Laser frequency stabilization device for locking optical path of adjustable optical resonant cavity

Abstract

The invention provides a laser frequency stabilization device capable of locking an optical path of an adjustable optical resonant cavity. The laser frequency stabilization device comprises a laser, the optical resonant cavity, an optical path controller, an optical modulator, a radio frequency signal source and a photoelectric detector, the optical path controller can control the optical path of the optical resonant cavity. Wherein the radio frequency signal source is configured to generate a first signal, a second signal and a third signal. A first signal is input to the light modulator, and laser output by the light modulator is input to the input end of the optical resonant cavity; the photoelectric detector is connected with the output end of the optical resonant cavity and converts an output optical signal into an electric signal; the second signal is used for generating a first control signal together with the first path of electric signal, so that the laser frequency output by the laser is locked on a first target locking frequency; and the third signal is used for generating a second control signal together with the second path of electric signal, so that the free spectral path of the optical resonant cavity is locked on a second target locking frequency.

Description

Technical Field

[0001] The present invention relates to a laser frequency stabilization device for locking and adjusting the optical path of an optical resonator, and particularly relates to technical fields such as laser mode locking, laser modulation, and integrated optics. Background Art

[0002] Narrow-linewidth and frequency-stable laser light sources have important applications in fields such as quantum computing and quantum precision measurement. Locking the laser frequency to a stable reference source can achieve laser frequency locking and linewidth compression. To stabilize the laser frequency, a stable reference source needs to be found, such as an optical resonator with a stable optical path (abbreviated as an optical cavity). One solution in the prior art is to select an ultra-stable cavity made of a material with a low thermal expansion rate as the reference source. However, this solution requires an environmental maintenance system such as vacuum, vibration isolation, and heat insulation, with high technical requirements and high costs. Another solution is to use an adjustable FP cavity (Fabry-Perot cavity) whose optical path can be locked to an atomic / molecular absorption line. However, this solution requires an additional molecular / atomic vapor chamber, also with high technical requirements, and the atomic / molecular spectral lines are generally wide, resulting in poor optical path locking accuracy. There is also a solution in the prior art that uses an active feedback method to stabilize the optical path of the optical cavity. As shown in Figure 1 , the laser output by the laser passes through a phase modulator and a polarization state controller, and is input from the second port of the optical circulator to the FP cavity. The transmitted light output of the FP cavity is detected by an optical power meter. The reflected light signal of the FP cavity returns to the second port of the optical circulator and is received by an optical detector connected to the third port. The optical detector converts the optical signal into an electrical signal; using a single additional radio frequency source, the radio frequency signal is mixed with the electrical signal converted by the above optical detector through a phase shifter to obtain an error signal, which is filtered by a low-pass filter and fed back to the FP cavity by a servo circuit, thereby locking the optical path of the FP cavity to the frequency of the laser. In the above solution, a radio frequency source is used to lock the optical path of the FP cavity using the frequency of the laser. However, the frequency of the laser itself is unstable and is easily affected by current and temperature, prone to drift. Therefore, the locked optical path of the FP cavity is also unstable. Summary of the Invention

[0003] Based on the deficiencies of the prior art, the present invention proposes a laser frequency stabilization scheme based on the adjustable optical cavity optical path, which can simultaneously achieve laser linewidth compression and central frequency stability. The present invention uses a radio frequency signal to modulate the laser, and locks two frequency components of the laser to two resonance peaks of the optical cavity respectively. Thus, the stability of the free spectral range of the optical cavity is determined by the stability of the radio frequency signal, and the stability of the laser frequency is also determined by the stability of the radio frequency signal. Specifically, the laser frequency stabilization device of the present invention includes: a laser, an optical resonator, an optical path controller, an optical modulator, a radio frequency signal source, and a photodetector; the optical path controller is capable of controlling the optical path of the optical resonator. Among them, the radio frequency signal source is configured to generate a first signal, a second signal, and a third signal, and among them, the first signal is input to the optical modulator, the optical modulator modulates the laser emitted by the laser, and the laser output by the optical modulator is input to the input end of the optical resonator; the photodetector is connected to the output end of the optical resonator and converts the output optical signal into an electrical signal, and the electrical signal is divided into two paths; the second signal is used to generate a first control signal together with the first path of electrical signal generated by the photodetector, and the first control signal is input to the laser, so that the laser frequency output by the laser is locked to the first target locking frequency; the third signal is used to generate a second control signal together with the second path of electrical signal generated by the photodetector, and the second control signal is input to the optical path controller, and the optical path controller changes the optical path of the optical resonator according to the second control signal, so that the free spectral range of the optical resonator is locked to the second target locking frequency.

