Optical fibers and methods for manufacturing optical fibers

Abstract

To provide an optical fiber excellent in optical characteristic and durability, and a manufacturing method of the optical fiber.SOLUTION: An optical fiber 20 includes fluoride glass, phosphate glass or fluorophosphate glass. The optical fiber 20 comprises a protection film 24 formed directly or indirectly on a side face. The manufacturing method of the optical fiber includes a precursor supply step and a gas supply step. In the precursor supply step, precursor is supplied to a chamber in which the optical fiber is placed. In the gas supply step, followed by the precursor supply step, the precursor remaining in the chamber is purged and then gas containing one or more of oxygen, nitrogen, fluorine or sulphur is supplied.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to optical fibers and methods for manufacturing optical fibers. [Background technology]

[0002] Optical fibers are used to transmit light. Optical fibers are also used as fiber sensors to detect components or their concentrations in gases or liquids. Optical fibers with a coating layer on their outer surface are known to improve durability.

[0003] Patent Document 1 discloses a coated optical fiber in which a dense coating layer made of fine titanium oxide particles is provided on the outer circumference of a quartz glass wire, and a coating layer made of an organic material is provided on the outer circumference of the dense coating layer. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-003670 [Overview of the project] [Problems that the invention aims to solve]

[0005] The coated optical fiber disclosed in Reference 1 has a coating layer made of organic material on its outer circumference. However, forming a coating layer made of organic material on the end face would affect the optical properties due to thin-film interference, making it difficult to provide a coating layer made of organic material on the end face and thus difficult to obtain durability on the end face. For this reason, there is a need for an optical fiber that has a protective layer that does not affect the optical properties and has excellent durability. Optical fibers used as fiber sensors also need to have a protective layer that does not affect the optical properties and have excellent durability. Similarly, optical fibers used in laser oscillators or ASE (Amplified Spontaneous Emission) light sources also need to have a protective layer that does not affect the optical properties and have excellent durability.

[0006] This invention was made to solve the above-mentioned problems, and aims to provide optical fibers and a method for manufacturing optical fibers that have excellent optical properties and durability. [Means for solving the problem]

[0007] To achieve the objectives of the present invention, one aspect of the optical fiber according to the present invention is: Optical fibers containing fluoride glass, phosphate glass, or phthalate glass, A protective film formed directly or indirectly on the side surface of the optical fiber. and, An end cap attached to the end of the optical fiber, Equipped with 、 The protective film is formed on the optical fiber and the end cap. ru, It is characterized by the following:

[0008] To achieve the objectives of the present invention, one aspect of the method for manufacturing optical fibers according to the present invention is: A method for manufacturing the aforementioned optical fiber, A precursor supply process that supplies a precursor to a chamber containing optical fibers, Following the precursor supply step, after purging the precursor remaining in the chamber, a gas supply step of supplying a gas containing one or more of oxygen, nitrogen, fluorine, or sulfur; characterized by comprising.

Effects of the Invention

[0009] According to the present invention, it is possible to provide an optical fiber excellent in optical characteristics and durability and a method for manufacturing the optical fiber.

Brief Description of the Drawings

[0010] [Figure 1] It is a diagram showing a fiber sensor according to a first embodiment. [Figure 2] It is a cross-sectional view showing an optical fiber according to a first embodiment. [Figure 3] It is a cross-sectional view III-III of FIG. 1. [Figure 4] It is a cross-sectional view IV-IV of FIG. 3. [Figure 5] It is a diagram showing a manufacturing apparatus for an optical fiber according to a first embodiment. [Figure 6] It is a flowchart showing a method for manufacturing an optical fiber according to a first embodiment. [Figure 7] It is a diagram for explaining a method for manufacturing an optical fiber according to a first embodiment. [Figure 8] It is a diagram for explaining a method for manufacturing an optical fiber according to a first embodiment. [Figure 9] It is a diagram for explaining a method for manufacturing an optical fiber according to a first embodiment. [Figure 10] It is a diagram for explaining a method for manufacturing an optical fiber according to a first embodiment. [Figure 11] It is a diagram for explaining a method for manufacturing an optical fiber according to a first embodiment. [Figure 12] It is a diagram for explaining the principle of a fiber sensor according to a first embodiment. [Figure 13]This is a cross-sectional view showing an optical fiber according to a modified example of the first embodiment. [Figure 14] This figure shows a laser oscillator according to a second embodiment. [Figure 15] This is a cross-sectional view showing an optical fiber according to a second embodiment. [Figure 16] (A) and (B) are cross-sectional views showing optical fibers according to a modified example of the second embodiment. [Figure 17] This is a diagram showing an ASE light source according to the third embodiment. [Figure 18] This is a cross-sectional view showing an optical fiber according to a third embodiment. [Figure 19] This is a cross-sectional view showing an optical fiber according to a modified example. [Figure 20] (A) and (B) are SEM images showing optical fibers according to the examples. [Figure 21] (A) to (D) are fluorescent X-ray images of the side surface of the optical fiber according to the embodiment. [Figure 22] (A) to (D) are fluorescent X-ray images of the boundary region of the optical fiber according to the embodiment. [Figure 23] This diagram illustrates a method for evaluating the durability of an optical fiber according to an embodiment. [Figure 24] This figure shows the durability of optical fibers according to the examples and comparative examples. [Figure 25] Figures (A) to (D) show the hydrophilicity of optical fibers according to the examples and comparative examples. [Modes for carrying out the invention]

[0011] The optical fiber, fiber sensor, and method for manufacturing the optical fiber according to this embodiment will be described below with reference to the drawings.

[0012] (First Embodiment) The fiber sensor 100 according to the first embodiment, as shown in Figure 1, comprises a light source 10, an optical fiber 20, a detector 30, and lenses 41 and 42. The optical fiber 20 has a detection unit 21. As a result, when light L emitted from the light source 10 passes through the optical fiber 20, the light L is absorbed by the detection unit 21 by the detection target R. The fiber sensor 100 detects the spectrum of the light L that has passed through the optical fiber 20 using the detector 30, and detects the components or concentration of the detection target R that has come into contact with the detection unit 21. The detection target R is not particularly limited, but includes fluids including gases or liquids, such as various hydrocarbon molecules having resonance lines in the mid-infrared region, carbon dioxide, ammonia, and water vapor.

