A laser fast frequency hopping locking method

Abstract

A rapid laser frequency hopping locking method belongs to the fields of atomic physics and laser frequency locking. This invention stabilizes the laser frequency through frequency shifting EOM and modulation transfer stabilization. Changing the laser tube temperature causes a corresponding change in the laser output frequency. The laser tube temperature is continuously changed, and a signal generator simultaneously generates a fast ramp voltage to scan the laser wavelength. The scanning voltage corresponding to the zero point of the frequency locking error signal is recorded on an oscilloscope. Multiple sets of zero-point voltage values ​​corresponding to the error signal at different laser tube temperatures are recorded. The measured voltage-frequency curves are fitted with a polynomial to obtain the relationship. During laser frequency hopping locking, a signal source controls the frequency shifting EOM to change the laser frequency to be locked. Based on the calculated voltage-frequency curve, the laser voltage is directly changed to obtain the error signal, achieving rapid laser frequency hopping locking. This method features fast laser frequency hopping locking speed and a large frequency hopping locking range.

Description

Technical Field

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

[0002] Atomic interferometry for measuring gravitational acceleration first requires loading atoms into a magneto-optical trap and then dropping them. During the atom drop, the atoms are prepared in the desired initial state. Light is then used to manipulate the atoms to complete the atomic interferometry experiment. Finally, the final state detection yields the atomic interference fringes. The entire process requires multiple lasers, including cooling lasers, re-pumping lasers, probe lasers, blow-away lasers, and Raman lasers. The cooling light corresponds to a red detuning of approximately 20 MHz at the resonant transition frequency from the ground state F=1 to the excited state F'=3 of the rubidium atom's D2 line, increasing to (60–100) MHz during the polarization gradient cooling stage. The re-pumping light corresponds to the resonant transition frequency from the ground state F=2 to the excited state F'=2. The blow-away and probe lights correspond to the resonant transition frequencies from the ground state F=2 to F'=3. The Raman laser, one of the two Raman beams, corresponds to a blue detuning at the ground state F=2 to the excited state F'=3. Therefore, the laser frequency needs to change rapidly multiple times within one interference cycle.

[0003] Currently, the main methods for achieving laser frequency locking are using acousto-optic modulators to generate sidebands for laser frequency locking and changing the reference frequency of an optical phase-locked loop (PLL) for laser frequency locking. The acousto-optic modulator method typically involves sending the modulation frequency of the target output laser to a frequency-shifting end effector (EOM) to generate a phase modulation sideband, resulting in frequency hopping. When using an optical PLL for frequency locking, the laser's reference frequency is changed, causing the laser to jump in frequency and lock. Existing laser frequency locking methods typically disable the PID frequency lock of the already frequency-locked laser and then directly hop the frequency by changing the reference frequency. However, this method cannot quickly lock onto the new frequency after hopping and also suffers from insufficient laser frequency response speed and poor frequency locking stability. Summary of the Invention

[0004] The purpose of this invention is to provide a method for rapid laser frequency hopping and locking. This method stabilizes the laser frequency through frequency shifting (EOM) and modulation transfer, enabling rapid frequency locking. It features fast laser frequency hopping and locking speed and a large frequency hopping and locking range. This invention is particularly suitable for use in quantum interferometers and other atomic physics experiments requiring rapid laser frequency switching and locking.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention discloses a laser fast frequency hopping locking method. The laser output frequency changes accordingly by altering the laser's temperature setting. After each temperature change, a ramp voltage is used to rapidly scan the laser wavelength, recording the scanning voltage corresponding to the zero point of the current output laser frequency error signal. The laser tube temperature is continuously changed, and multiple sets of voltage values ​​corresponding to the zero points of the error signal at different laser output frequencies are recorded, achieving accurate measurement of the zero points of the error signal and the corresponding control voltage curves at different laser frequencies. The measured voltage-zero point curves of the error signal at different laser frequencies are subjected to polynomial fitting, with the fitting result being V = F(f). A laser frequency shift locking system is constructed using a frequency-shifting EOM and a modulation transfer frequency stabilization unit. The laser is locked to the +1 level sideband of the frequency-shifting EOM. By changing the driving frequency of the frequency-shifting EOM, the locking frequency of the laser output is changed, and the current frequency is locked by the modulation transfer frequency stabilization unit. The control voltage before frequency hopping is V1. First, the PID of the laser frequency shift locking system is unlocked, and then the EOM driving frequency is triggered to generate a change in the locking frequency Δf. The signal source frequency and EOM response time reach the microsecond level. Then, according to V... i =V i-1 +F(f+△f) controls the laser voltage change, and PID is enabled to achieve fast frequency locking.

