed
for silicon chip fabrication.
[0038] The nominal multiplexed design of FIG. 2 uses four levels of
switching between a single laser and four output channels directed
respectively at target spots A-D. Assuming 80% transmission through
each switch level, this results in as much as a 4 dB loss due to
four switches through the output routing. Non-linear optical
polymer waveguides can be fabricated that have no more than 0.1-0.2
dB losses at the operating wavelength. Using this estimate, the
total losses in a single output channel with four levels of
switching should be no more than 5 dB. In a design using a column
of 64 spots for scanning a 4-mm width of surface in parallel (each
spot scans .+-.32 .mu.m), 16 lasers are required. Each laser feeds
a set of 4 output channels for write scanning at power levels high
enough to affect the surface, but is switched among the channels at
a 50% duty cycle. Read scanning generally requires much lower power
levels. In this mode each laser can feed 16 channels, each at a
100% duty cycle. This extra capacity (compared to the write mode)
is applied to achieve redundancy in reading by driving four
parallel columns of 64 spots each; the columns scan the same
surface area in sequence.
[0039] The light guides 617 (or optical wave guides) are formed
directly in the chip 616 using fabrication techniques similar to
those employed in the manufacture of integrated circuits.
Optoelectronic chips are formed in a layer-by-layer process
beginning with a suitable substrate such as silicon or glass wafer.
A thin metal film is applied to the substrate and patterned to
define electrodes and conductors. Next, a layer of material is
added to form the optical waveguides and the material is patterned
using photolithography. Switches may be formed by doping the
material to create non-linear optical effects in the switching
regions. In a purely additive process, additional material layers
can be applied sequentially, on each of which additional optical
paths, electrodes, and conductors can be formed.
[0040] In the embodiment of FIG. 2, the chip 616 is configured to
distribute the power input from one laser to four different output
channels that will be used for scanning. The optical railtaps 605a
through 605c are capable of selectively distributing the light
power flow (minus internal losses of a few dB) among the various
paths defined by light guides 617. Each optical rail tap 605a-605c,
has at least three operating modes. Referring to FIG. 3, in the
first, rail tap 605 permits all the light energy entering it at 651
to pass straight through to 653 (of course, there are losses).
Referring to FIG. 4, in the second mode, all of the energy entering
at 651 is bypassed to the branch at 652. Referring to FIG. 5, in
the third mode, half the energy is bypassed to branch 652 and half
permitted to pass straight through to branch 653. When all three of
the rail taps 605a-605c are set to 50% bypass, the third mode,
light passes through the output channels such that the energy
arriving at the four output apertures is substantially equal.
Referring now also to FIG. 2, if the three rail taps are operated
sequentially as indicated in the following table, all of the laser
output can be directed to the respective output apertures in
succession.
2 Rail tap positions Target Region 605a 605b 605c 605d A mode 2
mode 2 no effect Mode 1 B mode 2 mode 1 no effect Mode 1 C mode 1
no effect mode 1 Mode 1 D mode 1 no effect mode 2 Mode 1
[0041] As the terms are used in the following discussion, "write"
refers to making a durable change in a medium. The term "read"
refers to the process of collecting information from a medium
without permanently altering the medium. Assume that the maximum
laser output is just enough (after system losses) to supply one
channel with power for a writing scanning beam. A read/write head
with the chip in FIG. 2 would use the switching functions of the
optical railtaps to direct all of the laser power to each of the
four output channels in succession for writing, with precise
synchronization to address each channel at the time when its output
was positioned to write. Modulation of the writing power channel is
done using the first rail tap 605d. The chip will use that switch
to divert the laser output to the beam dump when the output channel
is writing a space and supply the full power when writing a mark.
In this way, the laser can remain on at constant power with less
stress and longer lifetime.
