Unambiguous Absolute Retardance Measurement via Multi-Wavelength Polarimetry
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for measuring the retardance of optical samples, such as polymers and crystals, face challenges in accurately determining absolute retardance due to limitations in phase difference measurement and ambiguity in multi-order retardance, especially when dealing with samples having arbitrary fast axis orientations and varying wavelengths.
Innovation Solution
The method involves directing source light with multiple wavelengths through a polarization state generator and analyzer, using imaging devices to detect intensity and calculate measurable retardance, and employing equations to determine absolute retardance by accounting for dispersion and wavelength fluctuations, thereby unwrapping the measured retardance into its absolute form across various wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single-wavelength measurement is used, then measurement simplicity is maintained, but measurement precision deteriorates due to ambiguity in multi-order retardance
Solution Approach 1:
The patent changes the wavelength parameter of the light source to resolve measurement ambiguity. By measuring at multiple discrete wavelengths and using the relationship between retardance and wavelength, the system can determine the absolute retardance order unambiguously. The computer identifies the correct integer order m by finding which wavelength combination yields consistent retardance values across all measured wavelengths.
2Measurement precision
If multi-wavelength measurement is implemented, then measurement precision improves for absolute retardance, but device complexity increases
Solution Approach 1:
The patent makes the measurement system universal by enabling it to measure absolute retardance for samples with any fast axis orientation and any retardance magnitude. The same multi-wavelength measurement and computer analysis procedure works for all samples regardless of their specific properties, making the system broadly applicable without requiring sample-specific calibration or configuration.
3Adaptability or versatility
If samples with arbitrary fast axis orientation are measured, then measurement versatility is improved, but measurement precision deteriorates due to orientation-induced errors
Solution Approach 1:
The patent eliminates the limitation of fast axis orientation by using multi-wavelength measurements combined with computer analysis. The system measures intensity variations at multiple wavelengths and uses mathematical relationships to extract both the retardance magnitude and the fast axis orientation simultaneously, making the measurement independent of the sample's orientation.
4Adaptability or versatility
If high retardance samples are measured, then measurement range is expanded, but measurement precision deteriorates due to phase wrapping ambiguity
Solution Approach 1:
The patent overcomes the phase wrapping limitation by introducing wavelength as an additional parameter. Since retardance is proportional to wavelength, measuring at multiple wavelengths provides redundant information that allows the computer to unwrap the phase and determine the absolute retardance order. This enables accurate measurement of high retardance samples that would otherwise be ambiguous in single-wavelength measurements.
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 enables robust, unambiguous measurement of absolute retardance across multiple orders, reducing errors and providing accurate retardance images even for samples with large spatial diversity and high retardance levels, spanning thousands of nanometers.
Implementation Method 1
directing, through a polarization state generator, source light with at least two different wavelengths; directing the light though the sample; directing the light though a polarization state analyzer
Implementation Method 2
Many important optical materials exhibit birefringence. Birefringence means that different linear polarizations of light travel at different speeds through the material.
Implementation Method 3
directing the light that emanates from the polarization state analyzer to an imaging device to thereby detect the intensity of the light and calculate a measurable retardance
Data Source
AI summary
This invention is directed to methods of unambiguously measuring the absolute retardance, δA of an optical sample. A method for measuring absolute retardance of an optical sample includes directing light comprising a plurality of wavelengths through a polarization state generator source, the optical sample, and a polarization state analyzer, detecting, at an imaging device, retardance measurement light emanating from the optical sample after also passing through the polarization state analyzer at the plurality of wavelengths, determining a measurement retardance associated with the detected retardance measurement light at each of the wavelengths, and determining an absolute retardance associated with the optical sample based on the measurement retardances determined at each of the wavelengths.