System and method for frequency stabilization of a wide spectrum multi-wavelength laser with atomic transition reference

Abstract

The application discloses a wide-spectrum multi-wavelength laser frequency stabilization system of an atomic transition reference, and a wide-spectrum multi-wavelength laser frequency stabilization method of an atomic transition reference, wherein the spectrum peak of an atomic hyperfine structure obtained by saturated absorption spectrum is used to realize the frequency stabilization of laser, and the frequency multiplication and frequency mixing of laser are used to realize the calibration of the long-term stability of the wavelength meter to multiple laser wavelengths without affecting the wavelength accuracy of the calibration laser. In addition, the calibrated wavelength meter is used to accurately measure multiple laser wavelengths, and the hierarchical feedback adjustment mechanism of coarse adjustment and fine adjustment is used to realize the accurate locking of multiple laser wavelengths. The application overcomes the wavelength measurement drift of the wavelength meter caused by environmental changes, improves the measurement accuracy of the wavelength meter, guarantees the long-term stable and accurate operation of the wavelength meter, and guarantees the high-precision frequency stabilization of multiple laser wavelengths.

Description

Technical Field

[0001] This invention relates to the field of atomic absorption spectroscopy, specifically to a broadband multi-wavelength laser frequency stabilization system based on atomic transitions, and also to a broadband multi-wavelength laser frequency stabilization method based on atomic transitions. This method uses internationally recognized atomic transition spectral lines as a reference to achieve high-precision wavelength meter calibration, thereby using the calibrated wavelength meter to achieve long-term stable locking of multiple laser wavelengths. Background Technology

[0002] In fields with high requirements for laser emission wavelength, such as Doppler lidar, resonant fluorescence lidar, and laser communication, changes in the wavelength of the probe light can significantly impact the accuracy of the results. Wavelength meters are commonly used as reference devices for wavelength measurement. However, during long-term operation, the measurement results of wavelength meters drift due to changes in environmental factors (temperature, humidity, vibration, etc.), leading to inaccuracies and greatly affecting the quality of data obtained by related equipment. Traditional wavelength meter calibration typically uses mercury lamps, neon lamps, and xenon lamps. Because the atoms in these light sources exhibit natural broadening, collisional broadening, and Doppler broadening during spectral emission, the obtained spectral lines are relatively wide, making it difficult to accurately locate the center wavelength of the spectral lines, resulting in errors in the wavelength meter calibration results. Therefore, a long-term, stable, and high-precision calibration method and device for wavelength meters with a wide spectral range is needed to enable the measurement of different laser output wavelengths and laser frequency stabilization.

[0003] The accuracy of saturated absorption spectroscopy is unmatched by wide-range mercury lamps or other calibration light sources. To improve the measurement accuracy of wavelength meters, this invention proposes an automatic calibration method for wavelength meters based on atomic saturated absorption spectroscopy. The main method is to use a saturated absorption spectral line derived from a reference to achieve ultra-high precision calibration of a wide range of wavelengths of the wavelength meter. In addition, the calibrated wavelength meter enables high-precision measurement and frequency stabilization of multiple laser emission wavelengths. Summary of the Invention

[0004] The purpose of this invention is to address the current state of existing technologies by providing a high-precision intelligent frequency stabilization system for wide-spectrum multi-laser wavelengths based on atomic transition benchmark calibration, and a high-precision intelligent frequency stabilization method for wide-spectrum multi-laser wavelengths based on atomic transition benchmark calibration.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A broadband multi-wavelength laser frequency stabilization system for atomic transition references includes a first wavelength tunable laser. The λ-wavelength output light generated by the first wavelength tunable laser is divided into three beams: a first λ-wavelength output light beam, a second λ-wavelength output light beam, and a third λ-wavelength output light beam.

[0007] The first λ-wavelength outgoing light is incident on the λ-wavelength reference light incident channel of the multi-in-one optical switch.

[0008] The third λ-wavelength output light is frequency-doubled by the second frequency doubler crystal to obtain a λ / 2 wavelength laser. This laser then passes through a saturable absorption device to obtain a frequency-stabilized λ / 2 wavelength laser. The frequency-stabilized λ / 2 wavelength laser is divided into three parts.

[0009] The first part of the frequency-stabilized λ / 2 wavelength laser is frequency-doubled by the first frequency doubler crystal to obtain λ / 4 wavelength laser, which is then input into the λ / 4 wavelength reference light incident channel of the all-in-one optical switch.

[0010] The second part involves the frequency-stabilized λ / 2 wavelength laser being incident on the λ / 2 wavelength reference light incident channel of the all-in-one optical switch.

[0011] The third part, after frequency stabilization, the λ / 2 wavelength laser and the second λ wavelength output light are combined and passed through a summing crystal to obtain the λ / 3 wavelength laser. The λ / 3 wavelength laser is input into the λ / 3 wavelength reference light incident channel of the multi-in-one optical switch.

[0012] The laser output from the laser in the wavelength-tunable laser array is transmitted to the wavelength meter through a multi-function optical switch. The controller controls the output channel of the multi-function optical switch to output the light input from each incident channel to the wavelength meter in a time-division manner. The output signal of the wavelength meter is transmitted to the computer. The computer transmits the feedback control drive signal of the laser in the wavelength-tunable laser array to the controller. The controller then tunes the wavelength of the corresponding laser in the wavelength-tunable laser array.

[0013] As described above, the saturable absorption device includes an atomic bubble. A λ / 2 wavelength laser generated by frequency doubling by a second frequency doubler crystal is transmitted through a half-wave plate and then incident on a polarizing prism for beam splitting. The light transmitted through the polarizing prism serves as the pump light in the saturable absorption process and is incident on the atomic bubble. The light reflected by the polarizing prism is incident on an optical cutoff. After passing through the atomic bubble and a quarter-wave plate, the pump light is incident perpendicularly on a semi-transparent mirror. The λ / 2 wavelength laser reflected by the semi-transparent mirror passes through a quarter-wave plate again and is incident on the atomic bubble, where it overlaps with the pump light to become the probe light. The probe light is then reflected by the polarizing prism to a photodetector, which is connected to the control system of the first wavelength tunable laser.

