Optical Microphone Frequency Modulation Noise Immunity
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Solution Overview
Problem
Conventional microphones using amplitude-modulation signals are sensitive to amplitude and phase noise, making them prone to errors and requiring additional electronics for noise mitigation.
Innovation Solution
An optical microphone system employing a vertical-cavity surface-emitting laser (VCSEL) with a membranous mirror and photodetectors that generate frequency-modulated signals, insensitive to amplitude noise, using a quarter-wave plate to convert polarizations and stimulate the laser, allowing for robust and accurate detection of acoustic input signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If amplitude-modulation signals are used for detection, then the microphone can detect acoustic input signals, but the system becomes sensitive to amplitude noise and phase noise
Solution Approach 1:
The patent replaces conventional amplitude-modulation detection with frequency-modulation detection using an optical cavity system. The acoustic signal modulates the optical frequency rather than amplitude, and the photodetector detects frequency changes through optical interference patterns, making the system insensitive to amplitude noise while maintaining detection accuracy
Solution Approach 2:
The patent changes the detection parameter from amplitude modulation to frequency modulation. By measuring frequency shifts in the optical signal rather than amplitude variations, the system achieves noise immunity while preserving measurement precision
2Object-affected harmful factors
If additional electronics are implemented to mitigate noise, then noise resistance improves, but device complexity increases
Solution Approach 1:
The patent replaces electronic noise mitigation circuits with an optical-based detection system. The optical cavity and photodetector inherently provide noise immunity through optical interference measurement, eliminating the need for complex electronic filtering and signal processing circuits
Solution Approach 2:
The patent introduces an optical cavity as an intermediary between the acoustic signal and the photodetector. This optical intermediary converts acoustic vibrations into frequency-modulated optical signals that are inherently resistant to noise, avoiding the need for additional electronic noise mitigation components
3Measurement precision
If VCSEL is coupled to optical cavity with moveable membrane, then lasing characteristics become sensitive to acoustic input, but amplitude noise affects the detection
Solution Approach 1:
The patent replaces amplitude-based detection with frequency-based detection in the VCSEL-optical cavity system. The acoustic signal causes frequency shifts in the lasing output through cavity length modulation, and these frequency shifts are detected by the photodetector through interference patterns, making the system insensitive to amplitude noise while maintaining acoustic detection sensitivity
Solution Approach 2:
The patent changes the detection parameter from optical amplitude to optical frequency. By monitoring frequency shifts in the VCSEL output caused by acoustic vibrations rather than amplitude variations, the system achieves both acoustic sensitivity and noise immunity
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 optical microphone system operates with improved noise resistance and accuracy, mitigating external factors like temperature changes and vibration, while enabling batch fabrication and simplified noise management compared to traditional microphone systems.
Implementation Method 1
a quarter-wave plate arranged between the laser and the membranous mirror, such that the quarter-wave plate can convert the optical beam from the first linear polarization to a circular-polarization and convert the reflected optical beam from the circular-polarization to the second linear polarization
Implementation Method 2
The reflected optical beam can thus stimulate the gain medium of the laser to periodically oscillate between emitting the optical beam at the first linear polarization and the second linear polarization
Implementation Method 3
The photodetector(s) can be configured to detect the periodic oscillation based on transitions between the first and second linear polarizations of the optical beam
Implementation Method 4
The membranous mirror can be configured to reflect the optical beam back toward the laser, and can be arranged to vibrate in response to an acoustic input signal
Data Source
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AI summary
One embodiment includes an optical microphone system. The system includes a laser configured to emit an optical beam at a linear polarization and an optical cavity system comprising a membranous mirror that is configured to reflect the optical beam and to vibrate in response to an acoustic input signal. The optical cavity system includes at least one photodetector configured to receive at least a portion of the optical beam to generate a microphone signal that is indicative of the vibration of the membranous mirror resulting from the acoustic input signal based on the reflection of the optical beam. The system further includes an acoustic processor configured to process the microphone signal to calculate a frequency of the acoustic input signal.