EXHIBITEXHIBIT
`
`EXHIBIT
`1008
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`
`
`10081008
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`

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`~A'Illl,llQfWJII~M!'llii!ES~ ¥RESE~1!1~ ~UI!mll,
`
`UNITED STATES DEPARTMENT OF COMMERCE
`United States Patent and Trademark Office
`
`February 07, 2013
`
`THIS IS TO CERTIFY THAT ANNEXED IS A TRUE COPY FROM THE
`RECORDS OF THIS OFFICE OF THE FILE WRAPPER AND CONTENTS
`OF:
`
`APPLICATION NUMBER: 111197,731
`FILING DATE: August 05, 2005
`PATENT NUMBER: RE40,927
`ISSUE DATE: October 06,2009
`
`By Authority of the
`Under Secretary of Commerce for Intellectual Property
`and Director of the United States Patent and Trademark Office
`
`;J? ·~
`
`M. TARVER
`Certifying Officer
`
`

`
`US 6,603,134 Bl
`
`9
`terns carried by missiles will be between about 10-3 and
`10-s radians which produce retroreflected beams of 10-6 to
`10-10 steradians. At a range of 1,000 feet the area of these
`beams would be 1.0 and 10-4 ft2 respectively. This diver(cid:173)
`gence is so small so that the retroreflected rays are substan(cid:173)
`tially collimated.
`It is herein to be noted that in microwave application
`corner reflectors have been utilized for retroreflecting pur(cid:173)
`poses. However, the present invention enables the detection
`of microwave apparatus, such as antennas and the like which 10
`do not have a corner reflector as an integral part thereof, by
`utilizing the inherent retroreflection characteristics of the
`apparatus as hereinbefore discussed. Thus, this apparatus
`and systems exhibiting the retroreflection phenomenon can
`be similarly detected by the use of radio frequency, 15
`microwave, X-ray, acoustical or any similar types of energy
`directed thereat.
`In many microwave antenna systems microwave lenses
`are utilized in place of re~ectors for the purposes of obtain(cid:173)
`ing wide angle scanning as compared with the system 20
`bandwidth. These microwave lenses exhibit characteristics
`which are equivalent to the optical lenses hereinbefore
`discussed, and thus a detailed explanation of the retroreflec(cid:173)
`tion of microwave and similar types of energy by these
`lenses, in conjunction with a reflective surface, will be 25
`readily apparent to those skilled in the art.
`In this connection, FIG. 13 is an illustration of a radar
`system which is to be detected by means of the retroreftec(cid:173)
`tion principles of the present invention. The radar system is
`generally indicated by the reference numeral 200 and 30
`includes a parabolic disk antenna 202 having a feed 204
`whose impedance mismatch is lowest at the operating fre-
`.
`quency of the radar system 200.
`When the radar system 200 is in an off condition, the
`resonant frequency of the antenna feed 206 can be detected 35
`by beaming swept frequency microwave energy at the
`system such as by utilizing a variable frequency klystron
`(not shown) or the like.
`The pulses produced by the klystron are indicated as 210
`in the waveforms shown in FIG. 14. The wave energy 210 40
`is retroreflected by the parabolic disk antenna 202 because
`the parabola focuses the energy at the feed born which in
`turn is mismatched. Hence, the energy reflected from it is
`recollimated by the parabola similar to the optical system
`descnbed heretofore. The energy is detected in a suitable 45
`manner and produces the waveforms indicated at 212 in
`FIG. 14, until such time that the frequency of the klystron is
`equal to the operating frequency of the feed 206. When this
`occurs, the energy beamed to the radar system is focused on
`the feed hom, absorbed by the feed 206 and is therefore not so
`retroreftected. This results in the waveform indicated as 214
`in FIG. 15. The dip or drop in power level indicates
`absorption of the beamed energy and thus the frequency of
`the operation of the radar system is now known. By further
`analysis of the retroreftected waves it is possible to obtain ss
`even more information concerning the electrical and
`mechanical characteristics of the radar system 200, such as
`the type of antenna system being utilized, its scan angle, its
`beamwidth, its gain, etc.
`It will be apparent to those skilled in the art that if the 60
`antenna were a sonar disk and acoustical energy were
`directed threat, the acoustical energy would be retroreftected
`and the retroreflected acoustical energy would be capable of
`detection.
