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Optics Express

Phase stabilization with triple wavelength bands for single-photon interference in quantum communication

Yohei Sugiyama, Akito Ozawa, Wataru Kokuyama, Tomoyuki Horikiri, Daisuke Akamatsu, Feng-Lei Hong

Published Dec 15, 2025• 0 citations
Publisher

Abstract

Optical interferometers are crucial for long-distance quantum communications. We propose a novel phase stabilization method employing triple wavelength bands for single-photon interference in optical fiber-based interferometers, incorporating a simplified laser frequency stabilization technique that utilizes a single nonlinear crystal. After stabilization, the residual phase noise of the fiber interferometer was 20 mrad for differential arm lengths (Δ L ) of 0 and 10 m. This represents a 9-fold and 7.5-fold improvement for Δ L = 0 and 10 m, respectively, compared with those observed in previous double-wavelength methods. These findings enhance the visibility and simplicity of quantum key and entanglement distributions in long-distance quantum communication.

DOI
10.1364/oe.581375

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Optical interferometers are crucial for long-distance quantum communications. We propose a novel phase stabilization method employing triple wavelength bands for single-photon interference in optical fiber-based interferometers, incorporating a simplified laser frequency stabilization technique that utilizes a single nonlinear crystal. After stabilization, the residual phase noise of the fiber interferometer was 20 mrad for differential arm lengths (Δ L ) of 0 and 10 m. This represents a 9-fold and 7.5-fold improvement for Δ L = 0 and 10 m, respectively, compared with those observed in previous double-wavelength methods. These findings enhance the visibility and simplicity of quantum key and entanglement distributions in long-distance quantum communication.
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The frequency noise of an external-cavity diode laser locked to an ultralow-expansion cavity (cavity-stabilized laser) and a whispering-gallery-mode (WGM) cavity optical-feedback semiconductor laser (WGM laser) was evaluated. The frequency noise of the WGM laser was approximately two orders of magnitude smaller than that of the cavity-stabilized laser at high Fourier frequencies. Using the WGM laser, phase noise reduction of approximately two orders of magnitude was observed in the dual-band stabilization of an optical-fiber-based interferometer at high Fourier frequencies. This noise reduction should improve the measurement fidelity in quantum key and entanglement distributions in long-distance quantum communication.
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We experimentally demonstrate stable and user-adjustable single-photon interference in a 1 km long fiber-optic Mach-Zehnder interferometer, using an active phase control system with the feedback provided by a classical laser. We are able to continuously tune the single-photon phase difference between the interferometer arms using a phase modulator, which is synchronized with the gate window of the single-photon detectors. The phase control system employs a piezoelectric fiber stretcher to stabilize the phase drift in the interferometer. A single-photon net visibility of 0.97 is obtained, yielding future possibilities for experimental realizations of quantum repeaters in optical fibers and violation of Bell's inequalities using genuine energy-time entanglement.
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