[0013] The light source 10 irradiates one end 20a of the optical fiber 20 with light L in the mid-infrared wavelength range of 2.5 μm to 3.8 μm, and it is preferable to use an ASE (Amplified Spontaneous Emission) light source. An ASE light source is amplified by stimulated emission of broadband spontaneously emitted light, such as rare-earth metal ions, which have absorbed excitation light irradiated from an excitation light source. It differs from a laser in that it does not have a wavelength selection mechanism using an optical resonator.

[0014] As shown in Figure 2, the optical fiber 20 has a detection unit 21, a core 22, a cladding 23, and a protective film 24, and is a fluoride-based optical fiber that transmits light L in the mid-infrared wavelength range of 2.5 μm to 3.8 μm. The length of the optical fiber 20 is not particularly limited and is selected according to the location where the detection unit 21 is placed.

[0015] As shown in Figures 3 and 4, the detection unit 21 is formed in the path of the optical fiber 20 and has a cladding 23 that is thinner than the cladding 23 in the area where the detection unit 21 is formed. In other words, the detection unit 21 is a portion of the cladding 23 in which a recess is formed, and is obtained by grinding the cladding 23 to a predetermined thickness T1. Specifically, a grinding rod having a cylindrical shape and an abrasive material coated on its surface is pressed against the location in the path of the optical fiber 20 where the detection unit 21 is to be formed while rotating it. As the grinding rod is moved in the optical axis direction of the optical fiber 20, the cladding 23 is ground to a predetermined thickness T1, forming a recess in the cladding 23, and an optical fiber 20 with the detection unit 21 formed is obtained.

[0016] The thickness T1 of the cladding 23 in the detection unit 21 is the thinnest part of the cladding 23 in the detection unit 21, and is preferably two-thirds or less of the thickness T2 of the cladding 23 other than the detection unit 21, more preferably three-fifths or less of the thickness T2, and even more preferably one-half or less of the thickness T2. Specifically, the thickness T1 of the cladding 23 in the detection unit 21 is preferably 20 μm or less, more preferably 15 μm or less. Also, the thickness T1 of the cladding 23 in the detection unit 21 is preferably greater than 0 times, more preferably one-third or more of the thickness T2, and even more preferably two-fifths or more of the thickness T2. Specifically, the thickness T1 of the cladding 23 in the detection unit 21 is preferably greater than 0 μm, and more preferably 5 μm or more. When the thickness T1 of the cladding 23 in the detection unit 21 is the above value, it is possible to measure the components or concentrations of the target R with high sensitivity. Furthermore, the lower limit of the length L1 of the detection unit 21 in the optical axis direction of the optical fiber 20 is not particularly limited, but is preferably 0.5 mm, more preferably 1 mm. Also, the upper limit of the length L1 of the detection unit 21 is not particularly limited, but is preferably 5 mm, more preferably 3 mm.

[0017] The core 22 is the portion through which the light L emitted from the light source 10 passes, and it is sufficient for it to transmit light in the wavelength range of 2.5 μm to 3.8 μm. For example, the core 22 may be a fluoride glass such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass, HBLAN (HfF4-BaF2-YF3-AlF3-NaF) glass, ZBYA (ZrF4-BaF2-YF3-AlF3) glass, AlF3 glass containing AlF3-BaF2-YF3-CaF2, AlF3-BaF2-YF3-ThF4, AlF3-BaF2-SrF2-CaF2-MgF2-YF3, InF3-ZnF2-BaF2-SrF2-LaF3, InF3-BaF2-YF3, or an InF3 glass containing InF3-ZnF2-BaF2-SrF2-BaF2, or a mixture thereof. Among these, the base material is preferably ZBLAN glass. Furthermore, the diameter D1 of the core 22 is, for example, 150 μm. In this case, the optical fiber 20 is a multimode fiber in which light L of mid-infrared wavelength is transmitted in multiple modes. A single-mode fiber may also be used as the optical fiber 20.

[0018] The cladding 23 has a lower refractive index than the core 22. The cladding 23 is made from the same material as the core 22. The diameter D2 of the cladding 23 is, for example, 200 μm. The thickness T2 of the cladding 23 other than the detection section 21 is, for example, 25 μm.

[0019] The protective film 24 shown in Figure 2 is formed continuously on the end faces of one end 20a and the other end 20b of the optical fiber 20, the side surface 20c, and the detection unit 21, thereby protecting the optical fiber 20. The protective film 24 contains metal oxides, metal nitrides, metal fluorides, or metal sulfides. Specifically, the protective film 24 contains metal oxides including Al2O3, TiO2, SiO2, HfO2, WO3, Gd2O3, Ta2O5, MgO, and ZrO2, metal nitrides including TiN, Si3N4, and AlN, or metal fluorides including MgF2, AlF3, and CaF2, and metal sulfides including ZnS and MoS2. The protective film 24 may have a film of one composition, a film of a mixture of two or more compositions, or films of different compositions may be laminated. For example, the protective film 24 may be an Al2O3 film with a TiO2 film laminated on top. In particular, Si3N4 is considered to have superior durability compared to oxide films. The lower limit of the thickness T3 of the protective film 24 is a single atomic layer. The thickness T3 of the protective film 24 is greater than 0 nm, preferably 10 nm or more, and more preferably 30 nm or more, so as to protect the optical fiber 20. The upper limit of the thickness T3 of the protective film 24 is not particularly limited, but for example, it is 10 μm. Furthermore, the thickness T3 of the protective film 24 is preferably 1 μm or less, and more preferably 500 nm or less, so as not to affect the optical properties. In addition, the thickness T4 of the protective film 24 formed on the end faces of one end 20a and the other end 20b of the optical fiber 20 is preferably the same as the thickness T3 of the protective film 24 formed on the side surface 20c. Furthermore, the thickness T5 of the protective film 24 formed on the detection unit 21 is preferably the same as the thickness T3 of the protective film 24 formed on the side surface 20c.

