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IEEE photonics journal

Long-Term Stable Polarized Adiabatic Interfered Decoder for Differential Phase Shift Quantum Key

You-Cheng Lin, You-Xin Wang, Shih-Chang Hsu, Hsing-Yi Huang, Yuanjie Yang, Yung-Hsuan Li, Kuan-Wei Hu, Gong‐Ru Lin

Published Oct 20, 2025• 0 citations
Publisher

Abstract

Under the quantum key distribution with differential phase-shift-keying protocol, the ultimate stability of the system is limited by the residual wavelength drift of the quantum-key carrier and the polarization/refractive-index/physical-length fluctuations induced by environmental thermal disturbance. To permanently overcome such a shortcoming, a 1-bit-delayed interferometric fiberized decoder with ultrastable visibility maintenance and long-term immunity to environmental perturbations is demonstrated by employing all polarization maintaining-fiber to construct an asymmetric-arm Mach-Zehnder interferometer, and surrounding such a delay-line interferometric decoder with thermal-isolated sponge and styrofoam container. Receiving the DPS-QKD bit-stream with a high sifting key rate and low bit-error ratio is approached by maintaining the high interfered visibility and eliminating the wavelength drift with a highly adiabatic package. Such an ultrastable long-term 1-bit delay interferometric decoder is particularly suitable for the persistent DPS-QKD operation towards future commercialization.

DOI
10.1109/jphot.2025.3624147

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Abstract We report on the adaptation of a commercially available fiber-based quantum key distribution (QKD) system with phase-time encoding to free-space operation. The proposed approach minimizes architectural modifications by replacing the single-mode receiving interferometer with a free-space multi-mode delay interferometer, enabling efficient detection of spatially distorted quantum states typical for atmospheric channels. Several interferometer configurations are experimentally investigated, and a multi-mode Michelson interferometer with polarization routing is identified as the optimal solution in terms of interference visibility, loss, and alignment robustness. The impact of chromatic and modal dispersion on phase-time interference is analyzed and shown to be manageable under realistic system parameters. A laboratory QKD experiment demonstrates stable operation with a quantum bit error rate of about 4.5% and a secret key rate of hundreds of bits per second, confirming the feasibility of extending fiber-based QKD platforms to free-space links.
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