Temperature adaptive frequency locking system and method applied to CPT atomic clock

Abstract

The invention provides a temperature self-adaptive frequency locking system and method applied to a CPT atomic clock, the system comprises a TEC heating sheet 1, a VCSEL laser 2, a temperature sensor 3, a gas chamber shell 4, a gas chamber 5 and the like, the VCSEL laser 2 is tightly attached to the surface of the TEC heating sheet 1, the temperature sensor 4 is arranged near the outer side of the gas chamber 5, the gas chamber 5 is wrapped by the gas chamber shell 4, and the TEC heating sheet 1 is arranged in the gas chamber shell 4. A heating resistor network 7 is arranged at the lower part of the air chamber 5; a laser beam emitted by the VCSEL laser 2 passes through the gas chamber 5 and then is received by the photoelectric sensor 6. The whole control is executed by a CPT atomic clock control system 9; and feedback signals of the temperature sensor 4 are respectively transmitted to the frequency drift algorithm processing module 10 and the control parameter adjustment algorithm processing module 11. Output signals of the two modules are transmitted to a CPT atomic clock control system 9; a feedback signal of the photoelectric sensor 6 is also transmitted to the CPT atomic clock control system 9; the VCO voltage-controlled crystal oscillator 8 is controlled by the CPT atomic clock control system 9 and outputs frequency to the outside.

Description

Technical Field

[0001] This invention relates to the field of coherent population trapping (CPT) atomic clock technology, and in particular to a temperature-adaptive frequency locking system and method for CPT atomic clocks. Background Technology

[0002] Coherent layout trapping (CPT) atomic clocks, due to their small size, low power consumption, and high stability, have become an important development direction for next-generation miniature atomic clocks. Their working principle relies on the quantum interference effect of atomic energy levels under coherent laser irradiation; the center frequency of the interference signal resonance peak determines the accuracy and stability of the CPT atomic clock's output signal. However, when the operating environment temperature is too high, the physical properties of the atomic energy level structure (such as the hyperfine level spacing of the ground state) and the working medium (such as rubidium and cesium) change, causing the center frequency of the CPT atomic clock to drift. In addition to the temperature drift of the center frequency, at high temperatures (above 85°C), the morphology of the CPT atomic clock's interference signal resonance peak also becomes distorted—the resonance peak half-width increases, and the absorption peak value decreases, leading to frequency locking inaccuracies.

[0003] To address the center frequency drift issue of CPT atomic clocks operating in high-temperature environments, the traditional solution is a temperature-compensation-frequency lookup table method. This involves measuring a series of temperature points and their corresponding center frequency drift during production, creating a compensation table, and storing it in the CPT atomic clock. During operation, a temperature sensor detects the ambient temperature and uses the table for compensation. However, this lookup table method relies on fixed parameters to modify the center frequency, but the temperature drift curves of each atomic clock differ, and a fixed compensation table cannot achieve precise individualized compensation. Therefore, a dynamic temperature compensation method that can adapt to different individual clocks is needed.

[0004] There is currently no particularly effective solution to the problem of resonance peak morphology distortion in CPT atomic clocks under high-temperature operating conditions, which directly limits the high-temperature operating temperature of CPT atomic clocks. Summary of the Invention

[0005] The purpose of this invention is to provide a temperature-adaptive frequency locking method for CPT atomic clocks, which solves the problems of center frequency drift and frequency locking inaccuracy caused by resonance peak morphology distortion in CPT atomic clocks operating at high temperatures.

[0006] Technical solution: In a first aspect, this application provides a temperature-adaptive frequency locking system for a CPT atomic clock, the system comprising the following hardware components: a TEC heating element 1, a VCSEL laser 2, a temperature sensor 3, a gas chamber housing 4, a gas chamber 5, a photoelectric sensor 6, a heating resistor network 7, a VCO voltage-controlled crystal oscillator 8, a CPT atomic clock control system 9, a frequency drift algorithm processing module 10, and a control parameter adjustment algorithm processing module 11, wherein: The VCSEL laser 2 is mounted in close contact with the surface of the TEC heating element 1. The temperature sensor 4 is located near the outside of the gas chamber 5, which is enclosed by a gas chamber shell 4. A heating resistor network 7 is located at the bottom of the gas chamber 5. The laser beam emitted by the VCSEL laser 2 passes through the gas chamber 5 and is received by the photoelectric sensor 6. The entire control is performed by the CPT atomic clock control system 9. The feedback signal from the temperature sensor 4 is transmitted to the frequency drift algorithm processing module 10 and the control parameter adjustment algorithm processing module 11, respectively. The output signals of these two modules are transmitted to the CPT atomic clock control system 9. The feedback signal from the photoelectric sensor 6 is also transmitted to the CPT atomic clock control system 9. The VCO voltage-controlled crystal oscillator 8 is controlled by the CPT atomic clock control system 9 and outputs its frequency.

