Vernier Effect Tunable Laser for Wide Range Stress Monitoring
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Solution Overview
Problem
Current semiconductor lasers with DBR filters have limited tunability, typically around 10 nm, which restricts the wide-range stress measurement capabilities in structural health monitoring applications, and increasing tunability through methods like SG-DBR or multiple ring resonators leads to inefficiencies and parasitic reflections, degrading the Side Mode Suppression Ratio (SMSR).
Innovation Solution
A structured optical fiber sensor using a wavelength-tunable laser with a cavity comprising a Sagnac mirror, an amplifying medium, and a tunable spectral filter employing the Vernier effect with at least three resonant rings in cascade, each with a Mach-Zehnder interferometric section and adiabatic directional couplers, to achieve extended tunability without degrading the SMSR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If SG-DBR or multiple ring resonators are used to increase tunability, then the tunability range is extended, but the heating efficiency decreases and energy operating cost increases
Solution Approach 1:
The patent divides the filtering function into multiple discrete resonant rings (first, second, and third rings) with different perimeters arranged in cascade. Each ring provides a specific free spectral range, and their combination achieves the overall wide tunability range of 100-160 nm. This segmentation allows each ring to be optimized for specific wavelengths, improving heating efficiency compared to a single large resonator.
Solution Approach 2:
The patent employs dynamic tuning of each resonant ring's resonance wavelength through independent heating elements. By dynamically adjusting the resonance of individual rings, the system can selectively enhance the Vernier effect at different wavelength ranges, optimizing energy efficiency across the entire tunability spectrum rather than requiring constant high energy input.
2Adaptability or versatility
If multiple ring resonators with large perimeters are used to achieve wide tunability, then the Free Spectral Range decreases, but the tunability increases
Solution Approach 1:
The patent segments the resonator system into three distinct rings with progressively smaller perimeters. The first ring has the largest perimeter for low-wavelength tuning, the second ring has intermediate perimeter, and the third ring has the smallest perimeter for high-wavelength tuning. This segmentation maintains adequate FSR in each ring while achieving wide overall tunability through the Vernier effect.
Solution Approach 2:
Each resonant ring is designed with specific local characteristics (different perimeters and resonance wavelengths) optimized for particular wavelength ranges. The first ring is optimized for lower wavelengths, the second for intermediate wavelengths, and the third for higher wavelengths. This local optimization ensures each ring maintains sufficient FSR for its designated range while contributing to the overall wide tunability.
3Adaptability or versatility
If the resonance order difference between two resonator rings is increased to expand tunability, then the Side Mode Suppression Ratio degrades
Solution Approach 1:
The patent uses three resonant rings instead of two, which provides better control over the resonance order differences. By having an odd number of rings with progressively smaller perimeters, the system can maintain resonance order differences of less than 1 between adjacent rings in the cascade, preserving high SMSR (>60 dB) while achieving wide tunability through the cumulative Vernier effect.
Solution Approach 2:
The patent carefully controls the perimeter parameters of each resonant ring to optimize the Vernier effect while maintaining SMSR. The perimeters are specifically designed so that the free spectral ranges create appropriate resonance order differences (less than 1) between adjacent rings. This parameter optimization allows wide tunability through resonance order changes while preventing parasitic modes that would degrade SMSR.
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 configuration enables wide tunability of up to 100 nm while maintaining a high Side Mode Suppression Ratio (SMSR) of over 60 dB, ensuring single-frequency laser emission and improved wavelength precision, suitable for precise stress and temperature measurements in structural health monitoring.
Implementation Method 1
a tunable spectral filter using the Vernier effect, said filter comprising at least three resonant rings arranged in cascade, each resonant ring incorporating a loop mirror at wavelength tunable reflectivity
Implementation Method 2
a first and a second Sagnac mirror; a cavity delimited by the first and second Sagnac mirror
Implementation Method 3
each resonant ring comprising a Mach-Zehnder interferometric section
Implementation Method 4
each of the first and second Sagnac mirrors is composed of an adiabatic directional coupler looped back by a waveguide
Implementation Method 5
the cavity comprising an amplifying medium
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The invention relates to a structured optical fiber sensor, comprising a light source (1), a detection system (2), and a Bragg grating optical fiber (3) connected to said source and system. The light source is a wavelength-tunable laser emission device (1) comprising a cavity (CA) delimited by a first and a second Sagnac mirror (M1, M2). The cavity includes an amplifying medium (MA) and a tunable spectral filter using the Vernier effect (F), said filter (F) comprising at least three cascaded resonant rings (R1, R2, RN-1, RN), each resonant ring incorporating a wavelength-tunable reflectivity loop mirror (MBR).