BER FLOORS DUE TO HETERODYNE COHERENT CROSSTALK IN-SPACE PHOTONIC SWITCHES FOR WDM NETWORKS

The occurrence of bit-error-rate floors due to coherent heterodyne cro sstalk in photonic space switches is studied, This source of errors oc curs when a particular switch is used to route signals of nominally th e same wavelength in a WDM network, DFB lasers are run at multigigabit rates, and wavelength referencing is held to a relatively tight toler ance to facilitate wavelength demultiplexing, In this letter we compar e the dependence of switch architecture and size on the rate of cohere ntly induced bit errors, Three regions of interest are identified: 1) random uniformly distributed laser phases with binomially distributed bit statistics in interfering channels, 2) random uniformly distribute d laser phases with ones in interfering channels, and 3) worst-case la ser phases with ones in interfering channels, Critical crosstalk value s are identified for four different switch architectures and two diffe rent switch sizes in order to avoid coherently induced errors and ther efore BER floors due to this mechanism, The minimum crosstalk required to avoid coherent errors can vary from -10 dB to -42 dB depending on the switch architecture, size, and requirement for short-term BER stab ility.