Laser frequency locking method and device with wide working temperature range

Abstract

The invention discloses a laser frequency locking method and device with a wide working temperature range, and belongs to the field of atomic physics, quantum optics and precision measurement. The method comprises the following steps: up-converting an initial atomic spectrum signal into a high-frequency atomic spectrum signal by using a modulation method; a down-conversion mixer is used as a demodulator, reference signal input is an amplified high-frequency atomic spectrum signal, local oscillation signal input is a modulation signal, and intermediate frequency signal output is an error signal for frequency locking; the amplifier has relatively high gain and a 1dB compression point, and can still amplify the amplitude of a high-frequency atomic spectrum signal to be higher than the 1dB compression point of the frequency mixer when the initial atomic spectrum signal is changed due to the change of the environment temperature, at the moment, the down-conversion frequency mixer works in a nonlinear saturation region, and the output of an intermediate-frequency signal does not change along with the amplitude of a reference signal; and the size of the error signal does not change along with the fluctuation of the environment temperature, so that laser frequency locking in a wide working temperature range is realized. The invention has the advantages of circuit simplification, cost saving, device size reduction, power consumption reduction and the like.

Description

Technical Field

[0001] The invention belongs to the fields of atomic physics, quantum optics and precision measurement, and relates to the locking of laser frequency, and in particular to a laser frequency locking method and device with a wide operating temperature range. Background Art

[0002] Laser technology has been widely used in production, scientific research, military and national defense. In the fields of atomic physics, quantum optics and precision measurement, lasers with high-precision frequency locking are required to achieve the preparation, manipulation and detection of atomic states. Generally, the long-term stability of the laser frequency is required to be better than 1MHz. There are currently two common laser frequency stabilization references, atomic spectrum reference and optical cavity reference. For example, through Doppler absorption spectroscopy, saturated absorption spectroscopy, four-wave mixing spectroscopy, electromagnetically induced transparent spectroscopy and other technologies, the laser frequency can be locked to the corresponding energy level transition of the atom. The PDH (Pound-Drever-Hall) frequency stabilization method can also be used to stabilize the laser frequency to the resonance peak of the FP cavity (Fabry-Perot resonant cavity).

[0003] In the traditional atomic spectrum reference frequency stabilization method, because the temperature change of the atomic gas chamber will cause the change of the atomic spectrum signal, and then the amplitude or bias of the frequency locking error signal will change, affecting the stability of the laser frequency locking, so in order to improve the operating temperature range of the laser frequency locking, it is necessary to perform temperature feedback control on the atomic gas chamber to keep its temperature constant, which will make the circuit structure more complicated and significantly increase the volume, weight and power consumption. In addition, the temperature heating and cooling devices often generate interfering magnetic fields, which is not conducive to the design of the magnetic shielding structure of the atomic gas chamber. Summary of the invention

[0004] The purpose of the present invention is to provide a laser frequency locking method and device with a wide operating temperature range, which can realize high-precision and high-stability atomic spectrum reference laser frequency locking in a wide operating temperature range without applying temperature control to the atomic gas chamber. The present invention has the advantages of reducing the requirements for magnetic field interference shielding, simplifying the circuit, saving costs, reducing the size of the device, reducing the weight of the device and reducing power consumption.

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

[0006] The present invention discloses a laser frequency locking method with a wide operating temperature range, wherein a laser generates an atomic spectrum signal in an atomic gas chamber, and a modulation and demodulation module is used to convert the atomic spectrum signal into an error signal for laser frequency locking. A laser frequency locking method with a wide operating temperature range comprises the following steps:

[0007] Step 1: The laser generates an initial atomic spectrum signal in the atomic gas chamber, and the initial atomic spectrum signal can be converted into a high-frequency atomic spectrum signal using high-frequency modulation.

[0008] Step 2: Amplify the high-frequency atomic spectrum signal as the reference input signal of the down-conversion mixer, and the modulated signal as the local oscillator input signal. The two are mixed in the mixer, and the intermediate frequency output is used as the error signal for laser frequency locking.

[0009] Step 3: Taking advantage of the amplifier's high gain and 1dB compression point characteristics, when the ambient temperature changes causing the initial atomic spectrum signal to change, the amplifier output signal amplitude can still be higher than the mixer's 1dB compression point.

