A laser frequency stabilization device, method, and multi-stage laser frequency stabilization device

Abstract

The present invention provides a laser frequency stabilization device, a method and a multi-stage laser frequency stabilization device, which relate to the technical field of optical laser frequency stabilization. The device includes a sum-frequency component, a detection component and a frequency stabilization component; the sum-frequency component is used for performing sum-frequency operation on the obtained first laser and second laser to obtain the sum-frequency laser; the frequency stability of the first laser and the frequency stability of the second laser meet the preset frequency stability threshold range; the detection component is arranged on the optical path of the sum-frequency laser; the detection component is used for determining the frequency shift amount according to the difference between the central frequency of the sum-frequency laser and the central frequency of the obtained reference laser; the frequency stabilization component is connected with the detection component; the frequency stabilization component is used for adjusting the central frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain the target laser. The present invention reduces the requirements for the preparation conditions of the target laser and can improve the frequency stability of the laser to be frequency stabilized based on a laser light source with a relatively low frequency stability level.

Description

Technical Field

[0001] The present invention relates to the technical field of optical laser frequency stabilization, and more specifically, to a laser frequency stabilization device, method and multi-stage laser frequency stabilization device. Background Art

[0002] Ultra-stable lasers refer to lasers with extremely high optical frequency stability, which are widely used in precision measurement fields such as optical clocks, time-frequency transfer, gravitational wave detection, laser ranging, and fiber optic sensing. Currently, the main method for preparing ultra-stable lasers is to use the Pound-Drever-Hall (PDH) frequency stabilization technique to lock the laser to an ultra-stable optical reference cavity. The stability of the finally output laser frequency is affected by the working environment factors of the optical reference cavity and the noise of the frequency stabilization loop. At the same time, there is also a theoretical limit to the frequency stability of the optical reference cavity, which depends on the thermal noise level caused by the Brownian motion of atoms and molecules in the reference cavity material. Accordingly, the frequency stability of the corresponding frequency-stabilized laser is also limited by the thermal noise limit of the optical reference cavity. Therefore, in order to obtain ultra-stable lasers with a high frequency stability level, it is necessary to suppress the noise of the optical reference cavity and the loop noise.

[0003] To prepare an optical reference cavity with a low noise level, it is necessary to select a material with an extremely low coefficient of thermal expansion, a cavity length as long as possible, and at the same time control the stability of environmental factors such as the temperature, vacuum, and vibration of the optical reference cavity. For this purpose, it is necessary to configure a high-precision temperature control system, an ultra-high vacuum system, active and passive vibration isolation devices, etc. At the same time, it is also necessary to control the temperature fluctuation and ground vibration level of the overall working environment of the ultra-stable laser. At the same time, to reduce the loop noise, it is necessary to select a narrow linewidth laser, a photodetector with a low noise level, and an electronic servo system. At the same time, the optical reference cavity also needs to have as high a finesse as possible, and the reflectivity of the cavity mirror coating needs to reach about 99.999%.

[0004] It can be seen that in order to prepare ultra-stable lasers with high optical frequency stability, the requirements for the environment, components, and servo feedback system are extremely high. The overall system is extremely complex, the implementation difficulty is great, and the cost is high at the same time. Summary of the Invention

[0005] In view of this, the present invention provides a laser frequency stabilization device, method and multi-stage laser frequency stabilization device.

[0006] An aspect of the present invention provides a laser frequency stabilization device, comprising: a sum-frequency component, a detection component, and a frequency stabilization component; the sum-frequency component is configured to perform sum-frequency operation on the acquired first laser and second laser to obtain a sum-frequency laser; the frequency stability of the first laser and the frequency stability of the second laser satisfy a preset frequency stability threshold range; the detection component is disposed on the optical path of the sum-frequency laser; the detection component is configured to determine a frequency shift amount according to the difference between the central frequency of the sum-frequency laser and the central frequency of the acquired reference laser; the frequency stabilization component is connected to the detection component; the frequency stabilization component is configured to adjust the central frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain a target laser.

[0007] According to an embodiment of the present invention, the frequency stabilization component includes a frequency modulator and a first beam splitter; the frequency modulator is connected to the detection component and disposed on the optical path of the laser to be frequency stabilized; the frequency modulator is configured to adjust the central frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain an adjusted laser to be frequency stabilized; the first beam splitter is disposed on the optical path of the adjusted laser to be frequency stabilized; the first beam splitter is configured to divide the adjusted laser to be frequency stabilized into a first split laser and a second split laser, and determine the first split laser as the target laser when twice the central frequency of the first split laser is equal to the sum of the central frequency of the sum-frequency laser and the frequency shift amount.

[0008] According to an embodiment of the present invention, the device further includes a first optical sum-frequency device and a second beam splitter; the first optical sum-frequency device is disposed on the optical path of the second split laser; the first optical sum-frequency device is configured to perform frequency doubling operation on the second split laser to obtain a frequency-doubled laser to be frequency stabilized, and use the frequency-doubled laser to be frequency stabilized as the reference laser; the second beam splitter is disposed on the optical paths of the reference laser and the sum-frequency laser; the second beam splitter is configured to combine the reference laser and the sum-frequency laser to obtain a combined laser.

[0009] According to an embodiment of the present invention, the detection component includes a photodetector and a phase-locked loop; the photodetector is disposed on the optical path of the combined laser; the photodetector is configured to collect the combined laser and convert it into an electrical signal; the phase-locked loop is electrically connected to the photodetector; the phase-locked loop is configured to determine the difference between the central frequency of the reference laser and the central frequency of the sum-frequency laser according to the electrical signal.