[0004] It should be noted that the optical path of the optical resonator in the present invention can be adjusted, including fiber optic ring cavities, fiber optic Fabry-Perot cavities, micro-ring cavities, etc. The optical path controller can adjust the optical path of the resonator by changing the cavity length of the resonator or the refractive index in the resonator. In the present invention, the input end and the output end of the optical resonator can be the same port or different ports. When they are the same port, the photodetector receives the reflected signal of the resonator, and when they are different ports, the photodetector receives the transmitted signal of the resonator.

[0005] Further, the optical modulator is a first electro-optic modulator, the first signal is a composite signal, the composite signal includes a first radio frequency frequency and a second radio frequency frequency, and the first radio frequency frequency is an integer multiple of the free spectral range of the optical resonator; the frequency of the second signal is the second radio frequency frequency; the frequency of the third signal is an integer multiple of the difference between the first radio frequency frequency and the second radio frequency frequency or an integer multiple of the sum of the first radio frequency frequency and the second radio frequency frequency.

[0006] The first target locking frequency is N1·Δν, where N1 is an integer and Δν is the free spectral range of the optical resonator; and

[0007] The second target locking frequency is f1 / M1, where M1 is an integer and f1 is the first radio frequency frequency.

[0008] Further, the first target locking signal is input to the first mixer via a first phase shifter, the first electrical signal is input to the first mixer, the output end of the first mixer is connected to a first low-pass filter, the output end of the first low-pass filter is connected to a first PID controller, and the output end of the first PID controller is connected to the laser, and the first control signal is generated by the first PID controller.

[0009] Further, a second signal is input to the first mixer via a first phase shifter, a first electrical signal is input to the first mixer, the output end of the first mixer is connected to a first low-pass filter, the output end of the first low-pass filter is connected to a first PID controller, the output end of the first PID controller is connected to the laser, and the first PID controller generates a first control signal.

[0010] Further, a third signal is input to the second mixer via a second phase shifter, a second electrical signal is input to the second mixer, the output end of the second mixer is connected to a second low-pass filter, the output end of the second low-pass filter is connected to a second PID controller, the output end of the second PID controller is connected to an optical path controller, and the second PID controller generates a second control signal.

[0011] Further, the RF signal source includes a first RF source and a second RF source, wherein the first RF source outputs a first RF signal having a first RF frequency, the second RF source outputs a second RF signal having a second RF frequency, and wherein the first RF signal and the second RF signal are combined and generate a first signal; the second RF signal outputs the RF signal source as a second signal; the first RF signal and the second RF signal are mixed and filtered to generate a third signal.

[0012] According to another aspect of the present invention, a laser frequency stabilization device is provided, which includes a laser, an optical resonator, an optical path controller, a radio frequency signal source, a first optical modulator, a second optical modulator, a third optical modulator, a first photodetector and a second photodetector; the radio frequency signal source is configured to generate a first signal, a second signal and a third signal; the optical path controller can control the optical path of the optical resonator. The output light of the laser is divided into two paths. The first path of laser is incident on the first end of the optical resonator through the first optical modulator. The first photodetector is connected to the second end of the optical resonator to detect the output light from the second end and convert the optical signal into a first electrical signal; the second path of laser is incident on the second end of the optical resonator after passing through the second optical modulator. The second photodetector is connected to the first end of the optical resonator to detect the output light from the first end and convert the optical signal into a second electrical signal; and a third optical modulator is further provided on either the first path of laser or the second path of laser. The first signal, the second signal and the third signal are respectively input into the first optical modulator, the second optical modulator and the third optical modulator. The first optical modulator modulates the first path of laser output by the laser, and the output end of the first optical modulator is connected to the first end of the optical resonator; the second optical modulator modulates the second path of laser output by the laser and transmits the modulated second path of laser to the second end of the optical resonator. The third optical modulator is serially connected to the first optical modulator to modulate the first path of laser, or serially connected to the second optical modulator to modulate the second path of laser. The first electrical signal is used to generate a first control signal together with the first signal, and the first control signal is input into the laser, so that the laser frequency output by the laser is locked at a first target locking frequency. The second electrical signal is used to generate a second control signal together with the second signal, and the second control signal is input into the optical path controller. The optical path controller changes the optical path of the optical resonator according to the second control signal, so that the free spectral range of the optical resonator is locked at a second target locking frequency.

