TDLAS Fiber Bundle Multiplexing for Wide-Wavelength Gas Sensing
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Solution Overview
Problem
Conventional TDLAS systems face challenges in simultaneously detecting multiple gas species over a wide wavelength range (760 nm to 2.33 microns) due to the inability of single-mode fiber to transmit these wavelengths with high transmission and low bend loss, necessitating a new multiplexing scheme for applications requiring sensitive CO detection and O2 measurement.
Innovation Solution
A system using a fiber bundle assembly with stripped single-mode fibers arranged in a triangular configuration, coupled with a time-division multiplexing scheme and dual band photodetector, allows for simultaneous detection of CO and O2 by transmitting each wavelength through a separate single-mode fiber and using a dual band detector to distinguish between different wavelengths without demultiplexing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-mode fiber is used to transmit wavelengths from 760 nm to 2.33 microns, then the fiber structure can be simplified, but the transmission quality deteriorates due to high bend loss and inability to support multiple wavelengths simultaneously
Solution Approach 1:
The patent divides the wavelength transmission into separate single-mode fibers, with each fiber dedicated to a specific wavelength range (e.g., one fiber for 760-1559 nm, another for 1559-2330 nm). This segmentation allows each fiber to operate optimally within its assigned band without the bend loss and mode interference problems that would occur if all wavelengths were transmitted through a single fiber.
Solution Approach 2:
The patent transitions from a single-dimensional fiber transmission approach to a multi-dimensional approach by using a fiber bundle with multiple cores, where each core transmits a different wavelength. This dimensional expansion in the fiber structure allows simultaneous transmission of multiple wavelengths without the constraints of single-mode fiber limitations.
2Length of moving object
If wavelength-multiplexed TDLAS systems use 1559 nm for CO detection, then the system can operate over long path lengths, but the detection sensitivity deteriorates for low CO concentrations
Solution Approach 1:
The patent segments the CO detection function across two different wavelength bands: the 1559 nm wavelength for long path length applications (such as coal-fired boilers with 10+ meter paths) and the 2.33 micron wavelength for high sensitivity detection of low concentrations (such as 100 ppm CO in short paths). This segmentation allows optimization of each detection scenario independently.
Solution Approach 2:
The patent changes the wavelength parameter to optimize detection sensitivity. By using the 2.33 micron wavelength (first overtone band) instead of 1559 nm (second overtone band), the absorption line strength increases approximately 500 times, enabling detection of much lower CO concentrations over shorter path lengths.
3Measurement precision
If the wavelength range is extended to 2.33 microns for sensitive CO detection, then CO detection sensitivity improves, but the fiber transmission capability deteriorates due to inability to maintain single-mode operation
Solution Approach 1:
The patent segments the wavelength transmission into separate fibers, assigning the 2.33 micron wavelength to a dedicated fiber that is optimized for this wavelength range. This allows the system to maintain single-mode operation and high transmission quality at 2.33 microns while using separate fibers for other wavelength ranges, avoiding the transmission problems that would occur in a single-fiber all-wavelength system.
Solution Approach 2:
The patent creates a universal measurement system by combining multiple wavelength-specific single-mode fibers into a single bundle that can transmit all required wavelengths (760 nm to 2.33 microns) simultaneously. Each fiber in the bundle serves its specific wavelength function, and the collective bundle provides universal coverage for all detection applications.
4Device complexity
If multiple wavelengths are transmitted through a single fiber, then the system architecture is simplified, but wavelength interference and mode coupling increase
Solution Approach 1:
The patent segments the wavelength transmission into separate single-mode fibers within a bundle, with each fiber dedicated to a specific wavelength range. This eliminates wavelength interference and mode coupling problems that would occur if multiple wavelengths were transmitted through a single fiber, while maintaining a relatively simple system architecture through the bundled configuration.
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 sensitive detection of CO and O2 over a wide wavelength range with reduced attenuation and interference, facilitating simultaneous measurement across multiple paths, suitable for applications like glass furnace monitoring.
Implementation Method 1
a first and second tunable diode laser generating laser light at a first wavelength and a second wavelength respectively each corresponding to respective absorption lines of a target species
Implementation Method 2
The photodetector signals are then analyzed to obtain an average concentration of the target species
Implementation Method 3
TDLAS relies on the unique absorption spectrum of the species being targeted to measure an attenuation of a diode laser beam at a very specific wavelength, tuned over an absorption line of the species being measured
Data Source
AI summary
Measuring a concentration of at least one target species is described. A first and second tunable diode laser are configured to generate laser light at a respective wavelength different from one another. A pitch head comprising a transmitting optic is optically coupled to the first and second tunable diode lasers via distal ends of the first and second optical fibers, and is oriented to project respective beams from each of the first and second distal ends through a measurement zone. A photodetector is configured to detect an optical power of light in the first and second wavelengths. A catch head located across the measurement zone from the pitch head is in optical communication with the pitch head to receive the respective beams from the first and second distal ends and direct the respective beams to the photodetector.