[0020] As shown in Figure 1, the detector 30 is positioned to detect light L irradiated from the other end 20b of the optical fiber 20, and detects the spectrum of light L in the mid-infrared region of 2.5 μm to 3.8 μm that has passed through the optical fiber 20. By analyzing the detected spectrum, the type of component of the target R that has come into contact with the detection unit 21 or the concentration of the target R can be detected.

[0021] Lens 41 focuses the light L emitted from the light source 10 onto the core 22 at one end 20a of the optical fiber 20. Lens 42 collimates or focuses the light L emitted from the other end 20b of the optical fiber 20 onto the sensor portion of the detector 30.

[0022] Next, a method for manufacturing the optical fiber 20 having the above configuration will be described.

[0023] As an example of a method for manufacturing optical fibers 20, the atomic layer deposition (ALD) method is described below. The ALD method is a thin-film deposition technique that utilizes a vacuum, and by taking advantage of the self-limiting properties of atoms, atoms can be deposited one layer at a time. In the ALD method, the ALD apparatus 200 shown in Figure 5 is used.

[0024] As shown in Figure 5, the ALD apparatus 200 includes a chamber 210, a holder 220, a heating device 230, a gas inlet 240, a first container 250, a second container 260, and a vacuum pump 270. With this configuration, the ALD apparatus 200 can deposit a protective film 24 on the optical fiber 20 using the ALD method.

[0025] The chamber 210 forms a sealed space that houses the holder 220 for holding the optical fiber 20, etc.

[0026] The holder 220 holds the optical fiber 20 and is located inside the chamber 210.

[0027] The heating device 230 heats the optical fiber 20 held in the holder 220 to a temperature of 30°C to 500°C, preferably 50°C to 100°C. The heating device 230 may be a resistance heating device or a lamp heating device.

[0028] The gas inlet 240 is an inlet for supplying a precursor and a gas containing one or more of oxygen, nitrogen, or fluorine. The gas inlet 240 also supplies a carrier gas as needed.

[0029] The first container 250 is a container for housing the precursor and is connected to the gas inlet 240 via a first valve 251. The precursor is preferably a compound containing at least one of Al, Ti, Si, Mg, Ca, Zr, Zn, Mo, Hf, W, Gd, and Ta, and more preferably a metal chloride or organometallic compound containing at least one of Al, Ti, Si, Mg, Ca, Zr, Zn, Mo, Hf, W, Gd, and Ta. When Al2O3 is formed as the protective film 24, the first container 250 contains, for example, TMA (TriMethylAluminium) as the precursor. Also, when a TiO2 film is formed, the first container 250 contains a Ti-containing compound such as TiCl4, and when a Si3N4 film is formed, it contains a Si-containing compound such as SiCl4.

[0030] The second container 260 is a container for holding a gas containing one or more of oxygen, nitrogen, or fluorine, and is connected to the gas inlet 240 via a second valve 261. When an oxide film such as an Al2O3 film or a TiO2 film is formed as the protective film 24, the second container 260 contains, for example, H2O or H2O2 as an oxygen-containing gas. The second container 260 also contains, for example, NH3 when a nitride film is formed, HF or TiF4 when a fluoride film is formed, or H2S when a sulfide film is formed.

[0031] The vacuum pump 270 is used to expel the air from the chamber 210.

[0032] Next, the manufacturing process for the optical fiber 20 having the above configuration will be described.

[0033] As shown in Figure 6, the manufacturing process for the optical fiber 20 includes a precursor supply step (step S101), a first purging step (step S102), a gas supply step (step S103), and a second purging step (step S104).

[0034] In the precursor supply process (step S101), the optical fiber 20 is fixed to the holder 220 of the ALD apparatus 200, and the precursor is supplied into the chamber 210. Specifically, the vacuum pump 270 is activated to raise the air pressure inside the chamber 210 to 2 × 10⁻¹⁰. 3 The pressure is reduced to below Pa. Next, the optical fiber 20 is heated to between 50°C and 100°C by the heating device 230. Then, as shown in Figure 7, the first valve 251 is opened and the precursor contained in the first container 250 is supplied to the chamber 210 from the gas inlet 240. The precursor contains at least one of Al, Ti, Si, Mg, Ca, Zr, Zn, Mo, Hf, W, Gd, and Ta. Preferably, the precursor is introduced together with the carrier gas CG. When depositing Al2O3, for example, TMA is supplied as the precursor. As a result, the precursor adheres (physical adsorption) to the surface of the optical fiber 20. The precursor is decomposed by heat, and one atom is first bonded, forming a nucleus. Next, as shown in Figure 8, the film grows laterally starting from the nucleus, and the precursor is deposited.

[0035] In the first purging step (step S102), excess precursors and other materials are purged. Specifically, when the first valve 251 is closed, the vacuum pump 270 exhausts any excess precursors and other materials remaining in the chamber 210. When TMA is used as the precursor, as shown in Figure 9, when the oxygen bonds on the surface of the optical fiber 20 are filled with Al, the excess TMA, CH4, and carrier gas CG are exhausted.

[0036] In the gas supply process (step S103), a gas containing one or more of oxygen, nitrogen, fluorine, or sulfur is supplied into the chamber 210. Specifically, the second valve 261 is opened, and the gas contained in the second container 260 is supplied to the chamber 210 from the gas inlet 240. When depositing Al2O3, H2O is used as the gas, as shown in Figure 10. When H2O is supplied into the chamber 210, the CH3 that was bonded to Al is replaced by O, as shown in Figure 11.

[0037] In the second purging step (step S104), excess gas is purged. Specifically, when the second valve 261 is closed, the vacuum pump 270 exhausts the excess gas remaining in the chamber 210. When TMA is used as the precursor and H2O as the gas, excess H2O and CH4 are exhausted.

