Laser frequency stabilization system with rapid switching and frequency locking functions

Abstract

The invention discloses a laser frequency stabilization system with rapid switching and frequency locking functions, and belongs to the field of laser frequency stabilization. The system comprises a laser unit, a frequency stabilization optical path unit and a feedback control unit. The laser unit enters the frequency stabilization light path unit in a beam splitting mode, EOM modulation is provided by the feedback control unit before the frequency stabilization light path unit, the feedback control unit scans input voltage of the laser unit, a saturated absorption signal and a modulation transfer signal are obtained from the frequency stabilization light path unit, and an error signal interval is determined through the saturated absorption signal; and demodulating the modulation transfer signal to obtain an error signal and locking the error signal. When frequency switching is carried out, the feedback control unit relieves frequency locking control, meanwhile, the EOM modulation frequency is changed, feed-forward voltage is applied to the laser so that the laser frequency jumps to be close to the new target frequency, and voltage scanning is started immediately so that an error signal can be obtained and locked. According to the invention, stable and rapid laser frequency switching locking is realized in a mode of combining feed-forward voltage and voltage scanning.

Description

Technical Field

[0001] The invention belongs to the technical field of laser frequency stabilization, and in particular relates to a frequency stabilization system suitable for a cold atom interferometer and capable of realizing rapid switching and locking of a laser frequency. Background Art

[0002] Cold atom interferometry is a quantum precision measurement technology that uses lasers to cool and manipulate atoms, thereby measuring a variety of physical quantities. During the entire measurement process, multiple lasers with different frequencies, including cooling light, pump light, detection light, and Raman light, are required. Therefore, the frequency of the laser needs to be switched rapidly multiple times within an interference cycle. Therefore, how to achieve laser frequency switching and locking is the key to conducting atomic interference experiments.

[0003] Laser frequency switching is achieved by calibrating the laser frequency-voltage conversion relationship. When the laser frequency-voltage relationship changes due to external factors such as temperature, the system cannot achieve frequency lock normally. It takes a very long time to obtain a new target frequency error signal through voltage scanning. Even if the scanning frequency is increased, the error signal cannot be detected if the voltage scanning speed is too fast due to the laser response frequency limitation and the small existence range of the error signal. Summary of the invention

[0004] The purpose of the present invention is to provide a laser frequency stabilization system with the function of fast switching and locking frequency, which can simultaneously obtain the modulation transfer spectrum and the saturation absorption spectrum, more conveniently determine the error signal scanning range, and then obtain the error signal, and combine the feedforward voltage and voltage scanning to achieve stable and fast laser frequency switching and locking. The present invention can greatly simplify the spatial optical path structure, and greatly improve its stability and environmental adaptability.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] The present invention discloses a laser frequency stabilization system with the function of fast switching and locking frequency, including a laser unit, a frequency stabilization optical path unit, and a feedback control unit. A beam of laser light emitted by the laser unit is split into the frequency stabilization optical path unit, and the feedback control unit applies a scanning signal to the output of the laser unit. The DC signal and AC signal obtained by the photodetector in the optical path are respectively input to the feedback control unit. The DC signal is a saturated absorption spectrum, which is used to determine the interval in which the error signal exists; and the AC signal is a modulation transfer spectrum, and the error signal can be obtained after demodulation. The feedback control unit determines the zero point of the error signal in the error signal interval through a peak extraction algorithm, and uses PID to lock it.

[0007] The structure of the frequency-stabilizing optical path unit is as follows: the laser is divided into two beams after passing through the optical fiber beam splitter, one of which is connected to the spatial optical path through a collimator, passes through the rubidium bubble, and is reflected by the PBS to hit the photodetector; the other beam passes through the EOM and then is connected to the spatial optical path through a collimator, and passes through the rubidium bubble from the other side. The optical paths of the two beams of light completely overlap in the rubidium bubble.

[0008] A feeder structure is added to the output end of the photodetector circuit to divide the output signal into a DC signal and an AC signal, wherein the DC signal is a saturated absorption spectrum and the AC signal is a modulation transfer spectrum.

[0009] A part of the output of the laser unit is connected to the frequency stabilization optical path unit. The modulation of the EOM in the frequency stabilization optical path unit is provided by the feedback control unit. The feedback control unit obtains the saturation absorption signal and the modulation transfer signal from the frequency stabilization optical path unit by scanning the bias voltage input to the laser unit. The error signal interval is determined by the saturation absorption signal. The feedback control unit demodulates the modulation transfer signal to obtain the error signal, identifies the zero point of the error signal through the peak extraction algorithm, and starts the PID control to lock the frequency. When frequency switching is required, the feedback control unit will release the PID control to unlock the laser frequency, change the modulation frequency of the EOM at the same time, and then apply a feedforward voltage to the laser to make the laser frequency jump to the vicinity of the new target frequency, and immediately start the voltage scan to obtain the error signal and lock it.

