Mode filtering optical fiber and laser device thereof

Abstract

The embodiment of the utility model discloses a mode filtering optical fiber and a laser device thereof. The mode filtering optical fiber comprises a fiber core, an inner cladding and an outer cladding, wherein the inner cladding comprises a matrix material and dielectric cylinders; the dielectric cylinders surround the fiber core and are periodically arranged in the matrix material in multiple layers, the dielectric cylinders on the inner layer are arranged in a regular hexagon shape, the dielectric cylinders on the outermost layer comprise four dielectric cylinder groups, and each dielectric cylinder group comprises three dielectric cylinders; a mode capable of being transmitted in a microstructure area formed by the dielectric cylinders and the matrix material forms a super-mode group, and an interval formed by the effective refractive index of the lowest-order mode and the effective refractive index of the highest-order mode in the super-mode group is a super-mode group interval. And the leakage loss of the fiber core mode in the super mode group interval is greater than that of other fiber core modes of which the effective refractive index is not in the super mode group interval. According to the utility model, large-mode-field and pure-fundamental-mode transmission is realized, and the dielectric cylinders are regularly arranged, so that the optical fiber is formed by tapering after being stacked in a rod shape, and the transmission mode of the few-mode optical fiber is effectively controlled.

Description

A filter-mode optical fiber and its laser device Technical Field

[0001] This utility model relates to the field of optical fiber communication, and in particular to a filter mode optical fiber and its laser device. Background Technology

[0002] In the field of optical communication, single-mode fiber has achieved a significant increase in information capacity through technologies such as time-division multiplexing, wavelength-division multiplexing, and polarization multiplexing, but its transmission capacity is approaching its limit. To address these issues, space-division multiplexing technology using multi-core or few-mode fiber has become a research hotspot.

[0003] Space division multiplexing (SDM) technology transmits information through different fiber cores or different modes within the same fiber. Each signal carries different information, and each signal can achieve high-capacity communication through time division multiplexing (TDM) and wavelength division multiplexing (WDM). In few-mode fiber applications, mode division multiplexing (MDM) technology carries independent signals through different modes, which can multiply the fiber transmission capacity. Meanwhile, high-order mode-selective excitation technology for few-mode fibers has significant application value in large-mode field single-mode transmission, dispersion compensation, ultrashort pulse transmission, and nonlinear effect modulation. However, the practical application of these technologies all depend on the effective manipulation and control of the transmission modes in few-mode fibers. Achieving high-precision mode modulation has become a key technical problem that urgently needs to be solved. Summary of the Invention

[0004] This utility model provides a filter-mode fiber and its laser device. The filter-mode fiber realizes large mode field and pure fundamental mode transmission. The dielectric pillars are regularly arranged, which makes it easy to stack them in the rod shape and then tape them to form an optical fiber, effectively manipulating and controlling the transmission mode of the few-mode fiber.

[0005] According to one aspect of the present invention, a filter mode optical fiber is provided, comprising a fiber core, an inner cladding disposed around the fiber core, and an outer cladding disposed around the inner cladding. The inner cladding comprises a matrix material and a dielectric pillar located in the matrix material. The refractive index of the fiber core, the refractive index of the dielectric pillar, and the refractive index of the outer cladding are all greater than the refractive index of the matrix material.

[0006] The dielectric pillars are parallel to the extension direction of the fiber core. The dielectric pillars are arranged in multiple layers periodically around the fiber core within the matrix material. The center of each layer of dielectric pillars is located on a regular hexagon. All the regular hexagons are concentrically arranged. The outermost layer of dielectric pillars includes four groups of dielectric pillars. Each group of dielectric pillars includes three dielectric pillars. Two groups of dielectric pillars are arranged on two opposite sides of the regular hexagon. The central dielectric pillars of the other two groups of dielectric pillars are respectively arranged on two vertices between the two opposite sides of the regular hexagon.