[0010] According to an embodiment of the present invention, the detection component further includes a band-pass filter; the band-pass filter is disposed at the incident port of the photodetector; the combined laser passes through the band-pass filter and is incident on the photodetector.

[0011] According to an embodiment of the present invention, the above sum-frequency component includes a third beam splitter and a second optical sum-frequency device; the third beam splitter is disposed on the optical paths of the first laser and the second laser; the third beam splitter is configured to combine the first laser and the second laser to obtain a first combined laser; the second optical sum-frequency device is disposed on the optical path of the first combined laser; the second optical sum-frequency device is configured to perform sum-frequency operation on the first combined laser to obtain the sum-frequency laser.

[0012] Another aspect of the present invention provides a laser frequency stabilization method, including: performing sum-frequency operation on the acquired first laser and second laser to obtain a sum-frequency laser; the frequency stability of the first laser and the frequency stability of the second laser satisfy a preset frequency stability threshold range; determining a frequency shift amount according to the difference between the center frequency of the sum-frequency laser and the center frequency of the acquired reference laser; adjusting the center frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain a target laser.

[0013] According to an embodiment of the present invention, the adjusting the center frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain a target laser includes: adjusting the center frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain an adjusted laser to be frequency stabilized; splitting the adjusted laser to be frequency stabilized to obtain a first split laser and a second split laser; when twice the center frequency of the first split laser is equal to the sum of the center frequency of the sum-frequency laser and the frequency shift amount, determining the first split laser as the target laser.

[0014] According to an embodiment of the present invention, the method further includes: doubling the adjusted laser to be frequency stabilized and using the doubled laser to be frequency stabilized as a reference laser.

[0015] Another aspect of the present invention provides a multi-stage laser frequency stabilization device, including: N cascaded laser frequency stabilization devices as described above; N is a positive integer greater than or equal to 2.

[0016] According to an embodiment of the present invention, using a sum-frequency component to perform sum-frequency operation on a first laser and a second laser, using a detection component to determine the difference between the center frequency of the sum-frequency laser and the center frequency of a reference laser, thereby obtaining a frequency shift amount, and finally using a frequency stabilization component to adjust the center frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain a target laser. Compared with the technical problem of extremely high requirements for the environment, components, and servo feedback system in the prior art for preparing an ultra-stable laser with high optical frequency stability, the present invention uses a first laser and a second laser whose frequency stability satisfies a preset frequency stability threshold range, and obtains a target laser with relatively high frequency stability through a sum-frequency component, a detection component, and a frequency stabilization component, reduces the requirements for the preparation conditions of the target laser, and improves the frequency stability of the laser to be frequency stabilized. Description of the Drawings

[0017] Through the following description of the embodiments of the present invention with reference to the accompanying drawings, the above and other objects, features and advantages of the present invention will become clearer. In the drawings:

[0018] Figure 1 A schematic structural diagram of a laser frequency stabilization device according to an embodiment of the present invention is shown.

[0019] Figure 2 A schematic structural diagram of a beam splitter according to an embodiment of the present invention is shown.

[0020] Figure 3 A schematic structural diagram of a laser frequency stabilization device based on two lasers according to an embodiment of the present invention is shown.

[0021] Figure 4 A flowchart of a laser frequency stabilization method according to an embodiment of the present invention is shown.

[0022] Figure 5 A simplified schematic structural diagram of a laser frequency stabilization device based on two lasers according to an embodiment of the present invention is shown.

[0023] Figure 6 A schematic structural diagram of a multi-stage laser frequency stabilization device according to an embodiment of the present invention is shown.

[0024] Figure 7 A schematic diagram of an experimental device for verifying the frequency stability of a sum-frequency scheme according to an embodiment of the present invention is shown. Detailed Embodiments

[0025] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In the following detailed description, for the sake of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, it is obvious that one or more embodiments can be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concepts of the present invention.

[0026] The terms used herein are merely for describing specific embodiments and are not intended to limit the present invention. The terms "including", "comprising" and the like used herein indicate the presence of the described features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0027] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0028] In the case of using expressions such as "at least one of A, B, and C", generally, it should be interpreted according to the meaning that those skilled in the art usually understand this expression (for example, "a system having at least one of A, B, and C" should include but not be limited to a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0029] In the embodiments of the present invention, in aspects such as the collection, update, analysis, processing, use, transmission, provision, invention, storage, etc. of the involved data (for example, including but not limited to user personal information), they all comply with the provisions of relevant laws and regulations, are used for legal purposes, and do not violate public order and good customs. In particular, necessary measures are taken for user personal information to prevent illegal access to user personal information data and to safeguard user personal information security, network security, and national security.

[0030] In the embodiments of the present invention, before obtaining or collecting user personal information, the authorization or consent of the user is obtained.

[0031] Figure 1 A schematic structural diagram of a laser frequency stabilization device according to an embodiment of the present invention is shown.

[0032] As Figure 1 shown, the laser frequency stabilization device includes a sum - frequency component, a detection component, and a frequency stabilization component. The sum - frequency component is used to perform sum - frequency operation on the obtained first laser and second laser to obtain sum - frequency laser; the frequency stability of the first laser and the frequency stability of the second laser satisfy a preset frequency stability threshold range. The detection component is arranged on the optical path of the sum - frequency laser; the detection component is used to determine the frequency shift amount according to the difference between the center frequency of the sum - frequency laser and the center frequency of the obtained reference laser. The frequency stabilization component is connected to the detection component; the frequency stabilization component is used to adjust the center frequency of the laser to be frequency - stabilized according to the frequency shift amount to obtain the target laser.

