U.S. patent application number 13/102895 was filed with the patent office on 2012-04-05 for laser illumination system with reduced speckle.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to Riccardo Leto, Yosuke MIZUYAMA.
Application Number | 20120080411 13/102895 |
Document ID | / |
Family ID | 45888908 |
Filed Date | 2012-04-05 |
United States Patent
Application |
20120080411 |
Kind Code |
A1 |
MIZUYAMA; Yosuke ; et
al. |
April 5, 2012 |
LASER ILLUMINATION SYSTEM WITH REDUCED SPECKLE
Abstract
A despeckling device and method in which an optical path
difference staircase element is disposed between a fly's eye lens
array and the image plane in a position near the focus position of
the fly's eye lens array, and a laser generating unit generates and
transmits pulsed laser beams to the optical path difference
staircase element, wherein the pulsed laser beams are driven at a
very short pulsed rate.
Inventors: |
MIZUYAMA; Yosuke; (Newton,
MA) ; Leto; Riccardo; (Arlington, MA) |
Assignee: |
PANASONIC CORPORATION
Osaka
JP
|
Family ID: |
45888908 |
Appl. No.: |
13/102895 |
Filed: |
May 6, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61388238 |
Sep 30, 2010 |
|
|
|
Current U.S.
Class: |
219/121.6 ;
359/486.01; 359/619; 359/622 |
Current CPC
Class: |
G02B 27/48 20130101;
G02B 27/286 20130101 |
Class at
Publication: |
219/121.6 ;
359/619; 359/486.01; 359/622 |
International
Class: |
B23K 26/00 20060101
B23K026/00; G02B 27/28 20060101 G02B027/28; G02B 27/48 20060101
G02B027/48 |
Claims
1. A despeckle unit, comprising: a first transparent element
comprising a plurality of microlenses to receive collimated light
having a coherence length and to output a beamlet from each of the
microlenses; and a second transparent element comprising a
plurality of steps having a one-to-one correspondence with the
plurality of microlenses, wherein each of the steps receives one of
the beamlets and outputs the beamlet to an image plane, where a
height of each step of at least two of the steps is configured to
produce an optical path difference of the beamlet longer than the
coherence length, wherein the second transparent element is
disposed approximately at a foci of the beamlets output from the
first transparent element.
2. The despeckle unit according to claim 1, wherein the collimated
light comprises pulsed laser beams driven by a pulse of less than
10 nanoseconds.
3. The despeckle unit according to claim 2, wherein the pulse
reduces a coherence of the laser beam and the steps are configured
to further reduce the coherence of the laser beam not reduced by
the pulse, to substantially despeckle the pulsed laser beam.
4. The despeckle unit according to claim 1, wherein the at least
two of the steps are configured as a one-dimensional staircase and
the microlenses are configured as a one-dimensional array of
microlenses.
5. The despeckle unit according to claim 1, wherein: the collimated
light is linearly polarized with a polarization direction; the
second transparent element comprises at least one physical step,
comprising: an optical wave plate disposed on a first portion of
the at least one physical step which is configured to change the
polarization direction of the collimated light, and a second
portion of the at least one physical step which does not include
the optical wave plate; and the optical waveplate and the second
portion each comprise one of the steps having the one-to-one
correspondence with the microlenses.
6. The despeckle unit according to claim 1, wherein: the collimated
light is linearly polarized with a polarization direction; the
second transparent element comprises at least one physical step,
comprising: a first optical wave plate disposed on a first portion
of the at least one physical step which is configured to change the
linearly polarized light to right circular polarized light, and a
second optical wave plated disposed on a second portion of the at
least one physical step which is configured to change the linearly
polarized light to left circular polarized light; and the first
optical wave plate and the second optical wave plate each comprise
one of the steps having the one-to-one correspondence with the
microlenses.
7. A despeckle unit, comprising: a first transparent element
comprising a plurality of microlenses to receive collimated light
having a coherence length and to output a beamlet from each of the
microlenses; and a second transparent element comprising a
plurality of steps having a one-to-one correspondence with the
plurality of microlenses, wherein each of the steps receives one of
the beamlets and outputs the beamlet to an image plane, wherein a
height of each step of at least two of the steps is configured to
produce an optical path difference of the collimated light longer
than the coherence length, wherein the second transparent element
is disposed in a location relative to the first transparent element
such that edges of the second transparent element parallel to an
optical path of the beamlets exiting the second transparent element
do not diffract the beamlets.
8. The despeckle unit according to claim 7, wherein the collimated
light comprises pulsed laser beams driven by a pulse of less than
10 nanoseconds.
9. A despeckling laser unit to despeckle a laser beam, comprising:
a laser generating unit to generate a pulsed laser beam having a
coherence length; a first transparent element comprising a
plurality of microlenses to receive the pulsed laser beam and to
output a beamlet from each of the microlenses; and a second
transparent element comprising a plurality of steps corresponding
to the plurality of microlenses, wherein each of the steps receives
one of the beamlets and outputs the beamlet to an image plane,
wherein a height of each step of at least two of the steps is
configured to produce an optical path difference of the pulsed
laser beam longer than the coherence length; wherein the second
transparent element is disposed approximately at the foci of the
beamlets output from the first transparent element.
10. The despeckling laser unit of claim 9, wherein the pulsed laser
beams are driven by a pulse of less than 10 nanoseconds.
11. The despeckling laser unit of claim 9, further comprising: a
collimator disposed between the laser generating unit and the first
transparent element to receive the pulsed laser beam and output a
collimated laser beam; and a field lens to receive the beamlets
output from the second transparent element and focus the received
beamlets on the image plane.
12. The despeckle unit according to claim 9, wherein the at least
two of the steps are configured as a one-dimensional staircase and
the microlenses are configured as a one-dimensional array of
microlenses.
13. The despeckle unit according to claim 9, wherein: the pulsed
laser beam is linearly polarized with a polarization direction; the
second transparent element comprises at least one physical step,
comprising: an optical wave plate disposed on a first portion of
the at least one physical step which is configured to change the
polarization direction of the pulsed laser beam, and a second
portion of the at least one physical step which does not include
the optical wave plate; and the optical waveplate and the second
portion each comprise one of the steps having the one-to-one
correspondence with the microlenses.
14. The despeckle unit according to claim 9, wherein: the pulsed
laser beam is linearly polarized with a polarization direction; the
second transparent element comprises at least one physical step,
comprising: a first optical wave plate disposed on a first portion
of the at least one physical step which is configured to change the
linearly polarized light to right circular polarized light, and a
second optical wave plated disposed on a second portion of the at
least one physical step which is configured to change the linearly
polarized light to left circular polarized light; and the first
optical wave plate and the second optical wave plate each comprise
one of the steps having the one-to-one correspondence with the
microlenses.
15. The despeckling laser unit of claim 9, further comprising a
third transparent element comprising another plurality of
microlenses disposed after the second transparent element and
corresponding to the plurality of microlenses in one-to-one
correspondence with the plurality of microlenses.
16. A despeckling laser array, comprising: a plurality of the
despeckling laser units according to claim 9; and a single field
lens to focus the beamlets output from each of the plurality of
despeckling laser units onto the image plane.
17. A despeckling laser assembly, comprising: the despeckling laser
array according to claim 16; a base plate to support the
despeckling laser array; a circuit board attached to one end of the
despeckling laser array; and at least one driver integrated circuit
mounted on the circuit board to drive the laser generating units of
the despeckling laser array.
18. An annealing system to anneal a substrate, comprising: a
plurality of the despeckling laser assemblies according to claim 17
disposed above a front surface of the substrate, such that each of
the despeckling laser assemblies is configured to focus the
beamlets on the substrate, wherein each of the despeckling laser
assemblies is movable to enable the annealing system to anneal the
front surface of the substrate.
19. The annealing system of claim 18, wherein the substrate
comprises amorphous silicon for organic LED displays.
20. A one-dimensional crossed despeckling unit, comprising: a first
transparent element comprising: a first surface having a first
plurality of first microlenses to receive collimated light having a
coherence length, and output a first plurality of first beamlets
corresponding to the first plurality of microlenses, and a second
surface having a second plurality of second microlenses to receive
the collimated light, and output a second plurality of second
beamlets corresponding to the second plurality of microlenses; and
a second transparent element comprising: a first plurality of first
steps oriented such that at least one of the first steps
corresponds to at least one of the first beamlets; and a second
plurality of second steps oriented such that at least one of the
second steps corresponds to at least one of the second beamlets,
wherein: a height of each step of at least two steps from among the
first steps and the second steps is configured to produce an
optical path difference of the pulsed laser beam longer than the
coherence length, and the second transparent element is disposed
approximately at a foci of the first beamlets and the second
beamlets output from the first transparent element.
21. The one-dimensional crossed despeckle unit according to claim
20, wherein the collimated light comprises pulsed laser beams
driven by a pulse of less than 10 nanoseconds.
22. The one-dimensional crossed despeckle unit according to claim
21, wherein the pulse reduces a coherence of the laser beam and the
steps are configured to further reduce the coherence of the laser
beam not reduced by the pulse, to substantially despeckle the
pulsed laser beam.
23. The one-dimensional crossed despeckling unit according to claim
20, wherein the first transparent element comprises a
one-dimensional crossed microlens array, and the second transparent
element comprises a combination of a first staircase element having
the first plurality of steps and a second staircase element having
the second plurality of steps.
24. The one-dimensional crossed despeckling unit according to claim
23, wherein the first steps each have the same first height, the
second steps each have the same second height, and the first height
is different from the second height.
25. The one-dimensional crossed despeckling unit according to claim
24, wherein the first staircase is provided in plural.
26. A laser module, comprising: a housing; a plurality of laser
diodes disposed at one end of the housing to generate respective
pulsed laser beams having respective coherence lengths; a first
transparent element, disposed after the plurality of laser diodes
in the direction of travel of the laser beams, comprising a
plurality of microlenses to receive the pulsed laser beams and to
output a beamlet from each of the microlenses; and the
one-dimensional crossed despeckling unit according to claim 25
disposed after the first transparent element in the direction of
travel of the laser beams, wherein each of the first staircases
corresponds to at least one of the laser diodes.
27. The laser module of claim 26, wherein: the laser diodes are
arranged in an M.times.N grid, where M an N are positive integers
respectively representing a number of laser diodes in columns and
rows of the grid; the plurality of first staircases comprise M
first staircases, and each one of the M first staircases
corresponds to a respective one of the M columns.
28. The laser module of claim 27, wherein: M>N, N.gtoreq.1,
M.gtoreq.2; a beam shaping axis is arranged in a direction
corresponding to the N laser diodes; and each one of the M.times.N
laser diodes generates approximately 0.2 watts (W) of output
power.
29. A method to despeckle a laser beam, comprising: generating a
pulsed laser beam having a coherence length; transmitting the
pulsed laser beam through a first transparent element comprising a
plurality of microlenses so that the pulsed laser beam is output as
a beamlet from each of the microlenses; and transmitting each one
of the beamlets through a respective step included in a second
transparent element comprising a plurality of the steps having a
one-to-one correspondence with the plurality of microlenses, to an
image plane, wherein a height of each step of at least two of the
steps is configured to produce an optical path difference of the
beamlets longer than the coherence length, wherein the second
transparent element is disposed approximately at the foci of the
beamlets output from the first transparent element.
30. The method according to claim 29, wherein the generating of the
pulsed laser beam comprises driving the pulsed laser beam using a
pulse of less than 10 nanoseconds.
31. The method according to claim 29, further comprising:
collimating the generated pulsed laser beam and outputting the
collimated generated pulsed laser beam to the first transparent
element; and focusing the received beamlets transmitted through the
respective steps by the second transparent element on the image
plane using a field lens.
32. The method according to claim 29, wherein the at least two of
the steps are configured as a one-dimensional staircase and the
microlenses are configured as a one-dimensional array of
microlenses.
33. The method according to claim 29, further comprising:
polarizing the pulsed laser beam with a linear polarization having
a polarization direction; and changing the polarization direction
of the pulsed laser beam by passing the pulsed laser beam through
an optical wave plate comprising one of the steps of the second
transparent element.
34. The method according to claim 29, further comprising:
polarizing the pulsed laser beam with a linear polarization; and
changing the linear polarization of the pulsed laser beam to right
and left circular polarization by passing the pulsed laser beam
through corresponding first and second optical wave plates each
comprising one of the steps of the second transparent element.
35. The method according to claim 29, further comprising
transmitting each one of the beamlets output from the second
transparent element through a third transparent element comprising
another plurality of microlenses in one-to-one correspondence with
the plurality of the microlenses.
36. A two-dimensional despeckling unit, comprising: a first
transparent element comprising: a surface having a plurality of
microlenses to receive collimated light having a coherence length
from a pulsed laser beam, each of the microlenses configured to
output a beamlet which is shaped in two-dimensions; and a second
transparent element comprising: a light incident surface forming a
two-dimensional area comprising two first boundaries and two second
boundaries perpendicular to and connecting the two first
boundaries; and a plurality of steps protruding out from the light
incident surface and arranged in rows, wherein the steps in each
row are configured to increase in height along a first direction
parallel to the first boundaries, and the rows increase in height
along a second direction parallel to the second boundaries, each of
the steps having a different height from each other, and each of
the steps being configured to receive a corresponding one of the
beamlets; wherein: the height of each step is configured to produce
an optical path difference longer than the coherence length, and
the light incident surface is disposed approximately at a foci of
the beamlets output from the first transparent element.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to and claims the benefit of
provisional U.S. application No. 61/388,238 filed Sep. 30,
2010.