[0007] The microstructure region composed of the dielectric pillar and the matrix material forms a supermode group. The interval formed by the effective refractive index of the lowest-order mode and the effective refractive index of the highest-order mode in the supermode group is the supermode group interval. Within the operating wavelength range, at least one core mode has an effective refractive index within the supermode group interval. The leakage loss of the core mode within the supermode group interval is greater than that of other core modes whose effective refractive index is not within the supermode group interval.

[0008] Optionally, in the operating wavelength range, the refractive index of the outer cladding of the filter fiber is above the supermode group range.

[0009] Optionally, in the filter fiber, the refractive index of the outer cladding satisfies:

[0010] n out -n ceff ≥0.0005;

[0011] Where n out n represents the refractive index of the outer cladding layer. ceff This represents the maximum effective refractive index of the inner cladding.

[0012] Optionally, in the filter fiber, the diameter of the dielectric pillar and the distance between two adjacent dielectric pillars satisfy the following:

[0013]

[0014] Where d rod The diameter of the medium column is represented by Λ, and the distance between two adjacent medium columns is represented by Λ.

[0015] Optionally, in the filter fiber, the number of layers of the dielectric pillar is greater than or equal to 3.

[0016] Optionally, the diameter of the core of the filter fiber is greater than or equal to 7 μm and less than or equal to 12 μm.

[0017] Optionally, the filter fiber has a cross-sectional distribution that is both axisymmetric and centrosymmetric.

[0018] Optionally, the core material of the filter fiber is solid.

[0019] Optionally, in the filter mode optical fiber, the dielectric column is a liquid column.

[0020] According to another aspect of the present invention, a laser device is provided, comprising a laser and a filter fiber as described above, wherein the output end of the laser is connected to one end of the filter fiber.

[0021] This invention provides a mode-filtering fiber. A microstructure region composed of high-refractive-index dielectric pillars and a matrix material forms a supermode group, which couples with the core transmission mode. By supplementing three dielectric pillars in each of the four directions of the periodically arranged high-refractive-index dielectric pillars, and utilizing the cladding to achieve high leakage loss in the supermode group, an effective mode-filtering mechanism is formed, enabling selective filtering of higher-order mode optical fiber modes. This invention achieves large mode field, pure fundamental mode transmission, and the regular arrangement of the dielectric pillars facilitates stacking and tapering into an optical fiber in a rod-like form, effectively manipulating and controlling the transmission mode of the few-mode fiber.

[0022] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this utility model, nor is it intended to limit the scope of this utility model. Other features of this utility model will become readily apparent from the following description. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 is a schematic diagram of the structure of a filter optical fiber provided in an embodiment of the present invention;

[0025] Figure 2 is a structural schematic diagram of a filter mode optical fiber dielectric pillar arrangement provided in an embodiment of the present invention;

[0026] Figure 3 is a schematic diagram of the transmission of the fundamental mode of a filter fiber in the fiber core according to an embodiment of the present invention;

[0027] Figure 4 shows a filter mode optical fiber LP provided in an embodiment of this utility model. 11 A schematic diagram of pattern transmission in the packet layer. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. 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 should fall within the protection scope of the present invention.

[0029] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this utility model 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 the utility model described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0030] Figure 1 is a structural schematic diagram of a filter fiber provided in an embodiment of the present invention; Figure 2 is a structural schematic diagram of a filter fiber dielectric pillar arrangement provided in an embodiment of the present invention; Figure 3 is a schematic diagram of the transmission of the fundamental mode in the fiber core of a filter fiber provided in an embodiment of the present invention; Figure 4 is a schematic diagram of a filter fiber LP provided in an embodiment of the present invention. 11 A schematic diagram of mode transmission in the cladding is shown in Figures 1 to 4. This embodiment of the present invention provides a filter mode optical fiber, including a core 10, an inner cladding 20 surrounding the core 10, and an outer cladding 30 surrounding the inner cladding 20. The inner cladding 20 includes a matrix material 21 and dielectric pillars 22 located in the matrix material 21. The refractive index of the core 10, the refractive index of the dielectric pillars 22, and the refractive index of the outer cladding 30 are all greater than the refractive index of the matrix material 21.