[0007] Furthermore, based on the relationship between frequency and voltage V i =V i-1 After finding the zero point of the error signal at different frequencies using +F(f+△f), the point to be locked is automatically determined based on the scanning voltage and phase-locked error signal data, as well as the point-finding logic algorithm. The output value of the digital controller is then set to the voltage to be locked, and the digital PID is activated to achieve fast and automatic frequency hopping locking.

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

[0009] Furthermore, the signal source frequency and EOM response time used can reach the microsecond level, enabling rapid frequency switching.

[0010] This invention discloses a laser fast frequency hopping locking device for implementing the aforementioned laser fast frequency hopping locking method. The laser fast frequency hopping locking device mainly comprises a laser unit, an error signal unit, a frequency-shifting electro-optic modulator, a digital controller, an adder, and a high-speed feedback loop. The laser unit is connected to the frequency-shifting electro-optic 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 closed-loop laser frequency locking.

[0011] The laser unit consists of a laser to be locked and an optical 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 ADC and DAC convert the acquired signals into analog signals for acquisition and output of electrical signals. The digital control chip processes the acquired electrical signals, and the conditioning circuit amplifies and buffers the analog signals.

[0013] The error signal unit consists of an error signal conditioning module and a reference microwave source. The error signal conditioning module optimizes the acquired error signal, and the reference microwave source generates a standard signal reference with a locked frequency.

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

[0015] Beneficial effects:

[0016] 1. This invention discloses a laser fast frequency hopping locking method. The laser frequency is stabilized using a frequency-shifting EOM and modulation transfer frequency stabilization. Changing the laser tube temperature causes a corresponding change in the laser output frequency. The laser tube temperature is continuously changed, and simultaneously a signal generator produces a fast ramp voltage to scan the laser wavelength. The scanning voltage corresponding to the zero point of the frequency locking error signal is recorded on an oscilloscope. Multiple sets of zero-point voltage values ​​corresponding to the error signal under different laser tube temperatures are recorded. The measured voltage-frequency curve is fitted with a polynomial to obtain its relationship. During laser frequency hopping locking, a signal source controls the frequency-shifting EOM to change the laser frequency to be locked. Based on the calculated voltage-frequency curve, the laser voltage is directly changed to obtain the error signal, thus achieving fast laser frequency hopping locking. This method features fast laser frequency hopping locking speed and a 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 change of the laser diode by multiple measurements and fitting, thereby realizing the rapid frequency locking of the laser after frequency hopping.

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

[0019] 4. The laser fast frequency hopping locking method disclosed in this invention, based on the relationship between frequency and voltage V i =Vi-1 After finding the zero point of the error signal at different frequencies using +F(f+△f), the point to be locked is automatically determined based on the scanning voltage and phase-locked error signal data, as well as the point-finding logic algorithm. The output value of the digital controller is set to the voltage to be locked, and the PID frequency locking is enabled through the algorithm to achieve frequency locking stability after frequency hopping. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a laser fast frequency hopping locking method provided in an embodiment of the present invention. Detailed Implementation

[0021] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0022] Example 1:

[0023] like Figure 1 As shown in the figure, 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 stabilize, change the laser tube temperature to change the output laser frequency. After each temperature change and the laser frequency stabilizes, use a signal generator to generate a fast ramp voltage, scan the laser wavelength, and record the scanning voltage corresponding to the zero point of the error signal.

[0025] Step 2: The zero-point voltage-frequency curves of the error signal at different laser temperatures are obtained by polynomial fitting to obtain the corresponding curves of the zero-point voltage of the error signal and the laser frequency.

