Optical Transmitting Device Random Modulation Shift
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Solution Overview
Problem
In quantum cryptography, increasing the number of photons per symbol to enhance light intensity for long-distance optical transmission compromises confidentiality due to reduced quantum fluctuation uncertainty, making it difficult to maintain secure communication.
Innovation Solution
An optical transmitting device that randomly shifts the modulation position of symbols within a signal identification region based on a pseudo or physical random number, ensuring confidentiality even with increased photon numbers, by using a symbol determining circuit and a shift circuit to alter the modulation position for each symbol transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the number of photons per symbol is increased to enhance light intensity for long-distance optical transmission, then the transmission distance and signal quality are improved, but the confidentiality is compromised due to reduced quantum fluctuation uncertainty
Solution Approach 1:
The patent applies dynamics by making the modulation position variable and random rather than fixed. The modulation position is dynamically shifted based on random numbers, creating uncertainty for eavesdroppers while allowing the legitimate receiver to correctly interpret the signal through synchronization. This dynamic positioning resolves the contradiction by maintaining confidentiality through randomness while enabling high-photon transmission.
Solution Approach 2:
The patent changes the parameter of modulation position from a fixed value to a randomly shifted value. By varying the modulation position parameter based on random numbers, the system maintains quantum fluctuation uncertainty even with increased photon counts, thus preserving confidentiality while allowing higher light intensity for long-distance transmission.
2Reliability
If random shifting of modulation position is implemented to maintain confidentiality, then the probability of eavesdropper inference is reduced, but the device complexity increases due to additional shift circuit and control mechanisms
Solution Approach 1:
The patent introduces an intermediary element - a random number - that mediates between the plain text and the modulation position. This random number acts as a key that both the transmitter and receiver use to synchronize the modulation position shifts, simplifying the overall system architecture while maintaining security. The intermediary random number coordinate system allows complex random shifts to be managed through a unified reference frame.
3Reliability
If modulation position is randomly shifted within signal identification region, then the signal confidentiality is maintained against eavesdropping, but the difficulty of detecting and measuring the signal increases for the legitimate receiver
Solution Approach 1:
The patent implements feedback through the random number coordinate system that both transmitter and receiver share. The random numbers used for shifting at the transmitter are known to the receiver, creating a feedback loop that enables the receiver to compensate for the random shifts and correctly detect the signal. This feedback mechanism resolves the detection difficulty while maintaining confidentiality against eavesdroppers who lack the random number key.
Data Source
AI summary
An optical transmitting device includes: a symbol determining circuit that determines one base from a plurality of bases for each input of plain text corresponding to one symbol and determines a modulation position of the symbol according to the plain text and the base; a shift circuit that randomly shifts the modulation position within a signal identification region set based on the base; and a modulator that modulates light emitted from a light source, according to a shifted position shifted by the shift circuit.