FIELD OF THE INVENTION
[0002] This invention relates to a laser annealing device with
reduced speckle, especially to a laser annealing machine to create
a thin film transistor for a large size organic LED display. This
invention also relates to laser display devices and laser display
methods, and more particularly, to laser display devices and laser
display methods directed to achieving reduced speckle.
RELATED ART
[0003] In general, a laser is an optical source that emits a
coherent light beam (also referred to herein as "coherent light" or
"laser light"). The coherent light may be emitted as a relatively
narrow beam and may be focused to very small spots. Because lasers
emit coherent light, lasers may be prone to speckle. Speckle is a
random intensity pattern on reflection from a diffuse surface
generally caused by mutual interference of multiple laser beams
from a coherent source reflected from different reflection points.
For example, a coherent light beam may be scattered at a rough
surface (e.g., a piece of paper, a display screen or a metallic
surface). Coherent light scattered by the rough surface can exhibit
variations in optical paths between any of two different raised
areas on the surface, to produce an interference (speckle) pattern
if the optical path is relatively shorter than the coherence length
of the laser source. The speckle pattern is typically observed as a
random granular pattern. Speckle patterns may severely degrade the
image quality of components illuminated with a laser source, such
as laser annealing, laser projection displays and laser
microscopes. Accordingly, it is desirable to reduce or eliminate
speckle from a laser source.
[0004] For light of high or moderate coherence, conventional
speckle reduction techniques typically involve generating many
independent speckle patterns that may average each other out at the
image plane. In general, speckle reduction methods may be
categorized as belonging to one of dynamic reduction methods and
static reduction methods. Dynamic reduction methods typically
involve the use of a time-varying component. For example, vibration
of a laser fiber or screen, rotation of a diffuser, random
shuttering of a light valve, and variation of polarization states
with time. Static reduction methods typically involve the use of
stationary components. For example, static methods may employ
stationary diffusers and stationary optical path difference
elements such as an optical fiber bundle in which each of the
individual optical fibers have different lengths.
[0005] Dynamic reduction methods typically outperform static
reduction methods, because the dynamic reduction methods are able
to more effectively average the speckle patterns. However, devices
that use dynamic reduction methods tend to be larger than those
devices that use static reduction methods, for example, because of
the number of additional mechanical components involved to generate
the time-varying component. Devices that use static reduction
methods may also be large. For example, devices that include static
optical path difference elements such as in an optical fiber may
use large path lengths to produce a substantial optical path
difference.
[0006] Another technique that may be used to produce a
homogenously-illuminated field includes the use of microlens
arrays, by splitting the incident laser beam into a number of
beamlets, depending on the number of microlenses. Microlens arrays,
however, tend to give rise to speckle because in forming the
ultimate image they merge the split beamlets.
[0007] A conventional despeckling method according to prior art
document JPA2008-159348 is shown in FIG. 1. As shown in FIG. 1, a
staircase element 1 is disposed between a laser diode 2 and a first
fly's eye lens array (not shown) on an optical path. That is, in
the direction of travel of the laser beam toward the image plane,
the staircase element is disposed after the laser diode and before
the first fly's eye lens array. Furthermore, the staircase element
is configured to make a path difference for each beamlet 4
generated from the received laser beam 3. These beamlets 4 are then
output from the staircase element 1 to the first fly's eye lens
array. The first fly's eye lens array then focuses the beamlets 4
onto approximately the first surface of the field lens to display
an image. By creating a path difference between each of the
beamlets, the staircase element 1 reduces interference between the
beamlets, thereby reducing speckle.
[0008] However, the conventional despeckling method shown in FIG. 1
has the following drawbacks.
[0009] First, because the incident beam 3 passes through the
staircase element 1 and gets diffracted before entering the first
fly's eye lens, the diffracted beamlets 4 may deviate in uniformity
before entering the first fly's eye lens, thereby reducing the
effectiveness of the despeckling.
[0010] Second, each of the beamlets 4 diffracted by the staircase
element 1 can enter not only the respective targeted lenslet, but
also an adjacent lenslet, thereby further reducing the
effectiveness of homogenization by using the fly's eye system.
SUMMARY OF THE INVENTION
[0011] Aspects of certain embodiments of the present invention
solve these and/or other problems associated with the related art
by providing an improved despeckling device and method in which an
optical path difference staircase element is disposed between the
first fly's eye lens array and the image plane in a position near
the focus position of the first fly's eye lens array, and a laser
generating unit generates and transmits pulsed laser beams to the
optical path difference staircase element, wherein the pulsed laser
beams are driven at a very short pulsed rate.
[0012] According to an aspect, there is provided an a despeckle
unit, comprising a first transparent element comprising a plurality
of microlenses to receive collimated light having a coherence
length and to output a beamlet from each of the microlenses; and a
second transparent element comprising a plurality of steps having a
one-to-one correspondence with the plurality of microlenses,
wherein each of the steps receives one of the beamlets and outputs
the beamlet to an image plane, where a height of each step of at
least two of the steps is configured to produce an optical path
difference of the beamlet longer than the coherence length, wherein
the second transparent element is disposed approximately at a foci
of the beamlets output from the first transparent element. The
collimated light may comprise pulsed laser beams driven by a pulse
of less than 10 nanoseconds. The pulse may reduce a coherence of
the laser beam and the steps may be configured to further reduce
the coherence of the laser beam not reduced by the pulse, to
substantially despeckle the pulsed laser beam. At least two of the
steps may be configured as a one-dimensional staircase and the
microlenses are configured as a one-dimensional array of
microlenses. The collimated light may be linearly polarized with a
polarization direction, and the second transparent element may
comprise at least one physical step comprising an optical wave
plate disposed on a first portion of the at least one physical step
which is configured to change the polarization direction of the
collimated light, and a second portion of the at least one physical
step which does not include the optical wave plate; and the optical
waveplate and the second portion may each comprise one of the steps
having the one-to-one correspondence with the microlenses.
Alternatively, the collimated light may be linearly polarized with
a polarization direction, and the second transparent element may
comprise at least one physical step comprising a first optical wave
plate disposed on a first portion of the at least one physical step
which is configured to change the linearly polarized light to right
circular polarized light, and a second optical wave plated disposed
on a second portion of the at least one physical step which is
configured to change the linearly polarized light to left circular
polarized light; and the first optical wave plate and the second
optical wave plate each comprise one of the steps having the
one-to-one correspondence with the microlenses.
[0013] According to another aspect, there is provided a despeckle
unit, comprising a first transparent element comprising a plurality
of microlenses to receive collimated light having a coherence
length and to output a beamlet from each of the microlenses; and a
second transparent element comprising a plurality of steps having a
one-to-one correspondence with the plurality of microlenses,
wherein each of the steps receives one of the beamlets and outputs
the beamlet to an image plane, wherein a height of each step of at
least two of the steps is configured to produce an optical path
difference of the collimated light longer than the coherence
length, wherein the second transparent element is disposed in a
location relative to the first transparent element such that edges
of the second transparent element parallel to an optical path of
the beamlets exiting the second transparent element do not diffract
the beamlets. The collimated light may comprise pulsed laser beams
driven by a pulse of less than 10 nanoseconds.
[0014] According to another aspect, there is provided a despeckling
laser unit to despeckle a laser beam, comprising a laser generating
unit to generate a pulsed laser beam having a coherence length; a
first transparent element comprising a plurality of microlenses to
receive the pulsed laser beam and to output a beamlet from each of
the microlenses; and a second transparent element comprising a
plurality of steps corresponding to the plurality of microlenses,
wherein each of the steps receives one of the beamlets and outputs
the beamlet to an image plane, wherein a height of each step of at
least two of the steps is configured to produce an optical path
difference of the pulsed laser beam longer than the coherence
length, wherein the second transparent element is disposed
approximately at the foci of the beamlets output from the first
transparent element. The pulsed laser beams may be driven by a
pulse of less than 10 nanoseconds. The despeckling laser unit may
further comprise a collimator disposed between the laser generating
unit and the first transparent element to receive the pulsed laser
beam and output a collimated laser beam; and a field lens to
receive the beamlets output from the second transparent element and
focus the received beamlets on the image plane. The at least two of
the steps may be configured as a one-dimensional staircase and the
microlenses are configured as a one-dimensional array of
microlenses. The pulsed laser beam may be linearly polarized with a
polarization direction; and the second transparent element may
comprise at least one physical step comprising an optical wave
plate disposed on a first portion of the at least one physical step
which is configured to change the polarization direction of the
pulsed laser beam, and a second portion of the at least one
physical step which does not include the optical wave plate; and
the optical wave plate and the second portion each comprise one of
the steps having the one-to-one correspondence with the
microlenses. Alternatively, the pulsed laser beam may be linearly
polarized with a polarization direction; and the second transparent
element may comprise at least one physical step comprising a first
optical wave plate disposed on a first portion of the at least one
physical step which is configured to change the linearly polarized
light to right circular polarized light, and a second optical wave
plated disposed on a second portion of the at least one physical
step which is configured to change the linearly polarized light to
left circular polarized light; and the first optical wave plate and
the second optical wave plate each comprise one of the steps having
the one-to-one correspondence with the microlenses. The despeckling
laser unit may further comprise a third transparent element
comprising another plurality of microlenses disposed after the
second transparent element and corresponding to the plurality of
microlenses, to provide focus control of the beamlets.
[0015] According to another aspect, there is provided a despeckling
laser array, comprising a plurality of the despeckling laser units
described above and a field lens to focus the beamlets output from
each of the plurality of despeckling laser units onto the image
plane.
[0016] According to another aspect, there is provided a despeckling
laser assembly, comprising a despeckling laser array as described
above; a base plate to support the despeckling laser array; a
circuit board attached to one end of the despeckling laser array;
and at least one driver integrated circuit mounted on the circuit
board to drive the laser generating units of the despeckling laser
array.
[0017] According to another aspect, there is provided an annealing
system to anneal a substrate, comprising a plurality of the
despeckling laser assemblies described above, disposed above a
front surface of the substrate, such that each of the despeckling
laser assemblies is configured to focus the beamlets on the
substrate, wherein each of the despeckling laser assemblies is
movable to enable the annealing system to anneal the front surface
of the substrate. In this annealing system, the substrate may
comprise amorphous silicon for organic LED displays.
[0018] According to another aspect, there is provided a
one-dimensional crossed despeckling unit, comprising a first
transparent element comprising a first surface having a first
plurality of first microlenses to receive collimated light having a
coherence length, and output a first plurality of first beamlets
corresponding to the first plurality of microlenses, and a second
surface having a second plurality of second microlenses to receive
the collimated light, and output a second plurality of second
beamlets corresponding to the second plurality of microlenses; and
a second transparent element comprising a first plurality of first
steps oriented such that at least one of the first steps
corresponds to at least one of the first beamlets; and a second
plurality of second steps oriented such that at least one of the
second steps corresponds to at least one of the second beamlets,
wherein a height of each step of at least two steps from among the
first steps and the second steps is configured to produce an
optical path difference of the pulsed laser beam longer than the
coherence length, and the second transparent element is disposed
approximately at a foci of the first beamlets and the second
beamlets output from the first transparent element. The collimated
light may comprise pulsed laser beams driven by a pulse of less
than 10 nanoseconds. The pulse may reduce a coherence of the laser
beam and the steps may be configured to further reduce the
coherence of the laser beam not reduced by the pulse, to
substantially despeckle the pulsed laser beam. The first
transparent element may comprise a one-dimensional crossed
microlens array, and the second transparent element may comprise a
combination of a first staircase element having the first plurality
of steps and a second staircase element having the second plurality
of steps. The first steps may each have the same first height, the
second steps may each have the same second height, with the first
height being different from the second height. The first staircase
may be provided in plural.
[0019] According to another aspect, there is provided a laser
module comprising a housing; a plurality of laser diodes disposed
at one end of the housing to generate respective pulsed laser beams
having respective coherence lengths; a first transparent element,
disposed after the plurality of laser diodes in the direction of
travel of the laser beams, comprising a plurality of microlenses to
receive the pulsed laser beams and to output a beamlet from each of
the microlenses; and the one-dimensional crossed despeckling unit,
as described above, disposed after the first transparent element in
the direction of travel of the laser beams, wherein each of the
first staircases corresponds to at least one of the laser diodes.
The laser diodes may be arranged in an M.times.N grid, where M an N
are positive integers respectively representing a number of laser
diodes in columns and rows of the grid, with the plurality of first
staircases comprising M first staircases, and each one of the M
first staircases corresponding to a respective one of the M
columns. In one aspect, M>N, N.gtoreq.1, M.gtoreq.2; a beam
shaping axis is arranged in a direction corresponding to the N
laser diodes; and each one of the M.times.N laser diodes generates
approximately 0.2 watts (W) of output power.
