Miniaturized vacuum microwave cavity for an integrated sphere cold atomic clock

Abstract

The application provides a miniaturized vacuum microwave cavity of an integrating sphere cold atomic clock, and belongs to the technical field of cold atomic frequency standards.The microwave cavity comprises, from top to bottom, a small-window piece fixing member, a small vacuum window piece, a flange upper cover, a dielectric inner cylinder, a cavity main body, a large vacuum window piece, a large-window piece fixing member and a waveguide coaxial conversion device arranged on the side wall of the cavity.The high-dielectric-constant ceramic coaxial waveguide conversion device in the application scheme makes excitation more stable, and the combination of the high-dielectric-constant and high-diffuse-reflectivity dielectric inner cylinder makes the microwave cavity smaller.The microwave cavity has good vacuum performance, the high-dielectric-constant ceramic coaxial waveguide conversion device has vacuum sealing function and microwave signal transmission function, the vacuum cavity and the microwave cavity are combined into one, and the system volume is obviously reduced.

Description

Technical Field

[0001] This invention relates to the field of cold atom frequency standard technology, and more particularly to a miniaturized vacuum microwave cavity for an integrating sphere cold atom clock. Background Technology

[0002] Time is the most fundamental physical quantity for describing the motion of matter, and ultra-high precision time and frequency standards (frequency standards) are the cornerstone of modern technology and basic science. In traditional atomic clocks, the atoms move at extremely high speeds at room temperature, which leads to a severe Doppler shift, causing the resonance peak to be broadened and shifted. In contrast, cold atom sources have the advantages of narrow central fringe linewidth and high quality factor of the frequency discrimination curve.

[0003] While traditional cold atom clocks and early magneto-optical traps offer extremely high precision, they are also large, complex, and fragile systems, sensitive to vibrations and orientation, making them unsuitable for the harsh environments of space stations and satellites. The integrating sphere cold atom clock replaces all the complex and precise optical paths of traditional cold atom experiments with a hollow body internally coated with a highly diffuse reflective material. This makes the process of generating cold atom clusters extremely simple, compact, and robust.

[0004] The microwave cavity is the "heart" of traditional atomic frequency standards, and its performance directly determines the stability and accuracy of the standard. From hot atomic beam tubes to cold atomic fountains, the design and fabrication of microwave cavities have continuously evolved, pushing the limits of time measurement accuracy. They utilize the principle of resonance to enhance and purify the microwave field, providing an ideal and controllable interaction region for the interaction between atoms and microwaves.

[0005] Currently, the atomic cooling cavity and microwave action cavity structures of diffuse reflection cold atom clocks are generally divided into two types: One type involves fixing a slightly smaller diameter spherical quartz bulb inside a spherical microwave cavity. The incident light from a multimode optical fiber is reflected by the polished inner wall of the microwave cavity to form a diffuse reflection light field. The disadvantages of this structure are that the spherical microwave cavity makes it difficult to control the microwave field shape distribution within the cavity, the central microwave uniformity area is small, the spherical cavity is difficult to fabricate, and the reliability of the quartz bulb when used in space is questionable. The other type involves spraying a diffuse reflection coating onto the outer wall of a spherical or cylindrical cavity made of quartz or glass to reflect the injected light and generate an isotropic light field. The cooling cavity is then fixed in the central region of the cylindrical microwave cavity for microwave action. While reflecting light, this coating significantly affects the microwave field shape distribution within the cavity, and the coating powder can contaminate the microwave cavity wall, especially under interference from external environments such as vibration and temperature changes, resulting in poor reliability.

