U.S. patent number RE32,735 [Application Number 06/886,518] was granted by the patent office on 1988-08-23 for line scan reader/writer by holographic collection.
This patent grant is currently assigned to Holographix Inc.. Invention is credited to Burton R. Clay, William O. Thrailkill.
United States Patent |
RE32,735 |
Clay , et al. |
August 23, 1988 |
Line scan reader/writer by holographic collection
Abstract
An electro-optical scanner which can write and read with common
optics by using a phase hologram near the focal plane of the
scanned surface.
Inventors: |
Clay; Burton R. (Wayland,
MA), Thrailkill; William O. (Boston, MA) |
Assignee: |
Holographix Inc. (Burlington,
MA)
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Family
ID: |
27004207 |
Appl.
No.: |
06/886,518 |
Filed: |
July 15, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
368494 |
Apr 15, 1982 |
04488042 |
Dec 11, 1984 |
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Current U.S.
Class: |
250/235; 250/566;
359/19 |
Current CPC
Class: |
G02B
5/32 (20130101); H04N 1/024 (20130101); H04N
1/02445 (20130101); H04N 1/0461 (20130101); H04N
1/1135 (20130101) |
Current International
Class: |
G02B
5/32 (20060101); H04N 1/113 (20060101); H04N
1/024 (20060101); H04N 1/04 (20060101); H01J
005/16 () |
Field of
Search: |
;350/3.7,3.71,3.72,3.73
;250/234,235,236,578,550,566,568 ;356/445,446 ;358/293,294
;365/125 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
IBM Technical Disclosure, "Formation of Optical Elements by
Holography", G. T. Sincerbox, Aug. 1967, pp. 267-268..
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Primary Examiner: Nelms; David C.
Attorney, Agent or Firm: Lahive & Cockfield
Claims
Having described the invention, what is claimed as new and novel
and for which it is desired to secure Letters Patent is:
1. Apparatus comprising:
A. a light source for providing a light beam;
B. an optical light beam splitter;
C. a first focusing lens for receiving said light beam through said
beam splitter;
D. collection means placed between said first lens and a surface
which includes information to be read in proximity with said
surface, said collection means having an unmodulated portion
through which said light beam is focused onto said surface and
having a modulated portion through which diverging light from said
surface is collected and directed to said beam splitter by means of
said first focusing lens;
E. detector means; and
F. a second focusing lens for focusing said light received by said
beam splitter from said surface for receipt by said detector
means.
2. Apparatus as in claim 1 wherein said collection means is
operable to separate signal representative of said information on
said surface to be read from noise and directing said signal to
said first focusing lens.
3. Apparatus as in claim 1 wherein said collection means is a
hologram.
4. Apparatus as in claim 3 wherein said hologram is a phase
hologram.
5. Apparatus as in claim 1 further comprising means for moving said
surface with respect to said collection means so that all of said
information on said surface may be read.
6. Apparatus as in claim 1 further comprising a scanning device
coupled in the optical path between said beam splitter and said
first focusing lens so that the operation of said scanning device
causes said light beam to be focused on different portions of said
surface without moving either said surface or said collection
means.
7. Apparatus as in claim 6 wherein the operation of said scanning
device causes said light beam to be focused along different
portions of said surface on a first axis and further comprising
means for moving said surface with respect to said collection means
along a second axis thereby enabling all of said information on
said surface to be read.
8. Apparatus as in claim 7 wherein said scanning device is a
rotatable multifaceted mirror.
9. Apparatus as in claim 1 wherein said beam splitter is capable of
being positioned in a first position or a second position, wherein
said first position locates said beam splitter in the path between
said light source and said first focusing lens thereby enabling
said light beam to be transmitted to said source and received by
said detector means from said surface so that said information may
be read, and wherein said second position locates said beam
splitter so that said detector means does not receive said light
beam from said surface.
10. Apparatus as in claim 9 wherein said second position of said
beam splitter enables said apparatus to write information on said
surface and with other optical means, including said first and
second focusing lens, enables the reading of said information on
said surface.
