Optical filter and laser device having the same

Abstract

The present invention provides an optical filter capable of suppressing damage to optical components caused by Raman scattering. The optical filter (1) includes a first optical fiber (10) and a second optical fiber (20) connected to the first optical fiber (10). The first optical fiber (10) is composed of a photonic bandgap fiber, which includes: a core region (11); and a plurality of high refractive index portions (13) having a refractive index higher than that of the core region (11), which are periodically arranged around the core region (11) to suppress the propagation of Raman scattering light within the core region (11). The second optical fiber (20) includes: a core (21); and a cladding (22) having a refractive index lower than that of the core (21), which covers the outer periphery of the core (21). The optical filter (1) includes: a high refractive index resin (50) that removes Raman scattered light incident on the cladding (22) of the second optical fiber (20) through the high refractive index portion (13) of the first optical fiber (10); and an optical fiber housing portion (30) that houses the optical fibers (10) and (20) and protects the connection portion of the optical fibers (10) and (20).

Description

Technical Field

[0001] The present invention relates to an optical filter and a laser device having the optical filter. Background Technology

[0002] In laser devices such as fiber lasers, if the output of the emitted laser beam increases, the power density of the laser beam propagating inside the fiber core increases, resulting in nonlinear phenomena such as stimulated Raman scattering. In recent years, to suppress such stimulated Raman scattering, the use of photonic bandgap fiber (PBGF) has been proposed (see, for example, Patent Document 1).

[0003] The PBGF comprises a core region and multiple high-refractive-index sections periodically arranged around the core region. Light of a specific wavelength band can propagate within the core region, but propagation of other wavelength bands is suppressed within the core region. By aligning the wavelength band whose propagation within the core is suppressed with the wavelength band of the Raman scattered light, Raman scattered light can be removed from the light propagating in the core. The Raman scattered light removed from the core propagates in the high-refractive-index sections of the PBGF; however, this Raman scattered light incident on the cladding of the optical fiber connected to the PBGF propagates within the cladding and may cause damage to various optical components.

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2020-20885 Summary of the Invention

[0005] (a) Technical problems to be solved The present invention was made in view of the problems of the prior art, and its object is to provide an optical filter capable of suppressing damage to optical components caused by Raman scattering light.

[0006] (II) Technical Solution According to one aspect of the present invention, an optical filter capable of suppressing damage to optical components caused by Raman scattering light is provided. The optical filter comprises: a first optical fiber composed of a photonic bandgap fiber, the photonic bandgap fiber including: a core region; and a plurality of high-refractive-index portions having a refractive index higher than that of the core region, periodically arranged around the core region to suppress the propagation of Raman scattering light within the core region; and a second optical fiber connected to the first optical fiber. The second optical fiber includes: a core optically coupled to the core region of the first optical fiber; and a cladding having a refractive index lower than that of the core, covering the outer periphery of the core. The cladding is optically coupled to the plurality of high-refractive-index portions of the first optical fiber. The optical filter further comprises: a first light removal portion that removes Raman scattering light incident on the cladding of the second optical fiber through the plurality of high-refractive-index portions of the first optical fiber; and an optical fiber receiving portion that receives the first optical fiber and the second optical fiber, protecting the connection between the first optical fiber and the second optical fiber. Attached Figure Description

[0007] Figure 1 This is a schematic top view of an optical filter according to a first embodiment of the present invention.

[0008] Figure 2 yes Figure 1 AA-line cross-section diagram.

[0009] Figure 3 yes Figure 1 The diagram shows the BB line cross-section of the first optical fiber.

[0010] Figure 4 yes Figure 1 The diagram shows the CC line cross-section of the second optical fiber.

[0011] Figure 5 This is a schematic cross-sectional view of an optical filter according to a second embodiment of the present invention.

[0012] Figure 6 This is a schematic cross-sectional view of an optical filter according to a third embodiment of the present invention.

[0013] Figure 7 This is a schematic cross-sectional view of an optical filter according to a fourth embodiment of the present invention.

[0014] Figure 8 This is a schematic cross-sectional view illustrating an embodiment of the optical filter system of the present invention.

[0015] Figure 9 This is a graph showing the proportion of Raman scattered light measured on the downstream side when the length of the first optical fiber of the optical filter of the first embodiment of the present invention is changed.

[0016] Figure 10 This is a block diagram schematically illustrating a laser device according to one embodiment of the present invention.

[0017] Figure 11 This is a block diagram schematically illustrating a laser device according to another embodiment of the present invention. Detailed Implementation

[0018] The following is for reference Figures 1 to 11 The optical filter of the present invention and embodiments of a laser device equipped with the optical filter will be described in detail. Figures 1 to 11 In this context, identical or equivalent constituent elements are labeled with the same reference numerals, and redundant descriptions are omitted. Additionally, in... Figures 1 to 11 In this work, there are instances where the scale and dimensions of each component are exaggerated, or where some components are omitted. In the following explanation, unless otherwise specified, terms such as "first" and "second" are used only to distinguish the components from each other and do not indicate a specific position or order.