[0014] The broadband multi-wavelength laser frequency stabilization method based on atomic transition references, utilizing the broadband multi-wavelength high-precision intelligent frequency stabilization system calibrated based on atomic transition references as described above, includes the following steps:

[0015] Step 1: Turn on the external thermostat to control the temperature of the atomic bulb, so that the atomic bulb operates at the set constant temperature;

[0016] Step 2: The first wavelength tunable laser is activated to obtain the output light of wavelength λ, the laser of wavelength λ / 2, the laser of wavelength λ / 3, the laser of wavelength λ / 4, as well as the pump light and the probe light in the saturable absorption device;

[0017] Step 3: The probe light is reflected by the polarizing prism to the photodetector;

[0018] Step 4: Using the saturated absorption spectrum obtained by the photodetector, find the spectral peak of the spectral line with a large signal-to-noise ratio, and determine the atomic emission spectrum wavelength corresponding to the spectral peak of the spectral line with a large signal-to-noise ratio.

[0019] Step 5: Lock the frequency-doubled λ / 2 wavelength output light from the first wavelength tunable laser at the laser wavelength corresponding to the peak of the saturation absorption spectrum.

[0020] Step 6: Calibrate the wavelength meter based on the locked λ wavelength output light, λ / 2 wavelength laser, λ / 3 wavelength laser, and λ / 4 wavelength laser of the first wavelength tunable laser;

[0021] Step 7: Set the frequency stabilization wavelength value of each laser in the wavelength tunable laser group. Stabilize the output laser of each laser in the wavelength tunable laser group by using the calibrated wavelength meter and the frequency stabilization wavelength value of each laser in the wavelength tunable laser group.

[0022] As described above, step 6 of calibrating the wavelength meter specifically includes the following steps:

[0023] Step 6.1: Determine the laser wavelength λ corresponding to the spectral peak of the saturated absorption spectrum based on the atomic absorption spectroscopy database;

[0024] Step 6.2: Based on the laser wavelengths corresponding to the spectral peaks of the saturated absorption spectrum, determine the actual wavelengths corresponding to the λ wavelength output light, λ / 2 wavelength laser, λ / 3 wavelength laser, and λ / 4 wavelength laser;

[0025] Step 6.3: Based on the measured wavelengths of the emitted light at wavelength λ, the laser at wavelength λ / 2, the laser at wavelength λ / 3, and the laser at wavelength λ / 4, and the actual wavelengths of the emitted light at wavelength λ, the laser at wavelength λ / 2, the laser at wavelength λ / 3, and the laser at wavelength λ / 4, perform partial least squares function fitting to obtain the fitting curve;

[0026] Step 6.4: Calculate the coefficient of determination R² of the fitted curve and the standard deviation RMSE (Δ0.1) of the difference between the actual wavelength and the fitted value corresponding to the partial least squares algorithm. 2 +Δ02 2 +Δ03 2 +Δ04 2) / 4, where the deviation Δ01 between the fitted value of the emitted light at wavelength λ and the actual wavelength of the emitted light at wavelength λ, the deviation Δ02 between the fitted value of the emitted light at wavelength λ / 2 and the actual wavelength of the emitted light at wavelength λ / 2, the deviation Δ03 between the fitted value of the emitted light at wavelength λ / 3 and the actual wavelength of the emitted light at wavelength λ / 3, and the deviation Δ04 between the fitted value of the emitted light at wavelength λ / 4 and the actual wavelength of the emitted light at wavelength λ / 4.

[0027] Step 6.5: If the obtained coefficient of determination R2 is greater than the standard value of the coefficient of determination N1, and the standard deviation RMSE of the difference between the actual wavelength and the wavelength fitting value corresponding to the partial least squares algorithm is less than the standard value of the calibration standard deviation N2, then the wavelengthmeter calibration is complete; otherwise, calculate the deviation Δ1 between the measured wavelength of the λ-wavelength emitted light and the actual wavelength of the λ-wavelength emitted light, the deviation Δ2 between the measured wavelength of the λ / 2-wavelength emitted light and the actual wavelength of the λ / 2-wavelength emitted light, the deviation Δ3 between the measured wavelength of the λ / 3-wavelength emitted light and the actual wavelength of the λ / 3-wavelength emitted light, and the deviation Δ4 between the measured wavelength of the λ / 4-wavelength emitted light and the actual wavelength of the λ / 4-wavelength emitted light, and select the actual wavelength corresponding to the maximum value among Δ1, Δ2, Δ3 and Δ4, calibrate the wavelengthmeter and return to step 6.3.

[0028] As described above, step 7 includes the following steps:

[0029] Step 7.1: Couple the emitted laser wavelength that needs to be frequency stabilized in the wavelength tunable laser array to the corresponding incident channel of the all-in-one optical switch;

[0030] Step 7.2: Set the frequency-stabilized wavelength values ​​of each laser in the wavelength-tunable laser group, and denot them as λ21, λ22, λ23 and λ24 respectively;

[0031] Step 7.3: Based on the calibrated wavelength meter, measure the corresponding wavelength value of the output laser of each laser in the wavelength tunable laser group that needs to be calibrated. The measured wavelength values ​​of each laser in the wavelength tunable laser group are recorded as λ11, λ12, λ13 and λ14 respectively.