[0038] Once the second purging step (step S104) is complete, it is determined whether or not to terminate the process (step S105). If the film has not been deposited to the desired thickness (step S105; NO), the process returns to step S101 and steps S101 to S105 are repeated. If the film has been deposited to the desired thickness (step S105; YES), the process is terminated. For example, when depositing Al2O3, approximately 1 Å (angstrom = 0.1 nm) can be deposited in one cycle, so to obtain a film thickness of 10 nm (100 Å), steps S101 to S105 are repeated 100 times. If the protective film 24 is a single atomic layer, steps S101 to S105 are completed in one cycle. Also, when stacking films of different compositions, one or both of the first container 250 and the second container 260 are replaced, and steps S101 to S105 are repeated. For example, when depositing a TiO2 film on an Al2O3 film, the first container 250 containing TMA is replaced with one containing a Ti-containing precursor, and steps S101 to S105 are repeated. When depositing a TiO2 film, for example, the precursor is TiCl4 and the gas is H2O.

[0039] Next, the principle by which the fiber sensor 100 having the above configuration detects the target R that has come into contact with the detection unit 21 will be explained.

[0040] When light L is shone from the light source 10 onto the core 22 of the optical fiber 20, as shown in Figure 12, because the refractive index of the core 22 is higher than that of the cladding 23, if the incident angle θ is greater than or equal to the critical angle, the light undergoes total internal reflection and is guided in the direction of the optical axis. At this time, it is thought that a portion of the light L penetrates the cladding 23 as evanescent light EL.

[0041] When the object to be detected R is in contact with the detection unit 21, it is thought that light L with a wavelength corresponding to the resonance line of the object to be detected R is absorbed by the detection unit 21 via evanescent light EL.

[0042] Next, the detector 30 shown in Figure 1 detects the spectrum of light L irradiated from the optical fiber 20. Since the spectrum is thought to be absorbed at wavelengths corresponding to the resonance lines of the target R, the type and concentration of the target R can be detected based on the absorbed wavelength and absorption intensity. Note that if the thickness T5 of the protective film 24 is set to a thickness that does not affect the optical properties, the type and concentration of the target R can be detected in the same way as when the protective film 24 is not provided.

[0043] As described above, the optical fiber 20 and the manufacturing method for the optical fiber 20 of this embodiment are made of fluoride glass, enabling low-loss transmission of mid-infrared light, which is not possible with general quartz optical fibers. It is possible to use light in the mid-infrared region, which is called the molecular fingerprint region, and it is possible to detect many molecules as the detection target R, such as various hydrocarbon molecules, carbon dioxide, ammonia, and water vapor, which have resonance lines in the mid-infrared region. On the other hand, optical fibers made of fluoride glass are known to have low water resistance and weather resistance, which is an obstacle to the practical application of fiber devices. Furthermore, because the surface of the fluoride glass and the resin coating have high water repellency, hydrophilic treatment of the detection unit 21 is required when the detection target R is a liquid. As a manufacturing method for the optical fiber 20 in this embodiment, a nanofilm formation technique using the ALD method, a type of vapor deposition method that deposits metal oxides and nitrides while controlling the thickness at the atomic layer level, is used. This makes it possible to form a dense amorphous film that is completely uniformly coated on all surfaces of a sample with a special shape like the optical fiber 20, without pinholes. The film thickness can be controlled on the order of angstroms (0.1 nm), and the protective film 24 can be formed on many optical fibers 20 at once. Therefore, the protective film 24 can be formed even on areas of the optical fiber 20 that are vulnerable to water, such as the coating interface and fusion surface, and can accommodate complex shapes such as plasmon sensors with attached metal nanoparticles. Furthermore, even with a film thickness of several tens of nm, which is sufficiently thin than the evanescent depth of the fiber propagation mode, a dense protective film 24 without pinholes is formed, so it has excellent water resistance and hydrophilicity without affecting optical sensing. In addition, the evanescent depth can be controlled by the protective film 24. Therefore, the optical fiber 20 and the method for manufacturing the optical fiber 20 in this embodiment are excellent in optical properties and durability because they include a protective film 24.

[0044] (Modified version of the first embodiment) The modified optical fiber 20 of the first embodiment has a detection unit 25 in which the core 22 is not covered by the cladding 23, as shown in Figure 13, whereas the optical fiber 20 of the first embodiment has a detection unit 21 in which a part of the cladding 23 is thinner than other parts. In this way, the core 22 is in direct contact with the target R to be detected, so depending on the type of target R to be detected, it is possible to detect the target R with high sensitivity. In the detection unit 25, although the core 22 is not covered by the cladding 23, the core 22 is protected by a protective film 24, resulting in excellent optical properties and durability.

[0045] Furthermore, in the above-described embodiment 1, an example was given in which the light source 10 irradiates light L in the mid-infrared wavelength range of 2.5 μm to 3.8 μm. The light source 10 can be any wavelength range that can be transmitted through the optical fiber 20, and may be ultraviolet light, visible light, or near-infrared light. In this case, the optical fiber 20 used is one that transmits light in the wavelength range of the light irradiated by the light source 10. In addition, in the above-described embodiment, an example was given in which an ASE light source was used for the light source 10, but the light source 10 can be any light source that can irradiate light L, and may be a light-emitting diode, halogen lamp, quantum cascade laser, solid-state laser, fiber laser, or supercontinuum light source, etc. It is possible to detect a target R having a resonance line corresponding to the wavelength of light L irradiated from the light source 10.

[0046] (Second Embodiment) The laser oscillator 110 according to the second embodiment is a mid-infrared fiber laser, as shown in Figure 14, comprising an excitation light source 11 that supplies excitation light, an optical fiber 50 to which excitation light is irradiated from the excitation light source 11, an end cap 51 placed at one end of the optical fiber 50, and a resonator 60 positioned to sandwich the optical fiber 50 and the end cap 51. The laser oscillator 110 oscillates a laser with a wavelength of 2.7 μm to 3.5 μm.

