GB2228338A

GB2228338A - Infra-red laser radar device

Info

Publication number: GB2228338A
Application number: GB8014040A
Authority: GB
Inventors: Roger Pierre Joseph Alexis; Fernand Rene Loy
Original assignee: Telecommunications Radioelectriques et Telephoniques SA TRT
Current assignee: Telecommunications Radioelectriques et Telephoniques SA TRT
Priority date: 1979-07-25
Filing date: 1980-04-30
Publication date: 1990-08-22
Anticipated expiration: 2000-04-30
Also published as: GB2228338B; FR2634903B1; IT8023589A0; FR2634903A1; DE3027744C1

Abstract

The device comprises means for scanning a field, raster scanning being made by an oscillating mirror (13) and line scanning by a rotating drum (14) having reflecting surfaces, the image of a pick-up (A) and of an emitting source (E) being transferred to a fixed point (A<1>) whose symmetrical point with respect to each reflecting surface describes the analyzed line. The field mirror (15), which deflects the raster scanning beams towards the line scanning system, has a width less than the distance between the images of the pick-up in two consecutive surfaces of the rotating drum (14) such that the beams have a common part. The sounding energy is sent to the common part from the source (E) which may be made up of laser diodes (23, 24, 25, 26), cylindrical lenses (27, 28, 29, 30) and a common lens (31) the source (E) being symmetrical with the pick- up (A) with respect to a flat mirror (20) formed with an orifice (21) placed in the image transfer system. Alternatively, the positions of the pick-up (A) and source (E) are reversed and the mirror (20) is replaced by a small mirror having the same dimensions as the orifice (21). <IMAGE>

Description

TITLE "INFRA-RED LASER RADAR SYSTEM" The invention relates to a radar device operating at an optical wave length, inter alia infra-red. It relates more particularly to the part of the device for optical scanning the field in two directions, and the transmission and reception of sounding energy.

A device for optically scanning and displaying scenes and objects detected e.g. by infra-red radiation was disclosed by the Applicants in a Parent Patent Application filed in Gt. Britain on 28 January 1976, No. 03370/76, followed by three applications for Patents of Addition, i.e.: 1st Patent of Addition, filed on 9 December 1977, No. 51454/77, 2nd Patant of Addition1 filed on 9 December 1977, No. 51455/77, 3rd Patent of Addition1 filed on 9 December 1977, No. 51456/77, followed finally by a recent Patent Application filed on 23 August 1979, No. 7929466.

In the afore.mentioned device, the scanned field is detected via an optical objective and scanning is carried out in two perpendicular directions.

One direction (the y or raster direction) forms a plane P with the optical axis of the objective. The other direction (x or line) is perpendicular to the plane P. The raster scanning means comprise a plane mirror rotating in alternate directions around an axis parallel to the x direction and placed in a convergent beam Behind the objective near the image of the field in the objective.The line scanning means comprise a drum rotating uniformly around an axis yy' in the plane P and having a large number of reflective flat surfaces regularly distributed around the drum periphery, and an image transfer system symmetrical with respect to the plane P and forming an mags of a radiation pick-up at a point A' on plane P, the drum being placed in a convergent beam in the path of the transfer system on the image side of the sensitive element, the point symmetrical with point A' with respect to each drum surface when the surface is perpendicular to plane P being a point D in the immediate neighbourhood of the point symmetrical with the focus of the objective relative to the raster mirror ina position parallel to YY'.The deuce comprises an optical system for reflecting the beams from the raster scanning system to the line scanning system, the optical system comprising a concave or field mirror having the plane P as its plane of symmetry and having its apex substantially at the point D. The mirror is designed so that, in co-operation with the raster mirror it conjugates the centre 0 of the exit pupil of the bjective with a fixed point C on plane P, i.e. the centre of the entrance pupil of the line scanning means, so that any beam striking the exit pupil of the objective converges on the pick-up. In order to maintain the aforementioned conjugation during raster scanning, the field mirror is, if required, moved in rciprocation by small amounts in phase with the mdion of the raster scanning means.In order to reduce te zero the dead scanning time between two consecutive lines, the width of the field mirror in the x direction is slightly less than the length of the analyzed line, which in turn is equal to the distance between the images of the detector in two consecutive surfaces of the rotating drum.