[0032] Step 7.4: Calculate the deviations between the stable wavelength value and the measured wavelength value for each laser in the wavelength-tunable laser group: Δ11 = λ21 - λ11, Δ12 = λ22 - λ12, Δ13 = λ23 - λ13, Δ14 = λ24 - λ14, and the relative standard deviation between the measured wavelength value and the stable wavelength value: RMSE1 = (Δ11 - λ12) / (λ23 - λ14). 2 +Δ12 2 +Δ13 2 +Δ14 2 ) / 4;

[0033] Step 7.5: Determine whether the calculated RMSE1 value is less than the frequency stabilization coarse adjustment discrimination standard value M1. If the relative standard deviation RMSE1 between the measured wavelength value and the frequency stabilization wavelength value is less than the frequency stabilization coarse adjustment discrimination standard value M1, then, based on the values ​​of deviation Δ11, Δ12, Δ13, and Δ14, fine-tune the output wavelength of each laser in the wavelength tunable laser group through the controller, and then proceed to step 7.6; if the obtained relative standard deviation RMSE1 between the measured wavelength value and the frequency stabilization wavelength value is greater than the frequency stabilization coarse adjustment discrimination standard value M1, then, based on the values ​​of deviation Δ11, Δ12, Δ13, and Δ14, coarsely adjust the output wavelength of the laser through the controller, and return to step 7.3;

[0034] Step 7.6: Calculate the deviations between the stabilized wavelength values ​​and the measured wavelength values ​​of each laser in the fine-tuned wavelength tunable laser group: Δ21 = λ21 - λ11, Δ22 = λ22 - λ12, Δ23 = λ23 - λ13, Δ24 = λ24 - λ14, and the relative standard deviation between the measured wavelength values ​​and the stabilized wavelength values ​​after fine-tuning: RMSE2 = (Δ21 - λ11) / (λ22 - λ12) / (λ23 - λ13) / (λ24 - λ14). 2 +Δ22 2 +Δ23 2 +Δ24 2 ) / 4;

[0035] Step 7.7: If the calculated relative standard deviation RMSE2 between the fine-tuned measured wavelength value and the stable wavelength value is less than the standard value M2 for determining the completion of frequency stabilization, then the laser corresponding to the wavelength tunable laser group will end the frequency stabilization process. If the calculated relative standard deviation RMSE2 between the fine-tuned measured wavelength value and the stable wavelength value is greater than the standard value M2 for determining the completion of frequency stabilization, then return to step 7.3.

[0036] As mentioned above, the coarse frequency stabilization judgment criterion value M1 is greater than the frequency stabilization completion judgment criterion value M2.

[0037] As mentioned above, steps 7.3 to 7.7 are all completed automatically by the controller.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] This invention provides a long-term, high-precision automatic calibration method for wavelength meters, based on internationally recognized atomic transition spectral lines. The main method involves using the spectral peaks of atomic hyperfine structures obtained from saturated absorption spectroscopy to stabilize the laser frequency, and then using the stabilized laser wavelength and its multiple harmonic wavelengths to achieve long-term stable calibration of the wavelength meter. Furthermore, the calibrated wavelength meter enables simultaneous high-precision measurement and frequency stabilization of multiple laser emission wavelengths. This method significantly improves the calibration accuracy of the wavelength meter and enhances the accuracy of measurement results, which is of great significance for the long-term stable and accurate operation of wavelength meters and their applications in scientific research, industrial manufacturing, and precision measurement. Attached Figure Description

[0040] Figure 1 This is a schematic diagram illustrating the working principle of the present invention;

[0041] Figure 2 This is a flowchart of the wavelength meter calibration process of the present invention;

[0042] Figure 3 This is a flowchart of the frequency stabilization process of the present invention;

[0043] Among them, 1-wavelength meter, 2-controller, 3-multi-function optical switch, 4-first frequency doubler crystal, 5-first reflector, 6-semi-transparent and semi-reflective mirror, 7-quarter-wave plate, 8-bubble, 9-photodetector, 10-half-wave plate, 11-second frequency doubler crystal, 12-second reflector, 13-first beam splitter, 14-second beam splitter, 15-first wavelength tunable laser, 16-polarizing prism, 17-optical cutoff, 18-third beam splitter, 19-sum frequency crystal, 20-wavelength tunable laser array, 21-fourth beam splitter, 23-computer, 22-dichroic mirror. Detailed Implementation

[0044] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention will be further described in detail below with reference to examples. The implementation examples described herein are only for illustration and explanation and are not intended to limit the present invention.

[0045] Example 1:

[0046] This invention provides a broadband multi-wavelength laser frequency stabilization system based on atomic transitions. The design principle utilizes the spectral peaks of the atomic hyperfine structure obtained from saturated absorption spectroscopy to achieve laser frequency stabilization. Through laser frequency doubling and mixing, multiple laser wavelengths are calibrated stably for long-term use on a wavelengthmeter 1 without affecting the accuracy of the calibrated laser wavelengths. Furthermore, the calibrated wavelengthmeter 1 is used to accurately measure multiple laser wavelengths, and a graded feedback adjustment mechanism with coarse and fine adjustments is employed to achieve precise locking of multiple laser wavelengths.

[0047] In this embodiment, the broadband multi-wavelength high-precision intelligent frequency stabilization system based on atomic transition reference calibration mainly includes a wavelength meter 1, a controller 2, an all-in-one optical switch 3, a first frequency doubler crystal 4, a second frequency doubler crystal 11, a first reflector 5, a second reflector 12, a semi-transparent mirror 6, a quarter-wave plate 7, an atomic bubble 8, a photodetector 9, a half-wave plate 10, a first beam splitter 13, a second beam splitter 14, a third beam splitter 18, a polarizing prism 16, an optical cutoff 17, a sum-frequency crystal 19, a first wavelength tunable laser 15, a wavelength tunable laser group 20, a computer 23, a fourth beam splitter 21, and a dichroic mirror 22. The wavelength meter 1 used in this embodiment is a high-precision wavelength meter with a measurement range of 192nm-11um and an absolute accuracy of up to 30MHz. The atomic bubble 8 is a sodium atomic bubble.