[0019] Figure 1 This is a schematic top view of the optical filter 1 according to the first embodiment of the present invention. Figure 2 yes Figure 1 The AA-line cross-sectional diagram. (See diagram below.) Figure 1 as well as Figure 2 As shown, the optical filter 1 includes a first optical fiber 10, a second optical fiber 20 fused to the first optical fiber 10, and an optical fiber receiving portion 30 for housing these optical fibers 10 and 20. An optical fiber receiving groove 31 extending along the long side is formed in the optical fiber receiving portion 30, and the optical fibers 10 and 20 are disposed within this groove 31. The first optical fiber 10 is fixed within the optical fiber receiving groove 31 by a fixing resin 32 filled at one end along the long side, and the second optical fiber 20 is fixed within the optical fiber receiving groove 31 by a fixing resin 33 filled at the other end along the long side. The optical fiber receiving portion 30 protects the optical fibers 10 and 20 and the fused connection portion 40 from external forces, impacts, and vibrations.

[0020] Figure 3 yes Figure 1 A cross-sectional view of the BB line of the first optical fiber 10. The first optical fiber 10 is composed of solid-core photonic bandgap fiber, as shown below. Figure 3 As shown, it includes a core region 11, a cladding region 12 located outside the core region 11, and a coating layer 18 covering the outer periphery of the cladding region 12. The coating layer 18 is formed, for example, from a UV-curable resin, and may also comprise multiple layers.

[0021] The cladding region 12 includes a plurality of high-refractive-index portions 13 periodically arranged around the core region 11, and low-refractive-index portions 14 filling the spaces between these high-refractive-index portions 13 and covering the outer sides of the high-refractive-index portions 13. The high-refractive-index portions 13 have a higher refractive index than the core region 11 and are arranged, for example, in a triangular lattice pattern around the core region 11. The low-refractive-index portions 14 have a lower refractive index than the high-refractive-index portions 13. In this embodiment, the refractive index of the core region 11 is the same as the refractive index of the low-refractive-index portions 14, but the refractive index of the core region 11 and the refractive index of the low-refractive-index portions 14 may also be different. Furthermore, the coating layer 18 has a lower refractive index than the low-refractive-index portions 14.

[0022] For example, the core region 11 and the low-refractive-index portion 14 can be formed using pure quartz glass (SiO2), and a dopant (e.g., germanium (Ge)) with properties that increase the refractive index can be added to the quartz glass (SiO2) to form the high-refractive-index portion 13. Alternatively, the high-refractive-index portion 13 can be formed using pure quartz glass (SiO2), and a dopant (e.g., fluorine (F) or boron (B)) with properties that decrease the refractive index can be added to the quartz glass (SiO2) to form the core region 11 and the low-refractive-index portion 14. In this embodiment, no active element is added to the core region 11, and the first optical fiber 10 is configured as a passive optical fiber that does not perform optical amplification.

[0023] Figure 4 yes Figure 1 The CC-line cross-section of the second optical fiber 20 is shown below. Figure 4 As shown, the second optical fiber 20 includes a core 21 optically coupled to the core region 11 of the first optical fiber 10, a cladding 22 covering the outer periphery of the core 21, and a coating 28 covering the outer periphery of the cladding 22. The cladding 22 is optically coupled to the high refractive index portion 13 of the first optical fiber 10. The coating 28 is formed, for example, of an ultraviolet-curable resin, and may also comprise multiple layers.

[0024] The cladding 22 has a lower refractive index than the core 21, and the coating 28 has a lower refractive index than the cladding 22. For example, the core 21 can be formed from pure quartz glass (SiO2), with dopants (e.g., fluorine (F) or boron (B)) added to the quartz glass (SiO2), thereby forming the cladding 22. Alternatively, the cladding 22 can be formed from pure quartz glass (SiO2), with dopants (e.g., germanium (Ge)) added to the quartz glass (SiO2), thereby forming the core 21.

[0025] like Figure 1 as well as Figure 2As shown, the cladding layer 18 of the first optical fiber 10 is peeled off a certain distance from its end, forming a cladding region 12 exposed from the cladding layer 18, resulting in a cladding exposure portion 12A. Similarly, the cladding layer 28 of the second optical fiber 20 is peeled off a certain distance from its end, forming a cladding exposure portion 22A. The cladding exposure portions 12A of the first optical fiber 10 and 22A of the second optical fiber 20 are fused together at the fusion splice connection portion 40.

[0026] The first optical fiber 10 is connected to a laser source, such as an optical fiber amplifier, as described later. The laser generated by the laser source propagates in the core region 11 of the first optical fiber 10 and in the core 21 of the second optical fiber 20. In the following description, the direction in which the laser propagates from the laser source through the first optical fiber 10 to the second optical fiber 20 is referred to as the "downstream side," and the opposite direction is referred to as the "upstream side."

[0027] The high-refractive-index portion 13 of the cladding region 12 of the first optical fiber 10 is periodically arranged around the core region 11 to suppress the propagation of Raman-scattered light within the core region 11. Therefore, if Raman-scattered light generated at the front end of the first optical fiber 10 is incident on the core region 11, the propagation of Raman-scattered light in the core region 11 is suppressed. Figure 2 As indicated by the arrow, Raman scattered light leaks from the core region 11 into the high refractive index section 13 and propagates within the high refractive index section 13. Furthermore, the Raman scattered light propagating in the high refractive index section 13 is incident on the cladding 22 of the second optical fiber 20.

