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Intensity fluctuation of a gain-switched semiconductor laser for quantum key distribution systems
Optics Express
|February 4, 2017
Summary
Quantum key distribution (QKD) systems require secure transmitters. This study found that gain-switched lasers in QKD systems exhibit intensity fluctuations, especially at low excitation, impacting key rates.
Area of Science:
- Quantum Information Science
- Semiconductor Laser Physics
- Optical Communications Security
Background:
- Quantum Key Distribution (QKD) systems are crucial for secure communication.
- Practical deployment of QKD necessitates robust security certification.
- Transmitter stability is a key factor in QKD system performance.
Purpose of the Study:
- Investigate optical pulse intensity fluctuations in gain-switched semiconductor lasers for QKD.
- Analyze the impact of these fluctuations on the decoy-BB84 protocol.
- Understand the underlying physical mechanisms causing intensity instability.
Main Methods:
- Experimental characterization of optical pulse intensity from a gain-switched laser.
- Implementation of the decoy-BB84 protocol using the characterized laser.
- Numerical simulation using rate equations to model laser dynamics.
- Analysis of pulse-to-pulse correlation and intensity fluctuation.
Main Results:
- Observed significant intensity fluctuation and negative correlation between adjacent pulses at low laser excitation.
- Demonstrated that increasing excitation reduces fluctuation and correlation.
- Successfully reproduced experimental findings using rate equation simulations.
- Identified intrinsic instability in periodically driven gain-switched lasers as the cause of fluctuation.
Conclusions:
- Gain-switched laser instability is a critical issue for GHz-clock QKD systems.
- Intensity fluctuations directly affect the final key rate in QKD.
- Strategies for reducing intensity fluctuations in QKD transmitters are essential for practical deployment.
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