Automatic spectrum calibration device and method for grating type spectrometer

Abstract

The invention discloses an automatic spectrum calibration device and method for a grating type spectrometer, and relates to the technical field of spectrum calibration, and the device comprises a tunable laser, a wavelength meter, a power meter, a beam splitter, a rotary integrating sphere, and a computer measurement and control system. Software connection of the tunable laser, the wavelength meter and the power meter is realized through the computer measurement and control system, and an automatic calibration function is set. The tunable laser performs light splitting through the two beam splitters, one path of laser enters the rotary integrating sphere for spectrum calibration, the other path of laser enters the wavelength meter for measuring and controlling the wavelength of the laser and performing frequency stabilization on the laser, and the other path of laser enters the power meter for monitoring the output power of the power meter. A computer measurement and control system is used, and parameters such as an initial wavelength, a sampling interval and a termination wavelength are set to realize automatic spectrum calibration of the grating type spectrometer. According to the invention, spectrum calibration can be provided for various grating type spectrometers.

Description

Technical Field

[0001] The present invention relates to the technical field of spectrum calibration, and in particular to an automatic spectrum calibration device and method for a grating type spectrometer, which is applicable to a grating type spectrometer with large array, full pixel, wide spectral range and high spectral resolution. Background Art

[0002] To proactively address climate change, quantitative detection of global greenhouse gases and trace gases has become a pressing research priority. Grating spectrometers, which can generate a three-dimensional cube of data consisting of two-dimensional spatial and one-dimensional spectral data, are an important technical tool for quantitatively studying global and regional greenhouse gas concentrations. The development trend for greenhouse gas detection payloads is toward high spectral resolution, high spatial resolution, and wide bandwidth. This trend indicates that the requirements for payload quantification are becoming increasingly stringent, necessitating the critical importance of high-precision spectral and radiometric calibration. Payloads that simultaneously address high spectral resolution, wide bandwidth, and high spatial resolution inevitably require a massive detector pixel size. High quantification requires spectral calibration across the entire spectral range and all pixels. Manually adjusting the laser wavelength and collecting payload output signals is time-consuming and inefficient. Manual calibration of large-array detectors is particularly time-consuming, making it prohibitive within the payload development cycle. Summary of the Invention

[0003] In order to solve the problems of low calibration accuracy and low calibration efficiency in the existing spectral calibration method of grating spectrometers, the present invention proposes an automatic spectral calibration device and method for grating spectrometers, which has the advantages of stable closed-loop structure, high efficiency, and strong adaptability. The present invention uses a tunable laser entering a rotating integrating sphere as a spectral calibration light source, and a wavelength meter measured by the National Institute of Metrology as a wavelength reference. The output wavelength value of the tunable laser is stabilized on the wavelength meter, and the spectral calibration device and the ground detection output control link are connected, which has an automatic spectral calibration function. Users can set the calibration step size, calibration range, etc. according to their needs to complete the automatic spectral calibration of large-array full-pixel and full-spectral segments. Compared with traditional spectral calibration methods, this calibration method takes less time and is easy to use. The device has the function of tracing back to the wavelength meter, has high spectral calibration accuracy, and is suitable for spectral calibration of various grating spectrometers.

[0004] The present invention uses a tunable laser method to automatically calibrate the spectrum of a grating spectrometer using a frequency-stabilized tunable laser light source. Software connections between the tunable laser, wavelength meter, and power meter are achieved through a computer measurement and control system, and an automated calibration function is provided. The tunable laser is split by two beam splitters. One laser beam enters a rotating integrating sphere for spectral calibration, one laser beam enters a wavelength meter for wavelength measurement and frequency stabilization, and one laser beam enters a power meter for monitoring output power. Using the computer measurement and control system, parameters such as the starting wavelength, sampling interval, and ending wavelength are set to achieve automated spectral calibration of the grating spectrometer. The present invention can significantly improve spectral calibration efficiency, shorten instrument development cycles, and provide technical support for rapid spectral calibration of grating spectrometers.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] An automated spectrum calibration device for a grating spectrometer comprises a tunable laser, a power meter, a wavelength meter, a first beam splitter, a second beam splitter, a DC motor, a rotating integrating sphere, and a computer measurement and control system. The tunable laser, power meter, and wavelength meter are arranged on one side of the rotating integrating sphere, and a grating spectrometer to be measured is arranged on one side of a light outlet of the rotating integrating sphere. Laser light output by the tunable laser is sequentially split into three beams by the first and second beam splitters. The main beam is irradiated onto the grating spectrometer to be measured via the rotating integrating sphere, and the remaining two beams enter the power meter and wavelength meter, respectively. After entering the rotating integrating sphere through the light outlet, the main beam is driven by the DC motor to rotate a diffuse reflection plate, resulting in multiple diffuse reflections, forming a surface light source at the light outlet of the rotating integrating sphere, and irradiating the grating spectrometer to be measured. The computer measurement and control system is used for automated control and data acquisition of the spectrum calibration process.