[0006] Furthermore, existing technologies, such as rubidium atomic clocks, often employ cylindrical metal cavity structures to achieve a stable resonant frequency of around 6.834 GHz and a high quality factor. These cavities typically have a diameter of approximately 40–60 mm and a length of approximately 50 mm, resulting in a relatively large overall volume. While this structure ensures good field distribution and frequency stability, the cavity volume occupies a significant portion of the physical packaging space of the atomic clock, limiting the miniaturization and integration of the system. The excessively large size of traditional cavities makes it difficult to meet the demands of new applications such as lightweight design, low power consumption, and environmental adaptability. In addition, large metal cavities are susceptible to dimensional errors and temperature variations during processing and assembly, leading to resonant frequency drift and decreased long-term stability. Although chip-scale atomic clocks (CSACs) have a very small volume, they can only receive a limited number of atoms, resulting in a poor signal-to-noise ratio. Moreover, the vertical-cavity surface-emitting laser (VCSEL) of a chip-scale atomic clock is a critical component with a fixed lifespan; once the laser's performance degrades, the entire clock will fail. Summary of the Invention

[0007] To address the aforementioned issues, this invention proposes a miniaturized vacuum microwave cavity for an integrating sphere cold atom clock. This microwave cavity utilizes a dielectric cylinder with high dielectric constant and high diffuse reflectivity to fill the cavity, thereby reducing the cavity volume. Simultaneously, the waveguide-coaxial converter used to excite the resonant cavity is also composed of a high dielectric constant dielectric. Compared with coupling ring excitation, this method is more stable.

[0008] A miniaturized vacuum microwave cavity for an integrating sphere cold atom clock, the microwave cavity comprising, from top to bottom, a small window fixing component, a small vacuum window, a flange cover, a dielectric inner cylinder, a cavity body, a large vacuum window, a large window fixing component, and a waveguide coaxial conversion device disposed on the cavity sidewall;

[0009] The flange cover and the cavity body are fixedly connected by multiple screws to form a cylindrical microwave cavity.

[0010] The bottom of the inner medium cylinder contacts the bottom of the cavity of the cavity body, and the top of the inner medium cylinder contacts the top of the cavity of the flange cover. Both the cavity body and the flange cover have a boss with the same inner diameter as the inner medium cylinder to fix the inner medium cylinder so that it is placed coaxially in the cavity.

[0011] The waveguide coaxial conversion device is coupled to the cavity body and then directly welded to the side wall of the cavity body;

[0012] After the large vacuum window is embedded in the bottom groove of the cavity body, the large window fixing member is fixedly connected to the bottom of the cavity body by multiple screws;

[0013] After the small vacuum window is embedded in the groove at the top of the flange cover, the small window fixing piece is fixedly connected to the top of the flange cover by multiple screws.

[0014] Furthermore, the flange cover has a first intermediate through hole in the middle, a first screw hole in the upper part, a second screw hole in the lower part, a third screw hole in the top, a groove in the top to embed the small vacuum window, and a vacuum through hole in the side wall of the flange cover with a sealing copper ring placed therein.

[0015] Furthermore, the inner dielectric cylinder is made of ceramic with high dielectric constant and high diffuse reflectance.

[0016] Furthermore, the waveguide-coaxial conversion device consists of a coaxial line, a dielectric coupling post, a metal cap, and a dielectric waveguide. After the surface of the dielectric waveguide is metallized, it is brazed together with the coaxial line and the metal cap, and then the edge of the metal cap is laser-welded together with the side wall of the cavity body.

[0017] Furthermore, the cavity body has a second intermediate through hole and a light-transmitting hole in the middle of its bottom, a groove in the bottom of the cavity body to embed the large vacuum window, a fourth screw hole in the bottom of the cavity body, a fifth screw hole and a groove for placing a vacuum sealing O-ring in the top of the cavity body, and a coupling hole in the side wall of the cavity body.

[0018] Furthermore, the large vacuum window and the small vacuum window are made of SiO2.

[0019] Furthermore, the large window fixing component has a sixth screw hole.

[0020] Furthermore, the small window fastener has a seventh screw hole.

[0021] Furthermore, an indium wire is placed between the large vacuum window and the large window fixing member, and an indium wire is placed between the small vacuum window and the small window fixing member.

