John P. Sharpe

Application of an optically addressed spatial light modulator to real-time speckle photography

Abstract The application of a bistable, binary, amorphous silicon ferroelectric liquid crystal optically addressed spatial light modulator to speckle photography is described. The system presented has a higher space-bandwidth product than a television system and can operate at greater than 500 Hz frame rates. The output is also amenable to further optical processing. The spatial light modulator is characterised for sensitivity, contrast ratio and resolution and speckle correlation fringes from a moving object are successfully obtained. Measurement of displacements in the range 20 μm to 70 μm with an rms error of 3 μm is demonstrated and the suitability of these devices to practical optical metrology is discussed.

A laboratory-based nonlinear dynamics course for science and engineering students

We describe the implementation of a new laboratory-based interdisciplinary undergraduate course on nonlinear dynamical systems. Geometrical methods and data visualization techniques are especially emphasized. A novel feature of the course is a required laboratory where the students analyze the behavior of a number of dynamical systems. Most of the laboratory experiments can be economically implemented using equipment available in many introductory physics microcomputer-based laboratories.

Smart-pixel spatial light modulator for incorporation in an optoelectronic neural network.

We present the design, fabrication, and testing of a novel liquid-crystal-on-silicon optically addressed spatial light modulator for use as a weight matrix in an ART-1 optoelectronic neural processor. Each pixel in the 50 x 83 element array occupies 75 microm x 75 microm and consists of a photodetector, a threshold circuit, a 1-bit (flip-flop) memory element, and a liquid-crystal modulating mirror. The array is designed to switch all the pixels initially to the ON state. Subsequently each pixel is independently switched to the OFF state if a superthreshold amount of light falls upon the pixels photodetector. The device has a contrast ratio of 20:1, a switch-on time (10-90% rise time) of 500 micros, and a switch-off time of ~500 micros (depending on the externally set threshold). Measured device uniformities and interpixel coupling are also described.

Observation of stochastic resonance using an optically addressed amorphous silicon/ferroelectric liquid crystal spatial light modulator

Abstract The phenomenon of stochastic resonance is predicted and experimentally verified using an amorphous silicon/ferroelectric liquid crystal optically addressed spatial light modulator. We exploit the bistability of aligned ferroelectric liquid crystal for use as the nonlinear element with the noise induced switching intensity set by an optical beam. Readout of the bistable system is also optical. Our measurements show the characteristic improvement in the output signal-to-noise ratio with increasing input noise intensity and the results agree qualitatively with both computer simulations and the predictions of a standard theory of stochastic resonance.

AN OPTOELECTRONIC SMART DETECTOR ARRAY FOR THE CLASSIFICATION OF FINGERPRINTS

Abstract The design and test results of an optoelectronic smart detector array for use in a fingerprint ridge extraction system are presented. The system comprises a microlens array for taking multiple Fourier transforms and an array of detectors with 8 or 16 elements. Each detector is composed of a set of wedge photodetectors with associated winner-take-all circuitry and encoders for reporting the maximally stimulated wedge element. The size of one pixel is 440 X 440 μm2. The rises and fall times of the detector were 80 and 750 μs, respectively. By using the system, the extraction of fingerprint ridge directions has been successfully demonstrated.

Morphological feature detection for cervical cancer screening

An optoelectronic system has been designed to pre-screen pap-smear slides and detect the suspicious cells using the hit/miss transform. Computer simulation of the algorithm tested on 184 pap-smear images detected 95% of the suspicious region as suspect while tagging just 5% of the normal regions as suspect. An optoelectronic implementation of the hit/miss transform using a 4f Vander-Lugt correlator architecture is proposed and demonstrated with experimental results.

Adaptive resonance theory and self-organizing morphological kernels

In this paper we describe our recent work developing automated methods for generation of kernels or structuring elements for use in the hit-or-miss transform. We show how a neural network algorithm (Fuzzy Adaptive Resonance Theory) generates hit and miss structuring elements that can be used with a fuzzy morphology to detect a class of objects and we illustrate with computer simulations.

Optoelectronic image processing for cervical cancer screening

Automation of the Pap-smear cervical screening method is highly desirable as it relieves tedium for the human operators, reduces cost and should increase accuracy and provide repeatability. We present here the design for a high-throughput optoelectronic system which forms the first stage of a two stage system to automate pap-smear screening. We use a mathematical morphological technique called the hit-or-miss transform to identify the suspicious areas on a pap-smear slide. This algorithm is implemented using a VanderLugt architecture and a time-sequential ANDing smart pixel array.

Optoelectronic feature extractor for classification of fingerprints

We present the design and test results of an optoelectronic feature detector array for use in a fingerprint ridge extraction system. The system comprises a microlens array for taking multiple Fourier transforms and an array of detectors. Each detector is composed of a set of wedge photodetectors with associated winner-take-all circuitry and encoders for reporting the maximally stimulated wedge element.