Optical communication wavemeter based on lithium niobate microcavity optical comb excitation rubidium atom two-photon transition

Abstract

The invention discloses an optical communication wavelength meter for exciting rubidium atom two-photon transition based on a lithium niobate microcavity optical comb. The optical communication wavelength meter comprises a microcavity optical comb module, a repetition frequency phase-locked loop, an initial frequency phase-locked loop, a rubidium atom gas chamber and a frequency-stabilized light source. The micro-cavity optical comb module is used for generating a fundamental frequency optical comb and a frequency doubling optical comb, rubidium atom two-photon transition is directly excited, the frequency stabilization light source achieves frequency stabilization through rubidium atom saturation absorption, and the repetition frequency phase-locked loop feeds back and adjusts repetition frequency according to error signals of two-photon transition fluorescence intensity. The initial frequency phase-locked loop feeds back and adjusts the initial frequency through beat frequency signals of the frequency multiplication optical comb and the frequency stabilization light source, and the two groups of phase-locked loops stabilize the frequency of the microcavity optical comb to two groups of transition energy levels, so that locking of the repetition frequency and the initial frequency is realized. According to the optical communication wavelength meter based on the lithium niobate microcavity optical comb excitation rubidium atom two-photon transition, the cross modulation effect in a pumping wavelength and pumping power combined adjustment mechanism is avoided, and the size of the optical communication wavelength meter is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of optical communication wavelength meters, and particularly relates to an optical communication wavelength meter based on the excitation of two-photon transitions of rubidium atoms by a lithium niobate microcavity optical comb. Background Art

[0002] Optical frequency standards are currently the atomic frequency standards with the highest stability and accuracy, and have important application prospects in precision measurement fields such as the measurement of fundamental physical constants and the detection of dark matter. Traditional optical clocks rely on ultra-fine resonant cavities and cold atom systems, with complex structures and large volumes. Moreover, since the atomic transition spectral lines used are in the ultraviolet or visible bands, it is difficult to be used as a reference source for optical communication. The method of optical frequency standard using an erbium-doped fiber optical comb to directly excite two-photon transitions of rubidium atoms eliminates the ultra-fine resonance of traditional optical clocks and simplifies the system structure. At the same time, the wavelength (778 nm) of the two-photon transition of rubidium atoms divided by two is exactly in the communication band and is also within the coverage band of the erbium-doped fiber optical comb. Therefore, after the optical comb is locked with the rubidium atom transition line to form an atomic frequency standard, it can be used as a wavelength meter for optical communication.

[0003] Limited by the volume and power consumption of the erbium-doped fiber optical comb, the above-mentioned optical communication wavelength meter using a fiber optical comb to excite two-photon transitions of rubidium atoms is difficult to be further miniaturized and thus difficult to move towards practical applications. In recent years, the emergence of microcavity optical combs generated by the strong four-wave mixing effect in highly nonlinear microresonators has made it possible to reduce the size of the optical comb resonator to the millimeter or even micrometer level, which can greatly reduce the volume and power consumption of the two-photon frequency standard system and lay a foundation for realizing a miniaturized and portable optical communication wavelength meter.

[0004] Currently, the prior art has realized an optical atomic frequency standard based on a microcavity optical comb for two-photon transitions of rubidium atoms. This method uses two microcavity optical combs. Among them, the optical comb with a repetition frequency in the THz range is used for extracting and locking f by the "f-2f" method ceo , and the microcavity optical comb with a repetition frequency of 22 GHz is used for locking with the two-photon transition frequency. The frequency stability of the entire system is achieved by interlocking the two optical combs. While the stability index is not reduced, the miniaturization of key devices such as the optical comb is realized.

[0005] In the above-mentioned wavelength meter method based on a microcavity optical comb, limited by the microcavity fabrication process, only optical combs with high repetition frequencies can directly generate octave-spanning optical combs in the cavity, while low-repetition-frequency microcavities cannot directly generate them in the cavity. Therefore, in constructing a complete optical frequency standard system, this method has to introduce a second optical comb and four phase-locked loops, resulting in an extremely large optical path and circuit outside the miniaturized resonator, which instead increases the complexity of the system and is not conducive to the miniaturization of the overall system.

