A microwave resonant device for CVD deposition of optical fiber preforms

Abstract

This invention belongs to the technical field of optical fiber preform processing equipment and discloses a microwave resonant device for CVD deposition of optical fiber preforms. The device includes an outer resonant cavity, an inner resonant cavity, a compressed waveguide, and an end cap. The inner and outer resonant cavities are fitted together to form a resonant cavity, which is then sealed by the end cap. The compressed waveguide is connected to the resonant cavity via a mother-daughter interface and has a tapered structure, meaning its inner dimensions gradually decrease towards the resonant cavity. Furthermore, a double-helix notch is provided on the inner wall of the resonant cavity. This invention not only increases the transmission electric field strength under the same power conditions but also provides a smoother connection between the waveguide and the resonant cavity interface, effectively avoiding microwave transmission losses. In addition, it significantly improves microwave feed uniformity and axial thermal uniformity, thereby contributing to improved core deposition efficiency and uniformity.

Description

Technical Field

[0001] This invention belongs to the technical field of optical fiber preform processing equipment, and more specifically, relates to a microwave resonant device for CVD deposition processing of optical fiber preforms. Background Technology

[0002] CVD (Continuous Chemical Deposition) is one of the main processes in the in-tube deposition of optical fiber preforms, and the process is completed using a CVD deposition lathe. During CVD, a resonant cavity transmits high-power microwaves to a quartz glass substrate and moves back and forth along the axial direction of the substrate at a certain speed within a high-temperature furnace. This causes the gas inside the substrate to oxidize and deposit on the inner wall of the glass substrate, ultimately forming an optical fiber preform with a deposition layer of a certain thickness. Throughout the entire CVD process, the appropriateness of the microwave resonant device is crucial for deposition efficiency and the uniformity of the preform deposition.

[0003] Further research indicates that multiple factors, including microwave transmission performance, interface flatness, operating temperature, electromagnetic wave feed uniformity, axial thermal uniformity, electromagnetic wave leakage, and reflection, all influence the final deposition quality of the fiber optic preform core. However, existing microwave resonator technologies still suffer from the following defects or shortcomings: First, the two-port aperture sizes of the microwave transmission system in existing microwave resonator devices are usually consistent, resulting in a lack of variation in microwave transmission performance and potential issues such as insufficient electric field strength after high-frequency microwaves are transmitted to the resonant cavity via the waveguide. Second, the lack of a matching structure at the interface between the waveguide and the resonant cavity in existing microwave resonator devices leads to larger installation errors and increased losses. Third, the electric field gaps in existing resonant cavities typically employ an asymmetric structure, which negatively impacts the uniformity of fiber preform deposition, and the existing resonant cavity water channel design can easily lead to uneven cooling of the entire resonant cavity. Finally, existing microwave resonator devices also suffer from overcooling in some areas, microwave leakage, and reflection phenomena, all of which can affect the final core deposition quality. Summary of the Invention

[0004] To address one or more of the aforementioned deficiencies or needs of existing technologies, this invention provides a microwave resonant device for CVD deposition of optical fiber preforms. By making targeted improvements to the specific structural forms and configurations of several key components, such as the compressed waveguide, resonant cavity, and mother-daughter interface, and by redesigning the supporting cooling circulation water path and heat-absorbing elements, this invention not only increases the transmission electric field strength under the same power conditions but also provides a smoother connection between the waveguide and resonant cavity interfaces, effectively avoiding microwave transmission losses. Furthermore, this invention significantly improves microwave feed uniformity and axial thermal uniformity, thereby contributing to increased core deposition efficiency and uniformity, making it particularly suitable for applications involving CVD deposition of optical fiber preforms.

[0005] To achieve the above objectives, according to the present invention, a microwave resonant device for CVD deposition of optical fiber preforms is provided. The microwave resonant device includes an outer resonant cavity, an inner resonant cavity, a compressed waveguide, and an end cap, wherein: The resonant inner cavity and the resonant outer cavity are fitted together to form a resonant cavity, and then the end cap is used to perform closure. The compressed waveguide and the resonant cavity are connected by a mother-daughter interface, and the compressed waveguide has a tapered structure, that is, its inner dimensions gradually decrease towards the resonant cavity. The inner wall of the resonant cavity is provided with a double helix vent. The double helix vent is symmetrical about the central axis of the resonant cavity. Each vent rotates once and the pitch is less than λ / 2, where λ is the wavelength of the transmitted microwave.

