Studies on polarization-state control in coherent optical fiber communications

Abstract

In this dissertation, the polarization-state control in coherent optical fiber communications is studied. A new automatic polarization-state control scheme called "polarization recombing" is proposed and experimentally verified. The system consists of a polarization beam splitter (a Wallaston prism), a 90° linear polarization rotator, and endless phase shifter, and a beam combiner. It features a very simple (probably the simplest) principle for polarization-state control and endlessness (resetting-free) in control is achieved. IN addition, in this scheme, the polarization-state of output light is always linear with a fixed inclination angle regardless of changes in the polarization-state of the incoming light. Such a characteristic is achieved without the aid of a polarimeter and is particularly useful in homodyne phase diversity receiver because a stable linearly polarized light is necessary for generating two lights having 90° phase difference. This feature has been demonstrated in simulated self-homodyne DPSK phase diversity receiver. It is fund that the scheme functions satisfactorily and the receiver sensitivity fluctuation is kept within 0.5 dB. at 200 Mbits/sec.