Light source generation system and method for CPT atomic clock

Abstract

The invention discloses a light source generation system and method for a CPT atomic clock, and the system comprises a high-precision voltage-controlled constant current source, a low-phase-noise microwave source, a bias device, a temperature control circuit, a vertical-cavity surface-emitting laser, a linear polarizer, a 1 / 4 slide, and a microcontroller, and the high-precision voltage-controlled constant current source and the low-phase-noise microwave source are connected with the bias device. The bias device and the temperature control circuit are connected with the vertical cavity surface emitting laser, the linear polaroid and the 1 / 4 slide are arranged at the center of a light path emitted by the vertical cavity surface emitting laser, and the microcontroller controls the high-precision voltage-controlled constant current source, the low-phase-noise microwave source and the temperature control circuit. The system has the advantages of being simple in structure, small in size, suitable for different alkali metal atomic clocks and the like, meanwhile, the microwave source is high in frequency resolution, low in phase noise, adjustable in output power and suitable for a high-performance miniaturized CPT atomic clock.

Description

Technical Field

[0001] The present invention relates to the technical field of atomic clocks, and in particular to a light source generation system and method for a coherent placement trapping (CPT) atomic clock, which is suitable for high-performance miniaturized CPT atomic clocks of different alkali metal atoms. Background Art

[0002] Since the CPT atomic clock does not require a microwave cavity, compared with traditional atomic clocks, it can significantly reduce size, power and cost while maintaining stability. Therefore, it has important practical value in many fields such as global positioning, communication networks, scientific experiments, etc.

[0003] The CPT atomic clock uses two laser beams to interact with the atomic three-level system, accurately locking the laser frequency difference to the CPT resonance frequency, thereby obtaining a standard frequency output. In order to generate coherent light with a frequency difference of the two laser beams equal to the CPT resonance frequency, the CPT atomic clock usually uses a vertical cavity surface emitting laser as the light source. After applying microwave signal modulation to the vertical cavity surface emitting laser drive current, the ±1 sideband of the vertical cavity surface emitting laser output frequency is taken as the target frequency.

[0004] As a key component for detecting atomic hyperfine transitions, the microwave source is one of the core factors that determine the short-term stability of the CPT atomic clock. It is also one of the important factors that restrict the improvement of the accuracy of the CPT atomic clock.

[0005] The influence of microwave source on the short-term stability of CPT atomic clock is mainly reflected in the intermodulation effect, which can be expressed as: Where f is the modulation frequency of the microwave source, v0 is the output frequency of the microwave source, and Sφ(2f) is the phase noise of the microwave source at a frequency offset of 2f; At the same time, the output wavelength of the vertical cavity surface emitting laser is affected by the driving current and temperature, which affects the stability of the CPT atomic clock. Generally, the current coefficient and temperature coefficient of the output wavelength of the vertical cavity surface emitting laser are 0.5 nm / mA and 0.06 nm / ℃, and the relationship between wavelength and frequency can be expressed as: Where c is the speed of light, λ1≈λ2 is the absorption wavelength of the alkali metal atom; The present invention proposes a light source generation system and method for a CPT atomic clock. Compared with conventional devices, the microwave source in the present invention has better phase noise performance than the same type of microwave sources. The high-precision voltage-controlled constant current source and temperature control module can greatly reduce the output wavelength fluctuation of the vertical cavity surface emitting laser, and can generate a more stable CPT atomic clock light source, thereby further improving the short-term stability of the CPT atomic clock. Summary of the invention

[0006] The present invention aims at the deficiencies of the existing light source generation system and method for CPT atomic clock, and proposes a light source generation system and method for CPT atomic clock. The present invention has the advantages of simple structure, small size, and applicability to different alkali metal atomic clocks. At the same time, the microwave source has high frequency resolution, low phase noise, and adjustable output power, and is suitable for high-performance miniaturized CPT atomic clocks.

