A bubble-type hot rubidium atomic clock optical clock

Abstract

The invention discloses a bubble-type thermal rubidium atomic clock optical clock. The optical signal generated by the optical fiber laser is divided into two laser signals by the optical fiber splitter after passing through the optical fiber isolator. The laser signal is phase modulated by the electro-optical phase modulator, and then the optical power is amplified and frequency-multiplied by the optical power amplification and frequency-multiplication waveguide component to obtain the excitation laser; the excitation laser is incident on the rubidium atomic bubble structure, and under the action of the bidirectional excitation laser signal matched by the optical field mode, the rubidium atom undergoes a two-photon transition and radiates a fluorescence signal; the fluorescence signal is detected by a photomultiplier tube and converted into an electrical signal, and then amplified by a low-noise preamplifier and enters the server. The server uses the modulated reference signal to process the detected fluorescence signal to generate an error signal, and the proportional integral differential controller is used to feedback control the optical fiber laser to achieve the output of the laser signal with high frequency stability. The scheme of the invention is simple, and has the advantages of high reliability, easy engineering implementation, and miniaturization.

Description

Technical Field

[0001] The invention belongs to the field of navigation technology and relates to a bubble-type thermal rubidium atomic clock optical clock. Background Art

[0002] The Global Navigation Satellite System is currently the most widely used and most convenient means of navigation, positioning and timing. It is an important national information infrastructure and strategic facility, and an important symbol of a country's comprehensive national strength. In the satellite navigation system, accurate navigation mainly depends on accurate time. The atomic clock is currently the most accurate and stable time and frequency measurement tool, and is widely used in precision measurement, verification of basic physical principles, satellite navigation positioning and high-speed network communications.

[0003] The frequency stability of traditional microwave clocks is difficult to improve further due to the limitation of the size of the clock transition frequency. In recent years, atomic clocks based on optical frequency transitions (optical clocks for short) have developed rapidly. Compared with microwave atomic clocks, the optical frequency is 4 to 5 orders of magnitude higher than the microwave frequency. The Q value of the clock transition spectrum line of optical clocks is higher and the environmental sensitivity of optical frequency transitions is lower. Therefore, optical clocks have greater advantages and potential in terms of frequency performance indicators. At present, laboratory optical clocks are mainly based on laser-cooled atoms and ultra-stable cavity frequency stabilization technology. They are highly complex, large in size and weight, and low in reliability. They are difficult to meet the application needs of miniaturized, highly reliable and practical optical clocks in future space-based space-time benchmarks, national integrated PNT, laser intersatellite links and time and frequency transmission, and precision measurement.

[0004] Existing laboratory optical clocks face the problems of high overall technical complexity, low reliability and difficulty in miniaturization when moving towards engineering applications. Summary of the invention

[0005] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and provide a bubble-type thermal rubidium atomic optical clock, which can eliminate Doppler frequency shift without the need for laser cooling technology, greatly reduces complexity, and can realize a miniaturized practical rubidium atomic optical clock.

[0006] The technical solution of the present invention is:

[0007] The invention discloses a bubble-type thermal rubidium atomic clock optical clock, comprising: an optical fiber laser, an optical fiber isolator, an optical fiber beam splitter, an optical power amplification and frequency doubling waveguide component, a rubidium atomic bubble structure, a photomultiplier tube, a low-noise preamplifier, a servo, an electro-optical phase modulator and a proportional integral differential controller; wherein the optical signal generated by the optical fiber laser passes through the optical fiber isolator and is divided into two laser signals by the optical fiber beam splitter, one laser signal is output, and the other laser signal is phase-modulated by the electro-optical phase modulator and then passes through the optical power amplification and frequency doubling waveguide component. The excitation laser is obtained after the power amplification and frequency doubling of the traveling light; the excitation laser is incident on the rubidium atomic bubble structure, and under the action of the bidirectional excitation laser signal matched with the light field mode, the rubidium atom undergoes a two-photon transition and radiates a fluorescence signal; the fluorescence signal is detected by a photomultiplier tube and converted into an electrical signal, and then amplified by a low-noise preamplifier and enters the server. The server uses the modulated reference signal to process the detected fluorescence signal to generate an error signal, and the error signal is fed back to control the fiber laser through a proportional-integral-differential controller, thereby achieving a laser signal output with high frequency stability.