[0007] Specifically, the TEC heating element 1 is used to heat or cool the VCSEL laser 2, maintaining the operating temperature set by the VCSEL laser 2, thereby achieving active control over its operating temperature; the VCSEL laser 2 is used to generate coherent two-color light, causing the rubidium atoms in the gas chamber 5 to be in the CPT state, producing the CPT phenomenon; the temperature sensor 3 is used to measure the actual operating temperature of the gas chamber; the gas chamber shell 4 is used for heat insulation and mechanical protection.

[0008] Specifically, the gas chamber 5 is encapsulated with alkali metal atomic vapor and buffer gas. When the laser passes through the gas chamber, it will undergo CPT interaction with the atoms. The gas chamber 5 is surrounded by a gas chamber shell 4, which has a light window to allow the laser to pass through. After being irradiated by the specific wavelength of bicolor light generated by the VCSEL laser 2, the CPT phenomenon is generated.

[0009] Specifically, the photoelectric sensor 6 is used to receive the light signal emitted by the VCSEL laser 2 through the gas cell 5; the photoelectric sensor 6 is used to detect the absorption change of the laser after passing through the gas cell due to the CPT effect, and convert the light intensity change into an electrical signal to form a feedback signal; the feedback signal is then transmitted to the CPT atomic clock control system 9 to achieve closed-loop locking of the laser frequency; by analyzing the intensity change of the output signal of the photoelectric sensor 6, the CPT atomic clock control system 9 determines whether the laser frequency deviates from the CPT resonance frequency of the atom, and adjusts the operating current of the VCSEL laser 2 or the temperature setting of the TEC heating element 1 accordingly, thereby achieving adaptive frequency stabilization.

[0010] Specifically, the heating resistance network 7 is used to maintain the stability of the atomic vapor pressure inside the gas chamber 5 and to ensure that the CPT resonance conditions do not change due to fluctuations in ambient temperature; the heating resistance network 7 heats the gas chamber uniformly and maintains it within the set operating temperature range.

[0011] Specifically, the output frequency of the VCO voltage-controlled crystal oscillator 8 is regulated by the CPT atomic clock control system 9. The CPT atomic clock control system 9 generates a corresponding control voltage by processing the CPT resonance signal, and adjusts the output frequency of the VCO voltage-controlled crystal oscillator 8 to lock it at the reference frequency corresponding to the atomic transition, thereby achieving high-precision time and frequency output.

[0012] Specifically, the CPT atomic clock control system 9 is used for the overall control of the CPT atomic clock, including the adjustment of control parameters and the adjustment of the center frequency. This system is used to control the center frequency output of the CPT atomic clock and to achieve precise frequency locking of the CPT atomic clock through feedback control parameters, microwave closed-loop feedback parameters and temperature closed-loop feedback parameters.

[0013] Specifically, the frequency drift algorithm processing module 10 is used to determine the compensation amount after frequency drift based on the measured air chamber ambient temperature; it is used to determine the compensation amount after frequency drift by fitting the temperature-frequency drift relationship using a third-order polynomial through the established fitting model △v = F1T between the frequency offset △v and the air chamber temperature T.

[0014] Specifically, the control parameter adjustment algorithm processing module 11 is used to determine the adjustment amount of the control parameters based on the measured air chamber ambient temperature; and to determine the offset amount ΔP of the signal characteristic quantity after signal distortion by using the established fitting model P = FT between the CPT signal characteristic quantity P and the air chamber temperature T.

[0015] Secondly, this application provides a temperature-adaptive frequency locking method for CPT atomic clocks, implemented using the aforementioned temperature-adaptive frequency locking system. The method includes: Step 1: By real-time monitoring of the ambient temperature T in the gas chamber and combining experimental measurement data, a polynomial fitting model is established between the laser frequency drift Δν and the ambient temperature T in the gas chamber; this model will provide a theoretical basis and feedback prediction foundation for subsequent temperature adaptive frequency locking control. Step 2: The CPT atomic clock control system 9 establishes a functional relationship model between the signal characteristic quantity and the gas chamber temperature, P = F(T), by real-time monitoring of the gas chamber ambient temperature T and combining the experimentally acquired CPT signal characteristic quantity P. This model describes the variation law of the intensity, width, position or signal-to-noise ratio key characteristic quantity P of the CPT resonance signal under different gas chamber ambient temperatures, providing a basis for the CPT atomic clock to achieve stable frequency locking under different temperature conditions.

