Use of an optical amplifier in a coherent receiver

The application of an optical amplifier in a coherent receiver is examined theoretically and experimentally. It is shown that in a preamplifier application an optical amplifier with a low noise figure is effective for improving the performance of a receiver which operates in thermal-noise dominant condition. It is also made clear that in an enhanced local oscillator system (ELOS), in which a local oscillator light is amplified by an optical amplifier with high output power, the improvement of a common-mode rejection ratio (CMRR) of a balanced receiver leads the system performance to nearly shot-noise-limited operation.<>