Comparison of six different RZ-DQPSK transmitter set-ups regarding their tolerance towards fibre impairments

Introduction: It is well known that the advanced return to zero (RZ) optical differential quadrature phase shift keying (DQPSK) modulation is transmitting two bits by each symbol and is thus advantageous for increasing the spectral efficiency by maintaining a high robustness towards non-linear fibre effects [1]. Increasing the transmitted bits per symbol can be achieved by using additional symbol states in the complex plane constellation using additional amplitude (AM) or phase modulation (PM). In [2] and [3] the RZ-DQPSK format was combined with a binary and quaternary AM resulting in 8 and 16 possible states and thus in 3 and 4 transmitted bits per symbol, respectively. Increasing the DQPSK phase states by a factor of two results in the 8DPSK modulation format. A coherent reception of 8DPSK was presented in [4]. However, according to our knowledge non-coherent reception of 8DPSK was only investigated by numerical simulations using different receiver methods with multi-level or binary reception techniques [5-9]. In this contribution we investigate experimentally the noise and chromatic dispersion tolerance of the 8DPSK modulation format at a symbol rate of 10.7 GSymbols/s and investigate which receiver structure is feasible for a non-coherent reception of the 8DPSK modulation format.