Compact bidirectional optical interconnects using arrays of vertical cavity surface-emitting lasers

A compact optical crosspoint switch is being fabricated at the University of Colorado. It consists of two identical smart pixels arrays (SPAs) which face one another. The arrays communicate using 64 optical channels in both forward and reverse directions. Each channel uses a vertical-cavity surface-emitting laser (VCSEL) which is collimated using a microlens. The collimated beam is routed to the appropriate photodetector on the facing array using a Fourier computer generated hologram (CGH). Each VCSEL has a separate hologram associated with it, allowing space variant interconnection between the facing arrays. Each SPA has an 8 by 8 array of VCSELs adjacent to an 8 by 8 array of photodetectors and smart pixel circuitry. These are integrated with the microlenses and holograms and packaged to form a compact and stable system, occupying several cm3. At present each smart pixel has several logic gates, but an optically similar system with approximately 1000 gates per pixel is under development. This type of interconnection is suited to board-to-board applications, and potentially offers high speed, low cost, high density bi-directional connections. The fabrication of the switch incorporates several novel integration techniques.