[0008] In the above-mentioned atomic clock optical clock, the rubidium atomic bubble structure includes a fiber collimator, a lens, a rubidium atomic bubble and a cat's eye optical structure; wherein, after the excitation laser is processed by the fiber collimator, it enters the rubidium atomic bubble after being focused by the lens, and the light beam passing through the rubidium atomic bubble is reflected by the cat's eye optical structure and then re-incident into the rubidium atomic bubble, and the optical paths of the bidirectionally propagating light beams coincide in the rubidium atomic bubble, realizing light field mode matching, and the rubidium atoms undergo two-photon transitions and radiate fluorescence signals.

[0009] In the above-mentioned atomic clock optical clock, the cat's eye optical structure includes a first narrowband filter F1, a polarizer, a beam splitter BS, a first lens Lens1, a first curved reflector M1, a second lens Lens2, a photomultiplier tube PMT and a second curved reflector M2; wherein the first lens Lens1 and the first curved reflector M1 are respectively located at X1 and X2 from one end of the rubidium atomic bubble, and the laser is incident on the rubidium atomic bubble after passing through the narrowband filter F1, the polarizer and the beam splitter BS to generate transmitted light, and the transmitted light is incident on the rubidium atomic bubble again after passing through the first lens Lens1 and the first curved reflector M1, and the two laser beams propagating in opposite directions jointly excite the rubidium atoms to generate 5S 1 / 2 Energy level transition to 5D 5 / 2 The fluorescence signal on one side of the rubidium atomic bubble is focused by the second lens Lens2 and collected by the photomultiplier tube PMT, while the fluorescence signal on the other side is reflected by the second curved reflector M2 and then focused by the second lens Lens2 onto the effective detection surface of the photomultiplier tube PMT.

[0010] In the above-mentioned atomic clock optical clock, the cat's eye optical structure also includes a second narrowband filter F2, which is located between the second lens Lens2 and the photomultiplier tube PMT and is used to filter out background stray light signals.

[0011] In the above-mentioned atomic clock optical clock, X1=14~16mm; X2=40~45mm.

[0012] In the above-mentioned atomic clock optical clock, the optical power amplification and frequency doubling waveguide component includes an optical power amplifier and a frequency doubling waveguide, wherein the optical power amplifier adopts a two-stage optical power amplification structure. The laser is amplified from 2 to 9 mW to 100 to 120 mW through the first stage amplification, and then amplified to 1 to 1.5 W through the second stage amplification, and then output after frequency doubling through the frequency doubling waveguide.

[0013] In the above-mentioned atomic clock optical clock, the optical power amplification and frequency doubling waveguide component includes a first coupler, a first isolator, an erbium-doped gain fiber, a wavelength division multiplexer, a first pump laser tube, a second isolator, a double-clad erbium-ytterbium co-doped gain fiber, a pump combiner, a second pump laser tube, a third isolator, a second coupler and a periodically polarized lithium niobate PPLN optical waveguide; wherein the laser is input into the erbium-doped gain fiber through the first coupler and the first isolator, and at the same time, the first pump laser tube is used to perform back pumping through the wavelength division multiplexer to achieve the first-stage amplification of the laser power; the laser after the first-stage amplification enters the double-clad erbium-ytterbium co-doped gain fiber through the second isolator, and at the same time, the second pump laser tube is used to perform back pumping through the pump combiner to achieve the second-stage amplification of the laser power; the laser after completing the two-stage optical power amplification passes through the third isolator and the second coupler, enters the PPLN optical waveguide for frequency doubling, and obtains frequency doubling laser output.

