Interferometric Movement Measurement Using Tilted Sensor
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Solution Overview
Problem
Existing methods for measuring small movements, such as those in the range of a few micrometers, are sensitive to temperature variations and require precise adjustment of optical components, are expensive due to the need for high-quality amplitude splitting beamsplitters, and are prone to errors from tilting and beam focus issues.
Innovation Solution
A method and arrangement that split the light beam into wavefront portions, using two reflective elements with parallel and aligned surfaces at rest, which interfere to produce a spatial interference pattern, allowing for precise calculation of movement without an amplitude splitting beamsplitter, and are less sensitive to temperature changes due to closer element placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Michelson interferometer is used to measure small movements, then measurement precision is improved, but the device becomes sensitive to temperature variations and requires precise adjustment of optical components
Solution Approach 1:
The patent merges the measurement of the sensor and reference mirror positions into a single interferometer arm by using a tilted sensor that reflects light from a single focal point. This combining of measurement paths eliminates temperature sensitivity between separate arms while maintaining high measurement precision through the interference pattern analysis.
Solution Approach 2:
The patent introduces a tilted sensor as an intermediary element that serves dual purposes: it acts as both the measurement target and the reference reflector. This intermediary approach allows a single beam splitter to divide the light path while the tilted sensor provides stable reference reflections, reducing sensitivity to temperature variations and alignment errors.
2Measurement precision
If a Michelson interferometer with amplitude splitting beamsplitter is used, then measurement precision is improved, but manufacturing cost increases due to high-quality component requirements
Solution Approach 1:
The patent replaces the expensive amplitude splitting beamsplitter with a simple beam direction changer (mirror or prism) that can be of lower quality and lower cost. The tilted sensor itself serves as the reference reflector, eliminating the need for a high-precision reference mirror and amplitude splitting beamsplitter, thereby reducing manufacturing costs while maintaining measurement precision through wavefront division.
Solution Approach 2:
The patent substitutes the mechanical amplitude splitting beamsplitter system with an optical wavefront division approach using a tilted sensor. This substitution eliminates the need for expensive, high-quality optical components while achieving the same measurement function through interference pattern analysis of the tilted sensor's reflection.
3Measurement precision
If the light beam focus is arranged exactly on the surface of the sensor and reference mirror, then measurement precision is improved, but the device becomes sensitive to tilting and requires precise adjustment
Solution Approach 1:
The patent inverts the traditional approach by making the sensor itself tilted rather than keeping it parallel to the reference mirror. This inversion allows the sensor to serve as both the measurement target and the reference reflector, eliminating the need for precise parallel alignment and focus adjustment while maintaining measurement precision through the interference pattern of the tilted surface.
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
Enables high-precision measurement of movements below 0.1 pm with reduced sensitivity to temperature variations and lower manufacturing costs, achieving a wide linear dynamic range and tolerating larger optical component tolerances, thus suitable for applications like pressure and temperature sensors.
Implementation Method 1
detecting means for detecting changes in a spatial interference pattern produced by the light reflected from the moving element and the reference element
Data Source
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AI summary
The present invention relates to an arrangement for measuring relative movement. The measuring arrangement comprises a light source (110, 210) for emitting a light beam, a moving element (120, 220) having a reflective surface (121, 221) adapted to reflect a first wavefront portion of the light beam, and a reference element (130, 230) having a reflective surface (131, 231) adapted to reflect a second wavefront portion of the light beam. The arrangement further comprises detecting means (140, 240) for detecting changes in a spatial interference pattern produced by the light reflected from the moving element and the reference element, and processing means (150, 160, 250, 260) for calculating the relative movement between the moving element and the reference element from the phase change in the detected spatial interference pattern. The invention also relates to a method for measuring relative movement.