# High-Capacity Coherent DCIs using PolMuxed Carrier and LO-Less Receiver

## TL;DR

This paper proposes a polarization multiplexed carrier self-homodyne link with adaptive polarization control as a practical, high-capacity alternative to PAM4 systems for data center interconnects, eliminating the need for LO and phase recovery.

## Contribution

It introduces a novel PMC-SH scheme with adaptive polarization control, demonstrating improved BER performance and potential doubling of data rates compared to PAM4 systems.

## Key findings

- PMC-SH scheme achieves better BER at same data rate
- Potential to double data rates within existing bandwidth
- Eliminates need for LO and phase recovery in coherent detection

## Abstract

A PAM4 based direct detection system has been standardized for short-distance data center interconnects because of its simple architecture. Performance of the PAM4 systems is limited for high dispersion values or demands complicated signal processing for further increase in data rates. A polarization multiplexed carrier based self-homodyne (PMC-SH) link with adaptive polarization control is a practical approach with an laser oscillator (LO)-less and carrier phase recovery (CPR)-free coherent receiver that can replace PAM4 links for achieving high data rates. We analytically find that PMC-SH scheme results in a significantly better BER for a given transmission rate or can achieve doubling of the data rate for given bandwidth of electronics and laser power (when compared with PAM4). Practical implementation of the proposed system with adaptive polarization control is also discussed. Presented theoretical frame work highlights the advantages of such self-homodyne systems over PAM4 based systems in terms of SNR requirements and capacity.