[0013] It should be noted that in the present invention, the photodetector can not only be configured to receive transmitted optical signals, but also be configured to receive reflected optical signals. Specifically, the output light of the laser is divided into two paths. The first path of laser light is incident on the first end of the optical resonator through the first optical modulator. The first photodetector is connected to the first end of the optical resonator to detect the output light from the first end and convert the optical signal into a first electrical signal. The second path of laser light is incident on the second end of the optical resonator after passing through the third optical modulator and the second optical modulator. The second photodetector is connected to the second end of the optical resonator to detect the output light from the second end and convert the optical signal into a second electrical signal. The first radio frequency signal, the second radio frequency signal, and the third radio frequency signal are respectively used as the first modulation signal, the second modulation signal, and the third modulation signal, and are respectively input into the first optical modulator, the second optical modulator, and the third optical modulator. The first optical modulator modulates the first path of laser light, and the output end of the first optical modulator is connected to the first end of the optical resonator. The third optical modulator and the second optical modulator sequentially modulate the second path of laser light. The output end of the third optical modulator is connected to the input end of the second optical modulator, and the output end of the second optical modulator is connected to the second end of the optical resonator. A first control signal is generated from the first electrical signal and the first signal, and the first control signal is input into the laser, so that the laser frequency output by the laser is locked at the first target locking frequency. A second control signal is generated from the second electrical signal and the second signal, and the second control signal is input into the optical path controller. The optical path controller changes the optical path of the optical resonator according to the second control signal, so that the free spectral range of the optical resonator is locked at the second target locking frequency.

[0014] It should be noted that in the present invention, the third optical modulator can not only be placed in the second optical path, but also be placed in the first optical path. Further, the first optical modulator is a first electro-optic modulator, the second optical modulator is a second electro-optic modulator, and the third optical modulator is an acousto-optic modulator or a third electro-optic modulator. The frequency of the first signal is the first radio frequency, the frequency of the second signal is the second radio frequency, and the frequency of the third signal is the third radio frequency. The third radio frequency is an integer multiple of the free spectral range of the optical resonator.

[0015] Further, the first target locking frequency is N2, where N2 is an integer and is the free spectral range of the optical resonator. The second target locking frequency is f3 / M2, where M2 is an integer and f3 is the third radio frequency.

[0016] Further, the first signal is input to the first mixer via the first phase shifter, the first electrical signal is input to the first mixer, the output terminal of the first mixer is connected to the first low-pass filter, the output terminal of the first low-pass filter is connected to the first PID controller, the output terminal of the first PID controller is connected to the laser, and the first PID controller generates a first control signal.

[0017] Further, the second signal is input to the second mixer via the second phase shifter, the second electrical signal is input to the second mixer, the output terminal of the second mixer is connected to the second low-pass filter, the output terminal of the second low-pass filter is connected to the second PID controller, the output terminal of the second PID controller is connected to the optical path controller, and the second PID controller generates a second control signal.

[0018] Further, the RF signal source includes a first RF source, a second RF source, and a third RF source. The first RF source outputs a first RF signal having a first RF frequency, the second RF source outputs a second RF signal having a second RF frequency, and the third RF source outputs a third RF signal having a third RF frequency. And the first RF signal is output as the first signal from the RF signal source; the second RF signal is output as the second signal from the RF signal source; the third RF signal is output as the third signal from the RF signal source. Description of the Drawings

[0019] Figure 1 is an optical path diagram of the prior art using a single RF source to lock the optical path of the FP cavity.

[0020] Figure 2 is a schematic structural diagram of the laser frequency stabilization device according to an embodiment of the present invention.

[0021] Figure 3 is Figure 2 a schematic structural diagram of the further-expanded RF signal source in the shown laser frequency stabilization device.

