Nonlinear optical interactions in on-chip inp semiconductor optical amplifiers

Abstract

Nonlinearities within semiconductor optical amplifiers (SOAs) play an important role especially when using short, (sub-) ps input laser pulses, and enable all-optical signal processing tasks such as wavelength conversion and signal amplification. However, to fully understand the complex interplay between different nonlinear effects in SOAs when excited with short laser pulses, further investigation is needed. In this thesis, we theoretically and experimentally investigate the behavior of nonlinearities in an on-chip integrated Indium Phosphide (InP) SOA in the telecom domain using a pump-probe setup. Two laser beams are injected simultaneously into the SOA: the pump pulsed beam excites the SOA, and the weak continuous wave (CW) probe beam experiences spectral changes that reveal the nonlinear effects taking place in the SOA. First, to model these nonlinear effects, we rely on a previously published model that links the gain and phase dynamics inside an SOA with the pump and probe output spectrum. We extend an earlier written MATLAB code to numerically simulate both the pump and probe output spectra under different excitation and SOA conditions. Secondly, we experimentally characterize a 0.5 mm-long on-chip INP SOA and calculate its small signal gain for a CW laser input beam while also determining the losses in the chip using a passive waveguide. Thirdly, we perform the actual pump-probe experiments with the on-chip INP SOA by injecting both strong ps pulses and a weak CW probe beam. We observed nonlinearityinduced blue and red-shifted spectral components in the probe output spectrum, in line with expectations. This study also shows a strong laser polarization dependence of the observed nonlinear effects. As such, our work provides new insights into the nonlinear behavior of on-chip SOAs under
pulsed excitation.

Date of Award	2023
Original language	English