[0006] Regarding the inability of microcavity optical combs with a repetition frequency in the tens of GHz range to lock f ceoRegarding the problem, two improved solutions have emerged later: one is to use highly nonlinear optical fiber outside the cavity to broaden the spectrum to an octave for self-reference locking of f ceo ; the other is to use two sets of transition spectral lines to lock two teeth of the optical frequency comb simultaneously to lock the initial frequency f ceo and the repetition frequency f rep . These two solutions can construct an optical communication optical frequency standard using only a single microcavity optical frequency comb double phase-locked loop.

[0007] However, the phase-locked loops in the above three solutions all use the method of joint feedback regulation of the pump frequency and pump power to stabilize the f rep and f ceo of the microcavity optical frequency comb. This solution has a cross-modulation effect, that is, adjusting the pump power may simultaneously cause a change in the pump wavelength.

[0008] In addition, the above three solutions all lock the atomic energy level transition spectral lines by doubling the frequency of a continuous-wave laser, and then lock the microcavity optical frequency comb to the frequency-stabilized laser to indirectly achieve the locking of the optical frequency comb and the atomic spectral lines. Since an additional laser is introduced and the frequency doubling process is still outside the cavity, the complexity of the entire wavelength meter system is also increased. Summary of the Invention

[0009] Therefore, the present application provides an optical communication wavelength meter based on a lithium niobate microcavity optical frequency comb exciting two-photon transitions of rubidium atoms to solve the problems of cross-modulation effect and large volume existing in the existing optical communication wavelength meters.

[0010] To achieve the above object, the present application provides the following technical solutions:

[0011] An optical communication wavelength meter based on a lithium niobate microcavity optical frequency comb exciting two-photon transitions of rubidium atoms, comprising a microcavity optical frequency comb module, a repetition frequency phase-locked loop, an initial frequency phase-locked loop, a photomultiplier tube, a rubidium atomic gas cell, and a frequency-stabilized light source;

[0012] The microcavity optical frequency comb module includes a pump light source, an erbium-doped fiber amplifier, a lithium niobate micro-ring resonator, and an electrode, and the lithium niobate micro-ring resonator and the electrode are integrally formed; wherein, the pump light source is used to generate laser as the initial light source for pumping the microcavity optical frequency comb, and the laser is amplified by the erbium-doped fiber amplifier and then coupled into the lithium niobate micro-ring resonator as pump light to generate a fundamental frequency optical frequency comb and a second harmonic optical frequency comb, and the electrode is used to regulate the repetition frequency of the optical frequency comb;

[0013] The frequency-stabilized light source is used to excite the saturated absorption resonance transition of the rubidium atom D1 line and is frequency-stabilized to the D1 line as the frequency reference of the initial frequency phase-locked loop;

[0014] The repetition frequency phase-locked loop feedback regulates the repetition frequency of the frequency-doubled optical comb according to the error signal of the fluorescence intensity of two-photon transition, so that a certain mode of the frequency-doubled optical comb is aligned with the two-photon spectral peak of rubidium atoms. Wherein, the fluorescence intensity of the atomic two-photon transition radiation in the rubidium atomic gas cell is collected by the photomultiplier tube;

[0015] In the initial frequency phase-locked loop, the frequency-stabilized light source beats with the m-th mode of the frequency-doubled optical comb, and the error is fed back to the pump light source through the initial frequency phase-locked loop;

[0016] The repetition frequency phase-locked loop and the initial frequency phase-locked loop continuously feedback the frequency difference between the comb tooth frequency and the atomic frequency standard to the feedback element of the microcavity optical comb until the frequency deviation is stable, thereby realizing the long-term locking of the comb teeth and the atomic energy level.

