GB1605266A

GB1605266A - Optical scanning device

Info

Publication number: GB1605266A
Application number: GB5145477A
Authority: GB
Inventors: Fernand Loy
Original assignee: Telecommunications Radioelectriques et Telephoniques SA TRT
Current assignee: Telecommunications Radioelectriques et Telephoniques SA TRT
Priority date: 1976-12-14
Filing date: 1977-12-09
Publication date: 1987-02-04
Also published as: FR2586519A2; FR2586519B2; IT1203126B; NL7713873A; NL190294B; NL9301384A; NL190294C

Abstract

This device ensures the optical scanning of a field of view in two perpendicular directions termed line and frame. The device ensures the convergence of the optical beams emanating from the various zones of the field on a sensitive element. The line scanning means include a fixed toric mirror which is axisymmetric about the axis of rotation of the said line scanning means forming an image of the sensitive element on the said axis of rotation. According to the invention, this mirror is formed of two parts each belonging to the concave surface of a paraboloid, the axes and vertices of the two paraboloids being situated on the said axis of rotation or respectively on the said axis and another axis which is perpendicular to it. Application to night vision. <IMAGE>

Description

(54) OPTICAL SCANNING DEVICE (71) We, TELECOMMUNICATIONS RADJOELECTRIQUES ET TELEPHONIQUES T.R.T., of 88, rue Brillat Savarin, 75013 Paris, France, a French Body Corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is a Patent of Addition to Patent Application No. 3370/76 (Patent No. 1605265).

It constitutes an improvement to the device for optically scanning a field of vision and displaying the field, disclosed in the aforementioned main Patent.

The main Patent relates to a device for optically scanning a field of vision divided into different regions and for displaying the field, scanning being made in two perpendicular directions, i.e. "line" scanning in a direction x and and "raster" or "image" scanning in a direction y, the device scanning along beams coming from different regions of the field and causing the beams to converge on to a detector sensitive to the radition in the beams, the device comprising the following components in order, in the direction of the path of the central incident beam from the field of vision: an objective, means for raster scanning in the y direction, and a system for deflecting the beams bounded by the detector and the aperture of the objective towards means for line scanning of the image field of the objective in the x direction, the display part of the device having optical means similar to the field of vision scanning means and comprising, instead of the detector, an electro-luminescent diode actuated by a signal coming from the detector, the device being characterised in that: the optical axis of the objective is in a plane P containing they direction and perpendicular to the x direction, the focal surface of said objective being curved and such that its centre of curvature is at the centre of the exit pupil of the objective, the raster scanning means comprise a plane mirror rotating in reciprocation around an axis parallel to the x direction and disposed in a convergent beam behind the objective near the field image in the objective, the line scanning means comprise, firstly, a drum rotating uniformly around a stationary axis YY' contained in the plane P and bearing a number of flat reflecting surfaces regularly distributed around the drum periphery and, secondly, an image-conveying means symmetrical with respect to the plane P and forming an image of the detector at a fixed point A' along the drum rotation axis YY', the drum being placed in a convergent beam in the path of the image conveying means on the image side of the detector, the point symmetrical with the point A' with respect to each surface of the drum, when the surface is perpendicular to the plane P, being in the neighbourhood of the point D which is symmetrical with the focus of the objective with respect to the raster mirror in a position parallel to the YY' axis, and the optical beam-deflecting system comprises a concave or "field" mirror having the plane P as the plane of symmetry, the apex of the mirror being near D on the ZZ' axis extending through D and perpendicular to the YY' axis, the mirror being so disposed that it conjugates the centre 0 of the exit pupil of the objective with a fixed point 0' on the YY' axis, point 0' being symmetrical with respect to the ZZ' axis with the point where the optical axis of the objective intersects the YY' axis; in order, if required, to ensure that the idle scanning time between two consecutive lines is zero, the field mirror also has a width in the x direction which 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 mirror being moved if required for small distances in phase with the movement of the raster scanning means, the small motion comprising reciprocation in translation along the ZZ' axis in the neighbourhood of D and reciprocating rotation around an axis parallel to the x direction, which is symmetrical with respect to the ZZ' axis, the amplitude of the motion in translation being such as to correct the defocusing introduced by the raster scanning means and the amplitude of the rotation being such as to ensure that the field mirror holds 0', the conjugate of the centre 0 of the exit pupil of the objective, in a constant position during the reciprocating rotation of the raster scanning means.

The improvement according to the invention relates to an embodiment of the line scanning means, more particularly of the means (symmetrical with respect to plane P) of conveying an image of the detector to a fixed point A' on axis YY'.

