Small integrating sphere cold atomic clock based on fiber scope

Abstract

The invention provides a fiber mirror-based small integrating sphere cold atomic clock, which comprises a diffuse reflection laser cooling system and an optical system, and is characterized in that the optical system comprises a DFB laser (1), an ECDL external cavity laser (2), a polarization beam splitter (3), an acoustic optical modulator (4), a 1 / 4 wave plate (5), a diaphragm (6), a reflector (7) and an optical fiber coupler (8); the diffuse reflection laser cooling system comprises a first optical fiber (9), a second optical fiber (10), a fiber mirror (11), a polytetrafluoroethylene cavity (12) and a photoelectric detector (13). The small integrating sphere cold atomic clock system based on the fiber mirror not only can provide a diffuse reflection laser cooling system for miniaturization, but also lays a solid foundation for further miniaturization of the whole integrating sphere cold atomic clock system.

Description

Technical Field

[0001] This invention relates to the field of cold atom frequency standard technology, and in particular to a small integrating sphere cold atom clock based on a fiber optic mirror. Background Technology

[0002] The basic working principle of the integrating sphere cooling process is to lock the output frequency of the local oscillator to the transition lines of cold atoms cooled by diffuse reflection laser, thereby enabling the local oscillator to output a highly stable and accurate frequency signal. Diffuse reflection laser cooling provides a compact cold atom system for quantum precision measurement processes, especially for integrating sphere cold atom clocks. Diffuse reflection laser cooling is an efficient magnetic field-free technique that can cool neutral atoms on the μK scale, providing a cold atom cloud for quantum precision measurement. It has been successfully used in integrating sphere cold atom clocks (ISCAC) and will be extended to many other fields, such as atomic gravimeters, magnetometers, and microwave measurements. The integrating sphere cold atom clock is a next-generation space atomic clock, and its prototype has shown excellent results: short-term frequency stability of 3 × 10⁻¹³ τ⁻¹ / ² and preliminary long-term frequency stability of 8.6 × 10⁻¹⁶. Diffuse reflection laser cooling, as a key technology of integrating sphere cold atom clocks, involves the process of cooling the laser, re-pumping the light, and then diffusely cooling the pump and probe lights within a cylindrical microwave cavity. Diffuse laser cooling is used to provide a diffuse optical field environment for integrating sphere systems. The laser beam is expanded by a lens and uniformly covers the inner surface of the diffuse cavity of the integrating sphere clock, while maintaining a high vacuum state within the cylindrical cavity. Diffuse laser cooling systems are relatively complex, but space integrating sphere cold atom clocks require miniaturization and lightweight design. Therefore, the less complex diffuse laser cooling system is one of the main development trends for integrating sphere cold atom clocks.

[0003] Currently, laboratories and industry have made numerous efforts and explored many excellent solutions, including compact designs of integrating sphere optical systems, miniaturization of vacuum systems, integration of integrating sphere microwave cavities, control of the shape of cold atom clouds in cylindrical cavities, and compact physical packaging of a vacuum chamber. Although traditional diffuse reflection laser cooling systems are relatively simple and compact, the volume of diffuse reflection laser cooling systems with cylindrical cavities is already close to 1L, making further miniaturization of integrating sphere cold atom clock systems difficult. To date, there are no feasible ideas for miniaturizing diffuse reflection laser cooling, therefore it is necessary to find other solutions for miniaturization. Summary of the Invention

[0004] This invention provides a small integrating sphere cold atom clock based on a fiber optic mirror, comprising: a diffuse reflection laser cooling system and an optical system. The optical system comprises: a DFB laser (1), an ECDL external cavity laser (2), a polarization beam splitter (3), an acousto-optic modulator (4), a quarter-wave plate (5), an aperture (6), a mirror (7), and a fiber optic coupler (8). The diffuse reflection laser cooling system comprises: a first fiber (9), a second fiber (10), a fiber optic mirror (11), a polytetrafluoroethylene cavity (12), and a photodetector (13).