[0028] As described above, the high-refractive-index portion 13 of the first optical fiber 10 can be formed by adding dopants such as germanium to quartz glass, and the cladding 22 of the second optical fiber 20 can be formed of quartz glass. In this case, the refractive index of the high-refractive-index portion 13 of the first optical fiber 10 can be greater than or equal to the refractive index of the cladding 22 of the second optical fiber 20.

[0029] When the refractive index of the core region 11 of the first optical fiber 10 is set to n1 and the refractive index of the core 21 of the second optical fiber 20 is set to n2, the refractive index difference between the core region 11 and the core 21 is set to Δ = (n1 / n2). 2 -n2 2 ) / 2n1 2 Within ±0.2%, the reflectivity R of the welded joint 40 is R = ((n1-n2) / (n1+n2)). 2 Suppressed below -60dB.

[0030] The optical filter 1 of this embodiment has a high-refractive-index resin 50 (first resin) as a first light removal section, which removes Raman scattered light incident on the cladding 22 of the second optical fiber 20. The high-refractive-index resin 50 is a resin having a refractive index higher than that of the cladding 22 of the second optical fiber 20, and it is sufficient to cover the entire circumference (outer periphery) of the exposed portion 22A of the cladding of the second optical fiber 20, extending at least a portion along its long side. For example, the high-refractive-index resin 50 is formed of a material that is light-transparent to the wavelength of the Raman scattered light incident on the cladding 22. Silicone resin is an example of a transparent material. Figure 1 as well as Figure 2 In the example shown, the high refractive index resin 50 covers the end of the cladding layer 28 of the second optical fiber 20, the entire length of the cladding exposure 22A, and a portion of the cladding exposure 12A of the first optical fiber 10.

[0031] like Figure 1 as well as Figure 2 As shown, when the high-refractive-index resin 50 covers the end of the cladding layer 28 of the second optical fiber 20, the refractive index of the cladding layer 28 of the second optical fiber 20 is preferably lower than or equal to the refractive index of the high-refractive-index resin 50. In particular, when the cladding layer 28 is composed of multiple layers, the refractive index of the innermost layer (main layer) of the cladding layer 28 that is in contact with the cladding layer 22 is preferably lower than or equal to the refractive index of the high-refractive-index resin 50.

[0032] Thus, the outer periphery of the exposed cladding portion 22A is covered by the high-refractive-index resin 50, making it easier for Raman scattered light incident on the cladding 22 of the second optical fiber 20 to leak from the cladding 22 into the high-refractive-index resin 50 as described above. Consequently, the Raman scattered light is released from the high-refractive-index resin 50 to the outside, effectively removing Raman scattered light from the cladding 22 of the second optical fiber 20. Therefore, damage to optical components located downstream of the second optical fiber 20 can be suppressed.

[0033] Here, the diameter D2 of the core 21 of the second optical fiber 20 (refer to...) Figure 4 The diameter D1 is preferably the smallest circle C that connects to the innermost high-refractive-index section 13A among the plurality of high-refractive-index sections 13 of the first optical fiber 10 (refer to...). Figure 3 By making the diameter D2 of the core 21 of the second optical fiber 20 less than or equal to the diameter D1 of the smallest circle C connected to the high refractive index section 13A, it is possible to suppress the Raman scattered light propagating in the high refractive index section 13 from coupling to the core 21 of the second optical fiber 20 and propagating downstream.

[0034] Figure 5This is a schematic cross-sectional view of the optical filter 101 according to the second embodiment of the present invention. In this embodiment, the high refractive index resin 50 is not provided, and the outer peripheral surface of the cladding exposed portion 22A is roughened, for example, by etching or the like, covering at least a portion of the long side direction. By forming such a rough surface 150 in the cladding 22, Raman scattered light incident on the cladding 22 of the second optical fiber 20 is easily scattered by the rough surface 150 and released to the outside, and Raman scattered light can be effectively removed from the cladding 22 of the second optical fiber 20. Thus, the rough surface 150 of the cladding exposed portion 22A in this embodiment functions as a first light removal portion, which removes Raman scattered light incident on the cladding 22 of the second optical fiber 20.

[0035] Figure 6 This is a schematic cross-sectional view of an optical filter 201 according to a third embodiment of the present invention. A portion of the Raman scattered light propagating in the high-refractive-index portion 13 of the first optical fiber 10 may leak into the low-refractive-index portion 14 outside the high-refractive-index portion 13. The optical filter 201 in this embodiment has a high-refractive-index resin 250 (second resin) as a second light removal portion, which removes the Raman scattered light leaking into the low-refractive-index portion 14 of the first optical fiber 10.

