Note: Descriptions are shown in the official language in which they were submitted.
OPTICAL INTEGRATOR AND ILLUMINATION DEVICE USING THE SAME
FIELD OF THE INVENTION
This invention relates to light beam illumination systems, and more
particularly relates to method and
apparatus for producing with a high efficiency flat top rectangular
illumination beam exhibiting high
uniformity of the transverse intensity distribution and a specified numerical
aperture.
BACKGROUND OF THE INVENTION
Precision illumination systems are used extensively in microscopy, in
projection, as well as in the
fabrication of microcircuits and electronic circuit boards. The varying
demands of applications of
illumination system are best served by an illumination system which
efficiently produces a light beam of
desired technical specifications. Typical variables to be optimized at the
target include: a. illumination light
wavelength (or wavelength range); b. geometry parameters of the light field
shape, e.g. circular,
rectangular, etc, and its dimensions; c. having the property of uniform
intensity distribution across the
illumination field; and d. having a desired, usually rather low, numerical
aperture (NA) of illumination.
Numerical aperture or NA of a converging and/or diverging light beam is the
sine of the half-angle of the
beam cone multiplied by a refractive index of the medium.
An approach of the prior art is to use some efficient source of light, such as
a laser or an arc lamp with
collimating optics, as a primary light source. This typically produces a
collimated light beam having non-
uniform profile, which in most cases has Gaussian, parabolic or cosine beam
profile. From these profiles
only a small portion of the beam has a low variation intensity distribution
illumination which is useful in
imaging. In another approach of the prior art, a diffuser plate etched to a
degree of roughness is used to
provide the desired uniformity property. A major disadvantage of such systems
is lacking in delivered light
use efficiency.
Another approach of the prior art, disclosed in detail in US Pat. 2186123, for
example, is to use fly's-eye
lenses to provide the uniformity property to the beam. The fly's-eye lens is a
two dimensional array of
lenslets assembled into a single optical element and used to spatially
transform light from a non-uniform
distribution light source to an uniform irradiance distribution at an
illumination plane. However this
approach cannot be used to provide flat top illumination beams with NA below
0.01; the beam profile is
very sensitive to small variations in the mutual positional and angular
alignments of the lenslet arrays,
laser, and other components; and much of the available light is lost during
the mixing process.
An alternative approach of the prior art, disclosed, for example, in US Pat.
5059013 and US Pat. 6205271
presented in Fig. 13). This approach is to use optical integrator rods to
provide the uniformity property to
the beam. An optical integrator rod is a hollow mirrored, or solid totally
internally reflective "light pipe"
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which uses multiple reflections of a focused light source by reflecting faces
to obtain homogenization of
round or irregular patterns of illumination and convert them into a flat top
rectangular pattern. The rod exit
face serves as an object plane for a relay lens system, which reproduces the
transverse distribution of
light at the exit face onto an illumination target. Thus, the optical
integrator rod is used to improve
uniformity and efficiently match the aspect ratio of the illumination source
to the target. However,
chamfers and glass chips on long side corners of the optical integrator rod
are known to cause image
shadow artifacts in the illumination pattern, especially in the case of usage
of so called 'point' light
sources, for example, focal spots of laser radiation. Such a cross-shaped
shadow of non-chamfered
corners as well as chip shadows are clearly visible on the transverse light
distribution map of FIG. 14.
Besides, a chamfer on the edges of the exit facet of the glass rod or a
rectangular aperture plate for
masking exit facet edge chips, if the chamfer is absent, restricts some of the
illumination. This figure often
amounts to about 10% and more of the useable light. The integrator rod is
typically made sufficiently long
to produce a resulting rectangular light beam of desired specs. Illumination
systems for spinning disk
confocal microscopy, for example, must project a flat top rectangular
illumination beam, having a very low
NA - 0.004 (US Pat. 2011/0134519), onto a relatively small target about 8mm x
8mm. The solid integrator
rod should be too much long and should have very frail design:length should be
, for example, more than
150 cm for a rod cross section - 2mm x 2mm.
SUMMARY OF THE INVENTION
A number of disadvantages and drawbacks are inherent in illumination systems
comprising one of the two
basic types of reflective integrators. The present invention is intended to
solve the aforementioned
problems. The major objective of the present invention is a provision of a
method of transformation of
non-uniform beam of illumination radiation, e.g. laser light, into a flat top
rectangular illumination beam
exhibiting high uniformity of the transverse intensity distribution and a
specified numerical aperture.