[0007] Furthermore, the output laser spectral range of the narrow-linewidth tunable laser covers the spectral response range of the grating spectrometer to be measured; the linewidth of the narrow-linewidth tunable laser is better than 300 kHz; the fine-tuning step size of the narrow-linewidth tunable laser is better than 2 pm, and its controller has a secondary programming development interface.

[0008] Furthermore, the rotating integrating sphere includes at least three openings, one of which is a light exit port, the diameter of which is larger than the entrance pupil diameter of the grating spectrometer to be measured and the aperture ratio of the rotating integrating sphere is better than 1 / 3; the second opening is a light entrance port, which is determined by the divergence angle of the laser and is larger than the laser incident spot, with a diameter selected to be greater than or equal to 25.4mm; the third opening is a diffuse reflection plate mounting hole, located at the position where the laser directly enters the inner wall of the rotating integrating sphere from the light entrance, the size of the third opening is larger than the laser incident spot, the diameter is selected to be greater than or equal to 25.4mm, and a rotating diffuse reflection plate is installed at the opening. The diffuse reflection plate is made of the same material as the inner wall of the rotating integrating sphere, generally polytetrafluoroethylene. The first opening is larger than the second and third openings, and the opening ratio of the integrating sphere is better than 1 / 3.

[0009] Furthermore, the rotation of the rotating integrating sphere refers to the rotation of the animated reflector after the DC motor is powered on, which is used to eliminate speckles.

[0010] Furthermore, the accuracy of the wavelength meter is better than 1 ppm, the wavelength range of the wavelength meter covers the spectral response range of the grating spectrometer to be measured, and it has a secondary programming development interface.

[0011] Furthermore, the power meter consists of a meter head and a probe. The meter head has display and control functions. The appropriate probe is selected according to the band and accuracy. The spectral response range of the probe covers the spectral response range of the grating spectrometer to be tested. The test power resolution is better than 10 nW. The power meter head has a secondary programming development interface.

[0012] Furthermore, the computer measurement and control system is used to connect the controller, wavelength meter, power meter and other equipment of the tunable laser into a whole through the measurement and control software, and cooperate with the ground detection software of the grating spectrometer to be measured to control the laser to output data according to a certain step size, thereby completing the automated data collection work; the computer measurement and control system completes the wavelength measurement of the tunable laser and can stabilize the wavelength on the wavelength meter, and can monitor and record the output value of the wavelength meter and the output value of the power meter in real time and complete the collection and storage of the ground detection system data.

[0013] The present invention also provides an automated spectrum calibration method for a grating-type spectrometer, comprising the following steps:

[0014] Step 1: Place a narrow-linewidth tunable laser, a rotating integrating sphere, a power meter, a wavelength meter, a beam splitter, and a reflector on a vibration-isolating optical platform. Adjust the laser output from the tunable laser to enter the light entrance of the rotating integrating sphere. At the same time, adjust the optical path so that the laser enters the rotating integrating sphere and reaches the diffuse reflection plate driven by the DC motor. Align the light entrance of the rotating integrating sphere with the optical entrance pupil of the grating spectrometer to be measured, ensuring that the optical entrance pupil of the grating spectrometer to be measured coincides with the center of the optical axis of the light entrance of the rotating integrating sphere. Split the laser output from the tunable laser into two beams through the first beam splitter. One beam enters the rotating integrating sphere, and the other beam is split into two beams through the second beam splitter. One beam enters the power meter, and the other beam enters the wavelength meter through the reflector.

[0015] Step 2: Connect the tunable laser, wavelength meter, and power meter to the computer measurement and control system and control them. Control the wavelength output of the tunable laser according to the settings and monitor its power and wavelength in real time. The wavelength meter is used to provide feedback and calibrate the output wavelength of the tunable laser. Connect the ground detection system of the grating spectrometer to be measured to the computer measurement and control system. After the tunable laser stabilizes, automatically record and store the spectral response data of the grating spectrometer to be measured.

[0016] Step 3: Set the starting wavelength, ending wavelength, wavelength scanning interval, wavelength stability and accuracy criteria, and the number of frames for grating spectrometer data storage on the computer measurement and control system.