[0048] The laser generated by the first wavelength tunable laser 15 produces a saturated absorption spectrum in the atomic bubble 8. Then, by identifying the peaks of the saturated absorption spectrum and employing a feedback adjustment mechanism, the output laser wavelength of the first wavelength tunable laser 15 is locked at the peak of the atomic saturated absorption spectrum, thereby achieving frequency stabilization of the output laser of the first wavelength tunable laser 15. Next, the wavelength meter 1 is calibrated using the frequency-stabilized laser and multiple frequency-doubled laser wavelengths generated based on the frequency-stabilized laser. Furthermore, the calibrated wavelength meter 1 is used to achieve long-term stable locking of multiple laser wavelengths in the wavelength tunable laser group 20.

[0049] The specific structure of the broadband multi-laser wavelength high-precision intelligent frequency stabilization system based on atomic transition benchmark calibration in this embodiment is as follows:

[0050] The λ-wavelength emitted light generated by the first wavelength tunable laser 15 is divided into three beams: the first λ-wavelength emitted light, the second λ-wavelength emitted light, and the third λ-wavelength emitted light. In this embodiment, the second beam splitter 14 and the first beam splitter 13 are used to split the λ-wavelength emitted light generated by the first wavelength tunable laser 15.

[0051] First, the λ-wavelength outgoing light generated by the first wavelength tunable laser 15 is incident on the second beam splitter 14. The λ-wavelength outgoing light reflected by the second beam splitter 14 is the first λ-wavelength outgoing light and is incident on the λ-wavelength reference light incident channel on the multi-in-one optical switch 3.

[0052] The λ-wavelength outgoing light transmitted by the second beam splitter 14 is incident on the first beam splitter 13 for beam splitting. The λ-wavelength laser reflected by the first beam splitter 13 becomes the second λ-wavelength outgoing light, and the second λ-wavelength outgoing light is transmitted through the dichroic mirror 22.

[0053] The λ-wavelength laser transmitted through the first beam splitter 13 becomes the third λ-wavelength output light. This third λ-wavelength output light is reflected by the second mirror 12 to the second frequency doubler crystal 11 for frequency doubling. The λ / 2-wavelength laser generated by the frequency doubling is then passed through a saturable absorption device to obtain a frequency-stabilized λ / 2-wavelength laser.

[0054] The saturable absorption stabilization device includes a semi-transparent mirror 6, a quarter-wave plate 7, an atomic bubble 8, a half-wave plate 10, a polarizing prism 16, and an optical cutoff 17. The specific optical path within the saturable absorption device is as follows: A λ / 2 wavelength laser generated by the second frequency doubler crystal 11 is transmitted through the half-wave plate 10 and then incident on the polarizing prism 16 for beam splitting. The light transmitted through the polarizing prism 16 serves as the pump light in the saturable absorption process and is incident on the atomic bubble 8. The light reflected by the polarizing prism 16 is incident on the optical cutoff 17 and absorbed. After passing through the atomic bubble 8 and the quarter-wave plate 7, the pump light is incident perpendicularly on the semi-transparent mirror 6. The λ / 2 wavelength laser reflected by the semi-transparent mirror 6 passes again through the quarter-wave plate 7 and is incident on the atomic bubble 8, where it recombines with the pump light to become the probe light. The probe light is then reflected by the polarizing prism 16 to the photodetector 9. The photodetector 9 converts the optical signal of the probe light into an electrical signal and transmits it to the control system of the first wavelength tunable laser 15 to realize feedback adjustment of the first wavelength tunable laser 15.

[0055] The frequency-stabilized λ / 2 wavelength laser is divided into three parts. In this embodiment, the frequency-stabilized λ / 2 wavelength laser is split into three parts by the third beam splitter 18 and the fourth beam splitter 21.

[0056] The frequency-stabilized λ / 2 wavelength laser is incident on the third beam splitter 18. The frequency-stabilized λ / 2 wavelength laser reflected by the third beam splitter 18 is the first part of the frequency-stabilized λ / 2 wavelength laser. The first part of the frequency-stabilized λ / 2 wavelength laser is reflected by the first reflector 5 to the first frequency doubler crystal 4. The λ / 4 wavelength laser generated after being frequency doubled by the first frequency doubler crystal 4 is transmitted to the λ / 4 wavelength reference light incident channel on the multi-in-one optical switch 3.

[0057] The frequency-stabilized λ / 2 wavelength laser transmitted through the third beam splitter 18 is incident on the fourth beam splitter 21. The frequency-stabilized λ / 2 wavelength laser transmitted through the fourth beam splitter 21 is the second part of the frequency-stabilized λ / 2 wavelength laser. The second part of the frequency-stabilized λ / 2 wavelength laser is incident on the λ / 2 wavelength reference light incident channel on the multi-in-one optical switch 3.

[0058] The frequency-stabilized λ / 2 wavelength laser reflected by the fourth beam splitter 21 is the third part of the frequency-stabilized λ / 2 wavelength laser. The third part of the frequency-stabilized λ / 2 wavelength laser is reflected by the dichroic mirror 22 and combined with the second λ wavelength output light and incident on the frequency summing crystal 19 for frequency summing. The λ / 3 wavelength laser generated by the frequency summing is coupled to the λ / 3 wavelength reference light incident channel on the multi-in-one switch 3.

[0059] In this way, a multi-wavelength high-precision frequency-stabilized reference laser with wavelengths of λ, λ / 2, λ / 3 and λ / 4 is formed for calibrating wavelength meter 1.

[0060] By frequency doubling and summing of the laser, wavelength conversion of the laser wavelength is achieved, thereby obtaining multiple laser wavelengths to enable wide-range calibration of the wavelength meter.

[0061] This invention uses an external thermostat to keep the atomic bubble 8 operating at a specific temperature. The optical path system consisting of a semi-transparent mirror 6, a quarter-wave plate 7, the atomic bubble 8, a photodetector 9, a half-wave plate 10, a polarizing prism 16, and an optical cutoff 17 is used to generate collinear laser beams with opposite propagation directions through the atomic bubble 8. The laser beam with higher energy is called the pump light, which excites the atoms in the atomic bubble 8. The other laser beam with lower energy and opposite propagation direction is called the probe light. Under the action of the pump light, the atoms in the atomic bubble 8 absorb the probe light relatively weakly. Therefore, after saturation absorption, the spectral line of the probe light will produce a peak with weakened absorption, namely the saturation absorption peak (the hyperfine structure of the atoms).