[0033] According to the embodiments of the present invention, the sum - frequency component, based on the nonlinear optical effect, performs frequency conversion on two fundamental - frequency lasers with different frequencies through a nonlinear crystal to obtain sum - frequency laser output. The detection component detects the difference between the center frequencies of the reference laser and the sum - frequency laser, and the reference laser can be the laser obtained by doubling the center frequency of the laser to be frequency - stabilized after adjustment, thereby forming a closed - loop control circuit. By detecting the difference between the center frequencies of the sum - frequency laser and the reference laser by the detection component to determine the change amount, the frequency stabilization component adjusts the center frequency of the laser to be frequency - stabilized according to the change amount, so as to obtain the target laser.

[0034] According to an embodiment of the present disclosure, the relationship between the frequency stability of the first laser and the frequency stability of the second laser satisfies the following formula:

[0035] (1)

[0036] where σ 1 is the frequency stability of the first laser; σ 2 is the frequency stability of the second laser.

[0037] According to an embodiment of the present invention, the frequencies of the first laser and the second laser are close to each other, that is, the frequency difference between the frequency of the first laser and the frequency of the second laser is within a preset range, so that the first laser and the second laser can achieve sum frequency.

[0038] According to an embodiment of the present disclosure, the laser to be frequency stabilized can be a laser completely independent of the first laser and the second laser, or it can be the laser after the first laser is split or the laser after the second laser is split. However, the frequency of the laser to be frequency stabilized is close to the frequency of the first laser, and the frequency of the laser to be frequency stabilized is also close to the frequency of the second laser, that is, the difference between the frequency of the laser to be frequency stabilized and the frequency of the first laser is within the range of the first preset frequency difference threshold, and the difference between the frequency of the laser to be frequency stabilized and the frequency of the second laser is within the range of the second preset frequency difference threshold. According to an embodiment of the present disclosure, the laser to be frequency stabilized can also be a laser with a frequency stability close to that of the first laser and the second laser, that is, the frequency stability difference between the frequency stability of the laser to be frequency stabilized and the frequency stability of the first laser satisfies the first preset frequency stability difference threshold range, and the frequency stability difference between the frequency stability of the laser to be frequency stabilized and the frequency stability of the second laser satisfies the second preset frequency stability difference threshold range.

[0039] According to an embodiment of the present invention, the first laser and the second laser are subjected to sum frequency operation by using a sum frequency component, and a detection component is used to determine the difference between the central frequency of the laser after sum frequency and the central frequency of a reference laser, so as to obtain a frequency shift amount. Finally, a frequency stabilization component is used to adjust the central frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain a target laser. Compared with the technical problems of extremely high requirements for the environment, components, and servo feedback system in the prior art for preparing an ultra-stable laser with high optical frequency stability, the present invention uses the frequency stability of the first laser and the second laser whose frequency stability satisfies the preset frequency stability threshold range, and obtains a target laser with higher frequency stability through a sum frequency component, a detection component, and a frequency stabilization component, reduces the requirements for the preparation conditions of the target laser, reduces the overall complexity of the laser frequency stabilization device, reduces the implementation difficulty of the laser frequency stabilization device, reduces the cost of the laser frequency stabilization device, and improves the frequency stability of the laser to be frequency stabilized.

[0040] According to an embodiment of the present invention, the frequency stabilization component includes a frequency modulator and a first beam splitter. The frequency modulator is connected to the detection component and is disposed on the optical path of the laser to be frequency stabilized; the frequency modulator is configured to adjust the center frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain the adjusted laser to be frequency stabilized; the first beam splitter is disposed on the optical path of the adjusted laser to be frequency stabilized; the first beam splitter is configured to divide the adjusted laser to be frequency stabilized into a first split laser and a second split laser, and determine the first split laser as the target laser when twice the center frequency of the first split laser is equal to the sum of the center frequency of the sum-frequency laser and the frequency shift amount.

[0041] According to an embodiment of the present disclosure, the first beam splitter divides the adjusted laser to be frequency stabilized into a first split laser and a second split laser. The center frequencies of the first split laser and the second split laser are the same, and are also the same as the center frequency of the adjusted laser to be frequency stabilized. Either the first split laser or the second split laser can be used as the target laser.

[0042] According to an embodiment of the present invention, the laser to be frequency stabilized is input to the input end of the frequency modulator; the frequency modulator performs frequency shift on the laser to be frequency stabilized. The magnitude of the frequency shift is related to the signal fed back by the phase-locked loop, and the frequency of the output laser changes compared to the input laser.

[0043] According to an embodiment of the present invention, the laser frequency stabilization device further includes a first optical sum-frequency device and a second beam splitter; the first optical sum-frequency device is disposed on the optical path of the second split laser; the first optical sum-frequency device is configured to perform frequency doubling operation on the second split laser to obtain the frequency-doubled laser to be frequency stabilized, and use the frequency-doubled laser to be frequency stabilized as the reference laser; the second beam splitter is disposed on the optical path of the reference laser and the sum-frequency laser; the second beam splitter is configured to combine the reference laser and the sum-frequency laser to obtain the combined laser.

[0044] According to an embodiment of the present invention, the output light of the first optical sum-frequency device is input to the second port of the second beam splitter; after being combined with the input light of the first port of the second beam splitter, it is output to the photodetector through the third port of the second beam splitter. The first optical sum-frequency device directly performs frequency doubling on the input laser, that is, the laser performs sum-frequency with itself, aiming to generate a laser with a frequency close to the sum-frequency light of the second optical sum-frequency device, which is convenient for subsequent phase locking.

