Fourier Transform Spectrometer Differential Reading Circuit
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Solution Overview
Problem
The dynamic range of the reading circuit in existing Fourier transform spectrometers limits the spectral resolution, resulting in a constrained signal-to-noise ratio for spectral energy distribution analysis.
Innovation Solution
The implementation of differential reading, where the read signal corresponds to the first derivative of the radiation intensity with respect to the optical path length difference, allowing for improved utilization of the reading circuit dynamics and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the dynamic range of the reading circuit is increased to improve spectral resolution, then the spectral resolution is improved, but the device complexity and cost increase
Solution Approach 1:
The detection cycle is segmented into two separate detection periods: a first detection period for detecting radiation at a first optical path length difference, and a second detection period for detecting radiation at a second optical path length difference. This segmentation allows the reading circuit to operate at reduced dynamic range while still achieving high spectral resolution through differential measurement of the two periods.
Solution Approach 2:
The invention changes the measurement parameter from absolute intensity measurement to differential intensity measurement. By measuring the difference in radiation intensity between two detection periods with different optical path length differences, the system achieves improved spectral resolution without requiring high dynamic range in the reading circuit, as the differential measurement cancels out common-mode noise and reduces the required measurement range.
2Reliability
If the dynamic range of the reading circuit is increased to improve signal-to-noise ratio, then the signal-to-noise ratio is improved, but the device complexity increases
Solution Approach 1:
The detection cycle is divided into two detection periods with different optical path length differences. By segmenting the measurement into these two periods and comparing the results differentially, the system reduces noise through cancellation of common-mode interference, achieving improved signal-to-noise ratio without requiring increased dynamic range in the reading circuit.
Solution Approach 2:
The invention converts the limitation of fixed detection cycle duration into a benefit by using it to enable differential measurement. The fixed cycle time constrains the integration period, but by measuring the difference between two such constrained periods with different optical path differences, the system achieves noise reduction and improved signal-to-noise ratio without needing extended integration times or high dynamic range circuits.
3Reliability
If the integration period is extended to improve signal-to-noise ratio, then the signal-to-noise ratio is improved, but the detection cycle duration increases
Solution Approach 1:
The invention converts the constraint of fixed detection cycle duration into a benefit by implementing differential measurement within that fixed cycle. By measuring radiation intensity at two different optical path length differences within the same fixed cycle time and computing the difference, the system achieves noise reduction and improved signal-to-noise ratio without extending the detection cycle duration.
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 enhances the signal-to-noise ratio by a factor of two or more, enabling better spectral resolution without increasing the dynamic range, and allows for reduced capacitance in the detector components.
Implementation Method 1
a photodetector, which is arranged to receive the final radiation beam, and which is suitable for detecting the radiation received by accumulating a control quantity as a function of an intensity of this radiation received
Implementation Method 2
the interference device, which is adapted to produce a variable difference in optical path length between at least two intermediate beams of radiation formed from an initial beam, and to combine these two intermediate beams into a final beam of radiation
Data Source
Figure 1
Figure 2a~2b
AI summary
The spectrometer has a photodetector (4) for receiving a final radiation beam (FS) and detecting an initial radiation beam based on intensity of the received final beam. An electronic control unit (5) controls detection of the initial beam by the photodetector within a detection cycle, and delivers a read signal (VL) at an end of the detection cycle. The spectrometer is arranged in such a manner that the read signal is equal to a difference between variations of cookie quantity occurring during two initial detection periods. An independent claim is also included for a method for spectral analysis of a radiation beam using a spectrometer.