11. Apparatus as in claim 10 further comprising a mirror coupled in
the path between said first focusing lens and said surface so that
said light beam is not received by said surface during a writing
operation, but rather is received by another surface in a different
location from said surface.
12. Apparatus as in claim 9 wherein said collection means is a
phase hologram.
13. Apparatus as in claim 12 further comprising means for moving
said surface with respect to said collection means so that all of
said information on said surface may be read.
14. Apparatus as in claim 9 further comprising a rotatable
multifaceted mirror coupled in the optical path between said beam
splitter and said first focusing lens so that rotation of said
mirror causes said light beam to be focused on different portions
of said surface without moving either said surface or said
collection means.
15. Apparatus as in claim 14 wherein rotation of said mirror causes
said light beam to be focused along different portions of said
surface on a first axis and further comprising means for moving
said surface with respect to said collection means along a second
axis thereby enabling all of said information on said surface to be
read.
16. Apparatus as in claim 15 wherein said phase hologram is placed
in a position substantially parallel to said surface. .Iadd.
17. A reader apparatus for reading information on a surface by
illuminating the surface and detecting the intensity of reflected
light therefrom, such apparatus comprising
A. a light source for providing a light beam,
B. first focusing means for focusing the light beam onto a surface
which bears information to be read,
C. collection means disposed between the first focusing means and
the surface, and proximal to the surface, the collection means
having a first portion through which the light beam is focused onto
the surface and having a modulated second portion through which
light reflected from the surface is collected and directed along an
optical path,
D. detector means for developing a signal indicative of light
intensity thereon, and
E. second focusing means for focusing onto the detector means the
reflected light directed by the modulated portion. .Iaddend.
.Iadd.18. Apparatus as in claim 17, wherein the modulated second
portion includes a hologram. .Iaddend. .Iadd.19. Apparatus as in
claim 18, wherein the hologram is disposed in a region of the
collection means substantially surrounding the first portion.
.Iaddend. .Iadd.20. Apparatus as in claim 19, wherein the hologram
is a phase hologram. .Iaddend. .Iadd.21. Apparatus as in claim 19,
further comprising means for moving the surface with respect to the
collection means for enabling the reading of information in a
region of
the surface. .Iaddend. .Iadd.22. Apparatus as in claim 19, further
comprising a scanning device in an optical path between the light
source and the first focusing means for directing the light beam
onto different portions of the surface. .Iaddend. .Iadd.23.
Apparatus as in claim 22, wherein said scanning device directs the
light beam on different portions of the surface located along a
first axis, and further comprising means for moving the surface
with respect to the collection means along a second axis, thereby
enabling the reading of information at different locations on the
scanned surface. .Iaddend. .Iadd.24. Apparatus as in claim 23,
wherein the scanning device includes a rotatable multifaceted
scanner. .Iaddend. .Iadd.25. Apparatus as in claim 24, wherein the
hologram is disposed substantially parallel to the scanned surface.
.Iaddend. .Iadd.26. An improved light gathering structure for use
in an optical reader of the type wherein a light beam scans a path
along a surface bearing information to be read, and the light
reflected from the surface is directed to a detector for developing
a signal representative of the information illuminated by the beam,
such light gathering structure comprising
a strip hologram having a first portion through which the light
beam scans the path and an adjacent modulated portion for
collecting light diffusely reflected from the surface. .Iaddend.
