U.S. patent application number 09/493982 was filed with the patent office on 2002-07-25 for method and apparatus for adjusting spot size of one color component of a multiple color co-axial laser beam.
Invention is credited to Cobb, Joshua M., Lebaron, Jennifer A..
Application Number | 20020097492 09/493982 |
Document ID | / |
Family ID | 23962521 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020097492 |
Kind Code |
A1 |
Cobb, Joshua M. ; et
al. |
July 25, 2002 |
Method and apparatus for adjusting spot size of one color component
of a multiple color co-axial laser beam
Abstract
A method of adjusting a first spot size for a first color
component (74) of a multiple color co-axial laser beam (70) that
comprises, focusing the multiple color co-axial laser beam (70).
Filtering the multiple color co-axial laser beam (70) with a filter
(50) to adjust the first spot size. The filter (50) is opaque to
the first color component (74) in an annular region (62) and
transparent to the first color component (74) in a center region
(60) of the multiple color co-axial laser beam (70). The filter
(50) is transparent to a second color component (76) of the
multiple color co-axial laser beam (70) in both the center region
(60) and the annular region (62).
Inventors: |
Cobb, Joshua M.; (Victor,
NY) ; Lebaron, Jennifer A.; (Rochester, NY) |
Correspondence
Address: |
PATENT LEGAL STAFF
EASTMAN KODAK COMPANY
343 STATE STREET
ROCHESTER
NY
14650-2201
US
|
Family ID: |
23962521 |
Appl. No.: |
09/493982 |
Filed: |
January 28, 2000 |
Current U.S.
Class: |
359/577 |
Current CPC
Class: |
G02B 26/10 20130101;
G02B 30/27 20200101 |
Class at
Publication: |
359/577 |
International
Class: |
G02B 027/00 |
Claims
What is claimed is:
1. A method of adjusting a first spot size for a first color
component of a multiple color co-axial laser beam comprising the
steps of: focusing said multiple color co-axial laser beam;
filtering said multiple color co-axial laser beam with a filter to
adjust said first spot size; wherein said filter is opaque to said
first color component in an annular region and transparent to said
first color component in a center region of said multiple color
co-axial laser beam; and wherein said filter is transparent to a
second color component of said multiple color co-axial laser beam
in both said center region and said annular region.
2. A method as in claim 1 wherein said filter is opaque to a third
color component of said multiple color co-axial laser beam in said
annular region and transparent to said third color component in
said center region.
3. A method as in claim 1 wherein said filter is located in a
converging portion of said co-axial laser beam.
4. A method as in claim 1 wherein said filter is located in a
diverging portion of said co-axial laser beam.
5. A method as in claim 1 wherein said filter is moved in a
direction parallel to said co-axial laser beam to vary said first
spot size of said first color component.
6. An apparatus for adjusting a first spot size of a first color
component of a multiple color co-axial laser beam comprising:
lasers for forming said multiple color co-axial laser beam; a
filter having an annular region which is opaque to said first color
component and a center region which is transparent to said first
color component, and transparent to a second color component of
said multiple color co-axial laser beam.
7. And apparatus as in claim 6 wherein said center region is
transparent to a third color component of said multiple color
co-axial laser beam and said annular region is opaque to said third
color component.
8. An apparatus as in claim 6 wherein said filter is located in a
converging portion of said co-axial laser beam.
9. An apparatus as in claim 6 wherein said filter is located in a
diverging portion of said co-axial laser beam.
10. An apparatus as in claim 6 wherein said filter is moved in a
direction parallel to said co-axial laser beam to vary said spot
size of said first color component.
11. A method of adjusting a first spot size for a first color
component of a multiple color co-axial laser beam comprising the
steps of: collimating said multiple color co-axial laser beam;
filtering said multiple color co-axial laser beam with a filter to
adjust said first spot size; wherein said filter is opaque to said
first color component in an annular region and transparent to said
first color component in a center region of said multiple color
co-axial laser beam; and wherein said filter is transparent to a
second color component of said multiple color co-axial laser beam
in both said center region and said annular region.
12. A method of adjusting a first spot size for a first color, with
respect to a second spot size of a second color and with respect to
a third spot size of a third color, of a color co-axial laser beam
comprising the steps of: filtering said multiple color co-axial
laser beam with a filter to adjust said first spot size and said
second spot size; wherein said filter has a first region which is
transparent to said first color, said second color, and said third
color; wherein said filter has a second region which is transparent
to only said first color and said second color; and wherein said
filter has a third region which is transparent to only said first
color.
13. A method as in claim 12 wherein said first region, said second
region, and said third region are annular regions.
14. A method as in claim 12 wherein said second region and said
third region are each covered with a dichroic interference filter.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to focusing co-axial laser
beams of different wavelengths, and in particular to varying of the
size of a focused laser spot of one color while not affecting the
size of a second, co-axial focused laser spot of a second color.