[0007] To achieve the above technical objectives, the present invention is implemented through the following technical solutions: A light source generation system and method for a CPT atomic clock, characterized by comprising a high-precision voltage-controlled constant current source, a low phase noise microwave source, a bias device, a temperature control circuit, a vertical cavity surface emitting laser, a linear polarizer, a 1 / 4 glass plate and a microcontroller.

[0008] The high-precision voltage-controlled constant current source is connected to the DC bias port of the bias device, and is used to drive the vertical cavity surface emitting laser to generate laser light of a specific wavelength. At the same time, the high-precision voltage-controlled constant current source is used to output a small fluctuation current to reduce the influence of current fluctuation on the output wavelength of the vertical cavity surface emitting laser; The low phase noise microwave source is connected to the RF port of the bias device and is used to modulate the vertical cavity surface emitting laser to generate two coherent light beams with a frequency difference equal to the hyperfine energy level difference of alkali metal atoms. The low phase noise microwave source is used to output a low phase noise microwave signal to improve the short-term stability of the CPT atomic clock. The temperature control circuit is connected to the vertical cavity surface emitting laser and is used to control the temperature change of the vertical cavity surface emitting laser during operation, so as to reduce the influence of the temperature change on the output wavelength of the vertical cavity surface emitting laser; The linear polarizer and the 1 / 4 glass plate are located at the center of the light path emitted by the vertical cavity surface emitting laser, the linear polarizer is used to convert the impure linear polarized light emitted by the vertical cavity surface emitting laser into pure linear polarized light, and the 1 / 4 glass plate is used to convert the pure linear polarized light converted by the linear polarizer into circularly polarized light; The microcontroller is used to configure the register of the high-precision voltage-controlled constant current source, so as to control the output current of the high-precision voltage-controlled constant current source, and can also modulate the high-precision voltage-controlled constant current source; The microcontroller is used to configure the registers of the low phase noise microwave source, so as to control the output frequency and output power of the low phase noise microwave source. The microcontroller realizes binary frequency shift keying modulation of the output microwave signal by periodically changing the frequency division value of the N divider of the low phase noise microwave source. The microcontroller is used to perform PID compensation on the temperature control circuit.

[0009] Compared with the prior art, the present invention has the following beneficial effects: The present invention designs a light source generation system and method for a CPT atomic clock, designs a high-precision voltage-controlled constant current source for driving a vertical cavity surface emitting laser, and has a small output current fluctuation of the constant current source, which effectively reduces the influence of the current fluctuation on the output wavelength of the vertical cavity surface emitting laser, thereby improving the stability of the CPT atomic clock; the high-precision voltage-controlled constant current source uses the output voltage of a digital-to-analog converter as a reference voltage, and is easy to perform triangular wave or sine wave modulation on its output current through a microcontroller, without the need for an AC-DC coupling circuit, thereby simplifying the circuit; the high-precision voltage-controlled constant current source includes a soft-start protection circuit, which can effectively protect the vertical cavity surface emitting laser, thereby improving the reliability of the system.

[0010] The low phase noise microwave source uses an ultra-low phase noise frequency synthesizer to multiply the reference frequency to the required frequency. The phase noise performance is excellent in the same phase-locked loop scheme, which effectively improves the short-term stability of the CPT atomic clock. The ultra-low phase noise frequency synthesizer integrates a phase detector, a charge pump, a voltage-controlled oscillator, and an N divider, which can effectively reduce the circuit size. At the same time, the microwave signal output power can be adjusted by a microcontroller without the need for an external power regulation circuit. In addition, the internal N divider of the ultra-low phase noise frequency synthesizer is a 32-bit fractional divider, which can achieve a frequency resolution of less than 1 Hz.

[0011] The temperature control circuit adopts an integrated temperature controller for temperature control, which has high temperature control accuracy and small circuit size. At the same time, the compensation scheme adopts digital PID + analog PID, which combines the advantages of digital PID and analog PID, with high flexibility and strong reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The present invention is a structural schematic diagram of a light source generation system and method for a CPT atomic clock according to an embodiment.