The scene is directly displayed by using an eiectrolutinescent diode actuated by the signal from the pick-up. In a variant or the device, the diode is placed in a position sysmetrical with the pick-up with respect to a first diohroic mirror, which is transparent to the light used for analysis but reflects light from the diode, the reflected light subsequently following the same path, in the opposite direction, as the analyzed light via the line and raster scanning systems, the image finally being formed in a different direction from the optical axis of the objective, owing to the presence of a second dichroic mirror identical with the first and placed in a convergent beam behind the objective.

If slightly modified, the device can operate as a laser radar system.

To this end, the electroluminescent diode actuated by the detector can be replaced by a laser diode emitting pulse4, e.g. infra-red, radiation and independent of the pick-up, and the first diohroic mirror can be replaced by a semi-transparent plate, the second dichroic mirror being omitted.

The pick-up will then receive the echo from an obstacle in the path of radiation emitted by the pulsed source, the output and return tracks operating at the same wavelength.

After being thus modified, the device has disadvantages, i.e.

dlfficulty of operation and inadequate efficiency for detecting obstacles such as electric power cables, which have small reflecting surfaces.

A first cause of these disadvantages is that the semi-transparent plate wastes half the energy of the emitted radiation and half the energy received from the obstacle. A second cause is the limitation in the energy of the laser diode (i.e. the power per unit solid angle) owing to the restrictions on the bulk of the optical device. The reason is as follows: If F is the focal length of the device, D is the diameter of itspupil, is the length of the diode and # is the aperture of its radiation diagram, the length of the beam emitted by the diode will be ss = Consequently, F must be increased to increase the energy.However, since the aperture size is g = F it is also necessary to increase D. The methodJof reducing C) increase the ; dimension of the source, which is thus a basic limitation on the energy. A third reason is that, in reality, the width of the transmitted and the energy-receiving beams vary during scanning of a line, since the width of the field mirror in the device is substantially equal to the length of the analyzed line and the beam is stored down to a varying extents at every instant by each drum surface. The result is that a given

o6jLacCe t being detected gives

having various energies, which are apt to introduce errors when they are interpreted.

In the present invention, the aforementioned prior-art device, or a device which can be obviously deduced therefrom, is given far-reaching modifications so as to obviate the aforementioned disadvantages.

A first modification, other things being equal, is to reduce the number of reflecting surfaces of the rowing drum, e.g. by a factor of 2.

This doubles the width of the beams of rays from each point on the analyzed line, reflected by a surface of the rotating drum. There is also a dead time between scanning one line and another line, and the beams have a common portion during the scanning of a line.

The sounding energy is injected, in the reverse direction, into the common portion after the beams have been focused on to the pick-ups.

To this end, in a second modification, the semitransparent plate is replaced by a mirror formed with an orifice adapted to the shape of the common beam portion.

There is thus no loss of energy on emission, and only a small part (about 25iso) is lost during reception, via the mirror orifice.

A third modification and improvement is made in the energy source, which is designed so as to radiate high energy. To this end, the laser diode symmetrical with the receiver with respect to the perforated mirror is replaced by N images of N laser diodes superposed by N image transfers, the transfers being brought about so that the resulting transmission source has a radiation diagram having the same aperture S as that of each laser diode, and transmission is directed towards the mirror orifice.

Thus, according to one aspect of the invention there is provided an optical radar device for scanning, by transmission and reception, a field in two perpendicular directions, i.e. by line scanning in an x direction and raster scanning in a y direction, the device scanning in the aforementioned manner by means of beams from the various regions of the field, and receiving on an element sensitive to radiation conveyed by the beams from the aforementioned regions and transmitting to the regions by means of the aforementioned beams of radiation emitted from a local source the device comprising the following in order in the receiving direction: an objective having its optical axis in a plane P containing the y direction and perpendicular to x, its focal surface being spherical and such that its centre of curvature is at the centre of the exit pupil of the objective; raster scanning means comprising a plane or raster mirror rotating in alternate directions around an axis parallel to the x direction and placed in a convergent beam behind the objective near the image of the field in the objective; line scanning means comprising a drum rotating uniformly around a stationary axis YY' in the plane P and having a number of reflecting surfaces regularly distributed around the drum periphery, and an image transfer system forming an image of the sensitive element and of the radiationemitting source at a point A' on plane P, the drum being placed in a convergent beam in the path of the transfer system on the image side of the sensitive element and the source, the point symmetrical with point A' with respect to each drum surface when the surface is perpendicular to plane P being a point D in the immediate neighbourhood of the point symmetrical with the focus of the objective relative to the raster mirror in the position parallel to YY', and an optical beam-deflecting system comprising a concave or "field" mirror having the plane P as its plane of symmetry and its apex substantially at point D, the mirror being such that, in co-operation with the raster mirror it conjugates the centre 0 of the exit pupil of the objective with a fixed point C on plane P, i.e. the centre of the entrance pupil of the line scanning means; characterised in that: the field mirror has a width in the X direction such that, allowing for the number of surfaces on the rotating mirror, the width is less than the distance between the image of the sensitive element and the image of the emitting source in two consecutive surfaces of the rotating drum, and the image transfer system, at the end downstream point of the path of the beams in the receiving direction, comprises a flat mirror formed with an orifice, the mirror concentrating radiation on to the sensitive element, the emitting source being placed in a position symmetrical with the sensitive element with respect to the mirror and emitting sounding energy into the mirror orifice in a portion of the beam common to all the line scanning beams.

