Heterodyne Interferometer for Opposite Target Displacement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing spatially separated heterodyne laser interferometers cannot accurately measure relative displacement between opposite moving targets due to their complex structures and inability to handle relative motion between multiple targets.
Innovation Solution
A heterodyne interferometer with a multi-target opposite displacement measurement system, featuring two spatially separated beams with different frequencies, polarization beam splitters, and a specific optical path structure that allows for relative displacement measurement between opposing targets, while reducing periodic nonlinear errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spatially separated heterodyne laser interferometer is used to suppress periodic nonlinear errors, then measurement precision is improved, but device complexity increases and cannot measure relative displacement between opposite moving targets
Solution Approach 1:
The interferometer is divided into two independent measurement channels (first and second measurement channels) that operate in parallel. Each channel measures displacement of one target relative to the other, and the results are combined to obtain the relative displacement between opposite moving targets. This segmentation allows the system to handle multiple targets while maintaining the simplicity and precision of spatially separated heterodyne interferometry in each channel.
Solution Approach 2:
The interferometer design uses universal components (beam splitter, mirrors, photodetectors) that serve multiple functions. The same optical components are used in both measurement channels, and the system can measure displacement in multiple directions (x-direction and y-direction) simultaneously, making the device versatile for measuring relative displacement between opposite moving targets.
2Device complexity
If conventional single-target heterodyne interferometer is used, then device structure is simpler, but it cannot measure relative displacement between opposite moving targets
Solution Approach 1:
The measurement function is segmented into two independent channels, each capable of measuring displacement of a single target. By combining these segmented measurement functions, the system achieves the versatility to measure relative displacement between opposite moving targets while keeping each channel's structure simple and conventional.
Solution Approach 2:
Two single-target measurement channels are merged into one integrated interferometer system. The optical paths, components, and signal processing of both channels are combined, allowing the system to simultaneously measure displacement of multiple targets and calculate their relative displacement, thereby enhancing adaptability without excessive complexity.
3Power
If acousto-optic modulator is used as beam splitter, then heterodyne frequency shift is achieved, but diffraction angle is very small and manufacturing defects cause frequency mixing
Solution Approach 1:
The patent extracts the frequency shift function from the beam splitter component. Instead of using an acousto-optic modulator that combines beam splitting and frequency shifting (causing interference), the frequency shift is achieved separately through other means, allowing the beam splitter to focus solely on beam division without the harmful effects of small diffraction angles and frequency mixing.
Solution Approach 2:
The patent introduces an intermediary approach where the frequency shift is not directly achieved in the beam splitter but through subsequent optical components or electronic processing. This intermediary method separates the beam splitting function from the frequency shifting function, eliminating the negative interactions caused by using acousto-optic modulators.
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 solution enables accurate measurement of relative displacement between opposite moving targets, reduces periodic nonlinear errors to the deep sub-nanometer level, and simplifies the interferometer structure for easier integration and assembly.
Implementation Method 1
a laser source for providing two spatially separated beams with different frequencies
Implementation Method 2
both of the first beam splitter and the second beam splitter are polarization beam splitters
Implementation Method 3
the first photodetector and the second photodetector are used to detect interference signals related to the reference beam and the measurement beam after reflection
Implementation Method 4
The first reflector and the second reflector group are used for reflecting the reference beam and the measurement beam
Data Source
AI summary
A heterodyne interferometer and a measurement method based on multi-target opposite displacement measurement are provided, technical points including: An output path of the laser source is sequentially arranged with a first beam splitter and a second beam splitter arranged in parallel on left and right sides, and both of which are polarization beam splitters; a first reflector is arranged above the first beam splitter, a third reflector is arranged on a right side of the second beam splitter, a second plane reflector is arranged in front of the second beam splitter, and a first plane reflector is arranged behind the second beam splitter; the first plane reflector and the second plane reflector jointly constitute a second reflector group; a left side of the first beam splitter is provided with a first photodetector and a second photodetector. The present invention realizes the measurement of relative displacement between opposing objects.