Filtering device

Abstract

The application provides a filtering device, and relates to the field of communication. The main body is a photonic crystal fiber. A first air hole layer, a second air hole layer and an elliptical air hole layer are arranged in the cladding. The first air hole layer is distributed along the circumference of the core. Multiple groups of first air holes in the first air hole layer are oppositely arranged. At least one inner wall of the first air hole is provided with a metal film. The elliptical air hole layer is located in a first space surrounded by the first air hole layer. The elliptical air hole layer comprises two rows of elliptical air holes which are spaced apart along a second direction. The elliptical air hole layer and the two first air holes opposite along a first direction form a second space. The core is located in the second space, and the cladding is located outside the second space. The second air hole layer comprises multiple second air holes. Multiple second air holes are arranged in the circumferential direction of each first air hole. The sizes of the first air hole and the second air hole are different. The filtering device can solve the problem of low data transmission efficiency in the data transmission process.

Description

Technical Field

[0001] This application relates to the field of communications, specifically to a filtering device. Background Technology

[0002] With the emergence and realization of smart cities and the era of big data, the demand for communication systems with ultra-high bandwidth capacity is becoming increasingly urgent. Fiber optic filtering equipment (hereinafter referred to as filtering equipment) is an essential optical component in wavelength division multiplexing (WDM) optical communication systems and fiber optic sensing systems. With the development of fiber optic communication and fiber optic sensing technologies, a large number of filtering devices are needed in multiplexing, demultiplexing, and communication sensing systems to select specific wavelengths.

[0003] Filtering devices offer advantages such as easy integration with fiber optic communication systems, tunable wavelength, and low insertion loss. They have become indispensable key components in fiber optic networks. Air holes are incorporated within the fiber core or cladding. By filling these air holes with special materials, the fiber can acquire more transmission characteristics. In related technologies, liquid channels are incorporated within the cladding to contain liquid. A metal film is placed on the inner wall of the liquid channel. The filling with liquid can alter the environment around the metal film, thereby modulating the resonant wavelength.

[0004] However, the liquid filling method does not significantly improve data transmission efficiency, and the liquid filling requires sufficient internal space, which can easily lead to an increase in the size of the filtering equipment, making it difficult to integrate with fiber optic communication systems. Summary of the Invention

[0005] This application provides a filtering device that can solve the problem of low data transmission efficiency during data transmission.

[0006] This application provides a filtering device, the main body of which is a photonic crystal fiber. The photonic crystal fiber includes a cladding and a core. The core is located in the central region of the cladding. The cladding is provided with a first air hole layer, a second air hole layer, and an elliptical air hole layer.

[0007] The first air hole layer is distributed along the circumference of the fiber core. The first air hole layer includes multiple sets of oppositely arranged first air holes, wherein one set of first air holes is oppositely arranged along a first direction, and another set of first air holes is oppositely arranged along a second direction. At least one set of first air holes has a metal film on the inner wall of two first air holes.

[0008] The elliptical air hole layer is located within the first space enclosed by the first air hole layer. The elliptical air hole layer includes two rows of elliptical air holes spaced apart along the second direction. Each row of elliptical air holes includes multiple elliptical air holes spaced apart along the first direction. The elliptical air hole layer and the two first air holes arranged opposite to each other along the first direction form a second space. The fiber core is located within the second space, and the cladding is located outside the second space.

[0009] The second air hole layer includes a plurality of second air holes, and each of the first air holes is provided with a plurality of second air holes in the circumferential direction. The size of the first air hole is different from the size of the second air hole.

[0010] According to one embodiment of this application, a first air hole layer is provided on the outer side of the fiber core, and a second air hole layer is provided circumferentially for each first air hole of the first air hole layer.

[0011] According to one embodiment of this application, the number of the first air holes is four, and the centers of the four first air holes are connected in sequence to form a rhombus, wherein a metal film is provided on the inner wall of two of the first air holes that are arranged opposite each other along the second direction.

[0012] According to one embodiment of this application, each of the first air holes is provided with four second air holes in the circumferential direction, and the centers of the four second air holes are connected in sequence to form a rectangle.

[0013] According to one embodiment of this application, the first space has four second air holes, the four second air holes surround to form a third space, and the elliptical air hole layer is located in the third space.