[0022] The beneficial technical effects of this invention are as follows:

[0023] This invention provides a miniaturized vacuum microwave cavity for an integrating sphere cold atom clock. The cavity is filled with a dielectric cylinder with high dielectric constant and high diffuse reflectivity, and the waveguide coaxial converter is also made of a dielectric with high dielectric constant. This makes the device smaller than the internal size of a traditional resonant cavity at the same frequency. Furthermore, using the waveguide coaxial converter to excite the resonant cavity is more stable than using a coupling ring. At the same time, because the ceramic waveguide coaxial converter can seal the vacuum, the vacuum cavity and microwave cavity are combined into one, resulting in a significant reduction in system volume and cost savings.

[0024] All openings in this device that connect to the cavity are sealed with vacuum windows and indium wire gaskets for window fixing components. All connections are designed with vacuum flange structures and sealed with O-rings or copper rings, so this device has excellent vacuum performance. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is an exploded view of a miniaturized vacuum microwave cavity for an integrating sphere cold atom clock provided in an embodiment of the present invention;

[0027] Figure 2 This is a front view of the miniaturized vacuum microwave cavity of the integrating sphere cold atom clock provided in an embodiment of the present invention;

[0028] Figure 3 This is a left view of the miniaturized vacuum microwave cavity of the integrating sphere cold atom clock provided in an embodiment of the present invention;

[0029] Figure 4 This is a top view of the miniaturized vacuum microwave cavity of the integrating sphere cold atom clock provided in an embodiment of the present invention;

[0030] Figure 5 This is a bottom view of the miniaturized vacuum microwave cavity of the integrating sphere cold atom clock provided in an embodiment of the present invention;

[0031] Figure 6 The embodiment of the present invention provides the following: Figure 5 A cross-sectional view with the dashed line AA in the middle;

[0032] Figure 7 This is provided by the embodiments of the present invention. Figure 5 A cross-sectional view with the dashed line BB in the middle.

[0033] Explanation of reference numerals in the attached drawings: 1—Flange top cover, 11—First intermediate through hole, 12—First screw hole, 13—Second screw hole, 14—Third screw hole, 15—Vacuum through hole, 16—Sealing copper ring, 2—Dielectric inner cylinder, 3—Waveguide coaxial conversion device, 31—Coaxial line, 32—Coupled post, 33—Metal cap, 34—Dielectric waveguide, 4—Cavity body, 41—Coupled hole, 42—O-ring groove, 43—Fifth screw hole, 44—Second intermediate through hole, 45—Light transmission hole, 46—Fourth screw hole, 5—Large vacuum window, 6—Large window fixing piece, 61—Sixth screw hole, 7—Small vacuum window, 8—Small window fixing piece, 81—Seventh screw hole. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] A miniaturized vacuum microwave cavity for an integrating sphere cold atom clock, such as Figures 1 to 7 As shown, the microwave cavity includes, from top to bottom, a small window fixing component 8, a small vacuum window 7, a flange cover 1, a dielectric inner cylinder 2, a cavity body 4, a large vacuum window 5, a large window fixing component 6, and a waveguide coaxial conversion device 3 disposed on the cavity sidewall;

[0036] The flange cover 1 and the cavity body 4 are fixedly connected by multiple screws to form a cylindrical microwave cavity.

[0037] The bottom of the inner medium cylinder 2 is in contact with the bottom of the cavity of the cavity body 4, and the top of the inner medium cylinder 2 is in contact with the top of the cavity of the flange cover 1. Both the cavity body 4 and the flange cover 1 have a boss with the same inner diameter as the inner medium cylinder 2 in the middle, so as to fix the inner medium cylinder 2 and place it coaxially in the cavity.

[0038] The waveguide coaxial conversion device 3 is coupled to the cavity body 4 and then directly welded to the side wall of the cavity body 4;

[0039] After the large vacuum window 5 is embedded in the bottom groove of the cavity body 4, the large window fixing member 6 is fixedly connected to the bottom of the cavity body 4 by multiple screws;

[0040] After the small vacuum window 7 is embedded in the top groove of the flange cover 1, the small window fixing piece 8 is fixedly connected to the top of the flange cover 1 by multiple screws.

