Observations of and applications for self-imaging in optical fibers

Experimental results of self-imaging in optical fibers are reported along with an analytical model that explains the observations. Some implications for sensor design are discussed.     

Space-variant optical logic operations based on operation-dependent encoding method

We propose performing space-variant optical logic operations in a space-invariant optical system by selectively assigning encoding states that are operation dependent. With this method, encoders using liquid-crystal cells and liquid-crystal light valves to perform space-variant encoding for all 16 Boolean functions are designed. Multiple-instruction-multiple-data processing can then be realized in optical logic systems.     

Shift-invariant interpattern association neural network

A shift-invariant neural network that uses the translation-invariant property of the modulus Fourier spectra with the heteroassociation interpattern association memory is proposed. A binary encoding of a spectral sampling of the training set is used to preserve the main features. Computer simulations and experimental demonstrations are provided that show the shift-invariant property of the proposed optical neural network.     

Three-channel solar radiometer for the determination of atmospheric columnar water vapor

The design of a three-channel solar radiometer used to determine total columnar atmospheric water-vapor amounts is presented. The main channel is located in the 0.94-μm water-vapor band, and two other channels are located in adjacent nonabsorption regions of the solar spectrum and are used to remove scattering effects from the main channel. Water-vapor transmittance is determined by means of a modified Langley approach, and these transmittances are converted to columnar water vapor by means of a band model developed at the University of Arizona. Several cases are presented in which columnar water-vapor amounts are determined through the use of the instrument and method described here. These results are compared with sounding-balloon results. Tests of the method indicate that columnar water vapor may be retrieved with an uncertainty of less than 10%.     

Object illumination angle measurement in speckle interferometry

Errors in measurement of the object illumination angle affect fringe interpretation accuracies in speckle interferometry. To measure the object illumination angle we propose a method based on the moiré effect. The technique is easy to implement and was found to yield fast and accurate measurements.     

High-bandwidth laser-pulse generator using continuous-wave lasers

A laser-pulse generator for the transfer of continous-wave (cw) absolute radiometric calibrations to high-speed pulse photodetectors is described. The cw input lasers are modulated by a spinning polygon mirror in a ring cavity to produce high-speed, constant-amplitude, constant-shape laser pulses. Constantamplitude outputs range temporally from cw to 15-ns full-width at half-maximum (FWHM) Gaussian pulses. An all-reflective optical design permits operation of the device from the visible to the far-infrared spectral regions. Design and performance estimates for the pulse generator as well as experimental verification are presented.     

White-light reconstruction setup for shearograms using optical-fiber waveguides

A white-light reconstruction setup for shearograms using optical-fiber waveguides is presented. The setup is compact, is not susceptible to dust and scratches, and enables the two-dimensional fringe pattern on shearograms to be viewed directly under uniform and enhanced illumination with minimal image distortion.     

On finite dynamic equations for fluid-saturated porous media

Summary The paper concerns the relations between two principally different approaches to the formulation of momentum balance equations in porous media theories, namely, the dynamic approach similar to Biot's theory and the modern approach as a result of mixture theories extended by the concept of volume fractions. In particular, it is shown that both approaches necessarily lead to the same type of momentum balance equations and furthermore contain, in a certain sense, within the geometrically linear case, the well-known classical equations of Biot's theory.     

Effect of inhomogeneous turbulence on imaging through turbulent layers

An analysis of the effect of inhomeogeneous turbulence on the point-spread function for imaging through a turbulent layer has been performed. The formulation retains the concept of the modulation-transfer function that has been used in the past for homogeneous turbulence layers, but the integration now depends on more than just the separation distance ρ in the plane of the aperture. An example is chosen in which the rms optical path difference increases by a factor of 3.51 from one side of the aperture to the other in the flow direction. It was found that the results were insensitive to the angle between the separation-distance vector ρ and the flow direction. Surprisingly it was found that the detailed resultswere within a few percent of those obtained with constant-turbulence parameters evaluated at the center line of the aperture.     

Validation of interferometric imaging from a pupil-masking experiment on a solar telescope

We present the results of a pupil-masking experiment that uses the Sun as the source object. The goal of our experiment was a proof-of-concept validation for a Fizeau (image-plane) interferometric beam combination with a complex source that overfilled the field of view. We employed a phase-diversity technique to measure the optical phases required to recover the instantaneous optical transfer function for the masked pupil. We used a Wiener filter to deconvolve the dirty images.