[0036] The high-refractive-index resin 250 is a resin with a refractive index higher than that of the low-refractive-index portion 14 of the first optical fiber 10, and it is sufficient to cover the entire circumference (outer periphery) of the cladding exposed portion 12A of the first optical fiber 10, extending at least a portion along its long side. For example, the high-refractive-index resin 250 is formed of a material that is light-transparent relative to the wavelength of Raman scattered light leaking into the low-refractive-index portion 14. Silicone resin can be cited as an example of a transparent material. Figure 6 In the example shown, high refractive index resin 250 covers the end of the cladding layer 18 of the first optical fiber 10 and a portion of the cladding exposure 12A.

[0037] like Figure 6 As shown, when the end of the cladding layer 18 of the first optical fiber 10 is covered by the high-refractive-index resin 250, the refractive index of the cladding layer 18 of the first optical fiber 10 is preferably lower than or equal to the refractive index of the high-refractive-index resin 250. In particular, when the cladding layer 18 is composed of multiple layers, the refractive index of the innermost layer (main layer) of the cladding layer 18 that is in contact with the cladding layer 22 is preferably lower than or equal to the refractive index of the high-refractive-index resin 250.

[0038] Thus, the outer periphery of the exposed cladding portion 12A is covered by a high-refractive-index resin 250, making it easier for Raman scattered light that leaks into the low-refractive-index portion 14 of the first optical fiber 10, as described above, to leak from the low-refractive-index portion 14 into the high-refractive-index resin 250. Consequently, Raman scattered light is released to the outside from the high-refractive-index resin 250, effectively removing Raman scattered light from the cladding region 12 of the first optical fiber 10.

[0039] In this embodiment, a high refractive index resin 250 is used as the second light removal part. However, the high refractive index resin 250 can also be substituted. Similar to the second embodiment, the outer periphery of the cladding exposed portion 12A of the first optical fiber 10 is roughened over at least a portion of the long side direction, and the second light removal part is formed by the roughened surface formed on the outer periphery of the cladding exposed portion 12A.

[0040] Figure 7 This is a schematic cross-sectional view of the optical filter 301 according to the fourth embodiment of the present invention. In the third embodiment described above, the first light removal section for removing Raman scattered light incident on the cladding 22 of the second optical fiber 20 and the second light removal section for removing Raman scattered light leaking into the low refractive index section 14 of the first optical fiber 10 are made of different high refractive index resins 50 and 250. However, in this embodiment, as... Figure 7 As shown, the first light removal section and the second light removal section are composed of a single high refractive index resin 350 (third resin).

[0041] The high-refractive-index resin 350 is a resin having a refractive index higher than that of the cladding 22 of the second optical fiber 20 and higher than that of the low-refractive-index portion 14 of the first optical fiber 10. The high-refractive-index resin 350 covers the entire circumference (outer periphery) of the exposed cladding portion 22A of the second optical fiber 20 and the entire circumference (outer periphery) of the exposed cladding portion 12A of the first optical fiber 10, extending at least a portion along its long side. For example, the high-refractive-index resin 350 is formed of a material that is optically transparent relative to the wavelength of Raman scattered light leaking into the low-refractive-index portion 14. Silicone resin is an example of such a transparent material. Figure 7 In the example shown, the high-refractive-index resin 350 covers the end of the cladding layer 28 of the second optical fiber 20, the entire length of the cladding exposed portion 22A, the entire length of the cladding exposed portion 12A of the first optical fiber 10, and the end of the cladding layer 18. Thus, by using a single high-refractive-index resin 350 to construct both the first and second light removal sections, Raman scattered light can be effectively removed with a smaller number of components. Furthermore, as in this embodiment, by using the high-refractive-index resin 350 to cover the entire length of the cladding exposed portion 22A of the second optical fiber 20 and the entire length of the cladding exposed portion 12A of the first optical fiber 10, the total amount of Raman scattered light removed by the high-refractive-index resin 350 (the first and second light removal sections) can be increased.

[0042] In this case, it is assumed that the amount of Raman scattered light propagating in the cladding 22 of the second optical fiber 20 is greater than the amount of Raman scattered light leaking into the low-refractive-index portion 14 of the first optical fiber 10. Therefore, in order to more effectively remove the Raman scattered light, such as Figure 7As shown, preferably, the length L2 of the cladding 22 covered by the high refractive index resin 350 along the long side direction of the second optical fiber 20 is longer than the length L1 of the exposed portion 12A (low refractive index portion 14) of the cladding covered by the high refractive index resin 350 along the long side direction of the first optical fiber 10.

[0043] Figure 8 This is a schematic cross-sectional view illustrating an embodiment of the optical filter system 401 of the present invention. Figure 8 As shown, the optical filter system 401 in this embodiment includes two optical filters 301 of the fourth embodiment, which are connected in series. That is, the optical filter system 401 includes a first optical processing unit 301A composed of the optical filters 301 of the fourth embodiment and a second optical processing unit 301B composed of the optical filters 301 of the fourth embodiment.

[0044] The core 21 of the second optical fiber 20 of the first optical processing unit 301A is optically coupled to the core region 11 of the first optical fiber 10 of the second optical processing unit 301B, and the cladding 22 of the second optical fiber 20 of the first optical processing unit 301A is optically coupled to the plurality of high refractive index portions 13 of the first optical fiber 10 of the second optical processing unit 301B. Compared with the optical filter 301 of the fourth embodiment, the optical filter system 401 with this structure can remove more Raman scattered light. Similarly, multiple optical filters 1, 101, and 201 from the first to third embodiments can be connected in series to form an optical filter system, or multiple optical filters connected in series can be combined to form an optical filter system.