More specifically, this invention relates to the adjustment of
laser spot sizes in a three-color digital laser scanning printer
for use in printing lenticular images.
BACKGROUND OF THE INVENTION
[0002] Lenticular overlays are a means of giving images the
appearance of depth or motion. A lenticular image is created using
a transparent upper layer having narrow, parallel lenticules,
semi-cylindrical lenses, on an outer surface, and an
image-containing media. The two layers form a lenticular system
wherein different portions of an image are selectively visible as a
function of the angle from which the system is viewed.
[0003] If the image is a composite picture made by bringing
together a number of different parts of a scene photographed from
different angles and the lenticules are oriented vertically, each
eye of a viewer will see different elements and the viewer will
interpret the net result as depth of field. The viewer may also
move her head with respect to the image thereby observing other
views with each eye and enhancing the sense of depth. When the
lenticules are oriented horizontally, each eye receives the same
image. In this case, the multiple images give illusion of motion
when the composite image is rotated about a line parallel to a line
formed by the viewers eyes.
[0004] One method of creating these images uses a lenticular sheet
with a color photographic emulsion on the side opposite the
lenticules. The stereoscopic images are exposed onto the lenticular
material by a laser scanner and the material is processed to
produce the lenticular image. See for example, U.S. Pat. No.
5,697,006 issued Dec. 9, 1997 to Taguchi et al.
[0005] The color image exposed on the lenticular material is
produced by three lasers each, a different color, e.g. red, green,
and blue. Typically, the red laser exposes a cyan layer of the
emulsion, the green laser exposes a magenta layer, and the blue
laser exposes a yellow layer. It is important that the width of
each scanned line be the correct size. If exposure by one color
produces a line which is wider than by exposure of another color, a
colored "fringe" will be produced around each scan line. This will
result in a colored shadow visible in the resultant lenticular
image. This color fringing may be visible in non-lenticular,
conventional laser printers, however, the magnifying effects of the
lenticules make a lenticular printer more sensitive to line width
error.
[0006] The widths of the lines are a function of the intensity
distribution of the focused laser spot and of the emulsion
characteristics. The emulsion characteristics are generally
different for each color. Thus, an identical intensity distribution
of separate laser wavelengths will not necessarily produce
identical linewidths. It thus becomes important to have good
control over the intensity distribution and thus, spot size
produced by each laser beam.
[0007] Since the intensity distribution of a point focus is not
constant or uniform, it is typical in the art to define a "spot
size" as it relates to the intensity distribution. For example,
when a gaussian laser beam is focused, the intensity distribution
of the focused spot is a gaussian distribution with a spot size at
the 1/e.sup.2 diameter equal to 1 .635 x N A ,
[0008] where NA equals Numerical Aperture. When a uniform intensity
distribution is focused, the result is an airy disc whose central
diameter is 2 1.22 N A .
[0009] So, by truncating an incident gaussian beam, it is possible
to slightly change the intensity distribution of the focused slot
and thus the spot size.
[0010] It is possible to control each laser's spot size separately
if the laser beams are spatially separated. However, there are
situations in which the laser beams are combined co-axially. It is
not practical or convenient to separate the laser beams, once
combined, in most applications. For example, the beams may be
carried by separate fiber optic cables and then combined through a
fiber multiplexer into a single fiber optic cable. The beams may
also be combined co-axially by dichroic prisms.
[0011] The intensity distribution of the focused laser spot is a
function of the laser wavelength, the aberrations of the optical
system focusing the laser beam, and the intensity distribution of
the laser inside the optical system. For a given optical system of
fixed image quality, i.e., the aberrations are constant, it is
possible to change the intensity distribution of a focused spot by
changing either the wavelength of the light or by changing the
intensity distribution of the laser somewhere in the optical
system.
SUMMARY OF THE INVENTION
[0012] It is an object of this invention to provide a method and
apparatus for changing the spot size of a focused laser spot of one
color while not substantially changing the spot size of a
co-axially focused laser spot of a second color. It is another
object of the invention to provide a means for continuous
adjustment of the spot size of a focused laser spot of one color
while not substantially changing the spot size of a co-axially
focused laser spot of a second color.
[0013] The present invention is directed to overcoming one or more
of the problems set forth above. Briefly summarized, according to
one aspect of the present invention, a method of adjusting a first
spot size for a first color component of a multiple color co-axial
laser beam comprises the steps of focusing the multiple color
co-axial laser beam; filtering the multiple color co-axial laser
beam with a filter to adjust the first spot size. The filter is
opaque to the first color component in an annular region and
transparent to the first color component in a center region of the
multiple color co-axial laser beam. The filter is transparent to a
second color component of the multiple color co-axial laser
beam.