.Iadd.27. A structure as in claim 26, wherein the strip hologram
includes a phase hologram. .Iaddend. .Iadd.28. A structure as in
claim 27, wherein the modulated portion directs the collected light
toward a fixed detector. .Iaddend. .Iadd.29. A structure as in
claim 28, wherein the modulated portion has a focusing
property. .Iaddend. .Iadd.30. A structure according to claim 29,
wherein the strip hologram includes a first fringe pattern formed
substantially parallel to the scan path. .Iaddend. .Iadd.31. A
structure as in claim 30, wherein the strip hologram further
includes a second fringe pattern formed substantially orthogonal to
the fringes of said first pattern. .Iaddend. .Iadd.32. A
light-gathering structure as in claim 26, wherein the first portion
extends along the scan path and wherein the modulated portion is
located adjacent thereto and comprises
a first hologram fringe pattern having fringes substantially
parallel to the path for collecting light diffusely reflected from
the surface, and
a second hologram fringe pattern having fringes substantially
orthogonal to the fringes of the first pattern, so that the two
sets of fringes behave as a crossed pair of cylindrical lenses at
each position along the scan path. .Iaddend. .Iadd.33. A
light-gathering structure as in claim 28, wherein the first portion
extends along the scan path and wherein the modulated portion is
located adjacent thereto and comprises
a first hologram fringe pattern having fringes substantially
parallel to the path for collecting light diffusely reflected from
the surface, and
a second hologram fringe pattern having fringes substantially
orthogonal to the fringes of the first pattern. .Iaddend. .Iadd.34.
A light-gathering structure as in claim 28, wherein the hologram
includes a fringe pattern corresponding to interference fringes
formed with illumination directed through a lens along a hologram
recording axis, said recording axis and said scan path defining a
recording beam plane, and wherein the angle between said recording
axis and said scan path is a function of position
along the scan path. .Iaddend. .Iadd.35. An improved method of
reading optical reflectance information born on a surface by
illuminating the surface along a scan path with a scanning beam and
reading the reflectance information by directing the light
reflected from the surface to a detector, the improvement
comprising the steps of:
placing proximal to the surface a strip hologram including a first
portion extending along the scan path, and also including an
adjacent modulated second portion,
illuminating the surface by scanning it with the scanning beam
through the first portion, and
directing through the modulated second portion, the light diffusely
reflected from the surface toward the detector. .Iaddend. .Iadd.36.
The method of claim 35, wherein the step of directing includes the
step of directing, along an optical path substantially coaxial with
the scanning beam, the light reflected from an illuminated spot on
the surface. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to electro-optical scanning devices,
particularly those devices used for reading any two dimensional
printed surface for the purpose of making a duplicate or digital
record of the information contained on the surface.
In one type of electro-optical reader, the subject surface is
illuminated by scanning with a focused laser beam and the light
reflected off the surface is collected to obtain a representation
of that surface.
In optical scanning systems it would be economically and
practically desirable to use a single optical system to illuminate
and read the document. However, in the past, certain system
incompatibilities have prevented this type of design. Because the
majority of surfaces of documents to be examined are opaque, such
an optical reader must be designed to extract its information from
light reflected off the opaque surface.
Light reflected off any surface may be characterized as having two
components: both a specular and a diffuse component. In the case of
a paper document, if the paper and ink have similar specular
reflectances, the specular reflection off the surface will be
devoid of information, while the diffuse component will carry all
the meaningful information to be extracted. Where the axis of
incident illumination is normal to the paper surface, the specular
reflection will also be centered about that axis. Therefore, to
increase the collection of the information-bearing or diffuse
component, the optical axis of the reader detector is placed at an
angle from twenty (20) degrees to fifty (50) degrees from the paper
normal. Since the specular reflection, like glare, is generally
much brighter than the diffuse component, the diffuse component
must be collected from the entire annulus surrounding the specular
component to improve the signal-to-noise ratio.
In the past, optical scanning readers have collected the diffuse
component from a portion of the desired collection annulus by
placing two or more linear arrays of optical fibers parallel to the
scan line at an angle of forty-five (45) degrees from the paper
surface, such that each array cuts through the desired collection
annulus. These fibers were bundled to terminate in a single
detector so that each illuminated position on the document surface
could be related to a time varying detector signal. Systems which
employ this type of fiber optic assembly are generally very
expensive, because of the cost of the fiber optic assembly itself,
and because they require a large area detector, for example, a
photomultiplier, to measure the collected light. A further
disadvantage of these systems is that their efficiency is limited
by the number of fiber arrays which can physically be placed in the
annulus, and by the size of the photomultiplier or detection
surface which terminates the fiber bundle.
