Personal ammonia sensor for industrial environments.

The realisation of an opto-chemical ammonia sensor suitable for personal monitoring tasks is described, comprising a cyanine dye immobilised in a microporous glass thin film. The fabrication of sensor platforms incorporating embossed grating couplers provides a compact optical design with effective waveguiding characteristics, resulting in reversible ammonia sensitivity in the 5-100 ppm range in under 2 min. Cross-sensitivity of sensor response with water and other potential interferents is considered.

Correlation and image recognition with surface-scattered light.

Image recognition by use of coherent optical processors and light diffusely scattered from the surface of an optically rough object is reported. A theoretical description is presented and shows that the image speckles are carriers for the Fourier spectra of the object at the matched spatial-filter plane. Experimental results of optical autocorrelation and cross correlation are given. The change in the intensity of the correlation peak that arises from the translation and the rotation of objects and from the lateral and axial movements of the matched filter are examined. The system is shown to be tolerant to misalignments in the positions of the object and matched filter. It is also shown that, when diffuse light is input into the coherent optical processor, the position of the Fourier plane is no longer precisely defined and spatial multiplexing would be possible.

Contrast enhancement of underwater images with coherent optical image processors.

The use of coherent optical processors for improving the quality of degraded underwater images is discussed, and a holographic filter suitable for the enhancement of contrast in underwater images is described. The filter is a modified matched spatial filter, and it performs a nonlinear local contrast enhancement. The theory of the operation of the coherent optical image processor with this new filter is presented and experimentally verified. The removal of the backscattered light from underwater images is demonstrated under laboratory conditions. The results show an improvement in the overall image contrast.

Fiducial markers for increasing the versatility of optical correlation in the measurement of faults on integrated-circuit wafers.

A microscope-coherent optical processor is used for the measurement of the registration errors on integrated-circuit wafers. The measurements are obtained from the optical correlation of wafers with reference wafer patterns by use of matched spatial filters. Previously, the intricate pattern of the active circuit area of wafers has been used in the correlation process, and a new matched spatial filter had to be created for each different integrated circuit. Here, the results of using comparatively plain fiducial markers on a wafer for the registration-error measurement are presented, and these show that the measurements can be made independent of the design of the integrated circuit while maintaining the advantages and accuracy of the optical correlation technique.

Wafer fault measurement by coherent optical processor.

A microscope coherent optical processor based on the VanderLugt optical correlator is applied to the measurement of registration error in multilayer integrated-circuit wafers. A treatment of the effects of wafer faults on the correlation signal is given. Threshold criteria and fault-induced peak splitting of the correlation signal from reject production samples are exploited to demonstrate the easy and rapid detection of faults in partially processed integrated-circuit wafers.

The application of a coherent image processor to the enhancement of radiological images.

Results of the investigation of the viability of using a coherent optical processor to improve image quality prior to digitization and analysis are presented. Optical processing of small (20 mmx20 mm) and large (100 mmx100 mm) radiological images to improve contrast and enhance edges is demonstrated. A brief summary of the principle of operation of the coherent optical processor is given. Results obtained with the apparatus described here are presented and discussed.