Fiber-optic joint time and frequency transfer with the same wavelength

TL;DR

This paper introduces a novel fiber-optic scheme that simultaneously transfers ultra-stable time and radio frequency signals at the same wavelength, achieving high stability and independence of signals over 110 km.

Contribution

A new coherent demodulation scheme for simultaneous time and frequency transfer on a single fiber wavelength, with active phase fluctuation cancellation and high stability.

Findings

Frequency instability of 1.7E-14 at 1s

Time transfer stability of sub-ps after 1000s

Successful 1GHz RF and 1PPS time transfer over 110 km

Abstract

Optical fiber links have demonstrated their ability to transfer the ultra-stable clock signals. In this paper we propose and demonstrate a new scheme to transfer both time and radio frequency with the same wavelength based on coherent demodulation technique. Time signal is encoded as a binary phase-shift keying (BPSK) to the optical carrier using electro optic modulator (EOM) by phase modulation and makes sure the frequency signal free from interference with single pulse. The phase changes caused by the fluctuations of the transfer links are actively cancelled at local site by optical delay lines. Radio frequency with 1GHz and time signal with one pulse per second (1PPS) transmitted over a 110km fiber spools are obtained. The experimental results demonstrate that frequency instabilities of 1.7E-14 at 1s and 5.9E-17 at 104s. Moreover, time interval transfer of 1PPS signal reaches sub-ps stability after 1000s. This scheme offers advantages with respect to reduce the channel in fiber network, and can keep time and frequency signal independent of each other.