Optical Communication System Phase Synchronization
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Solution Overview
Problem
In optical communication systems, increasing the multiplicity of signal transmission while maintaining high signal-to-noise ratio (S/N) is challenging due to phase noise and laser frequency fluctuations, limiting the accuracy of phase reproduction and signal demodulation, especially in conventional systems that rely on pilot carriers for phase synchronization, which can degrade signal quality and waste bandwidth.
Innovation Solution
An optical communication system that employs a transmitter outputting signal lights with phase-conjugate subcarriers and a receiver with a light phase synchronization mechanism using second-order nonlinear optical elements to generate sum frequency lights, allowing phase synchronization without a pilot carrier, and utilizing a non-degenerate optical phase-sensitive amplifier for amplification, enabling coherent demodulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the multiplicity of the modulation scheme is increased, then the system capacity is improved, but the S/N ratio deteriorates due to narrowed signal point intervals
Solution Approach 1:
The patent changes the fundamental parameter of optical amplification from spontaneous emission-based (EDFA) to stimulated emission-based (PSA), transforming the amplification mechanism to achieve noiseless amplification and maintain high S/N ratio while supporting high-multiplicity modulation
Solution Approach 2:
The patent replaces the conventional EDFA mechanical/amplification system with a PSA system based on optical parametric amplification, substituting the noise-generating spontaneous emission mechanism with a noiseless stimulated emission mechanism to resolve the S/N ratio deterioration
2Power
If conventional EDFA amplification is used, then signal amplification is achieved, but S/N ratio deteriorates by at least 3 dB due to spontaneously-emitted light noise
Solution Approach 1:
The patent converts the harmful spontaneous emission noise into beneficial stimulated emission by using the spontaneously-emitted light as a seed for PSA, transforming the noise source into a useful component for noiseless amplification and phase-sensitive detection
Solution Approach 2:
The patent fundamentally changes the amplification parameter from spontaneous emission (EDFA) to stimulated emission (PSA), altering the physical mechanism to eliminate the 3 dB S/N penalty and enable noiseless signal amplification
3Measurement precision
If pilot carriers are used for phase synchronization, then phase detection accuracy is improved, but bandwidth is wasted and signal quality deteriorates due to non-linear processes
Solution Approach 1:
The patent extracts and eliminates the pilot carrier component from the transmission signal, achieving phase synchronization without requiring dedicated bandwidth for pilot signals, thereby improving bandwidth utilization and reducing non-linear distortion
Solution Approach 2:
The patent enables the system to perform phase synchronization using only the signal light itself through PSA-based self-referenced homodyne detection, eliminating the need for external pilot carriers and achieving self-sufficient phase recovery
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 accurate and efficient transmission of high-multiplicity signals by reducing intensity and phase noise, eliminating the need for multiple pilot carriers and minimizing nonlinear noise, thus improving signal quality and bandwidth utilization.
Implementation Method 1
a second-order nonlinear optical element configured to generate a sum frequency light of the two subcarriers of the transmitted signal light
Implementation Method 2
a second-order nonlinear optical element configured to generate a second harmonic light of sideband light generated from a local oscillation light
Implementation Method 3
a non-degenerate optical phase-sensitive amplifier configured to use the synchronized light to amplify the transmitted signal light
Implementation Method 4
a coherent receiver configured to use the synchronized light to demodulate the amplified signal light
Data Source
AI summary
According to the present disclosure, it is possible to realize an optical communication system in which a relay-type PSA and homodyne detection are efficiently combined using a single phase synchronization mechanism. Intensity noise and phase noise can be suppressed to a very low level, and accurate transmission of signals with increased multiplicity is enabled. By utilizing the features of the PSA to extract the phase of a single carrier using the sum frequency light of the signal light and its phase-conjugated light, the number of pilot carriers can be reduced compared to the configuration of the conventional optical communication system, and it is possible to suppress unnecessary nonlinear noise.