[0005] Optionally, the DFB laser (1) is used to provide a specific frequency of repump light to the integrating sphere system, which, together with the cooling light, acts on the atoms to cool them into atomic clusters.

[0006] Optionally, the ECDL external cavity laser (2) is used to generate a specifically tuned laser beam to manipulate atoms and to generate laser light to provide cooling light, probe light and pump light for the integrating sphere cold atom clock. The cooling light and the re-pump light work together to cool the hot atoms into atomic clusters, and then the pump light is used to prepare the state. The probe light is used to detect the cold atomic clusters, wherein the pump light is used to prepare the cooled atoms to a specific ground state.

[0007] Optionally, the polarization beam splitter (3) is used for laser control, polarization state management and suppression of stray light in the beam, and is used to split the ECDL external cavity laser (2) into two beams, one of which is used as a pump light for backup and the other is used for cooling and detection backup.

[0008] Optionally, the acousto-optic modulator (4) is used to control the frequency and intensity of the laser beam emitted from the laser, and to shift the laser emitted by the DFB laser (1) and the ECDL external cavity laser (2) to the frequencies of the cooling light, pump light, re-pump light and probe light required for the diffuse reflection cooling absorption process.

[0009] Optionally, the quarter-wave plate (5) is placed after the acousto-optic modulator (4).

[0010] Optionally, the aperture (6) is used to block the unwanted light spot after the frequency shift of the acousto-optic modulator (4).

[0011] Optionally, the reflector (7) is used to change the direction of the light path.

[0012] Optionally, the first optical fiber (9) and the second optical fiber (10) are used to inject cooling light, pump light and probe light for diffuse reflection laser cooling into the diffuse reflection cavity.

[0013] Optionally, the photodetector (13) is used to detect the transmitted probe light.

[0014] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and accompanying drawings. Attached Figure Description

[0015] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0016] Figure 1 This is a schematic diagram of a small integrating sphere cold atom clock based on a fiber optic mirror according to an embodiment of the present invention. Detailed Implementation

[0017] To address the lack of a small integrating sphere cold atom clock based on a fiber optic mirror in related technologies, a small integrating sphere cold atom clock based on a fiber optic mirror is provided.

[0018] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention. Furthermore, the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0019] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of the embodiments of the present invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein.

[0020] This invention proposes a miniaturized integrating sphere cold atom clock based on a fiber optic mirror, aiming to provide a novel miniaturization solution for diffuse reflection laser cooling systems by combining fiber optic mirrors and diffuse reflection laser cooling technology. By simplifying the diffuse reflection laser beam, both the diffuse reflection laser cooling system and the integrating sphere cold atom clock are miniaturized. The miniaturized integrating sphere cold atom clock system based on a fiber optic mirror can significantly reduce the volume of the diffuse reflection cooling system, effectively shrinking the size of the integrating sphere cold atom clock system based on this miniaturized diffuse reflection cooling system.

[0021] The present invention relates to a miniaturized integrating sphere cold atom clock based on a fiber optic mirror. Its diffuse reflection laser cooling system mainly consists of an optical fiber, a fiber optic mirror, and a polytetrafluoroethylene (PTFE) cavity. The inner surfaces of the fiber optic mirror and PTFE provide the necessary surfaces for diffuse reflection, allowing atoms to be successfully cooled and detected within a miniaturized region. The fabrication of the fiber optic mirror and the simplified optical system enable the miniaturization of the laser cooling system, laying a solid foundation for further miniaturization of the overall integrating sphere cold atom clock system in the future. This miniaturized integrating sphere cold atom clock system based on a fiber optic mirror not only enables the miniaturization of diffuse reflection laser cooling systems but also lays a solid foundation for further miniaturization of the entire integrating sphere cold atom clock system.

