Self-compensating polarization modulator having directional phase shifter

Abstract

A modulator unit for modulating the phase of a polarization component of an optical signal contains a polarizing beam splitter and a phase shifter. The beam splitter splits an input signal into a first and a second polarization components having different polarization directions and sends the components in opposite directions via an optical ring containing the phase shifter. A polarization rotator is arranged in the optical ring, which changes the polarization direction of passing optical signals, so that the polarization components arriving at the phase shifter are polarized in the same direction. The phase shifter changes the polarization directions of the incoming optical signals such that they are polarized orthogonally to one another in the phase shifter. One polarization component is modulated. When the optical signals leave the phase shifter, their polarization direction is brought back to the original polarization direction.