[0042] In many cases (e.g. reading and writing on phase-change
optical storage media), much less light energy is used to read a
pattern already written than to write the pattern. In that case,
the chip 616 can divide the laser input power equally among the
four output channels during the reading function, and four reading
channels can be scanned simultaneously. For reading, each channel
output is on all the time, and the scanned pattern on the surface
modulates the return signal.
[0043] Referring to FIG. 6, a chip 617 with an optical railtap 605e
to allow crossover between the laser input channel, in case of a
laser failure, allows a neighboring or backup laser 608 to be
switched in to feed the outputs originally assigned to the source
that failed 606. This crossover feature could also be used as shown
in FIG. 7 to gang the output of several lasers to meet a scanning
intensity requirement that exceeded the output of a single laser.
The outputs of multiple lasers 306 can be combined for an
application that requires an output intensity greater than a single
laser can produce alone. In an optoelectronic chip 316, multiple
optical rail taps 320 are used to combine the outputs of more than
one laser 306 that could be, for example, phase-locked. In this
embodiment, four lasers combine to generate one combined output
325. This embodiment is particularly useful for use with laser
devices such as vertical cavity surface emitting lasers (VCSELs)
when used to write on materials requiring several milliwatts of
power.
[0044] Using the invention, laser light can be allocated among
several output channels with very fast switching rates for optimum
use of power for both reading and writing applications. Cost
savings can also be achieved. Single laser outputs requiring more
power than can be achieved with a single laser can be supported by
using the output-combining feature described. In addition, laser
output can be modulated without directly varying laser output
power, thus allowing the laser to operate in a continuous wave
(CW), long-lifetime, stable mode.
[0045] Referring to FIG. 8, the small size of the embodiments
discussed above lends itself to scanning using MEMS technology
motors. In an embodiment of the invention, a multiple output
scanning head, OE chip 581 according to any of the previous
embodiments discussed, has multiple outputs, as described. Although
the drawings only indicate schematic ray traces for three beams, it
is understood that the drawing is compatible with any number of
outputs. OE chip 581 is oscillated by a motor 584 based on
microelectromechanical systems (MEMS) technology. A scanning motion
of multiple spots 60 can be obtained with this arrangement. The
multiple focused spots 60 will scan over the surface 10 when the
source array 580 is oscillated relative to the optical axis 90 of
the lens system. In the embodiment of FIG. 8, the lens system 46 is
held fixed and the optoelectronic chip 581 is oscillated. In a
nominal lens system with 1:1 magnification, the spots move along
the surface 10 the same distance as the stage 581.
[0046] Referring to FIG. 9, in an alternative embodiment, similar
to that of FIG. 8, the focusing optics 46, as well as the light
guide array 580, is oscillated. The focusing optics 46 and the
source array 580 are supported on a single stage 521 which is
oscillated by a motor (not shown). Referring to FIG. 10, in still
another embodiment, lens system 546 is supported on stage 525 that
is oscillated relative to both the scanned surface 10 and the
source array 580. Preferably, the lens system is oscillated to
cause a rotary motion since a purely lateral oscillation would not
produce the same degree of oscillation in the focused spots 60.
[0047] Using the invention, laser light can be allocated among
several output channels with very fast switching rates for optimum
use of power for both reading and writing applications. Cost
savings can also be achieved. Single laser outputs requiring more
power than can be achieved with single laser can be supported by
using the output-combining feature described. In addition, laser
output can be modulated without directly varying laser output
power, thus allowing the laser to operate in a continuous wave
(CW), long-lifetime, stable mode.
[0048] Referring to FIG. 11, a laser array 806 supplies scanning
light to an array of light guides 817 formed in an optoelectronic
chip package 816. Optical fibers 39a-39d protrude from the
optoelectronic chip package 816 emitting light transmitted from
light guides 817 at a high numerical aperture ratio from tips 83.