[0022] Figure 1 An embodiment of the present invention illustrates a small integrating sphere cold atom clock based on a fiber optic mirror, comprising: a diffuse reflection laser cooling system and an optical system. The optical system comprises: a DFB laser (1), an ECDL external cavity laser (2), a polarization beam splitter (3), an acousto-optic modulator (4), a quarter-wave plate (5), an aperture (6), a mirror (7), and a fiber optic coupler (8). The diffuse reflection laser cooling system comprises: a first fiber (9), a second fiber (10), a fiber optic mirror (11), a polytetrafluoroethylene cavity (12), and a photodetector (13).

[0023] Optionally, the DFB laser (1) is used to provide a specific frequency of repump light to the integrating sphere system, which, together with the cooling light, acts on the atoms to cool them into atomic clusters.

[0024] The DFB laser (1) is one of the core components of the optical system, undertaking the key task of controlling the atomic population during atomic cooling. The narrow linewidth characteristic of the DFB laser (1) reduces Doppler broadening, improves cooling efficiency, and avoids frequency jumps caused by mode competition, ensuring spectral purity. It also has low phase noise characteristics, reduces laser linewidth, increases the number of cold atoms, and has high stability, reducing clock drift. Furthermore, the miniaturization and reliability of the DFB laser (1) are consistent with the compact design of integrating sphere clocks. Its core value lies in providing a laser output with stable frequency, narrow linewidth, and controllable power. The role of the DFB laser (1) is to provide a precisely frequencyd repump light for the integrating sphere system, which, together with the cooling light, acts on the atoms, causing them to cool into atomic clusters.

[0025] Optionally, the ECDL external cavity laser (2) is used to generate a specifically tuned laser beam to manipulate atoms and to generate laser light to provide cooling light, probe light and pump light for the integrating sphere cold atom clock. The cooling light and the re-pump light work together to cool the hot atoms into atomic clusters, and then the pump light is used to prepare the state. The probe light is used to detect the cold atomic clusters, wherein the pump light is used to prepare the cooled atoms to a specific ground state.

[0026] The ECDL external cavity laser (2) is one of the essential core components for achieving high performance (high stability, low noise) in the integrating sphere cold atom clock. It provides the necessary, high-quality "light" tool for preparing cold atom samples and accurately probing atomic states. The ECDL external cavity laser (2) is used to generate a highly stable, narrow-linewidth, precisely tunable laser beam for manipulating (cooling, pumping, and probing) atoms. The laser generated by the ECDL external cavity laser (2) provides cooling light, probe light, and pump light for the integrating sphere cold atom clock. The cooling light and the re-pump light work together to cool the hot atoms into atomic clusters, and then the pump light is used for state preparation. The probe light can detect the cold atomic clusters, and the pump light can prepare the cooled atoms to a specific fine ground state.

[0027] Optionally, the polarization beam splitter (3) is used for laser control, polarization state management and suppression of stray light in the beam, and is used to split the ECDL external cavity laser (2) into two beams, one of which is used as a pump light for backup and the other is used for cooling and detection backup.

[0028] The polarization beam splitter (PBS) (3) is an indispensable component in the integrating sphere optical system. It is mainly used for precise control of the laser, polarization state management, and suppression of stray light in the beam, ensuring efficiency and accuracy in the cold atom preparation and detection process. The polarization beam splitter (PBS) (3) first splits the ECDL external cavity laser (2) into two beams, one of which is used as a backup pump light, and the other is used for cooling and detection.

[0029] Optionally, the acousto-optic modulator (4) is used to control the frequency and intensity of the laser beam emitted from the laser, and to shift the laser emitted by the DFB laser (1) and the ECDL external cavity laser (2) to the frequencies of the cooling light, pump light, re-pump light and probe light required for the diffuse reflection cooling absorption process.