[0026] Step 3: Initiate laser voltage scanning. Input the laser signal during scanning into the frequency shift EOM and error signal unit to generate an error signal. Input the error signal and control voltage signal into the high-speed feedback loop for PID locking of the voltage corresponding to the zero point of the error signal. Feed this voltage value back to the laser control voltage 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 to be locked by the target switching frequency;

[0028] Step 5: Based on the fitted voltage-frequency curve, control the laser voltage to quickly follow the error signal to zero after frequency hopping. Repeat step 2 using the frequency locking algorithm, enable PID frequency locking, and complete the fast frequency hopping.

[0029] The voltage-frequency curve corresponding to the zero point of the error signal obtained by repeatedly measuring the temperature of the laser diode can be used as a reference for the laser to quickly lock, and can realize the rapid locking of the laser frequency after frequency hopping.

[0030] The signal source frequency and EOM response time used can reach the microsecond level, enabling rapid frequency switching;

[0031] After completing the rapid frequency jump and error signal zero-point finding, the PID frequency lock is enabled through the algorithm, which can continue to lock the frequency after frequency hopping, ensuring the frequency locking stability after the rapid frequency lock point switching.

[0032] This invention discloses a laser-based fast frequency hopping locking device, comprising a laser, an error signal unit, a frequency-shifting electro-optic modulator, a digital controller, an automatic locking algorithm, a high-speed feedback loop, and an adder. The error signal unit consists of an error signal conditioning module and a reference microwave source; the digital controller consists of a digital control chip, an ADC, a DAC, and conditioning circuits; the high-speed feedback loop consists of a bias circuit, a gain circuit, and multiple lead-lag circuits. This invention provides a method for achieving frequency hopping and fast locking using the relationship between the laser control voltage and the output frequency, while possessing advantages such as large frequency locking bandwidth, fast frequency hopping locking speed, and good frequency hopping locking stability.

[0033] Example 2:

[0034] like Figure 1 As shown in the figure, 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 diode of the laser to be locked to change the output frequency of the laser. After each temperature change, use a signal generator to scan the control voltage of the laser. At this time, the frequency of the laser 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 between the measured error signal zero-point voltage and the corresponding laser frequency to obtain the voltage-frequency polynomial fitting relationship.

[0037] Step 3: Start the voltage scanning of the laser, collect the zero point of the error signal generated by the scanning through the digital circuit, find the corresponding control voltage, and lock the target voltage using the high-speed feedback loop, thereby locking the frequency of the laser.

[0038] Step 4: Turn off the laser lock 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 scanning the error signal 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 frequency.

[0041] This embodiment discloses a laser fast frequency hopping locking device for implementing the aforementioned laser fast frequency hopping locking method. The laser fast frequency hopping locking device mainly comprises a laser unit, an error signal unit, a frequency-shifting electro-optic modulator, a digital controller, an adder, and a high-speed feedback loop. The laser unit is connected to the frequency-shifting electro-optic 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 closed-loop laser frequency locking.

[0042] The laser unit consists of a laser to be locked and an optical 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 ADC and DAC convert the acquired signals into analog signals for acquisition and output of electrical signals. The digital control chip processes the acquired electrical signals, and the conditioning circuit amplifies and buffers the analog signals.

[0044] The error signal unit consists of an error signal conditioning module and a reference microwave source. The error signal conditioning module optimizes the acquired error signal, and the reference microwave source generates a standard signal reference with a locked frequency.