[0010] Step 4: Since the mixer is always operating in the nonlinear saturation region, the intermediate frequency signal output amplitude remains unchanged and no longer changes with the reference input amplitude, that is, the error signal does not change with the initial atomic spectrum signal.

[0011] Step 5: The error signal is connected to the laser and the laser frequency is locked. Because the mixer is always working in the nonlinear saturation region, when the initial atomic spectrum signal changes due to factors such as temperature, the intermediate frequency output, that is, the error signal, remains unchanged, thus achieving laser frequency locking in a wide operating temperature range.

[0012] Furthermore, the atomic gas chamber is not temperature controlled, and changes in the ambient temperature will cause changes in the gas chamber temperature, thereby causing changes in the initial atomic spectrum signal. The initial atomic spectrum signal is up-converted to a high frequency using a modulation method and amplified using an amplifier.

[0013] Furthermore, a down-conversion mixer is used as a demodulation device, the reference signal input is the amplified high-frequency atomic spectrum signal, the local oscillator signal input is the modulation signal, and the intermediate frequency signal output is the error signal for frequency locking.

[0014] Furthermore, the amplifier has a relatively high gain and 1 dB compression point, and can always amplify the high-frequency atomic spectrum signal to a level higher than the 1 dB compression point of the mixer when the external temperature changes.

[0015] Furthermore, the down-conversion mixer operates in a nonlinear saturation region, the intermediate frequency signal output does not change with the reference signal amplitude, and the error signal size does not change with temperature fluctuations, thereby achieving laser frequency locking in a wide operating temperature range.

[0016] Furthermore, the atomic gas chamber does not need to be temperature controlled, which greatly simplifies the magnetic shielding structure of the atomic gas chamber.

[0017] Furthermore, the type of atomic spectrum does not impose any limitation on the method of the present invention, as long as a mixer can be used as a demodulation device.

[0018] Furthermore, the modulation method for up-converting the atomic spectrum signal to a high frequency in the modulation and demodulation module will not limit the method of the present invention.

[0019] Furthermore, because the error signal is insensitive to changes in the initial atomic spectrum signal, the method of the present invention achieves a laser frequency locking effect and is also insensitive to laser power fluctuations.

[0020] The invention discloses a laser frequency locking device with a wide operating temperature range, which is used to implement a laser frequency locking method with a wide operating temperature range. A laser frequency locking device with a wide operating temperature range includes a laser, a feedback controller, an optical path module, and a modulation and demodulation module. The optical path module is composed of a first beam splitter, an atomic gas chamber, a second beam splitter, a first reflector, an electro-optical modulator, a second reflector, and a detector; the modulation and demodulation module is composed of a signal generator, a power divider, a shifter, a down-conversion mixer, and an amplifier.

[0021] In the optical path module, after the laser output laser enters the optical path module, it is divided into two laser beams at the first beam splitter, namely, the detection light and the pumping light. After the coupling light passes through the first reflector, the electro-optic modulator, and the second reflector, it is reflected by the second beam splitter and enters the atomic gas chamber. The detection light also passes through the atomic gas chamber and is reversely combined with the coupling light by adjusting the first reflector and the second reflector. After the detection light passes through the atomic gas chamber and passes through the second beam splitter, it hits the detector to obtain an atomic spectrum signal.

[0022] Furthermore, in the modulation and demodulation module, the signal generator outputs a modulation signal, which is divided into two parts by a power divider. One part drives the electro-optical modulator of the optical path module to up-convert the initial atomic spectrum signal into a high-frequency atomic spectrum signal. The other part is used as the local oscillator signal of the down-conversion mixer after passing through the term shifter. The high-frequency atomic spectrum signal output by the detector of the optical path module is amplified by the amplifier and used as the reference signal of the mixer. By adjusting the phase shift size of the term shifter, the shape of the intermediate frequency signal output by the mixer can be adjusted to obtain a suitable frequency locking error signal.