[0022] Figure 4 is a schematic structural diagram of the laser frequency stabilization device according to another embodiment of the present invention. Detailed Embodiments

[0023] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the following further elaborates on the present invention in conjunction with specific embodiments and with reference to the accompanying drawings of the specification. It should be noted that in the drawings or the description of the specification, similar or identical parts are denoted by the same reference numerals. Implementations not depicted or described in the drawings are well-known to those of ordinary skill in the relevant technical field. Additionally, although the embodiments provide examples of parameters including specific values, it should be understood that the parameters need not exactly equal the corresponding values, but may approximate the corresponding values within an acceptable error tolerance or design constraint. When describing the present invention, the "optical resonator" in the optical path is generally abbreviated as the "optical cavity" or "cavity", which is well-known and common practice for those skilled in the art.

[0024] In the following embodiments of the present invention, an optical fiber ring cavity is adopted as the optical resonator. It should be noted that this choice does not limit the present invention. The present invention is also applicable to resonators such as fiber-based FP cavities and micro-ring cavities fabricated using micro-nano processing technologies, that is, it is applicable to fiber-based resonators or micro-ring cavities fabricated using micro-nano processing technologies. Using a fiber-based resonator can be compatible with an all-fiber solution and is easy to integrate; using a micro-ring cavity fabricated using micro-nano processing technologies can further increase the integration level.

[0025] Embodiment 1:

[0026] Figure 2 The structural schematic diagram of the laser frequency stabilization device described in Embodiment 1 of the present application is shown. Referring to Figure 2 as shown, the device includes a laser, an optical resonator 2, an optical path controller 18, an optical modulator 3, a radio frequency signal source 31, and a photodetector 4; the optical path controller 18 can control the optical path of the optical resonator 2; wherein the radio frequency signal source 31 is configured to generate a first signal, a second signal, and a third signal, and wherein, the first signal is input to the optical modulator 3, the optical modulator 3 modulates the laser emitted by the laser 1, and the laser output from the optical modulator 3 is input to the input end of the optical resonator 2; the photodetector 4 is connected to the output end of the optical resonator 2 and converts the output optical signal into an electrical signal, and the electrical signal is divided into two paths; the second signal is used to generate a first control signal together with the first path of electrical signal generated by the photodetector 4, and the first control signal is input to the laser 1, so that the laser frequency output by the laser 1 is locked at a first target locking frequency; the third signal is used to generate a second control signal together with the second path of electrical signal generated by the photodetector 4, and the second control signal is input to the optical path controller 18, and the optical path controller 18 changes the optical path of the optical resonator 2 according to the second control signal, so that the free spectral range of the optical resonator 2 is locked at a second target locking frequency.

[0027] Further, referring to Figure 2As shown, the optical modulator 3 is the first electro-optic modulator 3, the first signal is a composite signal, the composite signal includes a first radio frequency and a second radio frequency, and the first radio frequency is an integer multiple of the free spectral range of the optical resonator 2; the frequency of the second signal is the second radio frequency; the frequency of the third signal is an integer multiple of the difference between the first radio frequency and the second radio frequency or an integer multiple of the sum of the first radio frequency and the second radio frequency.

[0028] Further, the first target locking frequency is N1·Δν, where N1 is an integer and Δν is the free spectral range of the optical resonator; and the second target locking frequency is f1 / M1, where M1 is an integer and f1 is the first radio frequency. Δν is the free spectral range of the optical resonator 2

[0029] In addition, further reference Figure 2 As shown, the second signal is input to the first mixer 11 through the first phase shifter 10, the first electrical signal is input to the first mixer 11, the output end of the first mixer 11 is connected to the first low-pass filter 12, the output end of the first low-pass filter 12 is connected to the first PID controller 13, and the output end of the first PID controller 13 is connected to the laser 1. The first PID controller 13 generates a first control signal.

[0030] Further, the third signal is input to the second mixer 15 through the second phase shifter 14, the second electrical signal is input to the second mixer 15, the output end of the second mixer 15 is connected to the second low-pass filter 16, the output end of the second low-pass filter 16 is connected to the second PID controller 17, and the output end of the second PID controller 17 is connected to the optical path controller 18. The second PID controller 17 generates a second control signal.

[0031] Further, reference Figure 2 and Figure 3 As shown, the radio frequency signal source 31 includes a first radio frequency source 5 and a second radio frequency source 6, where the first radio frequency source 5 outputs a first radio frequency signal with a first radio frequency, the second radio frequency source 6 outputs a second radio frequency signal with a second radio frequency, and the first radio frequency signal and the second radio frequency signal are combined and generate a first signal; the second radio frequency signal is output as the second signal from the radio frequency signal source 31; the first radio frequency signal and the second radio frequency signal are mixed and filtered to generate a third signal.