[0014] In the above-mentioned atomic clock optical clock, the optical power amplifier also includes an input light detector and an output light detector, wherein the input light detector is set in the first coupler and the output light detector is set in the second coupler to monitor the optical power of the input and output lasers in real time.

[0015] In the above-mentioned atomic clock optical clock, the frequency doubling waveguide uses a periodically poled lithium niobate optical waveguide to achieve optical double frequency.

[0016] In the above atomic clock, the pump laser tube used in the optical power amplifier is a semiconductor laser diode, and the pumping method is back pumping.

[0017] The advantages of the present invention compared with the prior art are:

[0018] (1) The present invention is based on the rubidium atom 5S 1 / 2 To 5D 5 / 2In the 778nm two-photon transition between energy levels, the rubidium atom absorbs two photons with the same frequency and opposite propagation directions at the same time, and the total angular momentum finally transferred to the rubidium atom is zero, so a two-photon transition spectrum that eliminates Doppler broadening can be obtained. Compared with laboratory cold atomic optical clocks, Doppler frequency shift and broadening can be eliminated without the use of laser cooling technology.

[0019] (2) The present invention adopts the technology of storing hot rubidium atoms in atomic bubbles and the communication C-band narrow-linewidth fiber laser technology. There is no need to use a high-precision ultra-stable optical cavity to pre-stabilize the laser. The complexity of the overall technical solution is greatly reduced, and a miniaturized and practical rubidium atomic optical clock can be realized.

[0020] (3) Compared with the laser cooling and trapped atom technology based on magneto-optical traps and the ultra-stable optical cavity laser pre-stabilization technology solutions commonly used in current laboratory cold atom optical clocks, the bubble-type hot rubidium optical clock technology solution proposed in the present invention does not require a complex atom cooling laser system and an ultra-stable optical cavity for laser pre-stabilization. The overall technical solution is simpler and has the important advantages of high reliability, easy engineering implementation, and miniaturization. It can meet the application needs of future space-based space-time benchmarks, national comprehensive PNT, laser intersatellite links and time-frequency transmission, and precision measurement for miniaturized, highly reliable, and practical optical clocks. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a general technical scheme diagram of a bubble-type rubidium atomic optical clock of the present invention;

[0022] Figure 2 It is a schematic diagram of the laser optical power amplification and optical waveguide frequency doubling technical solution of the present invention;

[0023] Figure 3 Schematic diagram of the structure design of the rubidium atom two-photon transition and fluorescence collection optical path of the present invention DETAILED DESCRIPTION

[0024] The working principle and working process of the present invention will be further explained and illustrated below in conjunction with the accompanying drawings.

[0025] like Figure 1As shown, the present invention discloses a bubble-type thermal rubidium atomic clock optical clock, comprising: an optical fiber laser, an optical fiber isolator, an optical fiber beam splitter, an optical power amplification and frequency doubling waveguide component, a rubidium atomic bubble structure, a photomultiplier tube, a low-noise preamplifier, a servo, an electro-optical phase modulator and a proportional integral differential controller; wherein the optical signal generated by the optical fiber laser passes through the optical fiber isolator and is divided into two laser signals by the optical fiber beam splitter, one laser signal is output, and the other laser signal is phase-modulated by the electro-optical phase modulator and then passes through the optical power amplification and frequency doubling waveguide component. After optical power amplification and frequency doubling, an excitation laser is obtained; the excitation laser is incident on the rubidium atomic bubble structure, and under the action of the bidirectional excitation laser signal matched with the light field mode, the rubidium atom undergoes a two-photon transition and radiates a fluorescence signal; the fluorescence signal is detected by a photomultiplier tube and converted into an electrical signal, and then amplified by a low-noise preamplifier and enters the server. The server uses a modulated reference signal to process the detected fluorescence signal to generate an error signal, and the error signal is fed back to control the fiber laser through a proportional-integral-differential controller, thereby achieving a laser signal output with high frequency stability.