[0045] In order to remove more Raman scattered light from the core region 11 of the first optical fiber 10 to the high refractive index section 13 using the aforementioned light removal section, at least a portion of the first optical fiber 10 can be bent into an arc or circle shape upstream of the fixing resin 32. The bending diameter of the first optical fiber 10 in this case is, for example, 100 mm.

[0046] Here, it is argued that if the length of the first optical fiber 10 (photonic bandgap fiber) along its long side is short, Raman scattered light cannot sufficiently leak from the core region 11 to the high refractive index portion 13, and the Raman scattered light cannot be effectively removed in the aforementioned first light removal portion and second light removal portion. Based on this viewpoint, the inventors investigated, in the structure of the first embodiment, the length L along the long side of the first optical fiber 10 located on the upstream side, opposite to the direction of Raman scattered light propagation relative to the high refractive index resin 50 (first light removal portion). P How does the amount of Raman scattered light measured on the downstream side change when the parameters change?

[0047] Figure 9It is a graph representing the result. In Figure 9 In the diagram, the horizontal axis represents the length L along the long side of the first optical fiber 10 (photonic bandgap fiber) located upstream of the high-refractive-index resin 50. P (Reference Figure 2 The vertical axis represents the amount of Raman scattered light measured by a spectrometer located downstream. This amount of Raman scattered light is expressed as the ratio of the amounts of Raman scattered light measured downstream when the first fiber 10 is composed of the same double-clad fiber as the second fiber 20, and the second fiber 20 does not have the high-refractive-index resin 50. Figure 9 It can be seen that the length L of the first optical fiber 10 located upstream of the high refractive index resin 50 is... P In cases shorter than 1m, Raman scattered light is not sufficiently removed (Raman scattered light does not sufficiently leak from the core region 11 to the high refractive index portion 13). Therefore, the length L of the first optical fiber 10 located upstream of the high refractive index resin 50... P Preferably, it is 1m or longer. For the same reason, in Figure 6 In the structure shown, the length L' of the first optical fiber 10 along its long side is located on the opposite side (upstream) of the direction of Raman scattering light propagation relative to the high refractive index resin 250 (second light removal section). P Preferably, it is 1m or longer.

[0048] Figure 10 This is a block diagram schematically illustrating a laser device 501 according to an embodiment of the present invention. The laser device 501 includes: a first fiber amplifier 510, which serves as a laser source for generating laser light; an optical filter 301 described in the fourth embodiment above; a second fiber amplifier 530, which amplifies the laser light generated by the first fiber amplifier 510; and a laser emission section 540, which emits the laser light amplified by the second fiber amplifier 530. Hereinafter, an example using the optical filter 301 of the fourth embodiment is described, but optical filters of other embodiments can certainly be used. Hereinafter, the direction in which the laser light propagates from the first fiber amplifier 510 toward the laser emission section 540 will be referred to as the "downstream side," and the opposite direction will be referred to as the "upstream side."

[0049] The first fiber amplifier 510 is configured as a fiber laser and includes: an optical resonator 511; a plurality of excitation sources 512A that introduce excitation light into the optical resonator 511 from the upstream side; an optical combiner 513A connected to the excitation sources 512A; a plurality of excitation sources 512B that introduce excitation light into the optical resonator 511 from the downstream side; and an optical combiner 513B connected to the excitation sources 512B. The optical resonator 511 includes: an amplifying fiber 514 having a core with rare earth ions such as ytterbium (Yb), erbium (Er), thulium (Tm), and neodymium (Nd); a high-reflectivity section 515 that reflects light in a specified wavelength band (e.g., 1060 nm to 1100 nm) with high reflectivity; and a low-reflectivity section 516 that reflects light in the same wavelength band with a lower reflectivity than the high-reflectivity section 515. For example, the amplification fiber 514 is composed of a double-clad fiber having an inner cladding formed around the fiber core and an outer cladding formed around the inner cladding.

[0050] As excitation sources 512A and 512B, high-output multimode semiconductor lasers (LDs) with a wavelength of 915 nm can be used, for example. Optical combiner 513A couples the excitation light output from excitation source 512A into the inner cladding of amplifying fiber 514, and optical combiner 513B couples the excitation light output from excitation source 512B into the inner cladding of amplifying fiber 514. Thus, the excitation light propagates within the inner cladding of amplifying fiber 514.

[0051] The high-reflectivity section 515 is connected to the amplification fiber 514 and the optical combiner 513A, while the low-reflectivity section 516 is connected to the amplification fiber 514 and the optical combiner 513B. The high-reflectivity section 515 and the low-reflectivity section 516 are, for example, constructed using a fiber Bragg grating (FBG) formed by periodically changing the refractive index of the fiber along the direction of light propagation, and a reflector. Figure 10 In the example shown, the high-reflectivity section 515 and the low-reflectivity section 516 are constructed from fiber Bragg gratings. Using such a high-reflectivity section 515, amplifying fiber 514, and low-reflectivity section 516, an optical resonator 511 is constructed that amplifies light of a specific wavelength band back and forth between the high-reflectivity section 515 and the low-reflectivity section 516 to generate laser oscillation.