[0032] Specifically refer to Figure 2 and Figure 3As shown in the figure, in this embodiment, an independent first radio frequency source 5 and a second radio frequency source 6 are used. An adder 7 and a multiplier 8 respectively generate a composite signal (i.e., the first signal) and a signal with a frequency of |f1 - f2| (i.e., the third signal, whose frequency can also be an integer multiple of the difference between f1 and f2, or an integer multiple of the sum of f1 and f2). The second radio frequency source 6 also outputs another signal (i.e., the second signal) to a mixer 11 via a phase shifter 10. In this embodiment, the three signals are not limited to being generated by several radio frequency sources. They can be generated by one, two, or three radio frequency sources, nor is it limited by what method to obtain the three signals. The signals with the frequencies of these paths can be directly generated by the radio frequency sources, or can be obtained through components such as adders and multipliers. As Figure 2 shown, a radio frequency signal source 31 generates the above three signals. Figure 2 In the other reference numerals in the figure except for the reference numeral 31 are the same as those in Figure 3 All are the same, and the same reference numerals refer to the same components. The radio frequency signal source 31 can be any wave generator that generates three signals: a composite signal (i.e., the first signal) containing two frequencies f1 and f2, a signal with a frequency of |f1 - f2| (i.e., the third signal, whose frequency can also be an integer multiple of the difference between f1 and f2, or an integer multiple of the sum of f1 and f2), and a signal with a frequency of f2 (i.e., the second signal). The radio frequency signal source 31 can include two radio frequency sources, and in this case, it is Embodiment 1. The radio frequency signal source 31 can also include three radio frequency sources, and each radio frequency source respectively generates a composite signal containing two frequencies f1 and f2, a signal with a frequency of |f1 - f2|, and a signal with a frequency of f2.

[0033] Thus, an independent first radio frequency source 5 and a second radio frequency source 6 are used to respectively generate radio frequency signals RF1 and RF2 with frequencies of f1 and f2. The radio frequency signals RF1 and RF2 are added by an adder 7 to obtain a composite signal, which contains two frequencies f1 and f2. The composite signal is input to an electro-optic modulator EOM3 to perform phase modulation on the laser output by a laser 1. The laser light field after double-frequency modulation can be expressed as:

[0034]

[0035] where is the laser light field before modulation, E0 is the light field amplitude, f0 is the initial frequency, β1 and β2 are the amplitudes of the modulation signals respectively, and J is the Bessel function. It can be seen from the above formula that the laser light field after double-frequency modulation will generate sideband components with an initial frequency interval of nf1 + mf2, where n and m are both integers.

[0036] The laser output by the laser 1 is input to the optical resonator 2 after being modulated by the EOM 3. There is an optical path controller 18 on the optical resonator 2, which can control the optical path of the optical resonator 2. The optical path controller 18 can be a piezoelectric ceramic, or an electro-optic modulation device, or a magneto-optic modulation device, or an acousto-optic modulation device integrated in the optical resonator 2, etc. The frequency locking method of this embodiment must require that the frequency f1 of the radio frequency signal RF1 is an integer multiple of the free spectral range (FSR) of the optical resonator, that is, f1 = K·Δν, where K is an integer and Δν is the free spectral range of the optical resonator 2. This is easy to implement, and only the radio frequency of the first radio frequency source 5 needs to be independently adjusted. The output end of the optical resonator 2 is connected to the photodetector 4, and the photodetector 4 converts the optical signal output by the optical resonator 2 into an electrical signal. The output of the photodetector 4 is divided into two paths. One path is input to the multiplier 11, mixed with the radio frequency signal output from the second radio frequency source 6 and phase-shifted by the phase shifter 10, and then filtered by the low-pass filter 12 to obtain an error signal, which is the component with the frequency f2 in the electrical signal. The error signal is input to the PID controller 13, and the gain adjustment of the PID controller 13 obtains a control signal and inputs it to the laser 1, so that the laser 1 is locked at the first target locking frequency, where the first target locking frequency is N1·Δν, where N1 is an integer and Δν is the free spectral range of the optical resonator.

