Resonator-Based Laser Interferometer for Low-Frequency Demodulation
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Solution Overview
Problem
Existing laser Doppler measurement apparatuses require high-frequency circuits for demodulation, leading to increased costs due to the need for advanced arithmetic and signal conversion circuits.
Innovation Solution
A laser interferometer design that includes a light modulator with a resonator to reduce modulation signal frequency, combined with a demodulation circuit featuring DC offset removal, phase adjustment, and multiple filtering stages to demodulate the signal effectively, reducing the complexity and cost of the demodulation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a frequency shifter type light modulator with thickness-shear vibration resonator is used to achieve frequency shifting, then the modulation function is achieved, but the resonance frequency becomes high requiring expensive high-frequency circuits
Solution Approach 1:
The patent changes the vibration mode parameter of the resonator from thickness-shear vibration to surface acoustic wave vibration, which fundamentally alters the resonance frequency characteristics. This parameter change enables the use of lower frequency circuits while maintaining the frequency shifting function, directly resolving the contradiction between achieving modulation and avoiding high-frequency circuit requirements
2Reliability
If thickness-shear vibration resonator is used in light modulator, then frequency shifting is achieved, but the resonance frequency is high leading to increased cost of demodulation circuits
Solution Approach 1:
The invention changes the critical parameter of the resonator from thickness-shear vibration mode to surface acoustic wave vibration mode. This parameter change results in a lower resonance frequency that can be processed by less expensive demodulation circuits, thereby reducing manufacturing cost while preserving the frequency shifting capability
3Ease of operation
If high-frequency modulation signal is used, then the light modulation is achieved, but the demodulation circuit must cope with high-frequency signal increasing cost
Solution Approach 1:
The patent changes the frequency parameter of the modulation signal by using surface acoustic wave vibration instead of thickness-shear vibration. This results in a lower frequency modulation signal that can be demodulated by simpler, less expensive circuits, resolving the contradiction between achieving light modulation and reducing demodulation circuit 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 proposed design achieves reduced signal frequency processing, thereby lowering the cost and complexity of the demodulation circuit while maintaining high robustness against disturbances, particularly stray light noise.
Implementation Method 1
a light modulator which includes a resonator and is configured to add a modulation signal to the laser light using the resonator
Implementation Method 2
a photodetector configured to detect a change in intensity of the laser light including a sample signal added by the object and the modulation signal to output a laser light reception signal
Implementation Method 3
a first filter configured to remove a high-frequency component contained in the first multiplication signal, a second filter configured to remove a high-frequency component contained in the second multiplication signal
Data Source
AI summary
A laser interferometer includes a light modulator configured to add a modulation signal to a laser light by using a resonator, a photodetector configured to detect a change in intensity of the laser light including a sample signal and a modulation signal and output a laser light reception signal, a oscillator configured to generate a reference signal with a first frequency using the resonator as a vibratory source, and a demodulation circuit configured to demodulate the sample signal from the laser light reception signal based on the reference signal, wherein the demodulation circuit includes a DC offset remover, a first phase adjuster, a first multiplier, a first filter, a second multiplier, a second filter, and a phase calculator.