[0016] In summary, this invention provides a temperature-adaptive frequency locking method for CPT atomic clocks. Addressing the individual differences in the temperature drift curve of CPT atomic clocks, a third-order polynomial is used to fit the temperature-frequency offset relationship, which is then fed back to the CPT atomic clock control system. The CPT atomic clock control system adjusts the VCO output frequency to achieve real-time, adaptive, and precise compensation for the temperature drift of the CPT atomic clock. To address the problem of frequency locking inaccuracy caused by resonance peak morphology distortion under high-temperature operation, a fitting model of CPT signal characteristic quantities and chamber temperature is established. Based on the model and the real-time detected chamber temperature value, the control parameters of the CPT atomic clock control system are adjusted to achieve precise frequency locking of the CPT atomic clock under high operating ambient temperatures. This overcomes the shortcomings of existing temperature-frequency lookup table compensation methods that cannot address the individual differences in the temperature drift curve of CPT atomic clocks, reducing the temperature drift of the CPT atomic clock output and improving the accuracy of the clock's output across all temperatures. Furthermore, it solves the problem of frequency locking inaccuracy caused by resonance peak morphology distortion under high-temperature operation, raising the upper limit of the clock's normal operating temperature for frequency locking. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below.

[0018] Figure 1 This is a schematic diagram of a temperature-adaptive frequency-locking system for a CPT atomic clock provided in this application; Figure 2 This is a polynomial fitting model for the relationship between the laser frequency drift Δν and the ambient temperature T in the gas chamber. Figure 3 The fitting model for the CPT signal characteristic P and the air chamber temperature T is P = FT; Figure 4 This application provides a flowchart of a temperature-adaptive frequency locking method applied to a CPT atomic clock; Among them, 1-TEC heating element, 2- VCSEL laser, 3- temperature sensor, 4- air chamber housing, 5- air chamber, 6- photoelectric sensor, 7- heating resistor network. Detailed Implementation

[0019] Example 1 like Figure 1As shown, this application provides a temperature-adaptive frequency-locking system for a CPT atomic clock. The system includes the following hardware components: a TEC heating element 1, a VCSEL laser 2, a temperature sensor 3, a gas chamber housing 4, a gas chamber 5, a photoelectric sensor 6, a heating resistor network 7, and a VCO voltage-controlled crystal oscillator 8. These hardware components together constitute the physical system foundation of the CPT atomic clock, achieving stable locking between the laser frequency and the atomic transition frequency. The system also includes the following software processing modules: a CPT atomic clock control system 9, a frequency drift algorithm processing module 10, and a control parameter adjustment algorithm processing module 11, wherein: The VCSEL laser 2 is mounted in close proximity to the surface of the TEC heating element 1. The temperature sensor 3 is positioned near the outside of the gas chamber 5, which is enclosed by a gas chamber shell 4. A heating resistor network 7 is located at the bottom of the gas chamber 5. The laser beam emitted by the VCSEL laser 2 passes through the gas chamber 5 and is received by the photoelectric sensor 6. The entire control system is executed by the CPT atomic clock control system 9. The feedback signal from the temperature sensor 3 is transmitted to the frequency drift algorithm processing module 10 and the control parameter adjustment algorithm processing module 11, respectively. The output signals of both modules are transmitted to the CPT atomic clock control system 9. The feedback signal from the photoelectric sensor 6 is also transmitted to the CPT atomic clock control system 9. The VCO voltage-controlled crystal oscillator 8 is controlled by the CPT atomic clock control system 9 and outputs its frequency.

[0020] Specifically, the TEC heating element 1 is used to heat or cool the VCSEL laser 2, maintaining the set operating temperature of the VCSEL laser 2, thereby achieving active control over its operating temperature. This temperature control mechanism is crucial for stabilizing the laser's emission wavelength, because in a CPT atomic clock, the laser frequency needs to be precisely matched with the atomic transition frequency to excite CPT resonance.

[0021] Specifically, VCSEL laser 2 is used to generate coherent two-color light, so that rubidium atoms in gas cell 5 are in the CPT state, thus producing the CPT phenomenon.

[0022] Specifically, temperature sensor 3 is used to measure the actual operating temperature of the air chamber. Temperature sensor 3 includes PT1000.

