Polarisation Measurement Using Mechanical Chopper and Gated Imaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional imaging polarimeters face challenges in using conventional photo detector arrays due to high modulation frequencies required by optical phase modulators, necessitating complex and expensive custom sensors, which are difficult to integrate and reduce resolution.
Innovation Solution
A method involving a gating mechanism that synchronizes the exposure of the imaging device with the modulation frequency of the polarizing modulation, allowing conventional low-cost CCD arrays to be used by averaging intensity over gating periods, and employing an infinity corrected optical element to ensure each pixel experiences consistent optical paths for calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical phase modulators operating at high frequencies are used, then polarisation modulation capability is improved, but detector operating requirements become excessively demanding and costly
Solution Approach 1:
The patent applies periodic action by using a mechanical chopper to periodically interrupt the light beam at a low frequency (e.g., 50 Hz). This converts the continuous high-frequency modulation problem into a periodic sampling problem that can be handled by conventional detectors. The chopper creates distinct on/off cycles that allow the detector to integrate light over manageable time periods while still capturing the modulated signal.
Solution Approach 2:
The patent replaces the optical phase modulator system with a mechanical chopper system. Instead of using complex optical phase modulators that require high-frequency detector response, a simple mechanical chopper is used to modulate the light intensity at a low frequency. This mechanical substitution allows conventional detectors to operate within their capabilities while achieving the necessary modulation for polarisation measurement.
2Productivity
If conventional digital camera devices are used with high frame rates, then productivity is improved, but device complexity and cost increase due to custom sensors
Solution Approach 1:
The mechanical chopper provides periodic action at a low frequency that is easily handled by conventional digital cameras. The camera can capture frames at standard frame rates (e.g., 30 or 60 fps) while the chopper modulates the light at a lower frequency (e.g., 50 Hz). This allows the use of off-the-shelf cameras without requiring custom high-speed sensors, maintaining both productivity and simplicity.
Solution Approach 2:
The patent employs inexpensive, readily available digital camera devices instead of costly custom-built high-speed sensors. The mechanical chopper is a simple, low-cost component that can be easily manufactured and replaced if needed. This approach uses cheap, easily replaceable components to achieve the measurement function without investing in expensive specialized equipment.
3Productivity
If the frame rate of digital camera devices is increased, then productivity is improved, but the number of working detector pixels decreases and resolution is reduced
Solution Approach 1:
The mechanical chopper operates at a low frequency that allows the camera to use its full frame rate capability without sacrificing pixels. Each frame captures the light during a specific phase of the chopper cycle, and the periodic nature of the chopping allows the camera to accumulate sufficient signal over multiple frames without needing to reduce the number of active pixels or compromise spatial resolution.
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 the use of low-cost, conventional detectors in advanced polarimeters, reducing complexity and cost while maintaining resolution, and simplifies calibration by ensuring each pixel measures consistent optical effects, facilitating faster determination of polarisation parameters.
Implementation Method 1
a polarisation modulator to modulate a polarisation state of electromagnetic radiation received from a target object in response to an applied signal
Implementation Method 2
a detector to selectively measure an intensity of the modulated electromagnetic radiation
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A method and apparatus are disclosed for measuring polarisation of electromagnetic illumination. The method includes the steps of modulating a polarisation state of illumination received from a target object to generate modulated intensity illumination, selectively measuring an intensity of the modulated intensity illumination by periodically gating an exposure of an imaging device to the modulated intensity illumination at a first gating frequency; responsive to the measured intensity, determining polarisation parameters of the received illumination, and generating image data corresponding to the target object with a plurality of the polarisation parameters, wherein the illumination from the target object is modulated in accordance with a first frequency and the first gating frequency is associated with and synchronised with at least the first frequency.