Another objective of the present invention is a provision of an illumination
device capable to provide in an
object plane an illumination field that has a selected rectangular cross-
section of desired dimensions, flat
top transverse intensity distribution of high uniformity, and a specified
numerical aperture.
Yet another objective of the present invention is provision of reflective type
optical integrators whereby an
illumination light beam having a non-uniform transverse intensity distribution
may be transformed into a
flat top light beam having a substantially uniform transverse intensity
distribution by shaping and
homogenizing the light beam.
It is also objective of this invention to provide a homogenized flat top
illumination radiation beam without
creating any artifact patterns.
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These and further objectives have been achieved by the present invention in
which a light beam having a
possibly non-uniform spatial intensity distribution is transformed into a flat
top illumination light beam
having a substantially uniform transverse intensity distribution by
homogenizing the light beam with two
mutually orthogonal planar light guides (a transparent light passageway having
two flat internally
reflective surfaces). The first planar light guide performs homogenizing
transverse light beam distribution
along the first axis orthogonal to its reflecting side surfaces, the second
planar light guide serves to
homogenize light beam along a second axis orthogonal to the first one and to
its own reflecting surfaces.
Relay optics, positioned on the device's optical axis, focuses light outgoing
from the exit face of the first
planar light guide onto an entrance face of the second planar light guide and
images said exit face of the
first planar light guide onto an exit face of the second planar light guide).
Joint operation of sad optical
components performs conversion of the non-uniform illumination pattern
provided by the illumination unit
to a uniform flat top rectangular pattern at the exit face of the second
planar light guide. The last is
relayed further to an illumination target, where provides a highly uniform
rectangular illumination pattern
with a predetermined numerical aperture. The illumination pattern has no
artifact shadows inherent in the
integrator rods, because the method eliminates their origins.
Furthermore, a number of exemplary embodiments of the illumination device and
of a respective optical
integrator, which realize the method, are provided. They are seen as simple,
cost effective instruments
that provide high optical efficiency light homogenizing via optical
integration. The homogenizer proposed
may be used for the entire UV-visible-NIR wavelength range. The invented
illumination device design
makes it easy handling the integrator components and mounting them without
risk of damaging optical
surfaces. Another advantage of this device is that the beam profile is less
sensitive to variations in the
positional alignment of the light source and optical components. The new high
uniformity flat top
illumination technique can be integrated into various systems developed for
different applications such as
a spinning disk confocal microscope and/or fluorescent optical microscope to
obtain high quality
fluorescence images, into digital and analog projection systems, as well as
into photolithography
machines for production of integrated circuit chips and electronic circuit
boards.
Other features and advantages of the present invention will become apparent to
those skilled in the art
upon examination of the following drawings and the detailed description, and
in part will be obvious from
the description, or may be learned by practice of the invention. It is
intended that all such additional
features and advantages be included herein within the scope of the present
invention, as defined by the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments according to the present invention will now be described
hereinafter with reference to the
accompanying drawings, where like reference numerals designate similar or
identical features throughout
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the several views. In addition to the major optical members there may be shown
in the drawings optical
axis of the device, chief and/or marginal rays of an illumination light beam;
input and output light beams
may be illustrates by bold arrows.
It will be appreciated that for the simplicity and clarity of illustration,
elements shown in the figures have
not necessarily been drawn to scale, emphasis instead being placed upon
clearly illustrating the
principles of the present invention. For example, the dimensions of some of
the elements may be
exaggerated relative to other elements for clarity purposes.
FIGS. la and lb, depict simplified schematic YZ and XZ views, respectively, of
the first exemplary
embodiment of an illumination device in accordance with the present invention.
Fig. 2 depicts schematically the transformation of the illumination light beam
in a process of light beam
travel through the optical integrator of FIG. 1.
FIG. 3 depicts schematic perspective views of alternative exemplary
embodiments of planar light guides
for the optical integrator according to the present invention: a rectangular
glass slab (a); a glass
'sandwich' (b): a hollow planar light guide (c); a wedge-shaped glass slab
(d).
FIGS. 4, 5, are pictorial schematic views of alternative exemplary embodiments
of the illumination device
according the present invention.