[0023] Specifically, the gas chamber housing 4 serves for thermal insulation and mechanical protection. The interior of the gas chamber housing 4 is typically designed with a good thermal insulation layer to reduce the influence of the external environment on the temperature inside the gas chamber, thereby extending the operating temperature range of the CPT atomic clock.

[0024] Specifically, the gas chamber 5 is the core sensor of the CPT atomic clock, which encapsulates alkali metal atomic vapors such as cesium and rubidium, as well as a buffer gas. When the laser passes through the gas chamber, it will undergo CPT interaction with the atoms. The gas chamber 5 is enclosed by a gas chamber shell 4, which has a light window to allow the laser to pass through. When the laser is irradiated with bicolor light of a specific wavelength generated by the VCSEL laser 2, the CPT phenomenon is generated.

[0025] Specifically, photoelectric sensor 6 is used to receive the light signal emitted by VCSEL laser 2 through gas cell 5. Photoelectric sensor 6 detects the absorption change of the laser after passing through the gas cell due to the CPT effect, and converts the light intensity change into an electrical signal, forming a feedback signal. This feedback signal is then transmitted to the CPT atomic clock control system 9 to achieve closed-loop locking of the laser frequency. By analyzing the intensity change of the output signal of photoelectric sensor 6, the CPT atomic clock control system 9 can determine whether the laser frequency deviates from the CPT resonance frequency of the atoms, and adjust the operating current of VCSEL laser 2 or the temperature setting of TEC heating element 1 accordingly, thereby achieving adaptive frequency stabilization.

[0026] Specifically, the heating resistance network 7 is used to maintain the stability of the atomic vapor pressure inside the gas chamber 5 and ensure that the CPT resonance condition does not change due to fluctuations in ambient temperature. The heating resistance network 7 can uniformly heat the gas chamber and maintain it within the set operating temperature range.

[0027] Specifically, the output frequency of the VCO voltage-controlled crystal oscillator 8 is regulated by the CPT atomic clock control system 9. The CPT atomic clock control system 9 generates a corresponding control voltage by processing the CPT resonance signal, and adjusts the output frequency of the VCO voltage-controlled crystal oscillator 8 to lock it at the reference frequency corresponding to the atomic transition, thereby achieving high-precision time and frequency output.

[0028] Specifically, the CPT atomic clock control system 9 is used for the overall control of the CPT atomic clock, including the adjustment of control parameters and the center frequency adjustment. This system is used to control the center frequency output of the CPT atomic clock and achieves precise frequency locking of the CPT atomic clock through feedback control parameters (frequency locking misalignment threshold O, radio frequency closed-loop feedback parameters K1 (K1P, K1I, K1D), microwave closed-loop feedback parameters K2 (K2P, K2I, K2D) and temperature closed-loop feedback parameters K3 (K3P, K3I, K3D)).

[0029] Specifically, the frequency drift algorithm processing module 10 is used to determine the compensation amount after frequency drift based on the measured air chamber ambient temperature. This module is used to fit the temperature-frequency drift relationship using a third-order polynomial by establishing a fitting model △v = F1(T) between the frequency offset △v and the air chamber temperature T: △v = A1T 2+ A2T + A3 (A1, A2, A3 are calibration coefficients), determine the compensation amount after frequency drift; Specifically, the control parameter adjustment algorithm processing module 11 is used to determine the adjustment amount of the control parameters based on the measured ambient temperature of the air chamber. This module is used to determine the offset ΔP of the signal characteristic quantity after signal distortion by using the established fitting model P = F(T) between the CPT signal characteristic quantity P and the air chamber temperature T.

[0030] Example 2 This application provides a temperature-adaptive frequency locking method for CPT atomic clocks, including: Step 1: As Figure 2 As shown, by real-time monitoring of the gas chamber ambient temperature T and combining experimental measurement data, a polynomial fitting model was established between the laser frequency drift (Δν) and the gas chamber ambient temperature (T). This model will provide a theoretical basis and feedback prediction foundation for subsequent temperature-adaptive frequency locking control.

[0031] Specifically, step 1 includes: Step 11: The ambient temperature of the air chamber is detected by temperature sensor 3 to obtain the ambient temperature T of the air chamber; the ambient temperature of the air chamber is detected in real time by temperature sensor 3 located near the air chamber 5 to obtain the current ambient temperature T of the air chamber. Temperature sensor 3 has high measurement accuracy and response speed. Its output signal is an analog voltage or digital signal, which is transmitted to the CPT atomic clock control system 9 via frequency drift algorithm processing module 10 for subsequent temperature-frequency drift relationship modeling.