[0014] According to another aspect of the present invention, a
lenticular image is formed on a lenticular sheet having a
photographic emulsion coated on a side opposite the lenticules. A
beam used to form the image is comprised of at least two intensity
modulated beams of light of having different wavelengths, and
focused spots from the beam are scanned on the lenticular material.
The spots are scanned in a direction parallel to the long axes of
the cylindrical lenses to form a latent lenticular image in the
photographic emulsion. A filter is placed in the path of the
co-axial beams and is opaque in an annular region and transparent
in the center region to a first laser wavelength and transparent to
a second laser wavelength. The filter alters the incident intensity
distribution to one set of laser wavelengths while not affecting
the incident intensity distribution of another set of laser
wavelengths. The result of this is a final focused laser spot size
which is altered with respect to one wavelength.
[0015] In an alternate embodiment, the filter is placed in the path
of the co-axial beams in an area where the beams are either
converging or diverging, i.e., not in collimated light space. By
translating the filter along a line parallel to the co-axial beam
direction, the filter can be adjusted to apodize more or less of
one set of laser wavelengths. This has the effect of continuously
varying the focused intensity distribution over a predetermined
range.
[0016] The invention provides an accurate method and apparatus for
varying the intensity distribution, and thus the spot size, of a
focused laser of one wavelength while not affecting the intensity
distribution, and thus spot size, of a co-axially focused laser of
a different wavelength.
[0017] The invention and its objects and advantages will become
more apparent in the detailed description of the preferred
embodiment presented below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIGS. 1A-1C are plan views of segmented images used to form
a lenticular image.
[0019] FIG. 2 is a sectional view of a composite lenticular image
formed from the segmented images shown in FIGS. 1A-1C.
[0020] FIG. 3 is a plan view showing a single scan line composed of
different colors with different widths.
[0021] FIG. 4 is a schematic view of an optical system for scanning
co-axial lasers used for exposing lenticular images on emulsion
coated lenticular media.
[0022] FIG. 5 is a graph of a typical intensity distribution across
a single mode laser beam.
[0023] FIG. 6 is a perspective view of an annular filter which is a
preferred embodiment of the invention.
[0024] FIG. 7 is a plan view of the filter beam path.
[0025] FIG. 8 is a graph showing laser spot size as a function of
filter position and power loss as a function of filter
position.
[0026] FIG. 9 is a perspective view of an annular filter with a
central region slit.
[0027] FIG. 10 is a perspective view of a filter with three annular
regions.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Referring to FIGS. 1A-1C, lenticular images are formed by
digitally segmenting a plurality of images into slices. For
example, image 10, is digitally segmented into slices 11a-11j.
Image 20, is digitally segmented into slices 12a-12j. Image 30 is
digitally segmented into slices 13a-13j.
[0029] The slices 11a, 12a, and 13a are interleaved and placed
under the first lenticule 42 of the lenticular sheet 40, shown in
FIG. 2. Continuing in this fashion, the rest of the interleaved
images are placed under each lenticule until the final lenticule 44
contains the interleaved images 11j, 12j, and 13j. The lenticules
angularly separate the images of each image slice so that when the
lenticular sheet 40 is tilted, image 10, image 20, and image 30 are
reconstructed at different tilt angles.
[0030] The slices of each image can be exposed by scanning the
focused spots of three different colored lasers, for example, red,
green, and blue lasers, across the lenticular sheet 40 which has
been coated with a photographic emulsion 46. If the focused spot
size of one color is different from the focused spot size of
another color, a colored fringe will be visible where the two
colors do not overlap. This is illustrated in FIG. 3 wherein the
laser spot responsible for writing color 22 is larger than the one
responsible for writing color 21. The result is a colored fringe 24
around the slice 26 of the image which contains colors 21 and 22.
In a lenticular image, this manifests itself as a colored "ghost"
image. That is, referring back to FIG. 2, when viewing image 20 on
the lenticular sheet 40, a faint colored shadow of image 10 might
be visible. This is obviously objectionable to the viewer.
[0031] FIG. 4 illustrates one method of writing the images onto the
emulsion coated lenticular media. A fiber 50 carrying three
individually modulatable laser beams is placed at the input side of
a color corrected lens 51. This lens creates an image of the three
laser beam waists. After the laser beams come to focus, they pass
through an apodizing ring filter 52. The lasers are then shaped by
two cylindrical beam shaping mirrors 54, 56, reflect off of a
rotating scanning polygon 58, and are finally directed to the work
plane by fold mirror 59 and a cylindrical mirror 58 such that the
beam waists are imaged onto the lenticular sheet 40 at a
predetermined magnification.
[0032] The intensity distribution of the focused beam waists
generally takes the form of a gaussian as illustrated in FIG. 5.