[0030] The acousto-optic modulator (AOM) (4) plays a crucial role in the integrating sphere cold atom clock, primarily by precisely and rapidly controlling the frequency and intensity of the laser beam emitted from the laser. This control is essential for the preparation and detection of cold atoms. Its function in the system is to precisely shift the laser beams emitted from the DFB laser (1) and the ECDL external cavity laser (2) to the frequencies required for the diffuse reflection cooling absorption process, including the cooling light, pump light, re-pump light, and probe light. This creates conditions for the high stability and low noise performance of the integrating sphere cold atom clock.

[0031] Optionally, the quarter-wave plate (5) is placed after the acousto-optic modulator (4).

[0032] The quarter-wave plate (QWP) (5) plays a crucial role in the frequency shifting operation of the integrating sphere cold atom clock. After being placed in the acousto-optic modulator (AOM) (4), the fast axis angle of the quarter-wave plate can be precisely adjusted, correcting it back to high-quality linearly polarized light. This ensures that the laser entering the diffuse-reflection laser cooling cavity has high optical power.

[0033] Optionally, the aperture (6) is used to block the unwanted light spot after the frequency shift of the acousto-optic modulator (4).

[0034] The aperture (6) is used to block the unwanted light spot after the frequency shift of the acousto-optic modulator (AOM) (4), so as to prevent stray light from entering the diffuse reflection laser cooling cavity and ensure the diffuse reflection efficiency of the integrating sphere cold atom clock.

[0035] Optionally, the reflector (7) is used to change the direction of the light path.

[0036] The reflector (7) plays a crucial role in the optical components of the integrating sphere cold atom clock. The reflector (7) can change the direction of the light path, optimize the size of the optical system, and provide conditions for the miniaturization of the integrating sphere cold atom clock.

[0037] The fiber optic coupler (8) is a key device for injecting spatial light into the optical fiber. By adjusting the optical path direction between the fiber optic coupler and the spatial light, the coupling efficiency of the fiber optic coupler can be improved, allowing the spatial light to be injected into the optical fiber efficiently and avoiding the waste of optical power.

[0038] Optionally, the first optical fiber (9) and the second optical fiber (10) are used to inject cooling light, pump light and probe light for diffuse reflection laser cooling into the diffuse reflection cavity.

[0039] The first fiber (9) and the second fiber (10) are key components of the optical section of the integrating sphere cold atom clock. Cooling light, pump light, and probe light used for diffuse reflection laser cooling are injected into the diffuse reflection cavity.

[0040] For the fiber mirror (11), the surface of the fiber can be processed into a fiber mirror for laser reflection, with another identical fiber placed in the opposite direction. Two fiber mirrors fabricated by laser ablation have advantages in terms of smaller radius of curvature and lower surface roughness, resulting in a smaller size and higher reflectivity after coating. The two inherent fibers in the diffuse reflection laser cooling system reduce the number of laser beams and decrease the laser injection angle.

[0041] For the PTFE cavity (12), to prevent light from escaping between the two fiber mirrors, a PTFE cylindrical cavity is placed to surround the two fibers, which provides the inner surface required for diffuse reflection. Therefore, the combination of the two fiber mirrors and the PTFE cylindrical cavity can provide a reflective inner surface for diffuse laser cooling. The first fiber (9), the second fiber (10), the fiber mirror (11), and the PTFE cavity (12) together constitute the diffuse laser cooling system.

[0042] Optionally, the photodetector (13) is used to detect the transmitted probe light.

[0043] For the photodetector (13), it is used to detect the transmitted probe light.

[0044] In the aforementioned process, this method innovatively proposes a miniaturized integrating sphere cold atom clock based on a fiber mirror. Its diffuse reflection laser cooling system mainly consists of optical fibers, fiber mirrors, and polytetrafluoroethylene (PTFE). The inner surfaces of the fiber mirrors and PTFE provide the necessary inner surfaces for diffuse reflection, allowing atoms to be successfully cooled and detected within a miniaturized region. Furthermore, the optical system in this new scheme can be simplified, and the efficiency of laser power can be improved. Therefore, along with the simplified optical system, this new scheme not only enables the miniaturization of diffuse reflection laser cooling systems but also lays a solid foundation for further miniaturization of the entire ISCAC system.

