Spot-array generation using a 2-D acousto-optic deflector

Abstract

Spot array generation is essential for optical computing architectures based on free-space interconnections. Acousto-optic (AO) deflectors are potentially attractive for reconfigurable array generation or interconnection because of their large space bandwidth product and switching times of a few microseconds. In this paper, we describe the procedure and present experimental results of using a large aperture integrated two-dimensional (2-D) AO deflector to generate reconfigurable 2-D spot arrays. The generation of 2-D spot arrays is achieved by driving each of two orthogonally mounted AO deflectors with a high-frequency carrier that is phase modulated with an electronic equivalent of a holographic phase grating. The carrier deflects the incident beam by the Bragg angle, while the modulating signal gives rise to the spot pattern. The 2-D AO spot array is realized as the outer-product of two 1-D spot arrays. 1-D phase grating structures were calculated using several nonlinear optimization techniques including a genetic algorithm and the Gerchberg-Saxton algorithm. In our experiments, the AO device was used for realizing both discrete (e.g., binary, 4-level) and continuous phase gratings. The continuous phase profiles give higher diffraction efficiency. Practical limitations encountered in the generation of 13x13,21x21 and 50x50 spot arrays are discussed.