The width of the gaussian distribution is determined by diffraction
which is, in turn, affected by wavelength. The width of the
gaussian distribution at the work plane, or lenticular sheet, is
specifically determined by several things including the width of
the gaussian distribution at the fiber exit, the overall
magnification of the entire optical scanning system, and the shape
and size of any aperture in the system that obscures the beam. If
there are no physical obscurations to the beam, i.e, the sizes of
the mirrors and lenses are much larger than the 1/e.sup.2 beam
diameter, and there are no aberrations that limit the spot size,
then the size of the focused beam waist at the 1/e.sup.2 beam
diameter will be approximately (0.635*.lambda.)NA, where .lambda.
is the wavelength of light and NA is the Numerical Aperture as the
light is brought to focus at the work plane. This spot size is the
smallest that the laser can be focused to. Since the size of the
spot is affected by wavelength, physics dictates that each color
have a slightly different spot size. If the laser beam is obscured
or apodized, the intensity distribution of the focused laser spot
will change, and thus the size of the spot will grow.
[0033] This invention is to apodize one or more colors while not
apodizing another color. Thus, a first color focused spot size can
be changed without affecting a second color focused spot. FIG. 6
shows a filter 50 with a center region or window 60 of transparent
material and an annular region 62 coated with a highly reflective
for a first color. Filter 50 is highly transmissive for at least a
second color in both the center region and the annular region.
[0034] FIG. 7 shows a preferred method of use for the invention. A
co-axial laser beam 70 comprised of two or more laser beams is
brought to a focus 72. A filter 50, in this embodiment a ring
apodizer, is placed in the path of the divergent light. A second
component 76 color passes straight through the plate without being
obscured. A first color component 74 has gaussian profile
effectively truncated by the highly reflective ring for using
annular region 62. The apodizer can be translated laterally, in
either direction, as the arrow 78 illustrates. By translating this
filter, a different amount of truncation can be induced which will
vary the size of the focused waist.
[0035] Since the energy distribution across the aperture is a
gaussian, the truncation of the gaussian tails does not impose a
significant energy loss. FIG. 8 show a plot of the preferred
embodiment's power change with spot size change. The filter had a 2
mm diameter inner aperture and was placed between 50 mm and 80 mm
from the beam focus of an achromatic lens illustrated in FIG. 4.
The apodizing ring filter was highly transparent to red light and
highly reflective to blue and green light in the annular region.
The co-axial beam comprised a red laser beam, a blue laser beam,
and a green laser beam. By varying the distance between the
apodizing filter and the focused beams the plot in FIG. 8 shows how
the spot size in red is unaffected and the spot size in blue and
green gets larger as more of the gaussian tails are blocked by the
ring. Also, the right hand side of the plot illustrates the drop in
power for green light. This plot also illustrates the drop in power
when the ring is not created by a circular aperture, but a slit
aperture 61, as shown in FIG. 9. In some circumstances, it might be
desirable to vary the size of the spot in only one axis. In this
case, only one axis needs to be apodized by the filter. In this
case, the transmitting aperture of the filter could be a slit
instead of a circle. The advantage to the slit is that less power
is lost through the filter.
[0036] FIG. 10 shows another embodiment of the present invention
wherein filter 50 has three annular regions. A first region 80 is
transparent to a first color, a second color, and a third color. A
second region 82 is transparent to a first color and a second color
but not the third color. A third region 84 is transparent to the
first color but not the second color and the third color. This
allows changing the spot size of color two with respect to color
three and with respect to color one without changing the spot size
of color one.
[0037] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the scope of the invention. For example, the co-axial beam may be
comprised of beams other than laser beams. Also, the invention may
be used in any system that uses a co-axial beam comprised of
different wavelengths of radiation. Also, rather than focusing the
co-axial beam as a first step, the beam may be collimated.
1 PARTS LIST 10. Image 11a. Slice 11b. Slice 11c. Slice 11d. Slice
11e. Slice 11f. Slice 11g. Slice 11h. Slice 11i. Slice 11j. Slice
12a. Slice 12b. Slice 12c. Slice 12d. Slice 12e. Slice 12f. Slice
12g. Slice 12h. Slice 12i. Slice 12j. Slice 13a. Slice 13b. Slice
13c. Slice 13d. Slice 13e. Slice 13f. Slice 13g. Slice 13h. Slice
13i. Slice 13j. Slice 20. Image 21. Writing color 22. Writing color
24. Fringe 26. Slice 30. Image 40. Lenticular sheet 42. First
lenticule 44. Final lenticule 46. Emulsion 50. Fiber 51. Color
corrected lens 52. Filter 54. Beam shaping mirror 56. Beam shaping
mirror 60. Window 62. Annular region 70. Co-axial laser beam 72.
Focus 74. First color component 76. Second color component
* * * * *