Mixed Line-Rate Transmission (112-Gb/s, 450-Gb/s, and 1.15-Tb/s) Over 3560 km of Field-Installed Fiber With Filterless Coherent Receiver

We report the first superchannel field experiment where two multicarrier signals at 450 Gb/s and 1.15 Tb/s are copropagated with 112-Gb/s neighbors over 45 × 79.1 km spans of field-installed fiber with erbium-doped fiber amplifiers after each span. The superchannels use zero-guard interval all-optical orthogonal frequency-division multiplexing, with each optically generated subcarrier modulated by dual-polarization quadriphase-shift-keying signals (DP-QPSK). The heterogeneous data-rate channels are aggregated using wavelength selective switch in a flexible grid wavelength-division multiplexing architecture. The net spectral efficiencies of the channels vary from 2 b/s/Hz for the 112-Gb/s channels, to 3.33 b/s/Hz for the 1.15-Tb/s superchannel. We demonstrate that any of the signals can be detected using a common filterless digital coherent receiver. In particular, tuning a local oscillator laser midway between two optically generated subcarriers enables the coherent receiver (with proper signal-processing algorithm) to demodulate two subcarriers in one data capture. This allows flexible downconversion across the whole signal band. Our results show that superchannels can coexist harmoniously with 100 G DP-QPSK signals. Even though the superchannels use the same modulation format per subcarrier as the 100 G signals, the absence of guard bands enables higher spectral efficiency that is achievable with single-carrier modulation with minimal sacrifice in reach.