Optical System Polarizer Calibration at Arbitrary Angles
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Solution Overview
Problem
Current polarization calibration methods in optical systems are limited to normal or near-normal incidence angles and fail to decouple sample and system polarization effects, making them ineffective for arbitrary angles of incidence.
Innovation Solution
A calibration apparatus with a substrate and a polarizer, where the polarizer is either lithographically formed or attached to the substrate, allowing for precise determination of the polarizer orientation using a nonlinear regression algorithm and optionally aided by a crossed analyzer, enabling calibration at any arbitrary angle of incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the internal polarizer is stepped over a discrete set of angles for calibration, then the calibration process can be performed, but the relative orientation with respect to the polarized sample becomes a system-fitting parameter that depends on specific sample properties
Solution Approach 1:
A calibration sample with known polarization properties is introduced as an intermediary element between the system and the unknown polarized sample. This calibration sample allows the system to determine the relative orientation between the polarizer and the sample reference frame independently of the unknown sample's properties, thereby resolving the coupling between system and sample polarization effects.
Solution Approach 2:
The calibration process performs a preliminary determination of the polarizer's relative orientation with respect to the sample reference frame before actual measurement. By first characterizing the system response using a calibration sample with known properties, the system establishes a reference state that can be used to accurately measure unknown samples at any angle of incidence.
2Adaptability or versatility
If the calibration is performed using a non-polarized reference sample, then the system polarization response can be acquired, but the method is limited to broadband polarized reflectometers with normal or near-normal incidence
Solution Approach 1:
The invention changes the polarization state parameter of the calibration sample from non-polarized to polarized with known orientation. This allows the calibration to be performed at arbitrary angles of incidence by utilizing the known polarization properties of the calibration sample, thereby extending the method's applicability beyond normal incidence while maintaining calibration accuracy.
3Device complexity
If the polarizer orientation is determined without accounting for spectrometer misalignment, then the calibration process is simpler, but the precision is reduced
Solution Approach 1:
The calibration process incorporates feedback by using the measured system response from the calibration sample to iteratively determine the polarizer orientation. The known polarization properties of the calibration sample provide a reference that allows the system to account for spectrometer misalignment and other systematic errors, thereby improving orientation determination accuracy without significantly increasing process complexity.
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 accurate polarization calibration of optical systems at any angle of incidence, decouples sample and system polarization, and improves precision by accounting for spectrometer misalignment, allowing for flexible orientation and accurate determination of the polarizer orientation.
Implementation Method 1
a polarizer disposed on the substrate... indicating a polarization orientation of the polarizer
Data Source
AI summary
An apparatus to calibrate a polarizer in a polarized optical system at any angle of incidence. The apparatus decouples the polarization effect of the system from the polarization effect of the sample. The apparatus includes a substrate with a polarizer disposed on the surface. An indicator on the substrate indicates the polarization orientation of the polarizer, which is in a predetermined orientation with respect to the substrate.