Optical Fiber Microphone Using Space-Coupled Refractive Index Sensing
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Solution Overview
Problem
Conventional optical fiber microphones face challenges in accurately detecting sound due to significant differences in acoustic impedance between the sound generation environment and the covering member, leading to reflection and reduced sound pressure transmission, which affects the refractive index change and detection accuracy.
Innovation Solution
The microphone design includes a configuration where demultiplexed optical signals are returned via a space part connected to the transmission path, allowing direct refractive index change in the medium without passing through the optical fiber surface, using lenses and optical waveguides to minimize signal attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sound is transmitted through the optical fiber surface, then the optical fiber can detect sound pressure, but acoustic impedance mismatch causes sound reflection and reduces transmission accuracy
Solution Approach 1:
The patent introduces a coupling member as an intermediary substance between the sound source environment and the optical fiber surface. This coupling member has acoustic impedance that is intermediate between the surrounding medium and the fiber, reducing the impedance mismatch and minimizing sound reflection. By using this intermediary, more sound energy is transmitted into the fiber while maintaining accurate detection capability.
Solution Approach 2:
The patent changes the acoustic impedance parameter of the interface by introducing the coupling member with specific acoustic properties. This parameter change allows for better acoustic matching between the sound generation environment and the optical fiber, reducing reflection loss and improving sound pressure transmission efficiency without compromising detection accuracy.
2Measurement precision
If optical signal is transmitted through optical fiber in opposite directions, then interference detection is enabled, but acoustic impedance mismatch reduces the degree of refractive index change
Solution Approach 1:
The coupling member acts as an intermediary that improves acoustic energy transmission into the optical fiber. By reducing sound reflection at the interface, it ensures that sufficient sound pressure reaches the fiber to produce adequate refractive index changes, thereby maintaining the information content needed for accurate interference-based detection.
Solution Approach 2:
The patent replaces direct mechanical contact between the sound source and the fiber with an optical-based detection system. The optical signal carries information about sound-induced refractive index changes, substituting mechanical sound transmission with optical interference measurement to achieve more precise detection while overcoming acoustic impedance limitations.
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 accurate sound detection by clearly confirming phase changes in the optical signal, enhancing detection accuracy by directly sensing refractive index changes in the medium, thus improving sound detection capabilities.
Implementation Method 1
an optical fiber that transmits a demultiplexed optical signal demultiplexed by the optical coupler to the optical coupler in mutually opposite directions
Implementation Method 2
a sensor part that is connected to the transmission path and returns the demultiplexed optical signal to be transmitted by the transmission path to the transmission path via a space part
Implementation Method 3
a light receiving element that receives a multiplexed optical signal multiplexed by the optical coupler
Data Source
AI summary
A microphone 1 includes a light source 11 that outputs an optical signal, an optical coupler 12 that demultiplexes and multiplexes the optical signal, a transmission path 13 including an optical fiber 130 that transmits a demultiplexed optical signal demultiplexed by the optical coupler 12 to the optical coupler 12 in mutually opposite directions, a sensor part 14 that is connected to the transmission path 13 and returns the demultiplexed optical signal to be transmitted by the transmission path 13 to the transmission path 13 via a space part 40, and a light receiving element 15 that receives a multiplexed optical signal multiplexed by the optical coupler 12.