Laser rapid frequency hopping locking method

Abstract

The invention discloses a laser rapid frequency hopping locking method, and belongs to the field of atomic physics and laser frequency locking. The frequency of the laser is stabilized through frequency shift EOM and modulation transfer frequency stabilization, the temperature of the laser tube is changed, the laser output frequency is correspondingly changed, the temperature of the laser tube is continuously changed, meanwhile, a signal generator is used for generating fast ramp voltage, and the wavelength of the laser is scanned; a scanning voltage corresponding to a frequency locking error signal zero point is recorded on an oscilloscope, a plurality of groups of corresponding error signal zero point voltage values under different laser tube temperatures are recorded, and a voltage-frequency curve obtained through measurement is subjected to polynomial fitting to obtain a relational expression of the voltage-frequency curve. When laser frequency hopping locking is carried out, a signal source is used for controlling a frequency shift EOM to enable to-be-locked frequency of a laser to change, the voltage of the laser is controlled to change directly according to a voltage and frequency curve obtained through calculation, and an error signal is obtained to achieve rapid frequency hopping locking of the laser. And meanwhile, the laser has the characteristics of high frequency hopping locking speed, large frequency hopping locking range and the like.

Description

Technical Field

[0001] The invention belongs to the fields of atomic physics and quantum optics, and relates to a laser fast frequency hopping locking method for a cold atom interferometer. Background Art

[0002] Atomic interference measurement of gravitational acceleration first requires the magneto-optical trap to load atoms and the atoms to fall, then prepare the atoms in the initial state required for the experiment during the falling process, and then use light to manipulate the atoms to complete the atomic interference experiment, and finally give atomic interference fringes through final state detection. The entire process requires cooling laser, re-pumping laser, detection laser, blow-off laser, Raman laser and other lasers. The red detuning of the cooling light corresponding to the resonant transition frequency of the D2 line of the rubidium atom from the ground state F=1 to the excited state F'=3 is about 20MHz, which will increase to (60~100)MHz in the polarization gradient cooling stage, and the re-pumping light corresponds to the resonant transition frequency of the ground state F=2 to the excited state F'=2, and the blow-off light and the detection light correspond to the resonant transition frequency of the ground state F=2 to F'=3. The two beams of Raman light, of which the Raman laser corresponds to the ground state F=2 to the excited state F'=3, are blue detuned. Therefore, the frequency of the laser needs to change rapidly many times within an interference cycle.

[0003] At present, the main means to achieve laser frequency hopping lock are to use acousto-optic modulators to generate sidebands for laser frequency hopping lock and to change the reference frequency of optical phase-locked loops for laser frequency hopping lock. The frequency hopping lock method using acousto-optic modulators generally generates frequency jumps by giving the modulation frequency of the target output laser and sending it to the frequency-shifting EOM to generate phase modulation sidebands; when using an optical phase-locked loop for frequency hopping lock, the reference frequency of the laser is changed to make the laser to be locked generate frequency jumps and lock. The existing laser frequency hopping lock methods all turn off the PID frequency lock of the frequency-locked laser, and then change the reference frequency to directly hop the frequency. After the frequency hopping, it is impossible to quickly lock on the new frequency point. At the same time, there are also factors such as insufficient laser frequency response speed and poor frequency locking stability. Summary of the invention

[0004] The purpose of the present invention is to provide a laser fast frequency hopping locking method, which can realize fast laser frequency hopping locking by frequency shifting EOM and modulation transfer frequency stabilization, and has the characteristics of fast laser frequency hopping locking speed and large frequency hopping locking range. The present invention is particularly suitable for use in quantum interferometers and other atomic physics experiments with fast laser frequency switching and locking.