[0062] The laser output from the laser in the wavelength-tunable laser array 20 is transmitted to the wavelength meter 1 through the multi-in-one optical switch 3. The controller 2 controls the output channel of the multi-in-one optical switch 3 to output the light input from each incident channel to the wavelength meter 1 in a time-division manner. The output signal of the wavelength meter 1 is read and displayed by the computer 23. The computer 23 transmits the feedback control drive signal of the laser in the wavelength-tunable laser array 20 to the controller 2. Then, the controller 2 tunes the wavelength of the corresponding laser in the wavelength-tunable laser array 20.

[0063] This invention uses a high-precision calibrated wavelength meter 1 to access each laser in the wavelength-tunable laser array 20 that requires frequency stabilization. The deviation between the set value and the actual measured value of wavelength meter 1 is used as a reference to control the output wavelength of each laser in the wavelength-tunable laser array 20. When the all-in-one optical switch 3 is in automatic channel switching mode and the time of one cycle is close to the response time of laser fluctuations due to temperature, the wavelengths of the corresponding lasers in the wavelength-tunable laser array 20 can be stabilized simultaneously. Furthermore, it is also applicable when the all-in-one optical switch 3 is switched to connect only one input and output channel, allowing selective frequency stabilization of lasers of different wavelengths using a single wavelength meter 1, without the need to build separate devices for different wavelengths.

[0064] Example 2

[0065] A broadband multi-wavelength laser frequency stabilization method based on atomic transitions is proposed. Utilizing the aforementioned broadband multi-wavelength laser frequency stabilization system based on atomic transitions, this invention enables simultaneous frequency stabilization of multiple laser wavelengths. The specific implementation process is as follows:

[0066] Step 1: Turn on the external thermostat to control the temperature of Bubble 8. The feedback adjustment mechanism will keep Bubble 8 operating at the set constant temperature.

[0067] Step 2: The first wavelength tunable laser 15 operates. The λ wavelength output light of the first wavelength tunable laser 15 is divided into three beams, namely the first λ wavelength output light, the second λ wavelength output light, and the third λ wavelength output light.

[0068] The first λ-wavelength output light is incident on the λ-wavelength reference light incident channel of the multi-in-one optical switch 3.

[0069] The third λ-wavelength output light is frequency-doubled 11 times by the second frequency doubler crystal to obtain λ / 2 wavelength laser. The λ / 2 wavelength laser is then passed through a saturable absorption device to obtain a frequency-stabilized λ / 2 wavelength laser. The frequency-stabilized λ / 2 wavelength laser is divided into three parts.

[0070] The first part of the frequency-stabilized λ / 2 wavelength laser is frequency-doubled by the first frequency doubler crystal to obtain λ / 4 wavelength laser, which is then input into the λ / 4 wavelength reference light incident channel of the multi-in-one optical switch 3.

[0071] The second part of the frequency-stabilized λ / 2 wavelength laser is incident on the λ / 2 wavelength reference light incident channel of the all-in-one optical switch 3;

[0072] The third part, after frequency stabilization, the λ / 2 wavelength laser and the second λ wavelength output light are combined and passed through the sum-frequency crystal 19 to obtain the λ / 3 wavelength laser, which is then input into the λ / 3 wavelength reference light incident channel of the multi-in-one optical switch 3.

[0073] In the saturable absorption device, the λ / 2 wavelength laser generated by frequency doubling is transmitted through the half-wave plate 10 and then incident on the polarizing prism 16 for beam splitting. The light transmitted through the polarizing prism 16 serves as the pump light in the saturable absorption process and is incident on the atomic bubble 8. The light reflected by the polarizing prism 16 is incident on the optical cutoff 17 and absorbed by the optical cutoff 17. After passing through the atomic bubble 8 and the quarter-wave plate 7, the pump light is incident perpendicularly on the semi-transparent mirror 6. The λ / 2 wavelength laser reflected by the semi-transparent mirror 6 passes through the quarter-wave plate 7 again and is incident on the atomic bubble 8, where it recombines with the pump light to become the probe light.

[0074] Step 3: The probe light is reflected by the polarizing prism 16 to the photodetector 9, which converts the optical signal into an electrical signal.

[0075] Step 4: Using the saturated absorption spectrum obtained by photodetector 9, find the spectral peak of the spectral line with a large signal-to-noise ratio (in this embodiment, the Na atom D2a spectral line is selected), and determine the atomic emission spectrum wavelength corresponding to the spectral peak of the spectral line with a large signal-to-noise ratio (i.e., the Na atom D2a spectral line in this embodiment).

[0076] Step 5: Through the feedback adjustment mechanism, the frequency-doubled λ / 2 wavelength output light from the first wavelength tunable laser 15 is locked at the laser wavelength corresponding to the spectral peak of the saturation absorption spectrum.

[0077] Step 6: Calibrate the wavelength meter 1 based on the locked λ wavelength output light, λ / 2 wavelength laser, λ / 3 wavelength laser and λ / 4 wavelength laser of the first wavelength tunable laser 15.

[0078] Step 7: Set the frequency stabilization wavelength value of each laser in the wavelength tunable laser group 20, and stabilize the output laser of each laser in the wavelength tunable laser group 20 by using the calibrated wavelength meter 1 and the frequency stabilization wavelength value of each laser in the wavelength tunable laser group 20.

[0079] Step 6, calibrating wavelength meter 1, specifically includes the following steps:

[0080] Step 6.1: Determine the laser wavelength λ corresponding to the spectral peak of the saturated absorption spectrum based on the atomic absorption spectroscopy database.

