Shudong Wu

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.

Two-dimensional programmable optical neural network.

A 2-D hybrid optical neural network using a high resolution video monitor as a programmable associative memory is proposed. Experiments and computer simulations of the system have been conducted. The high resolution and large dynamic range of the video monitor enable us to implement a hybrid neural network with more neurons and more accurate operation. The system operates in a high speed asynchronous mode due to the parallel feedback loop. The programmability of the system permits the use of orthogonal projection and multilevel recognition algorithms to increase the robustness and storage capacity of the network.

Sensing with fiber specklegrams

The fiber specklegram is highly sensitive to the relative modal phases and is of multiplexing capability. Its properties are analyzed and experimentally demonstrated.

Optical disk based neural network.

Using an optical disk as a large capacity associative memory in an optical neural network is described. The proposed architecture is capable of data processing at high speed.

Speckle-induced phase error in laser-based phase-shifting projected fringe profilometry

Laser sources offer advantages over white-light sources in some phase-shifting projected fringe profilometry applications. These benefits, however, are gained at the cost of incurring speckle noise. Some basic statistics of speckle-induced phase-measurement errors are investigated based on the multiplicative noise model for image-plane speckles. First, the dependence of phase-error distribution and measurement uncertainty on speckle size and grating pitch is numerically studied, based on the Karhunen–Loeve expansion method. Then an analytical expression that relates phase-error distributions to optical system parameters is derived as a direct extension of the simulation results. This expression is useful for system design and optimization. Analysis shows that phase noise caused by speckles can be modeled as additive white Gaussian noise. Optical system design and noise-reduction algorithms are also briefly discussed, based on the simulation results.

High-performance nonscanning Fourier-transform spectrometer that uses a Wollaston prism array

A high-performance nonscanning Fourier-transform spectrometer is reported that is composed mainly of a Wollaston prism array and a two-dimensional photodetector array. It is a substantial improvement over existing Wollaston prism based nonscanning Fourier-transform spectrometers because it offers finer spectral resolution and smaller size. Such spectrometers will find important applications in remote chemical and biological sensing, environmental monitoring, medical diagnosis, etc. Experimental results are consistent with theoretical analyses.

Laser-modulated phase-stepping digital shearography for quantitative full-field imaging of ultrasonic waves

Measurement of surface displacements due to ultrasonic wave propagation in elastic solids has traditionally been studied using single-point measurement techniques such as ultrasonic transducers or interferometers. Full-field methods, excluding scanning techniques, are uncommon; examples include holographic interferometry and Schlieren imaging. In many cases, these techniques have been used to yield qualitative results due to inherent difficulties in processing the data. Laser-modulated phase-stepping digital shearography is a full-field, common-path, interferometric method which can be used to quickly visualize ultrasonic wave fields. A shearography system will be described that provides not only whole-field images of ultrasonic waves, but quantitative displacement data within these fields. Images are shown of propagating plate and bar waves, and mathematics relating the calculated optical phase to the ultrasonic wave parameters are presented.

Multichannel sensing with fiber specklegrams

A fiber specklegram sensor for multichannel sensing is presented. Analyses and experiments show that a fiber specklegram sensor (FSS) is highly sensitive to the modal phasing variation of a multimode-sensing fiber. It is shown that the FSS is less vulnerable to environmental factors than the two-arm interferometric fiber-sensing technique. Because the FSS processes a narrow spectral bandwidth, it is particularly suitable for wavelength multiplexing. One of the major advantages of the FSS must be the multiplexing capability, in which multiparameter sensing can be realized in a single fiber. Applications of the FSS system to acoustic-sensing array, structural fatigue monitoring, and smart emission detection are also discussed.

Application of Phase Shift Optical Triangulation to Precision Gear Gauging

Traditionally, gear tooth profile is measured by coordinate measurement machines using mechanical probe scanning, which is very time consuming. Therefore, normally only a few lines are scanned across the gear tooth surface, which often do not faithfully represent the whole tooth surface profile. In this paper, a phase-shift optical triangulation technique is applied to the gear profile measurement, which has the advantages of redundant information, speed and non-contact nature. When examining a 2 cm2 area, comparative measurement accuracy better than 1 micrometers and resolution about 0.1 micrometers has been successfully demonstrated with the system; this corresponds to a 5 by 10-5 relative accuracy. The measurement result from the optical system displaced good correlation with those form a mechanical probe on a coordinate measurement machine. A few teeth/second measurement speed can also be expected. Different factors to effect the measurement accuracy are discussed, and the possible solutions are provided.