Title of Invention	" A COMMON FRONT CHANNEL FOR INTEGRATED LASER RANGE FINDER CHAN THERMAL IMAGE"
Abstract	"A laser range finder cum thermal imager using binary optics". This invention relates to a laser range finder cum thermal imager using binary optics characterized in that a laser transmitter unit (2), a laser receiver unit (3), a thermal imager unit (4) and a common front channel (1) which is common to all these three units.

Full Text

FIELD OF INVENTION This invention relates to a common front channel for integrated 1aser range finder cum thermal imager for airborne applications to range the targets during day/night time. BACKGROUND INFORMATION For airborne applications, many types of sensors are required for day vision, night vision and ranging purposes and there is an increasing demand for lightweight sensors as weight is a extremely critical parameter for ai-borne operations. Laser range finders are used to find the range of targets while Thermal imagers are used for night vision purpose. The laser range finder computes the range of the object by measuring the time elapsed between the start of the pulse and return of echo pulse after reflection from the target and operates in the wavelength region corresponding to wavelength of laser used in the device. The laser range finders generally utilize Nd: YAG laser which operates at 1.06 micron. Thermal imagers image the objects by detecting the infrared energy radiated by them. These thermal imagers operate in the wavelength reg;on of 8-12 micron as most of the radiation energy emitted by the objects at normal temperature falls within the wavelength band. Normally, these two devices are used in a system through different channels thus making the complete system bulky. This is because of the fact that, it becomes extremely difficult to control the aberrations of the optical system throughout the entire band gap from 1.06 micron to 12 micron. Also, the transmission properties of conventional glass material utilized for collimator optics and receiver optics of laser range finder and Germanium material conventionally utilized for thermal imager optics is a limiting factor. While conventional glass material cannot transmit in 8 to 12 micron regions suitable for thermal .magers, Germanium materials can not transmit in 1.06 micron corresponding to Nd: YAG laser range finder. Because of these reasons, laser range finders and thermal imagers for airborne applications always operate through different channels. The use of common channel or common optics for laser range finder and thermal imager can make the system compact and lightweight. However because of the reasons mentioned above, integrated laser range finder cum thermal imager operating through common front channel having Nd: YAG laser range finder operating at 1.06 micron and thermal imager working in the wavelength region 8-12 micron is not known in the art. OBJECTS OF THE PRESENT INVENTION The primary object of the present invention is to propose an integrated laser range finder cum thermal imager system for ranging during night time having a front channel which is common for collimator as well as receiver of Nd: YAG laser range finder working. Another object of the present invention is to propose an integrated laser range finder cum thermal imager which uses binary optics in combination with refractive optics to improve the performance of the system. A further object of the present invention is to propose an integrated laser range finder cum thermal imager particularly for airborne application which is lightweight and compact with an improved optical layout. A still further object of the present invention is to propose an integrated laser range finder cum thermal imager which does not utilize toxic AMTIR lenses in thermal imager which are difficult to handle. STATEMENT OF INVENTION According to this invention there is provided a common front channel for integrated laser range finder cum thermal imager characterised in that a laser transmitter unit, a laser receiver unit, a themal imager unit characterised in that is a common front channel having two Zinc Sulphide Lenses which is common to all these three units. channel of two Zinc Sulphide lenses which is common to receiver as well as collimator of laser range finder working at 1.06 micron and dual magnification thermal imager operating in 8-12 micron region. The system! uses Jbiryi.ry optics in dualmagnification thermal imager which not only improves the performance of thermal imager but also helps in making the system light weight and compact as total number of lenses required for the system is reduced drastically. *• Binary optics which is a surface relief optics based on VLSI fabrication