[0045] According to an embodiment of the present disclosure, the second beam splitter is disposed at the intersection of the optical path of the reference laser and the optical path of the sum-frequency laser, so as to realize the operation of combining the reference laser and the sum-frequency laser to obtain the combined laser.

[0046] According to an embodiment of the present invention, the detection component includes a photodetector and a phase-locked loop; the photodetector is arranged on the optical path of the laser after beam combination; the photodetector is used to collect the laser after beam combination and convert it into an electrical signal; the phase-locked loop is electrically connected to the photodetector; the phase-locked loop is used to determine the difference between the center frequency of the reference laser and the center frequency of the laser after sum frequency according to the electrical signal.

[0047] According to an embodiment of the present invention, the detection signal of the photodetector is input into the phase-locked loop, and the phase-locked loop outputs a modulation signal to the optical frequency modulator to achieve optical frequency stabilization. Finally, the target laser that completes optical frequency stabilization is output through the third port of the first beam splitter.

[0048] According to an embodiment of the present invention, the detection component further includes a band-pass filter; the band-pass filter is arranged at the incident port of the photodetector; the laser after beam combination is incident on the photodetector through the band-pass filter.

[0049] According to an embodiment of the present invention, the photodetector inputs an optical signal and outputs an electrical signal through a cable. It can only detect the sum-frequency optical signal output by the sum-frequency component and does not respond to the fundamental-frequency optical signal. This can be achieved by setting a band-pass filter at the incident port of the photodetector.

[0050] According to an embodiment of the present invention, the photodetector, the phase-locked loop, and the sum-frequency modulator are connected by a cable. Photodetectors of different models respond to light in different frequency bands, and generally detectors will be marked, and they do not respond to optical signals of other frequencies outside the marked range. This can be achieved by setting a band-pass filter at the incident port of the photodetector. The sum-frequency light refers to the newly generated laser after passing through the sum-frequency component, and the fundamental-frequency light refers to the input light that has passed through the sum-frequency component but has not participated in the sum frequency. Among them, the band-pass filter can be a filter with a wavelength of ±3 nm of the second harmonic light output by the sum-frequency component.

[0051] According to an embodiment of the present invention, the sum-frequency component includes a third beam splitter and a second optical sum-frequency device. The third beam splitter is arranged on the optical paths of the first laser and the second laser; the third beam splitter is used to perform a beam combination operation on the first laser and the second laser to obtain a first combined laser; the second optical sum-frequency device is arranged on the optical path of the first combined laser; the second optical sum-frequency device is used to perform a sum-frequency operation on the first combined laser to obtain a laser after sum frequency.

[0052] According to an embodiment of the present disclosure, the third beam splitter is arranged at the intersection of the optical path of the first laser and the optical path of the second laser, so as to be able to perform a beam combination operation on the first laser and the second laser to obtain a first combined laser.

[0053] According to an embodiment of the present invention, the structures of the first beam splitter, the second beam splitter, and the third beam splitter are all Figure 2 the shown beam splitter structure, such as Figure 2As shown, the beam splitter includes four ports. The first port A is the input port, the second port B is the input port, the third port C is the output port, and the fourth port D is the output port.

[0054] According to an embodiment of the present invention, the output light of the frequency modulator is connected to the second port B of the first beam splitter. After beam splitting is completed, one path of the split light is output through the third port C of the first beam splitter, and the other path of the split light is output through the fourth port D of the first beam splitter to the first optical sum-frequency device.

[0055] Figure 3 The structural schematic diagram of a laser frequency stabilization device based on two lasers according to an embodiment of the present invention is shown.

[0056] As Figure 3 As shown, the first laser and the second laser are incident on the sum-frequency component 301. The sum-frequency component 301 includes a third beam splitter and a second optical sum-frequency device. The first laser and the second laser are incident on the third beam splitter to combine the first laser and the second laser. The combined laser is incident on the second optical sum-frequency device. The second optical sum-frequency device performs a sum-frequency operation on the first laser and the second laser in the combined laser to obtain the sum-frequency laser, and the sum-frequency laser is incident on the second beam splitter.

[0057] The laser to be frequency stabilized is incident on the frequency stabilization component 302 for the first time. The frequency stabilization component 302 includes a frequency modulator and a first beam splitter. When the laser to be frequency stabilized is incident on the frequency modulator for the first time, there is a corresponding initial frequency shift amount. The frequency modulator frequency-modulates the laser to be frequency stabilized according to the initial frequency shift amount to obtain the adjusted laser to be frequency stabilized. The adjusted laser to be frequency stabilized is incident on the first beam splitter and is split into two beams. One beam of laser is emitted from the laser frequency stabilization device, and the other beam of laser is incident on the first optical sum-frequency device. The first optical sum-frequency device doubles the frequency of the incident other beam of laser to obtain the frequency-doubled laser, and the frequency-doubled laser is incident on the second beam splitter.