[0020] According to another aspect, there is provided a method to
despeckle a laser beam, comprising generating a pulsed laser beam
having a coherence length; transmitting the pulsed laser beam
through a first transparent element comprising a plurality of
microlenses so that the pulsed laser beam is output as a beamlet
from each of the microlenses; and transmitting each one of the
beamlets through a respective step included in a second transparent
element comprising a plurality of the steps having a one-to-one
correspondence with the plurality of microlenses, to an image
plane, wherein a height of each step of at least two of the steps
is configured to produce an optical path difference of the beamlets
longer than the coherence length, wherein the second transparent
element is disposed approximately at the foci of the beamlets
output from the first transparent element. The generating of the
pulsed laser beam may comprise driving the pulsed laser beam using
a pulse of less than 10 nanoseconds. The method may further
comprise collimating the generated pulsed laser beam and outputting
the collimated generated pulsed laser beam to the first transparent
element; and focusing the received beamlets transmitted through the
respective steps by the second transparent element on the image
plane using a field lens. The at least two of the steps may be
configured as a one-dimensional staircase and the microlenses may
be configured as a one-dimensional array of microlenses. The method
may further comprise polarizing the pulsed laser beam with a linear
polarization having a polarization direction; and changing the
polarization direction of the pulsed laser beam by passing the
pulsed laser beam through an optical wave plate comprising one of
the steps of the second transparent element. The method may further
comprise polarizing the pulsed laser beam with a linear
polarization; and changing the linear polarization of the pulsed
laser beam to right and left circular polarization by passing the
pulsed laser beam through corresponding first and second optical
wave plates each comprising one of the steps of the second
transparent element. The method may further comprise transmitting
each one of the beamlets output from the second transparent element
through a third transparent element comprising another plurality of
microlenses, to provide focus control of the beamlets.
[0021] According to another aspect, there is provided a
two-dimensional despeckling unit, comprising a first transparent
element comprising a surface having a plurality of microlenses to
receive collimated light having a coherence length from a pulsed
laser beam, each of the microlenses configured to output a beamlet
which is shaped in two-dimensions; and a second transparent element
comprising a light incident surface forming a two-dimensional area
comprising two first boundaries and two second boundaries
perpendicular to and connecting the two first boundaries; and a
plurality of steps protruding out from the light incident surface
and arranged in rows, wherein the steps in each row are configured
to increase in height along a first direction parallel to the first
boundaries, and the rows increase in height along a second
direction parallel to the second boundaries, each of the steps
having a different height from each other, and each of the steps
being configured to receive a corresponding one of the beamlets;
wherein the height of each step is configured to produce an optical
path difference longer than the coherence length, and the light
incident surface is disposed approximately at a foci of the
beamlets output from the first transparent element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred non-limiting examples of exemplary embodiments of the
invention, and, together with the general description given above
and the detailed description of the preferred embodiments given
below, serve to explain the principles and concepts of the
invention, in which like reference characters designate like or
corresponding parts throughout the several drawings. Preferred
embodiments of the present invention will now be further described
in the following paragraphs of the specification and may be better
understood when read in conjunction with the attached drawings, in
which:
[0023] FIG. 1 depicts a conventional despeckling method;
[0024] FIG. 2(a) depicts a cross-section diagram of a laser beam
homogenizer according to a first embodiment of the present
invention, with respect to a fast axis;
[0025] FIG. 2(b) depicts a cross-section diagram of the laser beam
homogenizer shown in FIG. 2(a) with respect to a slow axis;
[0026] FIG. 3 depicts a magnified view of the despeckle unit shown
in FIGS. 2(a) and 2(b);
[0027] FIGS. 4(a), 4(b), 4(c) and 4(d) depict a comparison of a
power spectrum and visibility in continuous wave(CW) or non-short
pulse operation (FIGS. 4(a) and 4(b)) and in short pulse operation
according to embodiments of the present invention (FIGS. 4(c) and
4(d));
[0028] FIG. 5 depicts a laser beam homogenizer according to a
second embodiment of the present invention;
[0029] FIG. 6 depicts a despeckle unit according to a third
embodiment of the present invention;
[0030] FIG. 7 depicts a despeckle unit according to a fourth
embodiment of the present invention;
[0031] FIG. 8(a) depicts a cross-section diagram of array according
to a fifth embodiment of the present invention, with respect to
non-shaping axis;
[0032] FIG. 8(b) depicts a cross-section diagram of the array shown
in FIG. 8(a) with respect to beam shaping axis;
[0033] FIG. 9(a) depicts a side-plan view diagram of unit according
to a sixth embodiment of the present invention, with respect to the
x and y axes;
[0034] FIG. 9(b) depicts the unit shown in FIG. 9(a) with respect
to the x and z axes;
[0035] FIG. 9(c) depicts the unit shown in FIG. 9(a) with respect
to the y and z axes;
[0036] FIG. 10 depicts a top-plan view diagram of a system 1000
according to a seventh embodiment of the present invention;
[0037] FIG. 11(a) depicts a one-dimensional crossed staircase
element according to an eighth embodiment of the present
invention;
[0038] FIGS. 11(b) and 11(c) depict the one-dimensional crossed
staircase element shown in FIG. 11(a) in use, viewed from a top
perspective and a side perspective, respectively;
[0039] FIG. 12 depicts a one-dimensional crossed despeckling array
1300 according to a ninth embodiment of the present invention;
[0040] FIG. 13 depicts a 4.times.2 laser diode (LD) module for
laser displays according to a tenth embodiment of the present
invention;
[0041] FIG. 14 depicts a two-dimensional staircase element
according to an eleventh embodiment of the present invention along
with a projected plane representing the total step height of each
beamlet passing through the two-dimensional staircase element;
and
[0042] FIGS. 15(a) and 15(b) depict the two-dimensional staircase
element shown in FIG. 14 in use, viewed from a top perspective and
a side perspective, respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0043] Reference will now be made in detail to the presently
non-limiting, exemplary and preferred embodiments of the invention
as illustrated in the accompanying drawings. The nature, concepts,
objectives and advantages of the present invention will become more
apparent to those skilled in the art after considering the
following detailed description in connection with the accompanying
drawings. The following description is provided in order to explain
preferred embodiments of the present invention, with the particular
features and details shown therein being by way of non-limiting
illustrative examples of various embodiments of the present
invention. The particular features and details are presented with
the goal of providing what is believed to be the most useful and
readily understood description of the principles and conceptual
versions of the present invention. In this regard, no attempt is
made to show structural details of the invention in more detail
than is necessary for the fundamental understanding of the present
invention. The detailed description considered with the appended
drawings are intended to make apparent to those skilled in the art
how the several forms of the present invention may be embodied in
practice.
[0044] FIGS. 2(a) and 2(b) depict cross-sectional diagrams of an
exemplary laser beam homogenizer 100 (also referred to herein as
homogenizer 100), according to a first embodiment of the present
invention. In particular, FIG. 2(a) is a cross-section diagram of
homogenizer 100 with respect to a fast axis of laser source 102;
and FIG. 2(b) is a cross-section diagram of homogenizer 100 with
respect to a slow axis of laser source 102. FIG. 3 is a magnified
view of the despeckle elements or despeckle unit 106 shown in FIGS.
2(a) and 2(b).
[0045] Homogenizer 100 includes short pulse laser driver 101, laser
source 102, collimator 104, despeckle elements 106 and field lens
108. In operation, laser source 102 emits coherent light beam 116.
Collimator 104 collimates coherent light beam 116 received from
laser source 102, to form collimated light beam 118. It is
understood that collimator 104 may collimate coherent light beam
116 to form collimated light (collimated light with no divergence)
or approximately collimated light (collimated light with some
degree of divergence or convergence).
[0046] Despeckle elements 106 include a microlens array 114 (also
known as a fly's eye lens array) and a staircase element 112 formed
of a transparent material. The microlens array 114 receives the
collimated light beam 118 from the collimator 104 and splits the
collimated light beam 118 into beamlets 120. More specifically, the
microlens array 114 includes a number of microlenses and splits the
collimated light beam 118 into a number of beamlets corresponding
to the number of microlenses. As shown in FIGS. 2(a) and 3, the
microlens array 114 includes three microlenses 114-1, 114-2, and
114-3 (FIG. 3) and splits the collimated light beam 118 into three
corresponding beamlets 120-1, 120-2, and 120-3, although it is
understood by those skilled in the art that the microlens array 114
may have more than or less than three microlenses. The beamlets
120-1, 120-2 and 120-3 are then transmitted to the staircase
element 112, which functions as an optical path difference element.
By creating a path difference between each of the beamlets 120, the
staircase element 112 reduces the coherence of the beamlets 120 as
compared to the coherent light beam 116. The beamlets 120 are then
superimposed on an image plane 110 by a field lens 108, to produce
a homogenously illuminated field with remarkably reduced or
eliminated speckle.
[0047] As shown in FIGS. 2(a) and 2(b), a significant feature of
the despeckle elements 106 is that the staircase element 112 is
disposed between the microlens array 114 and the image plane (that
is, after the lens array 114 in the direction of travel of the
beamlets) and approximately at a focal point (foci) of each of the
beamlets 120-1 through 120-3. More specifically, the focal point of
beamlet 120-1 is located just before a front surface (i.e., a
vertical surface as shown in FIGS. 2(a) and 3) of the corresponding
step 112-1, the focal point of beamlet 120-2 is located just at the
front surface of the corresponding step 112-2, and the focal point
of beamlet 120-3 is located just before or after the front surface
of the corresponding step 112-3, according to the thickness of each
of the steps 112-1 through 112-3. As a result of this
configuration, as shown in FIG. 3, the beamlets 120-1 through 120-3
avoid passing through the horizontal edges 112-4, 112-5, 112-6 and
112-7 forming the horizontal boundaries of the steps 112-1 through
112-3 and which are parallel to the optical path of the beamlets
120-1 through 120-3. Therefore, the beamlets 120-1 through 120-3
are not diffracted at all by the horizontal edges 112-4-112-7,
resulting in a significantly improved despeckling. This
configuration achieves a remarkably superior despeckling
performance of a quality which heretofore has never been achieved
in the industry.
[0048] In FIGS. 2(a) and 2(b), laser source 102 is illustrated as
producing the coherent light beam 116 having a fast axis (FIG.
2(a)) (i.e., larger divergence angle) and a slow axis (FIG. 2(b))
(i.e., smaller divergence angle). The coherent light beam 116
illustrates an elliptically shaped beam. An exemplary beam
intensity distribution of coherent light beam 116 is generally a
Gaussian distribution, shown in Eq. (1) as:
I ( x , y ) .varies. exp [ - 2 x 2 w x 2 - 2 y 2 w y 2 ] ( 1 )
##EQU00001##
[0049] where w.sub.x, w.sub.y are the Gaussian waist size of
coherent light beam 116, along the x axis and the y axis,
respectively. Although the coherent light beam 116 is illustrated
as being elliptically-shaped, it should be understood that the
coherent light beam 116 may have any suitable beam shape, including
circularly-shaped, symmetrically-shaped, and
non-symmetrically-shaped beams.
[0050] The laser source 102 may include any suitable laser light
source capable of producing coherent light. Examples of laser
source 102 include, without being limited to, semiconductor lasers
(e.g., laser diodes) including vertical cavity surface emitting
lasers (VCSELs), superluminescent diodes (SLDs), light emitting
diodes (LEDs), gas lasers, solid-state lasers, disc lasers, and
fiber lasers. In general, a coherent light source may be
characterized by a coherence length defined by the temporal
coherence length times the speed of light in a vacuum, where the
coherence length in a material may be scaled by the refractive
index of the material. Sources having very narrow bandwidths are
typically characterized by higher temporal coherence (and larger
coherence lengths) than broadband sources. The example embodiments
described below use semiconductor lasers.
[0051] Speckle typically occurs due to the relatively long
coherence of a laser (i.e., high temporal coherence), to cause a
high contrast interference pattern (i.e., a speckle pattern) on the
image plane 110. A visibility (i.e., an interference contrast) of
the interference pattern due to the coherent light may be
represented by Eq. (2) as:
V = I max - I min I max + I min ( 2 ) ##EQU00002##
where and I.sub.min and I.sub.max are minimum and maximum
intensities, respectively, of the interference pattern. The
visibility may be measured, for example, using a Michelson
interferometer, as a function of optical path difference between
the coherent light split into two light beams. In general, the
visibility is typically high in lasers of long coherence,
particularly at locations corresponding to small path differences
of the split beams.
[0052] In order to reduce the visibility of the speckle pattern,
the intensity spectrum of the laser source 102 may be broadened.
According to an exemplary embodiment, the laser source 102 may be
operated at a short pulse (e.g., the gain medium may be driven with
a signal having a short pulse, for example, between about 0.5 ns
(nanoseconds) to about 100 ns depending on the laser power). By
driving the laser source 102 using a short pulse, a multi-mode
oscillation occurs in the laser source 102, thus broadening the
width of the wavelength band. By broadening the wavelength
bandwidth, the visibility degrades, according to the
Wiener-Khintchine theorem (owing to the Heisenberg uncertainty
principle).
[0053] Referring to FIGS. 4(a)-4(d), examples of the wavelength
bandwidth broadening and the effect on visibility are shown with
respect to an example laser diode operated at approximately 2 ns.
In particular, FIG. 4(a) shows an intensity spectrum of the laser
diode in continuous wave (CW) operation as a function of
wavelength; FIG. 4(b) shows a visibility of the laser diode in CW
operation as a function of optical path difference; FIG. 4(c) shows
an intensity spectrum of the laser diode in a pulsed operation as a
function of wavelength of a laser; and FIG. 4(d) shows a visibility
of the pulse-operated laser diode as a function of optical path
difference.
[0054] As shown in FIG. 4(a), in the CW operation, the laser diode
has a very narrow wavelength bandwidth in the intensity spectrum.
