Integrated Comb Laser With Active De-Multiplexer for Spectrally Sliced Coherent Receiver

Spectrally-sliced coherent receivers (SSRx) are potentially attractive for future high-speed access networks, as they allow the use of low-cost, low-bandwidth commodity components with minimal impact on performance. In this letter, we present such a receiver, and show that it is capable of detecting a single carrier, high bandwidth 100 Gb/s PDM-QPSK optical signal using two parallel coherent receivers with reduced front-end bandwidths as low as 6.5 GHz. The receivers utilize frequency separated local oscillators derived from an integrated injection-locked gain-switched comb laser assembly (iCLA) followed by an all-active $1\times 4$ demultiplexer photonic integrated circuit (PIC) to derive the spectral signal slices. The high mutual coherence of the comb lines is then exploited to enable signal reconstruction in the digital domain. The use of the active demultiplexer PIC is a key advance compared to previous work using passive comb demultiplexers as it delivers sufficient local oscillator power without the need for bulky, external optical amplifiers to compensate for demultiplexer losses. Furthermore, a minimal performance penalty is observed (< 1dB at the HD-FEC limit), compared to a conventional high-bandwidth receiver. Importantly, the active iCLA and demultiplexer PIC solutions demonstrated here are key building blocks required for a fully integrated spectrally-sliced coherent receiver for future coherent access networks.