It is accordingly a primary object of the present invention to
provide an improved apparatus for the reading and/or writing of a
surface.
SUMMARY OF THE INVENTION
The above and other objects of the present invention are achieved
by placing a phase hologram close to an illuminated subject surface
to collect and focus a substantial portion of the signal bearing
diffuse component into an optical detector or reader assembly. This
hologram simultaneously collects the diffuse component from all
meridians within the desired collection annulus while
discriminating against the specular informationless component. The
same optical assembly used to focus and illuminate such surface may
be used to relay the diffuse component collected by the hologram to
the optical detector for reading or to a writer assembly for
writing, thus reducing system complexity and cost.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects of the present invention are achieved
in the illustrative embodiment as described with respect to the
Figures in which:
FIGS. 1A and 1B show schematic side views of the subject invention
used as an optical reader and writer, respectively;
FIGS. 2A and 2B show in schematic side view an alternate embodiment
of the subject invention as an optical reader using a polygonal
scan mirror mechanism;
FIG. 3 shows an isometric view of the subject invention as an
optical reader using a polygonal scan mirror mechanism;
FIG. 4 shows an isometric view of an opto-mechanical scanning
copier comprising the subject invention;
FIG. 5 shows in cross section one method of fabricating a phase
hologram according to the present invention; and
FIGS. 6A and 6B show in cross section a second method of
fabricating a phase hologram according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1A and 1B, the device of the present invention
includes a source of illumination 10, a pivoting optical beam
splitter 11, a primary focussing lens or assembly 12, a phase
hologram ("hologram") 13, a subject surface to be examined 14, a
detector focussing lens or assembly 15, associated detector
aperture stops 16, and an optical detector 17.
As shown in FIG. 1A, light from source 10, for example, a helium
neon (HeNe) laser, passes through beam splitter 11 to focussing
assembly 12. Assembly 12 focuses the source through the unmodulated
portion 19 of hologram 13 to a point 20 on surface 14 of an opaque
document which is to be scanned and read. Typically, focusing point
20 might have a diameter of 100 microns. In practice, document
surface 14 could be systematically moved by some external mechanism
in two directions, for example, in a raster scan pattern, such that
every portion of document 14 would appear beneath spot 20 to effect
the read process.
The diffuse component of the light reflected off surface 14 at spot
20 is collected by the modulated portion 21 of hologram 13 and
focused through primary focusing lens 12 to beam splitter 11. This
reflected light is relayed by beam splitter 11 to optical detector
focussing assembly 15, and past optical stops 16 to detector
17.
FIG. 1B shows the same system with the beam splitter 11 removed
from the optical path. In this configuration, the same optical
system may be used as a noncontact or nonimpact (i.e., writer)
printer. Light from source 10 is focused by optical assembly 12
through the unmodulated portion 19 of hologram 13 to point 20 on
the recording surface 18. Thus, the same optical assembly can be
used as a reader as shown in FIG. 1A, or a writer, as shown in FIG.
1B. However, it is understood that such beam splitter 11 need not
be removed from such optical path, however, for maximum writing
efficiency, it should be. It should also be understood that the
surface to be written on need not be located such that the optical
path to such surface is through the unmodulated portion 19 of
hologram 13. Rather, as shown by dotted lines, the optical path to
a surface 92 to be written on may be coupled by use of a folding
mirror 90 which is pivoted out of the position shown when reading
the surface 14 as shown in FIG. 1A. For such writing purposes,
surface 92 may comprise a photosensitive material.
The optical reader hologram 13 may be produced in several ways.
