Multi-Carrier Coherent Receiver Based on a Shared Optical Hybrid and a Cyclic AWG Array for Terabit/s Optical Transmission

We describe a multi-carrier coherent-receiver scheme where the coherent beating between an ultra-high-speed multi-carrier signal and multiple optical local oscillators (OLOs) is conducted in a single optical hybrid, followed by carrier separation through an arrayed waveguide grating (AWG) array. Sharing the optical hybrid for multiple OLOs simplifies the coherent receiver complexity and eases the timing alignment among multiple modulated carriers. Based on this scheme, a compact coherent-receiver front end consisting of an integrated 4 × 40 AWG array following a polarization-diversity optical hybrid is demonstrated and used for complete demodulation of a 1.12-Tb/s multi-carrier signal having ten 112-Gb/s polarization-division multiplexed (PDM)-quadrature phase-shift keying (QPSK) carriers spaced at 50 GHz. The required optical signal-to-noise ratio for the 1.12-Tb/s signal is 27 dB at 10
^-3
bit error ratio. The cyclic feature of the AWG array allows the receiver to receive modulated carriers that are not adjacently spaced. We also extend this receiver scheme for multi-carrier signals whose carriers are closely spaced, e.g., under the orthogonal frequency-division multiplexing (OFDM) condition, for high-spectral-efficiency Terabit/s transmission applications.