Multichannel Bragg Cell Research Articles

Paratellurite: Propagation of the slow shear wave in the (001) plane. New formulations for the acoustic velocity and divergence

The propagation of the slow shear wave in paratellurite with an angular tilt θ from the [110] axis in the (001) plane is considered. Original formulations are given for the acoustic velocity, the power flow angle, and the acoustic divergence. For a small angular deviation, the acoustic spreading is greatly reduced. This configuration can be used for multichannel Bragg cells. In order to demonstrate the feasibility of such a device, a three-channel Bragg cell (θ=5°) has been designed and successfully tested.

Multichannel Bragg cells: design, performance, applications

Multichannel Bragg cells are important components in many two-dimensional optical information processing systems. Multichannel Bragg cell design principles are discussed for both multichannel deflectors and modulators. Particular emphasis is placed on minimization of acoustic and electrical crosstalk and thermal effects through the use of acoustically anisotropic materials, rf stripline techniques, and high thermal conductivity materials. The use of a self-collimating shear mode in gallium phosphide (GaP) is found to substantially reduce acoustic crosstalk from that found in the commonly used tellurium dioxide cells. The use of stripline transmission lines substantially reduces electrical crosstalk over that obtained using the more conventional microstrip techniques. The performance is described of three different GaP multichannel Bragg cell deflectors and a GaP multichannel Bragg cell modulator designed using the principles Bragg cell deflectors and a GaP multichannel Bragg cell modulator designed using the principles outlined in this paper. Optical processing systems using multichannel Bragg cells for phased array antenna signal processing, multichannel rf spectrum analysis, and digital optical computing are discussed.

Acousto‐optic two‐dimensional coherent optical modulator

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Simple Phase-Tracking Measurement Technique For Multichannel Bragg Cells

A simple and accurate phase-tracking measurement technique for multichannel Bragg cells is presented. The procedure is carried out by illuminating two adjacent channels at a time and then comparing the relative positions of the diffraction fringe patterns in the Fourier plane to obtain the relative phase distribution. The application of this technique is demonstrated using a five-channel Bragg cell.

Multichannel Bragg cells: compensation for acoustic spreading

In some applications, the performance of multichannel Bragg cells is compromised by the spreading of the acoustic waves as they propagate; the spreading causes the signals in the channels to overlap. The overlapping can be significantly reduced by a spatial filter in a Fourier–image plane. The spatial filter is shown to be a cylindrical lens whose power is a function of the distance from the transducer. The effects of changes in the drive frequency as well as those of displacements of the filter are calculated. The reduction in the modulation transfer function as a function of propagation distance is calculated, and some bounds on the time–bandwidth product and the number of channels are dserived. In general, the overall performance can be improved by increasing the center frequency of the Bragg cell while keeping the bandwidth fixed.