Phase-insensitive zero-IF coherent optical system using phase switching

The authors present a simple technique wherein phase-insensitive zero-IF coherent optical detection is achieved by imposing a periodic phase modulation on the transmitted signal. With differential phase shift keying (DPSK), this can be achieved by adding a square wave to the phase modulator drive voltage. A single branch receiver is used, avoiding the doubling of receiver hardware needed with conventional phase diversity techniques. The performance of this scheme is analysed and compared to that of heterodyne DPSK