Patent ID: 7295784

Claim:
An apparatus for performing electrically band-limited optical Differential Phase Shift Keying (DPSK) modulation, comprising: a light source; a Non-Return-to-Zero (NRZ) signal generator for generating a NRZ signal; a pre-coder for coding the NRZ signal generated by the NRZ signal generator into a differential signal; an electrical low pass filter for electrically limiting a bandwidth of the differential signal obtained through the pre-coder; and a Mach-Zehnder modulator provided with cosine transfer function characteristics and driven in a push-pull manner for modulating an optical signal input from the light source into a DPSK signal using the differential signal having the bandwidth electrically limited by the low pass filter, wherein the low pass filter electrically limits the bandwidth of the differential signal obtained through the pre-coder within a range of 60 to 80% of a data rate.