According to a further aspect of the invention there is provided an optical radar device for scanning, by transmission and reception, a field in two perpendicular directions, i.e. by line scanning in an x direction and raster scanning in a y direction, the device scanning in the aforementioned manner by means of beams from the various regions of the field, and receiving on an element sensitive to radiation conveyed by the beams from the aforementioned regions and transmitting to the regions by means of the aforementioned beams of radiation emitted from a local source, the device comprising the following in order in the receiving direction: an objective having its optical axis in a plane P containing the y direction and perpendicular to x, its focal surface being spherical and such that its centre of curvature is at the centre of the exit pupil of the objective; raster scanning means comprising a plane or raster mirror rotating in alternate directions around an axis parallel to the x direction and placed in a convergent beam behind the objective near the image of the field in the objective;; line scanning means comprising a dr= rotating uniformly around a stationary axis Yet in the plane P and having a number of reflecting surfaces regularly distribute!1 around the drT periphery, and an image transfer system forming an image of the sensitive element and of the viation- emitting source at a point A' on plane P, the drum being placed in a convergent beam in the path of the transfer system on the image side of the sensitive element and the source, the point symmetrical with point A with respect to each drum surface when the surface is perpendicular to plane P being a point D in the immediate neighbourhood of the point symmetrical with the focus of the objective relative to the raster mirror in the position parallel to YYt-, and an optical beam-deflecting system comprising a concave or "field" mirror having the plane P as its plane of symmetry and its apex substantially vt point D, the mirror being such that, in co-operation with the raster mirror, it conjugates the centre 0 of the exit pupil of the objective with 2 fixed point C on plane P, i.e. the centre of the entrance pupil of the line scanning means;; characterised in that: the field mirror has a width in the x direction such: that, allowing for the number of surfaces on the rotating mirror, the width is less than

the distance between the image4 of the sensitive element andlof the emitting source in two consecutive surfaces of the rotating drum; and the image transfer system1 at the exteme downstream end of the path of the beams in the receiving direction, comprises a sum211 mirror which returns the sounding energy to the emitting source in a portion common to all the line scanning beams, the sensitive element being placed in a position symmetrical with the emitting source with respect to the small mirror.

The invention will be described by way of example only with particular reference to the accompanying drawings in which: Figure 1 is a general view of the device in projection parallel to the line scanning direction; Figure 2 is a general view of the device in projection parallel to the optical axis of the device; Figure 3 is a view of the line scanning system in projection parallel to the axis of the rotating drum in a first position thereof, and Figure 4 is a view of the line scanning system in projection parallel to the axis of the rotating drum'in a second and third position thereof.

The device of the present invention has the general structural features of the aforementioned prior-art devices.

Figure 1 is a diagram of the device of the invention in projection perpendicular to the plane of the page parallel to the line ~ scanning direction. The diagram shows co=ponert from the aforementioned prior art, i.e. an objective 1l having an optical axis 12, a "raster" mirror 13, a rotating drum 14 having reflecting surfaces for line scannn, and a field mirror 15. The raster mirror 13 scans the field in a direction y parallel to the plane of the drawing. It can move around an axis 16 parallel to the x or line scanning direction perpedicular to the plane of the drawing. Drum 14 can move around an axis 17 parallel to the plane of the drawin=.The beams from the analyzed field, e.g. a central beam 18 having the axis 12, are focused on the field mirror 15, which deflects the beams towards line scanning means comprising more particularly the drum 14, the beams finally converging on a pick-up, the image of which is transferred to A', the image transfer means being explained hereinafter with reference to Fig. 2.