technology, facilitates creation of new unconventional optical elements and provides greater design freedom. Binary optics also helps in controlling t.h_e aberrations in the proposed optical system. In the proposed system, the aperture of two sine sulphide lenses used in the common front channel, has been decided keeping in view the requirement of collimator, receiver and thermal imager. The sine sulphide lenses of front channel alongwith negative lens in Laser range finder channel work as collimator of 4; same zinc sulphide lenses alongwith negative lens in combination with one small telephoto arrangement work as receiver optics of laser range finder. Again, these sine sulphide lenses alongwith other Germanium lenses constitute thermal imager in low magnification mode wherein magnification change over to high magnification mode is achieved by flipping out two Germanium lenses. DESCRIPTION OF THE FIGURES The present invention will now be illustrated with the accompanying drawings which are intended to illustrate an embodiment of the present invention. It is to be understood that the features of the present invention can he embodied with various modifications by those skilled in the art. These modification/adaptations are intended to be covered within the scope of the present invention. In the accompanying drawings: Fig 1': shows layout of the laser range finder cum dual magnification thermal imager P'ig 2: shows the laser transmitter unit Fig 3: shows the laser receiver unit Fig 4: shows the thermal imager in wide-angle mode Fig 5: shows the thermal imager in narrow—angle mode DESCRIPTION OF INVENTION Referring to Fig 1, the proposed laser range finder cum dual magnification thermal imager consists of common front channel (1), a. mirror with dichroic coating (7) to seperate laser range finder and thermal imager channel, laser transmitter unit (2) for sending collimated laser pulse towards the target, laser receiver unit (3) to receive the reflected laser radiation from the target to compute the range information, and dual magnification thermal imager (4) for day/night vision. Referring to Fig.2, the transmitter unit(2) consists of a Nd:YAG laser source having a laser rod(12), a dye(11) to Q-switch the laser beam, a polarising beam splitter cube(10) far creating two channels for transmitter(2) and receiver unit(3) of laser range finder, a quarter wave plate(9) to make emitted laser radiation circularly polarised light. Two Zinc Sulphide lenses (5) and (6) of common front channel alongwith negative lens(8) together work as 4x collimator optics of the transmitter unit. After passing through the collimator unit, the laser beam is directed towards the target. Referring to Fig.3, the receiver unit(3) consists of two common front channel Zinc Sulphide lenses(5) & (6), negative lens(B), quarter wave plate(9), polarising beam splitter cube(10), lenses (13), (14) & (15) of telephoto arrangement for receiver optics, interference filter (16) and Avalanche Photo Detector(APD)(17) for sensing the reflected laser radiation. Common front channel lenses(5) & (6), negative lens(8), quarter wave plate(9) and polarising beam splitter cube(10) are common to transmitter(2) as well as receiver unit(3). The laser pulse after reflection from the target becomes circularly polarised in opposite direction i.e. right handed circularly polarised beam becomes left handed circularly polarised beam and is received by two common front channel Zinc Sulphide lenses(5) ? reflected towards the telephoto lenses of the receiver optics from the face of polarising beam splitter cube(lO). After passing through the lensss(13), (14), (15) and interference filter(16), the laser beam is sensed by APD detector(17). The range counter unit in the receiver unit(3) finally computes the range of the target. The dual magnification thermal imager first works in the wide angle mode corresponding to low magnification in which search is made for the target. Once the target is located, the operation of thermal imager is changed to narrow angle mode corresponding to high magnification so as to magnify the details of the target. Fig. 4 shows the operation of the thermal imager in wide angle mode. Referring to Fig.4, the thermal imager consists of objective module as per the ensuing description to image the target, eyepiece module, as per description that follows, to make thermal telescope, scanner unit for covering the entire field of view in the object space, reimaging optics to image the aperture stop of the optical system onto the aperture v stop of the detector unit (27) and fianlly a detector--,., unit(28) to detect the thermal radiation. The two common front channel Zinc Sulphide lenses(5) & (6) together with Germanium