[0026] Among them, the rubidium atomic bubble structure includes a fiber collimator, a lens, a rubidium atomic bubble and a cat's eye optical structure; wherein, after the excitation laser is processed by the fiber collimator, it enters the rubidium atomic bubble after being focused by the lens, and the light beam passing through the rubidium atomic bubble is reflected by the cat's eye optical structure and re-incident into the rubidium atomic bubble. The optical paths of the bidirectionally propagating light beams coincide in the rubidium atomic bubble, realizing light field mode matching, and the rubidium atoms undergo two-photon transitions and radiate fluorescence signals.

[0027] The cat's eye optical structure includes a first narrow-band filter F1, a polarizer, a beam splitter BS, a first lens Lens1, a first curved reflector M1, a second lens Lens2, a photomultiplier tube PMT, a second narrow-band filter F2 and a second curved reflector M2; wherein the first lens Lens1 and the first curved reflector M1 are respectively located at X1 and X2 from one end of the rubidium atomic bubble. After passing through the narrow-band filter F1, the polarizer and the beam splitter BS, the laser is incident on the rubidium atomic bubble. In the bubble, the transmitted light passes through the first lens Lens1 and the first curved reflector M1 and then re-enters the rubidium atomic bubble. The two laser beams propagating in opposite directions jointly excite the rubidium atoms to produce a two-photon transition from the 5S1 / 2 energy level to the 5D5 / 2 energy level. The fluorescence signal on one side of the rubidium atomic bubble is focused by the second lens Lens2 and collected by the photomultiplier tube PMT. The fluorescence signal on the other side is reflected by the second curved reflector M2 and then focused by the second lens Lens2 on the effective detection surface of the photomultiplier tube PMT. Among them, X1 = 14 ~ 16mm; X2 = 40 ~ 45mm. The second narrowband filter F2 is located between the second lens Lens2 and the photomultiplier tube PMT to filter out background stray light signals.

[0028] Among them, the optical power amplification and frequency doubling waveguide components include an optical power amplifier and a frequency doubling waveguide. The optical power amplifier adopts a two-stage optical power amplification structure. The laser is amplified from 2 to 9 mW to 100 to 120 mW after the first stage amplification, and then amplified to 1 to 1.5 W after the second stage amplification, and then output after frequency doubling by the frequency doubling waveguide. The frequency doubling waveguide uses a periodically polarized lithium niobate optical waveguide to achieve optical double frequency. The pump laser tube used in the optical power amplifier is a semiconductor laser diode, and the pumping method is back pumping.

[0029] The optical power amplification and frequency doubling waveguide component comprises a first coupler, a first isolator, an erbium-doped gain fiber, a wavelength division multiplexer, a first pump laser tube, a second isolator, a double-clad erbium-ytterbium co-doped gain fiber, a pump combiner, a second pump laser tube, a third isolator, a second coupler, a periodically polarized lithium niobate PPLN optical waveguide, an input optical detector and an output optical detector; wherein the laser is input into the erbium-doped gain fiber through the first coupler and the first isolator, and the first pump laser tube is used to perform back pumping through the wavelength division multiplexer to achieve the first stage amplification of the laser power; the laser after the first stage amplification enters the double-clad erbium-ytterbium co-doped gain fiber through the second isolator, and the second pump laser tube is used to perform back pumping through the pump combiner to achieve the second stage amplification of the laser power; the laser after completing the two-stage optical power amplification passes through the third isolator and the second coupler, enters the PPLN optical waveguide for frequency doubling, and obtains frequency doubling laser output. An input light detector is arranged at the first coupler, and an output light detector is arranged at the second coupler, so as to monitor the optical power of the input and output lasers in real time.

