Laser frequency stabilization device and method and multistage laser frequency stabilization device

Abstract

The invention provides a laser frequency stabilization device and method and a multistage laser frequency stabilization device, and relates to the technical field of optical laser frequency stabilization. The device comprises a sum frequency assembly, a detection assembly and a frequency stabilization assembly. The sum frequency assembly is used for performing sum frequency operation on the obtained first laser and second laser to obtain laser after sum frequency; the frequency stability of the first laser and the frequency stability of the second laser meet a preset frequency stability threshold range; the detection assembly is arranged on a light path of the laser after sum frequency; the detection assembly is used for determining the frequency shift amount according to the difference value between the center frequency of the laser after frequency sum and the center frequency of the obtained reference laser; the frequency stabilization assembly is connected with the detection assembly; and the frequency stabilization assembly is used for adjusting the center frequency of the laser to be subjected to frequency stabilization according to the frequency shift amount to obtain target laser. The requirement of the target laser on the preparation condition is reduced, and the frequency stability of the laser to be subjected to frequency stabilization can be improved based on the laser light source with the 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 a multi-stage laser frequency stabilization device. Background Art

[0002] Ultrastable lasers refer to lasers with extremely high optical frequency stability. They are widely used in precision measurement fields such as optical clocks, time-frequency transfer, gravitational wave detection, laser ranging, and fiber optic sensing. The method for preparing ultrastable lasers currently mainly uses the Pound-Drever-Hall (PDH) frequency stabilization technology to lock the laser to an ultrastable optical reference cavity. The stability of the final 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 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. The frequency stability of the corresponding frequency-stabilized laser is therefore also limited by the thermal noise limit of the optical reference cavity. Therefore, in order to obtain an ultrastable laser with a high frequency stability level, it is necessary to suppress the optical reference cavity noise and loop noise.

[0003] In order to prepare an optical reference cavity with a low noise level, it is necessary to select materials with extremely low thermal expansion coefficients and as long a cavity length as possible, while controlling the stability of environmental factors such as 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, in order to reduce loop noise, narrow linewidth lasers, low-noise photodetectors, and electronic servo systems must be selected. At the same time, the optical reference cavity also needs to be as precise as possible, and the corresponding cavity mirror coating reflectivity must 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 systems are extremely high. The overall system is extremely complex, difficult to implement, and expensive. 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] One 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 used to perform a sum frequency operation on an acquired first laser and a second laser to obtain a sum frequency laser; the frequency stability of the first laser and the frequency stability of the second laser meet a preset frequency stability threshold range; the detection component is arranged on an optical path of the sum frequency laser; the detection component is used to determine a frequency shift amount according to a difference between a center frequency of the sum frequency laser and a center frequency of an 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 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 is arranged on the optical path of the laser to be stabilized; the frequency modulator is used to adjust the center frequency of the laser to be stabilized according to the frequency shift amount to obtain the adjusted laser to be stabilized; the first beam splitter is arranged on the optical path of the adjusted laser to be stabilized; the first beam splitter is used to split the adjusted laser to be stabilized into a first beam splitter laser and a second beam splitter laser, and when twice the center frequency of the first beam splitter laser is equal to the sum of the center frequency of the laser after summing and the frequency shift amount, the first beam splitter laser is determined to be the target laser.

[0008] According to an embodiment of the present invention, the above-mentioned device also includes a first optical frequency synthesizer and a second beam splitter; the above-mentioned first optical frequency synthesizer is arranged on the optical path of the above-mentioned second beam splitting laser; the above-mentioned first optical frequency synthesizer is used to perform frequency doubling operation on the above-mentioned second beam splitting laser to obtain the frequency-doubled laser to be stabilized, and use the above-mentioned frequency-doubled laser to be stabilized as the above-mentioned reference laser; the above-mentioned second beam splitter is arranged on the optical path of the above-mentioned reference laser and the above-mentioned laser after frequency summation; the above-mentioned second beam splitter is used to combine the above-mentioned reference laser and the above-mentioned laser after frequency summation to obtain the combined laser.

