Optical Transmitter Phase Stabilization via Loop-Type Conjugation
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Solution Overview
Problem
Conventional optical transmission systems face instability in amplifying polarization-multiplexed signals due to fluctuations in the polarization state, leading to unstable phase conditions between quadrature polarized components, which affects the stability of phase sensitive amplification operations.
Innovation Solution
An optical transmitter with a loop-type phase conjugate light generator using a shared second-order non-linear optical element, which separates and rotates polarized components, generates phase conjugate light, and adjusts optical path lengths to stabilize the relative phase between main signal and phase conjugate light, ensuring stable phase conditions for polarization-multiplexed signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional laser amplifiers are used to amplify signal light, then amplification gain is achieved, but spontaneous emission light contamination occurs and S/N ratio deteriorates by at least 3 dB
Solution Approach 1:
The patent converts the harmful spontaneous emission light into a beneficial resource by using it as pump light for optical parametric amplification. The spontaneous emission light that would normally contaminate the signal is instead utilized to generate phase-conjugate light, which enables amplification without S/N deterioration. This transforms the harmful factor into the essential energy source for the amplification process.
Solution Approach 2:
The patent replaces conventional electronic amplification mechanisms with optical parametric amplification based on nonlinear optical effects. Instead of using electronic parts for photoelectric conversion and amplification, the system uses optical processes involving second-order non-linear optical materials to achieve signal amplification while maintaining the optical form and avoiding electronic response speed limitations.
2Object-generated harmful factors
If phase sensitive amplification is used to amplify signal light while shaping waveforms, then S/N ratio is maintained, but phase stability between quadrature polarized components becomes unstable
Solution Approach 1:
The patent introduces a feedback mechanism where phase-conjugate light generated by optical parametric amplification is fed back to the input side to stabilize the phase of pump light. This feedback loop continuously adjusts and maintains phase stability between quadrature polarized components, ensuring that phase conditions remain stable throughout the amplification process while suppressing spontaneous emission light.
Solution Approach 2:
The patent dynamically adjusts optical parameters including pump light power, phase modulation depth, and waveguide temperature to maintain optimal phase matching conditions. By continuously monitoring and adjusting these parameters, the system stabilizes the phase relationship between quadrature polarized components while maintaining high amplification gain and suppressing spontaneous emission light.
3Productivity
If polarization-multiplexed signals are transmitted through optical fiber, then transmission capacity is increased, but polarization state fluctuations cause unstable phase conditions
Solution Approach 1:
The patent segments the polarization-multiplexed signal into separate quadrature polarized components and processes them independently through separate optical paths. By treating each polarization component separately and applying individual phase stabilization, the system maintains stability for each component while preserving the overall high-capacity polarization-multiplexed transmission.
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
The solution stabilizes the phase between quadrature polarized waves, enabling stable phase sensitive amplification and reducing phase variations, thus maintaining the quality of PDM signals and ensuring stable operation of phase sensitive amplifiers in polarization diversity configurations.
Implementation Method 1
A PSA has a function of shaping a signal light waveform or a phase signal having been deteriorated under the influence of dispersion of a transmission fiber. Spontaneous emission light having a quadrature phase that is independent of the signal can be suppressed and spontaneous emission light in phase with the signal can also be minimized.
Implementation Method 2
a loop-type phase conjugate light generator having, on a path from one to another of the two output ports, the polarization separator, a polarization rotator which rotates by 90 degrees a polarized wave of the signal light of the first polarized component, and a first second-order non-linear optical element equipped with a first optical waveguide that generates phase conjugate light of the polarization-rotated signal light and phase conjugate light of the signal light of the second polarized component
Data Source
AI summary
The present invention provides a configuration of a novel optical transmitter which outputs stable PDM signals. The novel optical transmitter generates phase conjugate light using a single second-order non-linear optical element included in a phase conjugate light generator with a looped configuration. A relative phase of main signal light with respect to excitation light and phase conjugate light of the main signal light stabilizes between two polarized components, and a PDM signal including a pair of a polarization-multiplexed signal and phase conjugate light in a stable phase state can be generated and transmitted. The present invention can provide an optical transmitter that generates a PDM signal in which a variation in a phase between quadrature polarized waves is suppressed. By stabilizing quality of a PDM transmission signal on a side of the optical transmitter, a phase sensitive amplifier in a polarization diversity configuration can be operated in a stable manner.