We report for the first time the experimental demonstration of doubly-differential quadrature-phase shift keying (DDQPSK) using optical coherent detection. This method is more robust against high frequency offsets (FO) than conventional single differential quadrature phase shift keying (SDQPSK) with offset compensation. DDQPSK is shown to be able to compensate large FOs (up to the baud rate) and has lower computational requirements than other FO compensation methods. DDQPSK is a simple algorithm to implement in a realtime decoder for optical burst switched network scenarios. Simulation results are also provided which show good agreement with experimental results for both SDQPSK and DDQPSK transmission.
In this paper we will demonstrate the improved BER performance of doubly differential phase shift keying in a coherent optical packet switching scenario while still retaining the benefits of high frequency offset tolerance.
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