In Fig. 2, the device is shove in perpendicular projection on the plane of the page parallel to the cptical axis 12. Fig. 2 shots the sane components as in Fig. 1, with the same numbers, i.e. objective 11 in the form of a circle, mirror 13 in the form of a rectangle havin

axis 16, the rotating drum 14 diarram.^atically shown as a polygon, the field mirror 15 in the form of an arc, and beam 18 represented by its cross-section through the raster mirror 13.Allowing for the position of the drum surface 34 perpendicular to the plane of Fig. 1, thebeam converges at Fg in the middle of arc 15, which represents a line scanned during rotation of the drum. The pick-up is placed at A. An assembly comprising plane mirror 20 and convergent element 19 conveys the image of the pick-up to A'.

Mirror 20 has an orifice 21 for supplying the device with pulsed radiation travelling in the opposite direction from the beam for analyzing the echo of the pulsed radiation. In Fig. 1, mirror 20 is shown in the form of a rectangle and orifice 21 is shown by its outline inside the cross-section (likewise shown) of beam 18 through the plane of mirror 20.

Pulsed radiation is emitted by a source E made of diodes having a small emission angle, e.g. laser diodes as explained hereinafter. Source E emits a beam 22, which is bounded by orifice 21. Fig. 2 shoves the beam in section through the plane of mirror 13, the section being inside the section of the analysis beam 18 through the same mirror. Constructional details of source E are shown on the left of Figs. 1 and 2. N images of N identical diodes are superposed at E by N image transfers but the width of the elementary radiation diagram of the diodes is preserved at point E.The emitting surface of each diode is in the form of a rectangular slot having a length of e.g. 100/um and a width y of ' being of the order of 15 in both directions of the rectanG~e.

In Figs. 1 and 2 there are four diodes 23, 24, 25, 26. They are disposed so that the major dimension of the slots is psra'lel to the line direction.

Each image transfer is made by means of a cylindrical convergent lens associated with each diode and a second cylindrical lens common to the N image transfer5. In Figs. 1 and 2, the lenses associated with each diode are cylindrical lenses 27, 28, 29 and 30 respectively, having cylinder generatrices parallel to the plane of Fig. 1 and parallel to the plane of Fig. 2 and axes which join each diode to point E. In Fig. 2 the lenses appear together in the form of a plate having parallel surfaces. The common lens is lens 31, having cylinder generatrices parallel to the plane of Fig. 2 and parallel to the plane of Eg.l, its axis being identical with the axis of the entire system. In Fig. 2, the lens is shown in the form of a plate having parallel surfaces. Owing to the use of the aforementioned cylindrical lenses, source E is rectangular. The magnification of lens 31 is e.g. unity, so that the length of the source is e and the radiation diagram aperture in a plane perpendicular to the aforementioned length is # . On the other hand, if the magnification of the N lenses is made eoual to N at the joint E for each elementary source. the width

will become

and the beam aperture will

The resulting source E will have a width N e' and, by addisekthe elementary apertures, will have a beam aperture of $ perpendicular to the aforementioned width.In practice, comparable values of 2 and N #' can be obtained if N is given the value of a few tens, and the resulting source will have high and substantially isotropic energy in its emission diagram.

Figs. 3 and 4 are views in projection of the line scanning system, showing its operation, on a plane perpendicular to the drum axis 17.

A' is the image of the pick-up given by the previously-described image transfer system. The rotating drum is shorn in the form of a polygon 14.

The line described by the image of the focus of the objective, substantially on the field mirror, is along an arc 32. 5 and 34 are two reflecting surfaces of the drum, which rotates in the direction of arrow 35. F is 0 the central point of the analyzed line, when face 3L; is perpendicular to F R'.The beam focused on the pick-up is, in projection, the beam 0 having the angle #0. When the drum rotates in the direction of arrow 351 face 34. roves from 34 to 34' and the point of the line under analyser moves from F0 to the end F2 of the line, which is fixed by the width of the field mirror. The beam focused on the pick-up then has an angle #2 equal to # 0.The number of faces of the rotating drum (or the width of each face) is such that when the image of the pick-up in face 34, in position 34', has finished scanning the line F2, the image of the pick-up in the next face 33, in position 33', has not yet begun to scan the line at F1. Scanning does not begin until face 33 has reached a position 33'' perpendicular to F1 A', when the beam focused on the pick-up has an angle equal to #0 and #2. During scaning, the focused beams have a common (shaded) part corresponding to beam 22 in Figs. 1 and 2, along which the energy from source E is emoted in the reverse direction.