[0030] Example

[0031] The present invention provides a technical solution for miniaturizing a bubble-type thermal rubidium atomic clock. The basic principle is that the rubidium atom absorbs two 778nm photons at the same time and changes from the ground state 5S 1 / 2 Transition to excited state 5D 5 / 2 , then relax to 6P 3 / 2 energy level, and finally returns to the ground state 5S through spontaneous radiation 1 / 2 , by detecting 6P 3 / 2 Return to 5S 1 / 2 The 420nm fluorescence signal of the spontaneous emission of the state is used to lock the frequency of the interrogation laser, thereby achieving a highly stable laser signal output. 1 / 2 -5P 1 / 2There is a small frequency difference between the two wavelengths (795nm), so a two-photon transition spectrum with a strong signal amplitude can be obtained. The two-photon transition energy level is detected by radiating 420nm fluorescence through the cascade of 5D-6P-5S. Since the 420nm fluorescence wavelength is far away from the 778nm laser, it is easy to filter out the background light noise in the 420nm fluorescence, and obtain the atomic transition spectrum with a high signal-to-noise ratio.

[0032] The technical solution of the present invention mainly includes two key technologies: laser optical power amplification and frequency doubling technology and rubidium atom 5S 1 / 2 To 5D 5 / 2 Energy level two-photon transition pumping and fluorescence collection technology.

[0033] Laser Optical Power Amplification and Frequency Doubling Technology

[0034] To achieve 5S of rubidium atoms 1 / 2 To 5D 5 / 2 778nm (385THz) two-photon transition between energy levels. In order to obtain the high-intensity two-photon transition spectrum signal of rubidium atoms, a high-intensity 778nm laser is required for pumping. Commercial communication C-band fiber lasers have the significant advantages of mature technology, high reliability, and narrow linewidth. The 778nm laser is obtained by optical power amplification and optical double frequency doubling of commercial 1556nm communication lasers, which can be used to pump rubidium atoms to produce two-photon transition signals without Doppler broadening. 1556nm laser optical power amplification adopts fiber amplification technology based on doping rare earth elements. Rare earth elements are doped into the core of the optical fiber, and the signal light passing through is amplified by pump light excitation. This technology has the characteristics of high reliability, compact structure and low power consumption. 1556nm laser optical power amplification is based on a two-stage amplification structure design, including pre-amplification and main amplification. The first-stage amplifier amplifies the 1556nm laser power from a few mW to about 100mW, and the second-stage amplifier amplifies the 1556nm laser power to about 1.5W.

[0035] The 1556nm laser is optically doubled by using a periodically poled lithium niobate (PPLN) optical waveguide to obtain a 778nm laser. The PPLN optical waveguide achieves π phase inversion by periodically changing the domain structure of the lithium niobate crystal to maintain the matching phase relationship between the fundamental wave and the generated harmonics, so that the total phase mismatch of each cycle is zero, thereby ensuring efficient harmonic generation. A single pump light enters the PPLN waveguide. When the pump light is located at the quasi-phase matching wavelength of the PPLN optical waveguide frequency doubling process, the pump light can undergo a frequency doubling process to generate new frequency doubling light, and the pump light photons are annihilated and generate frequency doubling light photons. Since the optical waveguide structure can confine the light energy in a waveguide area with a very small cross-sectional area, the optical power density is effectively improved. Therefore, by using periodically poled lithium niobate optical waveguides for optical frequency doubling, the 1556nm laser can be efficiently frequency doubling to a 778nm laser.

[0036] Rubidium Atom 5S 1 / 2 To 5D 5 / 2 Energy level two-photon transition and fluorescence collection technology

[0037] To obtain rubidium atoms 5S 1 / 2 To 5D 5 / 2 To eliminate the Doppler two-photon resonant transition spectrum of the energy level, the two photons absorbed simultaneously by the rubidium atom must have wave vectors of equal magnitude and opposite directions, that is, the two photons have the same frequency and propagate in opposite directions. In order to reduce the Doppler absorption line background, the two laser beams propagating in opposite directions should achieve light field mode matching as much as possible to ensure that the reflected beam and the incident beam strictly coincide. In the optical path structure of the two-photon transition bidirectional laser transmission, an optical design based on a "cat's eye" optical lens is adopted. Based on the optical simulation software, the surface shape and specific parameters of the lens and reflector in the rubidium atom two-photon transition pumping optical path are optimized, so that the Gaussian beam can achieve accurate mode matching when it is transmitted back and forth in the rubidium bubble.

