A modified 160 Gbit/s OTDM system based on QPSK Nyquist pulses and coherent detection

Abstract In this paper, we design and implement a 160 Gbit/s orthogonal time division multiplexing (OTDM) transmission system based on quadrature phase shift keying (QPSK) Nyquist pulses and coherent detection. We proposed an optimized Nyquist pulses generation scheme, which produce ultra-flat frequency combs with near-perfect rectangular spectrum and high suppression of out-of-band components by two cascaded Lithium Niobate Mach Zehnder modulators (LN-MZMs). Divided by variable length of optical delay line (Odl), 10GBaud QPSK Nyquist pulses are multiplexed to 80GBaud in a single wavelength. A set of training sequence (TS) which are inserted in front of data are employed to realize the inclusion of optical phase-locking and estimate channel transmission function. In this scheme, we make use of the TS overhead to achieve homodyne detection synchronization between local advanced receiver and Nyquist-pulses generator which is controlled by loop digital signal processing (DSP) module via an optical phase-locking loop. Meanwhile, for the advantage of the TS scheme and DSP, the Nyquist system compensates the residual physical dispersion and improves the transmission quality after 150 km transmission.