In a variant of the device, the positions of the detector at A and the emitting source at E are reversed and mirror 20 is replaced by a small mirror having the same dimensions and positions as orifice 21 and conveying the sounding energy in the direction of arrow 22, whereas beam 18 (not including beam 22) is not reflected by the small mirror. The laser diodes and optical elements for transferring images occupy positions symmetrical with those in Fig. 2, with respect to mirror 20.

In the preceding descriptior, the pick-up image is transferred. by lenses only. Of course, the device according to the invention can also be cmbodied by using mirrors to transfer the pick-up image, as described in the aforementioned prior art.

Of coarse the device

the invention can have all the improvements In the Patents and Certificates of Addition filed by the Aplicants as enumerated at the begining of the Patent Application, inter all the improvements relating to the motion of the field mirror in synchronism With the raster mirror or the improvements relating to line scanning.

Claims

1. An optical radar device for scanning, by transmission and reception, a field in two perpendicular directions1 i.e. by line scanning in an x direction and raster scanning in a y direction, the device scanning in the aforementioned manner by means of beams from the various regions of the field, and receiving on an element sensitive to radiation conveyed by the beams from the aforementioned regions and transmitting to the regions by means of the aforementioned beams of radiation emitted from a local source, the device comprising the following in order in the receiving direction:: an objective having its optical axis in a plane r containing the y direction and perpendicular to x, its focal surface being spherical and such that its centre of curvature is at the centre of the exit pupil of the objective; raster scanning means comprising a plane or raster mirror rotating in alternate directions around an axis parallel to the x direction and placed in a convergent beam behind the objective near the image of the field in the objective;; line scanning means comprising a drum rotating uniformly around a stationary axis YY' in the plane P and having a number of reflecting surfaces regularly distributed around the drum periphery, and an image transfer system forming an image of the sensitive element and of the radiationemitting source at a point A' on plane P, the drum being placed in a convergent beam in the path of the transfer system on the image side of the sensitive element and the source, the point symmetrical with point A' with respect to each drum surface when the surface is perpendicular to plane P being a point D in the immediate neighbourhood of the point symmetrical with the focus of the objective relative to the raster mirror in the position parallel to YY', and an optical beam-deflecting system comprising a concave or "field" mirror having the plane P as its plane of symmetry and its apex substantially at point D, the mirror being such that, in co-operation with the raster mirror it conjugates the centre 0 of the exit pupil of the objective with a fixed point C on plane P, i.e. the centre of the entrance pupil of the line scanning means; oharacterised in that:: the field mirror has a width in the x direction such that, allowing for the number of surfaces on the rotating mirror, the width is less than

the distance between the image of the sensitive element andlof the emitting source in two consecutive surfaces of the rotating drum, and the image transfer system, at the end downstream point of the path of the beams in the receiving direction, comprises a flat mirror formed with an orifice, the mirror concentrating radiation on to the sensitive element, the emitting source being placed in a position symmetrical with the sensitive element with respect to the mirror and emitting sounding energy into the mirror orifice in a portion of the beam common to all the line scanning beams.

