Patent ID: 8121494

Claim:
An optical receiver for receiving a differential phase-shift keyed (DPSK) optical signal from a wavelength-division multiplexed (WDM) optical transmission system, the optical receiver comprising: a demodulator, the demodulator including an optical delay interferometer (ODI) having: an optical input for receiving the DPSK optical signal, a constructive optical output associated with a constructive signal based on the DPSK optical signal, and a destructive optical output associated with a destructive signal based on the DPSK optical signal; and a power imbalance module that provides an additional relative power difference between the constructive and destructive signals, wherein the ODI has a free spectral range (FSR) that is larger than a symbol rate (SR) of the DPSK optical signal, and the additional relative power difference is dependent on the ratio between SR and FSR according to the following relation: Δ( P con /P des )≈( SR/FSR− 0.75)×15 dB, where P con is the power of the constructive signal, P des is the power of the destructive signal, and Δ(P con /P des ) is the additional power difference in dB.