[0010] The working method of a laser frequency stabilization system with a fast switching and frequency locking function disclosed in the present invention is as follows:

[0011] EOM is added to the input end of the frequency stabilizing optical path unit for modulation. The incident laser f0 is modulated to generate n pairs of sidebands f0+nω and f0-nω. The error signals generated by the sideband laser frequencies f0+ω and f0-ω are locked and controlled. The frequency difference between the main output frequency f0 of the laser and the locking point is the modulation frequency ω. Therefore, the laser locking frequency can be changed by changing the modulation frequency ω.

[0012] When the laser frequency f0 is switched, the laser frequency is first unlocked and the modulation signal frequency ω of the EOM is changed. Then, a preset feedforward voltage is given to the laser to make the laser frequency jump to near the target frequency. The voltage value is obtained by calibrating the frequency-voltage relationship of the laser. When the laser frequency jumps to near the target frequency, the voltage scan is started to obtain the error signal and lock it.

[0013] Beneficial effects:

[0014] 1. The laser frequency switching is realized by calibrating the laser frequency-voltage conversion relationship. When the laser frequency-voltage relationship is affected by external factors such as temperature and changes, the system cannot realize frequency locking normally. It takes a very long time to obtain a new target frequency error signal through voltage scanning. Even if the scanning frequency is accelerated, due to the laser response frequency limitation and the small existence range of the error signal, the error signal cannot be detected if the voltage scanning speed is too fast. The present invention discloses a laser frequency stabilization system with the function of fast switching and locking frequency, which combines the feedforward voltage and voltage scanning to perform fast laser frequency switching and locking.

[0015] 2. The present invention discloses a laser frequency stabilization system with the function of fast switching and locking frequency, which is mainly based on a laser unit, a frequency stabilization optical path unit, and a feedback control unit. The laser emitted by the laser unit splits a beam into the frequency stabilization optical path unit, and the feedback control unit applies a scanning signal to the output of the laser unit. The DC signal and AC signal obtained by the photodetector in the optical path are respectively input into the feedback control unit. The laser is divided into two beams after passing through the optical fiber beam splitter, one of which is connected to the spatial optical path through the optical fiber collimator, passes through the rubidium bubble, and is reflected by the PBS to hit the photodetector; the other beam passes through the EOM and then the collimator to connect to the spatial optical path, passes through the rubidium bubble from the other side, and the optical paths of the two beams of light completely overlap in the rubidium bubble. The spatial optical path structure of the present invention has been greatly simplified, so that its stability and environmental adaptability are greatly improved.

[0016] 3. The laser frequency stabilization system with the function of fast switching and locking frequency disclosed in the present invention can obtain the modulation transfer spectrum and the saturation absorption spectrum at the same time, and can more conveniently determine the error signal scanning range, thereby obtaining the error signal and realizing the modulation transfer frequency stabilization. In addition, the use of the saturation absorption spectrum can also meet the needs of wavelength modulation frequency stabilization, that is, the present invention can be applied to two frequency stabilization methods, so the present invention has strong flexibility and versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of a laser frequency stabilization system with the function of fast switching and locking frequency;

[0018] Figure 2 This is a schematic diagram of the structure of the optical path module:

[0019] Figure 3 is a schematic diagram of the photodetector circuit;

[0020] Among them: 1—laser unit, 2—frequency stabilization optical path unit, 3—feedback control unit, 201—EOM, 202—EOM, 203—1 / 2 wave plate, 204—PBS, 205—rubidium bubble, 206—1 / 2 wave plate, 205—rubidium bubble, 204—PBS, 207—photodetector, 2071—photodiode, 2072—operational amplifier, 2073—resistance, 2074—capacitance, 2075—inductance. DETAILED DESCRIPTION

[0021] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0022] Embodiment 1:

[0023] like Figure 1 As shown, the laser frequency stabilization system with the function of fast switching and locking frequency disclosed in this embodiment is mainly composed of a laser unit 1, a frequency stabilization optical path unit 2, and a feedback control unit 3.

[0024] A part of the output of the laser unit 1 is connected to the frequency stabilizing optical path unit 2. The modulation of the EOM 201 in the frequency stabilizing optical path unit 2 is provided by the feedback control unit 3. The feedback control unit 3 can obtain the saturated absorption signal and the modulation transfer signal from the frequency stabilizing optical path unit 2 by scanning the bias voltage input to the laser unit 1. The error signal interval can be determined by the saturated absorption signal. The feedback control unit 3 demodulates the modulation transfer signal to obtain the error signal, identifies the zero point of the error signal by the peak extraction algorithm, and starts the PID control to lock the frequency. When the frequency switching is required, the feedback control unit 3 will release the PID control to unlock the laser frequency, and change the modulation frequency of the EOM 201 at the same time, and then apply a feedforward voltage to the laser to make the laser frequency jump to the vicinity of the new target frequency (in order to achieve the best locking speed, the feedforward voltage value needs to be optimized and debugged according to the actual laser frequency difference), and immediately start the voltage scan to obtain the error signal and lock it.