[0017] Preferably, the initial frequency phase-locked loop includes a phase discriminator module. The phase discriminator module includes a first photodetector, a second photodetector, a frequency divider and a mixer. The first photodetector is used to obtain the frequency difference beat signal between the frequency-stabilized laser that is calculated and stabilized to the saturated absorption spectral line of the D1 line of rubidium atoms, the atomic frequency reference, and the saturated absorption frequency of the D1 line of rubidium atoms of the m-th mode of the frequency-doubled optical comb, and input it to the mixer; the second photodetector is used to input a homodyne signal to extract the repetition frequency signal of the frequency-doubled optical comb, and input the homodyne repetition frequency signal to the mixer through the frequency divider. The mixer is used to calculate the error between the atomic frequency reference with a stable beat signal and the homodyne frequency-divided signal of the repetition frequency.

[0018] Preferably, the pump light source adopts an external cavity semiconductor pump laser.

[0019] Preferably, the frequency-stabilized light source adopts a semiconductor laser.

[0020] Preferably, the lithium niobate micro-ring resonator is etched by a femtosecond laser ablation method.

[0021] Preferably, the electrode is made of an unetched chromium mask plate.

[0022] Preferably, it further includes a dichroic beam splitter, and the dichroic beam splitter is used to separate the optical comb generated by the lithium niobate micro-ring resonator into a fundamental frequency optical comb and a frequency-doubled optical comb.

[0023] Compared with the prior art, the present application has at least the following beneficial effects:

[0024] The present application provides an optical communication wavelength meter based on the excitation of two-photon transitions of rubidium atoms by a lithium niobate microcavity optical comb. Based on a lithium niobate microring resonator, by introducing an electrochromic dispersion repetition frequency regulation mechanism, the cross modulation of the pump power and wavelength in the traditional microcavity optical comb frequency standard system is avoided, and the independent feedback regulation and locking of the repetition frequency and the initial frequency are realized; based on the second-order nonlinear effect in the lithium niobate microring resonator, a frequency-doubled optical comb is directly generated in the cavity and directly locked to the two-photon transition and saturated absorption spectral lines of rubidium atoms, greatly reducing the use of continuous-wave lasers and external cavity self-reference optical paths and external cavity frequency-doubled optical paths, effectively reducing the volume of peripheral components while miniaturizing the core components, laying a foundation for the miniaturization and large-scale application of the optical communication wavelength meter. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] To more intuitively illustrate the prior art and the present application, exemplary drawings are given below. It should be understood that the specific shapes and structures shown in the drawings generally should not be regarded as limiting conditions when implementing the present application; for example, those skilled in the art are capable of making routine adjustments or further optimizations to the addition / deletion / attribution division of certain units (components), specific shapes, positional relationships, connection methods, dimensional proportional relationships, etc. based on the technical concept disclosed in the present application and the exemplary drawings.

[0026] Figure 1 It is a schematic structural diagram of the optical communication wavelength meter based on the excitation of two-photon transitions of rubidium atoms by a lithium niobate microcavity optical comb provided by the present application;

[0027] Figure 2 It is a schematic structural diagram of the microcavity optical comb module provided by the present application.

[0028] Description of the reference numerals in the drawings:

[0029] 1. Pump light source; 2. Erbium-doped fiber amplifier; 3. Lithium niobate microring resonator; 4. Electrode; 5. Dichroic beam splitter; 6. Optical communication frequency standard output; 7. Photomultiplier tube; 8. Rubidium atomic cell; 9. Frequency-stabilized light source; 10. Second photodetector; 11. Frequency divider; 12. Mixer; 13. First photodetector. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The following further details the present application through specific embodiments in conjunction with the drawings.

[0031] In the description of the present application: Unless otherwise specified, "a plurality" means two or more. The terms "first", "second", "third", etc. in the present application are intended to distinguish the objects being referred to and do not have special meanings in terms of technical connotations (for example, they should not be understood as emphasizing the importance or order, etc.). Expressions such as "including", "comprising", "having", etc. also mean "not limited to" (certain units, components, materials, steps, etc.).