`It is thus again reiterated that although only a few types 65
`of radiant energy have herein been discussed, any type of
`energy which can be retroreflected may be employed.
`
`10
`While we have shown and descnbed various embodi(cid:173)
`ments of our invention, there are many modifications,
`changes, and alterations which may be made therein by a
`person skilled in the art without departing from the spirit and
`scope thereof as defined in the appended claims.
`What is claimed is:
`1. The method of detecting an uncooperative optical
`system including a focusing means and a surface exhibiting
`some degree of reflectivity disposed substantially in the
`focal plane of said focusing means, said method comprising
`the step of directing optical energy at said optical system
`whereby that portion of said energy incident upon said
`optical system is retroreflected with an optical gain to
`thereby form a beam of retroreflected optical energy,
`and
`the step of detecting said retroreflected optical energy
`having a radiant flux density in excess of a preselected
`value to thereby indicate the presence of said optical
`system.
`2. The method of claim 1, including
`the step of scanning a predetermined geographical area to
`detect the presence of an optical system therein.
`3. The method of claim 2, including
`the step of tracking said optical system after the presence
`thereof bas been detected.
`4. The method of claim 3, including the step of directing
`a weapon at the position of said optical system after the
`detection thereof.
`5. The method of claim 1, wherein
`the radiant energy directed at said optical system is in the
`nonvisible region.
`6. The method of claim 1, wherein
`the radiant energy directed at said optical system is light
`energy in the nonvisible region.
`7. The method of claim 6, wherein
`the light energy in the nonvisible region is infrared.
`8. The method of claim 4, wherein
`said weapon is a laser.
`9. The method of claim 1, wherein
`the radiant energy is in the ultraviolet portion of the
`electromagnetic spectrum.
`10. The method of claim 1, wherein
`the radiant energy is X-ray energy.
`11. The method of claim 1, wherein
`the radiant energy comprises high energy particles related
`to quantum mechanics.
`12. The method of claim 1, wherein
`the radiant energy is acoustical energy.
`13. The method recited in claim 1 wherein
`said optical system is a telescope.
`14. The method recited in claim 1 wherein
`said optical system is a binocular.
`15. The method recited in claim 1 wherein
`said optical system is a periscope.
`16. The method recited in claim 1 wherein
`said optical system is a human eye.
`17. Apparatus for detecting the presence of an uncoop(cid:173)
`erative optical system including a focusing means and a
`surface exhibiting some degree of reflectivity disposed sub(cid:173)
`stantially in the focal plane of said focusing means, said
`apparatus comprising
`means for producing radiant energy,
`means for directing said energy toward said optical sys(cid:173)
`tem whereby said energy is retroreflected with an
`optical by said optical system, and
`
`

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`US 6,603,134 Bl
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`20
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`40
`
`11
`means for detecting said retroreflected energy having a
`radiant flux density in excess of a preselected value to
`thereby indicate the presence of said optical system.
`18. Apparatus in accordance with claim 17 wherein said
`means for producing radiant energy is a radiant energy
`source operative in the nonvisible region.
`19. Apparatus in accordance with claim 17, wherein said
`means for producing radiant energy is a radiant energy light
`source.
`20. Apparatus in accordance with claim 19, wherein said 10
`radiant energy light source is an infrared source.
`21. Apparatus in accordance with claim 17, wherein said
`means for producing radiant energy, said means for directing
`said energy toward said optical system, and said means for
`detecting the energy retroreflected by said optical system, 15
`form an optical transceiver.
`22. Apparatus in accordance with claim 21, wherein said
`means for producing rays of radiant energy,
`said means for directing said rays toward said optical
`instrument, and
`said means for detecting the rays retroreflected by said
`optical instrument are concentrically disposed with
`respect to one another.
`23. Apparatus in accordance with claim 22, wherein said
`means for producing radiant energy, said means for directing 25
`said energy toward said optical system, and said means for
`detecting said energy retroreflected by said optical system
`are concentrically disposed with respect to one another.