Because of the narrow wavelength bandwidth, the visibility, as
shown in FIG. 4(b), is high across a wide range of optical path
differences. The intensity spectrum is related to the visibility
through the Fourier transformation according to the
Wiener-Khintchine theorem. Qualitatively, a narrower bandwidth in
the intensity spectrum produces a higher visibility, i.e., a high
coherence. Accordingly, FIG. 4(b) indicates that the laser diode,
in CW operation at high frequency, has a high coherence.
[0055] In contrast, as shown in FIG. 4(c), in a short pulse
operation, the wavelength bandwidth of the laser diode is
broadened. Because of the wavelength bandwidth broadening, the
visibility, as shown in FIG. 4(d), is substantially reduced across
most of the optical path differences. Although a large visibility
still exists at main peak 402 (referred to herein as the zero path
difference), the remaining peaks 404, which are known as side-mode
interference (referred to herein as side-mode peaks), are also
substantially reduced (but are not eliminated). The side-mode peaks
404 appear at every optical path difference P calculated by:
p=2nL (3)
where n and L are the refractive index and the laser cavity length,
respectively. Thus, the laser source operated at a sufficiently
short pulse has a substantially reduced (i.e., degraded) coherence.
Accordingly, by operating laser source 102 (FIGS. 2(a) and 2(b)) at
a short pulse, a majority of the interference from different path
lengths may be removed.
[0056] Referring back to FIGS. 2(a) and 2(b), according to an
exemplary embodiment, the laser source 102 may be operated with
(driven by) a short pulse of between about 0.5 ns to about 100 ns,
and preferably less than 10 nanoseconds. For typical semiconductor
lasers, after the injection current is injected to the laser diode
chip (i.e., the laser resonator cavity), many modes may be excited
for the first few nanoseconds. Particularly during this duration
time, the wavelength bandwidth may be significantly broadened,
because of the multi-mode operation. After the first few
nanoseconds, some modes may quickly decay and, thus, only main
modes may remain (based on a rate equation for the carriers and the
electrons). Therefore, a pulse width of a few nanoseconds may be a
particularly effective duration time to reduce the coherence.
However, the coherence also depends on the strength of the
injection current. A longer pulse width may still produce a
broadened wavelength bandwidth if the injection current is high.
Some lasers may have poor coherence even when pulsed at 100 ns, for
example. A lower limit of an electronically driven short pulse may
be about 0.5 ns.
[0057] According to aspects of the present invention, the pulse
width may be used to broaden the wavelength bandwidth. The
operation frequency, in contrast, may be a function of a desired
average output power of the laser source 102. For example, a
frequency of 200 MHz may be selected if an average output power of
1 W is desired, for a 2.5 ns pulsed operation with a peak power of
2 W to equivalently achieve a 50% duty ratio. Another example
includes a case where only a small output power is desired (for
example, as in the application of a laser microscope). In this
case, the pulse width is desirably short, while the frequency may
be low, which is equivalent to a low duty ratio. Thus, the duty
ratio may be determined based on the output power requirement.
According to an exemplary embodiment, the laser source 102 may
include a single mode laser configured to produce multi-mode
oscillation, by being driven with a very short pulse. Multi-mode
high power diode lasers may also be used. For display purposes, the
laser source 102 may be pulsed with a duty ratio of more than about
50%, to avoid any potentially dangerous high peak power.
[0058] The collimator 104 collimates the coherent light beam 116 to
form the collimated light beam 118, without substantially changing
the beam shape and the beam intensity distribution of the coherent
light beam 116. The collimator 104 may be a curved focusing lens
having a numerical aperture (NA) defined by n sin .theta., where n
is the refractive index of the medium and .theta. is the focusing
angle, as shown, or any other collimating configuration of optical
elements known to persons skilled in the art. The collimator 104
may have any suitable NA for producing the collimated light beam
118, including, but not limited to, about 0.3.
[0059] The NA of the collimator 104 (referred to herein as the
collimator NA) may be determined by a desired coupling efficiency,
depending on the divergence angles of the laser diodes and an ease
of alignment. When the collimator NA is selected so that the
focusing angle and the divergence angle of the laser diode are
matched, an optimum coupling efficiency may be obtained (i.e., a
minimum loss due to vignetting by the collimator aperture is
produced). For lasers with very fast divergence angles, a high
collimator NA may be selected, for example, greater than or equal
to 0.8. The alignment for such a collimator, however, may be
difficult, and the collimator may not be tolerable to alignment
error. On the other hand, a low collimator NA may be selected, to
reduce the alignment constraints and relax the design tolerance. In
this case, however, the coupling efficiency is reduced and more
light may be lost (because only a portion of the light cone emitted
from the laser source 102 may be enclosed inside the collimator
104).
[0060] Although the collimator 104 is illustrated as being separate
from the laser source 102, it should be understood that the
collimator 104 may be integrated with the laser source 102.
According to an exemplary embodiment, the collimator 104 may
include two separate crossed single axis collimators, each of which
may collimate one of the fast or slow axes of a laser diode (as the
laser source 102). This configuration may provide an improved
coupling efficiency, because the divergence angles of laser diodes
may differ significantly between the fast axis and the slow
axis.
[0061] Referring to FIGS. 2(a), 2(b) and 3, the despeckle elements
106 are further described below. FIG. 3 is a cross-section
magnified view of the exemplary despeckle elements 106. As
described above, the despeckle elements 106 according to an
embodiment include the microlens array 114 and the staircase
element 112 disposed after the microlens array 114 and
approximately at a focal point (foci) of each of the beamlets 120-1
through 120-3.
[0062] The staircase element 112 includes steps 112-1, 112-2, and
112-3 of different heights. The steps 112-1 through 112-3 are
configured to form optical path difference generating elements,
which remarkably reduce or substantially eliminate speckle. The
microlens array 114 includes microlenses 114-1, 114-2, and 114-3,
arranged as a one dimensional fly's eye array, and alternatively
referred to as a lenticular lens. The microlenses 114-1 through
114-3 are configured to form a fly's eye illumination system and
produce a more homogeneously-illuminated field.
[0063] As shown in FIG. 3, each step 112-1 through 112-3 is formed
in a one-to-one correspondence with each microlens 114-1 through
114-3 (i.e., step 112-1 corresponds to microlens 114-1, step 112-2
corresponds to microlens 114-2, and step 112-3 corresponds to
microlens 114-3). In other words, a width and position of each
microlens 114-1, 114-2, and 114-3 is in a one-to-one correspondence
with a width (W) and position of the respective steps 112-1, 112-2,
and 112-3.
[0064] Each of the elements of the despeckle element 106, such as
the microlens array 114 and the staircase element 112, may be
formed of a transparent material having a refractive index (n).
Transparent, as used herein, means having substantial optical
transmission at those wavelengths at which illumination is
intended. The elements of the despeckle element 106 may be formed
from any suitable transparent material transparent, such as quartz,
BK7, sapphire and other optical grade glass, and transparent
plastic materials, such as acrylic and polycarbonate. For example,
ZEONEX.RTM. (manufactured by ZEON Chemical) is a plastic material
suitable for ultraviolet (UV) and UV-blue wavelengths in terms of
durability.
[0065] In FIGS. 2(a) and 3, three steps (112-1, 112-2, and 112-3)
and three microlenses (114-1, 114-2, and 114-3) are shown. It
should be understood, however, that the staircase element 112 may
have more or less than three steps, and the microlens array 114 may
correspondingly have more or less than three microlenses. In
general, the staircase element 112 includes N number of steps
(where N is greater than 2) (and a corresponding N number of
microlenses), so that the steps substantially reduce or eliminate
speckle and the microlenses provide a more uniformly illuminated
field.
[0066] The number of steps and microlenses may be determined
according to a desired flat top size and quality of uniformity of
the illumination, based on the theory for a fly's eye illumination
system, as explained below. Let W and f.sub.M stand for the width
and focal length of the lenslet of the microlenses, respectively.
Let f.sub.F be the focal length of the field lens and let n be the
refractive index of the medium. For light of wavelength .lamda.,
design parameters for the fly's eye illumination system may be
given in the following equations.
Flat top size : D = Wf F f M ( 4 ) Fresnel number : F .apprxeq. W f
M .lamda. ( 5 ) Grating pattern period : P = f F .lamda. nW ( 6 )
##EQU00003##
v The flat top size (eq. 4) determines the illumination line length
in the one dimensional case and the edge length of the illumination
area in the two dimensional case. The Fresnel number (eq. 5) and
grating pattern (diffraction) period (eq. 6) determine the quality
of the uniformity of the illumination.
[0067] In general, the fly's eye illumination system may be
designed to produce a sufficiently large Fresnel number, because
the uniformity degrades inversely proportional to the Fresnel
number. The Fresnel number (eq. 5) represents how many diffraction
rings exist in a Fresnel diffraction pattern. In the fly's eye
illumination system, each beamlet passing through each lenslet in
the microlenses produces a Fresnel diffraction pattern. Each of the
Fresnel diffraction patterns produced at each lenslet are
superimposed on the image plane and are averaged to form a uniform
illumination. If the number of Fresnel diffraction rings is small,
large waves exist in a Fresnel diffraction pattern, which may not
be averaged or eliminated by the superposition. Thus, a small
Fresnel number may produce a poor illumination uniformity.
[0068] On the other hand, larger Fresnel numbers produce more
waves, i.e., many smaller waves in a Fresnel diffraction pattern.
The many and smaller waves are washed out and become substantially
invisible in the averaged image. The diffraction period (eq. 6) is
another indicator of the roughness in the illumination. Diffraction
may occur in the fly's eye illumination system, because the fly's
eye lens may act as a grating (due to the periodic edges of each
lenslet). This diffraction appears on the image plane as a periodic
diffraction pattern with the minimum period given by Eq. (6).
[0069] Each step 112-1 through 112-3 has a width W and a height H,
with a total thickness T. In FIG. 3, the steps 112-1 through 112-3
are arranged in a staircase configuration. The width W may be
determined by a desired system specification but, more importantly,
may be determined by considering, as determined by the present
inventors, that the staircase diffracts the incident light beam at
the horizontal edge of the staircase, as described above. This
diffraction perturbs the function of the fly's eye illumination
system, by splitting the incident beam into at least 0th order
diffracted light and +/-1st order diffracted light. The separation
of the incident beam is approximately calculated by
T .lamda. nW , ( 7 ) ##EQU00004##
where n is the refractive index of the staircase element 112. In
some instances, it may be desirable to select a larger W, to
minimize this separation in order to obtain a more uniform
illumination on the image plane. It may also be desirable to select
a larger beam size, to include a sufficient number of lenslets for
a more pronounced averaging effect.
[0070] Furthermore, as shown in FIG. 3, the staircase element 112
and microlens array 114 are separated by a distance D, which is
calculated to approximately correspond to the focal distance of the
beamlets 120, so that the beamlets 120 focus right at or near the
center of the vertical edges of the steps 112-1 through 112-3. By
choosing an appropriate distance D, the despeckling elements 106
according to aspects of the present invention prevent the beamlets
120 from being diffracted by the horizontal edges 112-4 through
112-7, thereby achieving a superior despeckling ability.
[0071] As shown in FIG. 3, the steps 112-1 through 112-3
monotonically increase in height (i.e., are arranged in a staircase
configuration), so that each step has a different height. The steps
112-1 through 112-3 may also be arranged to have randomly varying
heights. The optical path difference (OPD) produced by a step with
height H is given by
(n-1)H (8)
In FIG. 3, there is an OPD of (n-1)H between step 112-1 and 112-2;
2(n-1)H between step 112-1 and 112-3; and (n-1)H between step 112-2
and 112-3. According to an exemplary embodiment, there may be a
path difference between any combination of arbitrary steps among
all of the steps. Thus, any combination of two arbitrary beamlets
120 among all of the beamlets 120 has a path difference and thus
has little or no correlation. Hence, speckle may be substantially
reduced or eliminated. In FIG. 3, steps 112-1 to 112-3
monotonically increase by H as 0, H, and 2H but may be configured
with any different heights. For example, as 0, H, 3H; or 1H, 3H,
5H. Also steps 112-1 to 112-3 may randomly increase. For example,
as 0, 2H, 1H; 0, 3H, H; or 1H, 5H, 3H. In an exemplary embodiment,
steps 112-1 to 112-3 each have a height H of less than about 1
mm.
[0072] As described above, the laser source 102 is configured to
provide the coherent light beam 116 having a substantially reduced
coherence. However, as shown in FIG. 4(d), there is still a high
coherence (i.e., interference) at the zero path difference peak
402. Accordingly, the steps 112-1 to 112-3 may be configured as
optical path difference elements, to substantially reduce or
eliminate the remaining interference (i.e., interference not
reduced by the laser source 102).
[0073] If an optical path difference is introduced between two (or
more) portions of the coherent light beam 116 that exceeds the
coherence length, the ability for interference to occur between the
portions is substantially reduced. Accordingly, all of the beamlets
120 emerging from a surface of the microlens array 114 become
interference free (i.e., having substantially no speckle). Because
the pulsed laser source 102 substantially reduces the coherence
except for the zero path difference peak 402, the height H of the
steps 112-1 to 112-3 may be selected to be greater than the
coherence length and less than the first coherence revival length
(i.e., the length to the first side-mode peak 404 (FIG. 4(d)) from
the zero path difference peak 402). For example, referring to FIG.
4(d), if the zero path difference peak 402 drops to nearly zero at
a path difference of about 0.5 mm, the optical path difference
element may be configured to have a step height of 0.5/(n-1)
(taking into account the refractive index n of the material of the
despeckle element 106). It should be understood that a step height
of 0.5/(n-1) merely represents one example.