[0041] like Figure 4 As shown, the flange cover 1 has a first intermediate through hole 11 in the middle, a first screw hole 12 in the upper part, a second screw hole 13 in the lower part, a third screw hole 14 in the top, a groove in the top to embed the small vacuum window 7, and a vacuum through hole 15 in the side wall of the flange cover 1 with a sealing copper ring 16 for connecting to a vacuum pump to draw a vacuum.

[0042] The inner dielectric cylinder 2 is made of ceramic with high dielectric constant and high diffuse reflectivity. The main body of the waveguide coaxial conversion device 3 is composed of a dielectric waveguide 34 with high dielectric constant. Except for the coupling post, the waveguide is surface metallized. After the waveguide is welded to the side wall of the cavity body 4 at ultra-high temperature, the coaxial line 31 is coupled into the waveguide and welded. Specifically, the waveguide coaxial conversion device 3 is composed of a coaxial line 31, a dielectric coupling post 32, a metal cap 33, and a dielectric waveguide 34.

[0043] like Figure 5 As shown, the cavity body 4 has a second intermediate through hole 44 and a light-transmitting hole 45 in the middle of its bottom. The cavity body 4 has a groove at its bottom to embed the large vacuum window 5. The cavity body 4 has a fourth screw hole 46 at its bottom. The cavity body 4 has a fifth screw hole 43 and a groove for placing a vacuum sealing O-ring, namely the O-ring groove 42, at its top. The cavity body 4 has a coupling hole 41 on its side wall.

[0044] The large window fixing component 6 has a sixth screw hole 61. After the large vacuum window 5 is embedded into the bottom groove of the cavity body 4, an indium wire is placed on it, and then the large window fixing component 6 is fixed to the cavity body 4 with screws to fix the large vacuum window 5 and maintain its airtightness.

[0045] The small window fixing component 8 has a seventh screw hole 81. After the small vacuum window 7 is embedded into the top groove of the flange cover 1, an indium wire is placed on it, and then the small window fixing component 8 and the flange cover 1 are fixed with screws to fix the small vacuum window 7 and maintain its airtightness.

[0046] The large vacuum window 5 and the small vacuum window 7 are made of SiO2.

[0047] In this embodiment, the large window fixing member 6 is connected to the bottom of the cavity body 4 using an M4 socket head cap screw with a length of 12mm;

[0048] The small window fastener 8 is connected to the top of the flange cover 1 using an M4 socket head cap screw with a length of 12mm.

[0049] The flange cover 1 and the cavity body 4 are fixedly connected by m4 internal hexagonal head screws with a length of 25mm and corresponding nuts to form a cylindrical microwave cavity.

[0050] Preferably, the inner dielectric cylinder 2 is made of ceramic, which has a relative permittivity of 9.6 and a diffuse reflectance of more than 98%.

[0051] Preferably, the upper and lower end faces of the inner surface of the microwave cavity are electroplated with silver to achieve a diffuse reflectance of greater than 98%.

[0052] The waveguide coaxial converter 3 performs microwave excitation via lateral coupling at half the height of the microwave cavity. This excitation method allows the desired frequency TE to be achieved. 011 The pattern is relatively uniform in the center of the microwave cavity.

[0053] Cooling light and pump light enter the microwave cavity at a certain divergence angle through four light-transmitting holes 45. Rubidium or cesium atoms diffuse into the microwave cavity through vacuum through-holes 15. Probe light enters along the central axis of the microwave cavity through the first intermediate through-hole 11 and the second intermediate through-hole 44.

