研究目的
To implement polarisation-encoded quantum key distribution in optical fibre networks by compensating for birefringence effects using a single polarisation controller to handle non-orthogonal bases simultaneously.
研究成果
The polarisation locker effectively compensates for birefringence in optical fibres, enabling simultaneous compensation of non-orthogonal bases for polarisation-encoded QKD. This reduces system size and cost compared to using multiple controllers. Future work should focus on automating the search algorithm for full integration into QKD systems.
研究不足
The system requires periodic interruption for test signals, which may reduce transmission efficiency. Environmental changes necessitate SOP stability tests for each new setup. The compensator's resolution limits the duration of test signals. The method is not fully automated yet, requiring manual adjustments in some cases.
1：Experimental Design and Method Selection:
The experiment uses a time division multiplexed (TDM) system with a test signal to monitor and compensate for birefringence in optical fibres. A polarisation locker is employed as an automated polarisation controller to correct the state of polarisation (SOP) of photons. The design aims to compensate non-orthogonal bases (rectilinear and diagonal) simultaneously by fixing the controller on the Poincaré sphere plane.
2：Sample Selection and Data Sources:
A pseudo-single photon source is used, generated by a pulsed laser at 1550 nm attenuated to single photon levels. The quantum channel consists of a fixed 1000 m single-mode fibre with a core diameter of 6 μm. Test signals are deployed periodically to adjust the compensator.
3：List of Experimental Equipment and Materials:
Pulsed laser source (wavelength 1550 nm), optical attenuator, polarisation state generator, single-mode fibre (core diameter 6 μm), polarisation-maintaining (PM) fibre, polarisation locker (automated polarisation controller), half-wave plate, polarisation beam splitter, single photon detectors, piezoelectric controllers, in-line polarimeter, digital signal processor.
4：Experimental Procedures and Operational Workflow:
Laser pulses are attenuated to create pseudo-single photons, polarised randomly by the polarisation state generator, transmitted through the fibre channel. A test signal is sent periodically; the polarisation locker adjusts based on feedback from the in-line polarimeter to compensate SOP changes. After compensation, photons pass through a half-wave plate for basis selection and are measured at detectors via a polarisation beam splitter.
5：Data Analysis Methods:
The effectiveness is measured by monitoring the SOP on the Poincaré sphere, ensuring linear states are maintained with minimal ellipticity. Error rates are calculated based on deviations in angle of inclination and ellipticity.
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polarisation locker
Thorlabs
Automated polarisation controller used to compensate for birefringence effects in optical fibres by adjusting the state of polarisation of light.
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single photon detectors
Detect single photons after polarisation compensation and basis selection.
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pulsed laser source
Generate laser pulses at 1550 nm wavelength, attenuated to simulate single photons.
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optical attenuator
Attenuate laser pulses to single photon levels.
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polarisation state generator
Randomly polarise photons before transmission.
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half-wave plate
Change the measurement basis of the polarisation beam splitter.
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polarisation beam splitter
Separate photons based on their polarisation for detection.
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single-mode fibre
Serve as the quantum channel for photon transmission.
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polarisation-maintaining fibre
Ensure state of polarisation is not changed after compensation.
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