OPTICAL INSTRUMENTS
The present invention relates to optical instruments, especially microscopes,
in particular optical instruments which have an exit pupil at which an image
of an object may be viewed by an observer, and diffractive optical elements
for use with the same.
I n conventional optical instruments, the size of the exit pupil is determined
by a function of the numerical aperture and overall magnification of the
optical instrument, and hence the size of the exit pupil is of fixed and
relatively-small dimension. Consequently, it is necessary for an observer to
accurately align the entrance pupil of his/her eye with the exit pupil of the
optical instrument in order properly to view an image.
The present applicant has previously developed a number of different optical
instruments which, through the provision of a diffractive element at an
intermediate image plane, provide an exit pupil which is effectively enlarged,
allowing an observer to view an image by placing his/her eye anywhere
within the enlarged exit pupil. These optical instruments are disclosed in
US-A-6028704, US-A-6608720, US-A-7123415 and GB-A-2360604. Another
optical instrument which incorporates an exit pupil expander is disclosed in
US-A-2005/0237615.
The present applicant has now developed improved optical instruments,
which still provide an exit pupil which is effectively enlarged, but which can
provide for greater optical clarity and also avoid the need for a field lens
arrangement, which, given the size of the field of view, usually represents
the most expensive component within the optical instruments, being a
precision-ground and polished glass component.
I n one aspect the present invention provides an optical instrument for
producing an optical image to be viewed by an observer, the optical
instrument comprising : an optical system for producing an optical image of
an object which is viewable by an observer at an exit pupil; and a diffractive
element located at an image plane of the optical system for producing an
array of the exit pupils, which are perceivable as a single, enlarged exit pupil
by the observer; wherein the diffractive element comprises a surface which
has an array of diffractive units, each of which generates one of the exit
pupils of the array of exit pupils, the diffractive units each comprising
replications of a pattern of a plurality of separated areas which are effective
to produce diffractive interference of light and generate a plurality of exit
pupils which are displaced relative to one another in the form of an array of
exit pupils, such as to be viewable as a single, continuous enlarged exit
pupil, and the areas comprise irregular features of different sizes, both in
horizontal and vertical section, which have curved surfaces at lateral faces
thereof; wherein the diffractive units are disposed progressively radially
outwardly from the optical axis of the diffractive element and configured
progressively to provide for an increasing angular offset, such that,
independent of location on the aperture of the diffractive element, light from
the received image is relayed to a common region on a viewing plane across
the aperture of the diffractive element.
In another aspect the present invention provides an optical instrument for
producing an optical image to be viewed by an observer, the optical
instrument comprising : an optical system for producing an optical image of
an object which is viewable by an observer at an exit pupil; and a diffractive
element located at an image plane of the optical system for producing an
array of the exit pupils, which are perceivable as a single, enlarged exit pupil
by the observer; wherein the diffractive element comprises a surface which
has an array of diffractive units, each of which generates one of the exit
pupils of the array of exit pupils, the diffractive units each comprising
replications of a pattern of a plurality of separated areas which are effective
to produce diffractive interference of light and generate a plurality of exit
pupils which are displaced relative to one another in the form of an array of
exit pupils, such as to be viewable as a single, continuous enlarged exit
pupil, and the areas comprise irregular features of different sizes, both in
horizontal and vertical section, which have curved surfaces at lateral faces
thereof.
I n one embodiment the diffractive element is configured to relay light from
the received image to a common region on a viewing plane across the
aperture of the diffractive element.
In one embodiment the diffractive units a re disposed progressively radially
outwardly from the optical axis of the diffractive element and configured
progressively to provide for an increasing angular offset, such that,
independent of location on the aperture of the diffractive element, light from
the received image is relayed to the common region on the viewing plane.
I n one embodiment the progressively-increasing angular offset is provided
by providing the areas within each diffractive unit of different radial position
with different size, shape and position.
