1996 International Topical Meeting on Optical Computing, Sendai, Japan, April 21-26.

2

ion-implanted MQW structure is low ~ 0.1mW/cm2 [4] and the gratings for the high spatial frequency components in the input image were saturated. In this case the carrier index gratings for all the spatial frequency components have the same strength which is equivalent to a thresholding operation on the power spectrum. Additionally some hard clipping in the index variation may be expected so that the device operates similar to the thresholded and binarized JTC [5]. Figure 3 shows the correlation result for two identical circles of light in the input image, the experimental result with the MQW device is shown above the simulation result for the thresholded and binarized JTC.
We used a video-rate frame grabber card to capture the image from a CCD camera and combined this with a previously stored image using a scan converter. This was input to the SLM allowing the correlation output to be recorded as the input was changed in real time against a fixed reference image. Results will be presented showing that the system showed high discrimination between different face inputs. Figure 4 shows a result of changing facial expression in the input. The correlation output is influenced most strongly by the high spatial frequency

components in the input, i.e. its edges. A change in facial expression still contains much of the original edge information and a large correlation peak results. Video input to the correlator allows changes in the input to be tested simply, such as the tolerance of the correlation signal to a few degrees of rotation. We will report on the auto-correlation and cross-correlation signals between different individuals [6].
The photorefractive MQW device has many advantages for a pattern matching system based on the JTC. It offers a low power and compact laser diode based system with diffraction limited resolution and high correlation rate. It has potential for high frame rate throughput for applications such as searching large data bases.

Acknowledgements. The semiconductor MQW device was grown by MBE, and the thin film layers deposited, at the Institute for Microstructural Sciences of NRC.

References.
[1]. A. Partovi, et. al., Appl. Phys. Lett. 62, 464 (1993). [2]. A. Partovi, A. M. Glass, T. H. Chiu, D. T. H. Liu, Opt. Lett. 18, 906 (1993). [3]. S. A. Boothroyd et. al. paper WJJ2, W. S. Rabinovich et. al. paper WX6, OSA annual meeting, Sept 10-15, Portland, Oregon 1995.
[4]. A. M. Glass et. al., Opt. Lett. 15, 264 (1990). [5]. B. Javidi, C. J. Kuo, Appl. Opts. 27, 663 (1988). [6]. Video clips of the real-time face input tests will be available on the internet at http://alpha.ps.iit.nrc.ca.

Figure 3. Auto-correlation peaks for input of two identical circles of light. See text for details.

Figure 4. Auto- and cross-correlation peaks from the face recognition system.