The emitted light is imaged to a spot 60 on a target surface 10 by
a lens (which could be lens system). Electro-optical switches 9a-9c
are controlled to switch the laser source 806 sequentially among
the four optical fibers 39a-39d to produce a series of scanning
spots 60 in succession on target surface 10. Note that imaging
using any of the above embodiments can be done using a focusing
lens system as shown in the embodiment of FIG. 11 or by positioning
the output channels very close to the target surface as shown in
FIG. 2. Note also that while in the above embodiments, the output
channels are oscillated by moving the entire optical circuit, it is
possible to achieve the required oscillatory motion by vibrating
the fibers by bending them using bimorph elements as described in
the copending applications incorporated herein by reference. That
is, the fibers can be moved by bimorph elements each driven by the
same excitation voltage source. Or the fibers could be mounted to a
stage, as discussed, and the stage oscillated. In the case of a
moving stage, the fiber tip array should protrude only one or two
fiber diameters from the chip and the entire chip moved with a fast
"shaker" (e.g. MEMS electrostatic actuator, piezoelectric drive,
etc.). In a nominal lens system design with 1:1 magnification, the
spot moves along the scanned surface the same distance that the
fiber tip moves perpendicular to the optical axis. If appropriate,
magnification ratios other than 1:1 can be used to have the
scanning spot move further than or less than the fiber tip moves.
If the fiber tip moves in such a way that its tip does not move in
a plane, the focusing lens system can, in some cases, be designed
to compensate for this non-planar motion and maintain planar motion
of the scanning spot if so desired. In addition, various ways of
accomplishing this are discussed above.
[0049] Fabrication of edge-emitting laser diode arrays is a mature,
advancing technology that provides compact, robust, and inexpensive
multiple laser light sources with relatively small power
requirements. For example, for an optical data storage scanner used
with phase change media, a single package laser array with 8-16
lasers will fit this application by meeting the following laser
requirements: (a) operation at good optical-out/electrical-in
efficiency to provide CW power onto the optical media for writing
(7-15 mW for 150 ns) and reading (10 .mu.W-5 mW) after subtracting
fiber optic transport and coupling losses and (b) operation at
wavelengths appropriate for digital optical data storage (<1
.mu.m).
[0050] Edge-emitting, single mode laser diode arrays with the
required power at 830 nm wavelength are available off-the-shelf.
Achieving smaller diffraction limited spot sizes for high density
optical storage requires laser arrays with the shorter wavelengths
now available in low-power discrete diode lasers (e.g. 670 nm at 15
mW). Vertical cavity surface emitting lasers (VCSELS) represent
another configuration of solid state laser that have output beam
characteristics more suited to optical scanners and are more
amenable to incorporation in a single chip multiple device
design.
[0051] Referring to FIG. 12, VCSELs are presently limited to lower
output power than edge-emitting lasers. For use in this invention,
the outputs of several VCSELs 846 may be ganged, for example with
phase locking, to provide power for writing when higher channel
power levels are required. The laser array may be integrated with
the optoelectronic chip to achieve low-loss coupling of the laser
output into the chip waveguides 817. Interfacing the chip
"switchyard" with the laser source, be it single laser or a ganged
device as shown in FIG. 12, can be accomplished by attaching
optical fibers between each laser and the switchyard input
("pigtailing"), using a hybrid arrangement with the laser array
butt-coupled to the optoelectronic chip, or totally integrating the
lasers in the optoelectronic chip.
[0052] The chip could also be designed with optical railtaps to
allow crossover between the laser input channels, so that, in case
of a laser failure, a neighboring or backup laser could be switched
in to feed the outputs originally assigned to the source that
failed. That is, for example, in the embodiment of FIG. 12, if one
of the lasers 846 fails, another one can be switched in to provide
a backup source. As described above, the same crossover feature is
used to gang the output of several lasers to meet a scanning
intensity requirement that exceeds the output of a single
laser.