[0014] According to one embodiment of this application, both the first air hole and the second air hole are circular holes, and the radius of the first air hole is larger than the radius of the second air hole.

[0015] According to one embodiment of this application, the radius of the first air hole is 0.8 micrometers, and the diameter of the second air hole is 0.45 micrometers.

[0016] According to one embodiment of this application, the thickness of the metal film is 25 micrometers.

[0017] According to one embodiment of this application, the major axis of the elliptical air hole is 0.5732 micrometers and the minor axis is 0.2 micrometers.

[0018] According to one embodiment of this application, the center distance between each second air hole and the corresponding first air hole is 0.2 micrometers.

[0019] The filtering device provided in this application, by setting a first air hole layer, a second air hole layer, and an elliptical air hole layer within the cladding, and setting a metal film in two oppositely arranged first air holes, can achieve a wide range of filtering effects without reserving liquid channels and injecting liquid based on the principle of surface plasmon resonance, thereby improving the sensitivity and stability of information transmission.

[0020] In addition to the technical problems solved by the embodiments of the present invention, the technical features constituting the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions as described above, other technical problems that the filtering device provided by the embodiments of the present invention can solve, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further described in detail in the specific embodiments. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0022] Figure 1 This is a schematic diagram of the structure of a photonic crystal fiber according to an embodiment of this application;

[0023] Figure 2 This is a schematic diagram of the structure of a photonic crystal fiber according to another embodiment of this application;

[0024] Figure 3 This is a graph showing the effective refractive index and confinement loss of a photonic crystal fiber according to an embodiment of this application.

[0025] Figure 4 This is a schematic diagram of the extinction ratio of a photonic crystal fiber according to an embodiment of this application.

[0026] Explanation of reference numerals in the attached figures:

[0027] 100-photonic crystal fiber;

[0028] 110-cladding;

[0029] 111 - First air-porous layer;

[0030] 111a - First air hole;

[0031] 112 - Second air-porous layer;

[0032] 112a - Second air hole;

[0033] 113-Elliptical air-pore layer;

[0034] 113a - Elliptical air hole;

[0035] 120-core;

[0036] 130-metal film;

[0037] A-First Space;

[0038] B-Second Space;

[0039] C - Third Space;

[0040] M - First direction;

[0041] N - Second direction.

[0042] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0043] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims. Clearly, the described embodiments are only a portion, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0044] The filtering device of this application can be used in a variety of communication optical instruments. By installing the filtering device at the receiving end of an optical coupler or optical multiplexer, different information transmitted at different wavelengths can be separated into the information of the required wavelength.

[0045] The filtering device of this application can also be applied to the fields of optical fiber communication, optical networks and optical devices, as well as to the financial field such as banking, and is not limited thereto in this application.

[0046] Photonic crystal fiber (PCF), also known as micro-structured fiber (MSF), contains periodically arranged air holes, with different air hole arrangements corresponding to different transmission modes. PCF has attracted widespread attention due to its outstanding advantages such as flexible structural design and high sensitivity.

[0047] Surface plasmon resonance (SPR) can selectively absorb energy at specific wavelengths and simultaneously perform high-loss filtering on orthogonal light to achieve sufficient filtering. SPR technology has many outstanding advantages, such as real-time monitoring, label-free operation, and high sensitivity. Therefore, SPR technology is widely used in life sciences, medical diagnostics, environmental monitoring, drug screening, food safety, and other fields.

[0048] In recent years, with the rapid development of optical fiber drawing technology and metal coating technology, the combination of photonic crystal fiber and surface plasmon resonance technology has enabled the rapid development of fiber optic sensing technology. Photonic crystal fiber sensing technology based on surface plasmon resonance has also become a new research hotspot.

[0049] Photonic crystal fibers consist of a cladding and a core. The core is the core of a photonic crystal fiber. The core is used to transmit optical signals. The cladding allows the optical signal to be transmitted within the core and also protects the core from external interference or damage. The core can be a defect that disrupts the periodic modulation of the refractive index, creating a longitudinal defect that allows light waves to propagate along the core. For example, the defect can be an air hole.