[0031] The dielectric pillars 22 are parallel to the extension direction of the fiber core 10. The dielectric pillars 22 are arranged in multiple layers and periodically within the matrix material 21 around the fiber core 10. The center of each layer of dielectric pillars 22 is located on a regular hexagon. All regular hexagons are arranged concentrically. The outermost layer of dielectric pillars 22 includes four groups of dielectric pillars. Each group of dielectric pillars includes three dielectric pillars 22. Two groups of dielectric pillars are arranged on two opposite sides of the regular hexagon. The central dielectric pillars 22 of the other two groups are arranged on two vertices between the two opposite sides of the regular hexagon.

[0032] The microstructure region composed of dielectric pillar 22 and matrix material 21 forms a supermode group of transportable modes. The interval formed by the effective refractive index of the lowest-order mode and the effective refractive index of the highest-order mode in the supermode group is the supermode group interval. Within the operating wavelength range, at least one core mode has an effective refractive index within the supermode group interval. The leakage loss of the core mode within the supermode group interval is greater than that of other core modes whose effective refractive index is not within the supermode group interval.

[0033] This invention provides a filter mode optical fiber, which includes a core 10, an inner cladding 20, and an outer cladding 30. The core 10 is located at the innermost part of the filter mode optical fiber and is used for the transmission of the fundamental mode. The refractive index n of the core 10 is... core The selection range is relatively wide, depending on the suppression mode required. The inner cladding 20 surrounds the fiber core 10 and includes a matrix material 21 and dielectric pillars 22 located within the matrix material 21. The dielectric pillars 22 are high-refractive-index cylindrical structures embedded in the matrix material 21 of the inner cladding 20 of the filter fiber. The refractive index of the dielectric pillars 22 can be n. rod =1.4935, the diameter of medium column 22 can be d rod =4.65μm, the matrix material 21 fills the gaps between the dielectric pillars 22, forming a background environment for the periodic microstructure. The matrix material 21 is made of a low refractive index medium, which can be silicon dioxide or other inert optical materials. The refractive index of the matrix material 21 can be n clad =1.45, the diameter of the matrix material 21 can be d clad =69.75μm; the outer cladding 30 is disposed around the inner cladding 20 and is located on the outermost side of the filter mode fiber. The diameter of the outer cladding 30 can be d. out =100μm, its function is to prevent the supermode from meeting the total internal reflection condition, resulting in leakage loss, thereby filtering out the conduction mode in the inner cladding 20.

[0034] Among them, LP 11 The mode is a typical high-order mode in filter fiber. Referring to Figure 4, its energy distribution resembles a petal shape, with four intensity peaks in the inner cladding 20 region, located in the four directions of the core 10 (up, down, left, and right). Based on its structural characteristics, dielectric pillars 22 are arranged in multiple layers periodically around the core 10 within the matrix material 21. The center of each layer of dielectric pillars 22 is located on a regular hexagon, and all regular hexagons are concentrically arranged. This design can generalize the filtering of common high-order modes. In addition, the uniform arrangement of standard hexagonal dielectric pillars 22 may not completely cover the LP. 11 The concentrated energy region of the mode leads to insufficient coupling efficiency and incomplete mode filtering. Therefore, an outermost dielectric pillar 22 is also provided. Referring to Figure 2, the outermost dielectric pillar 22 includes four dielectric pillar groups, each of which includes three dielectric pillars 22. Two of the dielectric pillar groups are arranged on two opposite sides of a regular hexagon, and the central dielectric pillars 22 of the other two dielectric pillar groups are arranged on the two vertices between the two opposite sides of the regular hexagon. The three dielectric pillars 22 of each dielectric pillar group are arranged in a small triangle, which expands the energy concentration of the LP. 11 The coverage area of ​​the modulus energy region increases the coupling probability.

