Reflective Semiconductor Optical Amplifier Direct Modulation Capability Enhancement Using Birefringent Fiber Loop

The feasibility of employing a birefringent fiber loop to enhance the performance of a directly modulated reflective semiconductor optical amplifier is experimentally demonstrated for the first time. The birefringent fiber loop acts as an optical filter of opposite slope than that of the reflective semiconductor optical amplifier electro-optical response and counteracts the finite reflective semiconductor optical amplifier modulation bandwidth of only 0.89 GHz. By proper adjustment of its detuning, the birefringent fiber loop tailors the spectral components that physically manifest due to the reflective semiconductor optical amplifier dynamic perturbation subject to direct modulation in the saturated gain regime, and suppresses the pattern-dependent distortions in the time domain. In this manner, the birefringent fiber loop manages to significantly improve the quality characteristics of the encoded signal at higher data rates than those enabled by the reflective semiconductor optical amplifier limited modulation capability. Owing to the birefringent fiber loop, the reflective semiconductor optical amplifier modulation range is extended to 4 Gb/s at the raw bit error rate of 1.0×10−9, and to 11 Gb/s at the forward error correction limit of 3.8×10−3. These results, which are unique against the evaluation criterion adopted in the first case, and the modulation speed achieved with post-filtering schemes in the second, highlight the beneficial role that the birefringent fiber loop can play in supporting reflective semiconductor optical amplifier operation for intensity amplification and modulation purposes.