224 Gb/s Optical Carrier-Assisted Nyquist 16-QAM Half-Cycle Single-Sideband Direct Detection Transmission over 160 km SSMF

We demonstrate 224  Gb/s single polarization direct detection transmission over 160  km standard single mode fiber with Nyquist 16-ary quadrature amplitude modulation half-cycle single-sideband (SSB) signal at C-band. The net bit rate is 203.4  Gb/s considering frame redundancy and hard-decision forward error correction (HD-FEC) with 7% overhead. After 160 km transmission, the bit error rate (BER) is 3.6 × 10−3, which is less than the BER threshold of 4.5 × 10–3 for 7% HD-FEC. To our best knowledge, it is the first report of C-band 200G single channel and single photodiode direct detection transmission, which sets a record of fiber link length for such systems. In our experiment, the optical carrier is added with an additional laser at the transmitter side, which is delivered along with the signal. For short reach transmission, the nonlinear interactions between the carrier and the signal are usually insignificant. Therefore, our scheme is equivalent to heterodyne coherent detection with a local oscillator and a single-ended photodiode. The system performance is studied by deducing the relationship between electrical signal-to-noise ratio and optical signal-to-noise ratio of an SSB signal. The spectrum efficiency and hardware complexity of our experiment are compared with other direct detection schemes. The signal–signal beat interference induced by the square-law detection of a single-ended photodiode is compensated by an iterative technique at the receiver side. The equalization-enhanced in-band noise in bandwidth-limited systems is compensated using a digital post filter together with maximum likelihood sequence decision. The demonstrated scheme can provide a promising technique for beyond 100G high-speed direct detection transmission aiming to datacenter interconnecting and some metropolitan area applications.