[0074] For example, the step height H may be selected as 1 mm for
the staircase element 112 having a refractive index of 1.5, because
the minimum OPD is (n-1)H=0.5 mm. For a step height of 0, H, 2H for
the three steps 112-1 to 112-3, the OPDs are 0.5 mm, 1.0 mm and 1.5
mm, respectively and the visibility for all of the OPDs is nearly
zero. For more than the three steps 112-1 to 112-3, one or more
OPDs of all possible OPDs may match the length of the side-mode
peak 404 (FIG. 4(d)). It may be desirable to design the beam size,
microlens size, step size, and step height so that the any of the
OPDs are far enough from the side-mode peaks 404 (FIG. 4(d)). The
OPD may be even larger than the first side-mode peak 404 (FIG.
4(d)) if there are no limitations in the physical size.
[0075] Although the steps 112-1 to 112-3 are illustrated as having
a same width W, the width of each step may be individually varied.
Furthermore, although the steps 112-1 to 112-3 are illustrated as
each having a monotonically increasing height, it is understood
that the height H of each step may also be individually varied. It
is further understood that a radius of curvature for individual
microlenses 114-1 to 114-3 may be adjusted to compensate for any
variation in the width W of the steps 112-1 to 112-3, so that the
microlenses all have the same focal length.
[0076] As illustrated in FIG. 3, the staircase element 112 includes
physical steps 112-1 to 112-3 arranged as a staircase to introduce
optical path differences, in order to substantially remove any
coherence from the collimated light beam 118. However, the
staircase element 112 is not limited to physical steps to reduce
the coherence. In general, the steps 112-1 to 112-3 represent
optical steps that may be used to reduce the coherence. The
staircase element 112 may also include differences in polarization
(described below with respect to FIGS. 6 and 7) and differences of
refractive index. For example, different refractive indices may be
introduced into the staircase element 112 of despeckle element 106
by selection of material or by coating, or doping, or implantation
of materials, or in any other manner known to those skilled in the
art.
[0077] Accordingly, the despeckle elements 106 provide a reduction
in coherence, based on the staircase element 112. In addition, the
despeckle elements 106 include the microlens array 114, which
splits the collimated light beam 118 into a plurality of beamlets
120-1, 120-2, 120-3, such that the number of beamlets 120 (e.g.,
three beamlets 120-1, 120-2, and 120-3) correspond to the number of
microlenses (e.g., three microlenses 114-1, 114-2, and 114-3). The
microlenses 114-1, 114-2, and 114-3 are configured to focus the
beamlets 120 to a point before or onto field lens 108.
[0078] If the despeckle elements 106 only included the microlens
array 114, without the staircase element 112, the microlenses
114-1, 114-2, and 114-3 would produce a more homogenously
illuminated field at the image plane 110. However, the beamlets 120
would still interfere with each other and produce speckle.
[0079] Interference (i.e., speckle) may occur when multiple
beamlets 120 come together at one spatial point. In conventional
illumination systems using coherent light sources, interference may
be caused by microlenses as they split a collimated light beam into
multiple beamlets. Accordingly, it is desirable to ensure that the
beamlets 120 from each of the microlenses 114-1, 114-2, and 114-3
have a reduced correlation, to avoid interference at the image
plane 110. According to aspects of the present invention, by
providing a one-to-one correspondence between the steps 112-1 to
112-3 and the microlenses 114-1 to 114-3, interference between the
beamlets 120 is reduced.
[0080] In FIGS. 2(a), 2(b) and 3, the despeckle elements 106 are
illustrated as a one dimensional array, with a one dimensional
array of steps 112-1 to 112-3 and a one dimensional array of
microlenses 114-1 to 114-3 extending in the fast axis. In this
example, the microlenses 114-1 to 114-3 may be formed as lenticular
lenses. It is to be understood, however, that the despeckle element
106 is not limited to a one-dimensional array and may include a
one-dimensional crossed configuration (FIGS. 11(a), 11(b), 11(c),
12, 13 and 14) or a two-dimensional array configuration (FIGS. 15,
16(a) and 16(b)). For example, if the coherent light beam 116 has a
circular beam shape, the despeckle element 106 may be formed as a
one-dimensional crossed array of steps and microlenses, described
further below with respect to FIGS. 11(a), 11(b), 11(c), 12, 13 and
14.
[0081] Referring back to FIGS. 2(a) and 2(b), the beamlets 120 are
directed to the field lens 108. The field lens 108 (e.g., a Fourier
lens) superimposes the multiple beamlets 120 together at the image
plane 110 (e.g., a specimen position) located near a focus
position, leading to a homogenously illuminated field. The field
lens 108 may be positioned anywhere between the despeckle elements
106 and the image plane 110. The position of the field lens 108 may
be used to change the energy distribution (e.g., from a Gaussian
profile to a flat-top profile) at the image plane 110 by coarse
positioning across the focus or to change the energy level of a
flat-top profile by fine positioning across near focus.
[0082] According to aspects of the present invention, the exemplary
homogenizer 100 produces the coherent light beam 116 with reduced
coherence and includes despeckle elements 106, which further reduce
the coherence. Accordingly, homogenizer 100 effectively eliminates
speckle, with a static configuration of elements, where the size of
the elements may be very small. By including the microlens array
114 and the staircase element 112 disposed after the microlens
array 114 at approximately the focal points of the beamlets 120,
the averaging effect by the beamlets 120 is increased.
[0083] FIG. 5 illustrates a laser beam homogenizer 500 according to
a second embodiment. The laser beam homogenizer 500 according to
the second embodiment includes various elements which are identical
to the elements included in the laser beam homogenizer 100
according to the first embodiment, and a detailed description of
these elements is omitted.
[0084] As shown in FIG. 5, the laser beam homogenizer 500 includes
despeckle elements 506 which include the microlens array 114 and
the staircase element 112 of the first embodiment, along with a
second microlens array 504 (fly's eye lens array) disposed after
the staircase element 112 which receives the beamlets 120
transmitted from the staircase element 112. By disposing a second
microlens array 504 after the staircase element 112 to receive the
beamlets 120, the laser beam despeckle elements 506 achieve a
tandem configuration which achieves improved uniformity in the flat
top profile generated by the laser beam homogenizer 500. It is to
be understood by those skilled in the art that the second microlens
array 504 can be disposed in various positions (e.g, closer to or
farther away from the staircase element 112) according to various
criteria known to those skilled in the art.
[0085] FIG. 6 illustrates a despeckle element 600 according to a
third embodiment. As shown in FIG. 6, the despeckle elements 600
according to a third embodiment include a staircase element 612
including a series of steps 612-1, 612-2, and 612-3, with each step
having an optical waveplate 602 disposed thereon. In particular,
the left side of FIG. 6 illustrates a cross-sectional diagram of
despeckle elements 600, and the right side of FIG. 6 illustrates a
cross-section diagram of the polarization directions for polarized
light 612-P and 612-S passed from a surface of the staircase
element 612 of the despeckle elements 600. Despeckle element 600 is
similar to despeckle element 106 (FIG. 1), except that despeckle
element 600 includes optical wave plates 602. FIG. 6 illustrates
three steps 612-1, 612-2, and 612-3 and three optical wave plates
602-1, 602-2, and 602-3 respectively disposed thereon, but it is
understood that more or less than three steps and three waveplates
can be used.
[0086] Despeckle element 600 includes a staircase element 612
formed of a transparent material and having physical steps 612-1,
612-2 and 612-3 formed in a staircase configuration as optical path
difference elements, as described above. In addition, despeckle
element 600 includes a respective wave plate 602 on a portion of
each physical step 612. Wave plate 602 is used to alter the
polarization state of incident light 610 received by despeckle
element 600. The staircase element 612 and the waveplates 602
disposed on the staircase element 612 are positioned around the
foci of a microlens array (not shown) to avoid undesired
diffraction.
[0087] In despeckle element 600, each wave plate 602 also
represents an optical step. Accordingly, microlenses of a microlens
array (not shown) used in conjunction with the despeckle element
600 are in a one-to-one correspondence with optical steps (physical
steps 612-1, 612-2 and 612-3 and wave plates 602-1, 602-2 and
602-3) of despeckle element 600. Thus, the despeckle element 600 is
configured to be used with a microlens array having six microlenses
respectively corresponding to physical step 612-1, optical
waveplate 602-1, physical step 612-2, optical waveplate 602-2,
physical step 612-3, and optical waveplate 602-3. For example, the
microlens array 114 of FIG. 1 could be modified to include six
microlenses instead of the three microlenses 114-1, 114-2, and
114-3 shown in FIG. 1, to be compatible with the despeckle element
600.
[0088] In an exemplary embodiment, wave plate 602 includes a half
wave plate, which changes the polarization direction of linear
polarized light (i.e., by rotating polarization axis A by
90.degree., making it orthogonal to incident beam 610). The
despeckle element 600 may be used, for example, instead of the
despeckle element 106 (as shown in any of FIG. 2(a), 2(b), 3, or 4)
or despeckle element 506 (FIG. 5), with the addition of a polarizer
(not shown) in the optical path between collimator 104 and field
lens 108.
[0089] As shown in FIG. 6, in operation, incident light beam 610
having polarized light (for example, p polarized light with a
polarization direction indicated by arrow A), passes through
despeckle element 600 to produce p-polarized light 612-P and
s-polarized light 612-S.
[0090] Polarized light 612-P (passed through physical steps 612-1,
612-2, and 612-3, but not passed through optical waveplates 602-1,
602-2, and 602-3) are passed without any change in the polarization
direction (i.e., as p-polarized light). Furthermore, incident light
beam 610 is also subject to optical path differences, due to the
difference in step heights of physical steps 612-1, 612-2 and
612-3. Because of the optical path differences of steps 612-1,
612-2 and 612-3, polarized light 612-P passing through, for
example, physical step 612-1 does not interfere with polarized
light 612-P passing through, for example, physical step 612-2 and,
similarly, polarized light 612-P passing through, for example,
physical step 612-2 does not interfere with polarized light 612-P
passing through, for example, physical step 612-3.
[0091] Polarized light 612-S (passed through optical waveplates
602-1, 602-2, and 602-3, respectively) is passed with a change in
the polarization direction. In addition, incident light beam 610 is
subject to optical path differences, due to the differences in step
heights of physical steps 612-1, 612-2 and 612-3. Because of the
optical path difference of steps 612-1, 612-2 and 612-3, polarized
light 612-S passing through, for example, optical waveplate 602-1
does not interfere with polarized light 612-S passing through, for
example, optical waveplate 602-2, and, similarly, polarized light
612-S passing through, for example, optical waveplate 602-2, does
not interfere with polarized light 612-S passing through, for
example, optical waveplate 602-1.
[0092] Since linearly polarized (e.g., p-polarized) and
orthogonally polarized (e.g., s-polarized) beams do not interfere
with each other, no step needs to be added to one of the two
adjacent positions on the staircase configuration. Accordingly,
wave plates 602-1, 602-2 and 602-3 may be formed directly on the
physical steps 612-1, 612-2, and 612-3 without increasing the step
height. Accordingly, a thickness of the despeckle element 600 may
be reduced to half of the thickness and half the number of physical
steps of a despeckle element where the optical steps are formed
only using physicals steps as optical path difference elements
(e.g., three physical steps in FIG. 6 as opposed to six physical
steps of a corresponding despeckle element similar to despeckle
element 106 of FIG. 2(a) but having six steps). Thus, the
despeckling element 600 according to a third embodiment of the
present invention has a reduced total thickness and is very
compact.
[0093] Furthermore, although FIG. 6 illustrates the wave plates 602
as being disposed on the steps 612-1, 612-2 and 612-3 of the
staircase element 612, it is understood that the wave plates 602
are not limited to being disposed on the staircase element 612, and
may instead be disposed on another element. In this case, the
waveplates 602 should still preferably be positioned around the
foci of the microlens array to avoid undesired diffraction.
Moreover, although FIG. 6 illustrates a respective wave plate 602
on a portion of each physical step 612-1, 612-2 and 612-3, wave
plates 602 may also be placed on every other physical step, or in
other arrangements known to those skilled in the art.
[0094] FIG. 7 illustrates a despeckle element 700 according to a
fourth embodiment. As shown in FIG. 7, the despeckle element 700
according to a fourth embodiment includes first and second optical
wave plates 702 and 704. In particular, the left side of FIG. 7 is
a cross-section diagram of despeckle element 700, and the right
side of FIG. 7 is a cross-section diagram illustrating polarization
directions for polarized light 712-L and 712-R passed from the
staircase element 712 of the despeckle element 700. Despeckle
element 700 is similar to despeckle element 600 (FIG. 6), except
that despeckle element 700 includes respective first and second
optical wave plates 702 and 704.
[0095] The despeckle element 700 includes a staircase element 712
formed of a transparent material and including physical steps
712-1, 712-2 and 712-3. The physical steps 712-1, 712-2 and 712-3
are formed in a staircase configuration as optical path difference
elements, as described above. In addition, the despeckle element
700 includes first and second wave plates 702 and 704 on each
physical step 712-1, 712-2 and 712-3. First and second wave plates
702 and 704 may be used to alter the polarization state of incident
light beam 710 received by the despeckle element 700. The staircase
element 712 and the waveplates 702 and 704 disposed on the
staircase element 712 are positioned around the foci of a microlens
array (not shown) to avoid undesired diffraction.
