Star-Coupler-Based Optical Cross-Connect Switch Experiments with Tunable Receivers

We discuss our research efforts aimed at exploring the feasibility of implementing an optical cross-connect switch using the star-coupler-based frequency-division-multiplex technique. In our experiments, we take advantage of state-of-the-art optical components such as monolithic tunable lasers and fiber Fabry-Perot (FP) filters. Two specific tunable receivers have been implanted. The first is a heterodyne receiver with a tunable laser as the LO, and the second is a tunable filter followed by a direct-detection receiver. In our system demonstrations, we have four frequency-locked transmitters with monolithic tunable lasers, each dithered with a slightly different frequency for the dual purpose of frequency locking (to a reference low-finesse fiber FP frequency comb) and positive channel identification upon signal reception. In the heterodyne receiver, the tunable LO is a monolithic three-section MQW DBR laser capable of a 1000 GHz tuning range. Receiver sensitivity was measured to be -38 dBm at 1 Gb/s (BER = 10−l0). The power margin in the system substantiated feasibility for a 400 × 400 switch. In the tunable-filter receiver, the tunable filter is a tunable two-stage fiber FP filter design consisting of a narrowband filter followed by a wideband filter. The tuning of the filters is computer controlled, and the combined filter has a tuning range of 15 000 GHz with a finesse of ≈ 5170. Therefore, it is capable of covering over 1000 channels of 2.9 GHz each. We measured receiver sensitivity to be −30 dBm at 1.7 Gb/s and −29 d Bm at 2.5 Gb/s (BER = 10−10). A brief discussion is provided for the tradeoffs between these two receiver techniques and their potential promises.