Preliminary Experimental Demonstration Research Articles

Absolute active frequency locking of a diode laser with optical feedback generated by Doppler-free collinear polarization spectroscopy

Absolute stabilization of the emission frequency of a laser diode can be achieved in a nearly all-optical scheme involving a resonant optical feedback from an atomic signal. We propose here two novel schemes of collinear Doppler-free polarization spectroscopy and report on preliminary experimental demonstrations of diode frequency locking performed on the D2 line of Rb.

Multiple-quantum-well nonlinear waveguide grating device

We report on the preliminary experimental demonstration of a multiple-quantum-well waveguide grating element. Due to optical nonlinearities in a multiple-quantum-well layer incorporated into the structure, the out-coupling angle of the grating is varied by the intensity of light in a guided mode. Experiments with GaAs-based planar as well as rib waveguide samples confirmed theoretical predictions. Changes in the coupling angle obtained are on the order of minutes. The demonstrated principle can be employed in fine tuning of the coupling angle, fine focusing of the output beam, or as a nonlinear beam-steering method for dispersion measurements.

Detection of multipath effect using a self-pumped optical phase-conjugate filter

A new optical Fourier domain filtering scheme that combines the conventional optical space-invariant linear filtering with a self-pumped nonlinear-optical phase-conjugation technique is proposed. The new method is used for a real-time detection and channel evaluation of the multipath information needed in radar, sonar, and communication signal-processing applications. Preliminary experimental demonstrations are included.

The determination of the microstructure of green coffee by acoustic microscopy

A ‘multiparameter’ method for indirect evaluation of intrinsic anisotropy values for prestressed engineering materials is discussed. The proposed method is based on simultaneous measurement of both the velocity of elastic waves and the parameters, characterizing the frequency dispersion and/or attenuation. Preliminary experimental demonstrations of the feasibility of such methods for common engineering materials are presented.

Microcomputer-Based Programmable Optical Signal Processor

A microcomputer-based real-time programmable optical signal processing system utilizing a magneto-optic spatial light modulator (MOSLM) and a liquid crystal light valve (LCLV) is described. This system can perform a myriad of complicated optical operations, such as image correlation, image subtraction, and matrix multiplication. Its important assets are its programmability and the capability of real-time addressing. These are important for telerobotic vision in space automation applications. Design specifications and suggestions for practical implementation of the system are discussed. Some preliminary experimental demonstrations are conducted to demonstrate applications of the proposed system to image correlation for optical pattern recognition, image subtraction for IC chip inspection, and matrix multiplication for optical computing.

Electronic damping of vibrations in optical structures

We have carried out a preliminary experimental demonstration of the feasibility of using external electronic circuits to damp mechanical vibrations in optical systems. The significance of the feasibility demonstration is that substantial levels of vibrational amplitude reduction were obtained with very small transducers in nonoptimal positions on noncritical portions of the optical structure. The prototype optical structure used in the experiment consisted of a membrane mirror stretched over a 25-cm diam glass frame with complex cross section. Five small piezoelectric transducers (19.05 x 3.18 x 0.28 mm) were applied with Duco cement at arbitrary positions on the glass frame. Acoustic excitation was then used to excite the resonances in the optical structure. These vibrational responses were measured, and one particular mode was chosen for the feasibility test. The structure was driven by external vibrations at the resonant frequency of the chosen mode until the membrane response was visible. One transducer as used to sense the vibrations in the frame, and this output was used to drive a negative feedback amplifier that drove one of the other transducers on the frame. With the feedback circuit active between two points on the frame, the vibrational response of the membrane to the external excitation was substantially reduced (7:1).