Ultrahigh-Speed Nyquist Pulse Transmission beyond 10 Tbit/s

This paper presents recent progress toward the realization of ultrahigh-speed optical time-division multiplexed transmission with a single-channel bit rate of more than 10 Tbit/s using a Nyquist pulse. We first describe non-coherent Nyquist pulse transmission with differential quadrature phase-shift keying (DQPSK). We present a single-channel 10.2 Tbit/s, DQPSK-300 km transmission, where the highest symbol rate of 2.56 Tbaud was demonstrated with an ultrashort Nyquist pulse train and an ultrafast demultiplexer using a nonlinear optical loop mirror. We then present a recent demonstration of a 1.28 Tbit/s/ch × 10 channel (total 12.8 Tbit/s) DQPSK transmission, where the transmission distance was successfully extended to 1500 km by employing a wavelength division multiplexing scheme and reducing the symbol rate to 320 Gbaud while retaining a total transmission capacity of more than 10 Tbit/s. Next, we describe coherent Nyquist pulse transmission with quadrature amplitude modulation (QAM). We present a single-channel polarization-multiplexed 1.28 Tbaud, 64 QAM-150 km transmission, where the highest transmission speed of 15.3 Tbit/s was achieved with a homodyne detection scheme using an optically phase-locked LO Nyquist pulse. Furthermore, we present recent results related to BER performance improvement in a 15.3 Tbit/s coherent Nyquist pulse transmission by newly constructing a low-nonlinearity, dispersion-compensated transmission line using a chirped fiber Bragg grating and a liquid crystal on silicon device. As a result, the required forward-error correction overhead was successfully reduced from 25.5% to 20%, and the spectral efficiency reached as high as 8.7 bit/s/Hz.