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

[0046] Example 3:

[0047] This embodiment discloses a laser fast frequency hopping locking method. It uses a frequency-shifting electro-optic modulator (EOM) and modulation transfer frequency stabilization. A portion of the stabilized laser light is input into the frequency-shifting locking system via a beam splitting system. When the laser is locked to the +1 sideband of the frequency-shifting EOM, its frequency is stabilized at this sideband. Changing the frequency of the EOM will cause the locked laser frequency to change accordingly. Based on the laser's working principle, changing the laser tube temperature will correspondingly change the laser output frequency. By continuously changing the laser tube temperature while simultaneously generating a fast ramp voltage using a signal generator, the laser wavelength is scanned. The scanning voltage corresponding to the zero point of the frequency locking error signal is recorded on an oscilloscope. Recording multiple sets of zero-point voltage values ​​corresponding to different laser tube temperatures allows for accurate measurement of the laser frequency scanning curve. The measured voltage-frequency curve is then fitted using a polynomial to obtain its relationship. When performing laser frequency hopping lock, a signal source is used to control the frequency shifter EOM to change the frequency of the laser to be locked. Based on the calculated voltage and frequency curve, the laser voltage is directly controlled to change, thereby obtaining an error signal to achieve rapid laser frequency hopping lock.

[0048] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description 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 within 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 by altering the laser's temperature setting. After each temperature change, a ramp voltage is used to rapidly scan the laser wavelength, recording the scanning voltage corresponding to the zero point of the current output laser frequency error signal. The laser tube temperature is continuously changed, and multiple sets of voltage values ​​corresponding to the zero points of the error signal at different laser output frequencies are recorded, achieving precise measurement of the zero points of the error signal and the corresponding control voltage curves at different laser frequencies. The measured voltage-zero point curves of the error signal at different laser frequencies are subjected to polynomial fitting, resulting in V = F(f). A laser frequency shift locking system is constructed using a frequency-shifting EOM and a modulation transfer frequency stabilization unit. The laser is locked to the +1 level sideband of the frequency-shifting EOM. By changing the driving frequency of the frequency-shifting EOM, the locked frequency of the laser output is changed, and the current frequency is locked using the modulation transfer frequency stabilization unit. The control voltage before frequency hopping is V1. First, the PID of the locked laser frequency shift locking system is deactivated, then the EOM driving frequency is triggered to generate a change in the locked frequency Δf. The signal source frequency and EOM response time reach the microsecond level. Then, based on V... i =V i-1 +F(f+△f) controls the laser voltage change, and PID is enabled to achieve fast frequency locking.

2. The 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 based on the relationship between frequency and voltage, Vi=Vi-1+F(f+△f), the point to be locked is automatically determined based on the scanning voltage and phase-locked error signal data, as well as the point-finding logic algorithm; the output value of the digital controller is made to be locked voltage, and then the digital PID is turned on, which can realize fast automatic frequency hopping locking.

3. The laser fast frequency hopping locking method according to claim 1, characterized in that: The voltage-frequency curve corresponding to the zero point of the error signal obtained by repeatedly measuring the temperature of the laser diode can be used as a reference for the laser to quickly lock, and can realize the rapid locking of the laser frequency after frequency hopping.

4. The 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, enabling rapid frequency switching.

5. A laser fast frequency hopping locking device, used to implement a laser fast frequency hopping locking method as described in claim 1, 2, 3 or 4, characterized in that: It mainly consists of a laser unit, an error signal unit, a frequency-shifting electro-optic modulator, a digital controller, an adder, and a high-speed feedback loop. The laser unit is connected to the frequency-shifting electro-optic modulator to change the frequency lock point. The error signal unit is connected to the digital controller to modulate the control signal and find the control frequency lock point. The digital controller is connected to the adder to demodulate the signal to be locked. The adder is connected to the high-speed feedback loop to form a closed-loop laser frequency lock. The laser unit consists of a laser to be locked and an optical fiber beam splitter; 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 ADC and DAC convert the acquired signals into analog signals for acquisition and output of electrical signals. The digital control chip processes the acquired electrical signals, and the conditioning circuit amplifies and buffers the analog signals. The error signal unit consists of an error signal conditioning module and a reference microwave source. The error signal conditioning module optimizes the acquired error signal, and the reference microwave source generates a standard signal reference with a locked frequency. The high-speed feedback loop consists of a bias circuit, a gain circuit, and multiple lead and hysteresis circuits. The bias circuit is used to provide a bias current within a preset range to determine the static output operating point; the gain circuit is used to provide amplification capability for the electrical signal; and the lead-lag circuit is used to lock the control voltage.

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