[0052] The transmission fiber 518 extends from the optical combiner 513B, and the optical filter 301 is fused to the transmission fiber 518 via the fusion splice 519. The core of the transmission fiber 518 is coupled to the core region 11 of the first fiber 10 of the optical filter 301.

[0053] The second fiber amplifier 530 is configured as a fiber laser, comprising: an amplification fiber 531; multiple excitation sources 532 that generate excitation light; an optical combiner 533 connected to the excitation sources 532; and a transmission fiber 534 extending from the optical combiner 533 to the laser emission section 540. The amplification fiber 531 is composed of a double-clad fiber, which has: a core containing rare-earth ions such as ytterbium (Yb), erbium (Er), thulium (Tm), and neodymium (Nd); an inner cladding formed around the core; and an outer cladding formed around the inner cladding. The refractive index of the inner cladding is lower than that of the core, and the core serves as an optical waveguide for the propagation of signal light. Similarly, the refractive index of the outer cladding is lower than that of the inner cladding, and both the inner cladding and the core serve as optical waveguides for the propagation of excitation light.

[0054] The optical filter 301 is fused to the amplifying optical fiber 531 via the fusion splice 535. The core of the amplifying optical fiber 531 is coupled to the core 21 of the second optical fiber 20 of the optical filter 301.

[0055] In this laser device 501 with such a structure, signal light is generated in a first fiber amplifier 510, which serves as the master oscillator (MO). Specifically, excitation light from excitation source 512A, introduced into optical resonator 511 via optical combiner 513A, and excitation light from excitation source 512B, introduced into optical resonator 511 via optical combiner 513B, propagate within the inner cladding and core of the amplifying fiber 514. This excitation light is absorbed by rare-earth element ions added to the fiber core as it passes through the core, and these rare-earth element ions are excited to generate spontaneous emission light. This spontaneous emission light is repeatedly reflected between a high-reflectivity section 515 and a low-reflectivity section 516, amplifying light of a specific wavelength (e.g., 1070 nm) to generate laser oscillation. The laser amplified by the optical resonator 511 propagates within the core of the amplifying fiber 514, with a portion passing through the low-reflectivity section 516. The laser light passing through the low-reflection section 516 propagates in the core of the transmission fiber 518 and is introduced into the second fiber amplifier 530, which serves as a PA (Power Amplifier), through the optical filter 301.

[0056] In the second fiber amplifier 530, the signal light from the first fiber amplifier 510 propagates inside the core of the amplifying fiber 531, while the excitation light from the excitation source 532 propagates inside the inner cladding and core of the amplifying fiber 531. As the excitation light propagates within the core, rare-earth element ions added to the core absorb the excitation light and are excited. The signal light propagating within the core is then amplified by stimulated emission. The amplified signal light is output from the laser emission unit 540 via the transmission fiber 534.

[0057] The Raman scattered light generated in the first fiber amplifier 510 is removed by the first light removal unit (or both a first light removal unit and a second light removal unit if a second light removal unit is provided) when passing through the optical filter 301. Therefore, damage to the optical components in the laser device 501 due to Raman scattered light can be suppressed.

[0058] exist Figure 10 In the example shown, in the first fiber amplifier 510, excitation sources 512A and 512B and optical combiners 513A and 513B are provided on both the high-reflectivity section 515 side and the low-reflectivity section 516 side, making it a bidirectional excitation type fiber laser. However, it is also possible to provide an excitation source and an optical combiner only on either the high-reflectivity section 515 side or the low-reflectivity section 516 side. Furthermore, in the second fiber amplifier 530, an excitation source 532 is provided only on the downstream side of the amplification fiber 531. However, it is also possible to provide an excitation source on the upstream side of the amplification fiber 531, or to provide excitation sources on both the upstream and downstream sides of the amplification fiber 531.

[0059] In addition, Figure 10 In the example shown, an optical filter 301 is connected between the first fiber amplifier 510 and the second fiber amplifier 530, but as Figure 11 As shown, besides such an optical filter 301, an optical filter 301 can also be connected between the second fiber amplifier 530 and the laser emission section 540. Figure 11 In the example shown, the optical filter 301 disposed between the second fiber amplifier 530 and the laser emitting unit 540 is fused to the transmission fiber 534 via fusion splice connections 551 and 552. Thus, when the optical filter 301 is connected between the second fiber amplifier 530 and the laser emitting unit 540, the optical filter 301 between the first fiber amplifier 510 and the second fiber amplifier 530 can be omitted. Furthermore, the optical filter connected between the second fiber amplifier 530 and the laser emitting unit 540 is not limited to the optical filter 301 of the fourth embodiment, but can also be an optical fiber of other embodiments.