[0017] The beneficial effects of the present invention are:

[0018] 1) High Calibration Efficiency: This invention automates the calibration of grating spectrometers, significantly shortening the calibration cycle. This is particularly true for large-array grating spectrometers requiring full-pixel calibration. This method enables pixel-by-pixel calibration across the entire spectrum, significantly improving calibration efficiency and significantly reducing calibration time compared to traditional methods. Simply set the parameters and start with a single click, eliminating complex operations and manual monitoring costs.

[0019] 2) High calibration accuracy: Compared with traditional spectral calibration methods, the present invention can not only monitor the wavelength of the calibration light source spectrum in real time but also monitor the power of the spectrum line in real time. It can correct the influence of the power stability of the spectral calibration light source on the spectral calibration accuracy, thereby improving the spectral calibration accuracy.

[0020] 3) Strong traceability: The present invention has the function of automatically correcting the wavelength, so that the results of spectrum calibration can be traced back to the wavelength meter. The wavelength meter is measured by the National Institute of Metrology and has the characteristics of high precision and automation.

[0021] 4) High system integration: The system integrates tunable laser, wavelength meter, power meter and data acquisition system into a unified measurement and control platform, which has good versatility and scalability.

[0022] In summary, the present invention demonstrates a simple structure. It integrates multiple devices through software, connecting links between them to achieve automated spectral calibration. Compared to traditional manual spectral calibration methods, this method significantly improves spectral calibration efficiency and enables rapid calibration of large-array grating spectrometers across the entire spectrum. Its spectral calibration accuracy is traceable to a wavelength meter. The present invention is highly versatile and can provide spectral calibration for a variety of other similar grating-type spectrometers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a schematic structural diagram of an automatic spectrum calibration device for a grating-type spectrometer according to the present invention.

[0024] Figure 2 This is a flow chart of the spectrum calibration method of the present invention.

[0025] Among them, the reference numerals are: tunable laser 1, power meter 2, wavelength meter 3, first beam splitter 4, second beam splitter 5, reflector 6, DC motor 7, rotating integrating sphere 8, grating spectrometer to be measured 9, and computer measurement and control system 10. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0027] The present invention utilizes a tunable laser as a light source for automated spectral calibration of grating spectrometers. The laser light output from the tunable laser source is split into three beams via two beam splitters. One beam enters a rotating integrating sphere, providing a Lambertian-like surface light source for calibration of the grating spectrometer under test. The other two beams enter a power meter and a wavelength meter, respectively, to monitor the laser's power and wavelength. The wavelength meter also provides feedback to the laser for frequency stabilization, stabilizing the laser output to the wavelength meter. A computer measurement and control system integrates the laser control software interface, the wavelength meter software interface, the power meter software interface, and the ground inspection software interface of the grating spectrometer under test, enabling automated acquisition of spectral calibration data for the grating spectrometer. The scanned calibration data is then fitted with a Gaussian (or super-Gaussian) fit to obtain the instrument linear shape (ILS), which in turn yields spectral calibration results such as center wavelength and spectral resolution. After full-pixel calibration, the dispersion function of the grating spectrometer under test is then fitted.

[0028] Specifically, if Figure 1As shown, the present invention discloses an automated spectral calibration device for a grating-type spectrometer, comprising a tunable laser 1, a power meter 2, a wavelength meter 3, a first beam splitter 4, a second beam splitter 5, a reflector 6, a DC motor 7, a rotating integrating sphere 8, and a computer measurement and control system 10. Each of these components is mounted on a vibration-isolating optical platform to ensure the overall stability of the system structure and a coaxial, flat optical path. The laser beam output by the tunable laser 1 first passes through the first beam splitter 4, which equally divides the laser beam into two paths. One path passes through the rotating integrating sphere 8 and is incident on the grating spectrometer 9 to be measured, serving as a surface light source for illumination. The other path continues to pass through the second beam splitter 5 and is equally divided into two paths, each leading to the probe of the power meter 2 and the reflector 6. The reflector 6 ultimately directs the beam into the wavelength meter 3. To eliminate laser speckle, the laser light output by the first beam splitter 4 that enters the rotating integrating sphere is ensured to strike the DC motor 7 with a diffuse reflector. The probe of the power meter 2 is an integrating sphere, facilitating spatial light input. In addition, the operating bands of the first beam splitter 4 and the second beam splitter 5 should match the laser output wavelength to ensure splitting efficiency and system stability. The computer measurement and control system 10 is used to uniformly control and integrate the software of the tunable laser 1, the power meter 2, the wavelength meter 3, and the grating spectrometer to be measured 9, thereby realizing automated control and data acquisition of the spectral calibration process. The computer measurement and control system 10 can communicate with the tunable laser 1 via a USB interface; communicate with the power meter 2 via a USB interface; communicate with the wavelength meter 3 via a USB interface or a network interface; and communicate with the grating spectrometer to be measured 9 via a network interface. Through the above-mentioned interface configuration, efficient coordination and synchronous control between the various devices are achieved, ensuring the continuity and accuracy of the automated calibration process.

