A low-loss and broadband all-fiber acousto-optic circulator

TL;DR

This paper introduces a low-loss, broadband all-fiber acousto-optic circulator suitable for quantum and classical networks, utilizing Mach-Zehnder interferometers with fiber null-couplers controlled by acoustic waves.

Contribution

It presents a novel fiber-based circulator with low loss, broad bandwidth, and high extinction, compatible with existing fiber networks and suitable for quantum communication.

Findings

Achieved 0.81 dB insertion loss

Demonstrated at least 50 GHz bandwidth

Provided high extinction up to 27 dB

Abstract

The introduction of low-loss optical fibers probably represents the single most important advance in the growth of our telecommunication system. To meet our needs for secure communications, it is likely that our classical network will soon be operating alongside what is known as a quantum network. The latter is very sensitive to loss and thus poses new constraints to the performance of current fiber components. In particular, recent quantum network prototypes underlined the absence of low-loss non-reciprocal fiber-based devices. Here, we present a solution to this issue by realizing low-loss (0.81 dB), broadband (at least 50 GHz bandwidth) and high-extinction (up to 27 dB) circulators, based on Mach-Zehnder interferometers including so-called fiber null-couplers. The latter are directional couplers, whose splitting-ratio can be controlled by launching acoustic waves along the coupling region. Fabricated from standard single-mode fibers and actuated electrically, these circulators can be made to fit any existing optical fiber networks and could turn out to be key for the transmission and processing of optically encoded quantum information.