[0050] Therefore, air holes can be provided within the cladding of a photonic crystal fiber to trap light waves of a certain wavelength within them, allowing total internal reflection to occur within the fiber core. In other words, the light waves can be confined to propagate within the fiber core.

[0051] The cladding in this technology incorporates liquid channels and multiple air holes. Liquid can be injected into the liquid channels. A metal film is deposited on the inner wall of the liquid channels. Therefore, by absorbing energy during surface plasmon resonance, the metal film can filter out unwanted wavelength components in the signal, enabling the photonic crystal fiber to have a wide filtering range. The filling of the liquid can alter the environment around the metal film, thereby modulating the resonant wavelength.

[0052] However, the applicant found that the liquid filling method did not significantly improve data transmission efficiency, and the liquid channel required a large internal space within the cladding, which could easily lead to an increase in the size of the filtering equipment and make it difficult to integrate with the fiber optic communication system. On the other hand, the liquid filling channel was not easy to process and the liquid filling method was not conducive to operation.

[0053] Therefore, this application provides a filtering device that, by setting the position, number, and quantity of air holes within the cladding, and based on the principle of surface plasmon resonance, can achieve a wide range of filtering effects without reserving liquid channels and injecting liquid, thereby improving the sensitivity and stability of information transmission.

[0054] The filtering device provided in this application will now be described with reference to the accompanying drawings and specific embodiments.

[0055] See Figure 1 and Figure 2 As shown, the main body of the filtering device in this embodiment is a photonic crystal fiber 100. The photonic crystal fiber 100 includes a cladding 110 and a core 120. The core 120 is located in the central region of the cladding 110. The cladding 110 is provided with a first air hole layer 111, a second air hole layer 112, and an elliptical air hole layer 113.

[0056] The first air pore layer 111 can be distributed circumferentially along the fiber core 120. The first air pore layer 111 includes multiple sets of opposing first air pores 111a. Among them, one set of first air pores 111a is opposite to each other and spaced apart along a first direction M. Another set of first air pores 111a is opposite to each other and spaced apart along a second direction N. At least two of the first air pores 111a in one set of first air pores 111a are provided with a metal film 130 on their inner walls.

[0057] The refractive index of the metal film 130 is fixed, so the operating wavelength of the filtering device can be changed by altering the refractive index of the metal. Furthermore, in the filtering device of this application, evanescent fields can easily penetrate the metal film 130 to generate a resonance phenomenon, thereby achieving polarization filtering functionality.

[0058] Furthermore, when a broadband light source enters the cladding 110 and forms an evanescent field that enters the metal film 130, it can excite surface plasmon resonance, thereby selectively absorbing energy of specific wavelengths to achieve a wide-range filtering effect and improve the sensitivity and stability of information transmission.

[0059] The first air hole layer 111 can enclose a first space A. An elliptical air hole layer 113 is located within the first space A. The elliptical air hole layer 113 includes two rows of elliptical air holes 113a spaced apart along a second direction N. Each row of elliptical air holes 113a includes multiple elliptical air holes 113a spaced apart along a first direction M. The elliptical air hole layer 113 and the two first air holes 111a spaced opposite each other along the first direction M form a second space B. The fiber core 120 is located within the second space B, and the cladding 110 is located outside the second space B.

[0060] The second air hole layer 112 includes a plurality of second air holes 112a. Each first air hole 111a has a plurality of second air holes 112a arranged circumferentially. The size of the first air hole 111a is different from the size of the second air hole 112a.

[0061] When light waves enter the filtering device and propagate within the photonic crystal fiber 100, light waves of different wavelengths propagate in specific modes within the photonic crystal fiber 100. The use of two different sized air holes, the first air hole 111a and the second air hole 112a, can enhance birefringence, thereby increasing data transmission throughput and improving data transmission stability. Furthermore, due to the asymmetric application of the elliptical air hole 113a in the filtering device, the elliptical air hole 113a can adjust the resonant wavelength and enhance birefringence, thereby increasing data transmission.

[0062] Furthermore, the elliptical air hole layer 113 and the two first air holes 111a disposed opposite to each other along the first direction M jointly separate the fiber core 120 and the cladding 110. Since light waves are mainly concentrated in the fiber core 120, the elliptical air holes 113a are disposed close to the fiber core 120, which can more effectively improve birefringence.