[0032] In this application, terms such as "upper", "lower", "left", "right", "middle", etc. cited are usually indications of the general relative position relationship for the convenience of intuitively understanding with reference to the attached drawings, and are not absolute limitations on the position relationship in the actual product.

[0033] Please refer to Figure 1 , this application provides an optical communication wavelength meter based on the excitation of two-photon transitions of rubidium atoms by a lithium niobate microcavity optical comb, and a new method for feedback regulating the frequency of the microcavity optical comb is obtained in principle. The regulation of f rep and f ceo is independently achieved by two feedback units respectively. The long-term stability of the microcavity optical comb frequency is realized by using the two-photon transition and saturated absorption of rubidium atoms, and the two-photon transition is directly excited by the optical comb. Considering that the teeth of the optical frequency comb can be expressed as f n =nf rep +f ceo , when two sets of atomic frequency standards are used to lock two teeth of the microcavity laser respectively, the repetition frequency f rep and the initial frequency f ceo can be stably repeated simultaneously, and the long-term stability of all teeth of the microcavity optical comb is realized. This frequency stabilization mode that uses two sets of transition spectra to stably lock two teeth at the same time not only overcomes the defect that it is difficult for a microcavity optical comb of dozens of GHz to self-reference, but also avoids the complex optical path introduced by external cavity self-reference. So far, the high stability of the atomic frequency standard is transmitted to the communication band through the microcavity optical comb, and an optical communication wavelength meter is realized. The wavelength meter includes a microcavity optical comb module, a rubidium atomic gas cell 8, a frequency-stabilized light source 9, a repetition frequency phase-locked loop, an initial frequency phase-locked loop, and a photomultiplier tube 7.

[0034] Specifically, the microcavity optical comb module includes a pump light source 1, an erbium-doped fiber amplifier 2, a lithium niobate micro-ring resonator 3, and an electrode 4. The lithium niobate micro-ring resonator 3 and the electrode 4 are integrally formed. Among them, the pump light source 1 uses an external cavity semiconductor pump laser (including a piezoelectric controller), the lithium niobate micro-ring resonator 3 is etched by the femtosecond laser ablation method, and the electrode 4 is made of an unetched chromium mask plate.

[0035] It should be noted that for the lithium niobate micro-ring resonator 3 after pattern transfer, chemical mechanical polishing technology is used to make the sidewall smooth, so as to improve the quality factor Q value of the micro-resonator; the external cavity semiconductor pump laser (ECDL) has the ability of direct wavelength tuning.

[0036] Please refer to Figure 2, the microcavity optical comb module is used to generate fundamental frequency optical combs and second harmonic optical combs. Specifically: The external cavity semiconductor pump laser in the communication band outputs continuous laser light, which is amplified by the erbium-doped fiber amplifier 2 and then used as the pump light for the lithium niobate micro-ring resonator 3 and coupled into the lithium niobate micro-ring resonator 3. Since the third-order nonlinear effect - Kerr effect for generating microcavity optical combs has a threshold, the pump light needs to reach the threshold to generate an optical comb in the lithium niobate micro-ring resonator 3. Therefore, the erbium-doped fiber amplifier 2 is indispensable. Because the electrode 4 on the lithium niobate micro-ring resonator 3 is made of an unetched chromium mask and the lithium niobate micro-ring resonator 3 and the electrode 4 are an integral whole, when the pump light enters the lithium niobate micro-ring resonator 3, a fundamental frequency optical comb is generated through the four-wave mixing effect in the cavity. The fundamental frequency optical comb undergoes second-order nonlinear effects in the cavity to generate a second harmonic optical comb, and both are simultaneously coupled and output outside the lithium niobate micro-ring resonator 3.

[0037] The microcavity optical comb module constructs a microcavity optical comb based on the lithium niobate micro-ring resonator 3 integrated with the electrode 4, realizing efficient coupling between the pump light and the microcavity, and deterministically achieving Kerr soliton mode locking in the microcavity; using the second harmonic generation effect of the lithium niobate micro-ring resonator 3 to generate the second harmonic of the fundamental soliton optical comb, realizing frequency doubling replication of the Kerr soliton optical frequency comb to obtain a second harmonic optical comb; by applying an electric field to change the effective optical path of the microresonator, realizing the regulation of the repetition frequency f rep of the microcavity optical comb; by adjusting the pump center wavelength, realizing the regulation of the center frequency of the microcavity optical comb, that is, the initial frequency f ceo of the microcavity optical comb.

