Passive Optical Phase Stabilization on a Ring Fiber Network

Abstract

Optical frequency transfer provides the means for high-fidelity frequency transfer across thousands of kilometers. A critical step in the further developing optical frequency transfer is its capability to transfer a high spectral purity feature from ultrastable lasers or optical clocks to any remote locations and, at the same time, its adaptability to incorporate the optical frequency transfer technique into any existing communication networks with different topologies. Here we for the first time report a technique that delivers optical-frequency signals to multiple independent remote hubs along a ring optical-fiber network with passive phase stabilization. The technique automatically corrects optical-fiber length fluctuations of arbitrary hubs along the loop by mixing and shifting optical signals. Without the help of an active phase tracker and a compensator, it could significantly mitigate some technical problems such as the limited compensation speed and phase recovery time, the phase jitter contamination caused by the servo bump in conventional phase noise cancellation. Moreover, by transmitting optical signals along both directions using the same optical source, it can improve the signal-to-noise ratio at each hub. This technique maintains the same delay-limited phase noise correction capability as in conventional techniques and, furthermore, improves the phase jitter by a factor of 3, opening a way to a broad distribution of an ultrastable frequency reference with high spectral purity and enabling a wide range of applications beyond metrology over a ring fiber network with the naturally impressive reliability and scalability.

Branching optical frequency transfer with enhanced post automatic phase noise cancellation

“…4, demonstrating that the phase noise rejection is optimized. Same with all the passive phase noise cancellation schemes [25], [24], [38], strong servo bumps have been effectively eliminated. of optical frequency transfer is improved by at least four orders of magnitude at the integration time of 10,000 s by activating the phase noise cancellation setup.…”

“…To incorporate the outside loop components into the loop such as the fiberpigtailed acousto-optic modulator (AOM) [25], allowing to reduce the length of the out-of-loop path, at each remote site only single AOM is simultaneously used as a frequency distinguisher for distinguishing its unique frequency from other sites' and as a phase compensator for compensating the phase noise coming from the optical fiber. Furthermore, in comparison with multiple-user optical frequency transfer over a ring and a bus fiber links [20], [38], in which the stabilization of each user end is strongly dependent on the main fiber link, high-performance multiple-user optical frequency transfer demonstrated here not only increases the adaptability of optical frequency transfer to the existing fiber network, but also improves the reliability of the network because the phase noise compensation of each user node is independent of each other. Moreover, the two-way optical frequency comparison method was used to measure the end-to-end stability for avoiding uncommon path from the measurement setup [42].…”

“…As the refractive of the air is the three orders of magnitude lower than that of the fiber, alternative way to suppress the interferometer noise is to build the interferometer with free-space optics [36]. The free-space interferometers have been widely demonstrated [29], [37], [38]. However, they are sensitive to the air flow and the long-term stability is still limited to the 10 −20 level [29], [37], [38], so that the precise temperature stabilization system is still necessary to perform the better long-term stability [29], [37], [38].…”

“…The free-space interferometers have been widely demonstrated [29], [37], [38]. However, they are sensitive to the air flow and the long-term stability is still limited to the 10 −20 level [29], [37], [38], so that the precise temperature stabilization system is still necessary to perform the better long-term stability [29], [37], [38]. Furthermore, the high cost and low reliability of the free-space interferometers will become a great challenge for the field-deployed application.…”

Absolutely Consistent Fiber-Optic Phase Synchronization Based On Fixed-Phase-Reference Optical Active Compensation

“…Hongwei Si et al have proposed a phase synchronization scheme based on optical fiber transmission [17]. The scheme is based on the passive compensation method of phase conjugation [18]- [20], avoiding the use of phase-locked loop. It can compensate for phase fluctuation caused by optical fiber link, and can achieve a repeatable phase difference under operations such as system restart and changing fiber path.…”