Method for determining optimal working temperature of spectrograph detector

Abstract

The invention relates to the technical field of detector working temperature determination, in particular to a method for determining the optimal working temperature of a spectrograph detector. The method comprises the following steps: carrying out theoretical analysis, determining a signal-to-noise ratio formula, analyzing a relation between a detector signal and temperature and a relation between detector noise and temperature, and theoretically calculating a relation between a signal-to-noise ratio and temperature; meanwhile, laboratory measurement including experiment setting and data acquisition and calculation is carried out; and finally, the optimal working temperature of the InGaAs detector is determined by integrating theoretical calculation and an actually measured signal-to-noise ratio result. According to the invention, the working temperature of the I nGaAs detector with the highest signal-to-noise ratio can be obtained, and when the I nGaAs detector is used for measurement, the temperature control module is used to stabilize the I nGaAs detector at the temperature all the time, so that the short wave infrared spectrometer based on the I nGaAs detector has better working performance, and the measurement precision of the spectrometer is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of detector working temperature determination, and in particular to a method for determining the optimal working temperature of a spectrometer detector. Background Art

[0002] Nowadays, the content of greenhouse gases is increasing year by year, and the greenhouse effect is intensifying, which brings great harm to people's work and life. The monitoring of greenhouse gases is imminent. Short-wave infrared imaging spectrometer is a commonly used greenhouse gas monitoring technology, and the infrared detector is the core component of the short-wave infrared imaging spectrometer. Its performance will directly affect the measurement accuracy of the infrared spectrometer. In addition, infrared detectors currently play an important role in modern industry and military, and various types of infrared detectors have been widely used in many fields.

[0003] Compared with visible light imaging technology and medium and long wave infrared imaging technology, short wave infrared imaging technology started late, and it did not rise until the emergence and continuous development of mercury cadmium telluride (MCT) materials. However, due to the fact that the detectors of MCT materials need deep cooling, its application in the short wave infrared band has always been slow. In recent years, the emergence of indium gallium arsenide (InGaAs) materials has strongly promoted the development of short wave infrared imaging technology. InGaAs material is a III-V pseudo binary semiconductor material with a zinc blende cubic crystal structure. Its cutoff wavelength can be adjusted by the content of In and Ga to achieve a change from 0.87μm to 3.5μm. InGaAs material can achieve a good match with III-V substrates to produce high-quality epitaxial structures. Mature growth technology makes it easier to have than materials such as MCT. At the same time, InGaAs near-infrared detectors have high quantum efficiency and extremely small dark current in the effective working wavelength range, and gradually reduce the requirements for cooling. It has been widely used in infrared imaging, infrared remote sensing, fiber optic sensing and other fields.

[0004] As early as the 1980s, many international research institutions began to study InGaAs material devices. Abroad, SUI of the United States, Sofradir of France, Xenics of Belgium, etc. are all committed to the research and development and production of InGaAs infrared imaging detectors, cameras, and imaging systems. With the advancement of science and technology, the imaging specifications, pixel size and other performance of InGaAs detectors have been continuously improved, and they have been widely used in military and industrial fields of various countries. For example, the spectrometer in MethaneAIR, the predecessor of the newly launched MethaneSAT satellite, uses InGaAs detectors. Carly Staebell and others have achieved high-precision CH4 measurement by studying the spectral calibration of the spectrometer, including stray light correction and instrument response function acquisition; secondly, Conway and others have improved the signal-to-noise ratio of the spectrometer through operations such as blind pixel masking, dark current subtraction, noise estimation, and pixel merging. In China, the research on InGaAs detectors started late. The main research institutions include the Shanghai Institute of Technical Physics, Chinese Academy of Sciences, the 44th Institute of China Electronics Technology Group Corporation, and the Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences. In recent years, some domestic semiconductor companies have also conducted research on InGaAs detectors, such as Guohui Optoelectronics and Liding Optoelectronics. After my country first developed an InGaAs detector with a pixel size of 40μm and a 128×128 element array in 2006, it has made continuous breakthroughs in technology and strived to catch up with the advanced level of foreign countries. In 2019, the Shanghai Institute of Technical Physics, Chinese Academy of Sciences, successfully developed a 1280×1024 element array InGaAs focal plane detector with a center distance of 15μm, reaching the forefront internationally. However, most of the application research on InGaAs detectors in my country is to improve the imaging quality of the detector by taking compensation measures. For example, the team of Fang Jiaxiong and Li Yongfu from Shandong University studied short-wave infrared imaging technology based on domestic InGaAs detectors, and improved the imaging quality of short-wave infrared imagers by studying blind pixel compensation and non-uniformity correction methods in InGaAs detectors. In addition, the team of Ding Lei and Niu Xinhua from the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences applied InGaAs detectors to the field of ultra-high spectrum detection for the first time. By studying its noise and laboratory calibration methods, they improved the signal-to-noise ratio of the spectrometer based on InGaAs detectors and improved the accuracy of CO2 measurement. However, few people have explored the optimal operating temperature of InGaAs detectors. Since InGaAs detectors are affected by the material band gap, doping level and temperature, their quantum efficiency is greatly affected by temperature. Therefore, choosing a suitable temperature for the detector is very necessary to improve the signal-to-noise ratio of the spectrometer.