[0032] Step 12: At the current ambient temperature T in the gas chamber, the control system drives the VCSEL laser 2 to emit laser light of a specific wavelength. The laser light passes through the gas chamber 5 and is received by the photoelectric sensor 6. The photoelectric sensor 6 converts the received light intensity signal into a voltage signal and feeds it back to the CPT atomic clock control system 9. The control system, combining the known characteristics of the atomic transition spectral lines, analyzes the position shift of the CPT resonance peak in the feedback signal, thereby calculating the laser frequency drift Δν. This drift Δν reflects the deviation between the VCSEL laser frequency and the atomic transition frequency at the current temperature.

[0033] Step 13: Repeat steps 11 to 12 at different ambient temperatures in the air chamber (T1, T2, T3, ..., T...). n The corresponding frequency drift values ​​(Δν1, Δν2, Δν3, …, Δν) were collected at each level. n These temperature points cover the temperature range where the CPT atomic clock might operate or be tested, for example, -40°C to +85°C. The acquired data pairs (T...) i , Δν i This will be used for subsequent modeling and analysis.

[0034] Step 14: Based on the collected temperature point and frequency drift data pairs, use the least squares method or other polynomial fitting algorithms (such as linear regression, nonlinear regression, etc.) to perform fitting analysis on the data and establish a polynomial model between the laser frequency drift Δν and the gas chamber ambient temperature T. For example, if the fitting results show that there is an approximate quadratic relationship between Δν and T, then a model of the following form can be established: Δν = A1T 2 + A2T + A3 in: Δν: Laser frequency drift (unit: MHz); T: Ambient temperature of the air chamber (unit: °C); A1, A2, A3: Fitting coefficients, calculated from experimental data using algorithms such as least squares.

[0035] This polynomial model can accurately reflect the effect of temperature changes on the frequency stability of lasers, and is especially suitable for CPT atomic clock systems that operate in non-constant temperature environments.

[0036] Step 15: Store the fitted model parameters A1, A2, and A3 into the model parameter database of the CPT atomic clock control system 9. The CPT atomic clock control system 9 calculates the corresponding frequency drift Δν in real time based on the currently detected temperature value T, and uses this value for pre-compensation control of the laser frequency. This model can be periodically updated with new temperature-frequency data to adapt to long-term drift factors such as laser aging and changes in the gas chamber state, thereby achieving a temperature-adaptive dynamic frequency locking mechanism.

[0037] Step 2: As Figure 3 As shown, the CPT atomic clock control system 9 establishes a functional relationship model P = F(T) between the signal characteristic quantity and the gas chamber temperature by real-time monitoring of the gas chamber ambient temperature T and combining it with the experimentally acquired CPT signal characteristic quantity P. This model describes the variation law of key characteristic quantities P such as intensity, width, position or signal-to-noise ratio of CPT resonance signal under different gas chamber ambient temperatures, providing a basis for the CPT atomic clock to achieve stable frequency locking under different temperature conditions.

[0038] Step 21: Under different ambient temperature conditions (e.g., -20℃, 0℃, 25℃, 50℃, 70℃, etc.), the VCSEL laser 2 is driven by the control system to emit laser light. The laser light passes through the gas chamber 5 and excites the CPT effect of atoms. The output CPT signal is collected by the photoelectric sensor 6. The collected signal characteristic quantity P may include, but is not limited to, the following indicators: The amplitude of the resonance signal (such as the depth of the CPT absorption peak); Resonance signal width (e.g., full width at half maximum (FWHM)); Resonance signal position (e.g., frequency or phase corresponding to peak center shift); Signal-to-noise ratio (SNR); The phase difference or symmetry index of the driving signal.

[0039] The CPT atomic clock control system 9 will measure the signal characteristic quantity P at each temperature point. i With the corresponding temperature T i Paired storage is performed to provide a foundation for subsequent modeling.

[0040] Step 22: Based on the collected dataset, a functional relationship model between the signal feature quantity P and the ambient temperature T of the air chamber is established using polynomial fitting: P = F(T) If the signal characteristics have an approximately linear or nonlinear relationship with temperature, polynomials of different orders can be selected for modeling. For example, if the relationship is nonlinear, a quadratic model can be fitted. P = a1T 2 + a2T + a3 Where a1, a2, and a3 are the fitting parameters, determined using the least squares method or a nonlinear regression algorithm. The model's fitting accuracy is evaluated using metrics such as mean square error (MSE) to ensure its good predictive ability in practical control.