[0063] Light waves can undergo total internal reflection within the photonic crystal core 120 by passing through the first air-hole layer 111, the second air-hole layer 112, and the elliptical air-hole layer 113. Since the evanescent wave generated by total internal reflection excites surface plasmon waves on the surface of the metal film 130, when the incident light wave and the surface plasmon wave have the same wave vector (i.e., the phase matching condition is met), surface plasmon resonance can occur. Most of the light energy can be transferred to the surface of the metal film 130, i.e., energy loss occurs. At a communication wavelength, the absorption of specifically positively polarized light energy by the metal film 130 during surface plasmon resonance filters the light wave. Filtering of orthogonal light at a communication wavelength is achieved by the metal film 130 absorbing energy during surface plasmon resonance.

[0064] In summary, by setting a first air hole layer 111, a second air hole layer 112, and an elliptical air hole layer 113 within the cladding 110, and setting a metal film 130 within the two relatively arranged first air holes 111a, based on the principle of surface plasmon resonance, a wide range of filtering effects can be achieved without reserving liquid channels and injecting liquid, thereby improving the sensitivity and stability of information transmission.

[0065] In some examples, when the filtering device is applied to the financial field such as banking, since the filtering device in this application embodiment can achieve a wider filtering range, the signal transmission can be made more stable during the transmission of data through the photonic crystal fiber 100 in the bank data center. This can solve the problem of low data transmission efficiency in the bank data transmission process and help improve the quality of information transmission.

[0066] See also some of the possible implementation methods. Figure 1As shown, the outer side of the fiber core 120 in this embodiment of the application is provided with a first air hole layer 111. A second air hole layer 112 is provided circumferentially for each first air hole 111a of the first air hole layer 111.

[0067] In this embodiment, a first air hole layer 111 is provided circumferentially around the fiber core 120. A second air hole layer 112 is provided circumferentially around the first air hole layer 111. Therefore, along the direction away from the fiber core 120, the cladding 110 has a first air hole layer 111 and a second air hole layer 112, for a total of two air hole layers. It is understood that the more air hole layers there are, the larger the size of the cladding 110 and the larger the volume of the photonic crystal fiber 100. The number of air hole layers in this application is relatively small. Therefore, the volume of the photonic crystal fiber 100 in this embodiment can be designed to be smaller, which is conducive to the miniaturization of the photonic crystal fiber 100. This facilitates integration with optical fiber communication systems and also makes manufacturing easier.

[0068] See also some of the possible implementation methods. Figure 1 and Figure 2 As shown, there are four first air holes 111a. The centers of the four first air holes 111a are connected sequentially to form a rhombus. Among them, the inner walls of the two first air holes 111a that are arranged opposite each other along the second direction N are provided with metal films 130.

[0069] It is understandable that the two diagonals of a rhombus can have different dimensions, thus allowing for efficient use of space near the shorter diagonal. In other words, more structures can be arranged in the region near the shorter diagonal than in the region near the longer diagonal, which helps save internal space in the cladding 110 and facilitates the miniaturization of the photonic crystal fiber 100. For example, another structure could be a second air hole 112a.

[0070] In some examples, the inner walls of the two air holes arranged opposite each other along the second direction N can be coated with a metal film 130 to increase the coupling effect of plasma resonance, thereby increasing the amount of light concentrated in the fiber core 120. The more concentrated the energy of the fiber core 120, the higher its signal transmission capability.

[0071] In some examples, the cladding 110 may be made of silicon dioxide (SiO2). The core 120 may also be made of silicon dioxide. The metal film 130 may be a gold (Au) film.

[0072] In some examples, the cross-sectional shape of the outer contour of the cladding 110 can be circular or elliptical.

[0073] See also some of the possible implementation methods. Figure 1As shown, each first air hole 111a has four second air holes 112a arranged circumferentially. The centers of the four second air holes 112a are connected sequentially to form a rectangle.