[0060] Alternatively, a configuration including [a specific component] can be configured between the first fiber amplifier 510 and the second fiber amplifier 530. Figure 8 The optical filter system with multiple optical filters shown can also be configured between the second fiber amplifier 530 and the laser emission unit 540, including... Figure 8 An optical filter system with multiple optical filters as shown. In addition, in any optical filter, in order to effectively remove Raman scattered light, it is preferable that the length of the first optical fiber 10 located upstream of the first light removal section (or the second light removal section if a second light removal section is provided) along its long side is 1 m or more.

[0061] As described above, the present invention includes the following methods.

[0062] Method 1 of the present invention is an optical filter. The first optical fiber is composed of a photonic bandgap fiber, which includes a core region and a plurality of high refractive index portions having a higher refractive index than the core region, which are periodically arranged around the core region to suppress the propagation of Raman scattered light in the core region. The second optical fiber, which is connected to the first optical fiber, includes: The fiber core, which is optically coupled to the aforementioned core region of the first optical fiber; and The cladding, having a refractive index lower than that of the fiber core, covers the outer periphery of the fiber core and is optically coupled to the plurality of high-refractive-index portions of the first optical fiber. A first light removal section removes Raman scattered light incident on the cladding of the second optical fiber through the plurality of high-refractive-index sections of the first optical fiber; and The optical fiber receiving section receives the first optical fiber and the second optical fiber and protects the connection between the first optical fiber and the second optical fiber.

[0063] In the optical filter of the present invention, Method 2 is based on Method 1. The diameter of the core of the second optical fiber is less than or equal to the diameter of the smallest circle that connects to the innermost high-refractive-index portion among the plurality of high-refractive-index portions of the first optical fiber.

[0064] In the optical filter of the present invention, embodiment 3 is based on embodiment 1 or 2 described above. The first light removal section is made of resin, which covers at least a portion of the long side of the second optical fiber and the outer periphery of the cladding of the second optical fiber, and has a refractive index higher than or equal to that of the cladding.

[0065] In the optical filter of the present invention, aspect 4 is an example of aspect 1 or 2 described above. The first light removal section is composed of a rough surface, which extends over at least a portion of the long side direction of the second optical fiber and is formed on the outer periphery of the cladding of the second optical fiber.

[0066] In embodiment 5 of the present invention, any one of the optical filters described in embodiments 1-4 is used. The photonic bandgap fiber located on the opposite side of the direction of Raman scattering light propagation relative to the first light removal section has a length of 1m or more along its long side.

[0067] In embodiment 6 of the present invention, in any one of the optical filters described in embodiments 1-5, The first optical fiber includes a low-refractive-index portion, which has a lower refractive index than the plurality of high-refractive-index portions, and covers the outer side of the plurality of high-refractive-index portions. The aforementioned optical filter further includes a second light removal section, which removes the Raman scattered light that leaks into the low-refractive-index portion of the first optical fiber.

[0068] In the optical filter of the present invention, embodiment 7 is based on embodiment 6 described above. The second light removal section is made of a second resin, which extends over at least a portion of the long side of the first optical fiber and covers the outer periphery of the low-refractive-index section of the first optical fiber, and has a refractive index higher than that of the low-refractive-index section.

[0069] In the optical filter of the present invention, embodiment 8 is based on embodiment 7 described above. The first light removal section and the second light removal section are both made of a single third resin. The single third resin covers at least a portion of the long side direction of the second optical fiber and at least a portion of the long side direction of the first optical fiber, covering the outer periphery of the cladding of the second optical fiber and the outer periphery of the low refractive index portion of the first optical fiber, and has a refractive index that is higher than or equal to the refractive index of the low refractive index portion and the refractive index of the cladding.

[0070] In the optical filter of the present invention, aspect 9 is based on aspect 8 described above. The length of the third resin covering the cladding along the long side of the second optical fiber is longer than the length of the third resin covering the low-refractive-index portion along the long side of the first optical fiber.

[0071] In the optical filter of the present invention, embodiment 10 is based on embodiment 6 described above. The second light removal section is composed of a rough surface, which extends over at least a portion of the long side direction of the first optical fiber and is formed on the outer periphery of the low refractive index section of the first optical fiber.

[0072] In embodiment 11 of the present invention, in any one of the optical filters described in embodiments 6-10 above, The photonic bandgap fiber located on the opposite side of the direction of Raman scattering light propagation relative to the second light removal section has a length of 1m or more along its long side.

[0073] In embodiment 12 of the present invention, in any one of the optical filters described in embodiments 1-11, At least a portion of the first optical fiber is bent into an arc or a circle.

[0074] Embodiment 13 of the present invention is an optical filter system comprising: A first optical processing unit comprising any one of the optical filters described in methods 1-12 above; and A second optical processing unit comprising any one of the optical filters described in methods 1-12 above. The core of the second optical fiber of the first optical processing unit is optically coupled to the core region of the first optical fiber of the second optical processing unit, and the cladding of the second optical fiber of the first optical processing unit is optically coupled to the plurality of high refractive index portions of the first optical fiber of the second optical processing unit.

[0075] Embodiment 14 of the present invention is a laser device comprising: Any one of the optical filters described in methods 1-12 above; and An amplification fiber connected to the first optical fiber of the aforementioned optical filter.

[0076] The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and can of course be implemented in various different ways within the scope of its technical concept.

