CN115773816A - Tunable traceable spectrum calibration device - Google Patents
Tunable traceable spectrum calibration device Download PDFInfo
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- CN115773816A CN115773816A CN202211520058.XA CN202211520058A CN115773816A CN 115773816 A CN115773816 A CN 115773816A CN 202211520058 A CN202211520058 A CN 202211520058A CN 115773816 A CN115773816 A CN 115773816A
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Abstract
The invention discloses a tunable traceable spectrum calibration device which comprises a tunable laser, a light frequency comb frequency stabilization module, a power monitoring module, an integrating sphere, a direct current motor, a computer and a spectrometer to be calibrated. The tunable laser provides a continuous light source for spectrum calibration; the optical frequency comb frequency stabilizing module locks the output optical frequency of the tunable laser to the optical frequency comb frequency; the power monitoring module is used for monitoring the output light power of the tunable laser in real time; the integrating sphere and the direct current motor are used for eliminating the speckle effect of the laser when the spectrum is calibrated; the computer is used for recording spectrum calibration data and processing an algorithm; the spectrometer to be calibrated is used for providing a measured object. The spectrum calibration device is suitable for fine spectrum calibration measurement application with high precision, high spectral resolution and traceability, and has the advantages that the light frequency comb frequency locking module is utilized to trace the light source frequency of spectrum calibration to the atomic time scale reference, and the high precision and traceability realization of the spectrum calibration are ensured from the source.
Description
The technical field is as follows:
the invention relates to a high-precision fine spectrum measurement technology, a continuous spectrum measurement technology in a certain spectrum range, a traceable spectrum measurement technology and the like, in particular to a high-precision tunable traceable spectrum calibration device which can be widely applied to the field of spectrum measurement of a spectrum instrument with high spectral resolution, high precision and need of tracing.
Background art:
with the development of aerospace technology, the spectral resolution, signal-to-noise ratio and the like of a detected load are higher and higher, and in order to realize high-quantification remote sensing, high-precision spectral calibration needs to be carried out on the load. At present, a laboratory spectrum calibration device cannot meet the requirement of hyperfine spectrum calibration. For example, the requirements of atmospheric fine component detection and climate detection pre-research, the wavelength calibration precision of a gas monitor with sub-nanometer spectral resolution is better than 10pm, the ILS (Instrument Line Shape) calibration precision is better than 1%, and the realization of the spectral calibration precision index provides new requirements for the precision, accuracy and stability of a laboratory spectral calibration system. The current laboratory spectrum calibration methods include a characteristic spectrum line method, a monochromatic collimation method, a gas absorption cell method, a tunable laser method and the like. When the characteristic spectrum method is used for spectral calibration, the wavelength is influenced by the characteristics of characteristic substances, the characteristic wavelength is limited, and the full-spectrum spectral calibration cannot be realized; the monochromatic collimation method can have a plurality of spectral lines, but the emergent light is uneven, the tuning resolution is low, and the high-precision requirement is not met. The gas absorption cell method can achieve high precision theoretically, but has high environmental requirements and many error sources, and is complex in comparison with a database. The tunable laser method can realize spectrum calibration with high spectral resolution, but the frequency stability of the light source is easily affected by the environment and cannot be traced. In recent years, with the development of optical frequency comb technology, optical frequency combs have attracted much attention in the field of precision measurement. At present, no similar technology to the present invention has been found in publicly investigated literature.
The invention content is as follows:
the invention mainly aims to overcome the defects of the technology, solve the problems of low light source frequency stability and incapability of tracing spectrum calibration in fine spectrum test of a hyperspectral instrument, and provide a high-precision tunable traceable spectrum calibration device by using a light frequency comb frequency stabilization module as a bridge.
In order to realize the task, the invention adopts the following technical scheme:
the spectrum calibration device comprises an optical frequency comb tooth frequency 1, an optical frequency comb frequency stabilization module 2, a power monitoring module 3, a rotary integrating sphere 4, a direct current motor 5, an instrument to be calibrated 6 and a computer 7. The method is characterized in that:
the optical frequency comb frequency stabilization module 2 comprises a pump amplifying device 8, a 1 × 3 polarization-maintaining fiber coupler 9, a frequency doubling crystal 10, a beat frequency device 11, an optical frequency comb 12, an optical filtering device 13, a photoelectric detector 14, an amplifying and filtering device 15, a reference signal source 16 (rubidium clock, hydrogen clock and the like), a frequency synthesizer 17, a fast phase-locked loop frequency locking circuit 18 and a wavelength meter 19. The optical frequency comb frequency stabilization module 2 is specifically shown in fig. 2.