`24. Apparatus in accordance with claim 22, wherein
`·said means for producing radiant energy comprises a 30
`radiant energy source
`said means for directing said energy toward said optical
`system comprises a primary mirror having a substan(cid:173)
`tially parabolic configuration, and
`said means for detecting said retroreflected energy com- 35
`prising
`a detector
`said primary mirror, and
`a secondary mirror having a substantially planar con-
`figuration
`said primary mirror having an aperture concentric with
`the principal axis thereof,
`said radiant energy source being positioned
`adjacent the non-reflecting surface of said secondary 45
`mirror,
`in the focal plane of said primary mirror,
`said secondary mirror being positioned
`adjacent said primary mirror, and
`having the reflecting surface of said secondary mirror 50
`facing the reflecting surface of said primary mirror,
`and
`said detector
`being positioned adjacent the non-reflecting surface of
`said primary mirror,
`being in axial alignment with the aperture thereof,
`being positioned in the focal plane of said detection
`means.
`25. Apparatus in accordance with claim 22, wherein
`said means for producing radiant energy comprises a
`radiant energy source,
`said means for directing said energy toward said optical
`system comprises
`a collecting mirror having a substantially elliptical
`configuration
`a primary mirror having a substantially parabolic
`configuration, and
`
`12
`a secondary mirror having a substantially planar
`configuration,
`said means for detecting said retorreflected energy com(cid:173)
`prising
`a detector, and
`said primary mirror,
`said primary mirror having an aperture concentric with
`the principal axis thereof,
`said secondary mirror being positioned with the reflecting
`surface thereof facing the reflecting surface of said
`primary mirror,
`said radiant energy source
`being positioned between the reflecting surfaces of said
`primary and secondary mirrors, and
`in axial alignment with said mirrors,
`said collecting mirror being positioned adjacent the non(cid:173)
`reflecting surface of said primary mirror,
`in axial alignment with the aperture thereof, and said
`detector being positioned in the focal plane of said
`direction means adjacent the non-reflecting surface
`of said secondary mirror in the focal plane of said
`primary mirror.
`26. Apparatus in accordance with claim 21, wherein
`said means for producing incident radiant energy is a
`radiant energy light source operative in the nonvisible
`region.
`27. Apparatus in accordance with claim 23, wherein
`said radiant energy light source is an infrared source.
`28. Apparatus in accordance with claim 17, wherein
`said means for directing said incident energy towards said
`optical system having scanning means operatively
`associated therewith to cause said rays to scan a pre(cid:173)
`determined geographical area to detect and locate said
`optical system.
`29. Apparatus in accordance with claim 28, including
`tracking means operatively associated with said scanning
`means to thereby track the movement of said optical
`system after detection thereof.
`30. Apparatus in accordance with claim 28, including
`weapon means operatively associated with said tracking
`means for use against said optical system after detec(cid:173)
`tion thereof.
`31. Apparatus in accordance with claim 30, wherein
`said weapon means is high energy source.
`32. Apparatus in accordance with claim 31, wherein
`said high energy source is a laser.
`33. The apparatus recited in claim 17 wherein said optical
`system is a telescope.
`34. The apparatus recited in claim 17 wherein
`said optical system is a binocular.
`35. The apparatus recited in claim 17 wherein
`said optical system is a periscope.
`36. The apparatus recited in claim 17 wherein
`said optical system is a human eye.
`37. Apparatus for measuring the retroreflective character(cid:173)
`istics of an optical system consisting of at least a focusing
`means and a surface exhibiting some degree of reflectivity
`60 disposed substantially in the focal plane of said focusing
`means, said apparatus comprising
`a radiant energy source,
`detection means,
`measuring means connected to said detection means, and
`means for directing said radiant energy produced by said
`source at said optical system,
`
`55
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`

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`US 6,603,134 Bl
`
`13
`whereby said radiant energy is retrore!lected with an
`optical gain by said optical system and detected by said
`detecting means and the output thereof is coupled to
`said measuring means.
`38. An optical system accordance with claim 37, includ(cid:173)
`ing
`means disposed between said radiant energy source and
`said optical system
`for transmitting a portion of the radiant energy produced
`by said radiant energy source toward said optical 10
`system, and
`for transmitting a portion of said energy retrorefiected by
`said optical system toward said detecting means.
`39. An optical system in accordance with claim 38, 15
`wherein said directing means and said detecting means are
`substantially concentric.