According to the main Patent, the conveying system may comprise a toric mirror of revolution around YY' having an elliptical cross-section through a plane containing axis YY', the detector being on the major axis.

According to another embodiment, the system for conveying the image at A' of the detector on axis YY' belonging to the line scanning means is an objective comprising lenses, the detector being outside the YY' axis, and the focal length of the objective being such that the image A' on the YY' axis of the detector is situated with respect to D as previously indicated.

In the first aforementioned embodiment, the use of an ellipsoid is not very appropriate when the detector is relatively large, since an ellipsoid is not aplanatic. Such a situation occurs when the detector comprises a mosaic of detectors.

The second embodiment, wherein the image is conveyed by an objective comprising lenses, has the disadvantage that parts of the spectrum of light, inter alia large infra-red and visible parts, are excluded from the analysis of objects.

The present invention obviates these disadvantages and shortcomings.

Instead of using an ellipse, it is proposed to use a set of two paraboloids of revolution around the YY' axis, the paraboloids being disposed face to face so that they optically conjugate the detector with the point A' on the YY' axis. Such a pair of mirrors is aplanatic, with the result that the detector can be relatively large (i.e. a mosaic of detectors) instead of using a single detector of reduced size.

In the case where the detector is outside the YY' axis. the invention uses a means of conveying the image to A' on the YY' axis, the means consisting entirely of mirror (' that analysis is performed in both the X isiblc and the infra-red parts of the spectrum.

More particularly, the image conveying means comprises the aforementioned two paraboloids of revolution, one of them being rotated so that its axis of revolution intersects YY' and its reflecting surface faces YY', the detector being disposed at its focus outside the YY' axis, and a system of one or more plane mirrors being used for deflecting the beam between the two paraboloids in parallel rays.

The invention will be more clearly understood from the following description of two embodiments given by way of nonlimitative example, the description being accompanied ls drawing > it Hhich: Fig. 1 shows a sectioi of .m embo('iile;it of the device according to the main Pat@@@ wherein the line scanning means e(,r -ç;c a mirror system ol the present inventi( a for conveying the image of a detector situated on the axis of rotation of the device, and Fig. 2 is a partial sectional view of an embodiment of the device according to the main Patent, wherein the line scanning means comprise a mirror system of the present invention for conveying the image of a detector situated outside the axis of rotation of the device.

Fig. 1 is a section, along its plane P of symmetry, through the general structure of the device according to the main Patent. Reference 11 denotes a stationary objective having an optical axis 12 and focus F. The objective 11 is made up of lenses, but as stated in the main Patent, the objective may alternatively be made up of mirrors. The optical axis 12 intersects the YY' axis at point E. The YY' axis is the axis of rotation of a system comprising a driving means 13 and a rotatable drum 13' having a large number of lateral reflecting surfaces. As stated in the main Patent, the drum can have a number of shapes. In the present case it is assumed to be prismatic, its reflecting surfaces being uniformly distributed around the YY' axis. One surface is shown at 17 in a position perpendicular to plane P. The plane mirror 14 can move around an axis perpendicular to the drawing and extending through E. Actually, in the invention, the axis does not necessarily extend through E. The feature shown in Fig. I is preferable only when the device, as stated in the main Patent, has additional means for directly displaying the field by means of electroluminescent diodes.

Mirror 14 reflects any beam coming from a region of the field and travelling through objective 11 to a concave mirror 16, where it forms an image of the field, substantially on mirror 16. Fig. I shows a beam 15 having a central ray coinciding with the optical axis 12.

The image forms at point D on the ZZ' axis perpendicular to the YY' axis, corresponding to the centre of the field.

Mirror 14 scans the field in the y direction perpendicular to axis 12 and in the plane of the drawing. Hereinafter, mirror 14 will be called the image analysis or raster analysis mirror.

In the present invention. the device comprises a concave mirror made up of a set of two paraboloid portions 1X and 18' of revolution around the YY' axis, the reflecting surfaces of the two portions being turned towards one another. The paraboloids have apices S, S' and foci A, A'. situated along the YY' axis. A' is symmetrical with D with respect to the drum face 17. Tic mirrors 18. 18' form an image at A' of .: tector I disposed at A.

When the rotatable drum 13' rotates. the system comprising drum 13', mirrors 18. 18' and detector 19 can be used for line-by-line analysis, in the direction x perpendicular to the plane of the drawing, of the field image given by objective 11 and mirror 14 near point D.