[0053] The return light from the surface is imaged back onto the
tip of the emitting fiber and passes back into the chip where it is
shunted by a respective directional coupling 8a-8d to a
corresponding photo detector 7a-7d. Silicon-based devices provide
response over the wavelength range from the near IR to visible blue
light, and PIN-type (p+.Arrow-up bold.intrinsic.vertline. n+)
silicon photo diodes are simple, fast, long-lived, inexpensive
devices routinely used in optical fiber data links and other
applications at rates of 1 GHz and higher. These devices are
integrated monolithically within a silicon substrate in the
chip.
[0054] The novel scanning and light allocation design of the
embodiments discussed above, and which are discussed further below,
require switching speeds on the order of 20 nanoseconds when
employed in optical data storage. Although electro-optic switching
is required, this is not a stressing demand on the technology since
sub-nanosecond switching times have been demonstrated. Similar
technology has been employed for multi-output data
transmission.
[0055] As discussed in the related applications incorporated herein
by reference and elsewhere in this application, the laser light
emitted from the tip of the properly designed fiber or waveguide
diverges with a high numerical aperture (NA) ratio. A simple, fast
lens system with matching NA is used to focus the light emitted
from the fiber tip or waveguide to a spot on the surface to be
scanned. For high resolution scanning applications, the fibers are
single mode. For optical data storage and other minimum scan spot
size applications, the lens system is designed to produce the
smallest practical diffraction limited spot on the scanned surface.
The light reflected from the surface is collected and re-imaged by
the same lens system back into the same fiber or waveguide tip. The
fiber or waveguide carries the return light back into the
optoelectronic chip for detection. The one-to-one mapping
properties of the imaging system constrain the optics to focus back
into each fiber tip all light that originates from the spot on the
surface illuminated by that fiber tip and reject any light coming
back from the target surface from another location. This acts as an
aperture stop and has the effect of limiting cross-talk among
parallel data channels fed by multiple scanning light spots. In
this design, the lens system could be made from a single
holographic element.
[0056] In the above embodiments, because each spot performs
multiple, overlapping scans to sweep the area that it is reading,
there is no need for micro-tracking systems to maintain
micron-scale positioning of the spots on the surface. Precision
autofocus control of the head as a unit will be necessary, as in
conventional optical heads. The focus quality signal will be based
on maximizing the signal level returned from a given surface area.
When the light collected back into the fiber tip is maximized, the
system is in focus.
[0057] Referring to FIG. 13, to illustrate design issues for this
invention, parameters are presented for an application example of
the integrated head: read/write scanning of a digital optical data
tape moving under it. The read/write head of this embodiment
includes an 8 by 4 array of output apertures, either the ends of
light waveguides or the tips of optical fibers according to any of
the above embodiments. Each output aperture is spaced apart by 64
microns. The data cells written and read are spaced on 1 micron
centers so that an array of 32 bits cells 901, is covered by a
.+-.32 micron sweep of each output aperture as the read/write head
is oscillated.
[0058] Phase-change optical media has shown the capacity to store
readable bits in cells spaced center-to-center at the smallest
practical diffraction limited spot diameter, which is of the order
the laser wavelength. However, under optimal conditions, several
techniques have been developed to achieve higher bit densities. The
above design assumes 1.times.1 .mu.m.sup.2 data cell dimensions.
Since each output aperture oscillates .+-.32 .mu.m the
corresponding spot on a tape medium sweeps over a 64 .mu.m long
strip perpendicular to the tape edge. As the nominal design has a
4.times.8 array of output apertures in a rectangle centered on the
optical axis of a 1-mm aperture lens system, at any instant of
time, the system projects a 4.times.8 array of light spots 913 on
the target surface. The 8 output apertures in each column of the
array are spaced on 64 .mu.m centers so that they cover a band 512
.mu.m across the tape. Referring to FIG. 14, a single module 848
consisting of the 4.times.8 array of output apertures with a single
imaging lens 843 may be duplicated eight-fold to produce a
read/write head 856 spanning a full 4-mm width. The modules in the
embodiment shown are arranged vertically and attached to a frame
850 for support. Such a read/write head 856 produces a 4 by 64
array of light spots. Although in the figure only eight central ray
traces are shown at 846 projected by each module 848, it is to be
understood that the embodiment includes four columns of eight ray
bundles. The direction of motion of the medium relative to the
read/write head 850 is indicated by the arrow 877. An arrow 878
indicates the direction of oscillation of the read/write head 856,
but not the magnitude which is about the size of the spacing
between adjacent output apertures as indicated by the spacing of
the origins of the ray central traces shown at 846.
