Presented principle of PSW is based on rate-equation model in the SOA.
The TE and TM modes experience different refractive indexes, which lead to phase difference between the two modes,
then they interfere at the output of the SOA, and the switching effect is obtained. The rate-equation model is effective in
describing the switching effect. But in experiments, this model is hard to realise and track on line, and there are many
difficulties for achieving the switching effect.
In the SOA, there are four nonlinear effects: cross-gain modulation, cross-phase modulation, cross-polarization
modulation, and four-wave mixing. These nonlinear effects are widely researched in optical devices. Several models that
describe the nonlinear effects had been presented. Moreover, these models are microscopic models that describe the
SOA carrier dynamics, and in many experimental setups, SOAs are pigtailed with standard signal mode fibers at input
and output. But the changes of polarization state in the pigtail fiber remain unnoticed. In this paper, we present a
macroscopic model of SOA that includes pigtailed fiber and SOA. In this model, we use principal states of polarizations
(PSP) to analyse the nonlinear polarization rotation. The PSPs are defined as those output SOPs that remain unchanged
to the first order approximation, when the parameter, such as bias current or power of optical control pulse, is adjusted.
Our model is a more practical design tool for optical switching configuration. We develop a theoretical relationship
between the polarization rotation and the bias current of the SOA. Then, the nonlinear polarization switching is
demonstrated. Compared with the reported Optical switching that based on rate-equation model, this switching is stable
and easier to be realised.
In section II, we present the model based on the principal states of polarizations (PSP). Experimental results show
that this model can explain the nonlinear polarization rotation in SOA. In section III, we demonstrate the polarization
switching use polarization rotation. We find an excellent agreement between our model and experimental results. We
conclude our paper by summarizing important finding in section IV.