Bidirectional reconfigurable optical add-drop multiplexer with power compensation built-in optical amplifiers

A power-compensated bidirectional reconfigurable optical add-drop multiplexer (Bi-ROADM) based on tunable fiber Bragg gratings is proposed and demonstrated. By splicing a fiber Bragg grating (FBG) within a piece of an erbium-doped fiber, a lossless, low-cost, and simply structured Bi-ROADM is obtained. The total pumping power is 40mW with 0.6m of gain fiber for both upstream and downstream signals. The Bi-ROADM performance is evaluated using a bidirectional four-channel 50km lightwave transmission link using a 2.5Gbits/s bit rate per channel. Bit-error-rate (BER) performances show that the power penalties are 0.49 and 0.76dB at a 10−9 BER, respectively, for the 25km dropped channel and the 50km passed-through channel as compared to the back-to-back condition. An extra power penalty of only 0.2dB is observed for bidirectional transmission compared to the unidirectional transmission case. Cross-talk issues and chromatic dispersion are also studied. The induced power penalty by adjacent channel cross talk is negligible (≦0.2dB) with a narrow channel spacing of 1.0nm. The induced power penalty by intraband (homodyne) cross talk is also negligible for the cross-talk level of −30dB, corresponding to 99.9% reflectivity of the FBG. The Bi-ROADM may find important applications in bidirectional WDM networks and/or bidirectional transmission.