[0038] Rubidium atoms are composed of 5S 1 / 2 Energy level transition to 5D 5 / 2 After the energy level relaxes to 6P 3 / 2 energy level, and then through spontaneous radiation from 6P 3 / 2 The energy level returns to the ground state 5S 1 / 2 , radiating 420nm fluorescence. Therefore, it is possible to detect the rubidium atom 6P 3 / 2 -5S 1 / 2 The spontaneous emission of 420nm fluorescence signal is used to obtain 5S of rubidium atoms 1 / 2 To 5D 5 / 2The intensity of the two-photon transition signal of the energy level. Since the intensity of the spontaneously emitted 420nm fluorescence signal is weak and the radiation direction is random, there is also a 778nm background stray light signal. Therefore, in order to obtain a high signal-to-noise ratio rubidium atom two-photon transition signal, the background light noise needs to be filtered out. The structural design of the high-efficiency fluorescence signal collection optical path with a large solid angle is an important factor affecting the fluorescence signal detection. In the optical path design, by setting a focusing lens group and a reflective surface on both sides of the rubidium bubble, the 420nm fluorescence radiated by the rubidium atom can be focused as much as possible on the effective detection surface of the photomultiplier tube. The constructed bidirectional fluorescence collection optical path is simulated by optical simulation software, and the collection solid angle of 420nm fluorescence can reach 0.96π.

[0039] The overall technical solution of bubble-type thermal rubidium atomic optical clock is as follows: Figure 1 As shown. The fiber laser with a central wavelength of 1556nm first passes through a fiber isolator, and then is split into two by a 10:90 fiber beam splitter. One path is output, and the other path is phase modulated by a waveguide electro-optical crystal modulator. After optical power amplification, the optical waveguide doubles the frequency to obtain a 778nm excitation laser. The 778nm laser is output by a fiber collimator, focused by a lens, and incident on the rubidium atomic bubble. The 778nm light beam that passes through the rubidium atomic bubble is reflected by the cat's eye optical structure and re-incident into the rubidium atomic bubble. The bidirectionally propagating 778nm light beam overlaps in the rubidium atomic bubble, achieving light field mode matching. The rubidium atom absorbs a photon in the forward and reverse directions at the same time, completing the two-photon transition, which is generated by 5S 1 / 2 Energy level transition to 5D 5 / 2 energy level, and then relaxes to 6P 3 / 2 Energy level, the last 6P 3 / 2 The rubidium atom on the energy level returns to the ground state 5S by radiating a 420nm fluorescence signal 1 / 2 By detecting the intensity of 420nm fluorescence, which reflects the situation of 778nm two-photon transition, the photomultiplier tube converts the detected 420nm fluorescence into an electrical signal, which then enters the servo module after low-noise preamplification. The servo module demodulates the signal to obtain an error signal, and finally controls the frequency of the 1556nm fiber laser through a frequency feedback controller, thereby achieving high-frequency and stable laser signal output.

[0040] Laser optical power amplification and frequency doubling technology solutions such as Figure 2As shown. The laser optical power amplifier is based on the structural design of two-stage optical power amplification. The 1556nm laser is input into the erbium-doped gain fiber through the coupler and isolator, and the pump laser tube is used to perform back pumping through the wavelength division multiplexer to achieve the first stage amplification of the 1556nm laser power. Then, the 1556nm laser power enters the double-clad erbium-ytterbium co-doped gain fiber through the optical isolator, and the pump laser tube is used to perform back pumping through the wavelength division multiplexer to achieve the second stage amplification of the 1556nm laser power. After completing the two-stage optical power amplification, the 1556nm laser passes through the isolator and coupler, and then enters the PPLN optical waveguide for double frequency, thereby obtaining a 778nm laser output. An input optical detector and an output optical detector are respectively set at the input end and the output end to monitor the optical power of the input and output lasers in real time. The power of the input 1556nm laser can be amplified from several mW to more than 1W through two-stage optical power amplification. Laser double frequency is realized by using periodically poled lithium niobate (PPLN) optical waveguide. After the optical power is amplified, the 1556nm laser enters the periodically poled lithium niobate (PPLN) optical waveguide and outputs 778nm laser. Since the optical waveguide structure can confine the light energy in the waveguide area with a very small cross-sectional area, the optical power density is effectively improved, so a high frequency doubling efficiency can be obtained.

