Abstract

The inherent parallelism of optics is attractive for true time delay beamforming in phased-array antennas performing wide instantaneous bandwidth over wide scan angles. Following the concepts presented in ref. (1), the microwave signal originates from the coherent detection by a high speed photodiode, of a dual frequency beam, obtained from an acousto optic Bragg cell. We present the implementation of an optical architecture based on polarization switching by N spatial light modulators of p × p pixels. This original arrangement of these modulators provides 2^N optically controlled time delays. Furthermore we also propose and experimentally demonstrate a new technique that provides a dynamic alignment of two beams at different frequencies over a wide bandwidth. It involves an original application of the interaction between the beams in a photorefractive BaTiO₃ crystal. A single frequency laser beam (ω₀/2π) is focused through a Bragg cell excited by a continuous microwave signal (fo). The emerging beams at (ω₀/2π) and (ω₀/2π+f₀) intersect in the BaTiO₃ crystal. They undergo self fanning processes and are coupled, via noise figures in the direction of the (ω₀/2π) beam. When fo is modified, the direction of the (ω₀/2π + f₀) beam changes but these two beams remain coupled in the fixed direction of (ω₀/2π), allowing the use of a large bandwidth microwave signal. The optical amplification of a microwave signal in a photorefractive crystal (2) is also discussed.

© 1990 Optical Society of America