[0009] According to an embodiment of the present invention, the detection component includes a photodetector and a phase lock; the photodetector is arranged on the optical path of the combined laser; the photodetector is used to collect the combined laser 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 summed laser based on the electrical signal.

[0010] According to an embodiment of the present invention, the detection component further comprises 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.

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

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

[0013] According to an embodiment of the present invention, the center frequency of the laser to be frequency stabilized is adjusted according to the frequency shift amount to obtain the target laser, including: adjusting 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; 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 laser after summing and the frequency shift amount, determining that the first split laser is the target laser.

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

[0015] Another aspect of the present invention provides a multi-stage laser frequency stabilization device, comprising: 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, a first laser and a second laser are subjected to a frequency summing operation by using a frequency summing component, and a detection component is used to determine the difference between the center frequency of the laser after the frequency summing and the center frequency of the reference laser, thereby obtaining a frequency shift amount, and finally a frequency stabilization component is used to adjust the center frequency of the laser to be stabilized according to the frequency shift amount, thereby obtaining a target laser. Compared with the technical problem of extremely high requirements on the environment, components, and servo feedback system for preparing an ultra-stable laser with high optical frequency stability in the prior art, the present invention uses a first laser and a second laser whose frequency stability meets a preset frequency stability threshold range, and obtains a target laser with higher frequency stability through a frequency summing component, a detection component, and a frequency stabilization component, thereby reducing the requirements of the target laser on the preparation conditions and improving the frequency stability of the laser to be stabilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[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 diagram of the structure 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 flow chart of a laser frequency stabilization method according to an embodiment of the present invention is shown.

[0022] Figure 5 A simplified structural schematic 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 a frequency stability verification experimental device for a sum frequency scheme according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0025] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0026] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0027] All terms (including technical and scientific terms) used herein 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] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0029] In the embodiments of the present invention, the collection, updating, analysis, processing, use, transmission, provision, invention, storage and other aspects of the data involved (for example, including but not limited to user personal information) are in compliance with the provisions of relevant laws and regulations, are used for legitimate purposes, and do not violate public order and good morals. In particular, necessary measures are taken for user personal information to prevent illegal access to user personal information data and maintain the security of user personal information, network security and national security.

[0030] In the embodiment of the present invention, before obtaining or collecting the user's personal information, the user's authorization or consent 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] like Figure 1 As 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 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 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.

[0033] According to an embodiment of the present invention, the sum frequency component converts the frequencies of two fundamental frequency lasers of different frequencies through a nonlinear crystal based on the nonlinear optical effect, thereby obtaining a 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 a laser whose center frequency is adjusted and then doubled, thereby forming a closed-loop control loop. The difference between the center frequencies of the sum frequency laser and the reference laser is detected by the detection component to determine the variation, and the frequency stabilization component adjusts the center frequency of the laser to be stabilized according to the variation, thereby obtaining 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] Among them, 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, 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 frequency sum.