[0096] In the despeckle element 700, first and second wave plates
702 and 704 also represent optical steps. Accordingly, microlenses
of the microlens array (not shown) are in a one-to-one
correspondence with the optical steps (first and second wave plates
702 and 704). Thus, the despeckle element 700 is configured to be
used with a microlens array having six microlenses respectively
corresponding to first waveplate 702-1, second waveplate 704-1,
first waveplate 702-2, second waveplate 704-2, first waveplate
702-3, and second waveplate 704-3. For example, the microlens array
114 of FIG. 1 could be modified to include six microlenses instead
of the three microlenses 114-1, 114-2, and 114-3 shown in FIG. 1,
to be compatible with the despeckle element 700.
[0097] In an exemplary embodiment, first wave plate 702 includes a
quarter wave plate and second wave plate 704 includes a
three-quarter wave plate. The quarter wave plate (i.e., first wave
plate 702) changes linearly polarized light to right circular
polarized light and the three-quarter wave plate (i.e., second wave
plate 704) changes linearly polarized light to left circular
polarized light. The despeckle element 700 may be used, for
example, instead of despeckle element 106 (as shown in any of FIG.
2A, 2B, or 3, 4, 7A-8D) or despeckle element 506 (FIG. 5), with the
addition of a polarizer (not shown) in the optical path between
collimator 104 and field lens 108.
[0098] As shown in FIG. 7, in operation, the incident light beam
710 having linearly polarized light (for example, p polarized light
with a polarization direction indicated by arrow A), passes through
despeckle element 700 to produce right-circular-polarized light
712-R and left-circular-polarized light 712-L.
[0099] Polarized light beams 712-R have right circular polarization
(from respective first wave plates 702-1, 702-2, and 702-3). In
addition, incident light beam 710 is subject to optical path
differences, due to the difference in step heights of physical
steps 712-1, 712-2, and 712-3. Because of the optical path
difference of steps 712-1, 712-2, and 712-3, polarized light 712-R
passing through, for example, first wave plate 702-1 does not
interfere with polarized light 712-R passing through, for example,
first wave plate 702-2 and, similarly, polarized light 712-R
passing through, for example, first wave plate 702-2 does not
interfere with polarized light 712-R passing through, for example,
first wave plate 702-3.
[0100] Polarized light beams 712-L have left circular polarization
(from respective second wave plates 704-1, 704-2 and 704-3). In
addition, incident light beam 710 is subject to optical path
differences, due to the difference in step heights of physical
steps 712-1, 712-2, and 712-3. Because of the optical path
differences of steps 712-1, 712-2, and 712-3, polarized light 712-L
passing through, for example, second wave plate 704-1 does not
interfere with polarized light 712-L passing through, for example,
second wave plate 704-2 and, similarly, polarized light 712-L
passing through, for example, second wave plate 704-2 does not
interfere with polarized light 712-L passing through, for example,
second wave plate 704-3.
[0101] Since right circular polarization and left circular
polarization beams do not interfere with each other, no step needs
to be added to one of the two adjacent positions on the staircase
configuration. Accordingly, both first wave plate 702 and second
wave plate 704 may be formed directly on staircase element 712
without increasing the step height. Thus, the thickness of
despeckle element 700 may be reduced to half of the thickness and
half the number of physical steps (e.g., three physical steps as
opposed to six physical steps) compared to a step of despeckle
element 106 (FIG. 2(a)) but having six steps. Thus, the despeckling
element 700 according to a fourth embodiment of the present
invention has a reduced total thickness and is very compact.
[0102] Furthermore, although FIG. 7 illustrates the wave plates 702
and 704 as being disposed on the steps 712-1, 712-2, and 712-3 of
the staircase element 712, it should be understood that the wave
plates 702 and 704 are not limited to being disposed on the
staircase element 712, and may instead be disposed on another
element. In this case, the waveplates 702 and 704 should still
preferably be positioned around the foci of the microlens array to
avoid undesired diffraction. Moreover, although FIG. 7 illustrates
a wave plate 702 and a wave plate 704 on each physical step 712-1,
712-2, and 712-3, wave plates 702 and 704 may also be placed on
every other physical step, or in other arrangements that achieve
similar effects to those described above.
[0103] FIGS. 8(a) and 8(b) illustrate an exemplary despeckling
laser array 800 (also referred to herein as "array 800") according
to a fifth embodiment of the present invention. In particular, FIG.
8(a) illustrates a cross-sectional diagram of array 800 with
respect to a slow axis of laser sources 102, and FIG. 8(b)
illustrates a cross-section diagram of array 800 with respect to a
fast axis of laser sources 102.
[0104] The array 800 is similar to the laser beam homogenizer 100
(FIGS. 2(a) and 2(b)), except that the array 800 includes a
plurality of laser sources 102-1, 102-2, and 102-3 having a
plurality of corresponding collimators 104-1, 104-2, 104-3 and a
plurality of corresponding despeckle elements 806-1, 806-2 and
806-3. Beamlets from the plurality of despeckle elements 806-1,
806-2 and 806-3 are superimposed together by field lens 808 at the
image plane 810.
[0105] Because laser sources 102-1, 102-2, 102-3 are independent
laser sources, they are not correlated with each other and do not
coherently interfere with each other. Thus, beamlets from the
plurality of despeckle elements 806-1, 806-2, and 806-3 may be
combined by a common field lens 808 and may overlap at the image
plane 810. The combined beam profile is thus averaged out and may
produce a more uniform intensity profile.
[0106] As shown in FIGS. 8(a) and 8(b), the array 800 is configured
to have three despeckle elements 806-1, 806-2 and 806-3 arranged in
a single row and 3 columns (one column for each of the despeckle
elements) (a 3.times.1 configuration). However, the array 800 is
not limited to being configured in this fashion, and instead may be
configured in any arbitrary way, such as, for example, a 3.times.2
configuration, a 6.times.3 configuration, etc. Also, when the array
800 is configured to include 1-dimensional despeckling elements,
such as despeckling elements 806-1, 806-2, and 806-3, the array 800
can be used for various purposes, such as laser annealing. In this
case, it is preferable that the beam shaping (flat top making) axis
be located on the side of the array having the smaller number of
either the rows or columns employed in the array, for example, the
1 row side (FIG. 8(b)) for a 3.times.1 array, the 2 row side for a
3.times.2 array, and the 3 row side for a 6.times.3 array, and that
the axis with the larger number of the rows or columns be chosen as
the non-shaping axis. This arrangement facilitates the design of
the field lens. In the beam shaping axis, there are microlens
arrays (fly's eye lens arrays) which diverge or converge beamlets,
thereby making certain field angles against the field lens. When
the field lens needs to be designed for the wider field and wider
field angle (i.e., the larger of the rows or columns), the design
of the field lens becomes more difficult. Therefore, the axis of
the shorter length (i.e., the fewer of the rows or columns in the
array), such as, for example, the short axis shown in FIG. 8(b), is
preferable to be used for beam shaping. On the other hand, the
other axis, for example, the long axis in FIG. 8(a), has no
microlens array and only transmits a collimated beam. Accordingly,
this makes the design of the field lens simpler and easier.
[0107] The despeckle elements 806-1, 806-2 and 806-3 may be the
same as the despeckle elements according to other embodiments, for
example, the despeckle element 106 according to a first embodiment
(FIG. 1). Furthermore, the array 800 may also include two or more
despeckle elements 806 per laser source 102, instead of only one.
Also, the array 800 may also include an additional microlens array,
as described above with respect to FIG. 5. The despeckle elements
806 may also include one or more optical wave plates, as described
above with respect to FIGS. 6 and 7. It should be understood that
any one or more of the embodiments described herein may be combined
into one optical system including a common field lens 808.
[0108] FIGS. 9(a) and 9(b) illustrate an exemplary despeckling
laser array assembly 900 (also referred to herein as "assembly
900") according to a sixth embodiment of the present invention. In
particular, FIG. 9(a) is a side-plan view diagram of assembly 900
with respect to the x and y axes; FIG. 9(b) is a cross-section
diagram along line 9B of assembly 900 with respect to the x and z
axes (relative to non-shaping axis); and FIG. 9(c) is a
cross-section diagram along line 9C of assembly 900 with respect to
the y and z axes (relative to beam shaping axis).
[0109] Assembly 900 includes a plurality of laser sources 902 each
having a corresponding collimator 904 and despeckle element 906.
Each of the despeckle elements 906 includes a microlens array 914
and a staircase element 912, and may have the same configuration as
the despeckle elements according to other embodiments of the
present invention. Beamlets from the plurality of microlens arrays
914 are combined by a common field lens 908. The assembly 900 also
includes a plurality of driver integrated circuits (ICs) 901
mounted on a printed circuit board 903. The driver ICs 901 may be
configured to drive respective laser sources 902.
[0110] The laser source 902, collimator 904, despeckling element
906 (including the microlens array 914 and the staircase element
912) and the field lens 908 form an assembly 900. Assembly 900 is
similar to array 800 (FIGS. 8(a) and 8(b)), except that assembly
900 is assembled in chassis 918. Although in an exemplary
embodiment chassis 918 is formed from molded aluminum, chassis 918
may be formed from any material suitable for housing array 922.
[0111] Each laser source 902 may be mounted in a separate holder.
Each holder may be adhered to chassis 918 after optical axis
adjustment with respect to tilt and/or x/y correction (i.e., the
correction of tilts of the incident light beam with respect to
optical axis 922). Each laser source 902 may then be electrically
connected to a respective driver IC 901 via circuit board 903. Each
collimator 904 may be mounted in respective holder 926, where
holder 926 may include adjustment notch 928 (shown in FIG. 9(c)).
Notch 928 may be configured to move holder 926 along optical axes
922, 924, in order to adjust the amount of collimation.
[0112] The despeckle elements 906 and field lens 908 may be adhered
to chassis 918. Once the array 922 is suitably secured in the
chassis 918, top lid 930 may be placed on chassis 918 and may be
secured to chassis 918 (for example, via screws). Chassis 918 may
be secured to bottom base plate 920 (for example, via bolts).
[0113] Although the despeckle elements 906 are positioned as shown
in FIG. 9(b), the despeckle elements 906 may be positioned
according to any of the configurations described above with respect
to any of the other embodiments. Furthermore, although assembly 900
is illustrated as including despeckle elements 906, it is
understood that assembly 900 is not limited to the illustrated
configuration. Furthermore, although FIGS. 9(a)-9(c) illustrate
laser sources 901 having elliptical beam shapes, laser sources 901
may have a circular beam shape. Accordingly, despeckle elements 906
may be replaced with one-dimensional crossed despeckle elements
(described below with reference to FIGS. 11(a)-13). Despeckle
elements 906 may also include one or more optical wave plates, as
described above with respect to FIGS. 6 and 7. It should be
understood that any one or more of the embodiments described herein
may be combined into assembly 900.
[0114] FIG. 10 illustrates a top-plan view diagram of an exemplary
system 1000 according to a seventh embodiment of the present
invention. As shown in FIG. 10, the exemplary system 1000 is used
for annealing a substrate 1002. System 1000 includes a
two-dimensional arrangement of assemblies 900 (FIGS. 9(a)-9(c))
along column and row directions, configured to produce annealing
lines 1004 (i.e., annealed portions) of substrate 1002. Substrate
1002 may include any suitable substrate for being annealed by laser
sources. For example, substrate 1002 may include, without being
limited to, amorphous silicon for large organic LED displays.
[0115] Assemblies 900 may be shifted or displaced relative to each
other in the column direction by an amount Xa. A beam line width Lb
of annealing lines 1004 is typically smaller than a width La of
assembly 900. Accordingly, in order to anneal the entire surface of
substrate 1002, assemblies 900 may be arranged in an interlace
configuration (e.g., similar to an inkjet line head), such that
assemblies 900 are shifted by an amount Ya in the row
direction.
[0116] For a beam line width Lb which is equal to an annealing
width, a gap Sb between annealing lines 1004 may be selected with
respect to laser array width La and a gap Sa between assemblies 900
according to Eq. (9) as:
(L.sub.b-S.sub.b)M=L.sub.a+S.sub.a (9)
for a total number of columns M for the case of one scanning
period. The shift Ya of assemblies 900 in the row direction may be
given by Eq. (10) as:
Y.sub.a=L.sub.b+S.sub.b (10)
The shift Xa of assemblies 900 in the column direction may be
arbitrarily selected. For a given shift Xa, a total length of
system 1000 in the column direction becomes MXa.
[0117] In FIG. 10, a total of M.times.N number of assemblies 900
are positioned above substrate 1002, where N represents a total
number of rows. FIG. 10 represents an example embodiment of system
1000. It is understood that system 1000 may include fewer columns
of assemblies 900, to scan the entire surface of substrate 1002.
For example, fewer columns of assemblies 900 may be scanned
multiple times while being shifted in the row direction (similar to
operation of a serial inkjet printer).
[0118] FIG. 11(a) depicts a one-dimensional crossed staircase
element 1100 according to an eighth embodiment of the present
invention. As shown in FIG. 11, the one-dimensional crossed
staircase element 1100 includes a first staircase element 1102
(also referred to herein as "horizontal staircase element 1102")
and a second staircase element 1104 (also referred to herein as
"vertical staircase element 1104"). The one-dimensional crossed
staircase element 1100 according to aspects of the present
invention achieves outstanding despeckling results for various
applications which require relatively high amounts of power, such
as laser annealing and laser displays.