[0077] This application claims priority to Japanese Patent Application No. 2024-046385, filed on March 22, 2024. The entire contents of this application are incorporated herein by reference.

[0078] Industrial availability This invention applies to optical filters and laser devices equipped with such optical filters.

[0079] Explanation of reference numerals in the attached figures 1, 201, 301, 401 optical filters 10 First Fiber Optic 11 Core Area 12. Cladding region 13 High Refractive Index Section 14 Low Refractive Index Section 18. Covering layer 20 Second optical fiber 21-core fiber 22 cladding layers 28. Cover layer 30 Fiber Optic Storage Unit 31 Fiber Optic Storage Slot 50 High refractive index resin (first light removal section, first resin) 150 Rough surface (first light removal section) 250 High refractive index resin (second light removal section, second resin) 301A First Optical Processing Department 301B Second Optical Processing Unit 350 High Refractive Index Resin (First Light Removal Section, Second Light Removal Section, Third Resin) 501 Laser Device

Claims

1. An optical filter, comprising: The first optical fiber is composed of a photonic bandgap fiber, wherein the photonic bandgap fiber comprises: Core area; And multiple high refractive index sections, which have a higher refractive index than the core region, are periodically arranged around the core region to suppress the propagation of Raman scattered light in the core region; The second optical fiber, which is connected to the first optical fiber, includes: A fiber core, which is optically coupled to the core region of the first optical fiber; and A cladding having a lower refractive index than the fiber core covers the outer periphery of the fiber core and is optically coupled to the plurality of high refractive index portions of the first optical fiber; A first light removal section removes the Raman scattered light incident on the cladding of the second optical fiber through the plurality of high-refractive-index sections of the first optical fiber; and The optical fiber receiving section houses the first optical fiber and the second optical fiber, and protects the connection between the first optical fiber and the second optical fiber.

2. The optical filter according to claim 1, characterized in that, The diameter of the core of the second optical fiber is less than or equal to the diameter of the smallest circle that connects to the innermost high-refractive-index portion among the plurality of high-refractive-index portions of the first optical fiber.

3. The optical filter according to claim 1 or 2, characterized in that, The first light removal section is made of resin, which extends over at least a portion of the long side of the second optical fiber and covers the outer periphery of the cladding of the second optical fiber, and has a refractive index higher than that of the cladding.

4. The optical filter according to claim 1 or 2, characterized in that, The first light removal section is composed of a rough surface, which extends over at least a portion of the long side direction of the second optical fiber and is formed on the outer periphery of the cladding of the second optical fiber.

5. The optical filter according to any one of claims 1-4, characterized in that, The photonic bandgap fiber located on the opposite side of the direction of Raman scattering light propagation relative to the first light removal section has a length of 1m or more along its long side.

6. The optical filter according to any one of claims 1-5, characterized in that, The first optical fiber includes a low-refractive-index section having a lower refractive index than the plurality of high-refractive-index sections, and covers the outer side of the plurality of high-refractive-index sections. The optical filter further includes a second light removal section, which removes the Raman scattered light that leaks into the low-refractive-index section of the first optical fiber.

7. The optical filter according to claim 6, characterized in that, The second light removal section is made of a second resin, which extends over at least a portion of the long side of the first optical fiber and covers the outer periphery of the low refractive index section of the first optical fiber, having a refractive index higher than that of the low refractive index section.

8. The optical filter according to claim 7, characterized in that, The first light removal section and the second light removal section are made of a single third resin. The single third resin covers at least a portion of the long side direction of the second optical fiber and at least a portion of the long side direction of the first optical fiber, covering the outer periphery of the cladding of the second optical fiber and the outer periphery of the low refractive index portion of the first optical fiber, and has a refractive index that is higher than the refractive index of the low refractive index portion and higher than the refractive index of the cladding.

9. The optical filter according to claim 8, characterized in that, The length of the third resin covering the cladding along the long side of the second optical fiber is longer than the length of the third resin covering the low-refractive-index portion along the long side of the first optical fiber.

10. The optical filter according to claim 6, characterized in that, The second light removal section is composed of a rough surface, which extends over at least a portion of the long side direction of the first optical fiber and is formed on the outer periphery of the low refractive index section of the first optical fiber.

11. The optical filter according to any one of claims 6-10, characterized in that, The photonic bandgap fiber located on the opposite side of the direction of Raman scattering light propagation relative to the second light removal section has a length of 1m or more along its long side.

12. The optical filter according to any one of claims 1-11, characterized in that, At least a portion of the first optical fiber is bent into an arc or a circle.

13. An optical filter system, comprising: A first optical processing unit comprising the optical filter according to any one of claims 1-12; and A second optical processing unit comprising the optical filter according to any one of claims 1-12, The core of the second optical fiber of the first optical processing unit is optically coupled to the core region of the first optical fiber of the second optical processing unit, and the cladding of the second optical fiber of the first optical processing unit is optically coupled to the plurality of high refractive index portions of the first optical fiber of the second optical processing unit.

14. A laser device comprising: The optical filter according to any one of claims 1-12; and An amplification fiber connected to the first optical fiber of the optical filter.

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