DSP-free Coherent Detection for Short-reach Frequency-synchronous Optical Networks

Rapidly growing data traffic drives the development of next-generation short-reach optical interconnects technology. Coherent detection has high-spectral efficiency, which is considered as a potential solution to break through the data-rate limitation of short-reach optical communication systems. Here, we introduce the concept of quasi frequency-synchronous optical network (FSON) architecture for short-reach optical communication in order to simplify coherent optical detection. We also demonstrate a novel optical carrier phase recovery scheme based on OPLL in FSON. In the OPLL, an acoustic optical modulator (AOM) is used as a feedback actuator to compensate for both the frequency offset and phase fluctuation introduced by the fiber link. In so doing, coherent detection requires neither MIMO nor carrier phase recovery DSP. We next present the world-first polarization and phase demultiplexing of DP-QPSK signals in optical domain without employing electronic DSP. The four tributaries of 100-Gb/s DP-QPSK signals are recovered below 3.8×10-3 BER threshold at -30-dBm receiver optical power. Our proposed DSP-free coherent detection provides an attractive solution for next generation datacenter transport with low cost and power consumption.