[0058] The sum-frequency laser and the frequency-doubled laser are combined through a second beam splitter to obtain a combined laser. The combined laser is incident on the detection component 303. The detection component 303 includes a photodetector and a phase-locked loop. The combined laser is incident on the photodetector, and the photodetector converts the combined laser into an electrical signal and transmits the electrical signal to the phase-locked loop; the phase-locked loop determines the difference between the center frequencies of the sum-frequency laser and the frequency-doubled laser based on the electrical signal, thereby determining the frequency shift amount. The frequency modulator continues to adjust the frequency of the laser to be frequency-stabilized according to the frequency shift amount to achieve closed-loop control. When twice the center frequency of the adjusted laser to be frequency-stabilized is equal to the sum of the center frequency of the sum-frequency laser and the frequency shift amount, the adjusted laser to be frequency-stabilized is incident on the first beam splitter. Since the center frequency of the adjusted laser to be frequency-stabilized is the same as the center frequencies of the two beams of laser emitted by the first beam splitter, that is, the center frequency of the adjusted laser to be frequency-stabilized is the same as the center frequencies of the first split laser and the second split laser, therefore, twice the center frequency of the adjusted laser to be frequency-stabilized is equal to the sum of the center frequency of the sum-frequency laser and the frequency shift amount, that is, twice the center frequency of the first split laser or the second split laser is equal to the sum of the center frequency of the sum-frequency laser and the frequency shift amount. One of the first split laser or the second split laser emitted from the first beam splitter is incident on the first optical sum-frequency device, and the other beam of laser is used as the target laser.

[0059] According to an embodiment of the present invention, the first laser is input into the first port A of the third beam splitter; the second laser is input into the second port B of the third beam splitter; after the third beam splitter combines the input light of the two ports, the light is output from the fourth port D of the third beam splitter to the second optical sum-frequency device. The sum-frequency light output by the second optical sum-frequency device is input into the first port A of the second beam splitter.

[0060] According to an embodiment of the present invention, when the laser to be frequency-stabilized is a laser independent of the first laser and the second laser, it means that the generation source of the laser to be frequency-stabilized has no correlation with the first laser and the second laser. For example, the laser to be frequency-stabilized is not generated by phase-locking, frequency doubling, etc. of the first laser or the second laser. The frequency of the output target laser × 2 = the frequency of the first laser + the frequency of the second laser + the phase-locked bias amount / 2, where the phase-locked bias amount is the frequency shift amount, and the frequencies of the first laser and the second laser cannot be too far apart, otherwise sum-frequency cannot be achieved. Therefore, the frequency of the output target laser is close to the frequencies of the first laser and the second laser.

[0061] An embodiment of the present invention provides a laser frequency stabilization method. Figure 4 The flowchart of a laser frequency stabilization method according to an embodiment of the present invention is shown. As Figure 4 shown, the method includes operation S401 to operation S403.

[0062] In operation S401, sum-frequency operation is performed on the acquired first laser and second laser to obtain a sum-frequency laser; the frequency stability of the first laser and the frequency stability of the second laser satisfy a preset frequency stability threshold range.

[0063] In operation S402, according to the difference between the central frequency of the sum-frequency laser and the central frequency of the acquired reference laser, the frequency shift amount is determined.

[0064] In operation S403, according to the frequency shift amount, the central frequency of the laser to be frequency-stabilized is adjusted to obtain a target laser.

[0065] According to an embodiment of the present invention, based on two laser light sources with similar frequency stabilities, the frequency stability of the output laser is improved. The central frequency of the sum-frequency laser can be the sum of the central frequencies of the first laser and the second laser. The frequency stability of the first laser and the frequency stability of the second laser are close to each other, and both the frequency stability of the first laser and the frequency stability of the second laser are within a preset frequency stability threshold range.

[0066] According to an embodiment of the present invention, the reference laser can be a preset laser, and the preset laser can be determined according to the actual situation. According to the difference between the central frequencies of the sum-frequency laser and the reference laser, the frequency shift amount is determined. According to the frequency shift amount, the value of the central frequency that the central frequency of the laser to be frequency-stabilized needs to be adjusted can be determined. By adjusting the central frequency of the laser to be frequency-stabilized according to the above value, a target laser can be obtained, wherein the frequency stability of the target laser is higher than the frequency stabilities of the first laser, the second laser, and the reference laser.

[0067] According to an embodiment of the present invention, sum-frequency operation is performed on the acquired first laser and second laser to obtain a sum-frequency laser; according to the difference between the central frequency of the sum-frequency laser and the central frequency of the acquired reference laser, the frequency shift amount is determined; according to the frequency shift amount, the central frequency of the laser to be frequency-stabilized is adjusted to obtain a target laser. Partially overcomes the technical problems of extremely high requirements for the environment, components, and servo feedback system for preparing an ultra-stable laser with high optical frequency stability, achieves reducing the requirements for the preparation conditions of the target laser, and can improve the frequency stability of the laser to be frequency-stabilized based on a laser light source with a relatively low frequency stability level.

[0068] According to an embodiment of the present invention, adjusting the central frequency of the laser to be frequency-stabilized according to the frequency shift amount to obtain a target laser includes: adjusting the central frequency of the laser to be frequency-stabilized according to the frequency shift amount to obtain an adjusted laser to be frequency-stabilized; splitting the adjusted laser to be frequency-stabilized to obtain a first split laser and a second split laser; when twice the central frequency of the first split laser is equal to the sum of the central frequency of the sum-frequency laser and the frequency shift amount, determining the first split laser as the target laser.

[0069] According to an embodiment of the present invention, according to the frequency shift amount, it can be determined that the center frequency of the laser to be frequency stabilized should be adjusted by the frequency shift amount / 2, so that twice the center frequency of the laser to be frequency stabilized after adjustment is equal to the sum of the center frequency of the laser after sum frequency and the frequency shift amount. This is because the laser after sum frequency is obtained by sum frequency of the first laser and the second laser, and the center frequency of the laser to be frequency stabilized is close to the center frequency of the first laser or the second laser. Therefore, the frequency shift amount / 2 should be adjusted.

[0070] According to an embodiment of the present invention, the laser frequency stabilization method further includes: doubling the frequency of the laser to be frequency stabilized after adjustment, and using the laser to be frequency stabilized after frequency doubling as the reference laser.

