Optical Code Communication System Coherent Detection
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Solution Overview
Problem
Optical code division multiplexing in the optical frequency or wavelength region faces challenges with sensitivity degradation due to beat noise and shot noise, limiting the number of multiplexed codes and affecting data transmission accuracy.
Innovation Solution
The implementation of an optical code communication system that maintains coherence between optical frequency chips and local light, using phase adjustments to suppress noise and interference, allowing for coherent detection and improved signal processing through an optical mixing decoder and detection adder-subtractor filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If optical code division multiplexing is used in the optical frequency region to enable multiple signals to share the same propagation media and frequency band, then the number of multiplexed codes increases, but sensitivity degradation occurs due to beat noise and shot noise
Solution Approach 1:
The patent replaces direct detection with coherent detection using local light. Instead of directly detecting the optical signal intensity, the system mixes the received coded light with local light that has the same frequency and phase characteristics, converting the optical signal into an electrical signal through interference. This substitution enables the system to suppress beat noise and shot noise, thereby maintaining sensitivity while increasing the number of multiplexed codes.
Solution Approach 2:
The patent changes the detection method from direct intensity detection to coherent detection by introducing local light with specific frequency and phase parameters. By adjusting the frequency and phase of the local light to match the coded light, the system can selectively enhance the desired signal while suppressing noise components, thus improving sensitivity and enabling more codes to be multiplexed.
2Object-affected harmful factors
If multiple access interference suppression is implemented through differential detection, then interference between codes is reduced, but sensitivity degradation due to noise from other coded lights cannot be ignored
Solution Approach 1:
The patent introduces local light as an intermediary to facilitate the detection process. The local light acts as a reference that mixes with the coded light, enabling the extraction of signal information while suppressing noise. By using local light with the same frequency and phase as the coded light, the system can differentiate between desired signals and noise from other codes, thereby reducing multiple access interference while maintaining sensitivity.
Solution Approach 2:
The patent employs a feedback mechanism where the received coded light is mixed with local light, and the resulting signal is processed to extract the transmitted information. The system uses the phase and frequency information from the local light to continuously adjust and optimize the detection process, enabling effective suppression of multiple access interference and noise through coherent detection.
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 significantly reduces sensitivity degradation and enhances data transmission accuracy by effectively canceling multiple access interference, enabling higher accuracy and increased number of multiplexed codes in optical communication systems.
Implementation Method 1
an optical mixing decoder for mixing the coded light from the optical transmitter and the local light
Implementation Method 2
the coded light from the optical transmitter has coherence between optical frequency chips constituting the coded light from the optical transmitter, when being detected in the detection adder-subtractor filter, and the local light has coherence between optical frequency chips constituting the local light
Data Source
AI summary
An optical code communication system comprises an optical transmitter, an optical receiver, and an optical transmission line. The optical receiver has an optical mixing decoder for mixing a coded light and a local light, dividing the mixed light into an object optical frequency and a non-object optical frequency, and outputting the lights and a detection adder-subtractor filter for detecting the object optical frequency and the non-object optical frequency, filtering the intermediate frequency signals, subtracting one of the intermediate frequency signal from the other, and outputting the resultant intermediate frequency signal. The coded light and the local light are coherent with each other between the optical frequency chips constituting the coded light when detected. The optical mixing decoder or detection adder-subtractor filter regulates the phase of the intermediate frequency signal within the passband when filtered so that the output value or the absolute value of the intermediate frequency signal within the passband when filtered is different when the optical receiver receives a coded light modulated with a different value of the transmission data.