This system is the line analysis or x analysis system. Mirror 16, which is symmetrical with respect to the ZZ', YY' plane, its apex being near D, optically conjugates the centre of the exit pupil 0 of objective 11 with the fixed point O' on axis YY', symmetrical with E with respect to axis ZZ', so that any beam striking the exit pupil of objective 11 converges on detector 19. Mirror 16 is called the field mirror, since it bounds the analyzed field.

Fig. 2 does not show the general structure of the device but only gives a view in section along the plane of symmetry of the device of those elements needed for describing the special contribution made by the present invention.

Fig. 2 shows the axis of rotation YY'of the device, the point A' symmetrical with point D with respect to drum face 17, and the portion of paraboloid 18' disposed as shown in Fig. 1, i.e.

with focus A' and apex S' on axis YY'.

In Fig. 2, the detector 19 is at a point A outside axis YY' and paraboloid 18'. In the invention, A and A' are optically conjugated, using mirrors only. To this end, firstly, the optical beam is bent and directed outside paraboloid 18'. It is bent e.g. by a plane mirror 21 which is at an angle to the beam of parallel rays reflected by mirror 18', the reflecting surface of mirror 21 being e.g. perpendicular to the plane of the drawing and facing the point A. Secondly, in the invention, the beam reflected by the plane mirror is focused at point A on to detector 19 by means of a portion of a paraboloid 2() which is e.g. symmetrical with respect to the plane of the drawing and has a focus A and apex S. Of course, the two paraboloids need not be identical, either here orin Fig. 1 . In Fig. 2, a single plane mirror21 is used, at an angle of 45" with respect to the YY' axis, and A and S are on the Y' Y' axis perpendicular to the YY' axis. Of course, in the case of a detector disposed outside the YY' axis, a bending mirror 21 can be inclined at a different angle from 45" with respect to the YY' axis, or alternatively a number of mirrors can be used and successively reflect the beam from paraboloid 18'. According to another alternative, the axis of paraboloid 2() is not necessarily perpendicular to the YY' axis.

A remarkable result of the invention, using the aforementioned line scanning means, is that the distance AA' can have any desired value since the optical path between the paraboloids is in parallel beams, so that the paraboloids can be moved apart whether the detector is on the YY' axis or not. This is not the case when the image of the detector on the YY' axis is conveyed by means of an ellipsoid, since the distance AA' must then be the distance between foci. According to the invention, the detector can easily be placed at some distance from the YY' axis, which is very advantageous when the detector is secured to bulky auxiliary means required for its operation, e.g. a cryogenic machine.

The abovc-described means for conveying the image of the detector on to the axis of rotation YY' may be introduced into the optical and mechanical scanning device according to the main patent, and the resulting device forms part of the present invention.

