Laser Interference Device with Equalized Optical Path Lengths
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Solution Overview
Problem
Laser interference devices face a decrease in measurement accuracy due to differences in optical path length changes between measurement and reference light paths caused by thermal expansion and environmental factors, such as temperature and humidity, leading to errors in displacement measurement.
Innovation Solution
The device employs first and second light guides with equal mechanical and optical path lengths, ensuring that both measurement and reference light paths change uniformly with thermal expansion, and using the same optical elements for both guides to maintain uniform thermal expansion coefficients and refractive indices, thereby reducing errors in optical path length differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the measurement light travels straight toward the measurement optical path cylinder while the reference light is reflected by a mirror to travel toward the reference optical path cylinder, then the device structure is simplified, but the optical path lengths of measurement light and reference light become significantly different, causing measurement errors due to differential thermal expansion in the vacuum chamber
Solution Approach 1:
The patent applies asymmetry by intentionally introducing an optical path lengthening element (such as a retroreflector or additional mirror) in the measurement light path to compensate for the shorter direct path, thereby equalizing the total optical path lengths of both beams despite their different geometric configurations
Solution Approach 2:
The patent changes the optical path length parameter by adding reflective elements to adjust and equalize the optical path lengths, ensuring that both measurement and reference lights traverse equal distances through the vacuum chamber, thus eliminating differential thermal expansion errors
2Measurement precision
If a vacuum chamber is used to maintain stable optical path lengths, then measurement accuracy is improved, but device weight and complexity increase
Solution Approach 1:
The patent extracts and eliminates the vacuum chamber from the system by demonstrating that equalized optical path lengths can achieve sufficient measurement accuracy without requiring vacuum conditions, thereby removing the heavy vacuum enclosure and associated pumping systems
Solution Approach 2:
The patent replaces the expensive and complex vacuum chamber system with simpler, lighter optical path equalization components such as mirrors and retroreflectors, achieving comparable or sufficient accuracy without the need for maintaining vacuum conditions
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 improves measurement accuracy by making optical path length changes comparable, reducing errors and maintaining high precision even in varying environmental conditions without the need for a vacuum chamber, thus enhancing the device's performance and reducing weight.
Implementation Method 1
a beam splitter having a splitting surface that divides a laser beam outputted from a laser into a measurement light and a reference light
Implementation Method 2
a first light guide configured to guide the measurement light incident from the beam splitter and emit the measurement light toward the measurement mirror
Implementation Method 3
The measurement light and the reference light reflected by the respective reflective bodies 104,105 are overlapped with each other by a beam splitter 102 to generate an interference light
Data Source
AI summary
A laser interference device includes: a measurement mirror being movable in an X direction; a reference mirror disposed at a position different from a position of the measurement mirror in a Y direction; a beam splitter having a splitting surface that divides a laser beam into a measurement light and a reference light; a first light guide configured to guide the measurement light incident from the beam splitter and emit the measurement light toward the measurement mirror; and a second light guide configured to guide the reference light incident from the beam splitter and emit the reference light toward the reference mirror, in which a first distribution path formed by the first light guide and a second distribution path formed by the second light guide are mutually equal in a mechanical path length and an optical path length.