In fig. 2, in order to solve the problem that the wavelength range of the optical frequency comb 12 cannot be covered in the 2.1-2.5 μm waveband, the pump source amplifying device 8 and the frequency doubling crystal 10 use an amplifying and frequency doubling method to double the frequency of the light output by the tunable laser 1 to the coverage range of the optical frequency comb 12. Laser output by the semiconductor laser enters a 1x3 polarization-maintaining optical fiber coupler 9 after passing through an optical isolator ISO and an optical fiber collimator C, the laser is divided into 3 paths through the 1x3 polarization-maintaining optical fiber coupler 9, and the 1 st path is directly output for spectrum calibration; the 2 nd path enters a wavelength meter 19 for measuring the wavelength of the output laser; the 3 rd path of the frequency doubling device enters a beat frequency device 11 after frequency doubling by a frequency doubling crystal 10.
In order to improve the signal-to-noise ratio of the beat frequency signals of the laser and the optical frequency comb, a light combining beat frequency device 11 consisting of a half-wave plate HWP, a polarization light splitting cube PBS and a polarizing plate P is adopted, and the direction of the half-wave plate is rotated to change the output optical power of the tunable laser 1 and the optical frequency comb 12 for beat frequency. The light output by the tunable laser 1 and the optical frequency comb 11 is combined and enters the optical filtering device 13, the device can adopt a grating or a Glan Taylor prism, the comb teeth of the optical frequency comb adjacent to the frequency of the grating or the Glan Taylor prism are incident to the photoelectric detector 14, the photoelectric detector 14 can adopt an avalanche photodiode, and thus the obtained beat frequency signal has the signal-to-noise ratio of about 30dB. After being processed by the amplifying and filtering device 15, beat frequency signals of the laser and the optical frequency comb are phase-discriminated with reference signals output by the frequency synthesizer 17 to form error signals, and the error signals are fed back to a driving control port of the laser to control current I and piezoelectric ceramic PZT after passing through the proportional-integral controller 18, so that output light and the optical frequency comb of the tunable laser (1) are realized(12) The frequency of the output light is locked. The optical-frequency comb 12 and the frequency synthesizer 17 are both connected to the same frequency reference source 16. The frequency reference source 16 may be a rubidium clock or a hydrogen clock, and thus the stability of the frequency of the locked optical frequency comb is substantially the same as the stability of the rubidium clock, i.e., 10 -12 And the magnitude ensures the high-frequency stability of the light source for spectrum calibration.
The average power of the output laser of the optical frequency comb 11 is greater than 30mW, the repetition frequency is greater than 100MHz, and the output spectrum range covers the wavelength range of the output light of the tunable laser 1 after frequency doubling. If the output spectrum of the optical frequency comb 12 cannot completely cover the output range of the tunable laser 1, the output light of the tunable laser 1 can be processed in an amplification-frequency doubling manner. The output wavelength of the tunable laser, such as 2.3 μm, is first frequency-doubled to 1.15 μm by using the pump amplification device 8 and the frequency doubling crystal 10, and the problem that the range of the optical frequency comb 12 cannot be covered is solved by adopting the mode. The output pulse width of optical frequency comb 12 is typically on the order of femtoseconds.
In order to tune the frequency of the laser, the laser frequency is tuned by "on-tuning-locking" the laser frequency to different optical frequency comb teeth, where the integer number of comb teeth can be measured with a high precision wavemeter 19. The wavelength measurement accuracy of the wavelength meter 19 should generally be less than 1/2 of the repetition frequency of the optical frequency comb, and may be 1/3 of the remaining margin. If the repetition frequency of the optical frequency comb is 150MHz, the precision of the wavelength meter can be selected to be 50MHz.
The output power of the tunable laser 1 used for spectral calibration should be generally greater than 30mW, and if the power is low, the light source should be amplified to a power of more than 30mW by the pump amplifier 8. The output light of the optical fiber is divided into 3 paths, and the 1 st path is directly output for spectrum calibration; the 2 nd path of the laser enters a wavelength meter (19) and is used for measuring the wavelength of the output laser; the 3 rd path enters a beat frequency device (11) after frequency multiplication by a frequency multiplication crystal (10).