[0074] In some examples, the number of second air holes 112a can be twelve. See also Figure 1 As shown, the cladding 110 has four rows and four columns of second air holes 112a. Specifically, the first and fourth rows each have two second air holes 112a, and the second and third rows each have four second air holes 112a. Furthermore, the first and fourth columns each have two second air holes 112a, and the second and third columns each have four second air holes 112a. Therefore, the multiple second air holes 112a within the cladding 110 can be distributed in a centrally symmetrical structure.

[0075] See also some of the possible implementation methods. Figure 2 As shown, the first space A has four second air holes 112a. The four second air holes 112a enclose a third space C. An elliptical air hole layer 113 is located within the third space C.

[0076] In some examples, the elliptical air hole layer 113 of this application embodiment can surround and form an elongated fiber core 120. The fiber core 120 is located within the second space B. The elliptical air holes 113a are positioned close to the fiber core 120, which can more effectively improve birefringence, thereby increasing the energy at the fiber core 120 and improving the signal transmission capability.

[0077] In some examples, the elliptical air pore layer 113 can be distributed in a centrosymmetric structure.

[0078] See also some of the possible implementation methods. Figure 2 As shown, both the first air hole 111a and the second air hole 112a are circular holes. The radius of the first air hole 111a is larger than the radius of the second air hole 112a.

[0079] In this embodiment, using two different sizes of first air holes 111a and second air holes 112a can improve birefringence and increase data transmission capacity. Furthermore, it is understood that having fewer types of air holes within the cladding 110 helps reduce fabrication difficulty and improve the manufacturing efficiency of the photonic crystal core 120.

[0080] In some possible implementations, the radius of the first air hole 111a in this embodiment is 0.8 micrometers. The diameter of the second air hole 112a is 0.45 micrometers.

[0081] In some feasible ways, the thickness of the metal film 130 in this embodiment of the application is 25 micrometers.

[0082] In some possible implementations, the major axis of the elliptical air hole 113a in this embodiment of the application is 0.5732 micrometers and the minor axis is 0.2 micrometers.

[0083] In some feasible ways, the center distance between each second air hole 112a and the corresponding first air hole 111a is 0.2 micrometers.

[0084] Based on the above parameter values, a structural model of the filtering device of this application was established using simulation software, and a computer simulation was performed on it using the finite element method to obtain the results. Figure 2 The diagram shows the working operation of the filtering device.

[0085] The transmission loss in this embodiment can be calculated using the following formula:

[0086]

[0087] Where λ represents the incident wavelength in μm, and Im[neff] represents the imaginary part of the effective refractive index of the fiber core's 120 fundamental mode. The relationship between the limiting loss and wavelength can be calculated using the transmission loss formula. The loss curve is shown below. Figure 3 As shown, x-polarized light is represented by line 1, and y-polarized light by line 2. Line 1 exhibits a relatively stable curve, while line 2 shows a higher peak value. Specifically, at a communication wavelength of 1310 nm, the transmission losses in the x-polarization and y-polarization directions are 75.86 dB / cm and 2305.72 dB / cm, respectively.

[0088] Understandably, when filtering orthogonal light at a single communication wavelength, if the transmission loss is high in one polarization direction (e.g., the y-polarization direction), resulting in a peak, the loss in the other polarization direction (e.g., the x-polarization direction) is relatively stable, and the loss value of x-polarized light is relatively small compared to the peak. This ensures a high extinction ratio, allowing the filtering device to simultaneously and adequately filter orthogonal light at a single communication wavelength.

[0089] The filtering device in this application embodiment has extremely high loss value in the y-polarization direction and very low loss value in the x-polarization direction, ensuring a high extinction ratio. This indicates that the filter can achieve sufficient filtering of orthogonal light simultaneously at the communication wavelength.

[0090] The extinction ratio of the embodiments of this application can be calculated using the following formula:

[0091] E = 20lg{exp[(α2-α1)L]}

[0092] Where α1 and α2 represent the limiting loss values ​​of the two orthogonal beams, respectively, and L represents the fiber length, calculated from the above formula. Figure 4 The extinction ratio curve shown is for reference. Figure 4As shown, the filtering device exhibits a high extinction ratio of 1936.83 dB at the communication wavelength of 1310 nm. With an extinction ratio greater than 20 dB, the bandwidth was calculated, and the filtering device achieved excellent transmission performance across an ultra-wideband 1000 nm range. Therefore, an ultra-wide optical bandwidth was obtained, improving filtering performance and effectively enhancing the transmission efficiency and stability of data in optical fiber.

