Performance comparison of optical modulation formats for 40 Gbit/s systems from the viewpoint of frequency utilization efficiency and tolerance for fiber nonlinearities

This is the authors' abstract. We don't add key points for this paper.

In wavelength division multiplex (WDM) systems for long distance and large capacity, it is desirable that the modulation format be tolerant to degradation by nonlinear effects and achieve high frequency utilization efficiency. This paper compares modulation formats by numerical calculation from the viewpoints of frequency utilization efficiency and tolerance for fiber nonlinearities. It is shown that duobinary, RZ‐DQPSK (0.5) and CSRZ‐DQPSK achieve high transmission performance in DWDM (dense WDM). It is also shown that NRZ‐DBPSK, RZ‐DBPSK (0.5), and CSRZ‐DQPSK achieve high transmission performance in CWDM (coarse WDM). Before concluding, various methods of bit‐error rate calculation are compared and discussed, aiming at the correct evaluation of the bit‐error rate. The application of theQmethod to the differential quadrature phase‐shift keying format is shown to be feasible.