[0045] In the aforementioned process, this method innovatively proposes a miniaturized integrating sphere cold atom clock based on a fiber mirror. Its diffuse reflection laser cooling system mainly consists of optical fibers, fiber mirrors, and polytetrafluoroethylene (PTFE). The inner surfaces of the fiber mirrors and PTFE provide the necessary inner surfaces for diffuse reflection, allowing atoms to be successfully cooled and detected within a miniaturized region. Furthermore, the optical system in this new scheme can be simplified, and the efficiency of laser power can be improved. Therefore, along with the simplified optical system, this new scheme not only enables the miniaturization of diffuse reflection laser cooling systems but also lays a solid foundation for further miniaturization of the entire ISCAC system.

[0046] This invention provides a miniature integrating sphere cold atom clock based on fiber optic mirrors. The scheme for a miniature integrating sphere cold atom clock based on fiber optic mirrors consists of a diffuse reflection laser cooling system and an optical system. The diffuse reflection laser cooling system mainly comprises optical fibers, fiber optic mirrors, and a polytetrafluoroethylene (PTFE) cylindrical cavity. The PTFE cylindrical cavity is used to surround the two optical fibers to prevent light from escaping between the two fiber optic mirrors, thus providing the inner surface required for diffuse reflection.

[0047] The small integrating sphere cold atom clock based on fiber mirrors consists of a fiber mirror-based diffuse reflection laser cooling system and an optical system. The fiber mirror-based diffuse reflection laser cooling system is composed of optical fiber, fiber mirror, and a cylindrical cavity made of polytetrafluoroethylene (PTFE), in which laser cooling, state preparation, microwave interrogation, and absorption detection occur simultaneously within the cavity.

[0048] The small integrating sphere cold atom clock system based on fiber mirrors consists of two optical fibers used for the transmission of cooling light, pump light, repump light, and probe light. The two inherent optical fibers in the diffuse reflection laser cooling system reduce the number of laser beams and decrease the laser injection angle.

[0049] A fiber mirror is created by processing the surfaces of two optical fibers to be used for laser reflection, with another identical fiber placed in the opposite direction. Two fiber mirrors fabricated by laser ablation offer advantages in terms of smaller radius of curvature and lower surface roughness, resulting in a smaller size and higher reflectivity after coating.

[0050] The PTFE cylindrical cavity is used to prevent light from escaping between the two fiber optic mirrors and is enclosed on the outer surface of the two optical fibers. This PTFE cylindrical cavity provides the inner surface required for diffuse reflection.

[0051] The operation process of the diffuse reflection laser cooling system based on fiber mirrors is as follows:

[0052] The incident cooling light, pump light, repump light, and probe light are all reflected by fiber optic mirrors and polytetrafluoroethylene, allowing atoms to be successfully cooled and detected in miniaturized regions.

[0053] The combination of two fiber mirrors and a PTFE cylindrical cavity provides a reflective inner surface for diffuse laser cooling. The incident laser beam is reflected by the fiber mirrors and PTFE, allowing atoms to be successfully cooled within a miniaturized diffuse laser cooling region. Furthermore, the cold atoms can interact with microwaves via a microwave horn to generate Ramsey fringes. Additionally, this system offers a novel absorption detection method where cold atoms interact with near-resonant probe light reflected from the inner surface; the transmitted probe light is detected by a detector (PD), implying improved efficiency of the cooling light.

[0054] The specific implementation of the optical system in the small integrating sphere cold atom clock based on fiber optic mirrors is as follows:

[0055] In the optical system, ECDL and DFB lasers provide the laser beams required for this small integrating sphere cold atom clock system based on fiber mirrors: cooling light, pump light, repump light, and probe light. For cesium, ECDL and DFB lasers provide frequency stabilization for the optical system, and an acousto-optic modulator (AOM) provides four laser frequency shift processes.