[0038] More specifically, the optical communication wavelength meter based on the excitation of rubidium atom two-photon transition by the lithium niobate microcavity optical comb provided in this application further includes a dichroic beam splitter 5, and the dichroic beam splitter 5 is used to spatially separate the fundamental frequency optical comb and the second harmonic optical comb generated in the lithium niobate micro-ring resonator 3.

[0039] In this application, the repetition frequency phase-locked loop ( Figure 1 the phase-locked loop 1 in it) uses the rubidium atom two-photon transition as the frequency reference and feeds back to the electrode 4 of the microcavity optical comb module for feedback regulation of the repetition frequency. Specifically, the photomultiplier tube 7 is used to collect the fluorescence intensity of the rubidium atom two-photon transition radiation in the rubidium atom gas cell 8 and extract the error signal of the fluorescence intensity. The repetition frequency phase-locked loop feedback-regulates the repetition frequency of the second harmonic optical comb according to the error signal of the fluorescence intensity, so that the nth mode of the second harmonic optical comb is aligned with the rubidium atom two-photon spectral peak.

[0040] More specifically, for the direct excitation of two-photon transitions by an optical frequency comb, the two-photon transition has the highest intensity if and only if a certain mode of the optical frequency comb is exactly located at the frequency strictly corresponding to the spectral peak. In this application, the fluorescence intensity of the two-photon transition radiation is collected by a photomultiplier tube 7, and the error signal of the fluorescence is extracted to feedback and regulate the repetition frequency of the optical frequency comb, so that the nth mode of the frequency-doubled optical frequency comb is exactly opposite the two-photon spectral peak. The mode frequency is f n = nf rep + 2f ceo , and the frequency of the two-photon spectral peak of rubidium atoms is f TPT , then it satisfies f TPT = f n = nf rep + 2f ceo .

[0041] In this application, the initial frequency phase-locked loop ( Figure 1 the phase-locked loop 2 therein) uses the rubidium atomic saturated absorption spectral line as the frequency reference and feeds back to the piezoelectric controller of the pump light source 1 of the microcavity optical frequency comb module, thereby realizing the feedback regulation of the initial frequency.

[0042] Specifically, the mth mode of the frequency-doubled optical frequency comb at 795 nm is used for the frequency stabilization of the rubidium atomic D1 line saturation absorption. The mode frequency is f m = mf rep + 2f ceo . The optical frequency comb cannot be directly frequency-stabilized through the saturated absorption spectral line and needs to be indirectly frequency-stabilized by means of a frequency-stabilized light source 9. The frequency-stabilized light source 9 is previously locked to the rubidium atomic saturated absorption D1 line, and the frequency is f SA . The signal frequency generated by the beat frequency of the two is f b = f SA - f m . Since f SA is a stable atomic frequency reference, stabilizing f m means that first of all, f b needs to be stabilized. Therefore, it is necessary to perform phase discrimination with a co-frequency signal (the frequency-doubled optical frequency comb generated by the microcavity optical frequency comb module), and feedback the error signal to the pump light source 1 end of the microcavity optical frequency comb module through the initial frequency phase-locked loop to adjust the f ceo (initial frequency) of the optical frequency comb. At this time, it satisfies f SA = f m + f b = mf rep + 2f ceo + f b .

[0043] It should be noted that the solution of this application needs to frequency-stabilize the frequency-doubled optical frequency comb, and the frequency of its kth mode can be expressed as f k = kf rep + 2f ceo , where frep is the repetition frequency of the fundamental frequency optical comb, and f ceo is the initial frequency of the fundamental frequency optical comb. Among them, the two-photon transition of rubidium atoms corresponds to the 778 nm band of the frequency-doubled comb, and a certain mode of the 795 nm frequency-doubled comb is used for the saturated absorption frequency stabilization of the D1 line of rubidium atoms.