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

[0006] The invention discloses a laser fast frequency hopping locking method. The laser output frequency is changed by changing the temperature setting of the laser. After each change of the temperature setting of the laser, a ramp voltage is used to quickly scan the laser wavelength, and the scanning voltage corresponding to the zero point of the error signal of the current output laser frequency is recorded. The laser tube temperature is continuously changed, and the voltage values ​​corresponding to the zero point of the error signal under multiple groups of different laser output frequencies are recorded, so as to realize the accurate measurement of the zero point of the error signal and the corresponding control voltage curve under different laser frequencies. The measured voltage-error signal zero point curve under different laser frequencies is subjected to polynomial fitting, and the fitting result is V=F(f). A laser frequency shift locking system is constructed by using a frequency shift EOM and a modulation transfer frequency stabilization unit. The laser is locked on the +1 level sideband of the frequency shift EOM, and the locking frequency of the laser output is changed by changing the frequency shift EOM driving frequency, and the current frequency is locked by the modulation transfer frequency stabilization unit. The control voltage before frequency hopping is V1, and the PID of the laser frequency shift locking system is firstly unlocked, and then the EOM driving frequency is triggered to generate a change △f of the locking frequency, and the signal source frequency and the EOM response time reach the microsecond level. Then, according to V i =V i-1 +F(f+△f) controls the laser voltage change, turns on PID, and achieves fast frequency locking.

[0007] Further, according to the relationship between frequency and voltage V i =V i-1 After finding the zero point of the error signal at different frequencies by +F(f+△f), the point to be locked is automatically determined according to the scanning voltage and phase-locked error signal data and the point-finding logic algorithm; the output value of the digital controller is made the voltage to be locked, and then the digital PID is turned on to achieve fast automatic frequency hopping locking.

[0008] Furthermore, by changing the temperature of the laser diode and measuring multiple times, the voltage-frequency curve corresponding to the zero point of the error signal can be used as a reference for rapid laser jump lock, and the laser frequency can be quickly locked after frequency hopping.

[0009] Furthermore, the signal source frequency and EOM response time used can reach the microsecond level, achieving fast frequency hopping.

[0010] The invention discloses a laser fast frequency hopping locking device, which is used to implement the laser fast frequency hopping locking method. A laser fast frequency hopping locking device is mainly composed of a laser unit, an error signal unit, a frequency shift electro-optical modulator, a digital controller, an adder and a high-speed feedback loop. The laser unit is connected to the frequency shift electro-optical modulator to change the frequency locking point, the error signal unit is connected to the digital controller to modulate the control signal and find the control frequency locking point, the digital controller is connected to the adder to demodulate the signal to be locked, and the adder is connected to the high-speed feedback loop to form a laser frequency closed-loop locking.

[0011] The laser unit consists of a laser to be locked and a fiber beam splitter.

[0012] The digital controller consists of a digital control chip, an analog-to-digital converter ADC, a digital-to-analog converter DAC, and a conditioning circuit; the analog-to-digital converter ADC and the digital-to-analog converter DAC convert the collected signals into digital-to-analog signals for collecting and outputting electrical signals, the digital control chip is used to process the collected electrical signals, and the conditioning circuit is used to amplify and buffer the analog signals.

[0013] The error signal unit is composed of an error signal conditioning module and a reference microwave source; the error signal conditioning module uses optimization processing to collect the error signal, and the reference microwave source is used to generate a standard signal reference for the locking frequency.

[0014] The high-speed feedback loop consists of a bias circuit, a gain circuit, and multiple lead-lag circuits. The bias circuit is used to provide a suitable bias current and determine the static output operating point, the gain circuit is used to provide the amplification capability of the electrical signal, and the lead-lag circuit is used to lock the control voltage.

[0015] Beneficial effects:

[0016] 1. The invention discloses a laser fast frequency hopping locking method, which stabilizes the frequency of the laser through frequency shift EOM and modulation transfer frequency stabilization, changes the temperature of the laser tube, so that the laser output frequency will produce corresponding changes, continuously changes the temperature of the laser tube, and simultaneously uses a signal generator to generate a fast ramp voltage, scans the laser wavelength, records the scanning voltage corresponding to the zero point of the frequency locking error signal on the oscilloscope, records multiple groups of corresponding error signal zero point voltage values ​​at different laser tube temperatures, and fits the measured voltage-frequency curve through a polynomial to obtain its relationship. When performing laser frequency hopping locking, a signal source is used to control the frequency shift EOM to change the frequency of the laser to be locked, and according to the calculated voltage and frequency curve, the laser voltage is controlled to change directly, thereby obtaining an error signal to achieve fast laser frequency hopping locking, and at the same time has the characteristics of fast laser frequency hopping locking speed and large frequency hopping locking range.