[0025] like Figure 2 As shown, in the frequency stabilization optical path unit 2, the laser emitted by the laser unit 1 passes through the EOM 201 and is divided into two beams by the optical fiber beam splitter, one of which passes through the optical fiber EOM 202 and enters the spatial optical path, and passes through the 1 / 2 wave plate 203, PBS204, and rubidium bubble 205 in sequence. The other beam is directly connected to the spatial optical path shown in the dotted line cabinet, and then passes through the 1 / 2 wave plate 206, rubidium bubble 205, PBS204 in sequence and hits the photodetector 207. The optical paths of the two beams of light completely overlap in the rubidium bubble 205.

[0026] like Figure 3As shown, the photodetector circuit includes a photodiode 2071, an operational amplifier 2072, a resistor 2073, a capacitor 2074, and an inductor 2075. The optical signal is converted into an electrical signal by the photodiode 2071, and the signal amplified by the operational amplifier 2072 is decomposed into an AC signal and a DC signal through the capacitor 2074 and the inductor 2075 and outputted respectively.

[0027] The working method of a laser frequency stabilization system with a function of fast switching and locking frequency disclosed in this embodiment is as follows:

[0028] EOM is added to the input end of the frequency stabilizing optical path unit 2 for modulation. The incident laser f0 is modulated to generate n pairs of sidebands f0+nω and f0-nω. The feedback control unit 3 performs locking control on the error signal generated by the sideband laser frequency f0+ω or f0-ω. The frequency difference between the main output frequency f0 of the laser unit 1 and the locking point is the modulation frequency ω. Therefore, the change of the laser locking frequency is achieved by changing the modulation frequency ω.

[0029] When the laser frequency f0 is switched, the laser frequency is first unlocked and the modulation signal frequency ω of the EOM is changed. Then, a preset feedforward voltage is given to the laser to make the laser frequency jump to near the target frequency. The voltage value is determined according to the frequency-voltage relationship of the laser. When the laser frequency jumps to near the target frequency, the voltage scan is started to obtain the error signal and lock it.

[0030] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A laser frequency stabilization system with the function of fast switching and locking frequency, characterized in that: It includes a laser unit, a frequency stabilizing optical path unit, and a feedback control unit; a beam of laser light emitted by the laser unit is split into a beam that enters the frequency stabilizing optical path unit, and at the same time the feedback control unit applies a scanning signal to the output of the laser unit; the DC signal and AC signal obtained by the photodetector in the optical path are respectively input into the feedback control unit; the DC signal is a saturated absorption spectrum, which is used to determine the interval in which the error signal exists; and the AC signal is a modulation transfer spectrum, and the error signal is obtained after demodulation; the feedback control unit determines the zero point of the error signal in the error signal interval through a peak extraction algorithm, and uses PID to lock it.

2. The frequency stabilizing optical path unit according to claim 1, characterized in that: The laser is divided into two beams after passing through the optical fiber beam splitter. One beam is connected to the spatial optical path through the optical fiber collimator, passes through the rubidium bubble, and is reflected by the PBS to hit the photodetector; the other beam is connected to the spatial optical path through the collimator after passing through the EOM, and passes through the rubidium bubble from the other side. The optical paths of the two beams completely overlap in the rubidium bubble; a feeder structure is added to the output end of the photodetector circuit to divide the output signal into a DC signal and an AC signal, where the DC signal is a saturated absorption spectrum and the AC signal is a modulation transfer spectrum.

3. A laser frequency stabilization system with fast switching and frequency locking function as claimed in claim 1, characterized in that: A part of the output of the laser unit is connected to the frequency stabilizing optical path unit. The modulation of the EOM in the frequency stabilizing optical path unit is provided by a feedback control unit. The feedback control unit obtains a saturated absorption signal and a modulation transfer signal from the frequency stabilizing optical path unit by scanning the bias voltage input to the laser unit. The error signal interval is determined by the saturated absorption signal. The feedback control unit demodulates the modulation transfer signal to obtain the error signal, identifies the zero point of the error signal by a peak extraction algorithm, and starts PID control to perform frequency lock.

4. A laser frequency stabilization system with fast switching and frequency locking functions as claimed in claim 1, characterized in that: Add EOM to the input end of the frequency stabilization optical path unit for modulation. The incident laser f0 is modulated to generate n pairs of sidebands f0+nω and f0-nω. The error signals generated by the sideband laser frequencies f0+ω and f0-ω are locked and controlled. The frequency difference between the main output frequency f0 of the laser and the locking point is the modulation frequency ω. Therefore, the change of the laser locking frequency is achieved by changing the modulation frequency ω. When the laser frequency f0 is switched, the laser frequency is first unlocked and the modulation signal frequency ω of the EOM is changed. Then, a preset feedforward voltage is given to the laser to make the laser frequency jump to near the target frequency. The voltage value needs to be determined based on the frequency-voltage relationship of the laser. When the laser frequency jumps to near the target frequency, the voltage scan is started to obtain the error signal and lock it.

Images