[0059] The four columns of output apertures along the translation
direction of the medium relative to the read/write head allow the
same area of the medium to be scanned independently four separate
times for redundancy as the medium moves under the read/write head.
In the write mode, the four scans may be used to: 1) read the tape
surface for previously written data or fiducial marks to determine
position; 2) write; 3) read to confirm what was written; 4) read
again. Note that, preferably, the lens systems are offset from each
other to cover the entire medium-displacement-path width, and thus
a continuous band across the medium will not be read
simultaneously.
[0060] To read or write 67 Mbits (8 MBytes) in 1 second for the
above design on 4-mm tape, each fiber in a column must scan 1 Mb/s.
With 64 bits per 64 .mu.m scan length, the fiber must complete at
least 16,384 data scans per second. Because oscillation frequencies
well above 100 kHz are easily achieved for MEMS systems, a fiber
scan rate several times higher than this minimum can be used in the
read mode. The net effect is that the set of 8 light spots from
each column of fibers sweeps a 512 .mu.m wide band of the tape
moving under it with enough oversampling that reflectivity data
from each data bit is received multiple times. In the write mode,
each fiber will oscillate at 16 kHz and write to 64 data cells in a
column on the tape during one half of a cycle only. Half the fibers
(32) may write during the downstroke, then the lasers will be
switched to the other half that will write during the upstroke.
This allows a 50% duty cycle for a laser to write through each
output aperture; if each laser can supply enough power to two
output apertures writing simultaneously, then 16 lasers can handle
all 64 fiber channels in one column spanning the 4-mm tape
width.
[0061] The vertical displacement (direction perpendicular to arrow
877, the direction of movement of the read/write head 856 relative
to the scanned surface 10) of successive columns of output
apertures in the embodiment of FIG. 14, for example, may be
non-zero, but less than the data-cell pitch, so that each column of
outputs scans a slightly different part of the surface. This
vertical displacement may also be zero. In either case, preferably,
the data streams from the detectors reading the return signals from
each fiber are digitized and processed. Thus, all the streams from
all four detectors are processed together so that data from
successive sweeps of the same area (or almost the same area, when
the vertical displacement of columns is non-zero) are presented to
an image processing computer. Using known image-processing
techniques (e.g., weighted averaging or most representative trace
for each cell), this information can be used to provide a very
fast, low error rate reading of the scanned surface pattern. The
lateral spacing of the fibers in each array of fiber scanners
(which determines the delay between the successive scans of the
same surface area) is determined by a tradeoff between physical
design constraints and data buffering/processing considerations.
For the tape scanning application described next, the
optoelectronic switching functions and the MEMS system requires at
least 50 MHz clock rates in an on-board controller.
[0062] Note that while in the embodiments described, the size of
the array of output apertures is 4.times.8, it is also possible to
form arrays with other dimensions to obtain the same benefits.