[0037] The radio frequency signals RF1 and RF2 are mixed by the multiplier 8 and then filtered by the low-pass filter 9 to obtain a radio frequency signal with the frequency |f1 - f2|. The radio frequency signal is phase-shifted by the phase shifter 14 and then input to the multiplier 15 together with the second path signal output by the photodetector 4 for mixing, and then filtered by the low-pass filter 16 to obtain an error signal, which is the component with the frequency |f1 - f2| in the electrical signal. The error signal is input to the PID controller 17, and the gain adjustment of the PID controller 17 obtains a control signal and inputs it to the optical path controller 18. The optical path controller 18 adjusts the optical path of the optical resonator 2 to lock the free spectral range of the optical resonator 2 at the second target locking frequency, where the second target locking frequency is f1 / M1, where M1 is an integer and f1 is the first radio frequency.

[0038] Embodiment 2:

[0039] Embodiment 2 uses an optical path different from that of Embodiment 1. The laser to be frequency-locked is divided into two paths and incident from both ends of the optical resonator 2 respectively. The specific optical path construction is as Figure 4 shown.

[0040] The laser beam emitted by the laser 1 is split into two paths. The first path is phase-modulated by the electro-optic modulator EOM23 and then enters the input end A of the optical resonator 2 through the polarization beam splitter 27, forming optical path 1. The second path is phase-modulated by the acousto-optic modulator AOM19 and the electro-optic modulator EOM3 and then enters from the other end B of the optical resonator 2 through the polarization beam splitter 26, forming optical path 2. On optical path 1, the first radio frequency source 5 generates a radio frequency signal RF1 with a frequency of f1 and inputs it to the EOM23 to phase-modulate the laser beam output by the laser 1. The modulated laser optical field can be expressed as:

[0041]

[0042] where is the laser optical field before modulation, E0 is the optical field amplitude, f0 is the initial frequency, β1 is the amplitude of the modulation signal, and J is the Bessel function. It can be seen from the above formula that the modulated laser optical field will generate sideband components with a frequency interval of nf1 from the initial frequency, where n is an integer.

[0043] On optical path 2, the third radio frequency source 20 generates a radio frequency signal RF3 with a frequency of f3, which is input to AOM19. AOM19 is used to frequency shift the laser output by laser 1, and after frequency shifting, frequency components of f0 + f3 are generated. The second radio frequency source 6 generates a radio frequency signal RF2 with a frequency of f2, which is input to EOM3. EOM3 is used to phase modulate the frequency-shifted laser, and after modulation, frequency components of f0 + f3 + mf2 and f0 + f3 - mf2 are generated, where m is an integer. In this embodiment, it is required that the frequency f3 of the radio frequency signal RF3 is an integer multiple of the free spectral range of the optical resonator. The photodetector PD1, as indicated by reference numeral 24, is placed on one side of the input end B of the optical resonator 2 to detect the output signal input to the optical resonator 2 via optical path 1. The photodetector PD1 converts the optical signal into an electrical signal, which is input to the multiplier 29, mixed with the radio frequency signal output from the first radio frequency source 5 and phase shifted by the phase shifter 28, and then filtered by the low-pass filter 12 to obtain an error signal. This error signal is the component with a frequency of f1 in the electrical signal. The error signal is input to the PID controller 13, and after the gain adjustment of the PID controller 13, a control signal is input to laser 1, so that the output frequency of laser 1 is locked at N2·Δν, where N2 is an integer and Δν is the free spectral range of the optical resonator. The photodetector PD2, as indicated by reference numeral 25, is placed on one side of the input end A of the optical resonator 2 to detect the output signal input to the optical resonator 2 via optical path 2. The photodetector PD2 converts the optical signal into an electrical signal, which is input to the multiplier 15, mixed with the radio frequency signal output from the second radio frequency source 6 and phase shifted by the phase shifter 30, and then an error signal is obtained after passing through the low-pass filter 16. This error signal is the component with a frequency of f2 in the electrical signal. The error signal is input to the PID controller 17, and after the gain adjustment of the PID controller 17, a control signal is input to the optical path controller 18. The optical path controller 18 adjusts the optical path of the optical resonator 2 to lock the free spectral range of the optical resonator 2 at f3 / M2, where M2 is an integer.

[0044] In this embodiment, a polarization beam splitter PBS is used as the beam splitting element, but this does not limit the present disclosure. Other types of beam splitting elements such as optical fiber circulators and wavelength division multiplexers can also be used.

