Cryogenic Fiber Optic Sensor Multilayer Coating
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Solution Overview
Problem
Cryogenic fiber Bragg grating sensor devices experience decreased sensitivity with decreasing temperature, limiting their effectiveness for temperature measurement in applications such as superconducting magnet systems and space exploration.
Innovation Solution
A fiber optic sensor device with a multilayer coating comprising a chrome layer, a copper layer, and an indium or lead layer, where the indium or lead layer has a thickness greater than the chrome and copper layers, ensuring dominant thermal contraction effects on the optical fiber and maintaining sensitivity at low cryogenic temperatures through controlled deposition processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a standard FBG sensor device is used, then the device structure is simple, but the temperature sensitivity decreases with decreasing temperature
Solution Approach 1:
The patent applies composite materials by creating a multilayer coating structure comprising a bonding layer (chrome), a metal layer (copper), and a cryogenic-sensitive layer (indium or lead). This composite structure combines materials with different thermal properties: the indium or lead layer provides dominant thermal contraction at cryogenic temperatures, while the copper and chrome layers provide mechanical support and strain transmission to the fiber. The composite nature of this multilayer coating enables the sensor to maintain high temperature sensitivity even at cryogenic temperatures below 20K, resolving the contradiction between measurement precision and device simplicity.
2Measurement precision
If the indium or lead layer thickness is increased to dominate thermal contraction effects, then temperature sensitivity is maintained, but manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by specifying precise thickness ranges for each layer to optimize performance while managing manufacturing complexity. The indium or lead layer is designed with a thickness of at least one-quarter (preferably at least one-half) of the optical fiber radius to ensure dominant thermal contraction effects. The copper layer thickness is controlled in the range of 10-500 nanometers, and the chrome bonding layer is controlled at 1-10 nanometers. These parameter specifications enable the manufacturing process to achieve the desired sensitivity while maintaining controllable complexity through defined thickness ranges.
3Measurement precision
If vapor deposition and electroplating processes are used to create the multilayer coating, then coating quality and sensitivity are improved, but manufacturing time and process complexity increase
Solution Approach 1:
The patent applies segmentation by dividing the coating process into distinct sequential stages: first, vapor deposition of the chrome bonding layer; second, vapor deposition of the copper metal layer; and third, electroplating of the indium or lead cryogenic-sensitive layer. Each stage uses an optimized deposition method suitable for that specific material and layer function. This segmented approach allows each layer to be deposited with appropriate quality control while maintaining a systematic manufacturing flow that balances coating quality with manufacturing efficiency.
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 multilayer coating enhances temperature sensitivity at cryogenic temperatures, maintaining sensitivity of about 1 picometer per Kelvin between 4 and 20K, significantly improving the device's performance compared to uncoated fibers.
Implementation Method 1
the indium or lead layer having a thickness larger than thicknesses of the bonding and metal layers... ensures that the contraction of the indium with decreasing temperature has a dominant effect on the optical fiber
Implementation Method 2
vapor deposition of a chrome layer on an optical fiber that comprises fiber section comprising a fiber Bragg grating
Implementation Method 3
vapor deposition of a copper layer on the chrome layer
Implementation Method 4
electroplating the copper layer with an indium layer having a thickness larger than thicknesses of the chrome and copper layers
Data Source
AI summary
A fiber optic sensor device comprising an optical fiber with a multilayer coating on the optical fiber at least in a fiber section of the optical fiber. The multilayer coating comprises a chrome layer on the optical fiber, a metal layer such as a copper layer on the chrome layer and an indium or lead layer on the metal layer. The indium or lead layer having a thickness larger than thicknesses of the chrome and metal layers, preferably with a thickness about equal to the radius of the optical fiber.