[0035] When there are many high-refractive-index dielectric pillars 22, the number of supermodes formed is also large. Therefore, a supermode group with a small effective refractive index difference is formed within a range near the effective refractive index of a single high-refractive-index dielectric pillar 22 mode. Since the lowest-order mode has the largest effective refractive index and the highest-order mode has the smallest effective refractive index, the range formed by the effective refractive indices of the lowest-order and highest-order modes in the supermode group can be defined as the supermode group range. Within the operating wavelength range, when any core mode is within the effective refractive index range of the supermode group, the core mode will couple with one or more supermodes within it. Because the supermode group forms a large number of densely packed effective refractive index ranges, the core mode can couple with one or more supermodes within it over a wide wavelength range, thus forming a broadband mode filtering effect.

[0036] When the effective refractive index of the core mode is above the supermode group range, since the refractive index of the core 10 is higher than that of the matrix material 21, its core mode satisfies the refractive index guiding mechanism. Therefore, the loss of the core mode is small. The possible reason for the loss is that the refractive index of the outer cladding 30 is higher than that of the effective refractive index of the core mode, which leads to leakage loss. As the difference between the effective refractive indices of the core mode and the supermode increases, the refractive index guiding effect is enhanced, and the leakage loss decreases as the effective refractive index of the core mode increases.

[0037] When the effective refractive index of the core mode is below the supermode group range, the core mode is still confined to the core 10 region for propagation. This is because the supermode formed by the high refractive index medium pillar 22 has a different effective refractive index from the core mode, resulting in a weak coupling effect. Therefore, the core mode still propagates in and around the core 10, while the outer cladding 30 is far from the core 10, ensuring that the propagation mode in the core 10 has low loss.

[0038] In summary, when the effective refractive index of the higher-order modes in the fiber core is within the supermode group range, the mode loss increases, which can achieve the purpose of filtering. However, when the effective refractive index of the fundamental mode is below the supermode group range, the leakage loss is low, and it can still be transmitted in the optical fiber.

[0039] It should be noted that the refractive indices of the core 10, the dielectric pillar 22, and the cladding 30 are all greater than that of the matrix material 21. Referring to Figure 3, the basis for light transmission in a filter fiber is total internal reflection. When the refractive index of the core 10 is greater than that of the matrix material 21, total internal reflection will occur at the interface between the core 10 and the inner cladding 20, and the light will propagate entirely within the core 10. When the refractive index of the dielectric pillar 22 is greater than that of the matrix material 21, the dielectric pillar 22 can support independent guided modes and complete transmission; otherwise, a supermode group cannot be formed, and the mode filtering mechanism will fail. When the refractive index of the cladding 30 is greater than that of the matrix material 21, the condition for total internal reflection cannot be met, and energy will leak through the cladding 30, thereby filtering out higher-order modes and achieving pure fundamental mode transmission. Furthermore, to make it easier for higher-order modes in the cladding 30 to experience leakage loss, the cladding 30 must be close to the outermost dielectric pillar 22.

[0040] By connecting multiple optical fibers with different filtering modes in series, multiple optical fiber modes can be filtered out, so that the few-mode fiber transmits only a single high-order mode. While filtering out the corresponding mode, other modes in the fiber can maintain low-loss transmission.

[0041] This invention provides a mode-filtering fiber. A microstructure region composed of high-refractive-index dielectric pillars and a matrix material forms a supermode group, which couples with the core transmission mode. By supplementing three dielectric pillars in each of the four directions of the periodically arranged high-refractive-index dielectric pillars, and utilizing the cladding to achieve high leakage loss in the supermode group, an effective mode-filtering mechanism is formed, enabling selective filtering of higher-order mode optical fiber modes. This invention achieves large mode field, pure fundamental mode transmission, and the regular arrangement of the dielectric pillars facilitates stacking and tapering into an optical fiber in a rod-like form, effectively manipulating and controlling the transmission mode of the few-mode fiber.

[0042] Optionally, within the operating wavelength range, the refractive index of the outer cladding layer 30 is above the supermode group range.

[0043] In this process, the refractive index of the outer cladding layer 30 must be above the supermode group range. At this time, the supermode formed by the high refractive index medium pillar 22 in the inner cladding layer 20 will be filtered out due to leakage loss because it does not meet the total internal reflection condition. Meanwhile, the fundamental mode in the fiber core 10 can be transmitted with low loss because its effective refractive index is lower than the supermode group range, thus achieving the effect of pure fundamental mode transmission in a large mode field.