[0045] In this embodiment, an acousto-optic modulator AOM19 is used as the frequency shift element on optical path 2. In addition, an electro-optic modulator can also be used as the frequency shift element.

[0046] Embodiment Three:

[0047] In the second embodiment, an independent first radio frequency source 5, a second radio frequency source 6, and a third radio frequency source 20 are used to generate three radio frequency signals respectively. In this embodiment, the three signals are not limited to be generated by several radio frequency sources. They can be generated by one, two, or three radio frequency sources, nor is it limited by what method to obtain the three signals. Among them, the radio frequency signal source is similar to the radio frequency signal source 31 in Figure 2 and Figure 3 and generates three signals. The three signals are respectively input into the EOM 23, EOM 3, and AOM 19, and the specific optical path diagram is not shown again.

[0048] In addition, preferably, in the present invention, the optical resonator 2 can be, for example, an optical ring resonator.

[0049] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A laser frequency stabilization device, characterized in that: It includes a laser (1), an optical resonator (2), an optical path controller (18), an optical modulator (3), a radio frequency signal source (31), and a photodetector (4); the optical path controller (18) is capable of controlling the optical path of the optical resonator (2). Wherein the radio frequency signal source (31) is configured to generate a first signal, a second signal, and a third signal, and wherein the first signal is input to the optical modulator (3), the optical modulator (3) modulates the laser emitted by the laser (1), and the laser output from the optical modulator (3) is input to the input end of the optical resonator (2); the photodetector (4) is connected to the output end of the optical resonator (2) and converts the output optical signal into an electrical signal, and the electrical signal is divided into two paths. The second signal is used to generate a first control signal together with the first-path electrical signal generated by the photodetector (4), and the first control signal is input to the laser (1) so that the laser frequency output by the laser (1) is locked at a first target locking frequency. The third signal is used to generate a second control signal together with the second-path electrical signal generated by the photodetector (4), the second control signal is input to the optical path controller (18), and the optical path controller (18) changes the optical path of the optical resonator (2) according to the second control signal so that the free spectral range of the optical resonator (2) is locked at a second target locking frequency.

2. The laser frequency stabilization device according to claim 1, wherein: The optical modulator (3) is a first electro-optic modulator (3), the first signal is a composite signal, the composite signal includes a first radio frequency and a second radio frequency, and the first radio frequency is an integer multiple of the free spectral range of the optical resonator (2); the frequency of the second signal is the second radio frequency; the frequency of the third signal is an integer multiple of the difference between the first radio frequency and the second radio frequency or an integer multiple of the sum of the first radio frequency and the second radio frequency.

3. The laser frequency stabilization device according to claim 2, wherein the first target locking frequency is N1·Δν, where N1 is an integer and Δν is the free spectral range of the optical resonator; and the second target locking frequency is f1 / M1, where M1 is an integer and f1 is the first radio frequency.

4. The laser frequency stabilization device according to claim 3, characterized in that: The second signal is input to the first mixer (11) through a first phase shifter (10), the first-path electrical signal is input to the first mixer (11), the output end of the first mixer (11) is connected to a first low-pass filter (12), the output end of the first low-pass filter (12) is connected to a first PID controller (13), the output end of the first PID controller (13) is connected to the laser (1), and the first PID controller (13) generates the first control signal.

5. The laser frequency stabilization device according to claim 3, wherein: The third signal is input to the second mixer (15) via the second phase shifter (14), the second electrical signal is input to the second mixer (15), the output end of the second mixer (15) is connected to the second low-pass filter (16), the output end of the second low-pass filter (16) is connected to the second PID controller (17), the output end of the second PID controller (17) is connected to the optical path controller (18), and the second PID controller (17) generates the second control signal.

6. The laser frequency stabilization device according to any one of claims 1-5, characterized in that, The radio frequency signal source (31) includes a first radio frequency source (5) and a second radio frequency source (6), wherein the first radio frequency source (5) outputs a first radio frequency signal having a first radio frequency, the second radio frequency source (6) outputs a second radio frequency signal having a second radio frequency, and wherein the first radio frequency signal and the second radio frequency signal are combined and generate the first signal; the second radio frequency signal is output from the radio frequency signal source (31) as the second signal; the first radio frequency signal and the second radio frequency signal are mixed and filtered to generate the third signal.

