Wavelength Control Using Multi-Etalon Splitter and Photodiode Coefficients
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Solution Overview
Problem
Existing wavelength control systems face challenges in achieving high-speed and accurate wavelength monitoring, particularly in dead bands where differential coefficients are small, and struggle to distinguish between wavelength changes and optical power changes.
Innovation Solution
A system utilizing a wavelength-tunable light source split into three optical signals, with three photodiodes and a controller calculating coefficients from their outputs to control the wavelength, allowing for high-speed and accurate monitoring across the entire wavelength range without requiring temperature adjustments for each setting wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single etalon filter is used for wavelength monitoring, then the system structure is simple, but the measurement precision deteriorates in dead bands where differential coefficients are small
Solution Approach 1:
The patent divides the wavelength monitoring function into multiple etalon filters (first etalon and second etalon) with different transmission characteristics. Each etalon covers different wavelength ranges effectively, eliminating dead bands where monitoring precision would deteriorate. This segmentation allows continuous high-precision monitoring across the entire wavelength range without requiring complex temperature adjustments.
Solution Approach 2:
The patent introduces a new dimension by using multiple etalon filters with different Free Spectral Ranges (FSR1 and FSR2) instead of relying on a single etalon. This multi-dimensional approach allows the system to maintain large differential coefficients across all wavelength ranges by selecting appropriate etalon combinations, thereby achieving high measurement precision without increasing thermal control complexity.
2Measurement precision
If temperature adjustments are made for each setting wavelength to maintain monitoring accuracy, then the measurement precision is improved, but the productivity deteriorates due to frequent temperature changes
Solution Approach 1:
The patent performs preliminary configuration by selecting etalon filters with specifically designed different FSR values before operation. This preliminary setup enables the system to achieve high-precision wavelength monitoring across the entire range without requiring subsequent temperature adjustments for each wavelength setting, thereby eliminating the trade-off between precision and switching speed.
Solution Approach 2:
The patent changes the key parameter of FSR (Free Spectral Range) between different etalon filters rather than changing temperature. By using etalons with different FSR values (FSR1 and FSR2), the system can maintain large differential coefficients across all wavelengths through parameter selection rather than thermal adjustment, achieving both high precision and high productivity.
3Measurement precision
If two photodiodes monitoring two optical beams with π/2 shifted characteristics are used, then the wavelength monitoring coverage is improved, but the ability to distinguish wavelength changes from optical power changes deteriorates
Solution Approach 1:
The patent introduces a third photodiode as an intermediary element that monitors the total optical power independently. This third photodiode serves as a reference that allows the system to distinguish between actual wavelength changes and mere optical power fluctuations by comparing the outputs of all three photodiodes, thereby resolving the information loss problem.
Solution Approach 2:
The patent segments the optical power monitoring function into two independent paths: one path uses the first and second photodiodes to monitor wavelength through etalon-filtered beams, while the third photodiode separately monitors total optical power. This segmentation allows independent analysis of wavelength and power variations, eliminating confusion between the two types of changes.
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
Enables high-accuracy wavelength control with large differential coefficients across the entire wavelength range, simplifying the system structure and eliminating the need for frequent temperature changes, thus achieving high-speed operation.
Implementation Method 1
a first photodiode configured to perform an optical electrical conversion of the first optical signal transmitting a first etalon; a second photodiode configured to perform an optical electrical conversion of the second optical signal transmitting a second etalon
Data Source
AI summary
A system includes: a splitter to branch an optical signal output by a wavelength-tunable light source into first to third optical signals; a first photodiode to perform an optical electrical conversion of the first optical signal transmitting a first etalon; a second photodiode to perform an optical electrical conversion of the second optical signal transmitting a second etalon, an FSR of the second etalon being identical to that of the first etalon, peak wavelengths of intensity of a transmitted light of the second etalon being different from those of the first etalon; a third photodiode to perform an optical electrical conversion of the third optical signal; and a controller to control the wavelength-tunable light source with use of a coefficient calculated by following formulas (1) or (2), Coefficient=(PD1−A·PD3)/(PD2−B·PD3) (1) and Coefficient=(PD2−B·PD3)/(PD1−A·PD3) (2).