Optical Transmission Phase Compensation via Faraday Reflectors
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Solution Overview
Problem
In optical transmission systems where real-timeness is not required, especially for integration processing times shorter than several seconds, the complexity and signal loss associated with phase-locked loop circuits and microwave signal phase shifters hinder phase stability and digitization, making multipoint transmission compensation difficult.
Innovation Solution
An optical transmission system that uses a two-lightwave generator to create coherent optical signals of different wavelengths, a polarization beam splitter, optical couplers, photodetectors, and a Faraday reflector to perform round-trip transmission phase compensation postprocessing, simplifying the system configuration and reducing signal loss while improving phase stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase-locked loop circuit and microwave signal phase shifter are used for real-time phase compensation, then phase stability is improved, but system complexity increases and signal loss increases
Solution Approach 1:
The patent extracts the real-time phase compensation function from the system by removing the phase-locked loop circuit and microwave signal phase shifter. Instead, it uses a simplified configuration with optical couplers and photodetectors to acquire phase compensation data at the transmission source, which is then applied at the transmission destination without requiring complex real-time control circuits.
Solution Approach 2:
The patent replaces the electronic/microwave-based phase shifting mechanism with an optical-based measurement and compensation approach. By using optical couplers to tap transmission light and photodetectors to convert optical phase information to electrical signals, the system substitutes complex microwave phase control with simpler optical measurement and post-processing.
2Reliability
If phase-locked loop circuit and microwave signal phase shifter are used for real-time phase compensation, then phase stability is improved, but signal loss increases
Solution Approach 1:
The patent removes the microwave signal phase shifter from the system, eliminating its associated signal loss. The compensation data is acquired optically through the transmission path itself using optical couplers, avoiding the need for separate microwave phase control paths that would introduce additional loss.
3Speed
If integration processing is performed for shorter than several seconds, then real-timeness is improved, but phase stability deteriorates without real-time compensation
Solution Approach 1:
The patent performs preliminary acquisition of round-trip transmission phase compensation data at the transmission source before the signal reaches the destination. By measuring the phase of transmission light that has completed a round trip through the optical fiber using optical couplers and photodetectors, the system prepares compensation information in advance that can be directly applied to short-integration-time signals without requiring real-time adjustment during the integration period.
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 simplifies the system configuration, reduces signal loss, and enhances phase stability, facilitating higher digitization and multipoint transmission compensation by acquiring round-trip phase compensation data synchronized with integration timings, thus enabling effective phase correction without the need for real-time phase shifting.
Implementation Method 1
a Faraday reflector for reflecting the two optical signals frequency-shifted by the optical modulator by applying Faraday rotation of 90 degrees thereto
Data Source
AI summary
An optical transmission system includes: a two-lightwave generator for generating optical signals having wavelengths λ1 and λ2 from laser light; a photodetector for detecting a microwave signal M12 from two optical signals distributed by an optical coupler; an optical modulator for frequency-shifting the two optical signals; a Faraday reflector for reflecting the two optical signals; an optical coupler for mixing the two optical signals that have been reflected by the Faraday reflector, frequency-shifted again, transmitted by an optical fiber, and guided by a polarization beam splitter, with two optical signals distributed by an optical coupler; an optical demultiplexer for wavelength-dividing four mixed optical signals into optical signals having the wavelengths λ1 and λ2; photodetectors for detecting respective beat signals of the wavelength-divided optical signals having λ1 and λ2; and a phase difference detector for detecting a phase difference between the beat signals of the optical signals having λ1 and λ2.