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arXiv:2405.12903

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

Martin Blaha, Arno Rauschenbeutel, Riccardo Pennetta

Published May 21, 2024• 0 citations
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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.

DOI
10.48550/arxiv.2405.12903

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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.
The introduction of low-loss optical fibers probably represents the single most important advance in the growth of telecommunication systems. 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 constraints to the performance of current fiber components. In particular, recent quantum network prototypes underline the absence of low-loss nonreciprocal 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.
Abstract Optical circulators are key components for integrated photonic information processing and quantum networks, yet realizing compact and magnet-free closed-loop circulation remains challenging. We propose an on-chip four-port optical circulator consisting of three evanescently coupled microring resonators, with directional quantum squeezing introduced into the central nonlinear resonator. The squeezing selectively enhances the effective inter-resonator coupling and renormalizes the resonance frequency for one propagation direction, while leaving the counterpropagating channel unaffected. This directional asymmetry breaks optical reciprocity and enables closed-loop circulation along 1 → 2 → 3 → 4 → 1. At the optimal operating point, the circulator achieves a fidelity of approximately 0.99 and an average insertion loss of about 0.22 dB. In addition, pump-induced quantum noise can be suppressed by injecting a phase-matched broadband squeezed-vacuum field, allowing low-noise operation from the classical to the single-photon regime. The proposed scheme provides a compact, magnet-free, and chip-compatible route to closed-loop optical circulation, with potential applications in integrated optical routing and quantum photonic networks.
Abstract In photonic quantum applications, optical routers are required to handle single photons with low loss, high speed, and preservation of their quantum states. Single-photon routing with maintained polarization states is particularly important for utilizing them as qubits. Here, we demonstrate a polarization-maintaining electro-optic router compatible with single photons. Our custom electro-optic modulator is embedded in a configuration of a Mach–Zehnder interferometer, where each optical component achieves polarization-maintaining operation. We observe the performance of the router with 2%–4% loss, 20 dB switching extinction ratio, 2.9 ns rise time, and >99% polarization process fidelity to an ideal identity operation.
Only one Mach-Zehnder interferometer is used in the proposed quantum bit distribution system where the two arms composing the Mach-Zehnder interferometer have been used as the transmission line. The loss of the photons due to absorption will decrease and the wavelets composing the photon are expected to transmit longer distance. The optical cable which contains many fiber belts which contain many fibers in parallel that is possible to make a Mach-Zehnder interferometer with its two arms as long as possible. This transmission system uses only two couplers and physically ensures transmission security.
Breaking optical reciprocity enables new regimes of light--matter interaction with broad implications for fundamental physics and emerging quantum technologies. Although various approaches have been explored to achieve optical nonreciprocity, realizing it at the single-photon level has remained a major challenge. Here, we demonstrate nonmagnetic optical nonreciprocity -- including both isolation and circulation -- in the quantum regime, enabled by efficient and noiseless all-optical frequency conversion on an integrated III-V photonic chip. Our device preserves the quantum coherence and entanglement of the input photons while delivering exceptional performance parameters, including a high extinction ratio of 34 dB, low insertion loss of 0.8 dB, broad bandwidth of 44 GHz, high operational fidelity of 97%, and widely tunable operation wavelength. This realization of quantum optical nonreciprocity in a scalable photonic platform opens a pathway toward directional quantum communication and noise-resilient quantum networks.