[0047] The excitation light source 11 is equipped with a semiconductor laser and is positioned to introduce excitation light into the optical fiber 50. The excitation light emitted from the excitation light source 11 is focused by the lens 43 and supplied to the optical fiber 50 after passing through the output mirror 62. For example, when Er:ZBLAN is used for the optical fiber 50, the excitation light source 11 emits laser light between 970 nm and 980 nm.

[0048] The optical fiber 50 includes a laser medium that amplifies light by absorbing excitation light irradiated from the excitation light source 11 and causing stimulated emission. The optical fiber 50 is, for example, an Er:ZBLAN fiber as shown in Figure 15, comprising a core 52 made of Er:ZBLAN that absorbs excitation light and causes stimulated emission of light, a cladding 53 with a lower refractive index than the core 52, and a protective film 54. Er:ZBLAN is ZBLAN doped with erbium (Er) and oscillates laser light in the range of 2.7 to 2.9 μm. The laser medium can be any material used in fiber lasers, such as Er:ZBLAN fiber, Er,Pr:ZBLAN fiber, Dy:ZBLAN fiber, or Ho:ZBLAN fiber.

[0049] The protective film 54 is formed continuously on the end face 50a and side surface 50b of the optical fiber 50 to protect the optical fiber 50. The composition and thickness T3 of the protective film 54 are the same as those of the protective film 24 in the first embodiment.

[0050] The end cap 51 functions as a deliquescence-suppressing part that protects one end of the optical fiber 50. The shape of the end cap 51 is not particularly limited as long as it can protect one end of the optical fiber 50. By placing the end cap 51 at one end of the optical fiber 50, long-term stabilization and high power output of the fiber laser are made possible. For example, when using an Er:ZBLAN fiber as the optical fiber 50, it is preferable to use CaF2 as the end cap 51. In this example, a protective film 54 is formed on the end face 50a and side surface 50b of the optical fiber 50, and the end cap 51 is attached to the end of the optical fiber 50 on which the protective film 54 is formed. Thus, the optical fiber 50 has a protective film 54 formed on the end face 50a and side surface 50b, and an end cap 51 placed at the end of the optical fiber 50 on which the protective film 54 is formed.

[0051] As shown in Figure 14, the resonator 60 comprises a reflector 61 that reflects stimulated light and an output mirror 62 that can extract a portion of the laser light to the outside. The reflector 61 and the output mirror 62 are positioned opposite each other with the optical fiber 50 in between. The reflector 61 is a concave mirror that reflects the stimulated light and excitation light emitted from the optical fiber 50. The output mirror 62 transmits a portion of the wavelength of light stimulated from the optical fiber 50 and reflects the rest. The output mirror 62, like the end cap 51, also functions as a deliquescence-suppressing part called an end cap that protects the other end of the optical fiber 50. The output mirror 62, like the end cap 51, is positioned at the other end of the optical fiber 50 after a protective film 54 is formed on the end face 50a and side surface 50b of the optical fiber 50. A reflector 44 is positioned between the excitation light source 11 and the output mirror 62 at a 45° angle with respect to the optical axis. The reflecting mirror 44 transmits light of the wavelength emitted from the excitation light source 11 and reflects light of the wavelength stimulated to be emitted from the optical fiber 50.

[0052] As described above, the optical fiber 50 of the second embodiment, like the first embodiment, is equipped with a protective film 54, and therefore exhibits excellent optical properties and durability, similar to the optical fiber 20 of the first embodiment. In particular, since the protective film 54 is formed on the end face 50a of the optical fiber 50, it can prevent temperature rise due to laser light irradiation at the end face 50a and prevent damage to the end face 50a. If the protective film 54 is not formed on the end face 50a, the fluorine groups on the end face 50a may be replaced with OH groups, and the OH groups will absorb laser light, causing a temperature rise and potentially damaging the end face 50a. Furthermore, the protective film 54 allows for control of optical properties by forming a dielectric multilayer mirror or an anti-reflective film. In addition, the end cap 51 further functions as a deliquescence suppression part that protects one end of the optical fiber 50, enabling long-term stabilization and high-power output of the fiber laser. When using Er:ZBLAN fiber as the optical fiber 50, and using CaF2 as the end cap 51, the affinity between ZBLAN glass and CaF2 crystals for thermal fusion is extremely high, and since CaF2 has high thermal conductivity, the thermal load can be significantly reduced.

[0053] (Modified version of the second embodiment) The optical fiber 50 according to Embodiment 2 has a protective film 54 formed on the end face 50a and the side surface 50b, and an end cap 51 placed at one end of the optical fiber 50 on which the protective film 54 is formed. In contrast, in the modified optical fiber 50 of the second embodiment, as shown in Figure 16(A), the end of the optical fiber 50 may be cut using a fiber cleaver or the like to expose the end face 50a, and the end cap 51 may be fused to it. In this case, the protective film 54 is not formed on the end face 50a, but the end face 50a is protected by the end cap 51. Furthermore, in the modified optical fiber 50 of the second embodiment, as shown in Figure 16(B), an end cap 51 is attached to one end of the optical fiber 50, and a protective film 54 is formed on the optical fiber 50 with the end cap 51 attached. The optical fiber 50 comprises an end cap 51 attached to one end of the optical fiber 50, and a protective film 54 formed on the optical fiber 50 and the end cap 51. Furthermore, the protective film 54 formed on the end face 51a of the end cap 51 is included in the protective film 54 indirectly formed on the end face 50a of the optical fiber 50. Even in this case, similarly, providing the optical fiber 50 with a protective film 54 results in superior optical properties and durability. In addition, an anti-reflective film may be formed on the end cap 51 to suppress Fresnel reflection on the surface of the end cap 50 and improve light transmittance.

[0054] (Third embodiment) The ASE light source 120 according to the third embodiment, as shown in Figure 17, comprises an excitation light source 12, an optical fiber 70, a transmission optical fiber 80, and a lens 45. The ASE light source 120 amplifies the excitation light emitted from the excitation light source 12 by spontaneous emission amplification and emits light in the wavelength range of 2.5 μm to 3.8 μm. The ASE light source 120 amplifies broadband spontaneous emission light such as rare earth metal ions by stimulated emission and differs from the laser oscillator 110 according to the second embodiment in that it does not have a wavelength selection mechanism using an optical resonator.