[0119] The horizontal staircase element 1102 includes a series of
three horizontal steps 1102-0, 1102-1 and 1102-2. The horizontal
staircase element 1102 may be formed of any transparent material
known to those skilled in the art, as described above with respect
to the other embodiments. According to an aspect of the present
invention, the first step 1102-0 has a step height of 0, and each
of the steps 1102-1 and 1102-2 has a step height of approximately 3
mm. However, it is understood that the steps 1102-1 and 1102-2 are
not limited to this height, but that any of the steps may be
various other heights depending on design conditions. It is further
understood that, although in this embodiment, a step height of "0"
refers to step 1102-0 literally having an absence of any height
(i.e., an absence of any material in the step), it is understood
that a step having a "step height of 0" is not limited to a step
having a complete absence of height/material, and can alternatively
refer to a reference step height wherein the step is formed with
some small amount of material and therefore has a non-zero height
which is the reference height "0" relative to the other steps. That
is, a step height of "0" may refer to a relative height of the step
in comparison to other steps, as would be appreciated by those
skilled in the art.
[0120] The vertical staircase element 1104 includes a series of
three vertical steps 1104-0, 1104-1 and 1104-2. The vertical
staircase element 1104 may be formed of the same materials as the
horizontal staircase element 1102, or may be formed of different
materials. According to an aspect of the present invention, the
first step 1104-0 has a step height of 0 (which, as explained above
with respect to the horizontal staircase element 1102, may refer to
either a literal absence of height or may be a zero reference
height), and each of the steps 1104-1 and 1104-2 has a step height
of approximately 1 mm. However, it is understood that the steps
1104-1 and 1104-2 are not limited to this height, but that any of
the steps may be various other heights depending on design
conditions. In the illustrated embodiment, the step heights of the
steps 1102-1 and 1102-2 of the horizontal staircase element 1102
are selected to be approximately three times the step heights of
the steps 1104-1 and 1104-2 of the vertical staircase element 1104,
for reasons explained further below.
[0121] The one-dimensional crossed staircase element 1100 may be
made of the same transparent material described above with respect
to the other embodiments, and may be formed in various ways. For
example, the horizontal staircase element 1102 and vertical
staircase element 1104 may be separately formed and then adhered
together, using any adhesive material known to those skilled in the
art.
[0122] FIGS. 11(b) and 11(e) illustrate the one-dimensional crossed
staircase element 1100 shown in FIG. 11(a) in use, viewed from a
top perspective and a side perspective respectively. In particular,
FIG. 11(b) illustrates the one-dimensional crossed staircase
element 1100 viewed from a top perspective along a fast axis, and
FIG. 11(c) illustrates the one-dimensional crossed staircase
element 1100 viewed from a side perspective along a slow axis.
[0123] As shown in FIG. 11(b), laser light 1110 passes through a
one-dimensional crossed microlens array 1114 (a fly's eye lens
array) and is transmitted to the one-dimensional crossed staircase
element 1100. Collectively, the "one-dimensional crossed microlens
array 1114" and the "one-dimensional crossed staircase element
1100" may also be referred to as a "one-dimensional crossed
despeckling unit." The laser light 1110 can be generated by, for
example, a laser diode as described with respect to other
embodiments of the invention. The one-dimensional crossed microlens
array 1114 includes two microlens arrays 1116, including a first
microlens array 1116-1 (FIG. 11(b)) which is configured to focus
the laser light 1110 along the fast axis, and a second microlens
array 1116-2 (HG. 11(b)) disposed on an opposite side of the first
microlens array 1116-1 and which is configured to focus the laser
light 1110 along the slow axis.
[0124] The number of microlenses 1117 in the first microlens array
1116-1 is set to match the number of steps in the horizontal
staircase element 1102. To achieve maximum despeckling results, it
is essential that the number of microlenses 1117 match the number
of steps in the horizontal staircase element 1102. In this
particular embodiment, the first microlens array 1116-1 includes
three microlenses 1117-1, 1117-2, and 1117-3, and the horizontal
staircase element 1102 includes three corresponding steps 1102-0,
1102-1, and 1102-2. Although the step 1102-0 has a step height of
zero, this step is still considered a step, and thus has a
corresponding microlens (1117-3). Furthermore, the reason why there
are only two steps with a non-zero step height (i.e., steps 1102-1
and 1102-2) in the horizontal staircase element 1102 is to make the
total thickness of the horizontal staircase element 1102 as thin as
possible for compactness, by making the first step height of step
1102-0 equal to zero. Thus, since the horizontal staircase element
1102 has three steps 1102-0, 1102-1 and 1102-2, the first microlens
any 1116-1 has three corresponding microlenses 1117-1, 1117-2 and
1117-3. In this way, along the fast axis, a first one of the
microlenses can transmit light through both steps with a non-zero
step height and the step with zero step height (i.e., steps 1102-2,
1102-1, and 1102-0) to achieve a maximum step height, a second one
of the microlenses can transmit light through one of the steps with
a non-zero step height and the step with zero step height (i.e,
steps 1102-1 and 1102-0) to achieve an intermediate step height,
and a third one of the microlenses can transmit light through only
the step with a zero step height (i.e., step 1102-0) to achieve a
minimum step height.
[0125] Similarly, the number of microlenses 1118 in the second
microlens array 1116-2 is set to match the number of steps in the
vertical staircase element 1.104. Thus, since the vertical
staircase element 1104 has three steps 1104-0, 1104-1 and 1104-2,
the second microlens array 1116-2 has three corresponding
microlenses 1118-1, 1118-2 and 1118-3. The step 1104-0 is
configured to have a step height of 0, for the same reasons as
mentioned above with respect to the step 1102-0 in the horizontal
staircase element 1102 (i.e., to achieve a very compact design),
and the steps 1104-1 and 1104-2 are configured to have non-zero
step heights. In this way, along the slow axis, a first one of the
microlenses can transmit light through both steps with a non-zero
step height and the step with zero step height (i.e., steps 1104-2,
1104-1 and 1104-0) to achieve a maximum step height, a second one
of the microlenses can transmit light through one of the steps with
a non-zero step height and the step with zero step height (i.e.,
steps 1104-1 and 1104-0) to achieve an intermediate step height,
and a third one of the microlenses can transmit light through only
the step with zero step height (i.e., step 1104-0) to achieve a
minimum step height.
[0126] The one-dimensional crossed microlens array 1114 can be
formed in various ways. For example, the first microlens array
1116-1 and the second microlens array 1116-2 can each be the same
as the microlens arrays described with respect to other embodiments
of the present invention (e.g., microlens array 114 described in
embodiment 1). The first microlens array 1116-1 and the second
microlens array 1116-2 can be integrally formed from the same
transparent material, or can be separately formed.
[0127] As shown in FIG. 11(b), in the top view plane, when the
laser light 1110 is passed through the one-dimensional crossed
microlens array 1114, the microlenses 1117-1, 1117-2 and 1117-3
focus the laser light 1110 into three column of beamlets.
Similarly, in the side view plane, when the laser light 1110 is
passed through the one-dimensional crossed microlens array 1114,
the microlenses 1118-1, 1118-2 and 1118-3 focus the laser light
1110 into three row of beamlets resulting in 3.times.3 nine
beamlets 1110-1, 1110-2, 1110-3, 1110-4, 1110-5, 1110-6, 1110-7,
1110-8 and 1110-9, which are then transmitted to the
one-dimensional crossed staircase element 1100. The one-dimensional
crossed staircase element 1100 is disposed near the foci of the
laser light 1110 passed through the one-dimensional crossed
microlens array 1114, to prevent edges 1108 of both the horizontal
staircase element 1102 and vertical staircase element 1104 which
are parallel to the optical path of the beamlets from creating
unnecessary diffraction of the beamlets 1110-1, 1110-2, and 1110-3,
and thereby achieving superior despeckling performance.
[0128] A column of beamlets 1110-7, 1110-8 and 1110-9 passes
through steps 1102-2, 1102-1 and 1102-0 of the horizontal staircase
element 1102. In this illustration, the step heights of the steps
1102-1 and 1102-2 are each 3 mm, and the step heights of the steps
1104-1 and 1104-2 are each 1 mm, and the step heights of 1102-0 and
1104-0 are zero, as an example. As shown in FIG. 11(a), the column
of beamlets 1110-7, 1110-8 and 1110-9 is always transmitted through
the horizontal steps 1102-0, 1102-1 and 1102-2 of the horizontal
staircase element 1102. Thus, the column of beamlets 1110-7, 1110-8
and 1110-9 always has at least a minimum step height of 6 mm
Additionally, some beamlets may experience path step heights
greater than 6 mm, depending on whether the beamlets are also
transmitted through either or all of the vertical steps 1104-0,
1104-1 and 1104-2 of the vertical staircase element 1104.
[0129] A beamlet 1110-7 only passes through the horizontal steps
1102-0, 1102-1 and 1102-2 and does not pass through either of the
vertical steps 1104-1 or 1104-2 having a non-zero step height, and
therefore has a step height of 6 mm (represented as the numeral "6"
in FIG. 11(a)). A second beamlet 1110-8 passes through the
horizontal steps 1102-0, 1102-1 and 1102-2 and additionally passes
through the vertical step 1104-0, 1104-1, and therefore has a step
height of 7 mm, which is the sum of the 6 mm from horizontal steps
1102-1 and 1102-2 and the 1 mm from vertical step 1104-0 and 1104-1
(represented as the numeral "7" in FIG. 11(a)). A third beamlet
1110-9 passes through the horizontal steps 1102-0, 1102-1 and
1102-2 and additionally passes through all of the vertical steps
1104-0, 1104-1 and 1104-2, and therefore has a step height of 8 mm,
which is the sum of the 6 mm from horizontal steps 1102-1 and
1102-2 and the 2 mm from vertical steps 1104-0, 1104-1 and 1104-2
(represented as the numeral "8" in FIG. 11(a)).
[0130] Furthermore, as shown in FIG. 11(b), a column of beamlets
1110-4, 1110-5 and 1110-6 is always transmitted through the
horizontal steps 1102-0 and 1102-1. Thus, the column of beamlets
1110-4, 1110-5 and 1110-6 always has at least a minimum step height
of 3 mm. Additionally, some beamlets may experience optical path
step heights greater than 3 mm, depending on whether the beamlets
are also transmitted through either or all of the vertical steps
1104-0, 1104-1 and 1104-2 of the vertical staircase element 1104. A
beamlet 1110-4 only passes through the horizontal steps 1102-0 and
1102-1 and does not pass through either of the vertical steps
1104-1 or 1104-2 having a non-zero step height, and therefore has a
step height of 3 mm (represented as the numeral "3" in FIG. 11(a)).
A beamlet 1110-5 passes through the horizontal steps 1102-0 and
1102-1 and additionally passes through the vertical step 1104-0 and
1104-1, and therefore has a step height of 4 mm, which is the sum
of the 3 mm from horizontal step 1102-1 and the 1 mm from vertical
step 1104-0 and 1104-1 (represented as the numeral "4" in FIG.
11(a)). A beamlet 1110-6 passes through the horizontal steps 1102-0
and 1102-1 and additionally passes through both of the vertical
steps 1104-0, 1104-1 and 1104-2, and therefore has a step height of
5 mm, which is the sum of the 3 mm from horizontal step 1102-1 and
the 2 mm from vertical steps 1104-0, 1104-1 and 1104-2 (represented
as the numeral "5" in FIG. 11(a)).
[0131] Moreover, as shown in FIG. 11(b), a column of beamlets
1110-1, 1110-2 and 1110-3 is not transmitted through either of the
horizontal steps 1102-1 or 1102-2, and is only transmitted through
step 1102-0 which has a zero step height. Thus, the column of
beamlets 1110-1, 1110-2 and 1110-3 may have an optical step height
of 0 mm. Additionally, some beamlets may experience path step
heights greater than 0 mm, depending on whether the beamlets are
also transmitted through either or both of the vertical steps
1104-0, 1104-1 and 1104-2 of the vertical staircase element 1104. A
beamlet 1110-1 does not pass through either of the vertical steps
1104-1 or 1104-2, and therefore has a step height of 0 mm
(represented as the numeral "0" in FIG. 11(a)). A beamlet 1110-2
passes through the vertical step 1104-0 and 1104-1, and therefore
has a step height of 1 mm (represented as the numeral "1" in FIG.
11(a)). A beamlet 1110-3 passes through both of the vertical steps
1104-0, 1104-1 and 1104-2, and therefore has a step height of 2 mm.
(represented as the numeral "2" in FIG. 11(a)).
[0132] FIG. 11(a) depicts a view of a one-dimensional crossed
staircase element with a projected plane representing the total
step height of each beamlet passing through the one-dimensional
crossed staircase element. In general, a principle behind the
selection of the step heights of the horizontal staircase element
1102 and vertical staircase element 1104 in the one-dimensional
crossed staircase element 1100 is based on the concept that each
beamlet passing through the one-dimensional crossed staircase
element 1100 should have a different step height from all of the
other beamlets passing through the one-dimensional crossed
staircase element 1100, in order to reduce or completely eliminate
interference.
[0133] For example, if a vertical staircase element and horizontal
staircase element were fabricated to have steps with the same step
height (e.g., 1 mm), a problem would exist in that, by configuring
both staircase elements and to have the same total step heights,
more than one beamlet of laser light passing through the
one-dimensional crossed despeckling element would have the same
total step height (optical path difference). Thus, these beamlets
with the same optical path difference would interfere with each
other, creating undesirable results.
