Pulsed Light Polarization Locking for CV-QKD Systems
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Solution Overview
Problem
Existing CV-QKD systems face challenges in real-time polarization state locking due to environmental fluctuations, leading to inefficiencies and interruptions in secure key distribution.
Innovation Solution
A pulsed light high-speed polarization locking method using time division multiplexing and polarization multiplexing, combined with a conditional simulated annealing algorithm and integral type optical signal detection, enables rapid polarization state adjustment and locking through real-time feedback and peak voltage monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If effective-value converter integration method is used for polarization locking, then polarization locking can be achieved, but the locking cycle becomes long and real-time tracking is lost
Solution Approach 1:
The patent uses pulsed light instead of continuous light to create periodic measurement cycles. The effective value converter integrates light signals during each pulse period, and the polarization controller adjusts parameters periodically based on these integration results. This periodic action enables real-time tracking of polarization state changes while maintaining locking capability, resolving the contradiction between achieving reliable locking and reducing locking cycle time.
Solution Approach 2:
The patent implements a closed-loop feedback system where the effective value converter continuously measures the polarization state, generates feedback signals, and the polarization controller adjusts the polarization parameters based on this feedback. This real-time feedback mechanism allows the system to track and correct polarization drift dynamically, achieving both reliable locking and real-time response, thereby reducing the effective locking cycle.
2Reliability
If polarization locking is performed using conventional methods, then polarization state can be locked, but quantum key distribution must be paused during locking period
Solution Approach 1:
The patent enables continuous quantum key distribution by performing polarization locking measurements and adjustments in parallel with the key distribution process. The pulsed light measurements and polarization controller adjustments occur continuously without interrupting the quantum signal transmission, allowing both polarization stabilization and key generation to proceed simultaneously, thus eliminating pauses and improving overall productivity.
3Measurement precision
If multiple pulsed light signals are integrated into DC voltage, then polarization locking feedback signal is obtained, but the locking speed is reduced
Solution Approach 1:
Instead of integrating multiple continuous signals which slows down the process, the patent uses periodic pulsed light signals where integration occurs rapidly during each short pulse period. The effective value converter processes signals in discrete time windows corresponding to each pulse, enabling fast integration and feedback generation. This periodic integration approach maintains measurement precision while significantly increasing locking speed compared to continuous integration methods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves high-speed polarization locking, enhancing the stability and security of CV-QKD systems by tracking and locking polarization states in real-time, even under complex external environments, and improves resistance to local oscillator dithering attacks.
Implementation Method 1
splitting the pulsed light into a local oscillator and a signal light through a beam splitter, transmitting the local oscillator and the signal light in a same fiber by time division multiplexing and polarization multiplexing manners
Implementation Method 2
conducting polarization demultiplexing of the local oscillator and the signal light on the rest portion of the light field through a dynamic polarization controller and a polarization beam splitter
Implementation Method 3
detecting and converting the first feedback signal into a peak voltage of an output electric pulse through an integral type optical signal detector
Implementation Method 4
transmitting the local oscillator and the signal light in a same fiber by time division multiplexing and polarization multiplexing manners at a transmitting end of a CV-QKD system, and reaching a receiving end after the local oscillator and the signal light are transmitted through a long-distance single-mode fiber
Implementation Method 5
the birefringent effect of the single-mode fiber due to the environment temperature, stress and weather change induces the polarization state fluctuation of the light
Data Source
AI summary
A pulsed light high-speed polarization locking method of a continuous variable quantum key distribution system is disclosed. An integral type optical detector is used for converting energy of a single pulsed light into a peak voltage of an output electric pulse in real time so as to achieve real-time measurement of light pulse energy without conducting high-speed data sampling and simplify the data acquisition and processing. By utilizing the FPGA hardware, a conditional simulated annealing algorithm is quickly operated to search the target polarization state and achieve high-speed polarization locking under the pulsed light. In addition, the power change of a local oscillator is monitored in real time to strengthen the resistance of the system against local oscillator dithering attack. The present invention can effectively solve a problem of rapid fluctuations of polarization state of pulsed light caused by complex external environments.