WHAT WE CLAIM IS: 1. A device for optically scanning a field of vision divided into different regions and for displaying the field, scanning being made in two perpendicular directiOns, i.e. "line" scanning in a direction x and "raster" or "image" scanning in a direction y, the device scanning along beams coming from different regions of the field and causing the beams to converge on to a detector sensitive to the radiation in the beams, the device comprising the following components in order, in the direction of the path of the central incident beam from the field of vision: an objective, means for raster scanning in the y direction, and a system for deflecting the beams bounded by the detector and the aperture of the objective towards means for line scanning of the image field of the objective in the x direction, the display part of the device having optical means similar to the field of vision scanning means and comprising, instead of the detector, an electro-luminescent diode actuated by a signal coming from the detector, the device being characterised in that the optical axis of the objective is in a plane P containing the y direction and perpendicular to the x direction, the focal surface of said objective being curved and such that its centre of curvature is at the centre of the exit pupil of the objective, the raster scanning means comprise a plane mirror rotating in reciprocation around an axis parallel to the x direction and disposed in a convergent beam behind the objective near the field image in the objective, the line scanning means comprise, firstly, a drum rotating uniformly around a stationary axis Y Y' contained in the plane P and bearing a number of flat reflecting surfaces regularly distributed around the drum periphery and, secondly, an image-conveying means symmetrical with respect to the plane P and forming an image of the detector at a fixed point A' along the drum rotation axis yyr, the drum being placed in a convergent beam in the path of the image-conveying means on the image side of the detector, the point symmetrical with the point A' with respect to each surface of the drum, when the surface is perpendicular to the plane P, being in the neighbourhood of the point D which is symmetrical with the focus of the objective with respect to the raster mirror in a position parallel to the YY' axis, and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. and detector 19 can be used for line-by-line analysis, in the direction x perpendicular to the plane of the drawing, of the field image given by objective 11 and mirror 14 near point D. This system is the line analysis or x analysis system. Mirror 16, which is symmetrical with respect to the ZZ', YY' plane, its apex being near D, optically conjugates the centre of the exit pupil 0 of objective 11 with the fixed point O' on axis YY', symmetrical with E with respect to axis ZZ', so that any beam striking the exit pupil of objective 11 converges on detector 19. Mirror 16 is called the field mirror, since it bounds the analyzed field. Fig. 2 does not show the general structure of the device but only gives a view in section along the plane of symmetry of the device of those elements needed for describing the special contribution made by the present invention. Fig. 2 shows the axis of rotation YY'of the device, the point A' symmetrical with point D with respect to drum face 17, and the portion of paraboloid 18' disposed as shown in Fig. 1, i.e. with focus A' and apex S' on axis YY'. In Fig. 2, the detector 19 is at a point A outside axis YY' and paraboloid 18'. In the invention, A and A' are optically conjugated, using mirrors only. To this end, firstly, the optical beam is bent and directed outside paraboloid 18'. It is bent e.g. by a plane mirror 21 which is at an angle to the beam of parallel rays reflected by mirror 18', the reflecting surface of mirror 21 being e.g. perpendicular to the plane of the drawing and facing the point A. Secondly, in the invention, the beam reflected by the plane mirror is focused at point A on to detector 19 by means of a portion of a paraboloid 2() which is e.g. symmetrical with respect to the plane of the drawing and has a focus A and apex S. Of course, the two paraboloids need not be identical, either here orin Fig. 1 . In Fig. 2, a single plane mirror21 is used, at an angle of 45" with respect to the YY' axis, and A and S are on the Y' Y' axis perpendicular to the YY' axis. Of course, in the case of a detector disposed outside the YY' axis, a bending mirror 21 can be inclined at a different angle from 45" with respect to the YY' axis, or alternatively a number of mirrors can be used and successively reflect the beam from paraboloid 18'. According to another alternative, the axis of paraboloid 2() is not necessarily perpendicular to the YY' axis. A remarkable result of the invention, using the aforementioned line scanning means, is that the distance AA' can have any desired value since the optical path between the paraboloids is in parallel beams, so that the paraboloids can be moved apart whether the detector is on the YY' axis or not. This is not the case when the image of the detector on the YY' axis is conveyed by means of an ellipsoid, since the distance AA' must then be the distance between foci. According to the invention, the detector can easily be placed at some distance from the YY' axis, which is very advantageous when the detector is secured to bulky auxiliary means required for its operation, e.g. a cryogenic machine. The abovc-described means for conveying the image of the detector on to the axis of rotation YY' may be introduced into the optical and mechanical scanning device according to the main patent, and the resulting device forms part of the present invention. WHAT WE CLAIM IS:

1. A device for optically scanning a field of vision divided into different regions and for displaying the field, scanning being made in two perpendicular directiOns, i.e. "line" scanning in a direction x and "raster" or "image" scanning in a direction y, the device scanning along beams coming from different regions of the field and causing the beams to converge on to a detector sensitive to the radiation in the beams, the device comprising the following components in order, in the direction of the path of the central incident beam from the field of vision: an objective, means for raster scanning in the y direction, and a system for deflecting the beams bounded by the detector and the aperture of the objective towards means for line scanning of the image field of the objective in the x direction, the display part of the device having optical means similar to the field of vision scanning means and comprising, instead of the detector, an electro-luminescent diode actuated by a signal coming from the detector, the device being characterised in that the optical axis of the objective is in a plane P containing the y direction and perpendicular to the x direction, the focal surface of said objective being curved and such that its centre of curvature is at the centre of the exit pupil of the objective, the raster scanning means comprise a plane mirror rotating in reciprocation around an axis parallel to the x direction and disposed in a convergent beam behind the objective near the field image in the objective, the line scanning means comprise, firstly, a drum rotating uniformly around a stationary axis Y Y' contained in the plane P and bearing a number of flat reflecting surfaces regularly distributed around the drum periphery and, secondly, an image-conveying means symmetrical with respect to the plane P and forming an image of the detector at a fixed point A' along the drum rotation axis yyr, the drum being placed in a convergent beam in the path of the image-conveying means on the image side of the detector, the point symmetrical with the point A' with respect to each surface of the drum, when the surface is perpendicular to the plane P, being in the neighbourhood of the point D which is symmetrical with the focus of the objective with respect to the raster mirror in a position parallel to the YY' axis, and