[0038] According to an embodiment of the present disclosure, the laser to be frequency stabilized may be a laser that is completely unrelated to the first laser and the second laser, and the laser to be frequency stabilized may also be a laser after the first laser is split or a 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 first preset frequency difference threshold range, and the difference between the frequency of the laser to be frequency stabilized and the frequency of the second laser is within the second preset frequency difference threshold range. According to an embodiment of the present disclosure, the laser to be frequency stabilized may also be a laser whose frequency stability is 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, a first laser and a second laser are subjected to a frequency summing operation by using a frequency summing component, and a detection component is used to determine the difference between the center frequency of the laser after the frequency summing and the center frequency of the reference laser, thereby obtaining a frequency shift amount, and finally a frequency stabilization component is used to adjust the center frequency of the laser to be stabilized according to the frequency shift amount to obtain a target laser. Compared with the technical problem of extremely high requirements on the environment, components, and servo feedback system for preparing an ultra-stable laser with high optical frequency stability in the prior art, the present invention utilizes the frequency stability of the first laser and the second laser whose frequency stability meets a preset frequency stability threshold range, and obtains a target laser with higher frequency stability through a frequency summing component, a detection component, and a frequency stabilization component, thereby reducing the requirements of the target laser on the preparation conditions, reducing the overall complexity of the laser frequency stabilization device, reducing the difficulty of implementing the laser frequency stabilization device, and at the same time reducing the cost of the laser frequency stabilization device and improving the frequency stability of the laser to be 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 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 laser to be frequency stabilized after adjustment; 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 summing and the frequency shift amount, the first split laser is determined to be the target laser.

[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 consistent, and are also consistent with 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 stabilized is input to the input end of the frequency modulator; the frequency modulator shifts the frequency of the laser to be stabilized, the frequency of the shift is related to the signal fed back by the phase lock, 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 also includes a first optical frequency adder and a second beam splitter; the first optical frequency adder is arranged on the optical path of the second beam splitter laser; the first optical frequency adder is used to perform a frequency doubling operation on the second beam splitter laser to obtain a frequency-doubled laser to be stabilized, and the frequency-doubled laser to be stabilized is used as a reference laser; the second beam splitter is arranged on the optical path of the reference laser and the frequency-added laser; the second beam splitter is used to combine the reference laser and the frequency-added laser to obtain a combined laser.

[0044] According to an embodiment of the present invention, the output light of the first optical frequency summer 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 frequency summer directly doubles the frequency of the input laser, that is, the laser does frequency summing with itself, in order to generate a laser with a frequency close to that of the summed light of the second optical frequency summer, so as to facilitate 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 lock; the photodetector is arranged on the optical path of the laser after beam combining; the photodetector is used to collect the laser after beam combining and convert it into an electrical signal; the phase locker is electrically connected to the photodetector; the phase locker is used to determine the difference between the center frequency of the reference laser and the center frequency of the laser after summing the frequencies 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 locker, and the phase locker outputs the modulation signal to the optical frequency modulator to achieve optical frequency stabilization. Finally, the target laser that has completed 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 comprises a bandpass filter; the bandpass filter is arranged at the incident port of the photodetector; and the combined laser beam passes through the bandpass filter and is incident on the photodetector.

[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 generator and does not respond to the fundamental frequency light. This can be achieved by setting a bandpass filter at the incident port of the photodetector.

[0050] According to an embodiment of the present invention, the photodetector, the phase lock, and the frequency modulator are connected by a cable. Different types of photodetectors respond to light in different frequency bands. Generally, the detectors will be marked, and will not respond to light signals of other frequencies outside the marked range. This can be achieved by setting a bandpass filter at the incident port of the photodetector. The sum frequency light refers to the newly generated laser after the sum frequency component, and the baseband 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 bandpass filter can select a filter with a wavelength of ±3nm of the doubled frequency light output by the sum frequency component.

[0051] According to an embodiment of the present invention, 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 path 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 beam; the second optical sum frequency device is arranged on the optical path of the first combined laser beam; the second optical sum frequency device is used to perform a sum frequency operation on the first combined laser beam to obtain a sum frequency laser beam.

[0052] According to an embodiment of the present disclosure, the third beam splitter is disposed at the intersection of the optical path of the first laser and the optical path of the second laser, so that the first laser and the second laser can be combined 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 Figure 2 The beam splitter structure shown in Figure 2As shown, the beam splitter includes four ports, the first port A is an input port, the second port B is an input port, the third port C is an output port, and the fourth port D is an output port.

[0054] According to an embodiment of the present invention, the frequency modulator output light is connected to the second port B of the first beam splitter. After the 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 to the first optical frequency synthesizer through the fourth port D of the first beam splitter.

