Spectral-Efficient Flexible Optical Multicasting in a Periodically Poled Lithium Niobate Waveguide

We experimentally demonstrate enhanced spectral efficiency (SE) within flexible multicasting operation in a periodically poled Lithium Niobate (PPLN) waveguide. Replicas of quadrature phase-shift keying (QPSK) and 16 quadrature amplitude modulation combs are generated in the C-band exploiting second-order nonlinear effects in a PPLN waveguide as second harmonic generation and sum frequency generation cascaded with difference frequency generation. This technique allows creating equally spaced replicas of the signal to be multicast, being independent of its modulation format. The bit error rate is measured for the signal replicas after transmission through 80 km of a standard single-mode fiber span. The SE obtained with the multicasting of a 25 Gb/s QPSK on 37.5 GHz spaced channels is about 1.3 b/s/Hz. By introducing the time-frequency packing technique, we demonstrate optical multicasting of a 60 Gb/s QPSK signal with 20 GHz spacing among the replicas by achieving a SE of 2.7 b/s/Hz.