[0071] According to an embodiment of the present invention, the laser to be frequency stabilized is first split into two beams by a beam splitter. One of the split lasers to be frequency stabilized is frequency doubled and used as the reference laser to determine the frequency shift amount with the laser after sum frequency. According to the frequency shift amount, the center frequency of the laser to be frequency stabilized is adjusted, and then it is split into two beams again. One of them is frequency doubled and continues to determine a new frequency shift amount with the laser after sum frequency, and then the center frequency of the laser to be frequency stabilized is adjusted according to the new frequency shift amount until twice the center frequency of the laser to be frequency stabilized after adjustment is equal to the sum of the center frequency of the laser after sum frequency and the frequency shift amount. At this time, the laser to be frequency stabilized after adjustment is split into two beams. One of them is output as the target laser, and the other continues to be frequency doubled and used as the reference laser. The target laser is obtained through a feedback method.

[0072] According to an open embodiment of the present invention, a multi - stage laser frequency stabilization device includes N cascaded laser frequency stabilization devices as described above; N is a positive integer greater than or equal to 2.

[0073] Figure 5 FIG. shows a simplified structural schematic diagram of a laser frequency stabilization device based on two lasers according to an embodiment of the present invention.

[0074] As Figure 5 shown, the simplified structure of the laser frequency stabilization device based on two lasers includes three input ports and one output port; the three input ports are respectively the first laser input port, the second laser input port, the laser to be frequency stabilized input port, and the target laser output port. The frequency of the target laser is close to the frequency of the first laser and / or the second laser, that is, the difference between the frequency of the target laser and the frequency of the first laser and / or the second laser satisfies a preset frequency threshold range, and this frequency threshold range can be determined according to the actual situation. The multi - stage laser frequency stabilization device includes multiple cascaded laser frequency stabilization devices as Figure 5 shown.

[0075] Figure 6 FIG. shows a structural schematic diagram of a multi - stage laser frequency stabilization device according to an embodiment of the present invention.

[0076] As Figure 6As shown, since the input laser and the output laser of the laser frequency stabilization device belong to lasers with similar frequencies, the target laser output by the laser frequency stabilization device can be regarded as a separate laser, so that the output target laser can be used as the input of another laser frequency stabilization device, thereby realizing sum frequency among three or more ultra-stable lasers. Among them, the first laser frequency stabilization device, the second laser frequency stabilization device, …, the Nth laser frequency stabilization device are all the simplified structures of the laser frequency stabilization device based on two lasers as shown in Figure 5 the figure.

[0077] The input laser 1-1 is the first laser of the first laser frequency stabilization device, the input laser 2-1 is the first laser of the second laser frequency stabilization device, and so on. The input laser N-1 is the first laser of the Nth laser frequency stabilization device. The input laser 1-2 is the second laser of the first laser frequency stabilization device, the input laser 2-2 is the second laser of the second laser frequency stabilization device, and so on. The input laser N-2 is the second laser of the Nth laser frequency stabilization device. Among them, the first laser or the second laser of each laser frequency stabilization device can be the target laser output by the laser frequency stabilization device. For example, the input laser N-2 can be the target laser output by the (N - 1)th laser frequency stabilization device. When, among the N laser frequency stabilization devices, the first laser of a laser frequency stabilization device is the target laser output by the laser frequency stabilization device, the second laser can be a preset laser that meets the requirements of the laser frequency stabilization device for the second laser; when, among the N laser frequency stabilization devices, the second laser of a laser frequency stabilization device is the target laser output by the laser frequency stabilization device, the first laser can be a preset laser that meets the requirements of the laser frequency stabilization device for the first laser.

[0078] The input laser 1-3 is the laser to be frequency stabilized of the first laser frequency stabilization device, the input laser 2-3 is the laser to be frequency stabilized of the second laser frequency stabilization device, and so on. The input laser N-3 is the laser to be frequency stabilized of the Nth laser frequency stabilization device. The laser to be frequency stabilized can be the target laser output by the previous-stage laser frequency stabilization device cascaded with the current laser frequency stabilization device, or a preset laser that meets the conditions. For example, the input laser N-3 can be the target laser output by the (N - 1)th laser frequency stabilization device.

[0079] According to an embodiment of the present invention, one of the cascading methods of the multi-stage laser frequency stabilization device is as follows: The input laser 1-1 serves as the first laser of the first laser frequency stabilization device, the input laser 1-2 serves as the second laser of the first laser frequency stabilization device, the input laser 1-3 serves as the laser to be frequency stabilized of the first laser frequency stabilization device. After the first laser frequency stabilization device completes frequency stabilization, the output target is the first target laser. The first target laser serves as the input laser 2-2 of the second laser frequency stabilization device, and the input laser 2-2 serves as the second laser of the second laser frequency stabilization device. The input laser 2-1 serves as the first laser of the second laser frequency stabilization device, and the input laser 2-3 serves as the laser to be frequency stabilized of the second laser frequency stabilization device. The target laser output after the second laser frequency stabilization device completes frequency stabilization is the second target laser. The second target laser serves as the input laser 3-2, that is, the second laser of the third laser frequency stabilization device. By analogy, the target laser output after the N-1th laser frequency stabilization device completes frequency stabilization is the N-1th target laser. The N-1th target laser serves as the input laser N-2 of the Nth laser frequency stabilization device, that is, the second laser of the Nth laser frequency stabilization device. The input laser N-1 serves as the first laser of the Nth laser frequency stabilization device, and the input laser N-3 serves as the laser to be frequency stabilized of the Nth laser frequency stabilization device. The target laser output after the Nth laser frequency stabilization device completes frequency stabilization serves as the output of the multi-stage laser frequency stabilization device, thereby realizing the cascaded sum frequency of N ultra-stable lasers.