2. An optical radar device for scanning, by transmission and reception, a field in two perpendicular directions, i.e. by line scanning in an x direction and raster scanning in a y direction, the device scanning in the aforementioned manner by means of beams from the various regions of the field, and receiving on an element sensitive to radiation conveyed by the beams from the aforementioned regions and transmitting to the regions by means of the aforementioned beams of radiation emitted from a local source, the device comprising the following in order in the receiving direction:: an objective having its optical axis in a plane P containing the y direction and perpendicular to x, its focal surface being spherical and such that its centre of curvature is at the centre of the exit pupil of the objective; raster scanning means comprising a plane or raster mirror rotating in alternate directions around an axis parallel to the x direction and placed in a convergent beam behind the objective near the image of the field in the objective;; line scanning means comprising a drum rotating uniformly around a stationary axis YY'in the plane P and having a number of reflecting surfaces regularly distributed around the drum periphery, and an image transfer system forming an image of the sensitive element and of the Ediation- emitting source at a point A' on plane P, the drum being placed in a convergent beam in the path of the transfer system on the image side of the sensitive element and the source, the point symmetrical with point A' with respect to each drum surface when the surface is perpendicular toane P being a point D in the immediate neighbourhood of the point symmetrical with the focus of the objective relative to the raster mirror in the position parallel to YYs, and an optical beam-deflecting system comprising a concave or "field" mirror having the plane P as its plane of symmetry and its apex substantially at point D, the mirror being such that, in co-operation with the raster mirror it conjugates the centre 0 of theexit pupil of the objective with a fixed point C on plane P, i.e. the centre of the entrance pupil of the line scanning means; characterised in that: : the field mirror has a width in the x direction such that, allowing for the number of surfaces on the rotating mirror. the width is less than

the distance between the image of the sensitive element andlof the emitting source in two consecutive surfaces of the rotating drum; and the image transfer system, at the extreme downstream end of the path of the beams in the receiving direction, comprises a

mirror which returns the sounding energy to the emitting source in a portion common to all the line scanning beams. the sensitive element being placed in a position symmetrical with the emitting source with respect to the

mirror.

2. An optical radar device for scanning, by transmission and reception, a field in two perpendicular directions, i.e. by line scanning in an x direction and raster scanning in a y direction, the device scanning in the aforementioned manner by means of beans from the various regions of the field, and receiving on an element sensitive to radiation conveyed by the beams from the aforementioned regions and transmitting to the regions by means of the aforementioned beams of radiation emitted from a local source, the device comprising the following in order in the receiving direction:: an objective having its optical axis in a plane P containing the y direction and perpendicular to x, its focal surface being spherical and such that its centre of curvature is at the centre of the exit pupil of the objective; raster scanning means comprising a plane or raster mirror rotating in alternate directions around an axis parallel to the x direction and placed in a convergent berm behind the objective near the image of the field in the objective;; line scanning means comprising a drtlm rotating uniformly around a stationary axis YYtin the plane P and having a number of reflecting surfaces regularly distributed around the drum periphery, and an image transfer system forming an image of the sensitive element and of the Ediation- emitting source at a point A' on plane P, the drum being placed in a convergent beam in the path of the transfer system on the image side of the sensitive element and the source, the point symmetrical with point A' with respect to each drum surface when the surface is perpendicular to plane P being a point D in the immediate neighbourhood of the point symmetrical with the focus of the objective relative to the raster mirror in the position parallel to YY.t, and an optical bean-deflecting system comprising a concave or "field" mirror having the plane P as its plane of symmetry and its apex substantially at point D, the mirror being such that, in co-operation with the raster mirror it conjugates the centre 0 of theexit pupil of the objective with a fixKd point C on plane P, i.e. the centre of the entrance pupil of the line scanning means; characterised in that:: the field mirror has a width in the x direction such that, allowing for the number of surfaces on the rotating mirror, the width is less than

the distance between the image of the sensitive element andlof the emitting source in two consecutive :surfaces of the rotating drum; and the image transfer system, at the extreme downstream end of the path of the beams in the receiving direction, comprises a small mirror which returns the sounding energy to the emitting source in a portion common to all the line scanning beams, the sensitive element being placed in a position symmetrical with the emitting source with respect to the small mirror.

3. A device as claimed in claim 1 or 2, wherein the image transfer is made by mirrors only.

4. A device as claimed in claim 1 or 2, wherein the image transfer means comprises lenses.

5. A device as claimed in any of claims 1 to 4 wherein the emitting source is the image of a set of N laser diodes, the rectangular emitting surface of which has a length and a width whereas their emission diagram has an aperture S perpendicular to the lastmentioned two dimensions, the diodes being placed parallel to one another along their length, the image being made up from N diode image transfers using N cylindrical lenses having generatrices parallel to the major dimension of the diodes, one lens per diode, and another cylindrical lens having generatrices parallel to the major dimension of the diodes common to the N image transfers, the first N lenses operating at unit magnification and the common lens at a magnification of N.

6. An optical radar device substantially as hereinbefore described and as shown in the accompanying drawings.

Amendments to the claims have been filed as follows