`40. The method of detecting the presence of devices
`which exhibit the phenomenon of retrorefiection, said
`method comprising
`the step of directing radiant energy at said devices
`whereby said radiant energy is retrorefiected with an
`optical gain by said devices, and
`the step of detecting said retrorefiected radiant energy
`which is in excess of a preselected radiant flux density 25
`level to thereby indicate the presence of said devices.
`41. The method of claim 40, including the step of ana(cid:173)
`lyzing said retroreflected radiant energy to thereby deter(cid:173)
`mine the spatial and temporal characteristics of said devices.
`42. Apparatus for detecting the presence of devices which 30
`exhibit the phenomenon of retrorefiection, said apparatus
`comprising
`means for producing radiant energy,
`means for directing said energy toward said devices
`whereby said energy is retroreflected with an optical 35
`gain by said devices, and
`means for detecting said retroreflected energy which is in
`excess of a preselected radiant flux density level to
`thereby indicate the presence of said devices.
`43. apparatus for measuring the retroreflective character(cid:173)
`istics of devices which exhibit the phenomenon of
`retrorefiection, said apparatus comprising
`
`20
`
`40
`
`14
`means for producing radiant energy,
`means for directing said energy toward said devices
`whereby said energy is retrorefiected with an optical
`gain by said devices,
`means for detecting said retrorefiected energy which is in
`excess of a preselected radiant flux density level to
`thereby indicate the presence of said devices, and
`means for analyzing said detected energy to thereby
`determine the characteristics of said devices.
`44. The method of detecting an uncooperative and non(cid:173)
`radiating microwave antenna system consisting of at least a
`microwave focusing means and a microwave feed hom
`disposed substantially at the focal point of said focusing
`means, said method comprising
`the step of directing swept frequency microwave energy
`at said antenna system whereby substantially all energy
`at the operating frequency of said antenna system
`which is impingent thereon is focused by said focusing
`means and absorbed by said feed hom and energy of
`any other frequency is retrorefiected by said antenna
`system with an energy density gain to thereby form a
`beam of retrorefiected microwave energy, and
`the step of detecting said retrorefiected energy having an
`energy density in excess of a preselected value to
`thereby indicate the presence of said antenna system.
`45. The method recited in claim 44 further including
`the step of determining the frequency at which the energy
`density of said retrorefiected energy is of a minimum
`level to thereby determine the operating frequency of
`said antenna system.
`46. The method recited in claim 44 further including
`the step of analyzing any temporal characteristics of said
`energy retrorefiected by said antenna system.
`47. The method recited in claim 44 further including
`the step of analyzing any spatial characteristics of said
`beam of energy retrorefiected by said antenna system.
`
`* * * * •
`
`

`
`1
`OPTICAL DETECTION SYSTEM
`
`US 6,603,134 Bl
`
`Applicants herein have made the discovery that any type
`of focusing device in combination with a surface, exhibiting
`any degree of reflectivity and positioned near the focal plane
`of the device, acts as a retro-reflector. A retroreflector is
`defined as a reflector wherein incident rays or radiant energy
`and reflected rays are parallel for any angle of incidence
`within the field-of -view. A characteristic of a retroreflector is
`that the energy impinging thereon is reflected in a very
`narrow beam, herein referred to as the retroreflected beam.
`This phenomenon is termed retroretlection.
`It is herein to be noted that the term radiant energy
`includes light energy, radio frequency, microwave energy,
`acoustical energy, X-ray energy, heat energy and any other
`types of energy which are part of the energy spectrum and IS
`which are capable of being retroreflected by the device,
`instrument or system sougllt to be detected.
`One type of optical device which exhibits this
`phenomenon, and thus is a particular type of retroretlector,
`is a corner reflector consisting of three mutually perpen- 20
`dicular reflecting planes, However, this type of retroreflector
`is both difficult and expensive to fabricate.
`Due to the applicants discovery, it has now become
`possible to accomplish a great many feats heretofore con(cid:173)
`sidered impossible, as will become more apparent from the 25
`discussion to follow hereinafter. In this context it should be
`noted that the eyes of human beings, as well as those of
`animals, operate as retroretlectors. Also, any optical instru(cid:173)
`ment which includes a focusing lens and a surface having
`some degree of reflectivity, no matter how small, positioned
`near the focal point of the lens, act as a retroreflector,
`whereby any radiant energy from a radiant energy source
`directed at these instruments is reflected back towards the
`source in a substantially collimated narrow beam.