[0044] Combining f TPT and f SA These two equations, considering that in the usual microcavity optical comb module, f rep is as high as dozens of GHz, and f rep > f b , when and only when f b is the d-division of f rep , that is, f b = f rep / d, the repetition frequency f of the microcavity optical comb can be determined by the frequency difference between the two sets of atomic transition spectral lines rep , there is:

[0045]

[0046] It can be seen from this that the repetition frequency of the microcavity optical comb is locked on the frequency difference between the two sets of rubidium atomic spectral lines. At this time, f ceo is also locked on a certain algebraic sum of the two sets of transition frequencies. In this way, the optical frequency standard of rubidium atoms is transferred to the communication band where the fundamental frequency optical comb is located, and this optical comb can be output through the optical communication frequency standard 6 and used to implement a wavemeter.

[0047] It should be noted that the error signal generated by the repetition frequency phase discrimination is directly fed back to the electrode 4 of the optical comb through the servo circuit to achieve the locking of the repetition frequency; similarly, the f ceo signal obtains the error signal through the phase-locked loop mixing phase discrimination, and is fed back to the piezoelectric actuator of the pump light source 1 through the servo circuit to adjust the wavelength of the pump light, so as to achieve the locking of f ceo .

[0048] Among them, the optical comb used for two-photon excitation directly generates a second-harmonic optical comb through the second-order nonlinear frequency doubling effect inside the microcavity, avoiding complex frequency doubling optical paths and continuous light locking structures, and significantly reducing the system volume; the semiconductor laser used for the saturated absorption frequency stabilization of rubidium atoms is a semiconductor laser at 795 nm, and the feedback signal is the beat frequency signal between the frequency-doubled optical comb and the frequency-stabilized laser. This method also avoids external cavity frequency doubling.

[0049] The optical communication wavelength meter based on the excitation of two-photon transitions of rubidium atoms by a lithium niobate microcavity optical comb provided by this application breaks through the bottleneck that existing microcavity optical combs are difficult to frequency control, and at the same time solves the problem that the volume of the peripheral part of the microcavity is difficult to compress. Specifically, based on the ferroelectric material system of lithium niobate, this application introduces a microcavity optical comb repetition frequency control mechanism with electro-optic refractive index change, and combines the microcavity optical comb central wavelength adjustment based on the pump frequency to achieve the optical comb repetition frequency f rep and the initial frequency f ceo independent control. At the same time, the second-order nonlinearity of the ferroelectric material is used to directly generate a frequency-doubled optical comb in the lithium niobate microring resonator 3, directly exciting the two-photon transition of rubidium atoms and locking it to the transition spectrum line, avoiding the introduction of an additional frequency-doubling optical path and a continuous light locking structure, effectively reducing the volume of the peripheral part, laying a foundation for the realization of a miniaturized optical communication wavelength meter, and making it widely used in the wavelength calibration of optical communication.

[0050] In summary, the optical communication wavelength meter based on the excitation of two-photon transitions of rubidium atoms by a lithium niobate microcavity optical comb provided by this application has the following advantages:

[0051] (1) By adjusting the electric field to change the dispersion in the lithium niobate microring resonator, fine adjustment of the repetition frequency is achieved, avoiding the cross-modulation effect in the combined adjustment mechanism of the pump wavelength and pump power, and realizing the independent control and locking of the optical comb repetition frequency and the initial frequency;

[0052] (2) By directly locking the frequency-doubled optical comb in the lithium niobate microring resonator to two groups of rubidium atom transition spectra, without introducing an external self-reference and an external frequency-doubling optical path, and at the same time minimizing the introduction of a continuous light laser, effectively reducing the volume of the peripheral components while miniaturizing the core components, laying a foundation for the large-scale application of the optical communication wavelength meter.