[0005] It was found that the quantum efficiency of InGaAs detectors in the short-wave infrared band gradually decreases with increasing temperature, and the dark current noise of the detector increases exponentially with increasing temperature. It is therefore inferred that at a certain temperature, the signal-to-noise ratio of the spectrometer has a maximum value. To verify this inference, an approximate calculation was performed using the signal-to-noise ratio formula, and laboratory measurements were performed to verify that 0°C was the optimal operating temperature for the InGaAs detector, so that the overall spectrometer system has the highest signal-to-noise ratio. Using a temperature control device to stabilize the detector temperature at 0°C can effectively improve the measurement accuracy of the InGaAs short-wave infrared spectrometer. This lays a solid foundation for subsequent solar radiation spectrum measurements and atmospheric CH4 measurements.

[0006] At present, most of the research on InGaAs detectors in my country is carried out on its imaging quality, such as blind pixels, non-uniformity, pixel size or number of pixels. Few people have explored the optimal operating temperature of InGaAs detectors. And most people would think that for InGaAs infrared detectors, the lower the temperature, the smaller the dark noise and the greater the signal-to-noise ratio. But in fact, due to the particularity of InGaAs materials, due to its material defects, process preparation and other problems, the quantum efficiency of most InGaAs detectors in the short-wave infrared band decreases with decreasing temperature. And because the main noise of InGaAs, dark current noise, decreases with decreasing temperature, it is inferred that InGaAs detectors have the highest signal-to-noise ratio at a certain temperature and exhibit the best working performance. Therefore, this application proposes a method for determining the optimal operating temperature of a spectrometer detector. Summary of the invention

[0007] The purpose of the present invention is to propose a method for determining the optimal operating temperature of a spectrometer detector in view of the fact that few people have explored the optimal operating temperature of InGaAs detectors in the background technology and it is impossible to know at what temperature the detector has the best working performance.

[0008] The technical solution of the present invention is a method for determining the optimal operating temperature of a spectrometer detector, the method comprising the following steps:

[0009] Conduct theoretical analysis, determine the signal-to-noise ratio formula, analyze the relationship between detector signal and temperature, analyze the relationship between detector noise and temperature, and theoretically calculate the relationship between signal-to-noise ratio and temperature;

[0010] Perform laboratory measurements, including experimental setup and data acquisition and calculation;

[0011] The optimal operating temperature of the InGaAs detector is determined by combining theoretical calculations with actual measured signal-to-noise ratio results.

[0012] Optionally, the signal-to-noise ratio is calculated as:

[0013]

[0014] Among them, S represents the light signal measured by the spectrometer under a fixed light source, expressed as S = L × QE, L refers to the product of other parameters determined after the spectrometer structure is designed, except for the detector quantum efficiency QE; N is the total noise of the detector during normal measurement, expressed as The detector noise is determined by the readout noise N read , shot noise N shot , dark current noise N dark and fixed pattern noise N FPN composition.

[0015] Optionally, analyzing the relationship between the detector signal and the temperature specifically includes:

[0016] The relationship between the quantum efficiency of InGaAs detectors and temperature was quantitatively analyzed. The response DN values ​​in the CH4 inversion band of 1630nm-1660nm were averaged, and a curve fitting was performed with temperature as the horizontal axis and the response average value as the vertical axis. The response average value was used instead of the detector measurement signal to calculate the relationship between the detector signal-to-noise ratio and temperature.

[0017] Optionally, at different temperatures, the integration time is 200ms, 100 dark background images at corresponding temperatures are collected and averaged to obtain the dark background noise grayscale response value result, and an exponential fitting is performed on the relationship between the dark noise response and the temperature.

