Silicon Photonic Carrier-Assisted Differential Detection Receiver With High Electrical Spectral Efficiency for Short-Reach Interconnects

Coherent detection is advantageous in achieving high electrical spectral efficiency (ESE) relative to direct detection (DD), due to its capability of field recovery. However, the stringent requirement on the laser sources prevents it from being widely utilized in cost-sensitive short-reach applications. Carrier-assisted differential detection (CADD) was proposed to retrieve the optical field without needing for a narrow-linewidth local oscillator (LO) in a receiver. To realize a compact CADD receiver, silicon photonic (SiP) integration is therefore of particular interest since it leverages the standard complementary metal-oxide semiconductor (CMOS) compatible fabrication, offering high yield, low cost, and compact footprint. The fabrication process does not introduce III-V materials as the CADD receiver is LO-free. In this article, we fabricated a SiP integrated CADD receiver and demonstrated the transmission and reception of a 240-Gb/s orthogonal frequency division multiplexing (OFDM) 16-ary quadrature amplitude modulation (16-QAM) signal transmitted over an 80-km single-mode fiber (SMF) link, with a bit error ratio (BER) below the 25% overhead (OH) soft-decision forward error correction (SD-FEC) threshold. To the best of our knowledge, we achieve a record 5.2-b/s/Hz ESE per polarization for an integrated DD receiver.