Heterodyne Interferometer Grating Polarization Control
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Solution Overview
Problem
Known interferometers suffer from measurement inaccuracies due to polarization leakages that produce errors not simply related to stage displacement, leading to unreliable displacement and rotation measurements.
Innovation Solution
The interferometer design incorporates a polarization beam splitter, diffraction grating, and optical retarders to manage polarization axes and frequencies, enabling heterodyne measurement and accurate displacement determination along multiple axes by using two distinct frequencies for the measurement and reference beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional interferometer uses a single beam split into reference and measurement beams, then the device complexity is low, but measurement precision deteriorates due to polarization leakages producing errors
Solution Approach 1:
The patent divides the measurement system into two separate interferometer channels (first and second measurement beams) operating at different frequencies. Each channel independently measures displacement along different axes, eliminating polarization leakage errors through frequency separation. This segmentation allows precise measurement while managing complexity through modular architecture.
Solution Approach 2:
The patent introduces frequency as an additional dimension by using two distinct frequencies (first and second frequencies) for the measurement and reference beams. This frequency dimensionality allows the system to distinguish between different optical paths and eliminate polarization errors, improving measurement precision without excessive complexity increase.
2Reliability
If polarization leakages are present in the interferometer, then the device complexity remains simple, but reliability deteriorates due to measurement inaccuracies
Solution Approach 1:
The patent introduces frequency as an intermediary parameter to mediate between the measurement and reference beams. By assigning different frequencies to different beams, the system can identify and eliminate polarization leakage errors that would otherwise compromise reliability. The frequency intermediary allows reliable measurement while keeping the optical path manageable.
3Measurement precision
If a single frequency is used for both measurement and reference beams, then the device complexity is low, but measurement precision deteriorates due to inability to distinguish polarization leakages
Solution Approach 1:
The patent changes the frequency parameter by using two distinct frequencies (first frequency for measurement beam, second frequency for reference beam) instead of a single frequency. This parameter change enables the system to distinguish between different optical paths and eliminate polarization leakage errors, improving displacement measurement precision while managing frequency complexity through systematic assignment.
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 minimizes measurement errors caused by polarization leakages, providing precise and accurate displacement and rotation measurements across multiple axes, enhancing the reliability of interferometric measurements.
Implementation Method 1
a diffraction grating disposed over the optical element configured to diffract the first measurement beam and the second measurement beam
Implementation Method 2
an optical element comprising a first portion comprising a polarization beam splitter
Implementation Method 3
a first optical retarder configured to rotate a polarization axis of the first optical beam by approximately 90°; and a second optical retarder configured to rotate a polarization axis of the second optical beam by approximately 90°
Implementation Method 4
The measurement beam is reflected from a mirror mounted on a moving object and is combined with the reference beam reflected from a stationary object to generate a phase difference. The phase difference is proportional to the amount of displacement
Data Source
AI summary
An interferometer has a first input configured to provide a first measurement beam at a first frequency, and a second measurement signal at the first frequency. The interferometer has a second input configured to provide a reference beam at a second frequency that is different than the first frequency; an optical element comprising a first portion comprising a polarization beam splitter; and a diffraction grating disposed over the optical element configured to diffract the first measurement beam and the second measurement beam.