Optical amplifiers are widely classified into two categories- fiber amplifiers and semi-conductor optical amplifiers (SOAs). The fiber amplifiers are widely deployed in the conventional communication systems. Owing to the advancement in the optical semiconductor fabrication technology and device design, the SOAs are evolving as a promising candidate for future deployable optical networks- especially for ultra wideband systems. This thesis focuses on two broad applications of SOA in the field of optical communication- as an optical amplifier and as a nonlinear media for optical signal processing. In the first application, the SOA is explored as an amplifier, especially for coherent optical communication systems. The major challenge in using it as an amplifier is its inherent phase distortion. We propose and demonstrate two techniques for low-distortion amplification using SOAs (a) using a holding beam, (b) sandwiching optical phase conjugator between two SOAs.

In the second part, SOA is explored for its utility as a nonlinear medium. A novel Bragg scattering based four-wave mixing in SOA is proposed theoretically. This is followed by a corresponding experimental demonstration with a counter-propagating orthogonally polarized single frequency pump for polarization-insensitive optical phase conjugate both in CW case and for QPSK modulated signals. The novel idea enables the generation of polarization-insensitive conjugate in both the ports of the SOA simultaneously. Noise figure estimation and the OSNR retention in SOA for the signal and the conjugate are established experimentally. We further experimentally demonstrate the simultaneous compensation of both dispersion and nonlinear effects in a 100 km optical fiber link using optical phase conjugation, without any digital signal processing to compensate for distortions due to chromatic dispersion and nonlinear effects in fiber. Phase conjugate generation in SOA being energy-efficient, it is further explored for phase-sensitive amplification,followed by phase quantization. The input power ratio of the interacting waves are obtained through optimization of gain extinction ratio and the optimized two-level and four-level phase-quantization are demonstrated experimentally using SOAs. In this talk we will be discussing these experimental demonstrations, its challenges and conclusions based on the achieved results.