[0018] Optionally, the relationship between the detector noise and temperature is analyzed as follows: the total noise in the signal-to-noise ratio calculation is replaced by the dark current noise of the detector, and the relationship between the signal-to-noise ratio and temperature is theoretically calculated:

[0019] Use the formula:

[0020]

[0021] An approximate calculation was performed, in which the average DN value of the CH4 inversion band response was used instead of the detector quantum efficiency, and the dark background noise grayscale response value was used instead of the dark current noise.

[0022] Optionally, the experimental setting includes:

[0023] An integrating sphere is used as the light source, and the short-wave infrared spectrometer is placed in front of the integrating sphere;

[0024] Adjust the brightness of the integrating sphere so that its response is within the appropriate range of the spectrometer.

[0025] Optionally, the data collection and calculation includes:

[0026] 200 sets of spectral responses at different temperatures were continuously measured, and the average value of the response was used as the signal and the standard deviation as the noise;

[0027] According to the formula:

[0028]

[0029] Get the actual measurement signal-to-noise ratio of the spectrometer.

[0030] Optionally, when the detector temperature is -1 to 1°C, the signal-to-noise ratio during spectrometer measurement will reach a maximum value. Combined with the stability and effectiveness of the temperature control of the detector in actual spectrometer measurement, 0°C is selected as the optimal operating temperature of the InGaAs detector.

[0031] Compared with the prior art, the present invention has at least one of the following beneficial technical effects:

[0032] Through theoretical approximate calculation and actual laboratory measurement, the operating temperature at which the InGaAs detector has the highest signal-to-noise ratio is calculated. When using the InGaAs detector for measurement, a temperature control module is used to stabilize the InGaAs detector at this temperature, so that the instrument has better working performance and improves the measurement accuracy of the instrument.

[0033] The present invention can ensure that the short-wave infrared imaging spectrometer developed based on the InGaAs detector has a higher signal-to-noise ratio, which is of great significance for accurately monitoring the content of greenhouse gases in the atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the fitting curve graph of the average value of the integrating sphere response;

[0035] Figure 2 This is the curve of dark background noise response DN value changing with temperature;

[0036] Figure 3 is a curve diagram of the ratio of the quantum efficiency of the InGaAs detector to the dark noise background response;

[0037] Figure 4 This is a graph showing the change in signal-to-noise ratio of a laboratory-measured spectrometer versus temperature. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0039] Example

[0040] The present invention proposes a method for determining the optimal operating temperature of a spectrometer detector, which is described in detail below.

[0041] The signal-to-noise ratio is a key indicator used to reflect the detector's ability to obtain effective target information. Specifically, it refers to the ratio of the signal collected by the instrument to the noise. The size of the signal-to-noise ratio directly affects the accuracy of the detection data and analysis results. Only when the signal-to-noise ratio requirements are met can the availability of the measurement signal be guaranteed. Detectors with low signal-to-noise ratios will cause a large amount of complex physical noise to submerge the image features, seriously affecting the recognition and interpretation of the measurement target. Therefore, ensuring a high signal-to-noise ratio of the detector is a prerequisite for ensuring that the developed short-wave infrared spectrometer can measure accurately.

[0042] The signal-to-noise ratio is calculated as:

[0043]

[0044] S represents the light signal measured by the spectrometer under a fixed light source. It can be specifically expressed by the following formula:

[0045] S=L(λ,r,φ)×τ×QE×A×ω×N sr ×Δλ×t int (2)

[0046] Where L(λ,r,φ) represents the spectral radiance obtained by the optical system under the conditions of solar zenith angle φ and ground albedo r, τ is the transmittance of the optical system, QE is the quantum efficiency of the detector in the working band, A is the entrance pupil area, ω is the instantaneous field of view of the system, Δλ is the spectral bandwidth covering a single pixel of the detector, which is equal to the instrument spectral resolution (the FWHM of the instrument) divided by the spectral sampling rate N sr , t int is the integration time of the system. Among the above parameters, except for the detector quantum efficiency, other parameters can be determined after the spectrometer structure is designed. Here L refers to the product of all parameters, that is, S can be expressed as:

[0047] S=L×QE (3)

[0048] N is the total noise of the detector during normal measurement. It is generally believed that the noise of the detector consists of four parts, including the readout noise N read , shot noise N shot , dark current noise N dark and fixed pattern noise N FPN The expression is as follows:

[0049]

[0050] Substitute the signal S (3) and the noise N (4) into the signal-to-noise ratio formula, as shown below. The following analyzes each parameter in the SNR expression.

