Francis T. S. Yu

Fiber Optic Sensors

Fiber optic sensors have become indispensable tools for biomedical study because of their unique features such as (1) high sensitivity, (2) small footprint and endoscopic compatibility, (3) multiple agent distributive sensing capability, and (4) immunity from electromagnetic interference. In this chapter, we will provide a brief overview on the basic principle of fiber optic sensors, types of fiber optic sensors, and their applications to biomedical sensing. As a result of the page limitation, important work in this area may not be included in this chapter. Readers may find those contents in the listed reference material. Keywords: fiber optic sensors; light; sensing mechanism; biomedical sensing

Adaptive real-time pattern recognition using a liquid crystal TV based joint transform correlator

Recently, many applications of the liquid crystal television (LCTV) to real-time signal processing have been reported. A basic description of the application of the LCTV to realtime pattern recognition was first reported by Liu et al. Gregory later also showed a successful space-invariant correlation using a LCTV as a spatial light modulator. Both methods were based on the use of a complex matched (VanderLugt) spatial filter. The joint transform architecture is an alternative approach to optical pattern recognition. The joint transform method has proved to be suitable for adaptive programmable correlation because no matched spatial filter is required. The reference pattern may simply be generated by a computer and input to a low space-bandwidth product (SBP), electronically addressed, spatial light modulator. Conversely, it is very difficult to generate a dynamic matched spatial filter in the Fourier plane. A microcomputer-based programmable optical correlator using a magnetooptical device (MOD) and a liquid crystal light valve (LCLV) was proposed recently by Yu and Ludman. In this Letter, a new implementation of the real-time joint transform correlator architecture using inexpensive LCTVs will be discussed. Preliminary experimental results are presented to verify the usefulness of the technique. There are three major objections to using commercially available liquid crystal TVs for optical processing applications: (1) low contrast ratio, (2) phase nonuniformity, and (3) low resolution and low SBP. These problems must be minimized if a LCTV is to be used as a spatial light modulator in a coherent optical system. The contrast uniformity

Self-organizing optical neural network for unsupervised learning

One of the features in neural computing must be the ability to adapt to a changeable environment and to recognize unknown objects. This paper deals with an adaptive optical neural network using Kohonens self-organizing feature map algorithm for unsupervised learning. A compact optical neural network of 64 neurons using liquid crystal televisions is used for this study. To test the performance of the self-organizing neural network, experimental demonstrations and computer simulations are provided. Effects due to unsupervised learning parameters are analyzed. We show that the optical neural network is capable of performing both unsupervised learning and pattern recognition operations simultaneously, by setting two matching scores in the learning algorithm. By using a slower learning rate, the construction of the memory matrix becomes more organized topologically. Moreover, the introduction of forbidden regions in the memory space enables the neural network to learn new patterns without erasing the old ones.

Effects of fringe binarization of multiobject joint transform correlation

A study of the effect of fringe binarization on the joint transform correlator has shown that the interference fringes for multiple targets could produce false alarms and misses.

Simple method for measuring phase modulation in liquid crystal televisions

The relative phase shift of light transmitted through a liquid crystal television (LCTV) panel as a function of the applied voltage on the LCTV can be obtained by writing a Ronchi grating pattern to the LCTV and measuring the intensities in the diffraction pattern at the Fourier plane combined with the amplitude modulation factor. A kinoform is synthesized on the LCTV based on the measured phase shift demonstrating the phase-mostly modulation.

Wavelength multiplexed holographic storage in a sensitive photorefractive crystal using a visible-light tunable diode laser

Abstract Wavelength multiplexed holograms using a Ce:Fe: doped LiNbO 3 crystal with a visible-light tunable diode laser are reported. The advantages of wavelength multiplexed reflection type holograms are discussed. It is shown that the wavelength multiplexed holograms offer a more uniform selectivity over all the construction angles, as compared with the angularly multiplexed crystal holograms.

Wavelength multiplexed reflection matched spatial filters using LiNbO3

Abstract The wavelength multiplexing properties of a reflection filter are investigated. A photorefractive LiNbO3 crystal was used to construct an experimental filter. The wavelength selectivity and shift invariant properties of the filter were analyzed and experimentally verified.

Reconfigurable interconnections using photorefractive holograms

Using coupled wave theory and the law of refraction, diffraction properties of volume holograms are discussed. Reconfigurable interconnections by either wavelength tuning or spatial division techniques are proposed. Reflection type volume holograms can be used for a large number of reconfigurable interconnections in terms of finite wavelength tunability. Transmission volume holograms encoded in pinhole holograms can be easily reconfigured by spatial light modulator. Experimental demonstrations obtained by using these methods are presented.

Submicrometer displacement sensing using inner-product multimode fiber speckle fields.

A multimode fiber sensor using the intensity inner product of speckle fields is presented. The sensitivity and the dynamic range of the displacement sensing are quantitatively analyzed. We show that the sensitivity of displacement can be in the submicrometer range. Experimental performances show that the results are consistent with the calculated results.

Microcomputer-based programmable optical correlator for automatic pattern recognition and identification

A microcomputer-based programmable optical correlator (MPOC) is proposed for automatic pattern recognition and identification. A programmable magneto-optic spatial light modulator and a liquid-crystal light value are used to perform a real-time joint-transform correlation operation. Since the proposed MPOC consists of a microcomputer and an optical processing system, it has the advantage of real-time programmable processing capability for large space-bandwidth-product information. The basic theory and a feasibility study of the technique are given.