[0081] Step 6.2: Based on the laser wavelengths corresponding to the spectral peaks of the saturated absorption spectrum, determine the actual wavelengths corresponding to the λ wavelength output light, λ / 2 wavelength laser, λ / 3 wavelength laser, and λ / 4 wavelength laser.

[0082] Step 6.3: Based on the measured wavelengths of the emitted light at wavelength λ, the laser at wavelength λ / 2, the laser at wavelength λ / 3, and the laser at wavelength λ / 4 measured by wavelength meter 1, and the actual wavelengths corresponding to the emitted light at wavelength λ, the laser at wavelength λ / 2, the laser at wavelength λ / 3, and the laser at wavelength λ / 4, a partial least squares function is used to fit the curves, and the fitted curves are obtained. The x-axis of the fitted curves corresponds to the actual wavelengths, and the y-axis corresponds to the fitted values.

[0083] Step 6.4: Calculate the coefficient of determination (R²) of the fitted curve and the standard deviation (RMSE) of the difference between the actual wavelength and the fitted value corresponding to the partial least squares algorithm. 2 +Δ02 2 +Δ03 2 +Δ04 2 ) / 4, where the deviation Δ01 between the fitted value of the emitted light at wavelength λ and the actual wavelength of the emitted light at wavelength λ, the deviation Δ02 between the fitted value of the emitted light at wavelength λ / 2 and the actual wavelength of the emitted light at wavelength λ / 2, the deviation Δ03 between the fitted value of the emitted light at wavelength λ / 3 and the actual wavelength of the emitted light at wavelength λ / 3, and the deviation Δ04 between the fitted value of the emitted light at wavelength λ / 4 and the actual wavelength of the emitted light at wavelength λ / 4.

[0084] Step 6.5: If the obtained coefficient of determination R2 is greater than the criterion value N1 (which can be set to 0.99999) and the standard deviation (RMSE) of the difference between the actual wavelength and the wavelength fitted by the partial least squares algorithm is less than the calibration standard deviation N2 (which can be set to 0.0000001), then the calibration of wavelengthmeter 1 is complete. Otherwise, calculate the deviation Δ1 between the measured wavelength of the λ-wavelength emitted light and the actual wavelength of the λ-wavelength emitted light, the deviation Δ2 between the measured wavelength of the λ / 2-wavelength emitted light and the actual wavelength of the λ / 2-wavelength emitted light, the deviation Δ3 between the measured wavelength of the λ / 3-wavelength emitted light and the actual wavelength of the λ / 4-wavelength emitted light, and select the actual wavelength corresponding to the maximum value among Δ1, Δ2, Δ3, and Δ4 to calibrate wavelengthmeter 1 and return to step 6.3.

[0085] Step 7 includes the following steps:

[0086] Step 7.1: Couple the emitted laser wavelength that needs to be stabilized in the wavelength tunable laser group 20 to the corresponding incident channel of the all-in-one optical switch 3;

[0087] Step 7.2: Set the frequency stabilization wavelength value of each laser in the wavelength tunable laser group 20, i.e. the laser wavelength value to be locked, and denoted as λ21, λ22, λ23 and λ24 respectively.

[0088] Step 7.3: Based on the calibrated wavelength meter 1, measure the corresponding wavelength value of the output laser of each laser in the wavelength tunable laser group 20 that needs to be calibrated. The measured wavelength values ​​of each laser in the wavelength tunable laser group 20 are recorded as λ11, λ12, λ13 and λ14 respectively.

[0089] Step 7.4: Calculate the deviations between the stable wavelength value and the measured wavelength value of each laser in the wavelength tunable laser group 20: Δ11 = λ21 - λ11, Δ12 = λ22 - λ12, Δ13 = λ23 - λ13, Δ14 = λ24 - λ14, and the relative standard deviation between the measured wavelength value and the stable wavelength value: RMSE1 = (Δ11 - λ12) / (λ23 - λ14). 2 +Δ12 2 +Δ13 2 +Δ14 2 ) / 4.

[0090] Step 7.5: Determine if the calculated RMSE1 value is less than the frequency stabilization coarse adjustment discrimination standard value M1 (the frequency stabilization coarse adjustment discrimination standard value M1 can be set to 0.01nm). If the relative standard deviation RMSE1 between the measured wavelength value and the frequency stabilization wavelength value is less than the frequency stabilization coarse adjustment discrimination standard value M1, then, based on the values ​​of deviation Δ11, Δ12, Δ13, and Δ14, the controller 2 fine-tunes the output wavelength of each laser in the wavelength tunable laser group 20. Fine-tuning involves changing the working cavity length of the laser (controlling the piezoelectric ceramic inside the laser) to achieve a small-range change in wavelength, and then proceed to step 7.6. If the obtained RMSE1 value is greater than M1, then, based on the values ​​of deviation Δ11, Δ12, Δ13, and Δ14, the controller 2 coarsely adjusts the output wavelength of each laser in the wavelength tunable laser group 20. Coarse adjustment involves changing the temperature of the laser working material, and then returns to step 7.3.

[0091] Step 7.6: Calculate the deviations between the stable wavelength values ​​and the measured wavelength values ​​of each laser in the tunable laser group 20 after fine-tuning: Δ21 = λ21 - λ11, Δ22 = λ22 - λ12, Δ23 = λ23 - λ13, Δ24 = λ24 - λ14, and the relative standard deviation between the measured wavelength values ​​and the stable wavelength values ​​after fine-tuning: RMSE2 = (Δ21 - λ11) / (λ22 - λ12) / (λ23 - λ13) / (λ24 - λ14). 2 +Δ22 2 +Δ23 2 +Δ24 2 ) / 4;

[0092] Step 7.7: If the calculated relative standard deviation RMSE2 between the fine-tuned measured wavelength value and the stable wavelength value is less than the frequency stabilization completion judgment standard value M2 (the frequency stabilization completion judgment standard value M2 can be set to 0.0000001nm), then the laser corresponding to the wavelength tunable laser group 20 ends the frequency stabilization. If the calculated relative standard deviation RMSE2 between the fine-tuned measured wavelength value and the stable wavelength value is greater than the frequency stabilization completion judgment standard value M2, then return to step 7.3.

