Polarization-Controlled Quantum Key Distribution Encoder
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Solution Overview
Problem
Existing quantum key distribution systems based on photon polarization are unstable and susceptible to disturbances, especially over long distances, due to interference in fiber communication channels, and are vulnerable to eavesdropping attacks.
Innovation Solution
A polarization-controlled quantum key distribution method and system that splits optical pulses into two paths, delays and recombines them while controlling their polarization states using Faraday mirrors and phase modulators, ensuring identical polarization states and enhanced stability and security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If photon polarization encoding is used in fiber communication, then the system is simple and suitable for quantum key distribution, but the polarization state is randomly changed during transmission due to fiber interference and disturbance
Solution Approach 1:
The optical pulse is divided into two separate paths (first path and second path) that traverse the fiber channel at different times. This segmentation allows the system to handle polarization disturbances by processing each path independently and then combining them, resolving the contradiction between simple encoding and stable polarization states.
Solution Approach 2:
The system performs preliminary polarization control by adjusting the polarization states of optical pulses in each path before they are combined. This preliminary action compensates for disturbances that occurred during transmission, ensuring stable polarization states at the combination stage despite fiber interference.
2Reliability
If Faraday mirrors are used to reflect optical pulses back to achieve self-balancing effect, then the anti-jamming ability is improved for short distance, but the maximum transmission distance is halved and the system becomes vulnerable to eavesdropping attacks
Solution Approach 1:
Instead of reflecting pulses back through the same path (which limits distance), the invention segments the transmission into two forward paths that are later combined. This allows each path to be optimized for distance while maintaining the balancing effect through controlled recombination, resolving the contradiction between anti-jamming ability and transmission distance.
Solution Approach 2:
The system introduces a polarization controller as an intermediary device that mediates between the two optical paths. This intermediary adjusts the polarization states to achieve the self-balancing effect without requiring backward reflection, enabling longer transmission distances while maintaining anti-jamming capabilities.
3Extent of automation
If optical pulses pass through different arms of interferometers in transmitter and receiver, then phase encoding can be achieved, but the disturbance suffered is not exactly identical and cannot be counteracted, reducing system stability
Solution Approach 1:
The system deliberately uses asymmetric path configurations where optical pulses travel through different arms of interferometers in the transmitter and receiver. This asymmetry is compensated by introducing polarization controllers that adjust the states to ensure disturbances are properly balanced, maintaining both phase encoding capability and system stability.
Solution Approach 2:
The system implements feedback mechanisms through polarization controllers that monitor and adjust the polarization states of optical pulses. This feedback ensures that disturbances accumulated in different interferometer arms are properly compensated, maintaining system stability while preserving phase encoding functionality.
4Length of moving object
If strong laser pulses are used and attenuated to single photon level after reflection, then transmission distance can be extended, but the system becomes vulnerable to eavesdropping attacks and power monitoring becomes ineffective
Solution Approach 1:
The system segments the optical signal into two separate paths that are transmitted forward and then combined, eliminating the need for reflection-based attenuation. This allows maintaining single-photon level security throughout the entire transmission path while achieving extended transmission distance through optimized path design.
Solution Approach 2:
The system performs preliminary attenuation and polarization control before the optical pulses enter the quantum channel, ensuring they are at the appropriate single-photon level from the start. This preliminary action prevents eavesdropping vulnerabilities while maintaining extended transmission distance through efficient path design.
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
The system achieves unconditional secure key distribution by compensating for channel disturbances and preventing eavesdropping, with improved stability and anti-jamming capabilities, reducing the impact of channel losses and enhancing the security of long-distance quantum key distribution.
Implementation Method 1
making the two optical pulses reflected odd times by 90 degree Faraday mirrors separately
Implementation Method 2
splitting an injected optical pulse into two optical pulses traveling along two different paths
Implementation Method 3
phase modulating at least one pulse after the splitting step or recombining step according to a quantum key distribution protocol
Data Source
AI summary
The invention relates to a polarization-controlled encoding method, encoder and quantum key distribution system, which is characterized in that polarization maintaining light path or 90 degree rotation Faraday mirror are used inside the encoder to keep the polarization of the output pulses same, and that in the quantum key distribution system employing the polarization-controlled encoder the pulse emitted from transmitter is unidirectional-transmitted to receiver and then quantum key distribution is implemented using interference in the pulses according to the quantum key distribution protocol. The quantum key distribution system using the polarization-controlled encoder of the invention has the ability of avoiding the wiretapping to transmitter, receiver and quantum channel. Detection units each of which separates reversed photon from other photons are added at the out port of the transmitter and the in port of receiver, respectively, so that Trojan horse is prevented from entering and photons with phase modulated information are prevented from leaving the safe area in receiver. Unconditionally safe key distribution can be accomplished by using the quantum key distribution system of the invention.