[0006] Based on the above concepts, on the one hand, since the compressed waveguide in this invention is designed with a gradient structure and uses a mother-daughter structure to connect with the resonant cavity, the high-frequency microwaves from the high-frequency microwave source are gradually compressed by the inner surface of the gradient structure when they reach the compressed waveguide, increasing the transmission electric field strength under the same power conditions before entering the resonant cavity. Moreover, the mother-daughter interface can better limit the offset at the docking point between the compressed waveguide and the resonant cavity, ensuring a smooth connection between the two, thereby effectively avoiding microwave transmission loss. On the other hand, since a double-helix vent is provided on the inner wall of the resonant cavity in this invention, when the high-frequency microwaves oscillate back and forth in the resonant cavity to form a standing wave, this double-helix vent allows the standing wave to vent more uniformly into the CVD reaction cavity to form plasma, thereby further effectively ensuring the radial uniformity of the core rod deposition.

[0007] As a further preferred embodiment of the present invention, the microwave resonant device is also equipped with a heat-absorbing element, which is symmetrically arranged at both ends of the resonant cavity and presents a gradually decreasing groove structure, that is, the radial dimension of the groove gradually decreases in the direction of the resonant cavity.

[0008] As a further preferred embodiment of the present invention, the microwave resonant device is also equipped with a cooling circulating water path, which is opened in the resonant outer cavity and includes a water inlet, a water outlet, and a cooling water channel that continuously winds around the circumferential direction of the resonant outer cavity.

[0009] As a further preferred embodiment of the present invention, for the compressed waveguide, its waveguide opening width W1 is set to be greater than λ / 2 and less than λ, where λ is the wavelength of the transmitted microwave.

[0010] As a further preferred embodiment of the present invention, the female-female interface includes a female interface and a female interface that are fitted together, wherein the female interface is processed on the compressed waveguide and has a female port depth L2 with positive tolerance, and the female interface is processed on the resonant cavity and has a female port depth L1 with negative tolerance.

[0011] As a further preferred embodiment of the present invention, for the heat-absorbing element, its slot width L3 is designed to be greater than or equal to λ / 8, where λ is the wavelength of the transmitted microwave.

[0012] As a further preferred embodiment of the present invention, each component of the microwave resonator is preferably made of copper and has a silver-plated surface treatment.

[0013] As a further preferred embodiment of the present invention, the end cap, the outer resonant cavity, and the inner resonant cavity of the microwave resonant device are connected by stainless steel screws, and then the cavity assembly is connected to the compressed waveguide by the female-female interface.

[0014] In summary, the technical solutions conceived by this invention have the following main technical advantages compared with the prior art: (1) This invention fully combines the working characteristics and specific requirements of CVD processing of optical fiber preforms, and makes targeted improvements to the specific structural forms and settings of several key components in its microwave resonant device, such as the compressed waveguide, resonant cavity and the mother-daughter interface. Among them, by adopting a compressed waveguide with a gradient structure, the microwave can increase the transmission electric field intensity before entering the resonant cavity under the same power condition. By adopting a mother-daughter interface between the compressed waveguide and the resonant cavity, the offset at the docking point between the compressed waveguide and the resonant cavity can be better limited, ensuring a smooth connection between the two, thereby effectively avoiding microwave transmission loss. In addition, on this basis, by setting a double helix opening on the inner wall of the resonant cavity, when the high-frequency microwave oscillates back and forth in the resonant cavity to form a standing wave, the double helix opening can make the standing wave more uniformly emerge into the CVD reaction cavity to form plasma, thereby further effectively ensuring the radial uniformity of the core rod deposition. (2) The present invention further redesigns the supporting cooling circulation water circuit and heat storage and absorbing elements. By designing a left-right symmetrical circulation water circuit, the temperature of the device can be effectively reduced while ensuring temperature uniformity. By setting heat storage and absorbing elements at both ends of the microwave resonant device and improving their specific structural form and setting method, the occurrence of microwave leakage and reflection can be effectively reduced. At the same time, the temporary storage of heat can be reasonably realized to avoid the core rod from becoming too cold and to avoid affecting the axial uniformity. (3) The present invention further optimizes the design of key processing parameters related to the double helix rupture, compression waveguide and heat storage absorbing element. Many actual tests show that these key processing parameters and their combination can not only make the overall structure more compact and easier to manufacture, but also help to exert the corresponding mechanism, thereby achieving the desired effect in the main aspects such as radial uniformity of core rod deposition and increase of microwave electric field intensity. (4) Compared with existing similar products, the microwave resonator of the present invention not only provides basic microwave resonant function, but also has better microwave transmission function, waveguide and cavity precision docking function, electric field collapse function, heat storage and wave absorption function and circulating cooling function. It also has the characteristics of compact structure and easy operation, and is therefore particularly suitable for high-quality and high-efficiency CVD deposition processing of optical fiber preforms. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the main structure of the microwave resonant device provided according to the present invention; Figure 2 This shows a more detailed schematic diagram of the compressed waveguide structure; Figure 3a This is a schematic diagram of the structure of a female-female interface according to a preferred embodiment of the present invention. Figure 3b and 3cThese are detailed schematic diagrams of the sub-interfaces and the parent interface, respectively. Figure 4 It is a more detailed schematic diagram showing the structure of the breach in the double helix; Figure 5 This is a schematic diagram of the cooling water circulation circuit according to another preferred embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of a heat-absorbing wave element according to another preferred embodiment of the present invention; In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-End cap; 2-Outer resonant cavity; 3-Inner resonant cavity; 4-Compressed waveguide; 5-Inner surface of gradient waveguide; 6-Sub-interface; 7-Female interface; 8-Break of double helix; 9-Water inlet; 10-Cooling water channel; 11-Water outlet; 12-Heat-absorbing wave element; 13-Resonant cavity; 14-Deposition cavity. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0017] It should be understood that expressions such as "comprising" and "may include" as used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "comprising" and / or "having" may be interpreted as indicating a specific characteristic, number, operation, constituent element, component, or combination thereof, but should not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0018] It should be understood that the terms “center,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0019] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0020] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0021] Figure 1 This is a schematic diagram of the main structure of the microwave resonant device provided by the present invention, as shown below. Figure 1 As shown, this microwave resonant device is used in the CVD deposition process of optical fiber preforms, and mainly includes components such as resonant outer cavity 2, resonant inner cavity 3, compression waveguide 4 and end cap 1. In addition, it can also be equipped with heat storage and microwave absorption elements, cooling circulating water circuits and other components, which will be explained one by one below.