Also, the data cell size may be other than as described in the
above embodiments. In any of the above embodiments, it is possible
to project light, and receive light back from the scanned surface,
by direct proximity of the output apertures as in FIG. 2 or by
using imaging optics as in FIG. 14. Note also that the lasers could
be switched on and off to modulate for writing rather than as in
the preferred system described where optical switches are used for
modulation. Note also that the image processing techniques
discussed can take the form of different kinds of data encoding, so
that data does not have to be written as separate data-cells. Other
kinds of surface modulation techniques may be employed in
connection with the invention and for each of these, redundant
scanning will achieve similar benefits in terms of high reading
rates, along with the benefits discussed above with respect to
writing as well. In addition, referring to FIG. 19, it is also
possible to arrange the output apertures and their spacing such
that redundancy is provided by sweeping the scan spots over
overlapping regions 66 by virtue of the range of motion of the
oscillations. That is, instead of sweeping apertures spaced on a 64
micron pitch and sweeping .+-.32 microns, the sweep could be
greater than the spot pitch so that the same areas are scanned more
than once. Thus, spot 47a and 47c sweep the same region 66. Image
processing could be applied to such data, buffered appropriately,
as well. For a series of identically positioned scans performed
serially across the same information area, the image processing
step could be as simple as a democratic vote that takes the most
agreed-up value among the 4 voting channels. For staggered
apertures, the image processing step in the simplest case would be
a best-fit to a series of stored expected images associated with
each possible value (which could include known erroneous
values).
[0063] Referring to FIG. 15, an image processor 852 receives
multiple channel signals, each from a respective one of the
detectors connected to the four apertures receiving signals from
the same or nearly same region of the scanned surface. Image
processor 852 receives the signal from read/write head 846. Only
four channels are shown, but in the embodiment of FIG. 14, for
example, 64 sets of 4 channels would be transmitted to be
image-processed. The result of image processing is a prediction of
the correct "value" of the cell read multiple times which may
output as a serial data stream on line 854. The term "value" is
used loosely here in that the data is stored as some sort of symbol
which may correspond to multiple independent numeric values
depending on the encoding scheme used. For example, the data could
be recorded with multiple bits per mark (gray scale).
[0064] The above embodiment, where separate output apertures sweep
the same regions of the scanned surface, is not the only way to
oversample the target surface. Referring to FIGS. 16, 17, and 18,
various alternative ways to achieve oversampling are shown. In FIG.
16, the output apertures 47 are staggered so that each sweeps over
a different area. The rate of oscillation relative to the rate of
translation of the surface, indicated by the zig-zag line 49, is
such that the same data cells 48 are scanned multiple times. In the
embodiment described above and shown in FIG. 17, the multiple fiber
(or, more generally, light-waveguide) configuration simply
multiplies the data rate by scanning/reading with several
light-spots over the same area. In the embodiment of FIG. 16, each
spot scans a different area (and this would require the spots be
staggered in the direction of the oscillation so that different
spots do not sweep the same regions), but each spot scans the same
area more than once. In the latter case, the operation of each spot
while scanning and collecting data is essentially independent of
the others. The physical configurations of these two alternatives
is the same as depicted in the other figures.
[0065] In another embodiment such as described by FIG. 16, a
cantilever-mounted fiber-optic bimorph, such as described in the
applications incorporated by reference below, (for example, in the
application entitled "Scanning Device Using Fiber Optic Bimorph.")
are used to generate the light spot. In this case, a single light
spot is generated by each bimorph. As shown in FIG. 16, in this
embodiment, oversampling is accomplished by having a spot perform
its scan oscillation with a frequency such that its center scans
through a data cell several times before crossing the columnar
boundary to the next data cell or region of the target surface.
[0066] For example, in an optical tape system, the data cells move
past the scanning locus of the spot oscillation as the tape moves
under the read/write head. The optical properties (e.g.,
reflectivity) of the data cell area are oversampled because more
than one trace of the sampling spot passes through the data cell
area, with the locus of each trace displaced from the previous one
by some fraction of the data cell width. The best measure of the
data cell can be formed by either processing the multiple traces
together (e.g., weighted averaging) or by selecting a best or most
representative data trace for each data cell.
