Heterodyne Optical Encoder Cyclic Error Reduction
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Solution Overview
Problem
Interferometric measuring systems face limitations due to cyclic errors, which are periodic measurement errors caused by beam mixing and polarization imperfections, leading to reduced accuracy in monitoring position changes.
Innovation Solution
The implementation of an interferometric heterodyne optical encoder system that includes a polarizing beam splitting element and an output component, such as a birefringent prism pair, to deflect spurious beams away from the detector, reducing cyclic errors by separating measurement and reference beams based on their polarization and propagation angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If beam mixing occurs due to polarization imperfections and component ellipticity, then the interferometer can operate with standard polarizing beam splitting elements, but cyclic errors are introduced that limit measurement accuracy
Solution Approach 1:
A second polarizing beam splitting element is introduced as an intermediary component between the first beam splitter and the detector. This second beam splitter acts as a mediator that selectively transmits only the desired measurement and reference beams while blocking spurious beams caused by polarization mixing, thereby eliminating cyclic errors without requiring changes to the initial beam generation process
Solution Approach 2:
The spurious beams caused by beam mixing and polarization imperfections are extracted and removed from the optical path by the second polarizing beam splitting element. By taking out these harmful spurious beams before they reach the detector, the system maintains measurement precision while continuing to operate with standard polarizing components
2Device complexity
If spurious beams are not deflected away, then the optical path remains simple, but cyclic errors increase due to ghost beams and polarization mixing
Solution Approach 1:
The second polarizing beam splitting element serves as an intermediary that selectively transmits desired beams while blocking spurious beams. This intermediate component filters out ghost beams and polarization mixing effects before they reach the detector, maintaining measurement precision without requiring complex error correction algorithms
Solution Approach 2:
The second polarizing beam splitting element converts the harmful effect of polarization mixing into a beneficial filtering mechanism. By exploiting polarization differences between desired and spurious beams, the system automatically separates and removes erroneous signals, turning what would be a source of error into a means of error elimination
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 approach effectively minimizes cyclic errors, enhancing the accuracy of position change measurements by distinguishing and isolating spurious beams, thereby improving the precision of the interferometric measurements.
Implementation Method 1
the interferometer has at least one polarizing beam splitting element for directing the first beam along a measurement path to define a measurement beam and the second beam along a reference path to define a reference beam
Implementation Method 2
the output component can be a birefringent output component. The output birefringent component can include a prism pair
Data Source
AI summary
An encoder interferometry system includes a beam splitting element positioned to receive an input beam from a light source, in which the beam splitting element is configured to direct a first portion of the input beam along a measurement path to define a measurement beam and a second portion of the input beam along a reference path to define a reference beam, an encoder scale positioned to diffract the measurement beam at least once, one or more optical components configured and arranged to alter a direction of a first diffracted portion of the measurement beam and a direction of a second diffracted portion of the measurement beam such that beam paths of the first diffracted portion and the second diffracted portion are non-parallel subsequent to the first diffracted portion and the second diffracted portion passing through the beam splitting element, and a detector positioned to receive the first diffracted portion.