[0017] 2. The present invention discloses a laser fast frequency hopping locking method, which obtains the voltage-frequency curve corresponding to the zero point of the error signal after the temperature of the laser diode changes through multiple measurements and fitting, so as to realize fast frequency locking after the laser frequency hopping.

[0018] 3. The present invention discloses a laser fast frequency hopping locking method, which utilizes the signal source frequency and the EOM fast response to achieve frequency hopping, and can achieve microsecond-level fast frequency hopping.

[0019] 4. A laser fast frequency hopping locking method disclosed in the present invention is based on the relationship between frequency and voltage V i =Vi-1 After finding the zero point of the error signal at different frequencies by +F(f+△f), the point to be locked is automatically determined according to the scanning voltage and phase-locked error signal data and the point-finding logic algorithm; the output value of the digital controller is made the voltage to be locked, and the PID frequency lock is turned on through the algorithm to achieve continuous frequency locking after frequency hopping, and to achieve frequency locking stability after rapid switching of the frequency locking point. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of a laser fast frequency hopping locking method provided by an embodiment of the present invention. 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 fast frequency hopping locking method disclosed in this embodiment has the following specific implementation steps:

[0024] Step 1: Turn on the laser. After the laser temperature control and power are stable, change the temperature of the laser tube to change the frequency of the output laser. Each time the temperature is changed, use the signal generator to generate a fast ramp voltage after the laser frequency is stable, scan the laser wavelength, and record the scanning voltage corresponding to the zero point of the error signal.

[0025] Step 2: The error signal zero-point voltage-frequency curves at different laser temperatures measured are subjected to polynomial fitting to obtain a corresponding curve of the error signal zero-point voltage and the laser frequency;

[0026] Step 3: Start the laser voltage scan, input the laser being scanned into the frequency-shifted EOM and error signal unit to generate an error signal, input the error signal and the control voltage signal into the high-speed feedback loop to perform PID locking of the voltage corresponding to the zero point of the error signal, and feed the voltage value back to the control voltage of the laser to lock the laser frequency

[0027] Step 4: Unlock the PID in the high-speed feedback loop and trigger the EOM drive frequency to generate the frequency change to be locked with the target jump frequency;

[0028] Step 5: According to the fitted voltage-frequency curve, the laser voltage is controlled to quickly follow the zero point of the error signal after frequency hopping, and the frequency locking algorithm is operated to repeat step 2, and the PID frequency locking is turned on to complete the fast frequency hopping lock.

[0029] By changing the temperature of the laser diode and measuring the error signal multiple times, the voltage-frequency curve corresponding to the zero point can be used as a reference for the laser to quickly jump and lock, and the laser frequency can be quickly locked after frequency hopping.

[0030] The signal source frequency and EOM response time used can reach the microsecond level, which can achieve fast frequency hopping;

[0031] After completing the rapid frequency jump and error signal zeroing, the PID frequency lock is turned on through the algorithm, which can continue to lock the frequency after the frequency jump, ensuring the frequency locking stability after the rapid switching of the frequency locking point.

[0032] The invention discloses a laser fast frequency hopping locking device, which is composed of a laser, an error signal unit, a frequency shifting electro-optical modulator, a digital controller, an automatic locking algorithm, a high-speed feedback loop and an adder. The error signal unit is composed of an error signal conditioning module and a reference microwave source; the digital controller is composed of a digital control chip, an ADC, a DAC, and a conditioning circuit; the high-speed feedback loop is composed of a bias circuit, a gain circuit, and a plurality of lead-lag circuits. The invention provides a method for completing frequency hopping and fast locking by utilizing the relationship between the laser control voltage and the output frequency, and has the advantages of large frequency locking bandwidth, fast frequency hopping locking speed, and good frequency hopping locking stability.

