  Modulation format identification (MFI) is crucial in next-generation optical
networks such as cognitive optical networks. An
integrated-clustering-algorithm-based MFI scheme in a coherent optical
communication system is proposed herein. Numerical simulations are performed to
test the performance of the scheme on the platform of a polarization domain
multiplexing system at a symbol rate of 28 Gbaud. Simulations show that the MFI
scheme can achieve an accuracy of 100% for five modulation formats considered
in this study when the optical signal-to-noise ratio values are lower than the
7% forward error correction threshold. Tolerances to residual chromatic
dispersion (CD) are discussed, and the results show that the proposed scheme
can perform well as the residual CD changes over a wide range of values.
Moreover, by selecting a number of key blocks, the proposed scheme is less
complex than other clustering-based MFI schemes.
