Laser Interferometer Optical Path Length Control
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Solution Overview
Problem
Existing laser interferometers face accuracy issues in measuring displacement and velocity due to the dependence on the characteristics of the laser light source, particularly the line width of the emission light, which affects measurement accuracy regardless of the type of light source used.
Innovation Solution
A laser interferometer configuration that includes a light source, a polarizing beam splitter, a light modulator, an optical path length change unit, and a controller, where the optical path length between the light splitter and the light modulator is adjusted to minimize the optical path difference, thereby reducing the impact of the light source's line width on measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional laser interferometer uses laser light with a large line width, then the device can be operated with various light sources, but the measurement precision of displacement and velocity deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-shifting the frequency of the reference light using an acousto-optic modulator before the interference measurement. This frequency shift is performed in advance to create a heterodyne detection scheme where the reference light and object light have different frequencies, allowing accurate measurement even when the laser line width is large. The frequency shift amount is set to be larger than the line width, which preliminarily resolves the frequency overlap issue that would otherwise degrade measurement precision.
Solution Approach 2:
The patent changes the frequency parameter of the reference light by applying an acousto-optic modulator that shifts the light frequency by a predetermined amount. This parameter change creates a frequency difference between reference light and object light, enabling the system to maintain high measurement precision regardless of the original laser line width. The frequency shift parameter is specifically chosen to exceed the line width, transforming the measurement capability.
2Device complexity
If the optical path length between the light splitter and the light modulator is not adjusted, then the device structure remains simple, but the measurement accuracy deteriorates due to the light source's line width
Solution Approach 1:
The patent changes the optical path length parameter by introducing an optical path length adjustment mechanism between the light splitter and the light modulator. This adjustment allows precise control of the optical path difference, compensating for the effects of large laser line width on measurement accuracy. By adjusting this parameter, the system maintains high precision without requiring fundamental structural changes.
Solution Approach 2:
The patent replaces simple mechanical path length adjustment with a more sophisticated control system that uses feedback from the interference signal. The system dynamically adjusts the optical path length based on detected signal characteristics, substituting crude mechanical adjustment with a controlled system that achieves both simplicity and precision.
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 accurate measurement of displacement and velocity regardless of the light source type, maintaining high measurement accuracy even with sources having large line widths, and provides flexibility in choosing light sources without compromising accuracy.
Implementation Method 1
a light modulator disposed on an optical path on which the first split light advances, and configured to modulate the first split light into reference light having a different frequency
Implementation Method 2
a photoreceptor configured to receive interference light of, object light generated by reflecting the emission light at the object to be measured, and the reference light
Implementation Method 3
an optical path length change unit provided between the light splitter and the light modulator, and configured to change a first optical path length being an optical path length between the light splitter and the light modulator
Implementation Method 4
a laser vibrometer that irradiates an object with laser light, and based on scattered laser light subjected to a Doppler shift, measures vibration velocity
Data Source
AI summary
A laser interferometer that includes a laser light source configured to emit emission light, a light splitter configured to split the emission light into first split light, and second split light incident on an object to be measured, a light modulator disposed on an optical path on which the first split light advances, and configured to modulate the first split light into a reference light having a different frequency from a frequency of the first split light, an optical path length change unit provided between the light splitter and the light modulator, and configured to change a first optical path length, the first optical path length being an optical path length between the light splitter and the light modulator, a photoreceptor configured to receive an interference light of the reference light and an object light generated by reflecting the emission light at the object to be measured, and to output a light reception signal, and a controller configured to control operation of the optical path length change unit in accordance with a second optical path length, the second optical path length being an optical path length between the light splitter and the object to be measured.