A 4.6pJ/b 200Gb/s Analog DP-QPSK Coherent Optical Receiver in 28nm CMOS.

Coherent detection with polarization multiplexing is widely used because of its high spectral efficiency. However, it utilizes analog-to-digital converters (ADCs) and digital signal processing (DSP), which consume a large amount of power and thereby hinder its application in power-sensitive short-reach links. In this article, we present a 200-Gb/s analog $C$ -band dual-polarization quadrature phase shift keying (DP-QPSK) coherent optical receiver (RX), which uses four-way time-interleaved sampling to relax the internal bandwidth limit. The RX utilizes a chromatic dispersion (CD) equalizer, a polarization demultiplexer (Pol. DEMUX), and carrier recovery (CR) to eliminate the intersymbol interferences induced by fiber impairments and the carrier frequency offset. A subsampling scheme is adopted for low-power adaptation. The decrease in the frequency offset detection range caused by subsampling is prevented using a consecutive slice sampling technique. Measurement results show that our RX supports equalization for impairments equivalent to a 10-km fiber and CR for a residual carrier frequency offset of 12 MHz. A bit error rate (BER) of less than $1e-10$ is achieved with an energy efficiency of 4.6 pJ/b.