[0093] Steps 7.3 to 7.7 above are all completed automatically by controller 2.

[0094] The aforementioned wide-spectrum multi-laser wavelength high-precision intelligent frequency stabilization system and method based on atomic transition reference calibration also has long-term stable calibration and monitoring functions for the wavelength meter. The main method is to divide the wavelength meter 1 into two modes during operation: calibration and frequency stabilization. In order to ensure long-term stable measurement of the wavelength meter 1, the wavelength meter 1 switches between these two modes during operation, thereby achieving high-precision measurement of the wavelength meter 1.

[0095] It should be noted that the specific embodiments described in this invention are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains can make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A broadband multi-wavelength laser frequency stabilization system based on atomic transitions, comprising a first wavelength tunable laser (15), characterized in that, The λ-wavelength emitted light generated by the first tunable laser (15) is divided into three beams: the first λ-wavelength emitted light, the second λ-wavelength emitted light, and the third λ-wavelength emitted light. The first λ wavelength outgoing light is incident on the λ wavelength reference light incident channel of the multi-in-one optical switch (3); The third λ-wavelength output light is frequency-doubled by the second frequency doubler crystal (11) to obtain a λ / 2 wavelength laser. The λ / 2 wavelength laser is then obtained by passing through a saturable absorption device to obtain a frequency-stabilized λ / 2 wavelength laser. The frequency-stabilized λ / 2 wavelength laser is divided into three parts. After the first part of the frequency-stabilized λ / 2 wavelength laser is frequency-doubled by the first frequency doubler crystal (4) to obtain λ / 4 wavelength laser, and then input into the λ / 4 wavelength reference light incident channel of the all-in-one optical switch (3); The second part of the frequency-stabilized λ / 2 wavelength laser is incident on the λ / 2 wavelength reference light incident channel of the all-in-one optical switch (3); The third part, after frequency stabilization, the λ / 2 wavelength laser and the second λ wavelength output light are combined and passed through the summing crystal (19) to obtain the λ / 3 wavelength laser. The λ / 3 wavelength laser is input into the λ / 3 wavelength reference light incident channel of the multi-in-one optical switch (3). The laser output from the laser in the wavelength-tunable laser group (20) is transmitted to the wavelength meter (1) through the multi-in-one optical switch (3). The controller (2) controls the output channel of the multi-in-one optical switch (3) to output the light input from each incident channel to the wavelength meter (1) in a time-division manner. The output signal of the wavelength meter (1) is transmitted to the computer (23). The computer (23) transmits the feedback control drive signal of the laser in the wavelength-tunable laser group (20) to the controller (2). The controller (2) tunes the wavelength of the corresponding laser in the wavelength-tunable laser group (20).

2. The broadband multi-wavelength laser frequency stabilization system based on the atomic transition reference according to claim 1, characterized in that, The saturable absorption device includes an atomic bubble (8). The λ / 2 wavelength laser generated by the second frequency doubler crystal (11) is transmitted through a half-wave plate (10) and then incident on a polarizing prism (16) for beam splitting. The light transmitted through the polarizing prism (16) is used as the pump light in the saturable absorption process and is incident on the atomic bubble (8). The light reflected by the polarizing prism (16) is incident on the optical cutoff (17). After passing through the atomic bubble (8) and the quarter-wave plate (7), the pump light is incident perpendicularly on a semi-transparent mirror (6). The λ / 2 wavelength laser reflected by the semi-transparent mirror (6) passes through the quarter-wave plate (7) again and is incident on the atomic bubble (8) to recombine with the pump light to become the probe light. Then the probe light is reflected by the polarizing prism (16) to a photodetector (9). The photodetector (9) is connected to the control system of the first wavelength tunable laser (15).

3. A broadband multi-wavelength laser frequency stabilization method based on atomic transition reference, utilizing the broadband multi-wavelength high-precision intelligent frequency stabilization system based on atomic transition reference calibration as described in claim 2, characterized in that... Includes the following steps: Step 1: Turn on the external thermostat to control the temperature of the atomic bulb (8) so that the atomic bulb (8) works at the set constant temperature; Step 2: The first wavelength tunable laser (15) operates to obtain the λ wavelength output light, λ / 2 wavelength laser, λ / 3 wavelength laser, λ / 4 wavelength laser, and the pump light and probe light in the saturable absorption device; Step 3: The probe light is reflected by the polarizing prism (16) to the photodetector (9); Step 4: Using the saturated absorption spectrum obtained by the photodetector (9), find the spectral peak of the spectral line with a large signal-to-noise ratio, and determine the atomic emission spectrum wavelength corresponding to the spectral peak of the spectral line with a large signal-to-noise ratio. Step 5: Lock the frequency-doubled λ / 2 wavelength output light from the first wavelength tunable laser (15) at the laser wavelength corresponding to the peak of the saturation absorption spectrum; Step 6: Calibrate the wavelength meter (1) based on the locked λ wavelength output light, λ / 2 wavelength laser, λ / 3 wavelength laser and λ / 4 wavelength laser of the first wavelength tunable laser (15); Step 7: Set the frequency stabilization wavelength value of each laser in the wavelength tunable laser group (20), and stabilize the output laser of each laser in the wavelength tunable laser group (20) by using the calibrated wavelength meter (1) and the frequency stabilization wavelength value of each laser in the wavelength tunable laser group (20).