[0067] Note that, the image-processing techniques can be applied in
an embodiment of the invention in which the parallel columns of
input apertures are offset relative to each other. That is, the
data readings are semi redundant in the sense that non-identical
portions of the same data cells are read and image-processed. That
is, slightly different portions of a data cell are read by each
column of input apertures. The image-processing algorithms may have
to take account of the offset (that is, have it predefined) and
therefore be different from (or more generalized versions
of--zero-offset is just a special case of variable offset) the
algorithms applicable to a zero-offset situation. Although it is
also possible to register the values of the offset by image
processing. Obviously the scans will contain information about the
repeating pattern which should make it possible to avoid specifying
the offset a priori in the algorithm. Also, the offset could be
determined through calibration using a medium with known fiducials
imprinted on it.
[0068] It is also possible to scan in a hybrid fashion such as
shown in FIG. 18. In this case, the surface displacement rate and
the oscillation speed are such that the spots sweep the same region
multiple times, but, in addition, at least one successive scan spot
47b follows the first 47a and sweeps over the same region of the
target surface. So redundant or partly redundant data are obtained
in two ways at the same time.
[0069] The optical design discussed above avoids the use of costly,
large aperture discrete optics through the use of integrated
fabrication techniques that reduce alignment problems and allow
low-cost manufacturing in quantity. In addition, the optoelectronic
chip controls the light distribution and permits the use of many
more scanning channels than lasers with low cost per added channel
and very high parallel data transfer rates. The optoelectronic chip
also allows lithographically-determined, precise spacing of output
apertures for separate laser sources. Also, the chip permits
efficient use of laser power including ganging of low power sources
such as VCSEL sources; and continuous wave laser operation during
write mode. Moreover, the design achieves scanning action through
optical fiber motion produced by either micro electromechanical
systems (MEMS) technology or a known micro scale vibratory motion
technique such as a piezoelectric transducer. In addition, the
invention includes the use of parallel, redundant laser scanning, a
low-cross-talk design, and an `image analysis` approach to signal
processing.
[0070] The best MEMS scanning method depends on the practical
engineering tradeoffs attending the specific application. For
example, the mass of the moving element, the amplitude of the
oscillation, and the frequency. One optimization goal might be to
opt for high frequency and therefore favor minimum mass of the
moving element. This would suggest an individual fiber is best.
Engineering, however, places other constraints on the application,
for example, the actual position of the surface emitting the light
relative to the focal point of the optics. See for example, Brei
et. al, incorporated herein by reference below.
[0071] Regarding the manufacturing of MEMS devices, for example,
the light emitting aperture, shape and surface treatment,
manufacturing issues are not a problem. For example methods have
been developed to apply metals to glass fibers to enable capacitive
coupling for driving the fiber motion. Individual methods of
fabrication and then manufacture may be addressed depending on the
availability of resources, e.g. metallization of a polymer "fiber"
or waveguide, or application of piezoelectric material to a
polymer. Regarding the optical properties of the fiber output,
particularly with regard to numerical aperture (NA), some trial and
error experimentation may be required to achieve an optimum
configuration. If constructed layer by layer, the fiber tip
construction is totally conventional. The optical quality and
properties of the exit aperture as mentioned above are critical,
and therefore exact recipes may require some trial and error
experimentation. For example, a graded index clad may be necessary,
or new process methods due to required design considerations. In
embodiment employing an optical fiber, the exit aperture may be
defined by cleaving. In embodiment employing a multilayer (e.g.
polymer) structure, processing at the end of the fiber is
important. Conventional methods at present include ion beam
"polishing" of the tip or exit aperture.
[0072] The cantilever "style" vibrating fiber structure requires a
waveguiding "core," as with any optical fiber. Also a cladding is
required to confine the optical energy. The fiber, or, more
generally, light guide, can have a round, square, or rectangular
cross section depending on design considerations for the purpose of
light "piping." A square or rectangular cross section is easiest to
deal with from a manufacturing and fabrication point of view, as
well as from the point of view of driving oscillations. Planar
"capacitive" plates are easily implemented in a layered, bimorph
configuration that optimizes energy transfer for driving
oscillation while minimizing the required power. However, this puts
severe constraints on optical design due to the need for
polarization conservation elsewhere in the system, as well as mode
conservation and balance. A layer by layer fabrication process is
the best approach; in that case, the "fixed end" of the fiber is on
top of the underlying structural and functional layers. The quality
checks necessary are both optical and mechanical. Longevity will be
related to mechanical work, with frequency, total number of
oscillations, material, composite structures, adhesion, etc. also
being contributing factors.
