Differential phase frame synchronization for coherent transponders

Future optical transmission systems using multi mode fibers as a transmission medium require data-aided based coherent receivers for stable and fast convergence, as blind estimation does not guarantee convergence and the convergence time significantly increases with respect to data-aided estimation. The problem with data-aided digital signal processing is that the training sequence should be found inside the received signal, which may be heavily distorted. We present an overhead efficient algorithm based on differential phase correlation to find the start of the training sequence and show its robustness towards linear transmission impairments and local oscillator offset in single mode fiber.