Open-Loop Polarization Mode Dispersion Mitigation for Fibre-Optic Time and Frequency Transfer

TL;DR

This paper introduces a passive, open-loop method using alternating polarization pulses to significantly reduce polarization mode dispersion in fiber-optic time and frequency transfer, enhancing stability without active feedback.

Contribution

The authors propose a novel passive polarization modulation technique that mitigates PMD effects in fiber-optic links for time and frequency transfer.

Findings

PMD reduced by over two orders of magnitude

Passive polarization modulation effectively stabilizes phase detection

Method applicable with simple, low-cost components

Abstract

The non-reciprocal and dynamic nature of polarization mode dispersion (PMD) in optical fibers can be a problem for accurate time and frequency transfer. Here a simple, passive solution is put forward that is based on transmitting optical pulses with alternating orthogonal polarization. The fast and deterministic polarization modulation means that the PMD noise is pushed far away from the frequencies of interest and upon reflection from a Faraday mirror at the receiver, the pulses have a well defined polarization when they return to the transmitter, which facilitates stable optical phase detection and fibre phase compensation. In an open-loop test setup that uses a mode-locked laser and a simple pulse interleaver, the polarization mode dispersion is shown to be reduced by more than two orders of magnitude