[0044] Optionally, the refractive index of the outer cladding layer 30 satisfies:

[0045] n out -n ceff ≥0.0005;

[0046] Where n out n represents the refractive index of the outer cladding layer 30. ceffThis represents the maximum effective refractive index of the inner cladding 20.

[0047] In this embodiment, the refractive index of the outer cladding layer 30 is greater than the maximum effective refractive index of the inner cladding layer 20 by more than 0.0005. The maximum effective refractive index n of the inner cladding layer 20 is... ceff =1.465, therefore the refractive index n of the outer cladding layer 30 is set to 1.465. out =1.4655, disrupting the total internal reflection condition of the supermode, causing it to be filtered out due to leakage loss. The reliability of the filtering effect is ensured by using a quantized refractive index difference threshold of 0.0005, avoiding incomplete filtering due to an excessively small difference. Ultimately, the effect of pure fundamental mode transmission in a large mode field is achieved.

[0048] Optionally, the diameter of the dielectric column 22 and the distance between two adjacent dielectric columns 22 satisfy the following:

[0049]

[0050] Where d rod Λ represents the diameter of the medium column 22, and Λ represents the distance between two adjacent medium columns 22.

[0051] The diameter and spacing of the dielectric pillars 22 ensure that the supermode group formed by the high refractive index dielectric pillars 22 in the inner cladding 20 can cover the effective refractive index of the higher-order modes of the fiber core 10, while avoiding the effective refractive index of the fundamental mode. By controlling the mode characteristics through the duty cycle, the transmission mode of the few-mode fiber is effectively manipulated and controlled.

[0052] Optionally, the number of layers in the medium column 22 is greater than or equal to 3.

[0053] The dielectric pillar 22 includes at least two layers of hexagonal dielectric pillars 22 and one supplementary dielectric pillar 22 located in four directions. The more layers of dielectric pillars 22 there are, the greater the total number of dielectric pillars 22, and the greater the number of supermode groups formed, enabling a wider range of filter mode structures, while also improving the mechanical strength and process compatibility of the filter fiber.

[0054] Optionally, the diameter d of the fiber core 10 core Greater than or equal to 7μm, less than or equal to 12μm.

[0055] It is understood that this embodiment of the invention uses a large-diameter fiber core 10, with a diameter greater than or equal to 7 μm and less than or equal to 12 μm. The larger the diameter of the fiber core 10, the larger the transmission area of ​​light in the filter fiber, and the larger the mode field area. A large mode field area can improve coupling efficiency, energy density, and signal quality. When the diameter is less than 7 μm, higher-order modes cannot be transmitted within the fiber core; the larger the fiber core diameter, the more higher-order modes can be transmitted. Considering all these factors, the diameter of the fiber core is limited to between 7 μm and 12 μm.

[0056] Optionally, referring to Figure 2, the cross-sectional distribution of the filter mode fiber has both axisymmetric and centrosymmetric properties.

[0057] The filter fiber contains multiple layers of periodically arranged dielectric pillars 22. The center of each dielectric pillar 22 is located on a regular hexagon, and all regular hexagons are concentrically arranged. The outermost dielectric pillar 22 includes four groups of dielectric pillars. The axisymmetric arrangement of the dielectric pillars 22 makes the effective refractive index range of the supermode group completely consistent in all directions of the circumference, ensuring the uniformity and stability of mode coupling. When the fiber is drawn, the preform of the axisymmetric structure shrinks radially uniformly at high temperature, avoiding deformation or breakage of the dielectric pillars 22 due to stress concentration. The axisymmetric arrangement of the dielectric pillars 22 makes the supermode group range a continuous and uniform annular band. As long as the effective refractive index of the higher-order mode falls into this annular band, it can be filtered out through the axisymmetric coupling path, achieving a broadband mode filtering effect and accurately suppressing the target higher-order mode.

[0058] Optionally, the core 10 may be made of a solid material.