[0080] Figure 7 Fig. shows a schematic diagram of an experimental device for verifying the frequency stability of the sum frequency scheme according to an embodiment of the present invention.

[0081] As Figure 7 shown, on the basis of the laser frequency stabilization device based on two lasers shown in Figure 3 , a fourth beam splitter, a second photodetector, and a frequency counter are added. The description of the laser frequency stabilization device based on two lasers shown in Figure 3 will not be repeated here. Connect the target laser output by the laser frequency stabilization device to one input end of the fourth beam splitter, and connect the detection laser with a known frequency stability of to the other input end of the fourth beam splitter. After the two are combined, they are output from the output end of the fourth beam splitter to the second photodetector for verification. The measured electrical signal is band-pass filtered and then the frequency stability is measured by the frequency counter, and the frequency stability of the target laser output by the laser frequency stabilization device is .

[0082] Compared with the frequency stability after using a single laser to lock an ultra-stable cavity or the frequency stability after doubling the frequency of a single laser, the present invention can improve the frequency stability of the output laser by the method of sum frequency of two or more lasers. The corresponding physical principle is as follows:

[0083] Suppose the frequency stability of the ultra-stable laser i is as follows:

[0084]

[0085] In the formula, is the relative frequency stability of the ultra-stable laser i, is the change in the absolute frequency stability of the ultra-stable laser i, is the frequency of the ultra-stable laser i, , after the ultra-stable laser i is frequency-doubled alone, according to the law of conservation of energy, we have:

[0086]

[0087] In the formula, is the Planck constant, is the frequency of the ultra-stable laser i, is the frequency of the ultra-stable laser i after frequency doubling. The frequency of the ultra-stable laser i after frequency doubling is , and at this time, the frequency stability of the frequency-doubled light is:

[0088]

[0089] In the formula, is the relative frequency stability of the ultra-stable laser i, is the relative frequency stability of the ultra-stable laser i after frequency doubling, is the change in the absolute frequency stability of the ultra-stable laser i, is the change in the absolute frequency stability of the ultra-stable laser i after frequency doubling, that is, the frequency stability of the laser does not change after simple frequency doubling.

[0090] When i = 1, the first laser is the ultra-stable laser 1, and the frequency stability σ 1 is the relative frequency stability of the ultra-stable laser 1; when i = 2, the second laser is the ultra-stable laser 2, and the frequency stability σ 2 is the relative frequency stability of the ultra-stable laser 2. When two lasers that meet the preset frequency stability threshold range are sum-frequency mixed, when considering the first laser with a frequency of f 1 and the second laser with a frequency of f 2 after sum-frequency mixing through an optical sum-frequency mixer, we have:

[0091]

[0092] In the formula, is the frequency of the laser after sum-frequency mixing of the first laser and the second laser. The frequency stability of the laser after sum-frequency mixing is:

[0093]

[0094] In the formula, is the relative frequency stability of the sum-frequency laser. When the relative frequency stability of the first laser is close to that of the second laser, that is, when the relative frequency stability of the first laser is approximately equal to that of the second laser, and the frequency of the first laser is close to that of the second laser, that is , , and when the correlation between the first laser and the second laser is not strong, Equation (6) is:

[0095]

[0096] In the formula, is the correlation degree between the first laser and the second laser. If it is completely correlated, then , and if it is completely uncorrelated, then . It can be seen from Equation (4) and Equation (7) that when the frequencies of two ultra-stable lasers are close, the frequency stabilities are close, and the common-mode noise is small, the sum-frequency scheme can be used to generate an ultra-stable laser with a higher frequency stability. And it can be seen from Equation (4) that simple frequency doubling will not change the frequency stability of the laser. Therefore, without changing the laser frequency, the frequency stability of the output laser can theoretically reach the times of the stability of a single original input laser at the lowest.

[0097] When three or more laser frequency stabilization devices are cascaded for sum-frequency, the frequency stability of the input laser of each laser frequency stabilization device can be calculated separately using Equation (7). Therefore, when , where is the frequency stability of the input laser 1-1 of the first laser frequency stabilization device; is the frequency stability of the input laser 1-2 of the first laser frequency stabilization device. When the correlation between the first laser and the second laser is not strong, the highest frequency stability of the target laser output by the first laser frequency stabilization device is:

[0098] (8)

[0099] After inputting the target laser with the frequency stability shown in Equation (8) output by the first laser frequency stabilization device into the second laser frequency stabilization device and sum-frequencying it with the input laser 2-1, Equation (7) is also used for calculation. Therefore, when , where is the frequency stability of the input laser 2-1 of the second laser frequency stabilization device. When the target laser output by the first laser frequency stabilization device, the input laser 2-1, and the input laser 2-3 are not strongly correlated, the highest frequency stability of the target laser output after frequency stabilization by the second laser frequency stabilization device is:

[0100] (9)

[0101] By analogy, when N lasers are cascaded for sum frequency mixing, when (N = 2, 3, 4…), where is the frequency stability of the input laser N - 1 of the Nth laser frequency stabilization device, and when the correlation between the first laser, the second laser, and the laser to be frequency - stabilized of each laser frequency stabilization device is not strong, the frequency stability of the target laser output by the Nth laser frequency stabilization device can ultimately be achieved as:

[0102] (10)

[0103] In the formula, is the frequency stability of the target laser output after frequency stabilization by the (N - 1)th laser frequency stabilization device, is the frequency stability of the target laser output after frequency stabilization by the Nth laser frequency stabilization device, and has the highest frequency stability.