[0022] The resonant inner cavity 3 and the resonant outer cavity 2 are fitted together to form a resonant cavity 13, and then the end cap 1 is used to close it, which constitutes the basic cavity structure of this device. As one of the key improvements of the present invention, the compressed waveguide 4 and the resonant cavity 13 are connected in the form of a mother-daughter interface, and the compressed waveguide 4 has a gradient structure, that is, its inner surface size gradually decreases in the direction of the resonant cavity 13.

[0023] More specifically, see also Figure 2 For the compressed waveguide 4, its waveguide opening width W1 is preferably set to be greater than λ / 2 and less than λ, where λ is the wavelength of the transmitted microwave. In this way, not only can it be ensured that only electromagnetic waves of the selected mode can pass through the waveguide, but it also helps to further enhance its function of increasing the transmission electric field strength. Correspondingly, see also... Figures 3a to 3c The female-female interface includes a female interface 6 and a female interface 7 that are fitted together. The female interface 6 is machined on the compressed waveguide 4 and has a positive tolerance female port depth L2, while the female interface 7 is machined on the resonant cavity 13 and has a negative tolerance female port depth L1. In this way, the connection plane can be kept in close contact to avoid arcing caused by gaps.

[0024] See Figure 4 As another key improvement of the present invention, the inner wall of the resonant cavity 13 is also provided with a double helix vent 8. The double helix vent 8 is symmetrical about the central axis of the resonant cavity 13. Each vent rotates once and the pitch is less than λ / 2, where λ is the wavelength of the transmitted microwave.

[0025] Because the invention provides a double-helix vent on the inner wall of the resonant cavity, when the high-frequency microwaves oscillate back and forth in the resonant cavity to form a standing wave, this double-helix vent allows the standing wave to vent more uniformly into the CVD reaction cavity to form plasma, thereby further ensuring the radial uniformity of the mandrel deposition.

[0026] See Figure 5 According to a preferred embodiment of the present invention, the microwave resonant device is further equipped with a heat-absorbing element 12, which is symmetrically arranged at both ends of the resonant cavity 13 and presents a gradually decreasing groove structure, that is, the radial dimension of the groove gradually decreases in the direction of the resonant cavity 13.

[0027] More specifically, for the heat-absorbing element 12, its slot width L3 is designed to be greater than or equal to λ / 8, where λ is the wavelength of the incoming microwave. This not only facilitates manufacturing but also ensures good absorption performance within this depth range, while storing sufficient heat. Furthermore, it reduces microwave leakage and reflection, while storing heat to prevent the core rod from overcooling and to avoid affecting axial uniformity.

[0028] See Figure 6 According to another preferred embodiment of the present invention, the microwave resonant device is further equipped with a cooling circulating water path, which is, for example, formed in the resonant outer cavity 2, and includes a water inlet 9, a water outlet 11, and a cooling water channel 10 continuously coiled along the circumferential direction of the resonant outer cavity 2. In this way, the circulating water path can be arranged in a left-right symmetrical form, thereby more effectively reducing the device temperature and ensuring temperature uniformity; According to another preferred embodiment of the present invention, each component of the microwave resonator is preferably made of copper and has a silver-plated surface treatment. Accordingly, the end cap 1, the outer resonant cavity 2, and the inner resonant cavity 3 of the microwave resonator are connected by stainless steel screws, and then the cavity assembly is connected to the compressed waveguide 4 using the female-female interface.

[0029] The following will explain in detail the usage process of the microwave resonator device of the present invention.

