Differential Phase-Shift Keying in Spatial Diversity Transmitters for Fade Mitigation

We investigate the use of differential phase-shift keying (DPSK) in multiwavelength spatial diversity transmitters for mitigation of atmospheric fading. By selecting the transmitter wavelengths to coincide with the transmission peaks of the delay-line interferometer in the receiver, the only modification required to a standard DPSK receiver is a wider optical filter. We examine the wavelength separation required to minimize penalties from beating between the wavelengths and find that a separation of twice the data rate is sufficient for a four-wavelength system with narrow filtering. We also demonstrate a reduction in scintillation loss for a four-wavelength DPSK system in a fading channel.