`It is therefore the primary object of the present invention
`to provide a method and apparatus for detecting objects 35
`exhibiting retrorefiection characteristics.
`It is another object of the present invention to provide a
`method and apparatus to detect objects having retroreftec(cid:173)
`tion characteristics by illuminating the same with a radiant
`energy source.
`It is a more particular object of the present invention to
`provide a method and apparatus for scanning an area to
`detect the presence of optical instruments such as
`binoculars, telescopes, periscopes, range finders, cameras,
`and the like.
`It is a further object of the present invention to provide
`means and apparatus for determining the characteristics of a
`device exhibiting retrorefiection characteristics from a
`remote location.
`It is a further object of the present invention to provide
`a method and apparatus for detecting optical instruments for
`rendering the instruments ineffective and for neutralizing
`humans utilizing said instruments by employing lasers or
`similar high energy sources.
`It is yet another object of the present invention to provide
`a method and apparatus for transmitting and receiving
`radiant energy utilizing concentric optics.
`These and other objects, features and advantages of the
`present invention will become more apparent from the
`following detailed discussion considered in conjunction
`with the accompanying drawings, wherein:
`FIG. 1 is a diagram showing a retroreflection system
`consisting of a lens and a reflector wherein the source
`radiation is parallel to the optical axis of the lens.
`FIG. 2 is a diagram of a retrorefiection system sinlilar to
`that of FIG. 1, wherein the source radiation is not parallel to
`the optical axis of the lens.
`
`30
`
`2
`FIG. 3 is a diagram of a retroreflection system similar to
`FIG. 1 wherein the lens is imperfect so as to form an image
`rather than focusing at a single point.
`FIG. 4 is a diagram of a retroreflection system wherein
`the reflector is obliquely positioned with respect to the
`optical axis of the lens.
`FIG. 5 is a diagram of a human eye, wherein there is
`depicted the retroreflection characteristics thereof.
`FIG. 6 is a schematic representation depicting a beam
`10 splitting optical system for transmitting and receiving radi(cid:173)
`ant energy.
`FIG. 7 is a schematic representation depicting a concen(cid:173)
`tric optical system for transmitting and receiving radiant
`energy.
`FIG. 7a is a schematic representation of another embodi(cid:173)
`ment of the concentric optical system depicted in FIG. 7.
`FIG. 7b is a schematic representation of still another
`embodiment of the concentric optical system depicted in
`FIG. 7.
`FIG. 8 is a schematic representation depicting an ordi(cid:173)
`nary telescope as an image forming system having retrore(cid:173)
`flection characteristics.
`FIG. 9 is a schematic representation depicting one half of
`an ordinary binocular as an image forming system having
`retroretlection.
`FIG. 10 is a schematic representation depicting an ordi(cid:173)
`nary periscope as an image system having retroreftection
`characteristics.
`FIG. 11 is a schematic representation depicting an ordi(cid:173)
`nary camera as an image forming system having retrore(cid:173)
`flection characteristics.
`FIG. 12 depicts a system for scanning an area to detect
`the presence of optical instruments by utilizing the retrore(cid:173)
`flection characteristics thereof and for neutralizing observers
`using said optical instruments, and/or rendering the instru(cid:173)
`ments ineffective.
`FIG. 13 is a diagram of a radar system, and more
`particularly of a radar antenna which is to be detected in
`accordance with the principles of the present invention.
`FIG. 14 depicts the waveforms obtained during the
`detection of the radar system shown in FIG. 13.
`In accordance with the general principles of the present
`invention an optical system consisting of a focusing lens and
`a reflective surface positioned near the focal plane of said
`45 lens has radiant energy rays supplied thereto by a radiant
`energy transmitter. The radiant energy rays reflected by the
`optical system due to its retroreflection characteristics are
`recovered by a radiant energy receiver to thereby detect the
`presence and relative position of said optical system. The
`so output of the radiant energy receiver may be applied to a
`utilization means for deternlining the characteristics of the
`retroretlector or for directing a weapon means.
