Interferometric Detector Phase Measurement Accuracy
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Solution Overview
Problem
The accuracy of polarization interferometers is limited by phase difference detector errors and environmental sensitivity, which affect the precision of distance and displacement measurements.
Innovation Solution
A novel configuration using a polarization-sensitive beam deflecting element, such as a Rochon or Wollaston prism, and a photodetector array to enhance phase difference measurement accuracy by introducing a divergence angle and spatially filtering the fringe pattern, providing improved reliability and reduced sensitivity to environmental variables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a quadrature detector with multiple beam paths is used to measure phase difference, then the measurement capability is provided, but differential phase and amplitude errors occur due to component differences and alignment variations
Solution Approach 1:
The patent combines the reference beam and object beam into a single beam path after they traverse the interferometer arms. By using a polarizing beamsplitter to combine these beams spatially and temporally, the system eliminates the need for separate detection paths, thereby removing differential phase and amplitude errors that arise from component mismatches and alignment variations between multiple paths.
Solution Approach 2:
The polarizing beamsplitter serves multiple functions: it initially separates the input beam into orthogonal polarized components for the reference and object paths, and later recombines these beams for detection. This multi-functional component enables a compact single-path detector design that maintains interferometric measurement capability while eliminating path-related errors.
2Measurement precision
If quadrature detectors with multiple components are used, then phase difference detection is enabled, but environmental sensitivity and changes over time increase
Solution Approach 1:
By merging the reference and object beams into a single detection path using a polarizing beamsplitter, the system minimizes the number of optical components and beam paths exposed to environmental variations. This reduction in system complexity directly decreases sensitivity to environmental factors such as temperature fluctuations, vibrations, and air currents that affect multiple separate components and alignment elements.
3Measurement precision
If conventional detectors are used, then basic wavelength-level measurement is achieved, but interpolation accuracy is limited
Solution Approach 1:
The patent introduces a polarization dimension to enable sub-wavelength interpolation. By measuring the phase difference between orthogonally polarized components of the combined beam and using quadrature detection on these polarization states, the system achieves interpolation accuracy of 1/1000 of a wavelength, far exceeding the basic wavelength-level measurement capability of conventional single-path detectors.
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 achieves phase difference measurement accuracy beyond the basic wavelength level, offering interpolation levels of 1/1000 of a wavelength and improved reliability, while minimizing errors and environmental sensitivity.
Implementation Method 1
a polarization-sensitive beam deflecting element, which deflects one or both of the orthogonally polarized beams to provide a desired divergence angle between the between the beams
Implementation Method 2
the polarization-sensitive beam deflecting element may be a polarization-sensitive prism, such as a Rochon prism, a Wollaston prism, or a Senarmont prism
Implementation Method 3
The diverging beams are input to a mixing polarizer, such that the beams exiting the mixing polarizer are similarly polarized and therefore interfere
Implementation Method 4
The interfering diverging beams will then form interference fringes, which may be parallel fringes. The spatial phase of the fringes relative to the detector characterizes the phase difference between the object and reference beams
Implementation Method 5
the spatial phase of the fringes relative to the detector may be sensed by a photodetector array configured to spatially filter the fringe pattern
Data Source
AI summary
A detector for interferometric distance or displacement measurement. The detector may receive orthogonally polarized object and reference path output beams, which are directed to a polarization-sensitive beam deflecting element. The beam deflecting element deflects one or both orthogonally polarized beams to provide a desired divergence angle between the beams. The diverging beams are input to a mixing polarizer. The beams exiting the mixing polarizer are similarly polarized and therefore interfere. The interfering diverging beams form interference fringes. The spatial phase of the fringes relative to a photodetector array characterizes the phase difference between the object and reference beams of the interferometer.