Generation and Coherent Reception of 107-GBd Optical Nyquist BPSK, QPSK, and 16QAM
We present a 107-GBd coherent optical system for the generation and reception of m-ary phase-shift keyed (PSK) and quadrature-amplitude modulated (QAM) signals, including Nyquist pulse shaping. It is based on phase-stable optical time-division multiplex (OTDM) of two tributaries, which are modulated at half the target symbol rate, optical Nyquist filtering, and a broadband digital coherent receiver. The system is analyzed in back-to-back experiments with binary PSK (BPSK) modulation, quadrature-PSK (QPSK) modulation, as well as with 16-ary QAM. Compared to all-ETDM implementations, the transmitter is based on independent electro-optical modulation of two time-division multiplex tributaries and subsequent optical interleaving after modulation. Although this scheme implies increased hardware complexity, it enables lower penalties with respect to theory compared to all-ETDM experiments presented so far. This is due to the reduced hardware speed requirements. The measured penalties at bit-error ratios of 1 × 10-3 are 0.5, 1.5, and 6 dB for single-polarization BPSK, QPSK, and 16QAM, respectively. Furthermore, the employed phase-stable optical multiplexer allows use of standard receiver DSP at the broadband digital coherent receiver without need for special treatment of the individual OTDM tributaries.