GB2244363A

GB2244363A - Optical feedback system

Info

Publication number: GB2244363A
Application number: GB9011556A
Authority: GB
Inventors: Stuart Andrew Reid
Original assignee: GEC Marconi Ltd; Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1990-05-23
Filing date: 1990-05-23
Publication date: 1991-11-27
Anticipated expiration: 2010-05-23
Also published as: GB2244363B; GB9011556D0

Abstract

An optical feedback system includes a polarising beam splitter 12 to receive light from an input 10 and direct light on to a first source 18 formed by detectors 14 and associated liquid crystal reflectors 16. A reflector, 20, having portions which either maintain or rotate the polarisation of the reflected light receives light reflected from the first source 18 and reflects light back to the beam splitter 12, the beam splitter 12 serving to direct the reflected light on to a second source 22, the arrangement being such that light can be reflected from the first source 18 on to the second source 22 and vice versa along the same path via the reflector 20. <IMAGE>

Description

Optical Feedback System The present invention relates to an optical feedback system and particularly, though not exclusively, to such a system for use in a neural network.

Previously proposed optical feedback systems have comprised a horizontal array of LED elements, the output from the LED elements being scanned vertically on to a mask having predefined transmissive regions and non-transmissive regions.

The output from each horizontal line on the mask is focused on to a corresponding detector in a vertical array of detectors.

The received signal at the array is then fed back to the LEDs to control the output therefrom. After several passes of a signal through the system, a substantially constant output state is achieved which represents the stored pattern of closest similarity to the input pattern.

Other previously proposed systems have included at least one source arrangement comprising a row of detections and a corresponding row of associated reflectors (hereinafter "sources").

The present invention arose in an attempt to provide a compact system which functions generally as described above.

According to the present invention, there is provided an optical feedback system comprising: a beam splitter to receive light from an input and arranged to direct light onto a first source, a reflector having reflective and non-reflective portions being arranged to receive light from said first source and to reflect light back to said beam splitter, the beam splitter serving to direct the reflected light on to a second source, the arrangement being such that light can be reflected from the first source on to the second source and vice versa along the same path through the system via the reflector.

Preferably, the first source is, a vertical array of detectors and reflectors and the second source is a horizontal array of detectors and reflectors.

The system conveniently operates when the light from a region of the first source is expanded horizontally before impinging upon the reflector and the light from a vertical array of parts of horizontally expanded regions is focused on to a region in the second source.

It is particularly preferred that light from the input is polarised, the beam splitter typically comprising a polarising beam splitter.

The reflector is typically variable such that the reflective and non-reflective portions can be changed.

The present invention will now be described, by way of example with reference to the accompanying drawings, in which: Figure 1 shows a plan view of a system according to one embodiment of the invention; Figure 2 shows a perspective view of the system shown in Figure 1; and Figure 3 shows a perspective view of a further embodiment of the present invention.

Referring now to Figures 1 and 2, the system shown therein comprises a light source 10 arranged to direct a beam onto a polarising beam splitter 12. The source 10 is typically a polarised laser source arranged to present a desired beam to the system. The laser light is vertically polarised with respect to claim of the drawing (indicated by *). The beam splitter 12 causes such polarised light to be directed on to vertical column of detectors 14 which together with associated liquid crystal reflectors 16 form a first source 18. In cases where light is detected by detector 14, the associated reflector 16 is enabled such that the polarisation of the reflected light is rotated by 900 (indicated by ^). In cases where the reflector is not enabled, the polarisation of the reflective light remains the same (*).The light reflected by the source either passes straight through the beam splitter if polarisation has been changed or is reflected out of the beam splitter if polarisation remains the same. A spatial light modulator (SLM) reflector 20 is arranged on the opposite side of the beam splitter 12 from the first source 18 and comprises a square array of reflectors which either maintain or rotate the polarisation of the reflected light according to a pre-programmed pattern. A second source 22 is arranged adjacent to the beam splitter 12 parallel to the first source to SLM path and a focusing device 24, typically a hologram lens, is disposed between the second source 22 and the beam splitter 12. Light which is reflected from the SLM 20 with rotated polarisation is directed from the beam splitter 12 via the hologram 24 on to the second source 22.The second source comprises a horizontal array of detectors 26 and reflectors 28 similar to the first source 18.

In use, light from the reflector 16 of the first source 18 which passes through the beam splitter 12 is scanned across a whole row 30 of reflective elements in the SLM 20 corresponding to a single reflector in the first source 18.

The light reflected from the SLM on to the second source is focused by the hologram 24 such that the light from a whole vertical row 32 is focused on to one detector/reflector element 34 of the second source 22. In the reversed direction, light from one element 34 of the second source is scanned on to the corresponding vertical column on the SLM via the hologram and the beam splitter and light from a horizontal row of the SLM is focused on to a corresponding detector of the first source. The pattern detected by the second source can be fed electrically to the first source if required.

Hence, a light signal can be fed between the first and second sources via the SLM and so the image pattern can be modified by programming the SLM and by feeding information between the first and second sources.

It will be appreciated that in this arrangement, the polarisation changes must be controlled if the appropriate feedback is to be achieved using such a beam splitter.

An alternative arrangement is shown in Figure 3 which utilises strip detectors 40 and strip polarising reflectors 42 to form the source 44, 46. The detectors 40 and reflectors 42 in one source are arranged at right angles to those in the other source to ,achieve the same effect as described above and two beam splitters 48, 50 are provided. In this case, no focusing means are required and the SLM 52 is disposed between the first source 44 and the beam splitters 48, 50.

A system such as that disclosed above can find uses in neural networks as it is possible to take image information which can be passed through the system several times between the first and second sources via the SLM until a substantially constant signal is received. In such a case, the information in the signal will then correspond to the programming of the SLM and allow a recognition pattern to be developed. It is suggested that approximately 15 passes of a signal through the system would be required to obtain a suitable output, each passage through the system taking less than 1 mS.

Claims

1. An optical feedback system comprising: a beam splitter to receive light from an input and arranged to direct light on to a first source, a reflector having reflective and non-reflective portions being arranged to receive light reflected from said first source and to reflect light back to said beam splitter, the beam splitter serving to direct the reflected light on to a second source, the arrangement being such that light can be reflected from the first source on to the second source and vice versa along the same path through the system via the reflector.

2. A system as claimed in claim 1, wherein the first source is divided in to a plurality of regions in a vertical array and the second source is divided in to a plurality of regions in a horizontal array.

3. A system as claimed in claim 2, wherein the first source comprises horizontally elongate regions and the second source comprises vertically elongate regions.

4. A system as claimed in any preceding claim, wherein light from each region of the first source is expanded horizontally before impinging upon the reflector and the light from a vertical array of parts of horizontally expanded regions is focused on to one of the regions in the second source.

5. A system as claimed in any preceding claim, wherein the light from the input is polarised and the beam splitter comprises a polarising beam splitter.

6. A system as claimed in any preceding claim, wherein the sources comprise co-linear arrays of detectors and operable reflecting elements.

7. A system as claimed in claim 5 or 6, wherein the operation of the reflecting elements serves to change the polarisation of reflected light.

8. A system as claimed in any preceding claim, wherein the reflective and non-reflective portions of the reflector can be changed.

9 A system which is substantially as herein described with reference to Figures 1 and 2.

10. A system which is substantially as herein described with reference to Figure 3.

11. A neural network comprising one or more systems as claimed in any preceding claim.