Fundamental Limitations of Rayleigh Backscattering Noise on Fiber-Based Multiple-Access Optical Frequency Transfer

Abstract

Ultimate limits of performance for single-sourcebidirectional architecture e.g., optical frequency transfer are set by delay fluctuations within the host material, e.g., optical fiber or atmospheric channel, which is dynamically induced. The most common manifestation of such phase disorder in the optical fiber is backscattering lights coming from Rayleigh backscattering and fresnel reflection, which is observed in nearly all single-sourcebidirectional architectures and can lead to both irreversible coherence losses as well as undesirable interference coupling.While it has been shown that backscattering induced phase noise can be suppressed by adopting acoustic-optic-modulators (AOMs) at the local and remote sites to break the frequency symmetry in both directions. However, this issue can not be avoided for conventional fiber-optic multiple-access coherent optical phase dissemination in which the interference of the signal light with the Rayleigh backscattered light will probably destroy the coherence of the stabilized optical signal. We suppress the backscattering effect by locally breaking the frequency symmetry at the extraction point by inserting an additional AOM. Here, we theoretically analyze and experimentally demonstrate an adddrop one more AOM approach for suppressing the Rayleigh backscattering within the fiber link. Near-complete suppression of backscattering noise is experimentally confirmed through the measurementthe elimination of a common interference term of the signal light and the Rayleigh backscattered light. The results demonstrate that the Rayleigh backscattering light has a limited effect compared to the residual delay-limited fiber phase noise on the system's performance. Our results also provide new evidence that it is possible to largely suppress Rayleigh and other backscattering noise within a long optical fiber link, where the accumulated phase noise could be large, by using frequency symmetry breaking at each access node to achieve robust multiple-access coherent optical phase propagation in spite of scatters or defects.

Passive Optical Phase Stabilization on a Ring Fiber Network

“…be completely avoided in our application. According to the results presented in [45], the Rayleigh backscattering induced fractional frequency instability can be as low as a few 10 −16 /τ (τ being the averaging time) over a 100 km fiber link. Thus, this effect can be neglected at our precision.…”

“…2 as the passive phase noise system. The active phase noise system we used is similar with our previous multiple-access optical frequency transfer system [45]. Figure 5(c) shows the residual phase noise PSDs at the 50/50 km hub over the 100 km fiber link with passive (a, red dashed curve) and active (b, blue solid curve) phase cancellation.…”