I n one embodiment the diffractive units provide for relaying of light from the
received image to the common region on the viewing plane without any
relay lens arrangement.
I n one embodiment the surface of the diffractive element is on a
substantially flat plane.
I n one embodiment the curved surfaces at the lateral faces of the areas
comprise frusto-conical or frusto-cylindrical surfaces and/or the lateral faces
of the areas within each diffractive unit include both inwardly and outwardly
curved sections.
I n one embodiment the lateral faces of the areas within each diffractive unit
are tilted or inclined, optionally as a rectilinear surface, tapering inwardly
away from the surface of the diffractive element.
In one embodiment the areas are projections which extend from the surface
of the diffractive element and/or depressions which extend into the surface
of the diffractive element.
In one embodiment the replications of the patterns of areas have a pitch of
from about 40 pm to about 100 pm or from about 60 m to about 100 pm.
I n one embodiment the areas each have one or more surfaces at an upper
surface thereof which are substantially parallel to the surface of the
diffractive element, inclined to the surface of the diffractive element and/or
arcuate.
In one embodiment the upper surface of each of the areas has a curved
peripheral edge.
I n one embodiment the areas each have an average dimension of from
about 1 pm to about 10 pm.
I n one embodiment the optical instrument is a microscope.
Preferred embodiments of the present invention will now be described
hereinbelow by way of example only with reference to the accompanying
drawings, in which :
Figure 1 illustrates an optical instrument in accordance with a first
embodiment of the present invention;
Figure 2(a) illustrates an elevational view of a diffractive element in
accordance with one embodiment of the optical instrument of Figure 1;
Figure 2(b) illustrates a perspective view of one diffractive unit (represented
by sections A in Figure 2(a)) of the diffractive element of Figure 2(a);
Figure 2(c) illustrates a plan view of the one diffractive unit of Figure 2(b);
Figure 2(d) illustrates a vertical sectional view (along section I-I in Figure
2(c)) of the diffractive element of Figure 2(a);
Figure 3 illustrates an optical instrument in accordance with a second
embodiment of the present invention; and
Figure 4 illustrates the expansion and beam steering provided by the
diffractive units of the diffractive element of the optical instrument of Figure
3.
Figure 1 illustrates a microscope in accordance with a first embodiment of
the present invention, in this embodiment a projection microscope.
The microscope comprises an objective lens 3 for producing a primary image
in an image plane, here a primary image plane PIP, of an object at an object
plane OP, in this embodiment as defined by an aperture stop 5.
I n this embodiment the microscope further comprises a projection lens 7
which images the primary image of the objective lens 3 to an image plane,
here a secondary image plane SIP, and produces an image of the aperture
of the objective lens 3 at the ray vertex 9 of the projection lens 7 .
The microscope further comprises a field lens arrangement 11, n this
embodiment comprising a pair of field lenses 15, 17, for relaying the exit
pupil to a viewing plane VP, such as to be viewable by an eye of an
observer.
The microscope further comprises a diffractive element 25, in this
embodiment a transmissive element, which is located at the secondary
image plane SIP, here intermediate the field lenses 15, 17 of the field lens
arrangement 11, and is effective to produce a array of exit pupils, each
corresponding to the exit pupil which would be produced in the absence of
the diffractive element 25.
Through suitable design, the diffractive element 25 can be configured to
provide that the exit pupils in the array of exit pupils are spaced apart or in
contact, and the configuration is chosen such that the array of exit pupils
appears to the eye of the observer in effect as a single, continuous enlarged
exit pupil.
I n one embodiment, as illustrated in Figures 2(a) to (d), the diffractive
element 25 comprises a principal surface 27 which has an array of diffractive
units 29, each of which generates one of the exit pupils of the array of exit
pupils. The profile and form of the individual diffractive units 29 determines
the comparative light energy within each of the individual pupil images.