FIG. 6 illustrates the transformation of the illumination light beam in a
process of light beam travel through
the optical integrator of FIG. 5.
FIG. 7 is a perspective view of alternative exemplary embodiment of the
optical integrator according the
present invention.
FIG. 8 depicts a schematic configuration of another exemplary embodiment of
the optical integrator
according the present invention comprising two image relaying planar light
guides.
FIGS. 9, 10, and 11 depict simplified schematic diagrams of yet other
exemplary embodiments of the
optical integrator, comprising image relaying gradient index (GRIN) planar
light guides.
FIG. 12 presents pictorial schematic views of yet another alternative
exemplary embodiment of a image
relaying planar light guide (a) and of the optical integrator (b) using the
same.
Fig. 13 is a schematic showing an example of an integration rod homogenizing
system. Prior art.
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Fig. 14 depicts a map of transverse light distribution across an exit face of
an integration rod of a light
homogenizer exibiting shadow artifacts. Prior art.
DETAILED DESCRIPTION OF THE INVENTION
All the exemplary embodiments disclosed hereinafter contain an optical
integrator assembly comprising
two mutually orthogonal single-axis optical integrator elements in the form of
planar light guides. For the
sake of definiteness and clarity, the axis orthogonal to reflecting planes of
the first planar light guide is
denoted as X-axis while the axis orthogonal the reflecting sides of the second
planar light guide is
denoted as Y-axis, a direction of light propagation is denoted as Z-axis
coinciding with an optical axis of
the illumination device. The first and the second single-axis optical
integrator elements are called
hereinafter "X-integrator" and "Y-integrator", respectively. However, the
invention is not intended to be
limited to the specific coordinate system selected, and it is to be understood
that any other specific
system of coordinate may be used.
In descriptions of exemplary embodiments of the present invention illustrated
in the drawings, specific
terminology is employed for the sake of clarity. However, the invention is not
intended to be limited to the
specific terminology selected, and it is to be understood that each specific
element includes all technical
equivalents that operate in a similar manner to accomplish a similar purpose.
The terms "light" and
"radiation" may be used interchangeably and refer to radiation in the UV-
visible-IR spectral range. The
term "light source" and "radiation source" may refer to any source able to
generate and emit radiation
having a characteristic spectrum and spatial distribution,.
FIG. 1 depicts simplified schematic YZ and XZ views (a and b, respectively) of
the first exemplary
embodiment of an illumination device comprising an optical integrator in
accordance with the present
invention. The entire assembly of the proposed embodiment preferably
comprises: an illumination unit 4;
optical integrator assembly 1; a projection lens system 5, and a target 6.
Said Illumination unit 4, providing nearby an entrance facet 102 of said X-
integrator10 a point-like light
source emitting a diverging beam of illumination radiation, characterized by
the light beam numerical
aperture (NA), is schematically shown, for example, in the form of a laser
source 41 with a focusing lens
42. Alternatively, said illumination module capable to provide a point-like
luminous light spot may be
implemented in a variety forms including but not limited to lasers with fiber
optic cable, super-continua
fiber sources, LEDs and super luminescent diodes with focusing optics, gas
discharge lamps with
focusing reflective optics, or any other suitable radiation sources as would
be apparent to someone
skilled in the art.
Said optical integrator assembly 1 comprises two mutually orthogonal single-
axis optical integrating
elements: X-integrator 10 and Y-integrator 20 turned around an optical axis of
the device orthogonally to
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said X-integrator and relay optics, schematically presented, for example, in
the form of a single bi-convex
lens 30 with its focal distance F30. Said X-integrator 10 may be, for example,
a rectangular glass slab, of
predetermined length Ll, thickness tl, and width wl. It has two opposing
mutually parallel internally
reflecting facets 101, 101', oriented orthogonally to X-axis, an entrance
facet 102,an exit facet 103, and
two non-optical side facets 104, 104' as depicted in FIG. 3a. Material of said
glass slab is transparent for
the illumination radiation and has a refractive index nl. Said Y-integrator 20
is a similar rectangular glass
slab having equal or differing design parameters: length L2, thickness t2,
width w2, and a glass refractive
index n2. It has two opposing mutually parallel internally reflecting facets
201,201', oriented orthogonally
to Y-axis, entrance and exit facets 202, 203, and non-optical side facets 204,
204'. Each of said glass
slabs 10, 20 operates as a planar light guide, that is light may travel in it
in the direction parallel to the
corresponding facets 101, 101' or 201, 201' being confined in it by total
internal reflection, Each of said
planar light guides 10, 20 performs functions of single-axis homogenizing
transverse light distribution
along the axis orthogonal to the corresponding reflecting facets 101, 101' and
201, 201'.
