Synchronous 16-QAM Transmission in a FPGA-Based Coherent Receiver with Different Phase Estimation Filter Lengths

In this article we present the implementation of a 16-QAM transmission system with feedforward realtime synchronous demodulation and data recovery. Different filter lengths (half-width N) were evaluated and a realtime data throughput of 2.5 Gbit/s was achieved. The 625 Mbaud (4x625 Mb/s) data is transmitted over one span of single-mode fiber, and is received in a realtime I&Q homodyne setup with standard external cavity laser. For powers larger than -30dBm, the average bit error rate (BER) is below forward-error correction (FEC) limit (7% overhead).