[0023] Furthermore, the mixer output error signal of the modulation and demodulation module is connected to the feedback controller, and the parameters of the feedback controller are adjusted to obtain the feedback control signal, which is transmitted to the laser. The laser output frequency is controlled by the feedback control signal so that it is locked to the zero point of the frequency locking error signal, thereby achieving laser frequency locking.

[0024] Furthermore, when the reference signal amplitude of the down-conversion mixer is higher than the 1dB compression point, the mixer operates in a nonlinear saturation region and the intermediate frequency signal output no longer changes with the reference signal amplitude. The output power 1dB compression point of the amplifier is much greater than the 1dB compression point of the mixer.

[0025] Furthermore, the output gain of the amplifier is relatively high, so that it can always amplify the high-frequency atomic spectrum signal to a level higher than the 1 dB compression point of the mixer when the external temperature changes. Furthermore, the error signal does not change with temperature fluctuations, that is, the laser frequency locking in a wide operating temperature range is achieved without applying temperature control measures to the atomic gas chamber.

[0026] Beneficial effects:

[0027] 1. The present invention discloses a laser frequency locking method and device with a wide operating temperature range. The method uses a modulation method to up-convert an initial atomic spectrum signal to a high-frequency atomic spectrum signal, and uses an amplifier to amplify the signal. A down-conversion mixer is used as a demodulation device, the reference signal input is the amplified high-frequency atomic spectrum signal, the local oscillator signal input is the modulation signal, and the intermediate frequency signal output is the error signal for frequency locking. The amplifier has a high gain and a 1dB compression point. When the ambient temperature changes and causes the initial atomic spectrum signal to change, the high-frequency atomic spectrum signal amplitude can still be amplified to a level higher than the 1dB compression point of the mixer. At this time, the down-conversion mixer operates in a nonlinear saturation region, and the intermediate frequency signal output does not change with the reference signal amplitude. Further, the error signal size does not change with ambient temperature fluctuations, thereby achieving laser frequency locking in a wide operating temperature range.

[0028] 2. The present invention discloses a laser frequency locking method and device with a wide operating temperature range. Since the error signal is insensitive to changes in the initial atomic spectrum signal, it is also insensitive to fluctuations in laser power. Stable laser frequency locking can be achieved without the need for atomic gas temperature control. Therefore, the present invention has the advantages of simplifying circuits, saving costs, and reducing device size, weight, and power consumption.

[0029] 3. The present invention discloses a laser frequency locking method and device with a wide operating temperature range. Since the error signal is insensitive to the fluctuation of the initial atomic spectrum signal, it is also insensitive to the fluctuation of the initial atomic spectrum signal caused by the laser power fluctuation, which helps to further improve the frequency locking accuracy or reduce the experimental conditions.

[0030] 4. The present invention discloses a laser frequency locking method and device with a wide operating temperature range. Because there is no influence of stray magnetic fields generated by temperature control devices, the magnetic field shielding scheme design of the atomic gas chamber can be simplified, and higher-performance magnetic field shielding can be achieved, which is helpful to further improve the frequency locking accuracy or reduce the experimental conditions.

[0031] 5. The present invention discloses a laser frequency locking method and device with a wide operating temperature range, which is not limited by the atomic spectrum type and modulation target. As long as the initial atomic spectrum signal can be up-converted to a high-frequency atomic spectrum signal and demodulated using a down-conversion mixer, the present invention can be applied to various types of atomic spectrum reference frequency locking schemes, thereby broadening the scope of application of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of a laser frequency locking device with a wide operating temperature range provided by an embodiment of the present invention.

[0033] Figure 2 The present invention provides a flow chart of a laser frequency locking method with a wide operating temperature range. DETAILED DESCRIPTION

[0034] 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.

[0035] Embodiment 1:

[0036] like Figure 2 As shown, the present embodiment discloses a laser frequency locking method with a wide operating temperature range, and the specific implementation steps are as follows:

[0037] Step 1: Turn on the laser to generate an initial atomic spectrum signal in the atomic gas chamber. Turn on the modulation and demodulation module to up-convert the initial atomic spectrum signal to a high-frequency atomic spectrum signal.

[0038] Step 2: After the high-frequency atomic spectrum signal is amplified, it is used as the reference input signal of the down-conversion mixer, and the modulation signal is used as the local oscillator input signal. The two are mixed in the mixer, and the intermediate frequency output is used as the error signal for laser frequency locking.

