Experimental investigation of polarization rotation in semiconductor optical amplifiers

Abstract

In this paper we present an experimental study of polarisation rotation in a semiconductor optical amplifier. We use two techniques to investigate the gain and birefringence along the two eigen modes of the component waveguide, with and without injection. The first investigation is based on the residual reflectivity of the facet mirrors. From the modulation depth of polarisation resolved spectra, we determine the gain and the refractive indices of these modes. The second investigation takes into account the variation of the eigen mode gain and refractive indices as a function of injected power over the range –15 dBm to –3 dBm. We compare the results of these two experiments and determine that the refractive index and the single pass gain along the horizontal axis of the waveguide are higher than those along the vertical axis. Both gain and refractive index differences increase as a function of injected power in the sample under test. Furthermore we can conclude that polarisation rotation in this component is largely influenced by the power dependence of the relative gain in the TE and TM modes and birefringence.