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Coherent PM-QPSK versus RZ-DQPSK and DPSK for High Bitrate Systems

Tool Used: OptSim

This example shows that coherent PM-QPSK offers a pre-FEC 2 dB sensitivity improvement over RZ-DQPSK and 1.3 dB improvement over DPSK systems.

The figure below depicts the OptSim layout for coherent PM-QPSK:

Layout for coherent PM-QPSK | Synopsys

The figure below depicts the layout for RZ-DQPSK:

Layout for RZ-DQPSK | Synopsys

The figure below depicts the layout for DPSK:

Layout for DPSK | Synopsys

The figure below compares OSNR sensitivities of coherent and non-coherent systems as above. As can be seen, coherent PM-QPSK offers a pre-FEC 2 dB sensitivity improvement over RZ-DQPSK and hence can be a viable solution for high bitrate systems.

Sensitivities of coherent and non-coherent systems | Synopsys