[0051]

[0052] ①Detector signal

[0053] In order to quantitatively analyze the relationship between the quantum efficiency of the InGaAs detector and temperature, the response DN values ​​in the CH4 inversion band of 1630nm to 1660nm are averaged and the result is used as the response value of the current temperature. The curve is fitted with temperature as the horizontal axis and the average response value as the vertical axis. The fitting curve is formula (6), which expresses the relationship between the detector signal and temperature. Figure 1 As shown:

[0054] y=-0.02853*x 3 -1.958*x 2 +45.01*x+5152 (6)

[0055] Depend on Figure 1 It can be seen that as the temperature increases, the average response value begins to rise slowly, and then begins to decline slightly after 10°C. The maximum value appears around 9°C. The average response value is used instead of the detector measurement signal to calculate the relationship between the detector signal-to-noise ratio and temperature, so as to find the optimal operating temperature of the InGaAs detector.

[0056] ②Detector noise

[0057] Usually the noise of the detector consists of four parts, including the readout noise N read , shot noise N shot , dark current noise N dark and fixed pattern noise N FPN However, after blind pixel compensation and non-uniformity correction are performed on the detector, the readout noise, shot noise and fixed pattern noise of the detector are less affected by temperature and can be ignored in the calculation of the relationship between signal-to-noise ratio and temperature. Therefore, the dark current noise of the detector is used to replace the total noise in the signal-to-noise ratio calculation.

[0058] Dark current noise refers to a type of noise generated in the absence of light, which is mainly caused by thermally generated carriers in the detector material. It is part of the output signal of the optoelectronic device under completely dark conditions and is the main source of noise when the detector's operating temperature changes. It has the characteristics of temperature dependence, time dependence, and pixel-to-pixel differences, that is, the dark current will increase with increasing temperature, because the higher the temperature, the more thermally generated carriers there are in the detector material. In order to quantify the relationship between dark current and temperature, at different temperatures, the integration time is 200ms, and 100 dark background images at the corresponding temperature are collected and averaged to obtain the dark background noise grayscale response value result, as shown below: Figure 2As shown, it can be seen that when the temperature of the InGaAs detector is high, the dark noise changes significantly with temperature. After the cooling temperature reaches -10°C, the dark noise curve becomes flat as the temperature decreases. Observe the image and perform exponential fitting on the relationship between the dark noise response and temperature. The fitting expression is as follows:

[0059] y=319.0286*e 0.072283*x +2544.24519

[0060] Through the above analysis, it is found that the signal-to-noise ratio of the short-wave infrared spectrometer based on InGaAs detector is only related to the detector's own quantum efficiency signal and dark current noise. It can be approximated by the following formula, where SNR T It represents the theoretically calculated instrument approximate signal-to-noise ratio, using the average DN value of the response in the CH4 inversion band of 1630nm to 1660nm to replace the detector quantum efficiency, and using the grayscale response value of the dark background noise to replace the dark current noise. Substituting the above fitting expression into the formula, the result is:

[0061]

[0062] like Figure 3 As shown in the figure, it can be seen that the calculated signal-to-noise ratio shows a trend of first increasing and then decreasing with the increase of temperature. After calculation, the theoretical approximate signal-to-noise ratio of the spectrometer reaches the maximum value at 0.5℃. Therefore, it can be approximately inferred that when the operating temperature of the InGaAs detector is 0.5℃, the short-wave infrared spectrometer has the highest signal-to-noise ratio.

[0063] ③Laboratory signal-to-noise ratio measurement

[0064] In actual measurements, the optical signal in the spectrometer is usually a response signal calculated by continuous measurement under laboratory conditions using a stable light source at a certain brightness; the noise in the signal-to-noise ratio is usually characterized by a statistical standard deviation; thereby obtaining the signal-to-noise ratio of the spectrometer during actual measurement, providing an important reference for detector performance testing and spectrometer measurement signal evaluation.

[0065] In this embodiment, an integrating sphere is used as the light source, a short-wave infrared spectrometer is placed in front of the integrating sphere, the brightness of the integrating sphere is adjusted so that its response is within the appropriate range of the spectrometer, 200 groups of spectral responses at different temperatures are continuously measured, the average value of the response is used as the signal, the standard deviation is used as the noise, and the actual measurement signal-to-noise ratio of the spectrometer is obtained according to the following formula:

[0066]

[0067] In the formula, SNR M Indicates the signal-to-noise ratio of the instrument during actual measurement. The results are as follows Figure 4As shown in the figure, it can be seen that the actual signal-to-noise ratio of the spectrometer measured experimentally has the same trend as the approximate signal-to-noise ratio curve calculated theoretically. As the temperature increases, both show a change that first increases and then decreases. The signal-to-noise ratio reaches its maximum value around 1°C.