Lengths LI L2 and distances between reflecting surfaces or thicknesses tl, t2
of said glass slabs 10, 20
have to satisfy the following condition:
ti2=711,2*ki,2.
L1,2 '=" (1)
Here: subscripts 1, 2 relate to the X-integrator and to the Y-integrator,
respectively, n1 >1 and n2 >1 are
refractive indexes of the slab glass material; NA/and NA2 are numerical
apertures of the corresponding
input radiation beams, e.g. NA1=N110, where NA0 is the numerical aperture of
the beam provided by the
illumination unit 4; 1(1 >1, k2 >1 are minimal desired numbers of reflections
of marginal rays of the
radiation beam from facets 101, 101' and 201, 201' of said glass slabs 10, 20,
respectively. The values kl
and k2 are defined by a grade of non-uniformity of illumination pattern
provided by the illumination unit 4
and by desired uniformity of a light distribution on the target 6
Widths HI, and w2 of the glass slabs 10, 20 must be large enough to eliminate
any contact of the
propagating light rays with non-optical narrow sides 104, 104' and 204, 204':
2NA1,2*L1,2
w1,2 > = 2t1,2 k1,2 (2)
For the sake of simplicity said projection lens system 5 is shown only
schematically as a single bi-convex
lens, it may be implemented in a variety of forms, previously developed for
illumination applications.
All said members 4, 10, 30, 20, 5, and 6 in the embodiment of FIG. 1 are
arranged along the optical axis
00' of the illumination device and symmetrically relative to it, so that X-
integrator reflecting facets 101,
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101' are perpendicular to the XZ-plane and said Y-integrator reflecting facets
201, 201' are perpendicular
to YZ-plane. Said imaging lens 30 is positioned downstream at a predetermined
distance z, from said X-
integrator facet 103; said Y-integrator 20 is positioned downstream at a
distance z2 form said imaging
lens 30 so that its entrance and exit facets 202, 203 reside in image planes
conjugate to corresponding
planes of said entrance and exit facets 102, 103 of said X-integrator 10. Said
exit facet 203 serves as the
optical integrator exit plane, relayed by said projection lens 5 onto said
target 6.
Operation of the optical integrator assembly of FIG. 1 is illustrated with
FIG. 2 that presents transversal
intensity distributions of the illumination light beam at the entrance (a) and
exit (b) facets of said X-
integrator 10 and at the entrance (c) and exit (d) facets of said Y-integrator
20. An illumination beam from
said illumination unit 4 may originally have a circular highly non-uniform
profile providing at said X-
integrator entrance facet 102 a transversal distribution So of FIG. 2a. Said
light beam is repeatedly
internally reflected by the facets 101, 101' of said X-integrator 10 to become
homogenized (mixed) along
the axis 'X' (FIG. 2b). Said relay optics 3 relays the original light spot So
and its multiple reflections S, (j =
1, 2, 3, 4 for k1 = 2, for example) from a plane of said X-integrator entrance
facet 102 to the conjugate Y-
integrator entrance facet 202 with a magnification m, = zi(Li + z1.), thus
providing a set of corresponding
light spots S's, S', (FIG. 2c), and relays said light distribution of FIG. 2b,
from said X-integrator exit facet
103 to a conjugate plane of the exit facet 203 of said Y-integrator 20 with a
magnification m2 = (L2 +
z2)/z1> m, Light entering said Y-integrator 20 via its facet 202 is repeatedly
internally reflected by the
facets 201, 201' to become homogenized along the axis 'Y', thus providing at
said Y-integrator exit facet
203 a flat top rectangular light pattern (FIG. 2d) with an aspect ratio
A = 2 (3)
t2
Its numerical apertures in the XZ and YZ planes, respectively, are:
NA x = NA0 > NA, = NA0/M2 (4)
The light pattern is relayed with said projection lens system 5 from said Y-
integrator exit facet 203 to said
illumination target 6 to provide there a magnified flat top rectangular
illumination pattern with a pre-
determined NA, exhibiting essential uniformity and high edge steepness.