lenses(lS), (19), (20) & Zinc Sulphide lenses (21) constitute objective module of the thermal imager in wide angle mode. Lenses(18), (19) & (2O) are having binary surfaces as shown in the figure which could be fabricated through micro-machining or through dry etching techniques. Germanium lenses(22) & (23) constitute eyepiece module of the thermal imager. A rotating polygon scanner(24) helps the detector unit(28) in covering the entire field of view in, the. abject space. Germanium lenses(23) &. (26) together form re imaging optical unit for imaging the aperture stop of *the telescope onto the aperture stop(27) of the thermal detector unit(28). Again lenses (23), (25) & (26) are having binary surfaces as shown in the figure. Reimatjing optics is necessary to match the numerical aperture of the optical system with the field of view of. the detector unit. Fig.5 shows the thermal imager in narrow angle mode corresponding to high magnification. The changeover from wide angle mode to narrow angle mode is made by flipping out lenses(lS) & (20) of the objective module of the thermal imager. Common front channel Zinc Sulphide lensea(S) & (6) together with Germanium lenses (19) & (21) constitute objective module of the thermal imager in narrow angle mode. The rest of the modules remain unchanged in the system as evident from Fig. 5. WE CLAIM; 1. A common front channel for integrated laser range finder cum thermal imager compeises a laser transmitter unit (2), a laser receiver unit (3), a themal imager unit (4) characterised in that is a common front channel (1) having two Zinc Sulphide Lenses (5) & (6) A'hich is common to all these three units. 2. A common front channel as claimec in claim 1, wherein a mirror with dichroic coating (7) separates the laser range finder channel and thermal imager channel. 3. A common front channel as claimed in claim 1, wherein the laser transmitter has a polarising beam splitter cube (10) which together with quarter wave plate :'9; separates out two channels of transmitter unit (2) and receiver unit (3) of laser range finder, a negative lens (8) which together with two Zinc Sulphide lenses (5) & (6) work as collimator optics oi 4x magnification. 4. A common front channel as claimed in claim 1, wherein the said receiver unit (3) consists of common front channel Zinc Sulphide lenses (5) & (6), negative lens (8), quarter wave plate (9). polarizing beam splitter cube (10) lenses (13), (14) 85 (15) of telephoto arrangement for receiver optics, interference filter (16) and Avalanche Photo Detecotor (APD) (17) for sensing the reflected laser radition. 5. A common front channel as claimed in claims 4 and 5, wherein Common front channel lenses (5) & (6). negative lens (8), quarter wave plate (9) and polarising beam splitter cube (10) are common to transmitter as well as receiver unit. 7. A laser range finder cum thermal imager using binary optics as claimed in claim 1 in uihi.cn the said thermal imager unit(4) consists of an abjective module, an eye piece module, a rotating polygon scanner(24), re-imaging optics module and detector unit(28). 8. A laser range finder cum thermal imager using binary optics as claimed in claim 1 in which the said objective module claimed in claim 7 of which besides common front channel Zinc Sulphide lenses(5), (6), comprises of Germanium lenses(lB), (19), (20) and zinc sulphide lens(21) in wide angle mode and only one Germanium lens(19) and zinc sulphide lens(21) in narrow angle mode. 9. A laser range finder cum thermal imager using binary optics as claimed in claim 1 in which the eyepiece module claimed in claim 7 comprises of two Germanium lenses(22) and (23) . 10. A laser range finder cum thermal imager as claimed in claim 1 in which the reimaging optics module consists of preferably Germanium lenses(25) and (26). 11. A laser range finder cum thermal imager as claimed in claim (1) in which Lenses(18), (19), (21), (25) & (26) have binary surfaces. 12. A laser range finder cum thermal imager as claimed in claim (1) in which the magnification changeover from wide angle mode to narrow angle mode is made by flipping out lens(lB) & (21). 13. A laser range finder cum thermal imager substantially described and illustrated herein.

Documents:

2661-DEL-1998-Abstract.pdf

2661-DEL-1998-Claims.pdf

2661-DEL-1998-Correspondence-Others-(19-08-2010).pdf

2661-del-1998-correspondence-others.pdf

2661-del-1998-correspondence-po.pdf

2661-DEL-1998-Description (Complete).pdf

2661-del-1998-drawings.pdf

2661-del-1998-form-1.pdf

2661-DEL-1998-Form-15-(19-08-2010).pdf

2661-del-1998-form-19.pdf

2661-DEL-1998-Form-2.pdf

2661-del-1998-form-3.pdf

2661-del-1998-gpa.pdf

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