Branching optical frequency transfer with enhanced post automatic phase noise cancellation

TL;DR

This paper introduces a passive phase noise cancellation technique for optical frequency transfer over branching fiber networks, achieving high stability and enabling simultaneous distribution to multiple users without active servo components.

Contribution

It presents a novel passive noise cancellation method using acousto-optic modulators and a long outside loop, significantly improving stability in optical frequency transfer over branching fiber links.

Findings

Achieved a stability of 2×10^{-16} at 1 s and 2×10^{-20} at 10,000 s in stabilization.

Demonstrated optical frequency transfer over 145 km fiber with a relative frequency instability of 3.4×10^{-15} at 1 s.

Enabled simultaneous optical signal transfer to multiple users within a local area.

Abstract

We present a technique for coherence transfer of laser light through a branching fiber link, where the optical phase noise induced by environmental perturbations via the fiber link is passively compensated by remote users without the requirements of any active servo components. At each remote site, an acousto-optic modulator (AOM) is simultaneously taken as a frequency distinguisher for distinguishing its unique frequency from other sites' and as an optical actuator for compensating the phase noise coming from the optical fiber. With this configuration, we incorporate a long outside loop path consisting of a fiber-pigtailed AOM into the loop, enabling the significant reduction of the outside loop phase noise in the passive way. To further address the residual out-of-loop phase noise coming from the interferometer and the two-way optical frequency comparison setup, we design a low-noise active temperature stabilization system. Measurements with a back-to-back system show that the stability in our stabilization system is $2\times10^{-16}$ at 1 s, reaching $2\times10^{-20}$ after 10,000 s. Adopting these techniques, we demonstrate transfer of a laser light through a branching fiber network with 50 km and 145 km two fiber links. After being compensated for the 145 km fiber link, the relative frequency instability is $3.4\times10^{-15}$ at the 1 s averaging time and scales down to $3.7\times10^{-19}$ at the 10,000 s averaging time. This proposed technique is suitable for the simultaneous transfer of an optical signal to a number of independent users within a local area.