[0039] Step 3: The amplifier has a higher gain and 1dB compression point, so that when the ambient temperature changes and causes the initial atomic spectrum signal to change, the amplifier output signal amplitude can still be higher than the 1dB compression point of the mixer.

[0040] Step 4: Further make the mixer always work in the nonlinear saturation region, at this time the intermediate frequency signal output amplitude remains unchanged and no longer changes with the reference input amplitude, that is, the error signal does not change with the initial atomic spectrum signal.

[0041] Step 5: The error signal is connected to the laser and the laser frequency is locked. Because the mixer is always working in the nonlinear saturation region, when the initial atomic spectrum signal changes due to factors such as temperature, the intermediate frequency output, that is, the error signal, remains unchanged, thereby achieving laser frequency locking in a wide operating temperature range.

[0042] like Figure 1As shown, a laser frequency locking device with a wide operating temperature range disclosed in this embodiment is used to implement a laser frequency locking method with a wide operating temperature range. A laser frequency locking device with a wide operating temperature range includes a laser, a feedback controller, an optical path module, and a modulation and demodulation module. The optical path module is composed of a first beam splitter, an atomic gas chamber, a second beam splitter, a first reflector, an electro-optical modulator, a second reflector, and a detector; the modulation and demodulation module is composed of a signal generator, a power divider, a shifter, a down-conversion mixer, and an amplifier.

[0043] In the optical path module, after the laser output laser enters the optical path module, it is divided into two laser beams at the first beam splitter, namely, the detection light and the pumping light. After the coupling light passes through the first reflector, the electro-optic modulator, and the second reflector, it is reflected by the second beam splitter and enters the atomic gas chamber. The detection light also passes through the atomic gas chamber and is reversely combined with the coupling light by adjusting the first reflector and the second reflector. After the detection light passes through the atomic gas chamber and passes through the second beam splitter, it hits the detector to obtain an atomic spectrum signal.

[0044] In the modulation and demodulation module, the signal generator outputs a modulation signal, which is divided into two parts by a power divider. One part drives the electro-optical modulator of the optical path module to up-convert the initial atomic spectrum signal into a high-frequency atomic spectrum signal. The other part is used as the local oscillator signal of the down-conversion mixer after passing through the term shifter. The high-frequency atomic spectrum signal output by the detector of the optical path module is amplified by the amplifier and used as the reference signal of the mixer. By adjusting the phase shift size of the term shifter, the shape of the intermediate frequency signal output by the mixer can be adjusted to obtain a suitable frequency locking error signal.

[0045] The mixer output error signal of the modulation and demodulation module is connected to the feedback controller. The feedback control signal can be obtained by adjusting the parameters of the feedback controller and transmitted to the laser. The laser output frequency can be controlled to lock it to the zero point of the frequency locking error signal, that is, the laser frequency is locked.

[0046] The mixer is used as a demodulation device. When the amplitude of the reference signal of the down-conversion mixer is higher than the 1dB compression point, the mixer works in a nonlinear saturation region, and the intermediate frequency signal output no longer changes with the amplitude of the reference signal.

[0047] The output power 1dB compression point of the amplifier is much greater than the 1dB compression point of the mixer.

[0048] The output gain of the amplifier is high, so that it can always amplify the high-frequency atomic spectrum signal to a level higher than the 1dB compression point of the mixer when the external temperature changes. Furthermore, the error signal size does not change with temperature fluctuations, that is, the laser frequency locking of the atomic gas chamber without temperature control is achieved.

[0049] The atomic gas chamber does not need to be temperature controlled, thus reducing circuit complexity, volume, weight, and power consumption, and simplifying the design of the atomic gas chamber magnetic shielding structure.

[0050] The modulation signal may be selected at a higher frequency, such as 10 MHz, so that the selection of the mixer and the amplifier is more convenient and universal.

[0051] The type of atomic spectrum does not impose any limitation on the method of the present invention. As long as a mixer can be used as a demodulation device, the applicable conditions of this embodiment are met.

[0052] The modulation method for up-converting the atomic spectrum signal to a high frequency in the modulation and demodulation module will not limit the method of this embodiment.