[0013] Figure 2 It is a schematic diagram of the structure of a high-precision voltage-controlled constant current source according to an embodiment.

[0014] Figure 3 The invention is a simplified schematic diagram of a soft start protection circuit in a high-precision voltage-controlled constant current source of an embodiment.

[0015] Figure 4 Schematic diagram of the structure of a low phase noise microwave source according to an embodiment.

[0016] Figure 5 2 is a schematic diagram of the input path structure of the embodiment.

[0017] Figure 6 2 is a schematic diagram of the temperature control circuit structure of an embodiment.

[0018] Figure numerals: 1. high-precision voltage-controlled constant current source; 2. low phase noise microwave source; 3. bias device; 4. temperature control circuit; 5. vertical cavity surface emitting laser; 6. linear polarizer; 7. 1 / 4 glass slide; 8. microcontroller; 9. digital-to-analog converter reference level; 10. digital-to-analog converter; 11. Howland current pump; 12. soft-start protection circuit; 13. 100 MHz temperature-compensated crystal oscillator; 14. ultra-low phase noise frequency synthesizer; 15. loop filter; 16. temperature measurement bridge; 17. integrated temperature controller; 18. analog PID compensation network; 19. digital PID compensation network; 20. semiconductor refrigerator. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings. The following examples are intended to provide a detailed description of the present invention, which will help the technical staff to better understand the principle of the present invention. However, these embodiments do not limit the scope of the present invention, and within the framework of the present invention, the technical staff can make various variations and improvements. It should be pointed out that the following are only preferred embodiments of the present invention, and the scope of protection is not limited to the embodiment, and all technical solutions belonging to the present invention's thinking should belong to the scope of protection of the present invention.

[0020] like Figure 1 As shown, the present invention relates to a light source generation system and method for a CPT atomic clock, including a high-precision voltage-controlled constant current source 1, a low phase noise microwave source 2, a bias device 3, a temperature control circuit 4, a vertical cavity surface emitting laser 5, a linear polarizer 6, a 1 / 4 glass slide 7 and a microcontroller 8.

[0021] In this embodiment, the high-precision voltage-controlled constant current source 1 and the low phase noise microwave source 2 are respectively connected to the DC coupling port and the RF port of the bias device 3, the bias device 3 is connected to the laser driving port of the vertical cavity surface emitting laser 5, the input and output of the temperature control circuit 4 are respectively connected to the thermistor port and the semiconductor refrigerator port of the vertical cavity surface emitting laser 5, the linear polarizer 6 and the 1 / 4 glass plate 7 are located at the center of the light path emitted by the vertical cavity surface emitting laser 5, the linear polarizer 6 is used to convert the impure linear polarized light emitted by the vertical cavity surface emitting laser 5 into pure linear polarized light, and the 1 / 4 glass plate 7 is used to convert the pure linear polarized light converted by the linear polarizer 6 into circularly polarized light; like Figure 2 As shown, the high-precision voltage-controlled constant current source 1 of the present invention includes a digital-to-analog converter reference level 9, a digital-to-analog converter 10, a Howland current pump 11, and a soft-start protection circuit 12.

[0022] In this embodiment, the digital-to-analog converter reference level 9 is connected to the digital-to-analog converter 10, providing an accurate reference level for the digital-to-analog converter 10 and serving as the power input of the digital-to-analog converter 10; the output of the digital-to-analog converter 10 is connected to the Howland current pump 11, and the digital-to-analog converter 10 adopts a 16-bit digital-to-analog converter to provide an accurate reference voltage for the Howland current pump 11 to output a constant current; the microcontroller 8 communicates with the digital-to-analog converter 10 through the SPI communication protocol, and the microcontroller 8 can control the output voltage of the digital-to-analog converter 10 by configuring the internal registers of the digital-to-analog converter 10, and can also perform triangular wave modulation or sine wave modulation on the output voltage of the digital-to-analog converter 10; the soft start protection circuit 12 is connected to the power port of the Howland current pump 11, providing power input for the Howland current pump 11, and the soft start protection circuit 12 can reduce the surge current through the soft start function, thereby protecting the vertical cavity surface emitting laser 5.