It should be noted that focusing lens 42 may be a positive cylindrical lens,
whose cylinder axis lies in the
YZ plane, and distance z2 between said relay lens 30 and said Y-integrator
front facet 202 is close to a
focal length of said lens 30. Said relay lens 30 projects a focal line,
oriented along X-axis, onto said Y-
integrator entrance facet 202 and relays an illumination pattern from said X-
integrator exit facet 103 to a
plane of said Y-integrator exit facet 203 as explained hereinabove.
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Said X-integrator 10 and Y-integrator 20 or planar light guides are described
herein as "glass slabs". This
is for sake of brevity and clarity only; they may be planar light guides,
implemented in a plurality of
alternative forms, some examples are depicted in FIG. 3. Although all the
numerals and explanations in
FIG. 3 are referred to the X- integrator hereinafter, they pertain equally to
the Y-integrator.
FIG. 3a is a schematic perspective view of the discussed hereinabove first
example of said planar light
guide 10 built in the form of a rectangular glass slab with two opposing
mutually parallel internally
reflecting facets 101, 101' and entrance and exit facets 102, 103 orthogonal
to said reflecting facets 101,
101'. Said side facets 104, 104' of the embodiment may be of any optical
quality and any shape, but
providing non-disturbed light propagation in said planar light guide.
FIG. 3b is a schematic perspective view of an alternative example of said
planar light guide 10, which is a
sandwich planar light guide comprising at least three flat layers 105, 106,
106' of glass materials with
different refractive indexes having mutually parallel interfaces, extending in
the directions parallel to their
interfaces. This operates as planar light guide only if the refractive index
of the middle or core layer 105 is
larger than that of the surrounding clad layers 106, 106', so that light may
be confined in the middle layer
105 by total internal reflection. Co-joint polishing of said front and back
faces 102, 103 makes it possible
to manufacture the planar light guide without chips and chamfers on the core-
clad division, and to solve
therewith the problem of decreased optical integrator efficiency as a result
of use of a masking aperture
or chamfering.
FIG. 3c is a perspective view of another alternative example of said planar
light guide 10, which is a
hollow or mirror slot planar light guide comprising a pair of highly
reflecting mirrors 107 and 107' with their
inward facing mirrored surfaces 108, 108' being fixed mutually parallel at a
predetermined distance t1
between them with, for example, of two spacers 109, 109'. A length Ll, a width
wl of, and the distance t1
between the mirrored surfaces of the planar light guide 10 are defined by the
same equations (1), (2),
where the refractive index n1 = 1.
FIG. 3d is a perspective view of yet another alternative example of said
planar light guides 10, 20
implemented in the form of wedge-shaped glass slabs of a diverging, T > t as
depicted or of a converging
configuration. Alternatively, said wedge-shaped planar light guide may have at
least one reflecting facet,
which is non-planar, but rather curved one having a gradually changing angle
with Z-axis. It should be
clear for one skilled in the art that wedge-shaped planar light guides may be
alternatively implemented in
the form of diverging or converging planar light guides, similar to those
depicted in FIGS. 3b, 3c.
It should be noted that, alternatively, at least one of facets 102, 103 of
said planar light guides of FIGS.
3a, 3b, and 3d may be not orthogonal to optical axis of said glass slab 10,
thus providing an optional
folding of the illumination device optical axis. Furthermore, the device
optical axis may be folded within
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the planar light guides of FIGS. 3a ¨ 3c by providing said planar light guides
with additional internally
reflecting surfaces or mirrors, depending on its design.
Optical material of said planar light guides 10, 20 is described herein as
"glass". This is for sake of brevity
and clarity only; it may refer to any plurality of optical materials
transparent in specified spectral ranges
including, but not limited to mineral or polymer glass, optical ceramics, mono-
and polycrystalline
semiconductor materialõ as it would be apparent to someone skilled in the art.