And the rotating integrating sphere 4 is used for eliminating the speckle effect of the laser output by the tunable laser 1 after frequency stabilization. The general method is that a part of an integrating sphere 4 is provided with a hole, a direct current motor 5 is arranged, the direct current motor 5 loads an inner diffuse reflection surface with the size of the integrating sphere hole, when laser is incident, the direct current motor 5 is opened, and the direct current motor is adjusted to a reasonable rotating speed so as to eliminate laser speckles.
The power monitoring module 3 adopts a power meter and is used for monitoring the output light power of the tunable laser in real time.
The spectrometer 6 to be calibrated is generally a high spectral resolution spectrometer and is the object to be measured.
The computer 7 is used for data acquisition, control and processing, and the acquired calibration data is generally obtained by a Gaussian fitting method or a Lorentzian fitting method.
It should be noted that the whole device is operated on an optical vibration isolation platform in a laboratory.
The tracing chain of the present invention is implemented as shown in FIG. 3 below.
The invention has the advantages that:
1) In the existing spectrum calibration technology, traceability is not realized in the calibration process of the technology such as a characteristic spectrum line method, a monochromatic collimation method, a gas absorption cell method, a tunable laser method and the like.
2) The limitation that the current optical frequency comb is 2.1 mu m in wavelength is broken through, the frequency of a continuous laser source (such as 2.3 mu m) is doubled to the coverage range of the optical comb by using an amplification-frequency doubling method, and the traceable calibration in the field of short-wave infrared spectrum calibration at home and abroad at present is realized.
3) The frequency stabilization of the tunable continuous laser source is realized, and the literature in research at present does not describe how to realize the frequency stabilization of the tunable continuous laser source to the optical frequency comb.
Description of the drawings:
fig. 1 is a schematic diagram of a system device, which is a structural diagram of a high-precision tunable traceable spectrum calibration device.
Fig. 2 is a schematic diagram of an optical frequency comb frequency stabilization module.
FIG. 3 is a diagram of the spectral calibration traceable to the national institute of standards and technology NIST.
Detailed Description
The features of the present invention and other related features are described in further detail below by way of example in conjunction with the accompanying drawings to facilitate an understanding of those skilled in the art. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention.
Fig. 1 is a block diagram of a high precision tunable traceable spectral scaling device according to an example of the invention. Which comprises the following steps: tunable laser 1, optical frequency comb frequency stabilization module 2, power monitoring module 3, rotatory integrating sphere 4, direct current motor 5, spectrometer 6 to be calibrated, computer 7:
the specific structure diagram of the optical frequency comb frequency locking module 2 is shown in fig. 2, where I represents an output current of a tunable laser, PZT represents piezoelectric ceramic, ISO represents an optical isolator, C represents an optical fiber collimator, HWP represents a half-wave plate, PBS represents a polarization splitting cube, P represents a polarization a/D represents an analog-to-digital converter, and the photodetector 13 may be an avalanche photodiode detector. In fig. 2, a solid black line represents a light propagation route, and a dashed black line represents an electric signal transmission route.
As shown in fig. 2, the tunable laser 1 may be a semiconductor external cavity tunable laser with an output wavelength of 2250-2450nm. Because the existing optical frequency comb 12 does not cover 2200-2400nm, the output light is amplified-frequency doubled to the coverage range of the optical comb, then the output laser is divided into 3 paths through a 1 × 3 polarization-maintaining optical fiber coupler 8, wherein one path is used for beat frequency, a specific beat frequency optical path is a light-combining beat frequency device 11 composed of an optical fiber collimator, a half-wave plate, a polarization cube and a polarizing plate, one end of the light-combining beat frequency device inputs the output laser of the tunable laser 1, the other end of the light-combining frequency device inputs the output light of the optical frequency comb 12, optical filtering is performed after beat frequency, the optical filtering device 13 is generally a Glan Taylor prism, a beat frequency signal is obtained after optical filtering, the beat frequency signal enters a photoelectric detector 13 for signal processing such as electronic amplification and filtering, and the like, and is compared with a reference frequency reference source 16 providing reference, such as a rubidium clock, an error signal is obtained, and then the current I of the tunable laser and the piezoelectric ceramic are controlled through a proportional integral controller 18, wherein the current I is coarse adjustment, and the piezoelectric ceramic is fine adjustment. Finally, the output laser frequency of the tunable laser 1 is locked to the frequency of the output laser of the optical frequency comb 12. Due to the optical frequency comb (12) and the frequency synthesizer (17)) Both connected to the frequency of the same frequency reference source (16), rubidium clock, the tunable laser 1 is locked to one comb of the optical frequency comb 12, so that the output frequency of the tunable laser 1 is locked to the output frequency of the reference signal source 16, rubidium clock, up to 10 -12 Magnitude. And further, the stability and traceability of the calibration source are ensured during spectrum calibration. It should be noted here that when locking the next wavelength after locking one wavelength point, it is necessary to lose the lock for about 10 seconds, then tune the tunable laser 1 to the next wavelength, and then lock to a different comb 12 of the optical frequency comb.