the optical beam-deflecting system comprises a concave or "field" mirror having the plane P as the plane of symmetry, the apex of the mirror being near D on the ZZ' axis extending through D and perpendicular to the YY' axis, the mirror being so disposed that it conjugates the centre 0 of the exit pupil of the objective with a fixed point 0' on the YY' axis, point 0' being symmetrical, with respect to the ZZ' axis, with the point where the optical axis of the objective intersects the YY' axis; in order, if required, to ensure that the idle scanning time between two consecutive lines is zero, the field mirror also has a width in the x direction which 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 mirror being moved if required for small distances in phase with the movement of the raster scanning means, the small motion comprising reciprocation in translation along the ZZ' axis in the neighbourhood of D and reciprocating rotation around an axis parallel to the x direction, which is symmetrical with respect to the ZZ' axis, the amplitude of the motion in translation being such as to correct the defocusing introduced by the raster scanning means and the amplitude of the rotation being such as to ensure that the field mirror holds 0', the conjugate of the centre 0 of the exit pupil of the objective, in a constant position during the reciprocating rotation of the raster scanning means, characterised in that the means for conveying the image of the detector which is disposed on the YY axis comprises a set of two concave mirrors in the form of portions of paraboloids of revolution having the YY' axis as a common axis of symmetry, the reflecting surfaces of the mirrors facing one another, the focus of one mirror being at point A' and the focus of the other being occupied by the detector.

2. A device for optically scanning a field of vision divided into different regions and for displaying the field, scanning being made in two perpendicular directions, i.e. "line" scanning in a direction x and "raster" or "image" scanning in a direction y, the device scanning along beams coming from different regions of the field and causing the beams to converge on to a detector sensitive to the radiation in the beams, the device comprising the following components in order, in the direction of the path of the central incident beam from the field of vision: an objective, means for raster scanning in the y direction, and a system for deflecting the beams bounded by the detector and the aperture of the objective towards means for line scanning of the image field of the objective in the x direction, the display part of the device having optical means similar to the field of vision scanning means and comprising, instead of the detector, an electro-luminescent diode actuated by a signal coming from thc detector.

the device being characterised in that the optical axis of the objective is in . plane P containing they direction and perpendicular to the x direction, the focal surface of said objective being curved and such that its centre of curvature is at the centre of the exit pupil of the objective, the raster scanning means comprise a plane mirror rotating in reciprocation around an axis parallel to the x direction and disposed in a convergent beam behind the objective near the field image in the objective, the line scanning means comprise, firstly, a drum rotating uniformly around a stationary axis YY' contained in the plane P and bearing a number of flat reflecting surfaces regularly distributed around the drum periphery and, secondly, an image-conveying means symmetrical with respect to the plane P and forming an image of the detector at a fixed point A' along the drum rotation axis YY'. the drum being placed in a convergent beam in the path of the image-conveying means on the image side of the detector, the point symmetrical with the point A' with respect to each surface of the drum, when the surface is perpendicular to the plane P, being in the neighbourhood of the point D which is symmetrical with the focus of the objective with respect to the raster mirror in a position parallel to the YY' axis, and the optical beam-deflecting system comprises a concave or "field" mirror having the plane P as the plane of symmetry, the apex of the mirror being near D on the ZZ' axis extending through D and perpendicular to the YY' axis, the mirror being so disposed that it conjugates the centre 0 of the exit pupil of the objective with a fixed point 0' on the YY' axis, point 0' being symmetrical with respect to the ZZ' axis with the point where the optical axis of the objective intersects the YY' axis; in order, if required, to ensure that the idle scanning time between two consecutive lines is zero, the field mirror also has a width in the x direction which 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 mirror being moved if required for small distances in phase with the movement of the raster scanning means, the small motion comprising reciprocation in translation along the ZZ' axis in the neighbourhood of D and reciprocating rotation around an axis parallel to the x direction, which is symmetrical with respect to the ZZ' axis, the amplitude of the motion in translation being such as to correct the defocusing introduced by the raster scanning means and the amplitude of the rotation being such as to ensure that the field mirror holds 0', the conjugate of the centre 0 of the exit pupil of the objective, in a constant position during the reciprocating rotation of the raster scanning means, characterised in that the means for conveying the image of the detector which is disposed outside the YY' axis comprises a set of two concave mirrors in the form of portions of paraboloids of revolution, one mirror having the YY' axis as axis of symmetry and the focus A', the detector being disposed at the focus of the other mirror, a system of one or more plane mirrors being used for deflecting the beam from one paraboloid to the other in parallel rays.

3. A device according to the main patent, and including a system of conveying the image of the detector on axis YY' according to Claim 1 or 2.

4. A device for optically scanning a field of vision, the device being substantially as herein described with reference to, and as shown in, Figure 1 alone or Figure 1 modified as shown in Figure 2 of the accompanying drawings.