[0041] Step 23: During system operation, the control system acquires the current ambient temperature T of the air chamber in real time and substitutes it into the model P = F(T) to calculate the signal characteristic quantity P at the current temperature. By comparing it with the standard signal characteristic quantity (or the target signal characteristic quantity), the offset ΔP of the signal characteristic quantity is calculated, and the adjustment amount of the control parameters is further derived. The control parameters involved include: Frequency lockout threshold O: Used to determine whether the current frequency deviates from the CPT resonance peak. When the frequency deviation causes the signal characteristic quantity to change beyond the threshold O, the frequency feedback adjustment mechanism is triggered.

[0042] RF closed-loop feedback parameters K1 (K1P, K1I, K1D): used to adjust the frequency or phase of the RF signal to maintain the CPT resonance condition.

[0043] Microwave closed-loop feedback parameters K2 (K2P, K2I, K2D): used to regulate the microwave drive source to ensure that its frequency is synchronized with the atomic transition frequency.

[0044] Temperature closed-loop feedback parameters K3 (K3P, K3I, K3D): used to control the TEC heating element 1 and the heating resistor network 7 to maintain the constant temperature of the laser and the gas chamber.

[0045] The CPT atomic clock control system 9 dynamically adjusts the control parameters based on the current temperature T and the signal characteristic quantity P predicted by the model, using adaptive algorithms (such as fuzzy control, gain-scheduled PID, neural network controller, etc.). For example: When the temperature rises, causing the resonant signal to widen and the signal-to-noise ratio to decrease, the CPT atomic clock control system 9 automatically adjusts the proportional gain KP in K1 and K2 to enhance the feedback response speed. When the temperature fluctuation is small, appropriately reduce the integral gain KI to prevent the system from overshooting; When the signal characteristic P is detected to deviate significantly from the model prediction value, the system can improve the K3 parameter of the temperature control loop, enhance the regulation capability of the TEC heating element 1 and the heating resistor network 7, and restore the temperature stability of the gas chamber and the laser.

[0046] Step 24: Based on the calculated control parameter adjustment, the CPT atomic clock control system 9 updates the PID parameters in the currently used RF, microwave, and temperature control loops and writes the new parameters into the corresponding control modules. The update process can be achieved through internal register writing or software parameter configuration.

[0047] After the update is completed, the system enters a new closed-loop control cycle, continues to collect CPT signals through photoelectric sensor 6, and monitors changes in ambient temperature through temperature sensor 3, ensuring that the CPT atomic clock control system 9 can still achieve high-precision and high-stability frequency locking under different temperature environments.

[0048] Example 3 like Figure 4 As shown, this embodiment provides a software control flow for a temperature-adaptive frequency locking method for CPT atomic clocks based on temperature feedback. The aim is to collect the temperature information of the gas chamber through the temperature sensor 3, and combine it with a pre-built fitting model to dynamically adjust the feedback control parameters and the voltage of the VCO voltage-controlled crystal oscillator 8, thereby achieving stable frequency locking and frequency drift compensation of the CPT atomic clock under high temperature conditions.

[0049] Step 1: Temperature sensor 3 measures the temperature T of the alkali metal gas chamber, and then proceeds to two branches: Step 2 and Step 7; Step 2: Determine if T is greater than 85℃. If it is equal to 85℃, proceed to Step 3; if it is greater than 85℃, proceed to Step 4.

[0050] Step 3: Keep the control parameters involved in step 23 unchanged and proceed to step 6.

[0051] Step 4: Consult the fitted model P = F(T), and determine the measured signal feature quantity P by the control parameter adjustment algorithm processing module 11, then proceed to step 5.

[0052] Step 5: Based on the fitted model P = F(T), determine the amount of control parameter modification, and proceed to Step 6.

[0053] Step 6: The CPT atomic clock control system modifies the control parameters and issues commands.

[0054] Step 7: Check the fitted model △v = A1T 2 + A2T + A3, the frequency drift algorithm processing module 10 determines the model point corresponding to the measured T, and proceeds to step 8.

[0055] Step 8: Based on the model points, determine the adjustment amount of the center frequency parameter, and proceed to Step 9.

[0056] Step 9: The CPT atomic clock control system 9 adjusts the voltage of the VCO voltage-controlled crystal oscillator 8 to achieve center frequency compensation.