[0033] Embodiment 2:

[0034] like Figure 1 As shown, the laser fast frequency hopping locking method disclosed in this embodiment has the following specific implementation steps:

[0035] Step 1: Turn on the laser to be locked, change the temperature of the laser diode to change the laser output frequency, and use the signal generator to scan the laser control voltage after each temperature change. At this time, the laser frequency will scan within a small range and generate a corresponding error signal. Record the voltage value corresponding to the zero point of the error signal obtained by scanning the voltage at different laser diode temperatures;

[0036] Step 2: Perform polynomial fitting on the measured zero-point voltage of the error signal and the corresponding laser frequency to obtain a polynomial fitting relationship between voltage and frequency;

[0037] Step 3: Start the voltage scan of the laser, collect the zero point of the error signal generated by the scan through the digital circuit, find the corresponding control voltage, use the high-speed feedback loop to lock the target voltage, and then lock the frequency of the laser;

[0038] Step 4: Turn off the laser locking PID program, operate the signal generator to make the frequency-shift electro-optic modulator generate frequency shift, and at the same time apply the corresponding voltage after the frequency jump to the laser according to the voltage-frequency fitting curve obtained in step 2;

[0039] Step 5: The error signal scanning module quickly starts the error signal scanning to obtain the precise control voltage corresponding to the zero point of the error signal;

[0040] Step 6: Start the frequency-locking PID program to lock the zero point of the error signal that changes the frequency.

[0041] The present embodiment discloses a laser fast frequency hopping locking device, which is used to implement the laser fast frequency hopping locking method. A laser fast frequency hopping locking device is mainly composed of a laser unit, an error signal unit, a frequency shift electro-optical modulator, a digital controller, an adder and a high-speed feedback loop. The laser unit is connected to the frequency shift electro-optical modulator to change the frequency locking point, the error signal unit is connected to the digital controller to modulate the control signal and find the control frequency locking point, the digital controller is connected to the adder to demodulate the signal to be locked, and the adder is connected to the high-speed feedback loop to form a laser frequency closed-loop locking;

[0042] The laser unit consists of a laser to be locked and a fiber beam splitter;

[0043] The digital controller consists of a digital control chip, an analog-to-digital converter ADC, a digital-to-analog converter DAC, and a conditioning circuit; the analog-to-digital converter ADC and the digital-to-analog converter DAC convert the collected signals into digital-to-analog signals for collecting and outputting electrical signals, the digital control chip is used to process the collected electrical signals, and the conditioning circuit is used to amplify and buffer the analog signals.

[0044] The error signal unit is composed of an error signal conditioning module and a reference microwave source; the error signal conditioning module uses optimization processing to collect the error signal, and the reference microwave source is used to generate a standard signal reference for the locking frequency.

[0045] The high-speed feedback loop consists of a bias circuit, a gain circuit, and multiple lead-lag circuits. The bias circuit is used to provide a suitable bias current and determine the static output operating point, the gain circuit is used to provide the amplification capability of the electrical signal, and the lead-lag circuit is used to lock the control voltage.

[0046] Embodiment 3:

[0047] The embodiment discloses a laser fast frequency hopping locking method. Through frequency shift electro-optic modulator EOM and modulation transfer frequency stabilization, a part of the laser after stabilization is input into the frequency shift locking system by using a spectroscopic system. When the laser is locked on the +1 level sideband of the frequency shift EOM, the frequency of the laser has been stabilized to the +1 level sideband of the frequency shift EOM. If the frequency of the frequency shift EOM is changed, the locked frequency of the laser will change with the frequency shift EOM frequency. According to the working principle of the laser, the laser output frequency will change accordingly by changing the temperature of the laser tube. The temperature of the laser tube is continuously changed, and a signal generator is used to generate a fast ramp voltage at the same time to scan the laser wavelength. The scanning voltage corresponding to the zero point of the frequency locking error signal is recorded on the oscilloscope. The corresponding zero point voltage values ​​of the error signal under multiple different laser tube temperatures are recorded to achieve accurate measurement of the laser frequency scanning curve. The measured voltage-frequency curve is subjected to polynomial fitting to obtain its relationship. When performing laser frequency hopping locking, a signal source is used to control the frequency shift EOM to change the frequency of the laser to be locked. According to the calculated voltage and frequency curve, the laser voltage is controlled to change directly, and then an error signal is obtained to achieve rapid jump locking of the laser frequency.