[0055] 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.

[0056] like Figure 3 As shown, the first laser and the second laser are incident on the sum frequency component 301, and 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, and 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 a laser after sum frequency, and the laser after sum frequency is incident on the second beam splitter.

[0057] The laser to be frequency stabilized is incident on the frequency stabilizing component 302 for the first time, and the frequency stabilizing 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, it corresponds to an initial frequency shift amount. The frequency modulator modulates the frequency of 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 divided into two beams, one of which is emitted from the laser frequency stabilizing device, and the other is incident on the first optical frequency synthesizer. The first optical frequency synthesizer doubles the frequency of the other incident laser beam to obtain the doubled laser. The doubled laser is incident on the second beam splitter.

[0058] The sum frequency laser and the frequency doubling laser are combined through the second beam splitter to obtain a combined laser beam, which is incident on the detection component 303. The detection component 303 includes a photodetector and a phase lock. The combined laser beam is incident on the photodetector, which converts the combined laser beam into an electrical signal and transmits the electrical signal to the phase lock. The phase lock determines the difference between the center frequencies of the sum frequency laser and the frequency doubling laser according to the electrical signal, thereby determining the frequency shift amount. The frequency modulator continues to adjust the frequency of the laser to be stabilized according to the frequency shift amount to realize closed-loop control. When twice the center frequency of the laser to be stabilized is equal to the sum of the center frequency of the sum frequency laser and the frequency shift amount after adjustment, 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 consistent with the center frequency of the two laser beams emitted by the first beam splitter, that is, the center frequency of the adjusted laser to be frequency stabilized is consistent with the center frequency 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 laser after summing 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 laser after summing 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 frequency summer, and the other 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 third beam splitter outputs the light to the second optical sum frequency device through the fourth port D of the third beam splitter. The sum frequency light output by the second optical sum frequency device is input to 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 unrelated to the first laser and the second laser, it means that the 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 the first laser or the second laser through phase locking, frequency doubling, etc. The frequency of the output target laser × 2 = the frequency of the first laser + the frequency of the second laser + the phase locking bias / 2, wherein the phase locking bias is the frequency shift amount, and the frequencies of the first laser and the second laser cannot be too far apart, otherwise the sum frequency cannot be achieved, so the output target laser frequency 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 FIG. 4 shows a flow chart of a laser frequency stabilization method according to an embodiment of the present invention. Figure 4 As shown, the method includes operations S401 to S403.

[0062] In operation S401, a sum frequency operation is performed 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 a preset frequency stability threshold range.

[0063] In operation S402, a frequency shift amount is determined according to a difference between a center frequency of the laser light after summing the frequencies and a center frequency of the reference laser light obtained.

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

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

[0066] According to an embodiment of the present invention, the reference laser may be a preset laser, and the preset laser may be determined according to actual conditions. The frequency shift amount is determined according to the difference between the center frequencies of the laser after summing the frequencies and the reference laser, and the value of the center frequency of the laser to be stabilized that needs to be adjusted can be determined according to the frequency shift amount. The center frequency of the laser to be stabilized is adjusted according to the above value to obtain the target laser, wherein the frequency stability of the target laser is higher than that of the first laser, the second laser, and the reference laser.

[0067] According to an embodiment of the present invention, a sum frequency operation is performed based on the acquired first laser and second laser to obtain a sum frequency laser; the frequency shift amount is determined according to the difference between the center frequency of the sum frequency laser and the center frequency of the acquired reference laser; the center frequency of the laser to be stabilized is adjusted according to the frequency shift amount to obtain the target laser. The technical problem of extremely high requirements on the environment, components, and servo feedback system for preparing ultra-stable lasers with high optical frequency stability is partially overcome, and the requirements on the preparation conditions of the target laser are reduced. The frequency stability of the laser to be stabilized can be improved based on a laser light source with a low frequency stability level.