[0041] The optical path design structure of rubidium atom two-photon transition and fluorescence collection is as follows Figure 3 As shown. The 778nm laser emitted from the optical fiber passes through the collimator (COL), 780nm narrowband filter (F1), polarizer (Polarizer) and beam splitter (BS), and then enters the rubidium atomic bubble (Rb Cell) to the right. The transmitted light passes through the cat's eye retro-reflector composed of lens (Lens1) and curved reflector (M1) and then re-enters the rubidium atomic bubble (Rb Cell) to the left. The two laser beams propagating in opposite directions jointly excite the rubidium atoms to produce a two-photon transition from the 5S1 / 2 energy level to the 5D5 / 2 energy level. Photodetectors (PD1) and (PD2) are used to monitor the intensity of the incident and reflected 778nm laser light, respectively. The 778nm two-photon transition of the rubidium atom can be obtained by detecting the 420nm fluorescence signal generated by the spontaneous radiation of the rubidium atom 6P3 / 2-5S1 / 2. The 420nm fluorescence collection optical structure is set on the optical path perpendicular to the propagation of the 778nm laser. In order to improve the fluorescence collection solid angle, the fluorescence on one side of the rubidium atomic bubble is focused by the lens group (Lens2) and detected by the photomultiplier tube (PMT), and the fluorescence on the opposite side is reflected by the curved reflector (M2), focused by the lens group (Lens2) and detected by the photomultiplier tube (PMT). In addition, a narrow-band optical filter (F2 420nm) with a central wavelength of 420nm can be used before the photomultiplier tube (PMT) to filter out the 778nm background stray light signal.

[0042] The above embodiments are only explanations of the present invention and cannot be used as limitations of the present invention. Therefore, all implementation methods similar to the concept of the present invention or implementation methods used in other similar structures but with similar concepts to the present invention are within the protection scope of the present invention.

[0043] The above description is only the best specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

[0044] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A bubble-type thermal rubidium atomic clock optical clock, characterized in that: include: Fiber laser, fiber isolator, fiber beam splitter, optical power amplification and frequency doubling waveguide component, rubidium atomic bubble structure, photomultiplier tube, low noise preamplifier, server, electro-optic phase modulator and proportional integral differential controller; wherein, the optical signal generated by the fiber laser passes through the fiber isolator and is divided into two laser signals by the fiber beam splitter, one laser signal is output, and the other laser signal is phase modulated by the electro-optic phase modulator, and then passes through the optical power amplification and frequency doubling waveguide component to obtain an excitation laser; the excitation laser is incident on the rubidium atomic bubble structure, and under the action of the bidirectional excitation laser signal matched by the light field mode, the rubidium atom undergoes a two-photon transition and radiates a fluorescence signal; the fluorescence signal is detected by the photomultiplier tube and converted into an electrical signal, and then amplified by the low noise preamplifier and enters the server, the server uses the modulated reference signal to process the detected fluorescence signal to generate an error signal, and the error signal is fed back to control the fiber laser through the proportional integral differential controller, thereby realizing the output of a laser signal with high frequency stability; The rubidium atomic bubble structure comprises an optical fiber collimator, a lens, a rubidium atomic bubble and a cat's eye optical structure; wherein, after the excitation laser is processed by the optical fiber collimator, the light is focused by the lens and then enters the rubidium atomic bubble; the light beam passing through the rubidium atomic bubble is reflected by the cat's eye optical structure and then re-incident into the rubidium atomic bubble; the optical paths of the light beams propagating in both directions coincide in the rubidium atomic bubble, thereby achieving light field mode matching; the rubidium atoms undergo two-photon transition and radiate fluorescence signals; The cat's eye optical structure comprises a first narrowband filter F1, a polarizer, a beam splitter BS, a first lens Lens1, a first curved reflector M1, a second lens Lens2, a photomultiplier tube PMT and a second curved reflector M2; wherein the first lens Lens1 and the first curved reflector M1 are respectively located at X1 and X2 from one end of the rubidium atomic bubble; after the laser passes through the narrowband filter F1, the polarizer and the beam splitter BS, it is incident into the rubidium atomic bubble to generate transmitted light; after the transmitted light passes through the first lens Lens1 and the first curved reflector M1, it is incident into the rubidium atomic bubble again; the two laser beams propagating in opposite directions jointly excite the rubidium atoms to generate 5S 1 / 2 Energy level transition to 5D 5 / 2 The fluorescence signal on one side of the rubidium atomic bubble is focused by the second lens Lens2 and collected by the photomultiplier tube PMT, while the fluorescence signal on the other side is reflected by the second curved reflector M2 and then focused by the second lens Lens2 onto the effective detection surface of the photomultiplier tube PMT.

