Design and tolerancing comparisons for S-SEED-based free-space switching fabrics

A series of experiments has been performed to determine the critical practical issues in high-density free-space optically interconnected systems. Some ofthese experiments have implemented switching fabrics by optically interconnecting 2-D arrays of symmetric seif-electro-optic effect devices (S-SEEDs). In the first, three 16 x 8 arrays of S-SEEDs, all operating as logic gates, were optically interconnected, and in the last experiment, afully interconnected switching fabric using six 32 x 32 S-SEED arrays was demonstrated. The practical realization of this technology represents a challenge to modern optomechanics because ofthe required optical resolution, mechanical precision, stability, and number of components involved. A comparison of these experimental systems shows that significant optical power loss may be incurred when theoretically "lossless" techniques are actually implemented, mainly because of the system complexity. The use of much simpler techniques is shown to dramatically decrease system assembly and alignment times and increase system stability, with similar overall loss. The tolerancing analysis used in these systems shows thatthe worst-case optical constraints result in mechanical tolerances in the micrometer to submicrometer range. The successful operation of these systems demonstrates the ability of relatively simple optical and mechanical techniques and materials to meet these tolerances.