4. The broadband multi-wavelength laser frequency stabilization method based on atomic transition reference according to claim 3, characterized in that, The calibration of the wavelength meter (1) in step 6 specifically includes the following steps: Step 6.1: Determine the laser wavelength λ corresponding to the spectral peak of the saturated absorption spectrum based on the atomic absorption spectroscopy database; Step 6.2: Based on the laser wavelengths corresponding to the spectral peaks of the saturated absorption spectrum, determine the actual wavelengths corresponding to the λ wavelength output light, λ / 2 wavelength laser, λ / 3 wavelength laser, and λ / 4 wavelength laser; Step 6.3: Based on the measured wavelengths of the emitted light at wavelength λ, the laser at wavelength λ / 2, the laser at wavelength λ / 3, and the laser at wavelength λ / 4 measured by the wavelength meter (1), and the actual wavelengths of the emitted light at wavelength λ, the laser at wavelength λ / 2, the laser at wavelength λ / 3, and the laser at wavelength λ / 4, the partial least squares method is used to fit the function and obtain the fitting curve; Step 6.4: Calculate the coefficient of determination R² of the fitted curve and the standard deviation of the difference between the actual wavelength and the fitted value corresponding to the partial least squares algorithm. Among them, the deviation Δ01 between the fitted value of the emitted light at wavelength λ and the actual wavelength of the emitted light at wavelength λ / 2, the deviation Δ02 between the fitted value of the emitted light at wavelength λ / 2 and the actual wavelength of the emitted light at wavelength λ / 2, the deviation Δ03 between the fitted value of the emitted light at wavelength λ / 3 and the actual wavelength of the emitted light at wavelength λ / 3, and the deviation Δ04 between the fitted value of the emitted light at wavelength λ / 4 and the actual wavelength of the emitted light at wavelength λ / 4. Step 6.5: If the obtained coefficient of determination R2 is greater than the standard value of the coefficient of determination N1, and the standard deviation RMSE of the difference between the actual wavelength and the wavelength fitting value corresponding to the partial least squares algorithm is less than the standard value of the calibration standard deviation N2, then the wavelength meter (1) calibration is completed; otherwise, calculate the deviation Δ1 between the measured wavelength of the λ wavelength emitted light and the actual wavelength of the λ wavelength emitted light, the deviation Δ2 between the measured wavelength of the λ / 2 wavelength emitted light and the actual wavelength of the λ / 2 wavelength emitted light, the deviation Δ3 between the measured wavelength of the λ / 3 wavelength emitted light and the actual wavelength of the λ / 3 wavelength emitted light, and the deviation Δ4 between the measured wavelength of the λ / 4 wavelength emitted light and the actual wavelength of the λ / 4 wavelength emitted light, and select the actual wavelength corresponding to the maximum value among Δ1, Δ2, Δ3 and Δ4, calibrate the wavelength meter (1) and return to step 6.

3.

5. The broadband multi-wavelength laser frequency stabilization method based on atomic transition reference according to claim 4, characterized in that, Step 7 includes the following steps: Step 7.1: Couple the emitted laser wavelength that needs to be stabilized in the wavelength tunable laser array (20) to the corresponding incident channel of the all-in-one optical switch (3); Step 7.2: Set the frequency-stabilized wavelength values ​​of each laser in the wavelength-tunable laser group (20), and denoted as λ21, λ22, λ23 and λ24 respectively; Step 7.3: Based on the calibrated wavelength meter (1), measure the corresponding wavelength value of the output laser of each laser in the wavelength tunable laser group (20) that needs to be calibrated. The measured wavelength values ​​of each laser in the wavelength tunable laser group (20) are recorded as λ11, λ12, λ13 and λ14 respectively. Step 7.4: Calculate the deviations between the stable wavelength value and the measured wavelength value of each laser in the wavelength tunable laser group (20), namely Δ11 = λ21 - λ11, Δ12 = λ22 - λ12, Δ13 = λ23 - λ13, Δ14 = λ24 - λ14, and the relative standard deviation between the measured wavelength value and the stable wavelength value. Step 7.5: Determine whether the calculated RMSE1 value is less than the frequency stabilization coarse adjustment discrimination standard value M1. If the relative standard deviation RMSE1 between the measured wavelength value and the frequency stabilization wavelength value is less than the frequency stabilization coarse adjustment discrimination standard value M1, then according to the values ​​of deviation Δ11, Δ12, Δ13 and Δ14, the controller (2) is used to finely adjust the output wavelength of each laser in the wavelength tunable laser group (20), and then proceed to step 7.

6. If the obtained relative standard deviation RMSE1 between the measured wavelength value and the frequency stabilization wavelength value is greater than the frequency stabilization coarse adjustment discrimination standard value M1, then according to the values ​​of deviation Δ11, Δ12, Δ13 and Δ14, the controller (2) is used to coarsely adjust the output wavelength of the laser, and then return to step 7.

3. Step 7.6: Calculate the deviations between the stable wavelength values ​​and the measured wavelength values ​​of each laser in the tunable laser array (20) after fine-tuning: Δ21 = λ21 - λ11, Δ22 = λ22 - λ12, Δ23 = λ23 - λ13, Δ24 = λ24 - λ14, and the relative standard deviation between the measured wavelength values ​​and the stable wavelength values ​​after fine-tuning. Step 7.7: If the calculated relative standard deviation RMSE2 between the fine-tuned measured wavelength value and the stable wavelength value is less than the standard value M2 for determining the completion of frequency stabilization, then the laser corresponding to the wavelength tunable laser group (20) ends the frequency stabilization. If the calculated relative standard deviation RMSE2 between the fine-tuned measured wavelength value and the stable wavelength value is greater than the standard value M2 for determining the completion of frequency stabilization, then return to step 7.

3.

6. The broadband multi-wavelength laser frequency stabilization method based on atomic transition reference according to claim 5, characterized in that, The coarse frequency stabilization discrimination standard value M1 is greater than the frequency stabilization completion discrimination standard value M2.

7. The broadband multi-wavelength laser frequency stabilization method for atomic transition reference according to claim 5, characterized in that, Steps 7.3 to 7.7 are all completed automatically by the controller (2).

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