FIGS. 4a and 4b depict simplified schematic XZ and YZ projections,
respectively, of another exemplary
embodiment of an illumination device in accordance with the present invention;
. The entire assembly of
the proposed embodiment is similar in general to one of FIG. 1, and comprises
the same major optical
components: an illumination unit 4, schematically presented in the form of a
laser 41 with a fiber optic
cable 43, the mutually orthogonal X-integrator 10 and Y-integrator 20, a
projection lens 5, and a target 6
(not shown); but relay optics 3 is rather comprising two positive lenses 31
and 32 separated one another
for a distance z3> z1,z2, and providing predetermined magnifications m1 and
m2. FIG. 4c is a perspective
view of said optical integrator assembly lcomprised
The proposed embodiment is operating in the same manner as one of FIG. 1,
illustrated by FIG. 2, i.e.
transforms non-uniform beam of illumination radiation into a flat top
rectangular illumination beam
exhibiting high uniformity of the transverse intensity distribution with an
aspect ratio A and numerical
apertures NA x and NA y governed by the same formulas (3) and (4)
respectively.
In one example, said X-integrator 10 and Y-integrator 20 in the embodiment of
FIG. 4 may be built with
the same glass with a refractive index n, and have equal lengths L and lenses
31, 32 may have equal
focal lengths F = L/2n. Said distances z1 and z2 may be much less than said
separation distance z3 2F.
In the case, the magnification m1 = lis provided mainly by said lens 31, while
the magnification m2 = lis
provided mainly by said lens 32. The flat top rectangular light pattern at
said Y-integrator exit facet 203
has an aspect ratio A = : t2; numerical apertures of the exit light beam are
NA x = NA y = NAo.
An example of implementation of the illumination device of Fig. 4 is an
illumination system for a spinning
disk confocal microscope for fluorescent imaging of biological specimens.
Typical specifications of the
microscope illumination system are (US Pat. 2011/0134519): illumination field
at the microlens spinning
disk plane, i.e. target size, is 8 mm x 8 mm, a light beam numerical aperture
at the target 6 must be NAIL
= NAx = NA y 50.004õ Major design parameters of such illumination system are:
a collimated beam of
excitation radiation, provided by the laser 41 and having a diameter d = 1.6
mm is to be focused with said
lens 42 having focal distance F42 = 12.5 mm to provide a luminous spot with
NA0 = 0.064; glass slab
lengths L1 = L2 = 35 mm, thicknesses t1 = t2 = 0.5 mm, widths w1 = w2 3 mm,
and indexes of refraction
n1 = n2 = 1.52; relay optics comprises a pair of lenses with focal lengths F31
= F32 = 15 mm; distances zi =
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z3 = 3.5 mm, z2 = 2F = 30 mm; exit numerical aperture of the optical
integrator NA = NA0 = 0.064. A
projection lens 5 must provide magnification m5 = 16 and, consequently, the
desired NA s 0.004.
It should be noted that the multi-component relay optics 3 may be an
astigmatic relay system i.e. at least
one lens of the system may be a cylinder lens. FIG. 5 is a perspective view of
an exemplary embodiment
of said optical integrator assembly 1 with astigmatic relay optics 3. The
entire assembly of the of the
optical integrator 1 is similar, in general, to one of embodiment of FIG. 4,
and comprises said mutually
orthogonal X-integrator 10 and Y-integrator 20, and relay optics 3 rather
comprising two crossed
cylindrical lenses 33 and 34 having focal lengths F33 and F34, respectively,
and similarly separated one
another for a distance z3. A cylinder axis of said lens 34 lies in a plane XZ,
orthogonal to said X-integrator
reflecting planes 101, 101', while a cylinder axis of said lens 35 lies in a
plane XZ, orthogonal to said Y-
integrator reflecting planes 201, 201'.
FIG. 6 illustrates the transformation of the illumination light beam traveling
through the optical integrator of
FIG. 5. There are presented transversal distributions of said light beam at
said entrance (a) and exit (b)
facets of said X-integrator 10 and at said entrance (c) and exit (d) facets of
said Y-integrator 20. The
distributions of FIGS. 6a, 6b, and 6d are identical to corresponding
distributions of FIG. 2. The line-
shaped distribution of the FIG. 6c is a sum of overlaid astigmatic light
projections of the original
illumination spot So and of said virtual light spots Si provided by said
cylindrical lens 34. A length of the
luminous line is defined by the light beam divergence; its width is equal to a
magnified diameter of the
original illumination spot S. Said cylindrical lens 35 provides an astigmatic
projection of said X-integrator
exit facet 103 onto a plane of said Y-integrator exit facet 203. Light
entering said Y-integrator 20 is
repeatedly internally reflected by the facets 201, 201' to become homogenized
along the axis 'Y', thus
providing a flat top rectangular light pattern of FIG. 6d with an aspect ratio
A and numerical apertures
NAx, NA y governed by equations (3), (4) respectively, where magnifications m1
and m2 are defined by the
corresponding cylindrical lenses 33 and 34.
