Multi-Gb/s Optical Cross-connect Switch Architectures: TDM versus FDM Techniques.

We study two specific techniques to implement an electro-optical cross-connect switch: Time Division Multiplex (TDM) and Frequency Division Multiplex (FDM). Both methods offer the potential of switch sizes larger than existing ones with lithium niobate couplers. In the TDM technique, data pulses from different inputs are time compressed so that they can be time multiplexed through a star coupler. At each output of the star coupler, an optical "AND" gate is used to pick out any desired input signal. In contrast, the FDM method puts different input data signals on different laser frequencies so that they are frequency multiplexed via the star coupler. Each output recovers its desired signal with a frequency tunable receiver, which can be implemented with either a frequency tunable laser (coherent receiver) or a tunable filter (direct detection receiver).