[0073] Note, regarding a fundamental mechanism of failure in
stressed single crystal materials, such as Si, defects in single
crystals diffuse thermally and aggregate in the material. This is
well known (see for example Silicon Processing for the VLSI Era, S.
Wolf and R. N. Tauber, Lattice Press and other books addressing the
processes in Si fabrication, particularly crystal growth). Note
that various embodiments could make use of the same lasers for both
reading and writing, as discussed above. In such a case, a head
could have separate exit apertures for reading and for writing, or
have one set of apertures serving both functions.
[0074] The respective entireties of the following United States
patent applications, filed concurrently herewith, are hereby
incorporated by reference in the present application:
[0075] Scanning Device Using Fiber Optic Bimorph (Adam Thomas
Drobot, Robert Courtney White)
[0076] Multiple Parallel Source Scanning Device (Adam Thomas
Drobot, Robert Courtney White, Newell Convers Wyeth)
[0077] Multiple Channel Data Writing Device (Adam Thomas Drobot,
Robert Courtney White, Newell Convers Wyeth, Albert Myron
Green)
[0078] Multiple Channel Scanning Device Using Optoelectronic
Switching (Adam Thomas Drobot, Robert Courtney White, Newell
Convers Wyeth)
[0079] Method and Apparatus for Controlling the Focus of a
Read/Write Head for an Optical Scanner (Edward Alan Phillips,
Newell Convers Wyeth)
[0080] Multiple Channel Scanning Device Using Oversampling and
Image Processing to Increase Throughput (Adam Thomas Drobot, Robert
Courtney White, Newell Convers Wyeth, Albert Myron Green, Edward
Alan Phillips)
[0081] The respective entireties of the following references are
hereby incorporated by reference in the present application:
[0082] M. Ataka, A. Omodaka, N. Takeshima, and H. Fujita,
"Fabrication and Operation of Polyimide Bimorph Actuators for a
Ciliary Motion System", JMEMS, Volume 2, No. 4, page 146.
[0083] D. E. Brei and J. Blechschmidt, "Design and Static Modeling
of a Semicircular Polymeric Piezoelectric Microactuator", JMEMS,
Volume 1, No. 3, page 106.
[0084] J. W. Judy, R. S. Muller, and H. H. Zappe, "Magnetic
Microactuation of Polysilicon Flexure Structures", JMEMS, Volume 4,
No. 4, page 162.
[0085] T. S. Low and W. Guo, "Modeling of a Three-Layer
Piezoelectric Bimorph Beam with Hysteresis", JMEMS.
[0086] Q. Meng, M. Mehregany, and R. L. Mullen, "Theoretical
Modeling of Microfabricated Beams with Elastically Restrained
Supports", JMEMS, Volume 2, No. 3, page 128 et. seq.
[0087] K. Minami, S. Kawamura, and M. Esashi, "Fabrication of
Distributed Electrostatic Micro Actuator (DEMA)", JMEMS, Volume 2,
No. 3, page 121 et. seq.
[0088] J. G. Smits, and A. Ballato, "Dynamic Admittance Matrix of
Piezoelectric Cantilever Bimorphs", JMEMS, Volume 3, No. 3, page
105 et. seq.
[0089] Yuji Uenishi, Hedeno Tanaka, and Hiroo Ukita, NTT
Interdisciplinary Research Laboratories (Tokyo, Japan),
"AlGaAs/GaAs micromachining for monolithic integration of optical
and mechanical components", Optical power driven cantilever
resonator. Proceedings SPIE et. seq.
* * * * *