FIG. 5 shows a method of producing the interference fringes
necessary to record the desired hologram. A lens 30 with hole 38
bored through the center allows passage of the reference beam 31
through the center, while the outer portion of the beam is focused
by lens 30 to a point below the hologram 13. The region of
interference between the two resulting wavefronts produces an
annular area on the surface of the holographic recording medium,
which may comprise a photoresist material. Stop 33 prevents
exposure of the central portion of the holographic surface, which
will be used only for transmission of the source illumination of
spot 20 on the document 14. A phase hologram results. A series of
overlapping holograms are required to create a hologram capable of
reading over the entire scan line width. This is accomplished by
translating the hologram along the desired scan line between
exposures. The hologram recording axis is rotated in the plane of
the scan beam as a function of scan position, such that the readout
beam axis will be colinear with the scan beam during illumination
and readout. For the system of FIGS. 2 and 3, a rectangular stop
80, as shown in FIGS. 5 and 6A, placed on or near the surface of
hologram 13 prevents exposure of unmodulated portion 19 of hologram
13 thereby producing the configuration of hologram 13 as shown in
FIG. 3. The light collected by a hologram recorded by this method
is limited by the maximum numerical aperture (N.A.) of the
recording lens 30, which is approximately 0.6. This corresponds to
a maximum collection angle 39 of approximately forty-five (45)
degrees.
An improvement in efficiency is possible by recording the hologram
13, as shown in FIG. 6. By using two cylindrical lenses 32, the
collection angle can be increased to approximately ninety (90)
degrees of the desired collection annulus. Three .[.reference.].
beams 61, 40 and 41, which are in phase, illuminate the holographic
surface 13 as shown. The generated interference fringes are not
circular, as in FIG. 5, but are parallel to the intended scan line.
In order to collect the diffuse component of the light reflected in
the orthogonal direction, a second fringe set recorded at ninety
(90) degrees to the first set is superimposed, as shown in FIG.
6B.
Referring to FIG. 6B, collimated reference beam 42 illuminates the
hologram 13 through microscope objective lens 34, stop 35,
cylindrical lens 36 and beam splitter 37 to create a
.[.spherical.]. .Iadd.cylindrical .Iaddend.wavefront as shown. The
object beam angle 44 matches the maximum scan angle of the optical
scanning system, for example thirty (30) degrees. A second plane
wavefront reference beam 71 is reflected off beam splitter 37
creating .[.circular.]. interference fringes in hologram 13. In
this case, the spatial frequency of the fringe sets follow a
Fresnel distribution, and, at playback, the two sets of
superimposed interference fringes behave as a crossed pair of
cylindrical lenses at each position along the scan line.
In an alternate embodiment of an electro-optical reader, as shown
in FIGS. 2A, 2B and 3, a traditional polygon line scan mechanism
22, having rotation axis 23, is inserted between the beam splitter
11 and the primary focussing assembly 12, such that the scan of
document 14 is affected by the optical scan of point 20 across the
document (as shown by the different positions of point 20 in FIGS.
2A and 2B) parallel to hologram 13 and axis 27 (see FIG. 3) in one
direction, and the mechanical feed of the document in the other
direction parallel to axis 25 (see FIG. 3). Light from source 10 is
transmitted through optical beam splitter 11, and reflected by
successive facets 26 of polygonal scan mirror 22 through focus
assembly 12 and unmodulated portion 19 of hologram 13 to the
surface of document 14. A sheet of some transparent substance, for
example, glass, separates the hologram from the document 14
surface.
As shown in FIGS. 3 and 4, hologram 13 is suspended with respect to
document surface 14 by a fixed framework 24, while document 14 is
moved along axis 25 by some mechanical feed mechanism. FIG. 4 shows
one embodiment of the described polygonal optical scanner with
holographic reader apparatus using belts 29 and motor 50 driven
mechanical feed assembly. Case 51 contains the optical scan
mechanism comprising the scan mirror 22, beam splitter 11, detector
focussing lens 15, detector 17 and source 10. Cover 24 holds
hologram 13. Transparent plate 28 and document 14 are shown above
the scan mechanism and may be held fixed by a case enclosing the
entire mechanism.
Numerous objects and advantages of the present invention have been
set forth in the foregoing description, together with details of
the structure and the functions of the invention, and the novel
features thereof are pointed out in the appended claims. The
disclosure, however, is illustrative only, and changes may be made
in detail, especially in matters of shape, size and arrangement of
parts, within the principles of the invention, to the full extent
indicated by the broad general meaning of the terms in which the
appended claims are expressed.
* * * * *