[0029] like Figure 2 As shown, the present invention also provides a grating-type spectrometer driven automatic spectrum calibration method, and the user sets the calibration parameters according to specific needs, including:

[0030] Enter the automatic calibration mode: start the automatic calibration software in the computer measurement and control system, and the user sets the calibration parameters according to specific needs (i.e. Figure 2 spectral calibration configuration item settings), including: starting wavelength and ending wavelength (determine the spectral range of calibration); scanning step (recommended to be set to 1 / 10 to 1 / 20 of the spectral resolution of the grating spectrometer 9 to be measured); acquisition frame number (the number of image frames acquired at each wavelength point); wavelength accuracy criterion (such as setting the deviation between the actual laser wavelength and the target wavelength to be less than or equal to 1 / 2 of the step length); wavelength stability criterion (such as the wavelength standard deviation or range within 10 seconds is less than or equal to 1 / 2 to 1 / 3 of the step length); data storage path, etc.

[0031] Wavelength scanning and stability control: The tunable laser is controlled to start scanning according to the set starting wavelength, and the wavelength meter monitors the output wavelength in real time. If the wavelength meets the set accuracy and stability criteria, data collection is performed; if the criteria are not met, the tunable laser is continuously fine-tuned until the conditions are met (i.e. Figure 2 The starting wavelength is determined), and the ground detection system of the grating spectrometer to be measured is entered (i.e. Figure 2 Ground detection control of the grating spectrometer under test).

[0032] Spectral data acquisition: After meeting the wavelength stability conditions, automatic synchronous acquisition: Grating type spectrometer ground detection system (i.e. Figure 2 The output data of the grating spectrometer to be tested, the real-time output data of the power meter, and the real-time output data of the wavelength meter.

[0033] Wavelength progression and looping (coarse and fine tuning): Determines whether the current wavelength has been acquired. If not, the process returns to the spectral data acquisition process. If so, the tunable laser performs wavelength adjustment (both coarse and fine) according to the set scan step size. First, coarse adjustment is performed, adjusting the tunable laser current to bring the wavelength close to the target value. After coarse adjustment is complete, the accuracy assessment phase begins. The accuracy criterion is that the deviation between the tunable laser's current actual wavelength and the target wavelength must be less than or equal to 1 / 2 of the set step size. If this accuracy requirement is met, the process proceeds to wavelength stability assessment. If not, the piezoelectric ceramic (PZT) fine-tuning mechanism is activated to fine-tune the laser wavelength until the aforementioned accuracy criteria are met. The wavelength stability criterion is that the standard deviation or range of the wavelength values ​​measured by the wavelength meter must be less than or equal to 1 / 3 of the step size for 10 consecutive seconds. If the stability requirement is met, the next step of spectrum calibration data acquisition is performed (including the synchronous acquisition of the grating spectrometer ground detection system, power meter, wavelength meter, etc.); if the stability requirement is not met, the PZT is used to fine-tune the tunable laser wavelength until the stability condition is met.

[0034] Determine whether the current wavelength reaches the end wavelength. If not, the laser advances at the set step size and repeats the wavelength adjustment and data acquisition process. If the end wavelength is reached, the automatic calibration process ends.

[0035] This invention utilizes a high-precision wavelength meter and power meter to form a closed-loop control system, enabling real-time monitoring and stabilization of the laser's output wavelength and power, ensuring the accuracy and traceability of spectral calibration. The resulting calibration data can be fitted with a Gaussian or super-Gaussian function to obtain the instrument line shape function (ILS) of the grating spectrometer under test. This can then be used to determine the central wavelength, spectral resolution, and pixel dispersion function, enabling high-precision automatic spectral calibration of all pixels.

