WHY FSK AND CPFSK HAVE IDENTICAL LINEWIDTH REQUIREMENTS

CPFSK is the most widely used modulation scheme in coherent optical tr ansmission. Theoretical analyses so far predicted a much more stringen t linewidth requirement compared to ASK and FSK systems with noncohere nt IF-detection. In this paper we present a unified linewidth analysis of ASK, FSK, CPFSK, and DPSK receivers, with leads to the conclusion that the linewidth performance of these different schemes is to a larg e extent identical. The inclusion of post-detection filtering in the a nalysis is critical for obtaining these results, which are supported b y practical system measurements on a 1 Gbit/s phase diversity CPFSK re ceiver.