[0057] The innovative aspects of this invention: 1. A high-precision, high-stability temperature sensor is used to continuously monitor the ambient temperature of the alkali metal gas chamber inside the CPT atomic clock, providing highly reliable input data for subsequent temperature compensation and parameter adjustment, and improving the system's temperature sensing capability in complex environments.

[0058] 2. Based on experimental data, a high-order nonlinear fitting model (such as a third-order polynomial model) is established between the gas chamber temperature and the CPT resonant frequency drift to accurately predict the frequency shift under different temperature conditions, thereby realizing real-time compensation of the VCO voltage-controlled crystal oscillator output frequency.

[0059] 3. By utilizing the calculation results of temperature sensing and frequency drift model, the input voltage of the VCO voltage-controlled crystal oscillator is adjusted in real time through the control system to dynamically correct the output frequency, so that it always keeps in line with the atomic transition frequency, effectively dealing with the frequency drift problem under high temperature environment.

[0060] 4. Through experimental data analysis, a fitting function relationship P = F(T) between CPT signal characteristic quantities (such as resonance peak amplitude, width, symmetry, etc.) and air chamber temperature is constructed, providing theoretical basis and data support for the adaptive adjustment of control system parameters.

[0061] 5. Under high temperature conditions (such as air chamber temperature above 85℃), the control system automatically adjusts the key parameters in the feedback control algorithm (such as the proportional, integral, and derivative coefficients of the PID controller) according to the current temperature value and the fitting model to adapt to the changes in CPT signal shape and improve frequency locking stability.

[0062] 6. The present invention adopts a dual-path closed-loop control architecture: one path is used to compensate for the center frequency drift caused by temperature changes; the other path is used to optimize control parameters according to the changes in CPT signal characteristics caused by temperature, thereby comprehensively improving the frequency locking accuracy and system robustness under high temperature environment.

[0063] 7. By employing a dynamic control strategy driven by temperature sensing and model, the frequency locking inaccuracy problem caused by atomic transition frequency drift and CPT resonance signal distortion under high-temperature conditions is effectively solved, significantly improving the frequency output stability of the CPT atomic clock across the entire temperature range.

[0064] 8. This invention effectively mitigates the negative impact of high temperatures on CPT signal quality through a temperature adaptive control strategy, enabling the atomic clock to maintain frequency locking function continuously in higher temperature environments, thus broadening its application scenarios in harsh environments.

[0065] 9. The entire temperature-adaptive frequency locking process is automatically completed by the software module, including temperature acquisition, model calculation, control parameter update and frequency compensation. It has a high degree of automation and intelligence and is suitable for high-precision frequency source applications that are unattended for long periods of time.

[0066] 10. The temperature-adaptive frequency locking method proposed in this invention is based on the general CPT atomic clock architecture design. The software module can be flexibly embedded in various control systems, and has good portability and scalability, providing a foundation for subsequent joint compensation of multiple physical quantities.

[0067] In summary, this invention provides a temperature-adaptive frequency-locking method for atomic clocks based on the principle of coherent population trapping (CPT). This method addresses the CPT center frequency drift caused by changes in atomic level structure and the physical properties of the working medium under high-temperature conditions, as well as the frequency-locking inaccuracy caused by resonance peak morphology distortion under high-temperature conditions.

Claims

1. A temperature adaptive frequency locking system applied to a CPT atomic clock, characterized in that, The system comprises a TEC heating sheet (1), a VCSEL laser (2), a temperature sensor (3), a gas chamber shell (4), a gas chamber (5), a photoelectric sensor (6), a heating resistance network (7), a VCO voltage-controlled crystal oscillator (8), a CPT atomic clock control system (9), a frequency drift algorithm processing module (10), and a control parameter adjustment algorithm processing module (11), wherein: The VCSEL laser (2) is tightly installed on the surface of the TEC heating sheet (1), the temperature sensor (4) is arranged near the outside of the gas chamber (5), the outside of the gas chamber (5) is wrapped by the gas chamber shell (4), and the lower part of the gas chamber (5) is configured with the heating resistance network (7); the laser beam emitted by the VCSEL laser (2) is received by the photoelectric sensor (6) after passing through the gas chamber (5); the whole control is executed by the CPT atomic clock control system (9); the feedback signals of the temperature sensor (4) are transmitted to the frequency drift algorithm processing module (10) and the control parameter adjustment algorithm processing module (11) respectively; the output signals of the two modules are transmitted to the CPT atomic clock control system (9); the feedback signal of the photoelectric sensor (6) is also transmitted to the CPT atomic clock control system (9); and the VCO voltage-controlled crystal oscillator (8) is controlled by the CPT atomic clock control system (9) and outputs a frequency.