In this embodiment the diffractive units 29 comprise replications of a pattern
of a plurality of separated areas 31 which are effective to produce diffractive
interference of light passing therethrough and generate a plurality of exit
pupils which are displaced relative to one another in the form of an array of
exit pupils, such as to be viewable as a single, continuous enlarged exit
pupil.
I n this embodiment the areas 31 comprise irregular features of different
sizes, both in horizontal and vertical section, which have arcuate or curved
surfaces at lateral faces 33 thereof, here frusto-conical or frusto-cylindrical
surfaces. These features can vary in size but typically are in the range of
about 1 m to about 10 m.
In this embodiment the lateral faces 33 of the areas 31 within each
diffractive unit 29 include both inwardly and outwardly curved sections.
In this embodiment the lateral faces 33 are tilted or inclined, tapering
inwardly away from the surface 27 of the diffractive element 25.
In this embodiment the areas 31 are projections which extend from the
surface 27 of the diffractive element 25. I n an alternative embodiment the
areas 31 could comprise depressions which extend into the surface 27 of the
diffractive element.
In this embodiment the replications of the patterns of areas 31 have a pitch
of about 80 pm. I n other embodiments the replications of the patterns of
areas 31 can have a pitch of from about 40 m to about 100 pm.
In this embodiment the areas 31 each have one or more surfaces at an
upper surface 35 thereof. I n this embodiment the one or more surfaces are
substantially parallel to the surface 27 of the diffractive element 25, but
could alternatively be inclined to the surface 27 of the diffractive element 25
or arcuate.
In this embodiment the upper surface 35 of each of the areas 31 has a
curved peripheral edge 37, here around its entirety.
I n this embodiment the areas 31 are formed by the patterning and
development of an actinic photoresist. I n one embodiment the pattern is
formed by direct writing a pattern, using a combination of controlled
electron beam and laser ablation, into actinic photoresist.
With this configuration, the microscope provides a single, enlarged exit pupil
having an effective size corresponding to the array of exit pupils, and the
array of exit pupils have desired optical characteristics, particularly in
providing for uniform energy distribution of a polychromatic image.
Figure 3 illustrates a microscope in accordance with a second embodiment of
the present invention.
The microscope of this embodiment is similar t o the microscope of the firstdescribed
embodiment, and thus, in order to avoid duplication of
description, only the differences will be described in detail with like parts
designating like reference signs.
The microscope of this embodiment differs from the first-described
embodiment in that the field lens arrangement 11 is omitted, and instead
the diffractive element 25 is configured to relay light from the received
image to a common region on the viewing plane VP across the aperture of
the diffractive element 25, in this embodiment centered on the optical axis
of the diffractive element 25.
I n this embodiment the diffractive units 29 which are disposed progressively
radially outwardly from the optical axis of the diffractive element 25 are
configured progressively to provide for an increasing angular offset, such
that, independent of location on the diffractive element 25, light from the
received image is relayed to a common region. Figure 4 illustrates the
expansion and beam steering provided by the diffractive units 29.
In this embodiment the progressively-increasing angular offset is provided
by the sizing, shaping and positioning of the areas 31 within each diffractive
unit 29. This sizing, shaping and positioning is determined by conventional
diffractive principles, and modelled, such as by Zemax (Radiant Zemax,
Redmond, USA) or LightTrans VirtualLab (Jenoptik Optical Systems, W.
Henrietta, USA).
Finally, it will be understood that the present invention has been described
in its preferred embodiments and can be modified in many different ways
without departing from the scope of the invention as defined by the
appended claims.
For example, in the described embodiments the diffractive element 25 is a
transmissive element, but it will be understood that the diffractive element
2 could be provided as a reflective element.