[0036] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An automated spectrum calibration device for a grating-type spectrometer, characterized in that: The system comprises a tunable laser, a power meter, a wavelength meter, a first beam splitter, a second beam splitter, a DC motor, a rotating integrating sphere and a computer measurement and control system; the tunable laser, the power meter and the wavelength meter are arranged on one side of the rotating integrating sphere, and the grating spectrometer to be measured is arranged on one side of the light outlet of the rotating integrating sphere; the laser output by the tunable laser is divided into three beams of light through the first beam splitter and the second beam splitter in sequence, the main beam of light is irradiated to the grating spectrometer to be measured through the rotating integrating sphere, and the other two beams of light enter the power meter and the wavelength meter respectively; after the main beam enters the light outlet of the rotating integrating sphere, the DC motor drives the diffuse reflection plate to rotate, forming multiple diffuse reflections, forming a surface light source at the light outlet of the rotating integrating sphere, and irradiating the grating spectrometer to be measured; the computer measurement and control system is used for automatic control and data acquisition of the spectrum calibration process.

2. The automatic spectrum calibration device for a grating type spectrometer according to claim 1, characterized in that: The computer measurement and control system integrates a tunable laser, a power meter, a wavelength meter and a control interface of the grating spectrometer to be measured to achieve unified drive and control.

3. The automatic spectrum calibration device for a grating type spectrometer according to claim 1, characterized in that: The output wavelength of the tunable laser covers the working spectrum response range of the grating spectrometer to be measured.

4. The automatic spectrum calibration device for a grating type spectrometer according to claim 1, characterized in that: The first beam splitter is used to preliminarily split the laser into two paths, one of which is further split by the second beam splitter and guided into the rotating integrating sphere and the power meter respectively.

5. The automatic spectrum calibration device for a grating type spectrometer according to claim 1, characterized in that: The power meter is provided with an integrator-type probe, and the detection wavelength range covers the working wavelength of the grating spectrometer to be measured; the light beams split by the first beam splitter and the second beam splitter are free-space beams, which directly enter the power meter for power detection.

6. The automatic spectrum calibration device for a grating type spectrometer according to claim 4, characterized in that: It also includes a reflector, and the light beam split by the second beam splitter is reflected by the reflector and then guided to the wavelength meter; the wavelength meter is coupled into the optical fiber through the collimator or directly receives the spatial light beam.

7. The automatic spectrum calibration device for a grating type spectrometer according to claim 1, characterized in that: The rotating integrating sphere has at least three openings, namely, a light outlet, a light inlet, and a diffuse reflection plate mounting hole; the diameter of the light outlet is larger than the entrance pupil diameter of the grating spectrometer to be measured, and the opening ratio of the rotating integrating sphere is not greater than 1 / 3; the opening size of the light inlet is determined by the divergence angle of the tunable laser, meeting the requirement of complete laser incidence; the diffuse reflection plate mounting hole corresponds to the position of the laser incident point, and is provided with a diffuse reflection plate driven to rotate by a DC motor.

8. The automatic spectrum calibration device for a grating type spectrometer according to claim 1, characterized in that: The material of the diffuse reflection plate is the same as that of the inner wall of the rotating integrating sphere, both being polytetrafluoroethylene; the DC motor drives the diffuse reflection plate to rotate 360 ​​degrees.

9. An automated spectrum calibration method for a grating spectrometer, characterized in that: The following steps are involved: Step 1: Place a narrow-linewidth tunable laser, a rotating integrating sphere, a power meter, a wavelength meter, a beam splitter, and a reflector on a vibration-isolating optical platform. Adjust the laser output from the tunable laser to enter the light entrance of the rotating integrating sphere. At the same time, adjust the optical path so that the laser enters the rotating integrating sphere and reaches the diffuse reflection plate driven by the DC motor. Align the light entrance of the rotating integrating sphere with the optical entrance pupil of the grating spectrometer to be measured, ensuring that the optical entrance pupil of the grating spectrometer to be measured coincides with the center of the optical axis of the light entrance of the rotating integrating sphere. Split the laser output from the tunable laser into two beams through the first beam splitter. One beam enters the rotating integrating sphere, and the other beam is split into two beams through the second beam splitter. One beam enters the power meter, and the other beam enters the wavelength meter through the reflector. Step 2: Connect the tunable laser, wavelength meter, and power meter to the computer measurement and control system and control them. Control the wavelength output of the tunable laser according to the settings and monitor its power and wavelength in real time. The wavelength meter is used to provide feedback and calibrate the output wavelength of the tunable laser. Connect the ground detection system of the grating spectrometer to be measured to the computer measurement and control system. After the tunable laser stabilizes, automatically record and store the spectral response data of the grating spectrometer to be measured. Step 3: Set the starting wavelength, ending wavelength, wavelength scanning interval, wavelength stability and accuracy criteria, and the number of frames for grating spectrometer data storage on the computer measurement and control system.

10. The automated spectrum calibration method according to claim 9, characterized in that: The step 3 includes: simultaneously storing output data of the wavelength meter, the power meter and the ground detection system of the grating spectrometer to be measured.

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