Laser Interferometer with Dual Phase Modulation for Doppler Demodulation
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Solution Overview
Problem
Existing laser interferometers face challenges in accurately measuring the velocity of an object due to reduced intensity of the modulation signal in the reference light, leading to inaccurate demodulation of the Doppler signal, particularly under certain vibration conditions of the vibrator.
Innovation Solution
A laser interferometer design that includes a light source, optical modulator with a vibrator having opposite-phase vibration portions, and a detour optical path to perform phase modulation twice or more on laser light, enhancing the signal-to-noise ratio and enabling accurate demodulation of the Doppler signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single optical modulator is used to modulate laser light, then the device complexity is reduced, but the signal-to-noise ratio deteriorates due to reduced modulation signal intensity
Solution Approach 1:
The patent combines two optical modulators in series within the same optical path, where the first optical modulator modulates the laser light and the second optical modulator further modulates the already-modulated light. This merging approach multiplies the modulation effects, significantly enhancing the modulation signal intensity and improving the signal-to-noise ratio while maintaining a unified optical path structure.
Solution Approach 2:
The patent introduces a detour optical path that causes the laser light to traverse the optical modulators multiple times. By extending the optical path length and creating a feedback loop, the light interacts with the modulators repeatedly, accumulating modulation effects and enhancing the overall modulation signal without requiring additional independent modulation stages.
2Measurement precision
If the modulation signal intensity is increased to improve demodulation accuracy, then the measurement precision improves, but the device complexity increases due to additional optical modulators
Solution Approach 1:
Two optical modulators are merged into a single integrated optical path, where their modulation effects are multiplied rather than added. This configuration achieves enhanced modulation signal intensity (improving velocity measurement accuracy) while maintaining a compact, unified structure that does not significantly increase overall device complexity.
Solution Approach 2:
The detour optical path extends the interaction length between light and modulators by creating a feedback loop. This dimensional extension of the optical path allows the same physical modulators to produce cumulative modulation effects, achieving high measurement precision without proportionally increasing the number of discrete components.
3Reliability
If a detour optical path is introduced to increase modulation times, then the signal-to-noise ratio improves, but the optical path length and device complexity increase
Solution Approach 1:
The detour optical path uses a folded geometry with mirrors to create an extended optical path within a compact physical footprint. By reflecting the light multiple times through the same modulators, the system achieves cumulative modulation effects (improving signal-to-noise ratio) while containing the optical components in a limited spatial volume.
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 allows for precise measurement of object velocity and position with high accuracy by increasing the signal-to-noise ratio, overcoming the limitations of previous interferometers.
Implementation Method 1
an optical modulator including a vibrator driven by a drive signal and configured to superimpose a modulation signal on the laser light using the vibrator
Implementation Method 2
a photodetector configured to receive the laser light including the modulation signal and a sample signal derived from an object and output a light receiving signal
Implementation Method 3
a laser interferometer that irradiates a vibrating object with a laser beam and measures a velocity of the object by using a frequency of the laser beam that changes due to the Doppler effect
Data Source
AI summary
A laser interferometer includes: a light source configured to emit laser light; an optical modulator including a vibrator driven by a drive signal and configured to superimpose a modulation signal on the laser light; a photodetector configured to receive the laser light including the modulation signal and a sample signal derived from an object and output a light receiving signal; a calculator configured to demodulate the sample signal from the light receiving signal based on a reference signal; and a signal generator configured to output the drive signal and the reference signal. The optical modulator includes: the vibrator including a first vibration portion and a second vibration portion that vibrates in a phase opposite to that of the first vibration portion; a first optical modulator provided in the first vibration portion and configured to modulate the laser light; a second optical modulator provided in the second vibration portion and configured to modulate the laser light modulated by the first optical modulator; and a detour optical path configured to cause the laser light modulated by the first optical modulator to enter the second optical modulator.