[0053] Because the error signal is insensitive to changes in the initial atomic spectrum signal, the method of this embodiment achieves a laser frequency locking effect and is also insensitive to laser power fluctuations.

[0054] Embodiment 2:

[0055] like Figure 1 As shown, a schematic diagram of a laser frequency locking device with a wide operating temperature range disclosed in this embodiment includes a laser, a feedback controller, an optical path module, and a modulation and demodulation module. The optical path module is composed of a first beam splitter, an atomic gas chamber, a second beam splitter, a first reflector, an electro-optical modulator, a second reflector, and a detector; the modulation and demodulation module is composed of a signal generator, a power divider, a shifter, a down-conversion mixer, and an amplifier.

[0056] The laser output wavelength is 780nm and the power is 20mW. After the laser enters the optical path module, it is divided into two laser beams at the first beam splitter, namely the detection light and the pumping light, which are 5mW and 15mW respectively. After the coupling light passes through the first reflector, the electro-optic modulator, and the second reflector, it is reflected by the second beam splitter and enters the atomic gas chamber. The gas chamber is filled with saturated vapor of alkali metal rubidium atoms, and the vapor pressure changes with the temperature of the gas chamber. The detection light also passes through the atomic gas chamber, and is reversely combined with the coupling light by adjusting the first reflector and the second reflector. After passing through the atomic gas chamber, the detection light passes through the second beam splitter and hits the detector, where an atomic spectrum signal up-converted to high frequency is obtained. The bandwidth of the detector is required to be greater than 10MHz.

[0057] The signal generator outputs a 10MHz modulated signal, which is divided into two parts by the power divider. One part drives the electro-optic modulator of the optical path module to make the laser generate phase modulation. The driving power can be adjusted appropriately to make the modulation strongest, so that the initial saturated absorption atomic spectrum signal is up-converted to a high-frequency modulation transfer atomic spectrum signal. The other part is used as the mixer local oscillator signal after passing through the term shifter. The high-frequency atomic spectrum signal output by the detector is amplified by the amplifier and used as the mixer reference signal. By adjusting the phase shift of the term shifter, the shape of the mixer intermediate frequency signal output can be adjusted to obtain a suitable frequency locking error signal.

[0058] The frequency-locking error signal is connected to the feedback controller. By adjusting the parameters of the feedback controller, a feedback control signal can be obtained and transmitted to the laser. The laser output frequency can be controlled so that it is locked to the zero point of the frequency-locking error signal, thereby achieving laser frequency locking.

[0059] The 1dB compression point of the mixer is 7dBm. When the mixing reference signal is less than 7dBm, the reference signal amplitude increases, and the intermediate frequency signal amplitude increases almost linearly. However, when the mixing reference signal is greater than 7dBm, the mixer begins to enter the nonlinear saturation region, and the intermediate frequency signal amplitude no longer changes with the reference signal amplitude, showing an obvious saturation output effect. The amplifier gain is 40dB, and the output power 1dB compression point is 17dBm, which is 10dB higher than the mixer 1dB compression point.

[0060] Because the atomic gas chamber is not temperature controlled, its temperature will change with the external temperature. For the alkali metal Rb87 atoms, when the temperature changes from 0 degrees to 40 degrees, the atomic number density in the atomic gas chamber changes by about 20dB, which is much smaller than the amplifier gain of 40dB. By adjusting the experimental parameters reasonably, the high-frequency atomic spectrum signal amplified by the amplifier, or the mixer reference input signal, can be kept greater than the mixer's 1dB compression point throughout the entire temperature range. The intermediate frequency output signal, that is, the error signal, does not change with temperature fluctuations, and high-precision and high-stability laser frequency locking with a wide operating temperature range can be achieved without the need to impose temperature control measures on the atomic gas chamber.

