Offset Nulling for Optical Power Meters Using Dual Temperature Sensors
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Solution Overview
Problem
Handheld optical power meters face challenges in accurately measuring optical power across varying ambient temperatures due to temperature-dependent dark current offsets, requiring frequent warm-up times and additional calibration steps, which are impractical for outdoor use.
Innovation Solution
Incorporating two temperature sensors to measure the photodiode and PCB ground plane temperatures, allowing for the derivation of a numerical model that predicts optical power offsets, enabling calibration at multiple temperature points and reducing the need for lengthy warm-up times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If factory offset nulling calibration is performed at a given room temperature, then the calibration is valid only within a narrow temperature range, but this avoids the need for repeated calibration steps in the field
Solution Approach 1:
The patent changes the parameter being measured from a single temperature point to multiple temperature points. By performing offset nulling calibration at multiple predetermined temperature points and storing separate calibration data for each temperature, the system adapts to varying temperature conditions while maintaining measurement precision. The processor selects the appropriate calibration data based on the current temperature, resolving the contradiction between narrow temperature validity and field usability.
2Object-affected harmful factors
If handheld optical power meters are made hermetically closed for outdoor use, then they can operate in harsh environments, but they require hours of warm-up time which is not acceptable in the industry
Solution Approach 1:
The patent performs offset nulling calibration at multiple predetermined temperature points in advance during manufacturing. By pre-calibrating at various temperatures and storing the calibration data, the system eliminates the need for lengthy warm-up periods in the field. The processor simply retrieves the appropriate pre-stored calibration data based on current temperature, enabling immediate use in harsh environments without hours of warm-up time.
3Extent of automation
If automated offset nulling is performed by blocking input light or switching the input electronic circuit, then the offset nulling can be automated, but the measurement process needs to be interrupted which requires additional time and hardware
Solution Approach 1:
The patent performs offset nulling calibration in advance at multiple temperature points during manufacturing and stores the calibration data in memory. During field operation, the processor automatically retrieves and applies the appropriate pre-calibrated offset values based on current temperature readings, eliminating the need for real-time automated nulling procedures that would interrupt measurements. This preliminary calibration approach enables continuous measurement without interruption while maintaining automation.
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 allows for accurate optical power measurements across a wide temperature range with minimal warm-up time, reducing calibration time and eliminating the need for specific temperature setpoints, thus enhancing the usability of handheld optical power meters in harsh environments.
Implementation Method 1
Optical power of light is typically measured using a photodiode which converts optical power received on the surface of the photodiode into photocurrent
Implementation Method 2
a numerical model is derived, which accounts for the thermal law of the photodiode, the transimpedance amplifier and the overall electrical amplification circuit
Data Source
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AI summary
There is provided an optical power measurement method, an offset calibration method and an optical power meter that is adapted to apply the offset calibration method. The optical power measurement method, the offset calibration method and the optical power meter are characterized in that two temperature sensors are used for more accurate predictions of the optical power offset. A first temperature sensor is positioned to read a temperature of the photodiode and a second temperature sensor is positioned to read a temperature of the PCB ground plane.