As shown in fig. 1, output light of the tunable laser after frequency multiplication is output by using space light or optical fiber, wherein one path of output light is directly coupled into an integrating sphere, the integrating sphere adopts a rotating integrating sphere 4, and a diffuse reflection surface on which laser is incident is driven to rotate by a direct current motor 5, so that the influence of laser speckles on a calibration system is eliminated. And (3) the light output by the rotating integrating sphere 4 enters an entrance pupil of a spectrometer 6 to be calibrated, and the response of each pixel point on a focal plane to different wavelengths is obtained by tuning the step length of the laser output by the tunable laser 1, so as to finally obtain the instrument linear function of the point. And the power monitoring module 3 adopts a power meter and is used for monitoring the optical power of the output light of the tunable laser in real time. The computer 7 in fig. 1 is used for the control, data recording and processing operations of the entire apparatus. And processing the calibration data by a Gaussian fitting algorithm to obtain a linear function of the to-be-calibrated instrument 6, and further obtaining the spectral resolution and the central wavelength of the to-be-calibrated spectrometer 6.
As shown in fig. 3, a link is implemented for light source traceability of a tunable traceable spectral scaling apparatus. The uncertainty of the spectral calibration comprises frequency deviation of rubidium clock signal output, the repetition frequency of a femtosecond optical comb, the uncertainty of carrier envelope offset frequency, the uncertainty of a laser light source, the uncertainty of data fitting and the like. And then, evaluating according to an evaluation method of uncertainty, and finally realizing the traceability of spectral calibration. FIG. 3 shows a schematic diagram of a spectral calibration apparatus 20 that is sourced to the National Institute of Standards and Technology (NIST) 22. The light source of the spectrum calibration device 20 is the tunable laser 1, the tunable laser 1 outputs the optical frequency to trace to the comb tooth frequency of the optical frequency comb 12, the output frequency of the optical frequency comb 12 is locked to the output frequency of the reference signal source 16, here, the rubidium clock frequency can be traced to the atomic time scale reference 21, the atomic time scale reference 21 can be traced to the National Institute of Standards and Technology (NIST) 22, and the traceability of the spectrum calibration device is ensured from the source.
Claims (10)
1. The utility model provides a tunable spectrum calibration device of traceable source, includes tunable laser (1), optical frequency comb frequency stabilization module (2), power monitoring module (3), rotatory integrating sphere (4), direct current motor (5), treats calibration spectrum appearance (6), computer (7), its characterized in that:
the spectrum calibration device takes a rotary integrating sphere (4) as a center, the left side of the spectrum calibration device is sequentially provided with a tunable laser (1) and an optical frequency comb frequency stabilization module (2), the right side of the spectrum calibration device is provided with a spectrometer (6) to be calibrated, the power monitoring module (3) is arranged above the spectrum calibration device, the computer (7) is arranged below the spectrum calibration device, and the direct current motor (5) is arranged on the rotary integrating sphere. The whole device is arranged on an optical platform with a vibration isolation function; light output by the tunable laser (1) passes through the optical frequency comb frequency stabilization module (2) and then partially enters the rotary integrating sphere (4) with the direct current motor (5) through the optical fiber beam splitter, the output light is used for spectral calibration of the spectrometer (6) to be calibrated, and the other part of the output light enters the power monitoring module (3) for power monitoring.