[0048] 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 fast frequency hopping locking method, characterized in that: The laser output frequency changes accordingly by changing the temperature setting of the laser. After each change of the laser temperature setting, the laser wavelength is quickly scanned using a ramp voltage, and the scanning voltage corresponding to the zero point of the error signal of the current output laser frequency is recorded; the laser tube temperature is continuously changed, and the voltage values ​​corresponding to the zero point of the error signal under multiple groups of different laser output frequencies are recorded, so as to achieve accurate measurement of the error signal zero point and the corresponding control voltage curve under different laser frequencies; the measured voltage-error signal zero point curve under different laser frequencies is subjected to polynomial fitting, and the fitting result is V=F(f); a laser frequency shift locking system is constructed using a frequency shift EOM and a modulation transfer frequency stabilization unit; the laser is locked on the +1 sideband of the frequency shift EOM, and the locking frequency of the laser output is changed by changing the frequency shift EOM driving frequency, and the current frequency is locked by the modulation transfer frequency stabilization unit; the control voltage before frequency hopping is V1, firstly, the PID of the laser frequency shift locking system is unlocked, and then the EOM driving frequency is triggered to produce a change △f in the locking frequency, and the signal source frequency and the EOM response time reach the microsecond level; then according to V i =V i-1 +F(f+△f) controls the laser voltage change, turns on PID, and achieves fast frequency locking.

2. A laser fast frequency hopping locking method according to claim 1, characterized in that: After finding the zero point of the error signal at different frequencies according to the relationship between frequency and voltage Vi=Vi-1+F(f+△f), the point to be locked is automatically determined according to the scanning voltage and phase-locked error signal data, and the point-finding logic algorithm; the output value of the digital controller is made the voltage to be locked, and then the digital PID is turned on to achieve fast automatic frequency hopping locking.

3. A laser fast frequency hopping locking method according to claim 1, characterized in that: By changing the temperature of the laser diode and measuring the error signal multiple times, the voltage-frequency curve corresponding to the zero point can be used as a reference for the laser to quickly jump and lock, and the laser frequency can be quickly locked after frequency hopping.

4. A laser fast frequency hopping locking method according to claim 1, characterized in that: The signal source frequency and EOM response time used can reach the microsecond level, achieving fast frequency hopping.

5. A laser fast frequency hopping locking device, used to implement a laser fast frequency hopping locking method as claimed in claim 1, 2, 3 or 4, characterized in that: It is mainly composed of a laser unit, an error signal unit, a frequency-shift electro-optical modulator, a digital controller, an adder and a high-speed feedback loop; the laser unit is connected to the frequency-shift electro-optical modulator to change the frequency locking point, the error signal unit is connected to the digital controller to modulate the control signal and find the control frequency locking point, the digital controller is connected to the adder to demodulate the signal to be locked, and the adder is connected to the high-speed feedback loop to form a laser frequency closed-loop locking; The laser unit consists of a laser to be locked and a fiber beam splitter; The digital controller is composed of a digital control chip, an analog-to-digital converter ADC, a digital-to-analog converter DAC, and a conditioning circuit; the analog-to-digital converter ADC and the digital-to-analog converter DAC perform digital-to-analog conversion on the collected signals to collect and output electrical signals, the digital control chip is used to process the collected electrical signals, and the conditioning circuit is used to amplify and buffer the analog signals; The error signal unit is composed of an error signal conditioning module and a reference microwave source; the error signal conditioning module uses optimization processing to collect the error signal, and the reference microwave source is used to generate a standard signal reference for the locking frequency; The high-speed feedback loop is composed of a bias circuit, a gain circuit, and multiple lead-lag circuits; The bias circuit is used to provide a bias current within a preset range and determine the static output operating point. The gain circuit is used to provide the amplification capability of the electrical signal. The lead-lag circuit is used to lock the control voltage.

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