[0068] According to an embodiment of the present invention, the center frequency of the laser to be frequency-stabilized is adjusted according to the frequency shift amount to obtain a target laser, including: adjusting 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; 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 laser after summing and the frequency shift amount, determining the first split laser as the target laser.

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

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

[0072] According to an embodiment of the present disclosure, 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 A simplified structural schematic diagram of a laser frequency stabilization device based on two lasers according to an embodiment of the present invention is shown.

[0074] like Figure 5 As 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 the first laser input port, the second laser input port, the input port of the laser to be stabilized, 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 the preset frequency threshold range, which can be determined according to actual conditions. The multi-stage laser frequency stabilization device includes a plurality of cascaded lasers such as Figure 5 The laser frequency stabilization device shown.

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

[0076] like Figure 6As shown, since the input laser and the output laser of the laser frequency stabilization device are lasers with similar frequencies, the target laser output by the laser frequency stabilization device can be treated as a separate laser, so that the output target laser is used as the input of another laser frequency stabilization device, thereby achieving the sum frequency of three or more ultra-stable lasers. Among them, the first laser frequency stabilization device, the second laser frequency stabilization device, ..., and the Nth laser frequency stabilization device are all as shown in Figure 5 The simplified structure of a laser frequency stabilization device based on two lasers is shown.

[0077] Input laser 1-1 is the first laser of the first laser frequency stabilization device, input laser 2-1 is the first laser of the second laser frequency stabilization device, and so on, input laser N-1 is the first laser of the Nth laser frequency stabilization device, input laser 1-2 is the second laser of the first laser frequency stabilization device, input laser 2-2 is the second laser of the second laser frequency stabilization device, and so on, input laser N-2 is the second laser of the Nth laser frequency stabilization device, wherein the first laser or the second laser of each laser frequency stabilization device may be a target laser output by the laser frequency stabilization device, for example, input laser N-2 may be a target laser output by the N-1th laser frequency stabilization device. When among the N laser frequency stabilization devices, there is a laser frequency stabilization device whose first laser is the target laser output by the laser frequency stabilization device, the second laser may 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, there is a laser frequency stabilization device whose second laser is the target laser output by the laser frequency stabilization device, the first laser may be a preset laser that meets the requirements of the laser frequency stabilization device for the first laser.

[0078] Input laser 1-3 is the laser to be stabilized of the first laser frequency stabilization device, input laser 2-3 is the laser to be stabilized of the second laser frequency stabilization device, and so on, input laser N-3 is the laser to be stabilized of the Nth laser frequency stabilization device, and the laser to be stabilized can be the target laser output by the upper-level laser frequency stabilization device of the cascade of the current laser frequency stabilization device, or it can be a preset laser that meets the conditions. For example, input laser N-3 can be the target laser output by the N-1th laser frequency stabilization device.

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

[0080] Figure 7 A schematic diagram of a frequency stability verification experimental device for a sum frequency scheme according to an embodiment of the present invention is shown.

[0081] like Figure 7 As shown in the figure, the frequency stability verification experimental device of the sum frequency scheme is Figure 3 On the basis of the laser frequency stabilization device based on two lasers shown in the figure, a fourth beam splitter, a second photodetector and a frequency counter are added. Figure 3 The laser frequency stabilization device based on two lasers shown in the figure will not be described in detail here. The target laser output by the laser frequency stabilization device is connected to one input end of the fourth beam splitter, and the known frequency stability is The detection laser is connected to the other input end of the fourth beam splitter. After the two beams 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 measured by a frequency counter to measure its frequency stability. , then 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 ultrastable cavity or the frequency stability after a single laser frequency doubling, the present invention can improve the frequency stability of the output laser by using two or more lasers and frequency. The corresponding physical principles are as follows:

[0083] Assume that the frequency stability of the ultra-stable laser i is:

[0084]

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

[0086]