The optical frequency comb frequency stabilization module (2) is used for locking the output optical frequency of the tunable laser (1) to comb teeth of the optical frequency comb;
the computer (7) controls a controller of the tunable laser (1), rotates the rotating speed of a direct current motor (5) on the integrating sphere (4), records output response data of the spectrometer (6) to be calibrated, processes the calibration data by a Gaussian fitting algorithm to obtain a linear function of the spectrometer (6) to be calibrated, and further obtains the spectral resolution and the central wavelength of the spectrometer (6) to be calibrated;
the spectrum calibration device is used for tracing the source by locking the laser frequency output by the calibration source to the comb tooth frequency of the optical frequency comb, and the comb tooth frequency of the optical frequency comb can be traced to American national standards and technical research institute, so that the spectrum calibration result can be traced.
2. The tunable traceable spectral scaling apparatus of claim 1, wherein: the optical frequency comb frequency stabilization module (2) comprises a pumping amplification device (8), a 1x3 polarization-maintaining optical fiber coupler (9), a frequency doubling crystal (10), a beat frequency device (11), an optical frequency comb (12), an optical filtering device (13), a photoelectric detector (14), an amplifying filtering device (15), a reference signal source (16), a frequency synthesizer (17), a proportional-integral controller (18) and a wavelength meter (19); laser output by the adjustable laser (1) is amplified by a pumping amplification device (8) and then is divided into 3 paths by a 1x3 polarization-maintaining optical fiber coupler (9), and the 1 st path is directly output for spectrum calibration; the 2 nd path of the laser enters a wavelength meter (19) and is used for measuring the wavelength of the output laser; the 3 rd path of the frequency doubling device enters a beat frequency device (11) after being frequency doubled by a frequency doubling crystal (10); laser output by the tunable laser (1) and laser output by the optical frequency comb (12) enter the beat frequency device (11) for light combination, then enter the optical filter device (13) and enter the photoelectric detector (14) to obtain a beat frequency signal; after being processed by the amplifying and filtering device (15), the beat frequency signal is phase-discriminated from a reference signal output by the frequency synthesizer (17) to form an error signal, and the error signal is fed back to a drive control port of the laser to control current and piezoelectric ceramics through the proportional-integral controller (18), so that the frequency locking of the output light of the tunable laser (1) and the output light of the comb teeth of the optical frequency comb (12) is realized; the optical frequency comb (12) and the frequency synthesizer (17) are both connected to the same frequency reference source (16); the frequency of the tunable laser (1) is locked to different comb frequencies of the optical frequency comb (12) by using an 'opening-tuning-locking' mode, so that the output optical frequency of the tunable laser (1) can be tuned.
3. The tunable traceable spectral scaling apparatus of claim 2, wherein: the tunable laser (1) is a semiconductor laser or an all-solid-state laser, the output laser power is generally more than 30mW, and the wavelength range can cover 1-2.5 μm.
4. The tunable traceable spectral scaling apparatus of claim 2, wherein: the beat frequency device (11) is composed of a half-wave plate, a polarization beam splitting cube and a polarizing plate.
5. The tunable traceable spectral scaling apparatus of claim 2, wherein: the optical frequency comb (12) is a femtosecond optical fiber oscillator, and the wavelength range can not completely cover the wavelength output range of the tunable laser.
6. The tunable traceable spectral scaling apparatus of claim 2, wherein: the optical filtering device (13) adopts a Glan Taylor prism or a grating.
7. The tunable traceable spectral scaling apparatus of claim 2, wherein: the photodetector (14) is an avalanche photodiode.
8. A tunable traceable spectral scaling apparatus according to claim 2, wherein: the reference signal source (16) is a rubidium clock or a hydrogen clock.
9. The tunable traceable spectral scaling apparatus of claim 2, wherein: the precision of the wavelength meter (19) is 1/3 of the repetition frequency of the optical frequency comb (12).
10. A tunable traceable spectral scaling apparatus according to claim 1, wherein: the rotating integrating sphere (4) is provided with a direct current motor (5) which can rotate 360 degrees.
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| CN202211520058.XA CN115773816A (en) | 2022-11-30 | 2022-11-30 | Tunable traceable spectrum calibration device |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117629426A (en) * | 2024-01-25 | 2024-03-01 | 中国计量科学研究院 | Optical wavelength measurement method and system capable of tracing to high-accuracy time-frequency reference |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117629426A (en) * | 2024-01-25 | 2024-03-01 | 中国计量科学研究院 | Optical wavelength measurement method and system capable of tracing to high-accuracy time-frequency reference |
| CN117629426B (en) * | 2024-01-25 | 2024-04-05 | 中国计量科学研究院 | Optical wavelength measurement method and system capable of tracing to high-accuracy time-frequency reference |
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