High-speed Transmission based on a 40 Gbaud DQPSK System

We describe a high-speed transmission system with a data rate = 80 Gbit/s. The system is based on RZ-DQPSK modulation with a symbol rate of 40 Gbaud. The experimental setup is described and discussed in detail. The transmitter to generate the DQPSK data signal consists of an RZ-pulse source and two cascaded phase modulators. The receiver contains a demodulator and a balanced photodetector. Compared to an OOK system, a DQPSK system with the same data rate has a reduced symbol rate and a higher spectral efficiency. Therefore the combination of DQPSK systems with multiplex techniques is very attractive. In this paper we present experiments where a data rate = 80 Gbit/s is reached by combining DQPK with wavelength-, time division and polarization multiplexing. Error-free transmission (BER < 10(exp -9) without FEC) of 640 Gbit/s in a single wavelength channel over 6 times 80 km is demonstrated.