In one example, said X-integrator 10 and Y-integrator 20 in the embodiment of
FIG. 5 may be built with
the same glass, may have the same lengths L, and cylindrical lenses 33, 34 may
have the same focal
lengths F and may be positioned at equal distances z1 = z3 = 2F - Lin from
corresponding planar light
guides 10, 20. In the case, the aspect ratio of said exit light pattern is A =
: t2; numerical apertures are
NAx NAy NA0.
It should be noted that a small shift Az F of said lens 32 in the embodiment
of FIG. 4 and/or lens 34 in
the embodiment of FIG. 5 along Z-axis results in a variation of the
magnification value m2 and provides a
capability of varying the illumination pattern aspect ratio A:
A = ( 1 - Az/F).
t2
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All the lenses are schematically presented in the FIGS. 1, 4, 5 in the form of
spherical or cylindrical singlet
lenses. This is for sake of brevity and clarity only; this may or may not be
the case. It may refer to any
plurality of focusing elements including but not limited to spherical and
cylindrical singlet lenses,
aspheric and acylinder singlet lenses, gradient index lenses, multicomponent
lenses, Fresnel and
diffractive lenses, or any other focusing elements, including reflective
focusing, elements. FIG. 7 depicts,
for example, a perspective view of an alternative exemplary embodiment of the
optical integrator
assembly 1 comprising two-component relay optics in the form of two concave
spherical or cylindrical
focusing mirrors 35, 36.
The glass slabs 10, 20 and corresponding nearest optical members (i.e. lenses
31, 32 in the arrangement
of FIG. 4 and cylindrical lenses 33, 34 in the arrangement of FIG. 5) may be
replaced by single pieces of
glass 11, 21 as for example, shown in FIG. 8, thereby eliminating two glass-to-
air transitions and two air-
to-glass transitions within the optical integrator. Corresponding convex
spherical or cylindrical surfaces
may be an exit surface 113 of said X-integrator 11 and an entrance surface 212
of said Y- integrator 21.
The planar light guides 11, 21 may perform not only integration functions, but
image relay functions as
well. The optical integrator of FIG. 8 is operating in the same manner as
corresponding exemplary
embodiments of FIGS. 4, 5, illustrated by corresponding FIGS. 2, 6.
FIG. 9 depicts schematic YZ (a) and XZ (b) projections of yet another
exemplary embodiment of the
optical integrator 1 according the present invention. The entire assembly
comprises mutually orthogonal
X-integrator 12 and Y-integrator 22 of corresponding lengths L12, L22 and
thicknesses -12t, -22 t, both
implemented in the form of planar gradient index (GRIN) lenses with radial
refraction gradients. Gradient-
index optics is the branch of optics employing optical effects produced by a
gradient of the refractive
index of a material. Such gradual variation can be used to produce lenses with
flat back and front
surfaces. Said integrating planar light guides 12, 22 which are radial GRIN
lenses, have quadratic
transversal index profiles:
az
n(r)=41__
r1 (5)
Where a is a gradient constant that may be taken equal for both GRIN planar
light guides 12, 22 without
loss of generality, r2 = x2 +y2, point r = 0 corresponds to the optical axis
of the GRIN lens. The index
profile will cause rays entering one face of the rod to follow sinusoidal
paths of the form r = ro sin(ar),
where the amplitude, ro is related to the angle of incidence at the axis of
the rod by tan(0) = aro. GRIN
lenses are characterized by their 'pitch length', p =- 2r/a. The pitch length
is the number of cycles that
light will make in the given length of the GRIN glass slab. GRIN planar light
guides 12, 22 will act as
image relays, when their lengths L12 and L22 satisfy the following conditions:
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Li = p(N1/2 ¨ 6); (6)
(7)
where I = 12, 22 relates to corresponding GRIN glass slabs and N = 0, 1, 2,
3... is a natural number. The
parameter 6 must have close values for both GRIN planar light guides 12, 22. A
distance z from an exit
facet 123 of said GRIN X-integrator 12 to an entrance facet 222 of sad GRIN Y-
integrator 22, positioned
downstream is:
z = ¨tan {n-(1 ¨ 26)} (8)
no
Said optical integrator of FIG. 9 operates similarly to the optical integrator
1 of FIG. 4, but image relay
functions are provided by said GRIN planar light guides 12, 22.