[0061] 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 locking method with a wide operating temperature range, characterized in that: The laser generates an atomic spectrum signal in the atomic gas chamber, and a modulation and demodulation module is used to convert the atomic spectrum signal into an error signal for laser frequency locking; the steps include: Step 1: The laser generates an initial atomic spectrum signal in the atomic gas chamber, and the initial atomic spectrum signal can be converted into a high-frequency atomic spectrum signal using high-frequency modulation; Step 2: Amplify the high-frequency atomic spectrum signal as the reference input signal of the down-conversion mixer, and the modulated signal as the local oscillator input signal. The two are mixed in the mixer, and the intermediate frequency output is used as the error signal for laser frequency locking; Step 3: Using the characteristics of the amplifier with high gain and 1dB compression point, when the ambient temperature changes and causes the initial atomic spectrum signal to change, the amplifier output signal amplitude can still be higher than the 1dB compression point of the mixer; Step 4: Since the mixer is always working in the nonlinear saturation region, the output amplitude of the intermediate frequency signal remains unchanged and no longer changes with the reference input amplitude, that is, the error signal does not change with the initial atomic spectrum signal; Step 5: The error signal is connected to the laser and the laser frequency is locked. Since the mixer is always operating in the nonlinear saturation region, when factors such as temperature cause the initial atomic spectrum signal to change, the intermediate frequency output, i.e. the error signal, remains unchanged, thus achieving laser frequency locking in a wide operating temperature range.

2. A laser frequency locking method with a wide operating temperature range according to claim 1, characterized in that: The down-conversion mixer operates in a nonlinear saturation region, the intermediate frequency signal output does not change with the reference signal amplitude, and the error signal size does not change with temperature fluctuations, thereby achieving laser frequency locking in a wide operating temperature range.

3. The laser frequency locking method with a wide operating temperature range according to claim 1, characterized in that: The atomic gas chamber does not need to be temperature controlled, which greatly simplifies the magnetic shielding structure of the atomic gas chamber.

4. A laser frequency locking device with a wide operating temperature range, used to implement a laser frequency locking method with a wide operating temperature range as claimed in claim 1, 2 or 3, characterized in that: It includes a laser, a feedback controller, an optical path module, and a modulation and demodulation module; the optical path module is composed of a first beam splitter, an atomic gas chamber, a second beam splitter, a first reflector, an electro-optical modulator, a second reflector, and a detector; the modulation and demodulation module is composed of a signal generator, a power divider, a shifter, a down-conversion mixer, and an amplifier; In the optical path module, after the laser output laser enters the optical path module, it is divided into two laser beams at the first beam splitter, namely, the detection light and the pumping light. After the coupling light passes through the first reflector, the electro-optic modulator, and the second reflector, it is reflected by the second beam splitter and enters the atomic gas chamber. The detection light also passes through the atomic gas chamber and is reversely combined with the coupling light by adjusting the first reflector and the second reflector. After the detection light passes through the atomic gas chamber and passes through the second beam splitter, it hits the detector to obtain an atomic spectrum signal.

5. A laser frequency locking device with a wide operating temperature range according to claim 4, characterized in that: In the modulation and demodulation module, the signal generator outputs a modulation signal, which is divided into two parts by a power divider. One part drives the electro-optical modulator of the optical path module to up-convert the initial atomic spectrum signal into a high-frequency atomic spectrum signal; the other part is used as the local oscillator signal of the down-conversion mixer after passing through the term shifter; the high-frequency atomic spectrum signal output by the detector of the optical path module is amplified by the amplifier and used as the reference signal of the mixer, and the phase shift size of the term shifter is adjusted, and the shape of the intermediate frequency signal output of the mixer is adjusted to obtain a suitable frequency locking error signal.

6. A laser frequency locking device with a wide operating temperature range according to claim 5, characterized in that: The mixer output error signal of the modulation and demodulation module is connected to the feedback controller, and the parameters of the feedback controller are adjusted to obtain the feedback control signal, which is transmitted to the laser. The laser output laser frequency is controlled by the feedback control signal so that it is locked to the zero point of the frequency locking error signal, thereby achieving laser frequency locking.

7. The laser frequency locking device with a wide operating temperature range according to claim 6, characterized in that: The mixer is used as a demodulation device. When the amplitude of the reference signal of the down-conversion mixer is higher than the 1dB compression point, the mixer operates in a nonlinear saturation region, and the intermediate frequency signal output no longer changes with the reference signal amplitude; the output power 1dB compression point of the amplifier is much greater than the 1dB compression point of the mixer.

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