[0104] Therefore, without changing the laser frequency, N laser frequency stabilization devices can be cascaded, and the frequency stability of the output target laser can theoretically reach as low as times the frequency stability of the initially input first laser or second laser. Among them, the frequency stability refers to the stability of the laser relative frequency, and the smaller this value is, the higher the frequency stability of the output laser.

[0105] Compared with the frequency stability after using a single laser to lock an ultra - stable cavity in the prior art, the method of sum frequency mixing of two or more lasers can further improve the frequency stability of the output laser, enabling the requirements for the working environment, devices, frequency stabilization servo, etc. to be reduced under the premise of achieving the same frequency stability index, reducing the difficulty of preparing a single ultra - stable laser, and improving the system robustness. At the same time, it can reduce the cycle of environmental construction and device research and development, and reduce the related procurement, development, and maintenance costs.

[0106] The above describes the embodiments of the present invention. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Although the embodiments are described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination. Without departing from the scope of the present invention, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should all fall within the scope of the present invention.

Claims

1. A laser frequency stabilization device, characterized in that: The laser frequency stabilization device comprises a sum frequency component, a detection component and a frequency stabilization component; The sum frequency component is used to perform sum frequency operation on the acquired first laser and second laser to obtain sum frequency laser; the frequency stability of the first laser and the frequency stability of the second laser meet the preset frequency stability threshold range; The detection component is arranged on the optical path of the sum frequency laser; the detection component is used to determine the frequency shift amount according to the difference between the center frequency of the sum frequency laser and the center frequency of the acquired reference laser; The frequency stabilization component is connected to the detection component; the frequency stabilization component is used to adjust the center frequency of the laser to be stabilized according to the frequency shift amount to obtain the target laser; The frequency stabilization component includes a frequency modulator and a first beam splitter; The frequency modulator is connected to the detection component and is arranged on the optical path of the laser to be frequency stabilized; the frequency modulator is used to adjust the center frequency of the laser to be frequency stabilized according to the frequency shift amount to obtain the adjusted laser to be frequency stabilized; The first beam splitter is arranged on the optical path of the adjusted laser to be frequency-stabilized; the first beam splitter is used to split the adjusted laser to be frequency-stabilized into a first split laser and a second split laser, and when twice the center frequency of the first split laser is equal to the sum of the center frequency of the laser after sum frequency addition and the frequency shift amount, the first split laser is determined to be the target laser; The laser frequency stabilization device also includes a first optical frequency summator; The first optical frequency synthesizer is arranged on the optical path of the second split laser beam; the first optical frequency synthesizer is used to perform frequency doubling operation on the second split laser beam to obtain the frequency-doubled laser beam to be stabilized, and use the frequency-doubled laser beam to be stabilized as the reference laser beam.

2. The laser frequency stabilization device according to claim 1, characterized in that: The laser frequency stabilization device also includes a second beam splitter; The second beam splitter is arranged on the optical path of the reference laser and the sum frequency laser; the second beam splitter is used to combine the reference laser and the sum frequency laser to obtain the combined laser.

3. The laser frequency stabilization device according to claim 2, characterized in that: The detection component includes a photodetector and a phase lock; The photoelectric detector is arranged on the optical path of the combined laser beam; the photoelectric detector is used to collect the combined laser beam and convert it into an electrical signal; The phase lock is electrically connected to the photodetector; the phase lock is used to determine the difference between the center frequency of the reference laser and the center frequency of the sum-frequency laser according to the electrical signal.

4. The laser frequency stabilization device according to claim 3, characterized in that: The detection assembly also includes a bandpass filter; The bandpass filter is arranged at the incident port of the photodetector; the combined laser beam passes through the bandpass filter and is incident on the photodetector.

5. The laser frequency stabilization device according to claim 1, characterized in that: The sum frequency assembly includes a third beam splitter and a second optical sum frequency device; The third beam splitter is arranged on the optical paths of the first laser and the second laser; the third beam splitter is used to combine the first laser and the second laser to obtain a first combined laser; The second optical frequency summator is arranged on the optical path of the first combined laser beam; the second optical frequency summator is used for performing frequency summation operation on the first combined laser beam to obtain the frequency summation laser beam.

6. A laser frequency stabilization method, characterized in that: The method comprises: Performing a sum frequency operation on the acquired first laser and the second laser to obtain a sum frequency laser; the frequency stability of the first laser and the frequency stability of the second laser satisfy a preset frequency stability threshold range; Determine the frequency shift amount according to the difference between the center frequency of the laser after the sum frequency calculation and the center frequency of the reference laser obtained; The center frequency of the laser to be stabilized is adjusted according to the frequency shift amount to obtain a target laser; The step of adjusting the center frequency of the laser to be frequency-stabilized according to the frequency shift amount to obtain the target laser comprises: According to the frequency shift amount, the center frequency of the laser to be frequency stabilized is adjusted to obtain an adjusted laser to be frequency stabilized; Splitting the adjusted laser beam to be frequency-stabilized to obtain a first split laser beam and a second split laser beam; When twice the center frequency of the first split laser beam is equal to the sum of the center frequency of the sum-frequency laser beam and the frequency shift amount, determining that the first split laser beam is the target laser beam; The second split laser is frequency-doubled to obtain frequency-doubled laser to be stabilized, and the frequency-doubled laser to be stabilized is used as the reference laser.

7. A multi-stage laser frequency stabilization device, characterized in that: The multi-stage laser frequency stabilization device comprises N cascaded laser frequency stabilization devices according to any one of claims 1 to 5; N is a positive integer greater than or equal to 2.

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