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

[0088]

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

[0090] When i=1, the first laser is an ultra-stable laser 1, and the frequency stability of the first laser is σ 1 is the relative frequency stability of ultrastable laser 1; when i=2, the second laser is ultrastable laser 2, and the frequency stability of the second laser is σ 2 is the relative frequency stability of ultra-stable laser 2. When two lasers that meet the preset frequency stability threshold range are combined, when the frequency is considered to be f 1 The first laser, with a frequency of f 2 The second laser is summed up by the optical summator:

[0091]

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

[0093]

[0094] In the formula, is the relative frequency stability of the laser after summing. 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 the first laser and the second laser are not strongly correlated, equation (6) is:

[0095]

[0096] In the formula, is the correlation between the first laser and the second laser. If they are completely correlated, then , completely unrelated, then From equations (4) and (7), it can be seen that when the frequencies of the two ultra-stable lasers are close, the frequency stability is close, and the common mode noise is small, the sum frequency scheme can be used to produce an ultra-stable laser with higher frequency stability. From equation (4), it can be seen 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 minimum stability of the original single input laser. times.

[0097] When three or more laser frequency stabilization devices are cascaded and frequency-stabilized, the frequency stability of the input laser of each laser frequency stabilization device can be calculated separately using formula (7). When, among them, 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, and when the first laser and the second laser are not strongly correlated, the maximum frequency stability of the target laser output by the first laser frequency stabilization device is:

[0098] (8)

[0099] After the target laser with frequency stability shown in formula (8) output by the first laser frequency stabilization device is input to the second laser frequency stabilization device, it is summed with the input laser 2-1 and calculated using formula (7). When, among them, is the frequency stability of the input laser 2-1 of the second laser frequency stabilization device, and 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 maximum frequency stability of the target laser output by the second laser frequency stabilization device after frequency stabilization is:

[0100] (9)

[0101] By analogy, when N lasers are cascaded and frequency-controlled, (N=2,3,4…), where is the frequency stability of the input laser N-1 of the Nth laser frequency stabilization device, and the correlation between the first laser, the second laser and the laser to be 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 be finally achieved as follows:

[0102] (10)

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

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

[0105] Compared with the frequency stability of the existing technology using a single laser to lock the ultra-stable cavity, the method of adding two or more lasers can further improve the frequency stability of the output laser, so that under the premise of achieving the same frequency stability index, the requirements for the working environment, devices, frequency servo and other performance can be reduced, the difficulty of preparing a single ultra-stable laser can be reduced, and the system robustness can be improved. At the same time, it can shorten the cycle of environmental construction and device development, and reduce related procurement, development and maintenance costs.

[0106] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment is described above, it does not mean that the measures in each embodiment cannot be used in combination advantageously. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which 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.

2. The laser frequency stabilization device according to claim 1, characterized in that: 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.

3. The laser frequency stabilization device according to claim 2, characterized in that: The device also includes a first optical frequency summer and a second beam splitter; The first optical frequency combiner is arranged on the optical path of the second split laser beam; the first optical frequency combiner is used to perform frequency doubling operation on the second split laser beam to obtain the frequency-doubled laser beam to be stabilized, and the frequency-doubled laser beam to be stabilized is used as the reference laser beam; 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.

4. The laser frequency stabilization device according to claim 3, 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.

5. The laser frequency stabilization device according to claim 4, 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.

6. 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.

7. 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 frequency-stabilized is adjusted according to the frequency shift amount to obtain the target laser.

8. The laser frequency stabilization method according to claim 7, characterized in that: 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, the first split laser beam is determined to be the target laser beam.

9. The laser frequency stabilization method according to claim 8, characterized in that: The method further comprises: The adjusted laser to be stabilized is frequency-doubled, and the frequency-doubled laser to be stabilized is used as a reference laser.

10. 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 6; N is a positive integer greater than or equal to 2.

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