Lossless polarization attraction of telecom signals: application to all-optical OSNR enhancement

We propose an all-optical fiber-based device that is able to accomplish polarization control and OSNR enhancement of an amplitude modulated optical signal at the same time. The proposed device is made of a nonlinear lossless polarizer (NLP), which performs polarization control, followed by an ideal polarizing filter, which removes the orthogonally polarized half of additive noise. The task of the NLP is to impose signal polarization aligned with the transparent eigenstate of the polarizing filter. In order to effectively control the polarization of an amplitude modulated signal in the presence of additive noise, we show how one of the two different NLP configurations (with counter- or co-propagating pump laser) is needed, as a function of the signal polarization coherence time. We demonstrate that an OSNR gain close to 3 dB can be achieved by using the proper NLP configuration. Finally, we show how the achievable OSNR gain can be estimated theoretically.