[0068] ④Conclusion

[0069] Combining theoretical calculations and actual measured signal-to-noise ratio results, it is found that when the detector temperature is -1 to 1°C, the signal-to-noise ratio of the spectrometer measurement will reach its maximum value. Combined with the stability and effectiveness of the temperature control of the detector in the actual measurement of the spectrometer, 0°C was finally selected as the optimal operating temperature of the InGaAs detector, which can ensure that the detector has a high signal-to-noise ratio and high imaging quality. This provides a reference for the application measurement of the short-wave infrared spectrometer system developed based on the InGaAs detector, and lays the foundation for the accurate monitoring of CH4 in the atmosphere.

[0070] The above specific embodiments are only several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant inspirations of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A method for determining the optimal operating temperature of a spectrometer detector, characterized in that: The method comprises the following steps: Conduct theoretical analysis, determine the signal-to-noise ratio formula, analyze the relationship between detector signal and temperature, analyze the relationship between detector noise and temperature, and theoretically calculate the relationship between signal-to-noise ratio and temperature; Perform laboratory measurements, including experimental setup and data acquisition and calculation; The optimal operating temperature of the InGaAs detector is determined by combining theoretical calculations with actual measured signal-to-noise ratio results.

2. A method for determining the optimal operating temperature of a spectrometer detector according to claim 1, characterized in that: The signal-to-noise ratio calculation formula is: Among them, S represents the light signal measured by the spectrometer under a fixed light source, expressed as S = L × QE, L refers to the product of other parameters determined after the spectrometer structure is designed, except for the detector quantum efficiency QE; N is the total noise of the detector during normal measurement, expressed as The detector noise is determined by the readout noise N read , shot noise N shot , dark current noise N dark and fixed pattern noise N FPN composition.

3. A method for determining the optimal operating temperature of a spectrometer detector according to claim 1, characterized in that: Analysis of the relationship between detector signal and temperature specifically includes: The relationship between the quantum efficiency of InGaAs detectors and temperature was quantitatively analyzed. The response DN values ​​in the CH4 inversion band of 1630nm-1660nm were averaged, and a curve fitting was performed with temperature as the horizontal axis and the response average value as the vertical axis. The response average value was used instead of the detector measurement signal to calculate the relationship between the detector signal-to-noise ratio and temperature.

4. A method for determining the optimal operating temperature of a spectrometer detector according to claim 3, characterized in that: At different temperatures, the integration time was 200ms, and 100 dark background images at the corresponding temperatures were collected and averaged to obtain the grayscale response value of the dark background noise. An exponential fitting was performed on the relationship between the dark noise response and the temperature.

5. A method for determining the optimal operating temperature of a spectrometer detector according to claim 4, characterized in that: The relationship between detector noise and temperature is analyzed as follows: the dark current noise of the detector is used to replace the total noise in the signal-to-noise ratio calculation, and the relationship between the signal-to-noise ratio and temperature is theoretically calculated: Use the formula: An approximate calculation was performed, in which the average DN value of the CH4 inversion band response was used instead of the detector quantum efficiency, and the dark background noise grayscale response value was used instead of the dark current noise.

6. A method for determining the optimal operating temperature of a spectrometer detector according to claim 1, characterized in that: The experimental setup includes: An integrating sphere is used as the light source, and the short-wave infrared spectrometer is placed in front of the integrating sphere; Adjust the brightness of the integrating sphere so that its response is within the appropriate range of the spectrometer.

7. A method for determining the optimal operating temperature of a spectrometer detector according to claim 6, characterized in that: The data collection and calculation include: 200 sets of spectral responses at different temperatures were continuously measured, and the average value of the response was used as the signal and the standard deviation as the noise; According to the formula: Get the actual measurement signal-to-noise ratio of the spectrometer.

8. The method for determining the optimal operating temperature of a spectrometer detector according to claim 1, characterized in that: When the detector temperature is -1 to 1°C, the signal-to-noise ratio during spectrometer measurement will reach its maximum value. Combined with the stability and effectiveness of the temperature control that the detector can achieve in actual spectrometer measurements, 0°C is selected as the optimal operating temperature of the InGaAs detector.

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