[0055] The excitation light source 12 is equipped with a semiconductor laser and is connected to one end 80a of the transmission optical fiber 80. The excitation light emitted from the excitation light source 12 passes through the transmission optical fiber 80 and is supplied to the optical fiber 70. The wavelength of the excitation light emitted by the excitation light source 12 is preferably between 790 nm and 1000 nm.

[0056] As shown in Figure 18, the optical fiber 70 has a core 72, a cladding 73, and a protective film 74, and absorbs excitation light irradiated from the excitation light source 12, causing stimulated emission to amplify and emit light. One end 70a of the optical fiber 70 is fusion spliced ​​to the other end 80b of the transmission optical fiber 80. An end cap 71 is attached to the other end 70b of the optical fiber 70 shown in Figure 17, which protects the other end 70b and functions as a deliquescence suppression part. It is preferable to use CaF2 as the end cap 71. The method of attaching the end cap 71 is the same as the end cap 51 in the second embodiment shown in Figure 15 or Figure 16. In this example, the optical fiber 70 is a double-cladded fiber, and the cladding 73 has a first cladding 75 arranged outside the core 72 and a second cladding 76 arranged outside the first cladding 75.

[0057] The core 72 includes a matrix, a first rare earth metal ion contained in the matrix, and a second rare earth metal ion that emits light by undergoing energy transfer from the first rare earth metal ion that absorbed excitation light. The first rare earth metal ion is preferably Nd 3+ Er 3+ , Tm 3+ , or Yb 3+ It contains at least one of the following. The second rare earth metal ion is preferably Dy 3+ This includes the core 72, Dy 3+ And, Er 3+In the case where the above is present, the wavelength of the excitation light emitted by the excitation light source 12 is preferably 970 nm to 980 nm. The base material does not need to absorb the excitation light or light in the wavelength range of 2.5 μm to 3.8 μm. For example, the base material may be fluoride glass such as ZBLAN glass, ZBYA glass, AlF3 glass, or InF3 glass, or a mixture thereof. The diameter D3 of the core 72 is, for example, 15 μm. In this case, the optical fiber 70 is a single-mode fiber in which light of mid-infrared wavelengths is transmitted in a single mode.

[0058] The first cladding 75 is the portion through which the excitation light emitted from the excitation light source 12 passes, and is made of an optical material having a lower refractive index than the core 72 and not absorbing light in the wavelength range of the excitation light emitted from the excitation light source 12. The first cladding 75 may be one glass or a mixture of two or more glasses selected from the group consisting of oxide glass, fluoride glass, tellurite glass, and chalcogenide glass. The second cladding 76 is made of an optical material having a lower refractive index than the first cladding 75. The diameter D4 of the first cladding 75 is, for example, 200 μm, and the diameter D5 of the second cladding 76 is, for example, 400 μm.

[0059] The transmission optical fiber 80 transmits excitation light emitted from the excitation light source 12 shown in Figure 17 to the optical fiber 70. The other end 80b of the transmission optical fiber 80 is fusion spliced ​​to one end 70a of the optical fiber 70. The transmission optical fiber 80 has a core 81 and a cladding 82 arranged outside the core 81. The core 81 is made of an optical material that does not absorb light in the wavelength range of the excitation light. The core 81 may be made of one glass or a mixture of two or more glasses selected from the group consisting of oxide glass containing quartz glass, fluoride glass, tellurite glass, and chalcogenide glass. The cladding 82 is made of an optical material having a lower refractive index than the core 81. The diameter D6 of the core 81 is, for example, 105 μm, and the diameter D7 of the cladding 82 is, for example, 300 μm. Because the diameter D6 of the core 81 of the transmission optical fiber 80 is larger than the diameter D3 of the core 72 of the optical fiber 70, the excitation light that has passed through the core 81 of the transmission optical fiber 80 is introduced into the first cladding 75 of the optical fiber 70.

[0060] The protective film 74 is formed continuously on the side surface 70c of the first cladding 75 and the side surface 80c of the transmission optical fiber, protecting the optical fiber 70 and the transmission optical fiber 80. The composition and thickness T3 of the protective film 74 are the same as those of the protective film 24 in the first embodiment. Preferably, the protective film 74 is formed by the ALD method after the other end 80b of the transmission optical fiber 80 and one end 70a of the optical fiber 70 are fusion spliced ​​together. In this way, the optical fiber 70 and the transmission optical fiber 80 are protected. In particular, the fusion splice, which is the connection point between the optical fiber 70 and the transmission optical fiber 80, is also protected.

[0061] The lens 45 shown in Figure 17 collimates or focuses the ASE light emitted from the other end 70b of the optical fiber 70.

[0062] As described above, the optical fiber 70 of the third embodiment, like the first and second embodiments, is equipped with a protective film 74, resulting in excellent optical properties and durability. In particular, by forming the protective film 74 even in areas with weak water resistance, such as the fusion splice between the other end 80b of the transmission optical fiber 80 and one end 70a of the optical fiber 70, excellent durability can be obtained.

[0063] (modified version) In the first to third embodiments described above, examples were given in which the optical fibers 20, 50, and 70 comprise cores 22, 52, 72, and 81, and cladding 23, 53, 73, and 82, respectively. However, the optical fibers 20, 50, and 70 may include fluoride glass and may be coreless optical fibers. Even if the optical fibers 20, 50, and 70 are coreless optical fibers, they have excellent optical properties and durability by including protective films 24, 54, and 74. Furthermore, instead of fluoride glass, the optical fibers 20, 50, and 70 may be phosphate glass containing P2O5-CaO-Na2O, P2O5-CaO-MgO-Na2O, P2O5-CaO-MgO-Na2O-Al2O3, or phthalate glass containing P2O5-AlF3-CaF2-SrF2-MgF2-BaF2. Although phosphate glass and phthalate glass are hygroscopic, even in this case, the presence of protective films 24, 54, and 74 provides excellent optical properties and durability.