`Referring now to the drawings and more particularly to
`FIG. 1 thereof, there is shown an optical system consisting
`ss of a lens 20 and a reflective surface 22, which herein is a
`mirror, positioned in the focal plane 24 of the lens 20. Rays
`of radiation 26 and 28, respectively, are directed towards the
`system, and more particularly towards the lens 20, from a
`radiation source (not shown); the incident rays in the present
`60 illustration being parallel to the optical axis 30 of the lens.
`It is herein to be noted that for the purpose of clarity the
`incident rays are herein shown as being confined to the top
`half of the lens 20. The incident rays 26 and 28 are refracted
`by the lens 20 and focused at the focal point 32 of the lens,
`65 which focal point lies on the mirror 22. The rays are then
`reflected by the mirror so that the angle of reflection equals
`the angle of incidence, and are returned to the lower half of
`
`40
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`US 6,603,134 Bl
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`3
`the lens where they are again refracted and emerge there(cid:173)
`from as retroreflected rays 26R and 28R. The rays 26R and
`28R are returned to the radiation source parallel to the
`incident rays 26 and 28 thereof. However, as shown in the
`drawing, the relative positions of the rays 26 and 28 are
`inverted so that the image returned to the radiation source is
`also inverted.
`In the optical system depicted in FIG. 2, similar parts are
`de-noted by similar reference numerals. In this system the
`rays 34 and 36 are not parallel to the optical axis 30A of both 10
`the lens 20A and the mirror 22A, the mirror 22A being
`positioned in the focal plane 24A of the lens. The rays 34 and
`36 are refracted by the lens 20A and focused at a point 37
`removed from the optical axis but still on the focal plane. 15
`The rays 34 and 36 are reflected by the mirror. Both of the
`rays 34 and 36 would normally emerge from the lens as
`retroreflected rays 34R and 36R, after refraction by the lens,
`and would be returned to the source of the rays 34 and 36 in
`a direction parallel thereto. However, since the lens 20A is 20
`of finite size, the reflected ray 34R will miss the lens and will
`not be retroreflected. The loss of reflected rays in this
`manner is called "vignetting".
`In the system depicted in FIG. 3 wherein similar parts are
`de-noted by similar reference numerals, the lens 20B is 25
`assumed to be imperfect; i.e., it has aberrations. In this case
`the rays 38 and 40 are parallel to the optical axis JOB but are
`not focused at a single point on the focal plane 24B, and
`instead form an image on the mirror 22B, which image is
`referred to as the circle of confusion. In most practical 30
`optical systems there are circles of confusion and the mirror
`is normally positioned at the plane of least circle of
`confusion, herein depicted by the reference numeral 42.
`Thus, the image formed on the mirror by means of the rays 35
`38 and 40 can be considered to be a radiant source, and the
`retroreflected rays 38R and 40R exit from the lens 20B
`substantially parallel to each other. This is possible since
`each emerging ray can be paired with a parallel incident ray
`which radiates from a common point of the image source 40
`located at the mirror 22B.
`In the system depicted in FIG. 4, the reflecting surface or
`mirror 22C, and its axis 44, is tilted with respect to the
`optical axis 30C of lens 20C. However, the ray 48 is again
`retroreflected by the system and the retroreflected ray 48R is 45
`returned parallel to the incident ray 48. The retroreflected
`ray 46R, due to the ray 46, is lost because of vignetting.
`The concept set forth herein above in conjunction with
`FIG. 3, that the retroreflected rays be considered as radiating
`from a source on the image plane, is highly significant. With 50
`this concept in mind, it will be readily apparent that even if
`the retroreflecting surface is dispersive, curved, or tilted, (as
`shown in FIG. 4), the system will still exhibit retroreflective
`properties for any and all rays which are returned to the lens
`by the reflecting surface.
`The rays retroreflected by the optical systems depicted in
`FIGS. 1 to 4 are in the form of a narrow, substantially
`collimated beam having a high radiant flux density. It is to
`be noted that there is an actual increase in the radiant flux 60
`density of the retroreflected beam due to the narrowing
`thereof. This increase in radiant flux density is herein termed
`optical gain.
`For example, if the irradiance produced by the radiating
`source at the collecting lens in FIG. 3 is 100 watts/cm2 and 65
`the area of the lens is 100 cm2
`, then the radiant flux at the
`image or focal plane (circle of confusion) is
`
`55
`
`4
`
`100
`a:;tts x 100 cm2, or 10' watts.