[0053] The technical features of the above embodiments can be combined arbitrarily (as long as there is no contradiction in the combination of these technical features). For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope described in this specification.

Claims

1. An optical communication wavelength meter based on lithium niobate microcavity optical comb excitation of rubidium atom two-photon transition, characterized in that: It includes a microcavity optical comb module, a repetition frequency phase-locked loop, an initial frequency phase-locked loop, a photomultiplier tube, a rubidium atomic gas chamber and a frequency-stabilized light source; The microcavity optical comb module includes a pump light source, an erbium-doped fiber amplifier, a lithium niobate microring resonant cavity and an electrode, wherein the lithium niobate microring resonant cavity and the electrode are integrally formed; wherein the pump light source is used to generate laser as the initial light source for pumping the microcavity optical comb, and the laser is amplified by the erbium-doped fiber amplifier and coupled into the lithium niobate microring resonant cavity as pump light to generate a fundamental frequency optical comb and a frequency-doubled optical comb, and the electrode is used to regulate the repetition frequency of the optical comb; The frequency-stabilized light source is used to excite the saturated absorption resonance transition of the D1 line of rubidium atoms, and stabilize the frequency to the D1 line as the frequency reference of the initial frequency phase-locked loop; The repetition frequency phase-locked loop performs feedback adjustment on the repetition frequency of the frequency-doubling optical comb according to the error signal of the fluorescence intensity of the two-photon transition, so that the nth mode of the frequency-doubling optical comb is directly opposite to the two-photon spectrum peak of the rubidium atom, wherein the fluorescence intensity of the two-photon transition radiation of the atoms in the rubidium atom gas chamber is collected by the photomultiplier tube; The initial frequency phase-locked loop, the frequency-stabilized light source and the mth mode of the frequency-doubling optical comb perform frequency beats, and the error is fed back to the pump light source through the initial frequency phase-locked loop; The repetitive frequency phase-locked loop and the initial frequency phase-locked loop continuously feed back the frequency difference between the comb tooth frequency and the atomic frequency standard to the feedback element of the microcavity optical comb until the frequency deviation is stable, thereby achieving long-term locking of the comb teeth and the atomic energy level.

2. The optical communication wavelength meter based on lithium niobate microcavity optical comb exciting two-photon transition of rubidium atoms according to claim 1 is characterized in that: The initial frequency phase-locked loop includes a phase detection module, which includes a first photodetector, a second photodetector, a frequency divider and a mixer. The first photodetector is used to obtain a beat frequency signal of a frequency-stabilized laser stabilized to the saturated absorption line of the D1 line of the rubidium atom and the mth mode of the frequency-doubled light comb, and input it to the mixer; the second photodetector is used to extract a repetition frequency signal of the frequency-doubled light comb, and input the repetition frequency signal to the mixer via the frequency divider. The mixer is used to obtain an error between the beat frequency signal and the repetition frequency divided signal.

3. The optical communication wavelength meter based on lithium niobate microcavity optical comb exciting two-photon transition of rubidium atoms according to claim 1 is characterized in that: The pump light source adopts an external cavity semiconductor pump laser.

4. The optical communication wavelength meter based on lithium niobate microcavity optical comb exciting rubidium atom two-photon transition according to claim 1 is characterized in that: The frequency-stabilized light source adopts a semiconductor laser.

5. The optical communication wavelength meter based on lithium niobate microcavity optical comb exciting two-photon transition of rubidium atoms according to claim 1, characterized in that: The lithium niobate micro-ring resonant cavity is etched by a femtosecond laser ablation method.

6. The optical communication wavelength meter based on lithium niobate microcavity optical comb exciting two-photon transition of rubidium atoms according to claim 1, characterized in that: The electrode is made of an unetched chromium mask plate.

7. The optical communication wavelength meter based on lithium niobate microcavity optical comb exciting two-photon transition of rubidium atoms according to claim 1, characterized in that: It also includes a two-color beam splitter, which is used to separate the light comb generated by the lithium niobate microring resonator into a fundamental frequency light comb and a frequency doubling light comb.

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