7. A laser frequency stabilization device, characterized in that: It includes a laser (1), an optical resonator (2), an optical path controller (18), a radio frequency signal source, a first optical modulator (23), a second optical modulator (3), a third optical modulator (19), a first photodetector (24) and a second photodetector (25); the radio frequency signal source is configured to generate a first signal, a second signal and a third signal; the optical path controller (18) can control the optical path of the optical resonator (2); The output light of the laser (1) is divided into two paths. The first path of laser light is incident on the first end of the optical resonator (2) via the first optical modulator (23). The first photodetector (24) is connected to the second end of the optical resonator (2) to detect the output light from the second end and convert the optical signal into a first electrical signal; the second path of laser light is incident on the second end of the optical resonator (2) after passing through the second optical modulator (3). The second photodetector (25) is connected to the first end of the optical resonator (2) to detect the output light from the first end and convert the optical signal into a second electrical signal; and, the third optical modulator (19) is also provided on either the first path of laser light or the second path of laser light; The first signal, the second signal and the third signal are respectively input to the first optical modulator (23), the second optical modulator (3) and the third optical modulator (19). The first optical modulator (23) modulates the first path of laser light output by the laser (1), and the output end of the first optical modulator (23) is connected to the first end of the optical resonator (2); the second optical modulator (3) modulates the second path of laser light output by the laser (1) and transmits the modulated second path of laser light to the second end of the optical resonator (2); The third optical modulator (19) is serially connected to the first optical modulator (23) to modulate the first laser beam, or serially connected to the second optical modulator (3) to modulate the second laser beam; The first electrical signal is used to generate a first control signal together with the first signal, and the first control signal is input to the laser (1) so that the laser frequency output by the laser (1) is locked at a first target locking frequency; The second electrical signal is used to generate a second control signal together with the second signal, and the second control signal is input to the optical path controller (18). The optical path controller (18) changes the optical path of the optical resonator (2) according to the second control signal so that the free spectral range of the optical resonator (2) is locked at a second target locking frequency.

8. The laser frequency stabilization device according to claim 7, wherein: The first optical modulator (23) is a first electro-optic modulator, the second optical modulator (3) is a second electro-optic modulator, and the third optical modulator (19) is an acousto-optic modulator or a third electro-optic modulator; the frequency of the first signal is a first radio frequency, the frequency of the second signal is a second radio frequency, the frequency of the third signal is a third radio frequency, and the third radio frequency is an integer multiple of the free spectral range of the optical resonator (2).

9. The laser frequency stabilization device according to claim 8, characterized in that: The first target locking frequency is N2·Δν, where N2 is an integer and Δν is the free spectral range of the optical resonator (2); the second target locking frequency is f3 / M2, where M2 is an integer and f3 is the third radio frequency.

10. The laser frequency stabilization device according to claim 9, wherein: The first signal is input to the first mixer (29) via the first phase shifter (28), the first electrical signal is input to the first mixer (29), the output end of the first mixer (29) is connected to the first low-pass filter (12), the output end of the first low-pass filter (12) is connected to the first PID controller (13), the output end of the first PID controller (13) is connected to the laser (1), and the first PID controller (13) generates the first control signal.

11. The laser frequency stabilization device according to claim 9, characterized in that: The second signal is input to the second mixer (15) via the second phase shifter (30), the second electrical signal is input to the second mixer (15), the output end of the second mixer (15) is connected to the second low-pass filter (16), the output end of the second low-pass filter (16) is connected to the second PID controller (17), the output end of the second PID controller (17) is connected to the optical path controller (18), and the second PID controller (17) generates the second control signal.

12. The laser frequency stabilization device according to any one of claims 7-11, characterized in that: The radio frequency signal source includes a first radio frequency source (5), a second radio frequency source (6), and a third radio frequency source (20), wherein the first radio frequency source (5) outputs a first radio frequency signal having a first radio frequency, the second radio frequency source (6) outputs a second radio frequency signal having a second radio frequency, the third radio frequency source (20) outputs a third radio frequency signal having a third radio frequency, and wherein the first radio frequency signal outputs the radio frequency signal source as the first signal; the second radio frequency signal outputs the radio frequency signal source as the second signal; the third radio frequency signal outputs the radio frequency signal source as the third signal.

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