Linearizing Mercury Cadmium Telluride Photodetector Response
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Solution Overview
Problem
Photodetectors used in various infrared bands exhibit non-linear responses to input optical radiation, which can lead to inaccurate comparisons of small and large signal values and introduce frequency components unrelated to the sample properties in applications like Fourier Transform spectroscopy.
Innovation Solution
The method involves directing a modulated optical beam to a test photodetector, determining calibration coefficients based on the modulation amplitude of the photo-signal, and storing these coefficients in a memory device. A reference photodetector can also be used to refine these coefficients, ensuring linearization of the photodetector response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If photodetectors are used for detection over wide power ranges, then detection capability is improved, but non-linear response causes inaccurate signal comparisons
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements before actual detection. The system measures the photodetector's response at multiple known power levels and stores calibration coefficients that are later used to linearize unknown signals, enabling accurate measurements across wide power ranges
Solution Approach 2:
The patent changes parameters by measuring the photodetector response at multiple different optical power levels (e.g., 0 dBm, -10 dBm, -20 dBm, -30 dBm) and using these varying parameters to determine calibration coefficients that compensate for non-linear behavior across the full operating range
2Measurement precision
If calibration is performed to linearize photodetector response, then measurement accuracy is improved, but system complexity increases
Solution Approach 1:
The patent uses an intermediary approach by introducing a calibration system that includes a signal generator and measurement apparatus separate from the main photodetector. This intermediary calibration system determines coefficients that are then applied to linearize the photodetector output without requiring modification of the photodetector itself
Solution Approach 2:
The calibration process is performed as a preliminary action before actual measurement. The system pre-determines calibration coefficients by measuring known power levels and storing these coefficients for later use, simplifying the actual measurement process while achieving linearization
3Measurement precision
If multiple calibration coefficients are determined, then linearization accuracy is improved, but processing time increases
Solution Approach 1:
Multiple calibration coefficients are determined in advance during a calibration phase before actual measurement. The system measures responses at multiple power levels and calculates all necessary coefficients beforehand, storing them for rapid application during operation, thus avoiding time-consuming calculations during measurement
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 effectively linearizes the photodetector response, enabling accurate comparisons of signal values across wide power ranges and reducing frequency components unrelated to the sample, thereby enhancing the reliability of measurements in applications like FTIR spectroscopy.
Implementation Method 1
obtaining a modulation amplitude of a photo-signal associated with detection of a first portion of the modulated optical beam by the test photodetector
Data Source
AI summary
Methods for linearization of photodetector response include establishing one or more static calibration coefficients based on comparison of test photodetector response to a linear reference photodetector. In some examples, dynamic calibration coefficients are determined based on average photodetector signals. In some applications such as FTIR, linearized ratios are obtained with a single calibration coefficient.