[0093] In some examples, when applied to data transmission in banks, the filtering device of this application embodiment has an ultra-wide bandwidth during signal transmission, which can effectively increase the amount of data transmitted through the link per unit time and increase throughput, thereby improving the data rate.

[0094] Furthermore, the filtering device in this application embodiment does not generate much heat during operation, and when the filtering device is applied to the indoor environment of the banking and other financial industries, the indoor temperature is relatively constant. Therefore, the continuity of data transmission can be guaranteed while ensuring data transmission efficiency, thereby alleviating packet loss.

[0095] It should be noted that the numerical values ​​and ranges involved in this application are approximate values. Due to the influence of the manufacturing process, there may be a certain range of errors, which can be considered negligible by those skilled in the art.

[0096] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0097] In the description of this application, it should be understood that the terms “center,” “length,” “width,” “thickness,” “top,” “bottom,” “upper,” “lower,” “left,” “right,” “front,” “rear,” “vertical,” “horizontal,” “inner,” “outer,” “axial,” and “circumferential,” etc., used to indicate orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the indicated position or component must have a specific orientation, or a specific structure and operation, and therefore should not be construed as a limitation of the present invention.

[0098] The devices or elements referred to in the embodiments of this application or implied herein must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the embodiments of this application. In the description of the embodiments of this application, "a plurality of" means two or more, unless otherwise precisely specified.

[0099] The terms "first," "second," "third," "fourth," etc. (if present) in the specification, claims, and accompanying drawings of this application 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 of this application described herein can be implemented, for example, in orders other than those illustrated or described herein.

[0100] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0101] The term "multiple" in this article refers to two or more. The term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Furthermore, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects; in formulas, the character " / " indicates a "division" relationship between the preceding and following related objects.

[0102] It is understood that the various numerical designations used in the embodiments of this application are merely for descriptive convenience and are not intended to limit the scope of the embodiments of this application.

[0103] It is understood that, in the embodiments of this application, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

Claims

1. A filtering device, characterized in that, The main body of the filtering device is a photonic crystal fiber, which includes a cladding and a core. The core is located in the central region of the cladding, and the cladding contains a first air hole layer, a second air hole layer, and an elliptical air hole layer. The first air hole layer is distributed along the circumferential direction of the fiber core. The first air hole layer includes multiple sets of oppositely arranged first air holes, wherein one set of first air holes is oppositely arranged along a first direction, and another set of first air holes is oppositely arranged along a second direction. At least one set of first air holes has a metal film on its inner wall. The elliptical air hole layer is located within the first space enclosed by the first air hole layer. The elliptical air hole layer includes two rows of elliptical air holes spaced apart along the second direction. Each row of elliptical air holes includes multiple elliptical air holes spaced apart along the first direction. The elliptical air hole layer and the two first air holes arranged opposite to each other along the first direction form a second space. The fiber core is located within the second space, and the cladding is located outside the second space. The outer side of the fiber core is provided with a first air hole layer, and a second air hole layer is provided circumferentially for each first air hole of the first air hole layer. The second air hole layer includes a plurality of second air holes, and each first air hole is provided with four second air holes in the circumferential direction. The centers of the four second air holes are connected in sequence to form a rectangle. The size of the first air hole is different from the size of the second air hole. The first space has four second air holes, and the four second air holes surround a third space, with the elliptical air hole layer located within the third space.

2. The filtering device according to claim 1, characterized in that, Both the first air hole and the second air hole are circular holes, and the radius of the first air hole is larger than the radius of the second air hole.

3. The filtering device according to claim 2, characterized in that, The radius of the first air hole is 0.8 micrometers, and the diameter of the second air hole is 0.45 micrometers.

4. The filtering device according to claim 1, characterized in that, The thickness of the metal film is 25 nanometers.

5. The filtering device according to claim 1, characterized in that, The major axis of the elliptical air hole is 0.5732 micrometers, and the minor axis is 0.2 micrometers.

6. The filtering device according to claim 1, characterized in that, The center distance between each second air hole and the corresponding first air hole is 0.2 micrometers.

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