[0064] Furthermore, in the first to third embodiments described above, the optical fibers 20, 50, and 70 do not have a covering portion. However, the modified optical fiber 90, in addition to the optical fibers 20, 50, and 70 of the first to third embodiments, further includes a covering portion 91 that protects the outer circumference 90c, as shown in Figure 19. The covering portion 91 is made of a resin including a synthetic resin or a photocurable resin. By further including a covering portion 91 that protects the core 92 and cladding 93 of the optical fiber 90, it is possible to prevent damage to the optical fiber 90 even if external force is applied to it. In this case, the protective film 94 is continuously formed on the end face 90a, side surface 90b of the exposed portion of the optical fiber 90, and the end face 91a, side surface 91b of the covering portion 91, thereby protecting the optical fiber 90. The composition and thickness T3 of the protective film 94 are the same as those of the protective film 24 in the first embodiment. In this case, when the protective film 94 is formed by the ALD method, it can be formed without gaps and with a uniform thickness on the end face 90a and side face 90b of the optical fiber 90, and on the end face 91a and side face 91b of the coating portion 91. The protective film 94 is also formed on areas with weak water resistance, such as the boundary between the side face 90b of the optical fiber 90 and the end face 91a of the coating portion 91. This makes it possible to protect the optical fiber 90, resulting in an optical fiber 90 with excellent optical properties and durability. Note that the protective film 94 formed on the side face 91b of the coating portion 91 is included in the protective film 94 indirectly formed on the side face 90b of the optical fiber 90. Even in this case, similarly, providing the optical fiber 90 with the protective film 94 results in excellent optical properties and durability.

[0065] Furthermore, while the ALD method was described as an example of a manufacturing method for optical fibers 20, 50, 70, and 90, optical fibers 20, 50, 70, and 90 only need to be equipped with protective films 24, 54, 74, and 94. The protective films 24, 54, 74, and 94 may be formed by CVD (Chemical Vapor Deposition), vapor deposition, or sputtering. Even if the protective films 24, 54, 74, and 94 are formed by these methods, optical fibers 20, 50, 70, and 90 with excellent optical properties and durability can be obtained. [Examples]

[0066] The effects of the optical fiber were demonstrated by the following examples. These examples show one embodiment of the present disclosure, and the present disclosure is not limited thereto.

[0067] In Example 1, using the ALD apparatus 200 shown in FIG. 5, an Al2O3 film with a thickness of 50 nm and a TiO2 film with a thickness of 50 nm were formed as protective films on a φ100 μm coreless fluoride (ZBLAN) optical fiber having a coating portion containing resin. The ALD apparatus 200 used was manufactured by Picosecond Co., Ltd. The coating portions at the ends and the middle of the fluoride optical fiber were removed so that the fluoride optical fiber was exposed.

[0068] First, the fluoride optical fiber was placed in the chamber 210, the vacuum pump 270 was operated, and the pressure in the chamber 210 was reduced to 2×10 3 Pa or less. Next, the optical fiber 20 was heated to 80° C. by the heating device 230. Next, a precursor containing TMA and a gas containing H2O were alternately supplied to the chamber 210, and an Al2O3 film was formed as the protective film 24 on the optical fiber. Details of the method for forming the Al2O3 film are described in the manufacturing process of the optical fiber 20 in the first embodiment. Thereafter, a precursor containing TiCl4 and a gas containing H2O were alternately supplied to form a TiO2 film on the Al2O3 film. Thereby, the fluoride optical fiber of Example 1 in which a 50 nm Al2O3 film and a 50 nm TiO2 film were laminated was obtained. Although it was heated to 80° C. during film formation, the coating portion did not deteriorate due to heat because it was lower than the heat resistance temperature of the resin in the coating portion.

[0069] Next, SEM (Scanning Electron Microscope) images and X-ray fluorescence images of the fluoride optical fiber of Example 1 were observed. SEM images of the side and boundary of the fluoride optical fiber of Example 1 are shown in Figures 20(A) and 20(B), respectively. X-ray fluorescence images of the side are shown in Figures 21(A) to 21(D), and X-ray fluorescence images of the boundary are shown in Figures 22(A) to 22(D). This confirmed that a 50 nm thick alumina (Al2O3) / 50 nm thick titania (TiO2) laminated film was deposited on the fluoride optical fiber of Example 1 by ALD (Aligned Laminated) method, and that the glass fiber portion, coating portion, and coating removal interface were all uniformly coated. Note that in Figures 22(A), 22(C), and 22(D), the amount of Al, O, and Ti decreased in the areas indicated by the arrows due to scratches during observation, and in Figure 22(B), the amount of F increased. This also indicates that an alumina / titania film was deposited.

[0070] Next, as shown in Figure 23, the intermediate portion 131 of the fluoride optical fiber 130 of Example 1 was immersed in water heated to 60°C (harsh conditions), and an accelerated degradation test was performed by tracking the change in optical loss over time using visible probe light to evaluate the optical properties and durability. The fluoride optical fiber 130 of Example 1 is a coreless optical fiber in which the coating portion 132 of the intermediate portion 131 has been removed for a length L2 = 30 mm, and a protective film of 50 nm Al2O3 and 50 nm TiO2 has been laminated over the entire fiber. For comparison, a coreless fluoride optical fiber of Comparative Example 1 was used, which also had the coating portion 132 of the intermediate portion removed for a length L2 = 30 mm, but without a protective film. The fluoride optical fiber of Comparative Example 1 has the same configuration except that it does not have a protective film. Durability was evaluated by irradiating one end with laser light of a wavelength of 638 nm from the light source 13, and measuring the intensity of the light emitted from the other end with a detector 31 including a photodiode.

