Optical Microphone Using Retroreflected Diffracted Light
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Solution Overview
Problem
Conventional optical microphones with mechanical vibrating sections are prone to damage from strong sound waves, and existing optical microphones using light waves for acoustic detection face sensitivity issues due to frequency-dependent diffracted light angles and require complex optical systems.
Innovation Solution
An optical microphone design that utilizes a propagation medium with a refractive index distribution caused by acoustic waves to produce 0th-order and ±1st-order diffracted light waves, which are retroreflected to maintain constant interference overlap area, independent of acoustic wave frequency, using a simple structure without specialized instruments like laser Doppler vibrometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical vibrating section is used in a conventional microphone, then the microphone can detect sound waves effectively, but the vibrating section may break when detecting very strong sound waves
Solution Approach 1:
The patent replaces the mechanical vibrating section with an optical detection system. A light wave passes through a propagation medium (such as air or gas) and interacts with acoustic waves without mechanical contact. The acoustic wave modulates the light wave's properties (phase, frequency, or intensity), which is then detected by a photoelectric conversion element, eliminating mechanical stress and potential breakage.
2Reliability
If an optical microphone uses diffracted light for acoustic wave detection, then mechanical damage is avoided, but sensitivity becomes dependent on acoustic wave frequency due to varying diffracted light angles
Solution Approach 1:
The patent extracts and utilizes the 0th-order diffracted light component (undeviated light) from the diffraction pattern, rather than relying on angle-dependent higher-order diffracted light. By detecting modulation in the 0th-order light, the system achieves frequency-independent sensitivity because this component does not vary its propagation angle with frequency changes.
Solution Approach 2:
The optical detection system is designed to detect acoustic waves across a broad frequency range using the same optical path and detection mechanism. The propagation medium and optical components serve multiple functions: they handle both low-frequency and high-frequency acoustic waves uniformly, making the system universally applicable across the audible spectrum without requiring frequency-specific adjustments.
3Measurement precision
If specialized instruments like laser Doppler vibrometers are used for acoustic wave detection, then detection accuracy is improved, but device complexity and size increase
Solution Approach 1:
The patent uses a simplified optical setup that copies the essential detection function of complex instruments like laser Doppler vibrometers. Instead of using sophisticated Doppler shift measurement systems, it employs a straightforward arrangement where a light source, propagation medium, and photoelectric converter directly detect acoustic wave-induced light modulation, achieving comparable accuracy with much simpler components.
Solution Approach 2:
The propagation medium itself (air or gas) serves as the detection element by naturally modulating the light wave in response to acoustic waves. This eliminates the need for separate, complex sensing mechanisms, as the medium's interaction with light provides the detection function inherently, reducing overall system complexity.
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 design achieves constant sensitivity across varying acoustic wave frequencies and reduces the complexity and size of the microphone, enhancing its durability and detection accuracy.
Implementation Method 1
a 0th-order diffracted light wave, a +1st-order diffracted light wave and a −1st-order diffracted light wave are produced by virtue of a refractive index distribution across the propagation medium portion caused by the propagation of the acoustic wave therethrough
Implementation Method 2
refractive index distribution across the propagation medium portion caused by the propagation of the acoustic wave
Implementation Method 3
a reflecting section for retroreflecting the light wave having passed through the propagation medium portion
Implementation Method 4
a photoelectric conversion section for receiving the light wave having been reflected by the reflecting section and passed through the propagation medium portion to output an electric signal
Implementation Method 5
refractive index distribution across the propagation medium portion caused by the propagation of the acoustic wave therethrough
Data Source
AI summary
An optical microphone includes: a propagation medium portion; a light source to output a light wave passing through the propagation medium portion across the acoustic wave propagating through the propagation medium portion; a reflecting section to retroreflect the light wave having passed through the propagation medium portion; and a photoelectric conversion section to receive the light wave having been reflected by the reflecting section and passed through the propagation medium portion to output an electric signal. 0th-order, +1st-order and −1st-order diffracted light waves are respectively produced on outward and return paths, by virtue of a refractive index distribution across the propagation medium portion caused by the propagation of the acoustic wave therethrough. The photoelectric conversion section detects interference light between the +1st-order or −1st-order diffracted light wave of the outward path and the −1st-order or +1st-order diffracted light wave of the return path.