[0054] The high diffuse reflectivity ceramic coaxial waveguide conversion device in this invention makes the excitation more stable. Combined with the dielectric inner cylinder with high dielectric constant and high diffuse reflectivity, the microwave cavity size is reduced. The microwave cavity has excellent vacuum performance. The high dielectric constant ceramic coaxial waveguide conversion device has vacuum sealing function and microwave signal transmission function, realizing the integration of vacuum cavity and microwave cavity into one, and the system volume is significantly reduced.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A miniaturized vacuum microwave cavity for an integrating sphere cold atom clock, characterized in that, The microwave cavity includes, from top to bottom, a small window fixing piece (8), a small vacuum window (7), a flange cover (1), a dielectric inner cylinder (2), a cavity body (4), a large vacuum window (5), a large window fixing piece (6), and a waveguide coaxial conversion device (3) disposed on the cavity sidewall. The flange cover (1) and the cavity body (4) are fixedly connected by multiple screws to form a cylindrical microwave cavity; The bottom of the inner medium cylinder (2) is in contact with the bottom of the cavity of the cavity body (4), and the top of the inner medium cylinder (2) is in contact with the top of the cavity of the flange cover (1). The cavity body (4) and the flange cover (1) both have a boss with the same inner diameter as the inner medium cylinder (2) to fix the inner medium cylinder (2) so that it is placed coaxially in the cavity. The waveguide coaxial conversion device (3) is coupled to the cavity body (4) and then directly welded to the side wall of the cavity body (4); After the large vacuum window (5) is embedded in the bottom groove of the cavity body (4), the large window fixing piece (6) is fixedly connected to the bottom of the cavity body (4) by multiple screws; After the small vacuum window (7) is embedded in the top groove of the flange cover (1), the small window fixing piece (8) is fixedly connected to the top of the flange cover (1) by multiple screws.

2. The miniaturized vacuum microwave cavity of the integrating sphere cold atom clock according to claim 1, characterized in that, The flange cover (1) has a first intermediate through hole (11) in the middle, a first screw hole (12) in the upper part, a second screw hole (13) in the lower part, a third screw hole (14) in the top, a groove in the top to embed the small vacuum window (7), and a vacuum through hole (15) in the side wall of the flange cover (1) with a sealing copper ring (16) placed thereon.

3. The miniaturized vacuum microwave cavity of the integrating sphere cold atom clock according to claim 1, characterized in that, The inner cylinder (2) is made of ceramic with high dielectric constant and high diffuse reflectance.

4. The miniaturized vacuum microwave cavity of the integrating sphere cold atom clock according to claim 1, characterized in that, The waveguide coaxial conversion device (3) consists of a coaxial line (31), a dielectric coupling post (32), a metal cap (33), and a dielectric waveguide (34). After the surface of the dielectric waveguide (34) is metallized, it is brazed together with the coaxial line (31) and the metal cap (33). Then, the edge of the metal cap (33) is laser-welded to the side wall of the cavity body (4).

5. The miniaturized vacuum microwave cavity of the integrating sphere cold atom clock according to claim 1, characterized in that, The cavity body (4) has a second intermediate through hole (44) and a light-transmitting hole (45) in the middle of its bottom. The cavity body (4) has a groove at its bottom to embed the large vacuum window (5). The cavity body (4) has a fourth screw hole (46) at its bottom. The cavity body (4) has a fifth screw hole (43) and a groove for placing a vacuum sealing O-ring at its top. The cavity body (4) has a coupling hole (41) on its side wall.

6. The miniaturized vacuum microwave cavity of the integrating sphere cold atom clock according to claim 1, characterized in that, The large vacuum window (5) and the small vacuum window (7) are made of SiO2.

7. The miniaturized vacuum microwave cavity of the integrating sphere cold atom clock according to claim 1, characterized in that, The large window fastener (6) has a sixth screw hole (61).

8. The miniaturized vacuum microwave cavity of the integrating sphere cold atom clock according to claim 1, characterized in that, The small window fastener (8) has a seventh screw hole (81).

9. The miniaturized vacuum microwave cavity of the integrating sphere cold atom clock according to claim 1, characterized in that, An indium wire is placed between the large vacuum window (5) and the large window fixing member (6), and an indium wire is placed between the small vacuum window (7) and the small window fixing member (8).

Images