[0023] like Figure 3 As shown, it is a simplified schematic diagram of the soft start protection function of the soft start protection circuit 12 of the present invention. The INR / SS value can be controlled by NR / SS Control, thereby controlling the delay time of the soft start protection circuit. The delay time can be expressed as: like Figure 4 As shown, the low phase noise microwave source 2 of the present invention includes a 100 MHz temperature compensated crystal oscillator 13, an ultra-low phase noise frequency synthesizer 14, and a loop filter 15, wherein the ultra-low phase noise frequency synthesizer 14 internally integrates an input path, a phase detector, a charge pump, a voltage-controlled oscillator, an N divider, and an output path.

[0024] In this embodiment, the output end of the 100 MHz temperature-compensated crystal oscillator 13 is connected to the reference signal input end of the ultra-low phase noise frequency synthesizer 14. The ultra-low phase noise frequency synthesizer 14 receives the received 100 MHz temperature-compensated crystal oscillator 13 signal through the input path as an input signal of the phase detector. The input path is composed of Figure 5 As shown, it includes a 2-time frequency circuit, an R pre-frequency divider circuit, a frequency multiplier circuit, and a post-R frequency divider circuit; the output signal of the voltage-controlled oscillator is connected to the N frequency divider, and after frequency division, it is used as another input signal of the phase detector; the phase detector is connected to the charge pump, and the output signal of the charge pump is input to the voltage-controlled end of the voltage-controlled oscillator after passing through the loop filter 15 to adjust the output frequency of the voltage-controlled oscillator; the output signal of the voltage-controlled oscillator generates a microwave signal output after passing through the output path, and the microwave signal can be directly output by the voltage-controlled oscillator, and can also be output by the voltage-controlled oscillator after frequency division by the channel frequency divider.

[0025] In this embodiment, the N divider is a 32-bit fractional divider, which can achieve a frequency resolution lower than 1 Hz; the N divider frequency division value is controlled by the microcontroller 8, thereby changing the output frequency of the microwave source; at the same time, the microcontroller 8 can periodically change the N divider frequency division value, thereby realizing binary frequency shift keying modulation of the microwave signal.

[0026] In this embodiment, the microcontroller 8 can adjust the output power of the ultra-low phase noise frequency synthesizer 14 by configuring the internal registers thereof, without the need for an external power regulation circuit.

[0027] like Figure 6 As shown, the temperature control circuit 4 of the present invention includes a temperature measuring bridge 16, an integrated temperature controller 17, an analog PID compensation network 18, a digital PID compensation network 19, and a semiconductor refrigerator 20, wherein the integrated temperature controller 17 internally integrates a buffer, an operational amplifier, and a pulse width modulation (PWM) module.

[0028] In this embodiment, the temperature measuring bridge 16 is connected to the internal buffer of the integrated temperature controller 17, and the output end of the buffer is connected to the input end of the operational amplifier inside the integrated temperature controller 17. After the operational amplifier performs differential amplification on the buffer output signal, the output signal is connected to the analog PID compensation network 18 and the analog-to-digital converter inside the microcontroller 8; after the analog PID compensation network 18 processes the operational amplifier output signal, it is input into the analog-to-digital converter inside the microcontroller 8 for sampling; after the analog-to-digital converter inside the microcontroller 8 samples the operational amplifier output signal, it performs digital PID compensation on it, and after the digital PID compensation result and the analog PID compensation result sampled by the analog-to-digital converter inside the microcontroller 8 are weighted, they are input into the internal PWM module of the integrated temperature controller 17 to adjust its duty cycle, and then adjust the current input to the semiconductor refrigerator 20, thereby reducing the temperature fluctuation of the vertical cavity surface emitting laser 5.

