Optimization of time and frequency fiber-optic links exploiting bi-directional amplifiers, based on real-time performance measurement

Abstract

Long-distance fiber-optic time and frequency transfer links exploit bi-directional optical amplifiers whose gains need to be optimized to limit the noise propagating along with the desirable signals. Unlike the usual optimization of such links that are based on simulations or on a trial and error approach, we propose here a technique where the link is initially set-up with a pre-set algorithm, using optical powers measured in the amplifiers installed along the link. After that the final optimization is performed based on jitters measured in the end terminals of the link with a dedicated hardware. All the required parameters (i.e. the optical powers and jitters) are measured in a real-time in a live link. Various methods of assessment of the link performance, using the jitter measurements performed either in one or both end terminals, as well as various optimization criteria (like minimax, square root of sum of RMS jitters or analysis of a single-end jitter measurements), are investigated. The developed procedures were tested experimentally in the laboratory and also during a field trial in a real fiber telecom infrastructure. Obtained results (55% jitter reduction, 7 dB SNR improvement, comparing to the link state after its initial set-up) suggest that the proposed solutions allow optimizing effectively the link performance and may be used to supplement or replace simulation methods, particularly on initial start-up or when reconfiguring the link (e.g. due to a link route modification or after a fiber break).