Coherent Optical Modulation for Secure Key Distribution
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Solution Overview
Problem
Current methods for simultaneous transmission of information and cryptographic key distribution require separate optical channels and two different light sources, making them inefficient and insecure, especially in standard telecommunications infrastructure.
Innovation Solution
The use of modified coherent modulation formats like BPSK, QPSK, and QAM, where a single optical carrier wavelength encodes both information and cryptographic key bits, allowing secure communication using phase and amplitude modulation with phase-sensitive detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate optical channels and two different light sources are used for information transmission and cryptographic key distribution, then security and reliability are improved, but device complexity and infrastructure requirements worsen
Solution Approach 1:
The patent combines information transmission and cryptographic key distribution into a single optical channel using one light source. The modulator simultaneously encodes both information bits and key bits onto the same optical carrier by manipulating amplitude and phase, eliminating the need for separate channels and light sources while maintaining security through quantum mechanical principles
Solution Approach 2:
The optical channel and light source are designed to perform multiple functions: transmitting both information and cryptographic keys simultaneously. The modulator acts as a multi-functional device that encodes different types of data (information and key bits) using the same physical resource (optical carrier), improving efficiency without compromising security
2Productivity
If a single optical channel is used for simultaneous transmission of information and cryptographic key, then infrastructure efficiency is improved, but the difficulty of detecting and measuring eavesdropping worsens
Solution Approach 1:
The patent implements a feedback mechanism where the receiver measures the statistical properties of the received signal and compares them against expected thresholds. When an eavesdropping attempt is detected (through abnormal variance in signal measurements), the system provides feedback to abort key distribution while continuing information transmission, enabling real-time security monitoring in a shared channel
Solution Approach 2:
The patent uses statistical analysis of signal variance as an intermediary indicator to detect eavesdropping. Instead of directly detecting the eavesdropper, the system measures the variance of received signal values and uses this intermediate measurement to infer the presence of eavesdropping attempts, making detection feasible in a single shared channel
3Reliability
If cryptographic key distribution is aborted when eavesdropping is detected, then security is improved, but information transmission productivity worsens
Solution Approach 1:
The patent segments the transmitted signal into two independent components: information bits and key bits. When eavesdropping is detected, only the key distribution portion is aborted while information transmission continues uninterrupted. This segmentation allows selective abandonment of the compromised function while maintaining productivity of the secure function
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 approach enables secure communication over standard telecommunications infrastructure, detecting eavesdropping and maintaining security even with varying signal power, while allowing information transmission to continue despite potential eavesdropping detection.
Implementation Method 1
phase and amplitude modulation of an optical carrier wave
Implementation Method 2
phase and amplitude modulation of an optical carrier wave
Implementation Method 3
phase-sensitive detection, such as homodyne or heterodyne detection
Implementation Method 4
phase-sensitive detection, such as homodyne or heterodyne detection
Data Source
Figure 1(a)~1(d)
Figure 2(a)~2(e)
Figure 3(a)~3(g)
AI summary
The subject matter of the present invention is a method for coherent transmission of an optical signal with simultaneous transmission of information bits and distribution of cryptographic key bits using amplitude-phase modulation of a laser beam, characterised by using a first modulation with defined areas in the IQ plane, where I and Q are two light quadratures of said laser beam, with phase shifted by π/2, and encoding the information bits by means of the first modulation, wherein defining symbols of a second modulation within the areas of the first modulation in the IQ plane, wherein the symbols of the second modulation are used to encode cryptographic key bits, and the Euclidean distance on the IQ plane between any two symbols of the second modulation located in different areas of the first modulation is at least three times larger than the largest Euclidean distance between any two symbols of the second modulation located in the same area of the first modulation. The invention also includes a method for receiving the optical signal and a method for optical communications. Furthermore, the invention includes an optical signal transmitter, an optical signal receiver and a system for coherent optical communications.