CLAIMS
1. An optical instrument for producing an optical image to be viewed by
an observer, the optical instrument comprising:
an optical system for producing an optical image of an object which is
viewable by an observer at an exit pupil; and
a diffractive element located at an image plane of the optical system
for producing an array of exit pupils, which are perceivable as a
single, enlarged exit pupil by the observer;
wherein the diffractive element comprises a surface which has an
array of diffractive units, each of which generates one of the exit
pupils of the array of exit pupils, the diffractive units each comprising
replications of a pattern of a plurality of separated areas which are
effective to produce diffractive interference of light and generate a
plurality of exit pupils which are displaced relative to one another in
the form of an array of exit pupils, such as to be viewable as a single,
continuous enlarged exit pupil, and the areas comprise irregular
features of different sizes, both in horizontal and vertical section,
which have curved surfaces at lateral faces thereof;
wherein the diffractive units are disposed progressively radially
outwardly from the optical axis of the diffractive element and
configured progressively to provide for an increasing angular offset,
such that, independent of location on the aperture of the diffractive
element and without any relay lens arrangement, light from the
received image is relayed to a common region on a viewing plane
across the aperture of the diffractive element.
2 . A optical instrument for producing an optical image to be viewed by
an observer, the optical instrument comprising :
an optical system for producing an optical image of an object which is
viewable by an observer at an exit pupil; and
a diffractive element located at an image plane of the optical system
for producing an array of exit pupils, which are perceivable as a
single, enlarged exit pupil by the observer;
wherein the diffractive element comprises a surface which has an
array of diffractive units, each of which generates one of the exit
pupils of the array of exit pupils, the diffractive units each comprising
replications of a pattern of a plurality of separated areas which are
effective to produce diffractive interference of light and generate a
plurality of exit pupils which are displaced relative to one another in
the form of an array of exit pupils, such as to be viewable as a single,
continuous enlarged exit pupil, and the areas comprise irregular
features of different sizes, both in horizontal and vertical section,
which have curved surfaces at lateral faces thereof.
3 . The instrument of claim 2, wherein the diffractive element is
configured to relay light from the received image to a common region
on a viewing plane across the aperture of the diffractive element.
4 . The instrument of claim 3, wherein the diffractive units are disposed
progressively radially outwardly from the optical axis of the diffractive
element and configured progressively to provide for an increasing
angular offset, such that, independent of location on the aperture of
the diffractive element, light from the received image is relayed to the
common region on the viewing plane.
5. The instrument of any of claims 2 to 4, wherein the diffractive units
provide for relaying of light from the received image to the common
region on the viewing plane without any relay lens arrangement.
6. The instrument of any of claims 1 to 5, wherein the progressivelyincreasing
angular offset is provided by providing the areas within
each diffractive unit of different radial position with different size,
shape and position.
7. The instrument of any of claims 1 to 6, wherein the surface of the
diffractive element is on a substantially flat plane.
8. The instrument of any of claims 1 to 7, wherein the curved surfaces at
the lateral faces of the areas comprise frusto-conical or frustocylindrical
surfaces and/or the lateral faces of the areas within each
diffractive unit include both inwardly and outwardly curved sections.
9. The instrument of any of claims 1 to 8, wherein the lateral faces of
the areas within each diffractive unit are tilted or inclined, optionally
as a rectilinear surface, tapering inwardly away from the surface of
the diffractive element.
10. The instrument of any of claims 1 to 9, wherein the areas are
projections which extend from the surface of the diffractive element
and/or depressions which extend into the surface of the diffractive
element.
11. The instrument of any of claims 1 to 10, wherein the replications of
the patterns of areas have a pitch of from about 40 m to about 100
mhi or from about 60 pm to about 100 pm.
12. The instrument of any of claims 1 to 11, wherein the areas each have
one or more surfaces at an upper surface thereof which are
substantially parallel to the surface of the diffractive element, inclined
t o the surface of the diffractive element and/or arcuate.
13. The instrument of claim 12, wherein the upper surface of each of the
areas has a curved peripheral edge.
14. The instrument of any of claims 1 to 13, wherein the areas each have
an average dimension of from about 1 pm to about 10 m.
The instrument of any of claims 1 to 14, wherein the optical
instrument is a microscope.