[0030] When installing the device according to the present invention, first connect the end cap 1, the resonant outer cavity 2, and the resonant inner cavity 3 tightly with screws, and then connect the cavity assembly to the compression waveguide 4 through the sub-interface 6 and the female interface 7. Before use, clean each part with ultrasonic cleaning to ensure that the connection of each component is tight and reliable. Open the water circuit to pressurize and check for leaks. It can only be used after there are no problems.

[0031] When the device according to the present invention is working, high-frequency microwaves are gradually compressed through the inner surface 5 of the tapered waveguide in the compression waveguide 4. Then, the microwaves enter the resonant cavity 13 to form a standing wave. The electric field in the resonant cavity is fed into the deposition cavity 14 through the gap 8 of the double helix to form plasma, and the core rod begins to be deposited uniformly. At the same time, circulating cooling water flows into the cooling water channel 10 from the water inlet 9 and then flows out from the water outlet 11 to cool the entire microwave resonant device. In addition, the heat from the high-temperature heating furnace outside the resonant cavity enters the heat storage and absorbing element 12 to prevent the structural components from becoming too cold. The electromagnetic waves in the reaction cavity pass through the heat storage and absorbing element 12 to prevent leakage and reflection.

[0032] In summary, the microwave resonant device according to the present invention makes targeted improvements to the specific structural forms and arrangements of several key components such as the compressed waveguide, resonant cavity, and mother-daughter interface. At the same time, the supporting cooling circulating water circuit and heat storage absorbing elements are redesigned. Consequently, it can not only increase the transmission electric field strength under the same power conditions, but also better provide a smooth connection between the waveguide and the resonant cavity interface, effectively avoiding microwave transmission loss.

[0033] Therefore, compared with existing similar products, the microwave resonator of the present invention, in addition to providing basic microwave resonant function, also has better microwave transmission function, waveguide and cavity precision docking function, electric field collapse function, heat storage and wave absorption function, and circulating cooling function. It also has the characteristics of compact structure and easy operation, and is therefore particularly suitable for high-quality and high-efficiency CVD deposition processing of optical fiber preforms, and has good practical value and application prospects.

[0034] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A microwave resonant device for CVD deposition of optical fiber preforms, characterized in that, The microwave resonant device includes an outer resonant cavity (2), an inner resonant cavity (3), a compressed waveguide (4), and an end cap (1), wherein: The resonant inner cavity (3) and the resonant outer cavity (2) are fitted together to form a resonant cavity (13), and then the end cap (1) is used to perform the sealing. The compressed waveguide (4) and the resonant cavity (13) are connected by a mother-daughter interface, and the compressed waveguide (4) has a gradient structure, with its inner surface dimensions gradually decreasing towards the resonant cavity (13). The inner wall of the resonant cavity (13) is provided with a double helix puncture (8). The double helix puncture (8) is symmetrical about the central axis of the resonant cavity (13). Each puncture rotates once and the pitch is less than λ / 2, where λ is the wavelength of the transmitted microwave.

2. The microwave resonant device as described in claim 1, characterized in that, The microwave resonant device is also equipped with a heat-absorbing element (12), which is symmetrically arranged at both ends of the resonant cavity (13) and has a gradually decreasing groove structure. The radial dimension of the groove gradually decreases in the direction of the resonant cavity (13).

3. The microwave resonant device as described in claim 2, characterized in that, The microwave resonant device is also equipped with a cooling circulation water channel, which is opened in the resonant outer cavity (2) and includes a water inlet (9), a water outlet (11), and a cooling water channel (10) that is continuously coiled along the circumferential direction of the resonant outer cavity (2).

4. The microwave resonant device according to any one of claims 1-3, characterized in that, For the compressed waveguide (4), its waveguide opening width is set to be greater than λ / 2 and less than λ, where λ is the wavelength of the transmitted microwave.

5. The microwave resonant device as described in claim 4, characterized in that, The female-female interface includes a female interface (6) and a female interface (7) that are fitted together, wherein the female interface (6) is machined on the compressed waveguide (4) and has a positive tolerance female port depth L2, and the female interface (7) is machined on the resonant cavity (13) and has a negative tolerance female port depth L1.

6. The microwave resonant device as described in claim 2, characterized in that, For the heat-absorbing element (12), its slot width L3 is designed to be greater than or equal to λ / 8, where λ is the wavelength of the transmitted microwave.

7. The microwave resonant device according to any one of claims 1-3, characterized in that, All components of the aforementioned microwave resonator are made of copper and have been silver-plated.

8. The microwave resonant device as described in claim 7, characterized in that, The end cap (1), resonant outer cavity (2) and resonant inner cavity (3) of the above microwave resonant device are connected by stainless steel screws, and then the cavity assembly is connected to the compressed waveguide (4) by the female-female interface.

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