FIG. 10 depicts schematic YZ (a) and XZ (b) projections of an alternative
exemplary embodiment of the
optical integrator 1 comprising mutually orthogonal X-integrator 13 and Y-
integrator 23, implemented in
the form of single-axis GRIN glass slabs, operating as cylindrical lenses with
their refraction gradients
oriented along Y- axis and along X-axis, respectively. Said GRIN planar light
guides 13, 23 have similar
quadratic index profiles (5), wherein r = y and r = x, respectively. Both
!lengths L13 and L23 of said GRIN
planar light guides 13, 23 and distance z between them have to satisfy the
same condition (6) (8), but
with differing requirements for parameter 6 close or equal for both single
axis GRIN planar light guides:
(9)
The optical integrator of FIG. 10 operates similarly to the exemplary
embodiment of FIG. 5, but astigmatic
focusing functions are provided by said single-axis GRIN planar light guides
13, 23.
FIG. 11 is a perspective view of an example of the illumination device
comprises GRIN planar light guides
13, 23, whose parameters ox oy = 0. The exit facet 133 of said GRIN X-
integrator 13 is to be close-
spaced from or to be in a contact with the entrance facet 232 of said GRIN Y-
integrator 23. In the
example of FIG. 11 said cylindrical GRIN relays 13, 23 are characterized by
unit value magnifications: ml
= m2 = 1. A resulting flat top rectangular pattern at said exit facet 233 has
an aspect ratio A = t13: t23 and
numerical apertures equal to one of the illumination unit 4: NAx= NA y = NA().
It should be noted that that single-axis optical integrators comprised in the
embodiments of FIGS. 4, 5, 7
- 11 may be implemented in the form of multilayer 'sandwich' planar light
guides similar to one of FIG. 3b
and/or in the form of wedge-shaped glass slabs of the diverging or converging
configuration, illustrated by
FIG 3d as would be apparent for someone skilled in the art.
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Alternatively, optical integrating planar light guides may have internal
components or design features
exhibiting properties of refractive and/or reflective image relaying optical
members as, for example, planar
light guides presented in FIG 12, where 00' is an input optical axis and 0'0"
is a folded exit optical axis.
FIG. 12a presents a top view of such an image relaying X-integrator 14 (or Y-
integrator 24), which may be
a glass slab with two opposing mutually parallel internally reflecting facets
141, 141', entrance facet 142,
exit facet 143, mirrored cylindrical surface 145 with the cylinder axis
orthogonal to said reflecting facets
141, 141', and two non-optical facets 144, 144'. When sum of distances // and
/2 is close to the doubled
radius R of the cylindrical mirrored surface 145, the last acts as an
astigmatic relay, i.e. provides an
astigmatic projection of a light spot from the entrance facet 142 onto exit
facet 143. FIG. 12b is a
schematic perspective view of the optical integrator assembly1, comprising
identical mutually orthogonal
X-integrator 14 and Y-integrator 24 implemented in the form of relaying planar
light guides of FIG. 12a.
The proposed hereinbefore exemplary embodiments may comprise additional
optical members such as,
for example, lenses, and focusing and folding mirrors, retarder plates,
bandpass filters for multi-spectral
illumination, light modulators, choppers, phase randomizers in the form of
spinning light diffusers, or other
optical elments as would be apparent to someone skilled in the art.
It should be noted that the specific exemplary embodiments has been
particularly shown and described
heretofore only for the purpose of explaining and illustrating the present
invention. It will therefore be
apparent to those skilled in the art that various changes, modifications or
alterations to the invention as
described herein, may be made without departing from the spirit and scope of
the invention and essential
characteristics thereof. Furthermore, although the preferred application field
of the present invention, as
set forth herein, is fluorescent and spinning disk confocal optical
microscopy, other general illumination
applications are contemplated. All such embodiments and variations are
believed to be within the sphere
and scope of the invention as defined by the claims appended hereto.
Dr. Peter A. Vokhmin
Date: September 12, 2018
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