Polarization Imaging System Using Gated CMOS Camera
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Solution Overview
Problem
Existing systems for measuring birefringence properties of optical materials are limited by their ability to perform sequential, point-based measurements, which are time-consuming and inefficient for determining in-plane and out-of-plane birefringence over a wide range of incidence angles, especially in materials like LCD panels where birefringence varies with viewing angle.
Innovation Solution
A system utilizing oscillating photoelastic modulators (PEMs) and a CMOS or CCD camera with a gating mechanism that synchronizes light pulses with the PEMs' modulation states, allowing for simultaneous, spatially resolved imaging of in-plane and out-of-plane birefringence properties across a wide range of angles, thereby overcoming the limitations of slow camera integration times and reducing dark current and light pollution noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sequential point-based measurements are used to measure birefringence, then measurement precision can be achieved, but measurement time increases significantly and productivity decreases
Solution Approach 1:
The patent divides the measurement process into multiple simultaneous measurements at different spatial locations and incidence angles. Instead of measuring one point sequentially, the system uses an imaging detector to capture birefringence properties across multiple points simultaneously, while also measuring at multiple incidence angles through beam splitting and combiner optics.
Solution Approach 2:
The patent transitions from one-dimensional sequential measurement to multi-dimensional simultaneous measurement. By using imaging detectors with multiple pixels and optical beam combining, the system measures birefringence at multiple spatial locations and incidence angles simultaneously, adding spatial and angular dimensions to the measurement process.
2Device complexity
If imaging detectors with slow integration times are used, then device complexity is reduced, but the ability to capture rapid PEM modulation states is lost and measurement precision deteriorates
Solution Approach 1:
The patent employs periodic action by synchronizing the imaging detector's integration periods with the PEM modulation frequency. The detector is gated to open only during specific phases of the PEM cycle when the polarization state is in a known state, allowing the slow integrating detector to capture rapid modulation information through temporal synchronization.
Solution Approach 2:
The system uses feedback from the PEM modulation cycle to control the detector gating. The detector receives timing information about the PEM state and adjusts its integration window accordingly, ensuring that data is captured when the modulation state is known and stable, thus maintaining precision despite the detector's slow integration capability.
3Illumination intensity
If the camera integrates light continuously, then signal strength increases, but dark current and light pollution noise increase and measurement precision deteriorates
Solution Approach 1:
The patent applies periodic action by using pulsed gating of the imaging detector synchronized with the PEM modulation cycle. Instead of continuous integration, the detector is activated only during specific time windows when the PEM is in known states, reducing the total integration time and thereby minimizing dark current and light pollution noise while maintaining adequate signal strength during the active periods.
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 precise, simultaneous measurement of birefringence properties across a wide area, improving measurement efficiency and accuracy by ensuring that the camera captures data only when the PEMs are in known states, thus enhancing the signal-to-noise ratio and reducing measurement time.
Implementation Method 1
oscillating photoelastic modulators (PEMs) for highly stable modulation of the polarization of the light that is directed through the sample
Implementation Method 2
oscillating photoelastic modulators (PEMs) and a CMOS or CCD camera with a gating mechanism that synchronizes light pulses with the PEMs' modulation states
Implementation Method 3
Birefringence causes different linear polarizations of light to travel at different speeds through the material
Data Source
AI summary
This disclosure is generally directed to systems for imaging polarization properties of optical-material samples. As one aspect, there is provided a system for precise, simultaneous imaging of both the in-plane and out-of-plane birefringence properties of sample material over a wide range of incidence angles. The spatially resolved imaging approach described here is amenable to determination of a wide range of polarimetric properties, in addition to the in-plane and out-of-plane birefringence measure discussed as a preferred embodiment.