Optical Microphone Using Polarization Detection for Environmental Stability
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Solution Overview
Problem
Conventional optical microphones face challenges in downsizing and stability against environmental changes such as vibrations and temperature fluctuations, due to the use of narrow-range light sources and optical interferometers, which affect their ability to detect a wide range of frequencies and maintain accuracy.
Innovation Solution
The design incorporates a light source, first and second polarizers, and an acoustic medium with a sound velocity less than air, where linearly-polarized light passes through the acoustic medium to detect changes in polarization state caused by acoustic signals, eliminating the need for optical interferometers and acousto-optic modulators, and includes an elliptically-polarized light generation section to enhance sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical microphones use narrow-range light sources and optical interferometers, then they can detect acoustic signals, but they become large in size and unstable against environmental changes
Solution Approach 1:
The patent extracts and removes the optical interferometer and narrow-range light source from the conventional optical microphone system. Instead, it uses a broad-range light source combined with polarization detection to measure acoustic-induced refractive index changes, thereby eliminating the components that cause size and stability problems while preserving the core acoustic detection function.
Solution Approach 2:
The patent replaces the mechanical/optical interferometer system with a polarization-based detection system. By using polarized light and measuring polarization state changes caused by acoustic signals, the system achieves acoustic detection without the complex interferometric machinery, reducing both size and environmental sensitivity.
2Measurement precision
If conventional optical microphones use optical interferometers, then they can measure acoustic signals, but they are sensitive to vibrations and temperature fluctuations
Solution Approach 1:
The patent converts the harmful effect of environmental vibrations and temperature fluctuations into a beneficial measurement mechanism. By using polarization detection of broad-range light, the system becomes insensitive to these environmental factors while maintaining acoustic detection capability, as polarization state changes are specifically caused by refractive index changes from acoustic signals rather than environmental noise.
Solution Approach 2:
The patent changes the detection parameter from optical path length (in interferometers) to polarization state. This parameter change makes the measurement immune to vibrations and temperature effects that primarily affect optical path length, while still capturing acoustic signal information through refractive index-induced polarization changes.
3Adaptability or versatility
If conventional optical microphones use narrow-range light sources, then they can provide stable interference patterns, but they cannot detect a wide range of frequencies
Solution Approach 1:
The patent makes the light source universal by using a broad-range light source that can detect acoustic signals across multiple frequency ranges. The polarization detection method universally responds to refractive index changes regardless of frequency, enabling the same system to detect both audible and ultrasonic frequencies without requiring frequency-specific optimization.
Solution Approach 2:
The patent substitutes the frequency-dependent interference pattern mechanism with a frequency-independent polarization detection mechanism. This allows the system to maintain measurement stability across a wide frequency range, as polarization state changes occur consistently across different frequencies when acoustic signals pass through the medium.
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 allows for a compact, environmentally stable optical microphone that can detect acoustic signals across a wide range of frequencies with high sensitivity, reducing noise interference from environmental changes.
Implementation Method 1
an acoustic medium having a smaller sound velocity than an air, wherein an acoustic signal entering through the opening propagates through the acoustic medium
Implementation Method 2
the linearly-polarized light having passed through the first polarizer is given different phase shifts in two orthogonal directions which are each different from a polarization direction
Implementation Method 3
a first polarizer for allowing linearly-polarized light, of light output from the light source, to pass therethrough; a second polarizer for allowing linearly-polarized light having a different polarization plane from the first polarizer to pass therethrough
Implementation Method 4
a photodetector for converting an intensity of light having passed through the second polarizer to an electric signal
Data Source
AI summary
An optical microphone includes: a light source; a first polarizer for allowing linearly-polarized light, of light output from the light source, to pass therethrough; a second polarizer for allowing linearly-polarized light having a different polarization plane from the first polarizer to pass therethrough; a sound-receiving section including an acoustic medium having a smaller sound velocity than the air, wherein an acoustic signal propagates through the acoustic medium, the sound-receiving section being arranged so that the linearly-polarized light from the first polarizer passes through the acoustic medium and enters the second polarizer; and a photodetector for converting an intensity of light having passed through the second polarizer to an electric signal, wherein between the first polarizer and the second polarizer, the linearly-polarized light having passed through the first polarizer is given different phase shifts in two orthogonal directions which are each different from a polarization direction.