Terahertz Quantum Well Detector Responsivity Calibration
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Solution Overview
Problem
Current methods for calibrating the absolute responsivity of terahertz quantum well detectors are inaccurate and inefficient due to interference from infrared and visible light, water vapor absorption, and complex calculations, especially under varying environmental conditions and low temperature operations.
Innovation Solution
A calibration device and method using a single frequency laser source, terahertz array detector, and dynamometer to measure and calculate the incident laser power directly, simplifying the calibration process by locking in the periodicity of the laser source and reducing the impact of environmental factors through single frequency light and direct power measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a standard black-body is used as calibration radiation source, then the detector responsivity can be calculated through integration of photocurrent spectrum, but infrared light and stray visible light in the environment have large influence on the calibration accuracy
Solution Approach 1:
The patent segments the calibration process into two distinct stages: first measuring the total radiation power using a thermopile detector, then measuring the spectral distribution using a Fourier transform spectrometer. This segmentation allows separate optimization of each measurement, reducing the impact of environmental light interference on the final responsivity calculation.
Solution Approach 2:
The patent introduces an intermediary approach by using a chopper modulator to convert the continuous black-body radiation into periodic signals at a specific frequency. This modulation technique allows the use of lock-in amplification to selectively detect only the modulated signal at the reference frequency, effectively rejecting unmodulated environmental infrared and visible light interference.
2Ease of operation
If calibration is performed under atmospheric environment, then the measurement can be conducted in normal conditions, but water vapor absorption causes large deviation in the calculated responsivity
Solution Approach 1:
The patent implements feedback by using the Fourier transform spectrometer to measure the actual spectral distribution of radiation reaching the detector, including atmospheric absorption effects. This measured spectrum is then used to correct the responsivity calculation, compensating for water vapor absorption and other atmospheric effects that would otherwise cause large deviations.
Solution Approach 2:
The patent changes the measurement parameters by measuring not just the total power but also the full spectral distribution. By obtaining the spectral information, the system can identify and correct for frequency-dependent atmospheric absorption, particularly water vapor absorption peaks, thereby improving accuracy while maintaining atmospheric calibration conditions.
3Productivity
If rapid rotation of the chopper is used during calibration, then the measurement speed increases, but the disturbance to environment causes large deviation in water vapor absorption deduction
Solution Approach 1:
The patent applies preliminary action by measuring the spectral distribution and atmospheric absorption characteristics before performing the final responsivity calculation. The Fourier transform spectrometer captures the complete spectral information in advance, allowing the system to account for atmospheric effects without requiring rapid chopper rotation during the critical measurement phase.
4Measurement precision
If conventional calibration method with multiple components is used, then the calibration process can be performed, but the complex calculations and multiple measurement steps reduce efficiency
Solution Approach 1:
The patent merges multiple measurement functions into a unified calibration system. The Fourier transform spectrometer simultaneously provides both the spectral distribution information and the total power measurement (through integration), while the lock-in amplifier integrates the signal over multiple cycles to improve signal-to-noise ratio. This merging eliminates the need for separate measurement steps and complex sequential calculations, thereby improving calibration efficiency while maintaining precision.
Data Source
AI summary
A calibration method for an absolute responsivity of a terahertz quantum well detector and a calibration device thereof, in which the device at least comprises: a driving power supply, a single frequency laser source, an optic, a terahertz array detector, a terahertz dynamometer, a current amplifier and an oscilloscope. The calibration method adopts a power detectable single frequency laser source as a calibration photosource, to obtain the absolute responsivity parameters of the detector at the laser frequency; a normalized photocurrent spectrum of the detector is used to further calculate the absolute responsivity parameters of the detector at any detectable frequency. the single frequency laser source with periodically output is adopted as a calibration photosource, the terahertz array detector and the dynamometer are adopted to directly measure and obtain the incident power of the calibrated detector.