[0059] Understandably, using a solid material for the fiber core 10 is beneficial for industrial applications. The stable physical properties of the solid fiber core 10 provide a foundation for processes such as fusion splicing and tapering, and the controllability of the solid fiber core 10 facilitates the preparation of preforms, enabling precise shaping. Furthermore, the stability of the solid structure during fusion splicing effectively avoids the collapse problem at high temperatures, further improving the reliability and process feasibility of optical fiber manufacturing and engineering applications.

[0060] Optionally, the medium column 22 is a liquid column.

[0061] It is understandable that the medium column 22 is a liquid column, and its refractive index can be quickly adjusted by means of temperature, pressure, etc., thereby dynamically changing the effective refractive index range of the supermode group region. At the same time, it can achieve efficient thermal management, low cost, and strong compatibility.

[0062] This utility model also provides a laser device, including a laser and any of the filter mode optical fibers provided in the above embodiments, wherein the output end of the laser is connected to one end of the filter mode optical fiber.

[0063] Since the laser device in this embodiment includes any of the above-mentioned filter mode optical fibers, it has the beneficial effects of the corresponding filter mode optical fibers.

[0064] The specific embodiments described above do not constitute a limitation on the scope of protection of this utility model. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A filter-mode optical fiber, characterized in that, The device includes a fiber core, an inner cladding surrounding the fiber core, and an outer cladding surrounding the inner cladding. The inner cladding includes a matrix material and dielectric pillars located within the matrix material. The refractive indices of the fiber core, the dielectric pillars, and the outer cladding are all greater than the refractive index of the matrix material. The dielectric pillars are parallel to the extension direction of the fiber core and are arranged in multiple layers periodically within the matrix material. The center of each layer of dielectric pillars is located on a regular hexagon, and all the regular hexagons are concentrically arranged. The outermost layer of dielectric pillars includes four groups of dielectric pillars, and each group of dielectric pillars includes three dielectric pillars, two of which are... The dielectric pillar groups are arranged on two opposite sides of a regular hexagon, and the central dielectric pillars of the other two dielectric pillar groups are respectively arranged on two vertices between the two opposite sides of the regular hexagon. The microstructure region composed of the dielectric pillars and the matrix material forms a supermode group. The interval formed by the effective refractive index of the lowest-order mode and the effective refractive index of the highest-order mode in the supermode group is the supermode group interval. Within the operating wavelength range, at least one core mode has an effective refractive index within the supermode group interval. The leakage loss of the core mode within the supermode group interval is greater than that of other core modes whose effective refractive index is not within the supermode group interval.

2. The filter-mode optical fiber according to claim 1, characterized in that, Within the operating wavelength range, the refractive index of the outer cladding layer is above the supermode group range.

3. The filter-mode optical fiber according to claim 2, characterized in that, The refractive index of the outer cladding layer satisfies: n out -n ceff ≥0.0005; where n out n represents the refractive index of the outer cladding layer. ceff This represents the maximum effective refractive index of the inner cladding.

4. The filter-mode optical fiber according to claim 1, characterized in that, The diameter of the medium column and the distance between two adjacent medium columns satisfy the following: ; where d rod The diameter of the medium column is represented by Λ, and the distance between two adjacent medium columns is represented by Λ.

5. The filter-mode optical fiber according to claim 1, characterized in that, The number of layers in the medium column is greater than or equal to 3.

6. The filter-mode optical fiber according to claim 1, characterized in that, The diameter of the fiber core is greater than or equal to 7 μm and less than or equal to 12 μm.

7. The filter-mode optical fiber according to claim 1, characterized in that, The cross-sectional distribution of the filter mode optical fiber has both axisymmetric and centrosymmetric properties.

8. The filter-mode optical fiber according to claim 1, characterized in that, The core material is solid.

9. The filter-mode optical fiber according to claim 1, characterized in that, The medium column is a liquid column.

10. A laser device, characterized in that, It includes a laser and a filter fiber as described in any one of claims 1 to 9, wherein the output end of the laser is connected to one end of the filter fiber.

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