2. The system of claim 1, wherein, The TEC heating sheet (1) is used for heating or refrigerating the VCSEL laser (2) to maintain the working temperature set by the VCSEL laser (2) and thus actively control the working temperature; the VCSEL laser (2) is used for generating coherent double-color light to make the rubidium atoms in the gas chamber (5) in a CPT state and generate a CPT phenomenon; the temperature sensor (3) is used for measuring the actual working temperature of the gas chamber; and the gas chamber shell (4) is used for heat insulation and mechanical protection.

3. The system of claim 1, wherein, The gas chamber (5) encapsulates alkali metal atom vapor and buffer gas, and the laser interacts with the atoms through CPT when passing through the gas chamber; the outside of the gas chamber (5) is wrapped by the gas chamber shell (4), and the shell has a light window allowing the laser to pass through and be irradiated by the double-color light of a specific waveband generated by the VCSEL laser (2) to generate a CPT phenomenon.

4. The system of claim 1, wherein, The photoelectric sensor (6) is used for receiving the light signal emitted by the VCSEL laser (2) and passing through the gas chamber (5); the photoelectric sensor (6) is used for detecting the absorption change of the laser after passing through the gas chamber due to the CPT effect, converting the light intensity change into an electric signal, and forming a feedback signal; the feedback signal is then transmitted to the CPT atomic clock control system (9) to realize closed-loop locking of the laser frequency; by analyzing the intensity change of the output signal of the photoelectric sensor (6), the CPT atomic clock control system (9) determines whether the laser frequency deviates from the CPT resonance frequency of the atoms, and adjusts the working current of the VCSEL laser (2) or the temperature setting of the TEC heating sheet (1) accordingly, so as to realize adaptive stabilization of the frequency.

5. The system of claim 1, wherein, The heating resistor network (7) is used to maintain the stability of the atomic vapor pressure inside the gas cell (5) and ensure that the CPT resonance condition does not change due to environmental temperature fluctuations; the heating resistor network (7) uniformly heats the gas cell and maintains it within a set operating temperature range.

6. The system of claim 1, wherein, The output frequency of the VCO voltage-controlled crystal oscillator (8) is regulated by the CPT atomic clock control system (9); the CPT atomic clock control system (9) generates a corresponding control voltage by processing the CPT resonance signal, adjusts the output frequency of the VCO voltage-controlled crystal oscillator (8), and locks it at the reference frequency corresponding to the atomic transition, thereby achieving high-precision time and frequency output.

7. The system of claim 1, wherein, The CPT atomic clock control system (9) is used for the overall control of the CPT atomic clock, including control parameter adjustment and center frequency adjustment; this system is used to control the center frequency output of the CPT atomic clock and to achieve precise frequency locking of the CPT atomic clock through feedback control parameters, microwave closed-loop feedback parameters, and temperature closed-loop feedback parameters.

8. The system of claim 1, wherein, The frequency drift algorithm processing module (10) is used to determine the compensation amount after frequency drift based on the measured gas cell environmental temperature; it is used to determine the compensation amount after frequency drift by establishing a fitting model of frequency offset Δv and gas cell temperature T Δv = F1(T), using a third-order polynomial to fit the temperature-frequency offset relationship.

9. The system of claim 1, wherein, The control parameter adjustment algorithm processing module (11) is used to determine the adjustment amount of the control parameter based on the measured gas cell environmental temperature; it is used to determine the offset amount ΔP of the signal feature quantity after signal distortion by establishing a fitting model of the CPT signal feature quantity P and the gas cell temperature T P = F(T).

10. A temperature adaptive frequency locking method applied to a CPT atomic clock, characterized in that, The method is implemented using the temperature adaptive frequency locking system of claims 1-9, and the method comprises: Step 1: Establish a polynomial fitting model between the laser frequency drift (Δν) and the gas cell environmental temperature (T) by monitoring the gas cell environmental temperature T in real time and combining experimental measurement data; this model will provide a theoretical basis and feedback prediction basis for subsequent temperature adaptive frequency locking control; Step 2: The CPT atomic clock control system (9) establishes a function relationship model P = F(T) between the signal feature quantity and the gas cell temperature by monitoring the gas cell environmental temperature T in real time and combining the CPT signal feature quantity P collected in the experiment; this model describes the variation of the CPT resonance signal intensity, width, position, or signal-to-noise ratio key feature quantity P under different gas cell environmental temperatures, providing a basis for stable frequency locking of the CPT atomic clock under different temperature conditions.

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