High-order compensation of self-phase modulation in laser communication systems

Abstract

Self-phase modulation (SPM) creates a power and fiber-length dependent spectral broadening that reduces signal-to-noise ratio in free-space laser communication systems which use a fiber to connect their transmitter's high-power optical amplifier to its telescope optics. The effects of SPM can be mitigated by using a phase modulator to down-chirp pulses before passing through the receiver's matched filter. This thesis tests and evaluates a new SPM compensation technique-applying a phase modulation determined from a measurement of the SPM-distorted waveform's optical intensity-and benchmarks it against sinusoidal phase modulation compensation. The spectra and throughput of the compensated signal are calculated and measured to determine the effectiveness of the new technique. It is found that the two techniques perform within 0.2 dB of each other for fiber lengths less than three times the nonlinear length, and it is expected that the new technique will outperform sinusoidal phase modulation for greater fiber lengths.