Hybrid Direct-Detection Differential Phase Shift Keying-Multipulse Pulse Position Modulation Techniques for Optical Communication Systems

摘要

A hybrid differential phase shift keying-multipulse pulse position modulation (DPSK-MPPM) technique to enhance the receiver sensitivity of optical communication systems is presented. Both binary and quadrature formats are adopted in the proposed systems. Direct-detection DPSK schemes that are based on asymmetric Mach-Zehnder interferometers with a novel ultrafast discrete delay unit are presented to simplify the receiver implementation. Our results reveal that the proposed hybrid schemes are more energy-efficient and have higher receiver sensitivity compared with the traditional ones while improving the bandwidth-utilization efficiency. Furthermore, at an average launch power of −8 dBm and BER=10⁻³, the hybrid DQPSK-MPPM system with a total frame length of eight time slots including two signal time slots outreaches a traditional DQPSK system by 950 km. The proposed DPSK-MPPM modulation system accommodates adjustable (or variable) bit rates, by virtue of the programmable delay integrated to the receiver system.