Optical Fiber Pressure Sensor Uniform Diaphragm Fabrication
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Solution Overview
Problem
Existing optical fiber sensors with micromachined cavities face challenges such as limited cavity length control, sensitivity, and integration difficulties due to temperature fluctuations and non-uniformity, as well as fragility and poor temperature stability from adhesive bonding methods.
Innovation Solution
A silica, silicon oxide, or silicon nitride diaphragm is bonded directly to an optical fiber to form a cavity with a uniform thickness, using techniques like deep reactive ion etching and localized heating to ensure precise control over cavity length and sensitivity, eliminating the need for adhesives and improving thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If adhesive bonding methods are used to attach diaphragms to optical fibers, then assembly is simplified, but temperature stability degrades due to differential expansion and bonding failure at high temperatures
Solution Approach 1:
The patent removes the adhesive layer from the bonding process entirely. Instead of using glue or epoxy to bond the diaphragm to the optical fiber, the invention employs direct fusion bonding through localized heating, eliminating the intermediate adhesive material that causes temperature stability problems.
Solution Approach 2:
The patent replaces the chemical bonding mechanism (adhesive) with a thermal bonding mechanism (fusion bonding). By using localized heating to directly fuse the diaphragm material to the optical fiber, the system substitutes a thermally stable bonding method for the temperature-sensitive adhesive bonding.
2Manufacturing precision
If surface micromachining is used to fabricate cavities, then cavity length control is improved, but cavity length is limited to small values (0.6-1.6 μm) reducing sensitivity
Solution Approach 1:
The patent transitions from surface micromachining (two-dimensional processing on the surface) to bulk micromachining (three-dimensional processing through the substrate). This dimensional change allows creation of deeper cavities with controlled lengths exceeding the 0.6-1.6 μm limitation of surface techniques, thereby increasing sensor sensitivity while maintaining precision through controlled etching processes.
3Device complexity
If bulk micromachining is used to simplify fabrication, then manufacturing complexity is reduced, but cavity length uniformity deteriorates due to wafer thickness variations
Solution Approach 1:
The patent applies localized processing to specific regions of the wafer rather than uniform bulk processing. By using focused ion beam etching or localized chemical etching, the cavity length can be precisely controlled in each individual sensor location, compensating for wafer thickness variations and achieving uniform cavity lengths across multiple wafers while maintaining simplified bulk micromachining approaches.
4Ease of manufacture
If polyimide spacers are used for bonding, then direct fiber-to-sensor bonding is achieved, but temperature dependence increases making sensors unsuitable for harsh environments
Solution Approach 1:
The patent changes the material parameters of the bonding interface by selecting diaphragm materials (such as silica, silicon nitride, or silicon oxide) that have thermal expansion coefficients matching or closely resembling those of the optical fiber. This parameter matching eliminates differential thermal expansion, enabling direct bonding without polyimide while maintaining temperature independence in harsh environments.
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 provides a highly sensitive, stable, and cost-effective miniature optical fiber pressure sensor with improved repeatability and durability, suitable for harsh environments and applications like cardiovascular monitoring and industrial pressure measurements.
Implementation Method 1
using techniques like deep reactive ion etching and localized heating to ensure precise control over cavity length and sensitivity
Implementation Method 2
Light transmitted through the fiber reflects off both the end of the fiber and the diaphragm, creating a signal that varies with the cavity length
Implementation Method 3
Light transmitted through the fiber reflects off both the end of the fiber and the diaphragm, creating a signal that varies with the cavity length
Implementation Method 4
Optical fiber sensors that use Fabry-Perot cavities to detect pressure and/or temperature are very sensitive and compact
Data Source
AI summary
An optical fiber sensor can be used to measure pressure with high sensitivity and fine resolution. As a cavity at the end of the sensor expands or contracts, the spectrum of a beam reflected from the end of fiber shifts, producing a change linked to pressure exerted on the sensor. Novel aspects of the present inventive sensor include the direct bonding of a silica thin film diaphragm to the optical fiber with localized or confined heating and a uniform thickness of the diaphragm. The resulting sensor has a diameter that matches the diameter of the optical fiber. Because the sensor is all silica, it does not suffer from temperature-induced error. In addition, the sensor can be very sensitive because the diaphragm can be very thin; it can also make highly repeatable measurements due to its very uniform thickness.