[0134] Therefore, as shown in FIG. 11(a), a principle governing the
selection of step heights in the one-dimensional crossed staircase
element 1100 according to aspects of the present invention is to
select step heights to ensure that each beamlet passing through the
one-dimensional crossed staircase element 1100 has a different step
height from every other beamlet passing through the one-dimensional
crossed staircase element 1100. As shown in FIG. 11(a), the
vertical staircase element 1104 has three steps, wherein step
1104-0 has a step height of 0, and steps 1104-1 and 1104-2 each
have a step height of 1 mm, for example (as indicated by the arrow
labeled "1," which indicates that light passing through step 1104-1
has a step height of 1 mm, and as indicated by the arrow labeled
"2," which indicates that light passing through step 1104-2 has a
step height of 2 mm as a result of passing through both steps
1104-1 and 1104-2). To prevent interference, the step heights of
the horizontal staircase element 1102, which also has three steps,
are selected so that step 1102-0 has a step height of 0, and steps
1102-1 and 1102-2 each have a step height of 3 mm (as indicated by
the arrows labeled "3" and "6", respectively). As a beamlet passes
through the steps in the horizontal staircase element 1102 and/or
the steps in the vertical staircase element 1104, the beamlet
experiences a total step height according to a sum of the steps
that it passes through, as indicated by the projected plane 1150
shown in FIG. 11(a). For example, the beamlet which only passes
through step 1102-0 (step height=0) and step 1104-0 (step height=0)
has a total step height of 0 (0+0=0), as indicated by the box "0"
in the upper left-hand corner of the projected plane 1150. The
beamlet which passes through step 1102-1 and step 1104-2 has a
total step height of 5(3+2=5), as indicated by the box "5" in the
bottom center of the projected plane 1150. As indicated in the
projected plane 1150, by selecting the step heights in this
fashion, it can be guaranteed that no beamlets experience the same
optical step heights as each other, and thus, interference is
prevented. It should be understood that this description is
exemplary only, and the steps are not limited to being set in units
of 1 mm, and it should be further understood that the step heights
are not limited to being selected in this fashion, and may instead
be selected in various other fashions which also reduce
interference.
[0135] FIG. 12 illustrates a one-dimensional crossed despeckling
array 1300 according to a ninth embodiment. As shown in FIG. 12,
the one-dimensional crossed despeckling array 1300 (also referred
to herein as "array 1300") shown in FIG. 12 is similar to the
one-dimensional crossed staircase element 1100 shown in FIGS.
11(a)-11(c), except that the array 1300 includes a plurality of the
horizontal staircase elements. In particular, the array 1300
includes four horizontal staircase elements 1302-1, 1302-2, 1302-3,
and 1302-4 instead of one horizontal staircase element, each of the
horizontal staircase elements 1302-1, 1302-2, 1302-3, and 1302-4
include four steps, and the vertical staircase element 1304
includes four steps, instead of the three steps included in the
horizontal and vertical staircase elements 1102 and 1104. Also,
another difference between the array 1300 and the one-dimensional
crossed staircase element 1100 is that, unlike the horizontal
staircase element 1102 which has one step having a step height of
"0", each of the steps of each of the horizontal staircase elements
1302-1, 1302-2, 1302-3 and 1302-4 have a non-zero step height. The
reason for this configuration is to provide additional structural
support so as to strengthen each of the horizontal staircase
elements 1302-1, 1302-2, 1302-3 and 1302-4. The array 1300 can be
formed in various ways known to those skilled in the art, and can
be formed in substantially similar ways as those mentioned above
with respect to the other embodiments. Furthermore, it is
understood that arrays according to other aspects of the present
invention can include more or less than four horizontal staircase
elements and one vertical staircase element, and any combination is
possible.
[0136] FIG. 13 illustrates an M.times. N laser diode (LD) module
1400 for laser displays according to a tenth embodiment of the
present invention. As shown in FIG. 13, the laser module 1400
includes a housing 1410 which houses the array 1300 shown in FIG.
12 along with additional components. More specifically, the laser
module 1400 includes an M.times.N (e.g., 4.times.2) grid of laser
diodes 1402 (e.g., for a total of 8 laser diodes) to generate and
transmit coherent laser light to the array 1300. The laser diodes
1402 may be the same as the laser diodes described above in other
embodiments. The laser module further includes a first microlens
1404 disposed before the array 1300 to focus the light generated by
the laser diodes 1402 into beamlets and transmit the beamlets
towards the array 1300.
[0137] The array 1300 is configured to receive the beamlets
transmitted from the first microlens 1404 and reduce speckle of the
beamlets, as explained above with respect to the eighth and ninth
embodiments. Similar to the other embodiments, the array 1300 is
positioned near the foci of the beamlets transmitted from the first
microlens array 1404 and reduces or completely eliminates
diffraction of the beamlets. The beamlets with reduced speckle are
transmitted through the array 1300 to a second microlens 1406,
which relays the beamlets onto a field lens 1408. The field lens
1408 then focuses the beamlets with drastically reduced (or no)
speckle onto an image plane. Additionally, various types of
integrated circuits (not shown) and other components known to those
skilled in the art may be included in the laser module 1400.
[0138] If a typical laser diode outputting approximately 0.25 W of
output power is used and the laser module 1400 uses eight laser
diodes 1402 arranged in a 4.times.2 grid pattern, the laser module
1400 can achieve nearly 2 W total output power or less considering
the coupling loss between the laser diode and the collimator and
losses by reflection from optics, which is more than powerful
enough to create a laser annealing system and a laser display unit.
Furthermore, since the laser module 1400 uses the array 1300, the
laser module 1400 outputs coherent laser light with remarkably
reduced or no speckle.
[0139] Furthermore, it is understood that the laser module 1400 is
not limited to using a 4.times.2 grid of laser diodes 1402, and may
instead use any combination of laser diodes known to those skilled
in the art. According to aspects of the present embodiment, the
laser module 1400 may be used with an M.times.N grid of laser
diodes 1402, where M and N are positive integers respectively
representing a number of laser diodes arranged in columns and rows
of the grid, and where M>N, N.gtoreq.1, and M.gtoreq.2 (e.g.,
the 4.times.2 grid described above). By setting M>N, the laser
module 1400 may be designed so that the field lens 1408 does not
need to be the same length in each direction, which simplifies the
design of the field lens 1408. Furthermore, the laser module 1400
may be configured so that the beam shaping axis is perpendicular to
the direction of the grid which has relatively more laser diodes
1402. Thus, in the case of an M.times.N grid where M>N, the beam
shaping axis should be in the direction of and correspond to the N
laser diodes (as shown, for example, in FIGS. 8(a) and 8(b), where
the beam shaping axis corresponds to the fast axis of 8(b)).
However, it is understood that in the grid of laser diodes 1402
used in the array 1400, M need not be different from N; for
example, in the grid 1402 M may be equal to N (e.g., yielding a
3.times.3 grid), in which case the field lens 1408 is configured to
be the same length in each direction. It is further understood that
the laser diodes 1402 are not limited to being arranged in a
rectangular or square grid, and may alternatively be arranged in
various other configurations as well (e.g., a triangular shape).
Moreover, the laser module 1400 may be combined or modified in
accordance with any of the other embodiments described above, as
understood by those skilled in the art.
[0140] FIG. 14 depicts a two-dimensional staircase element 1500
according to an eleventh embodiment of the present invention. The
main difference between the two-dimensional staircase element 1500
shown in FIG. 14 and the one-dimensional crossed staircase element
1100 shown in FIGS. 11(a)-11(c) is that the fabrication process to
make the two-dimensional staircase element 1500 differs from the
fabrication process to make the one-dimensional crossed staircase
element 1100, even though both staircase elements 1500 and 1100
achieve substantially the same superior despeckling results.
Specifically, the two-dimensional staircase element 1500 is formed
by a single piece of transparent material and has a common flat
entrance surface 1504 on one end, from which each of the steps 1502
protrude (similar in appearance to buildings protruding out from a
common piece of land), whereas the one-dimensional crossed
staircase element 1100 is formed by separately forming the
horizontal staircase element 1102 and vertical staircase element
1104 and then adhering the horizontal staircase element 1102 and
vertical staircase element 1104 together so that the steps protrude
out in different directions from a middle area as in, e.g., FIG.
11(a), using any suitable adhesive material known to those skilled
in the art.
[0141] As shown in FIG. 14, the two-dimensional staircase element
1500 includes a series of steps 1502 oriented parallel to each
other. Each of the steps 1502 has a unique (different) step height
as compared to each of the other steps 1502, to ensure that the
beamlets passing through each of the steps 1502 do not interfere
with each other, for the same reasons as described above with
respect to the other embodiments. Thus, as exemplarily illustrated
in FIG. 14, step 1502-0 has a step height of 0, step 1502-1 has a
step height of 1, step 1502-2 has a step height of 2, and so forth.
The step heights can be any value known to those skilled in the
art, similar to the other embodiments of the present invention.
[0142] The two-dimensional staircase element 1500 functions in a
similar fashion to the one-dimensional crossed staircase element
1100, and achieves similarly beneficial despeckling results.
[0143] FIGS. 15(a) and 15(b) depict the two-dimensional staircase
element 1500 shown in FIG. 14 in use, viewed from a top perspective
and a side perspective, respectively. In particular, FIG. 15(a)
illustrates the two-dimensional staircase element 1500 viewed from
a top perspective along a fast axis, and FIG. 15(b) illustrates the
two-dimensional staircase element 1500 viewed from a side
perspective along a slow axis.
[0144] As shown in FIG. 15(b), laser light 1510 passes through a
two-dimensional microlens array 1514 (a fly's eye lens array) and
is transmitted to the two-dimensional staircase element 1500. The
two-dimensional microlens array 1514 is similar to the
one-dimensional crossed microlens array 1114 (FIGS. 11(b), 11(c)),
except that the two-dimensional microlens array 1514 is formed out
of a single piece of material and has a common single surface from
which the microlenses protrude, instead of being formed as two
separate microlens arrays and then combined, like the
one-dimensional crossed microlens array 1514. Collectively, the
"two-dimensional microlens array 1514" and the "two-dimensional
staircase element 1500" may also be referred to as a
"two-dimensional despeckling unit." The laser light 1510 can be
generated by, for example, a laser diode as described with respect
to other embodiments of the invention. The two-dimensional crossed
microlens array 1514 includes a microlens arrays 1516 which is
configured to focus the laser light 1510 along the optical
axis.
[0145] The two-dimensional despeckling unit shown in FIGS. 15(a)
and 15(b) functions in a similar way and achieves similar
beneficial despeckling results as the one-dimensional crossed
despeckling unit shown in FIGS. 11(b) and 11(c), and a detailed
description of the functioning of the two-dimensional despeckling
unit is therefore omitted.
[0146] In the two-dimensional despeckling unit shown in FIGS. 15(a)
and 15(b), the two-dimensional staircase element 1500 is not
limited to being used with only the two-dimensional microlens array
1514, and may alternatively be used with the one-dimensional
crossed microlens array 1114. Similarly, the one-dimensional
crossed staircase element 1100 is not limited to being used with
only the one-dimensional crossed microlens array 1114, and may
alternatively be used with the two-dimensional crossed microlens
array 1514.
[0147] Furthermore, any of the components described above with
respect to the two-dimensional despeckling unit shown in FIGS.
15(a)-15(b) may be combined or modified in accordance with any
other embodiments described, as would be apparent to those skilled
in the art. For example, the laser module 1400 (FIG. 13) could
implement the two-dimensional staircase element 1500 alternatively
to the one-dimensional crossed staircase element 1100.
[0148] The foregoing description illustrates and describes
embodiments of the present invention. However, the disclosure shows
and describes only the preferred embodiments of the invention, but
it is to be understood that the invention is capable of use in
various other combinations, modifications, and environments. Also,
the invention is capable of change or modification, within the
scope of the inventive concept, as expressed herein, that is
commensurate with the above teachings and the skill or knowledge of
one skilled in the relevant art. For example, one or more elements
of each embodiment may be omitted or incorporated into the other
embodiments.
[0149] The foregoing implementations and embodiments of the
invention have been presented for purposes of non-limiting
illustration and description. Although the present invention has
been described herein with reference to particular structures,
materials and embodiments, the present invention is not intended to
be limited to the particular features and details disclosed herein.
Rather, the present invention extends to all functionally
equivalent structures, methods and uses, such as are within the
scope of the appended claims. Especially the present invention
extends to all functionally equivalent reflective system in which
either or all of the transmissive components such as fly's eye lens
arrays and staircase element is made of reflective material. The
descriptions provided herein are not exhaustive and do not limit
the invention to the precise forms disclosed. The foregoing
embodiment examples have been provided merely for purposes of
explanation and are in no way to be construed as limiting the scope
of the present invention. The words that have been used herein are
words of description and illustration, rather than words of
limitation. The present teachings can readily be realized and
applied to other types of apparatuses. Further, modifications and
variations, within the purview, scope and spirit of the appended
claims and their equivalents, as presently stated and as amended
hereafter, are possible in light of the above teachings or may be
acquired from practicing the invention. Furthermore, although
elements of the invention may be described or claimed in the
singular, the plural is contemplated unless limitation to the
singular is explicitly stated. Alternative structures discussed for
the purpose of highlighting the invention's advantages do not
constitute prior art unless expressly so identified. No one or more
features of the present invention are necessary or critical unless
otherwise specified.
* * * * *