[0029] The specific embodiments described above further illustrate the technical problems, technical solutions and beneficial effects solved by the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A light source generation system and method for a CPT atomic clock, characterized in that: It includes a high-precision voltage-controlled constant current source (1), a low phase noise microwave source (2), a bias device (3), a temperature control circuit (4), a vertical cavity surface emitting laser (5), a linear polarizer (6), a quarter glass plate (7) and a microcontroller (8); The high-precision voltage-controlled constant current source (1) is connected to the DC bias port of the bias device (4) and is used to drive the vertical cavity surface emitting laser (5) to generate laser light of a specific wavelength. The high-precision voltage-controlled constant current source (1) is used to output a small fluctuation current to reduce the influence of current fluctuation on the output wavelength of the vertical cavity surface emitting laser (5); The low phase noise microwave source (2) is connected to the radio frequency port of the bias device (4) and is used to modulate the vertical cavity surface emitting laser (5) to generate two coherent light beams with a frequency difference equal to the hyperfine energy level difference of the alkali metal atoms. The low phase noise microwave source (2) is used to output a low phase noise microwave signal to improve the short-term stability of the CPT atomic clock; The temperature control circuit (4) is connected to the vertical cavity surface emitting laser (5) and is used to control the temperature change of the vertical cavity surface emitting laser (5) during operation, so as to reduce the influence of the temperature change on the output wavelength of the vertical cavity surface emitting laser (5); The linear polarizing plate (6) and the quarter glass plate (7) are located at the center of the light path emitted by the vertical cavity surface emitting laser (5); the linear polarizing plate (6) converts the impure linear polarized light emitted by the vertical cavity surface emitting laser (5) into pure linear polarized light, and the quarter glass plate (7) converts the pure linear polarized light converted by the linear polarizing plate (6) into circularly polarized light; The microcontroller (8) configures the register of the high-precision voltage-controlled constant current source (1), thereby controlling the output current of the high-precision voltage-controlled constant current source (1), and can also modulate the high-precision voltage-controlled constant current source (1); The microcontroller (8) configures the registers of the low phase noise microwave source (2) to control the output frequency and output power of the low phase noise microwave source (2); the microcontroller (5) periodically changes the frequency division value of the N frequency divider of the low phase noise microwave source (2) to achieve binary frequency shift keying modulation of the output microwave signal; and the microcontroller (8) performs PID compensation on the temperature control circuit (4).

2. A light source generation system and method for a CPT atomic clock according to claim 1, characterized in that: The high-precision voltage-controlled constant current source (1) comprises a digital-to-analog converter reference level, a digital-to-analog converter, a Howland current pump and a soft-start protection circuit; The high-precision voltage-controlled constant current source (1) is controlled by the microcontroller (8), and the microcontroller (8) configures the digital-to-analog converter register so that the high-precision voltage-controlled constant current source (1) performs triangular wave modulation or sine wave modulation on the basis of outputting a direct current; The soft start protection circuit is used to protect the vertical cavity surface emitting laser (5), and the delay time of the soft start protection circuit is adjustable.

3. A light source generation system and method for a CPT atomic clock according to claim 1, characterized in that: The low phase noise microwave source (2) comprises a 100 MHz temperature compensated crystal oscillator, an ultra-low phase noise frequency synthesizer and a loop filter. The ultra-low phase noise frequency synthesizer internally integrates a phase detector, a charge pump, a voltage-controlled oscillator and an N frequency divider; the N frequency divider is a 32-bit fractional frequency divider that can achieve a frequency resolution lower than 1 Hz. The microcontroller (8) can periodically change the frequency division value of the N frequency divider to achieve binary frequency shift keying modulation of the microwave signal.

4. A light source generation system and method for a CPT atomic clock according to claim 1, characterized in that: The temperature control circuit (4) comprises a temperature measuring bridge, an integrated temperature controller, a digital PID+analog PID compensation network and a semiconductor refrigerator.

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