2. The bubble-type thermal rubidium atomic clock optical clock according to claim 1, characterized in that: The cat's eye optical structure further includes a second narrowband filter F2, which is located between the second lens Lens2 and the photomultiplier tube PMT and is used to filter out background stray light signals.

3. The bubble-type thermal rubidium atomic clock optical clock according to claim 1, characterized in that: X1=14~16mm; X2=40~45mm.

4. The bubble-type thermal rubidium atomic clock optical clock according to claim 1, characterized in that: The optical power amplification and frequency doubling waveguide component includes an optical power amplifier and a frequency doubling waveguide, wherein the optical power amplifier adopts a two-stage optical power amplification structure, the laser is amplified from 2 to 9 mW to 100 to 120 mW through the first stage amplification, and then the power is amplified to 1 to 1.5 W through the second stage amplification, and then the power is doubled through the frequency doubling waveguide for output.

5. The bubble-type thermal rubidium atomic clock optical clock according to claim 4, characterized in that: The optical power amplification and frequency doubling waveguide component comprises a first coupler, a first isolator, an erbium-doped gain fiber, a wavelength division multiplexer, a first pump laser tube, a second isolator, a double-clad erbium-ytterbium co-doped gain fiber, a pump combiner, a second pump laser tube, a third isolator, a second coupler and a periodically polarized lithium niobate PPLN optical waveguide; wherein the laser is input into the erbium-doped gain fiber through the first coupler and the first isolator, and the first pump laser tube is used to perform back pumping through the wavelength division multiplexer to achieve the first stage amplification of the laser power; the laser after the first stage amplification enters the double-clad erbium-ytterbium co-doped gain fiber through the second isolator, and the second pump laser tube is used to perform back pumping through the pump combiner to achieve the second stage amplification of the laser power; the laser after completing the two-stage optical power amplification passes through the third isolator and the second coupler, and enters the periodically polarized lithium niobate PPLN optical waveguide for frequency doubling to obtain frequency doubling laser output.

6. The bubble-type thermal rubidium atomic clock optical clock according to claim 5, characterized in that: The optical power amplifier also includes an input optical detector and an output optical detector, wherein the input optical detector is arranged at the first coupler and the output optical detector is arranged at the second coupler, so as to monitor the optical power of the input and output lasers in real time.

7. The bubble-type thermal rubidium atomic clock optical clock according to claim 4, characterized in that: The frequency doubling waveguide realizes optical double frequency by using a periodically poled lithium niobate optical waveguide.

8. The bubble-type thermal rubidium atomic clock optical clock according to claim 4, characterized in that: The pump laser tube used by the optical power amplifier is a semiconductor laser diode, and the pumping method is back pumping.

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