[0071] As shown in Figure 24, the fluoride optical fiber 130 of Example 1 showed almost no degradation, with a transmittance of 1 up to 40 minutes. After 40 minutes, the transmittance gradually decreased up to 180 minutes. In Example 1, where alumina and titania were deposited, it was confirmed that the degradation rate was significantly reduced. In contrast, the fluoride optical fiber of Comparative Example 1 showed a decrease in transmittance immediately after measurement, and the transmittance became approximately 0 after 40 minutes. The reason for the decrease in transmittance is thought to be devitrification due to deliquescence. Therefore, it was found that the fluoride optical fiber 130 of Example 1 has excellent optical properties and durability.

[0072] Next, the hydrophilicity of fluoride optical fibers having a detection unit 21 was observed. Specifically, the hydrophilicity of the fluoride optical fiber of Example 2, which had a 50 nm Al2O3 film deposited on it, the fluoride optical fiber of Example 3, which had a 50 nm TiO2 film deposited on it, the fluoride optical fiber of Comparative Example 2, which had no film deposited on it, and the fluoride optical fiber of Comparative Example 3, which was resin-coated, was observed. The hydrophilicity was observed by dropping a water droplet onto the fiber and measuring the contact angle.

[0073] As shown in Figures 25(A) to (D), the fluoride optical fiber of Example 2 had an Al2O3 film deposited, resulting in a contact angle of approximately 30°. The fluoride optical fiber of Example 3 had a TiO2 film deposited, resulting in a contact angle of approximately 20°. In contrast, the fluoride optical fiber of Comparative Example 2 had no film deposited, resulting in a contact angle of approximately 50°. The fluoride optical fiber of Comparative Example 3 was resin-coated, resulting in a contact angle of 80° to 90°. This confirmed, from the water contact angle measurement, that although fluoride optical fibers are hydrophobic, depositing alumina or titania by the ALD method changes them to hydrophilic. Therefore, it was found that by depositing an Al2O3 film or a TiO2 film, as in the fluoride optical fibers of Examples 2 and 3, the detection unit 21 can be made hydrophilic, and thus fluoride optical fibers with a detection unit can be easily used in liquid sensors and the like.

[0074] As described above, the fluoride (ZBLAN) optical fiber in this embodiment had an Al2O3 / TiO2 laminated film deposited by the ALD method, and it was confirmed by fluorescence X-ray imaging that the glass fiber portion, coating portion, and coating removal interface were all uniformly coated. Furthermore, an accelerated degradation test was performed by tracking the change in optical loss over time using visible probe light while immersing the coreless ZBLAN optical fiber in heated water. As a result, it was confirmed that the degradation rate was significantly reduced in the samples with Al2O3 or TiO2 deposited. In addition, although fluoride optical fibers are hydrophobic, it was confirmed by measuring the water contact angle that they become hydrophilic by depositing Al2O3 or TiO2. From this embodiment, it was demonstrated that the fluoride optical fiber with the deposited film has a uniform hydrophilic coating across the entire fiber surface and possesses excellent optical properties and durability. It is thought that similar effects can be obtained by depositing Al2O3 or TiO2 on optical fibers containing phosphate glass or fluorine phosphate glass. Furthermore, it is believed that similar effects can be obtained with films made of components other than Al2O3 or TiO2.

[0075] This invention allows for various embodiments and modifications without departing from the broad spirit and scope of the invention. Furthermore, the embodiments described above are for illustrative purposes only and do not limit the scope of the invention. In other words, the scope of the invention is indicated not by the embodiments, but by the claims. Various modifications made within the scope of the claims and the equivalent scope of the meaning of the invention are considered to be within the scope of this invention. [Explanation of Symbols]

[0076] 10, 13...Light source 11, 12… Excitation light source 20, 50, 70, 90… Fiber optics 20a, 70a, 80a...One end 20b, 70b, 80b...Other end 20c, 50b, 70c, 80c, 90b, 91b...side 21, 25... Detection unit 22, 52, 72, 81, 92... cores 23, 53, 73, 82, 93... Clad 24, 54, 74, 94...protective film 30, 31… Detectors 41, 42, 43, 45… lenses 44...Reflector 50a, 90a, 91a...end face 51, 71… End caps 60...Resonator 61...Reflector 62…Output mirror 75... The first cladding 76... The Second Clad 80… Optical fiber for transmission 90c…outer circumference 91, 132... Covering part 100... Fiber sensor 110… Laser oscillator 120…ASE light source 130...Fluoride optical fiber 131...Middle section 200…ALD equipment 210... Chamber 220... Holder 230...Heating device 240...Gas inlet 250...First container 251...First valve 260... Second container 261...Second valve 270… Vacuum pump D1~D7…Diameter T1~T5...Thickness L1, L2... Length L…Light CG... Carrier gas EL... Evanescent light R...Detection target θ…Incidence angle

Claims

1. Optical fibers containing fluoride glass, phosphate glass, or phthalate glass, A protective film formed directly or indirectly on the side surface of the optical fiber, An end cap attached to the end of the optical fiber, Equipped with, The protective film is formed on the optical fiber and the end cap. Optical fiber characterized by the following features.

2. The protective film is formed directly or indirectly on the side and end faces of the optical fiber, and is formed continuously on the end face and side faces. The optical fiber according to feature 1.

3. The optical fiber path includes a detection unit formed therein. The protective film is formed on the detection unit. The optical fiber according to feature 1 or 2.

4. The thickness of the protective film is greater than 0 nm and less than or equal to 1 μm. The optical fiber according to any one of claims 1 to 3.

5. The protective film comprises a metal oxide, a metal nitride, a metal fluoride, or a metal sulfide. The optical fiber according to any one of claims 1 to 4.

6. A method for manufacturing optical fibers according to any one of claims 1 to 5, A precursor supply process that supplies a precursor to a chamber containing optical fibers, Following the precursor supply step, a gas supply step is performed in which the precursor remaining in the chamber is purged, and then a gas containing one or more of oxygen, nitrogen, fluorine, or sulfur is supplied. A method for manufacturing optical fibers, characterized by comprising the following features.

7. In the precursor supply step, a precursor containing at least one of Al, Ti, Si, Mg, Ca, Zr, Zn, Mo, Hf, W, Gd, and Ta is supplied. A method for producing fibers according to commodity 6.

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