[0056] After laser frequency shifting, four laser beams are injected into the diffuse reflection laser cooling system through a single-mode polarization-maintaining fiber.

[0057] In the aforementioned process, this method innovatively proposes for the first time a miniaturized integrating sphere cold atom clock based on a fiber mirror. In this miniaturized diffuse reflection laser cooling system, the diameter of the fiber mirror is 100–150 μm, which facilitates miniaturization. Therefore, the system volume primarily depends on the size of the PTFE cavity. Considering the required cold atom cloud is on the order of mm³, and the PTFE wall thickness is on the order of mm, the system volume can be predicted to be mm³. Compared to traditional diffuse reflection laser cooling systems, the volume of the new diffuse reflection laser cooling system is reduced by at least five orders of magnitude. This signifies a significant reduction in the ISCAC physics system. Notably, the components of this system exhibit good stability in an ultra-high vacuum environment, and their high reflectivity can be maintained long-term, meeting the experimental conditions required for ISCAC operation. Furthermore, the optical system providing the required laser beam can be constructed using miniaturized optical components, which also has miniaturization potential.

[0058] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0059] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A miniature optical-fiber-mirror-based integrated-sphere cold atomic clock, characterized in that, It comprises: A diffuse reflection laser cooling system and an optical system, the optical system comprising: a DFB laser (1), an ECDL external cavity laser (2), a polarization beam splitter (3), an acousto-optic modulator (4), a 1 / 4 wave plate (5), an aperture (6), a mirror (7), and a fiber coupler (8); the diffuse reflection laser cooling system comprising: a first optical fiber (9), a second optical fiber (10), a fiber mirror (11), a polytetrafluoroethylene cavity (12), and a photodetector (13).

2. The atomic clock of claim 1, wherein, The DFB laser (1) is used to provide specific frequency repumping light for the integrating sphere system, and works together with the cooling light on the atoms to cool the atoms into an atomic group.

3. The atomic clock of claim 2, wherein, The ECDL external cavity laser (2) is used to generate a laser beam with specific tuning, for manipulating atoms, for generating laser light to provide cooling light, probe light and pumping light for the integrating sphere cold atom clock, the cooling light works together with the repumping light on the atoms to cool the hot atoms into an atomic group, and then the state is prepared by the pumping light, and the probe light is used to realize the detection of the cold atomic group, wherein the pumping light is used to prepare the cooled atoms to a specific ground state.

4. The atomic clock of claim 1, wherein, The polarization beam splitter (3) is used for laser control, polarization state management and stray light suppression in the beam, and is used to split the ECDL external cavity laser (2) into two beams, one of which is used as a standby pumping light, and the other is used as a standby cooling and detection.

5. The atomic clock of claim 1, wherein, The acousto-optic modulator (4) is used to control the frequency and intensity of the laser beam from the laser, and is used to shift the frequency of the laser emitted by the DFB laser (1) and the ECDL external cavity laser (2) to the cooling light, pumping light, repumping light and probe light frequencies required by the diffuse reflection cooling absorption process.

6. The atomic clock of claim 1, wherein, The 1 / 4 wave plate (5) is placed behind the acousto-optic modulator (4).

7. The atomic clock of claim 1, wherein, The aperture (6) is used to block the unwanted light spots after the frequency shift of the acousto-optic modulator (4).

8. The atomic clock of claim 1, wherein, The mirror (7) is used to change the direction of the light path.

9. The atomic clock of claim 1, wherein, The first optical fiber (9) and the second optical fiber (10) are used to inject the cooling light, pumping light and probe light for diffuse reflection laser cooling into the diffuse reflection cavity.

10. The atomic clock of claim 1, wherein, The photodetector (13) is used to detect the transmitted probe light.

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