Optical logic planes and interconnect components for optical digital processing demonstrators

Opto-thermal bistable nonlinear interference filters (NLIFs), despite being relatively slow devices (in the range 1 µs-1 ms), are better suited to building optical digital circuits than the faster (1 ns to 100 ns) nonlinear GaAs etalons which have a continuing problem with regard to stability under continuous operating conditions. ZnSe NLIFs, when configured as bistable etalons with absorbed transmission (BEAT) devices, can operate stably at near-infrared wavelengths 830 nm, 1.06 µm, etc.) with input powers of a few milliwatts. The authors describe recent advances in the fabrication of these devices with particular reference to thermal engineering of substrates, including pixellation, and the preparation of devices with very high spatial uniformity suitable for optical logic array operation. The latter involves the use of a novel molecular beam deposition (MBD) technique to produce very high quality layers of ZnSe and other materials in a UHV environment, with thickness variations of as little as ± 0.05% over 80 mm diameter. Of equal importance are the holographic techniques which can provide both the optical wiring between arrays of optical logic elements and the input optics for providing multiple power beams needed for operation. Both spatially-invariant and spatially-variant holographic optical elements (HOEs) have been developed for a variety of functions. Development of a 16 × 16 optical logic array which utilizes both the NLIF-BEAT and HOE technologies is described.