`
`It is a characteristic of a retroreflector to return the
`retroreflected energy or rays in a very narrow beam. The
`dimensions of the retroreflected beam is a function of the
`angular resolution of the retroreflector which includes the
`lens and the reflecting surface.
`The solid angle into which the incident radiant flux will
`be retroreflected is determined by the square of the angular
`resolution of the retroreflector. If, for example, the resoltuion
`of the optical system is 10-4 radians, the solid angle into
`which the retroreflected beam will be returned is 10-a
`steradians. One steradian being the solid angle subtended at
`the center of a sphere by a portion of the surface of area
`equal to the square of the radius of the sphere. Thus at a
`distance of 1Q4 em from the focal plane the area of the
`retroreflected beam is only 1.0 cm2
`• The retroreflector, by
`radiating into such a small solid angle, bas radiant intensity
`of
`
`10' Watts
`I o-11 steradian, or I 012 warulsteradian.
`
`In order to obtain a measure of the optical gain we must
`compare the retroreflector to a standard or reference. This
`reference bas been taken to be a diffuse surface known in the
`art as a Lambertian radiator. If the 104 watts of incident
`radiant flux were simply re-radiated in a Lambertian man(cid:173)
`ner; i.e., into a solid angle of 3.14 (:n;) steradians, the radiant
`intensity would be
`
`10' watts
`3.1 4 steradians' or 3.1 x tal warulsteradian.
`
`Thus, the retroreflector bas an overall optical gain equal to
`
`1012 waru/steradian
`- - - - - - - , or 3.14><108
`3.1 x Jol warulsteradian
`
`Although there is no actual increase in radiant flux, the
`retroreflector has a radiant intensity which is 3.14xHf
`greater than that of a Lambertain radiator which emits the
`same radiant flux. Thus, for example, a telescope having a
`collecting area of 100 cm2 and an angular resolution of 0.1
`milliradian would appear similar in size to about 3.5x10S
`cm2 of a diffuse or Lambertian radiator.
`It should be noted that in almost all cases, the retrore(cid:173)
`fiector will be disposed within an environment that produces
`background radiation in a Lambertian manner. Thus, the
`radiant intensity of the retroreflector is so much greater than
`that of a Lambertian radiator that it is easily discernible from
`the background, even when, (as shown in FIG. 2) a large
`percentage of the retroreflected radiant flux is lost due to
`vignetting.
`It is herein to be noted that the radiant intensity of the
`retroreflected beam is dependent upon the characteristics of
`the optical system employed. If an optical system of the type
`shown in FIGS. 1, 2, and 4 were possible and there were no
`loss of energy (power) entering the system, then the radiant
`intensity gain would be almost infinite since the energy
`would be retroreflected in an almost perfectly collimated
`beam, i.e. a retroreflected beam whose divergence angle is
`
`

`
`US 6,603,134 Bl
`
`10
`
`5
`almost zero. However, almost all optical systems resemble
`that shown in FIG. 3 and the factor which determined the
`divergence angle of the retroreflected beam is the size of the
`circle of confusion and more particularly, the least circle of
`confusion. The size of the least circle of confusion is
`dependent upon the resolution of the system and in particu-
`lar upon the resolution of the focusing lens. Thus, the less
`aberrations in the lens, the better the resolution, the smaller
`the circle of least confusion, the smaller the divergence
`angle of the retroreflected beam, and thus the greater the
`optical gain.
`Referring to FIG. 5, there is shown a magnified cross(cid:173)
`sectional view of a human eye denoted generally by the
`reference numeral 50. The eye includes a cornea 52, an
`anterior chamber 54, a lens 56, and a retina 58. The retina
`has a small portion or point 60 thereon termed the yellow
`spot or macula lutea, which is approximately 2 mm in
`diameter. At the center of the macula lutea is the fovea
`centralis 62 whose diameter is approximately 0.25 m. The
`acuity of vision is greatest at the macula lutea and more
`particularly at the fovea centralis. Thus, the eye is always
`rotated so that the image being examined or the rays entering
`thereon fall on the fovea 62. As seen in FIG. 5, rays 64 and
`66 enter the eye and pass through the cornea 52 and the
`anterior chamber 5