Optical fiber light source

Abstract

To provide an optical fiber light source having high spectral wavelength flexibility and enabling incoherent continuous-wave output in a single transverse mode.SOLUTION: An optical fiber light source has: an optical fiber having a first end, a second end, and a tapered part positioned between the first and second ends, which is a single mode fiber; a wavelength conversion part; a light source for exciting the wavelength conversion part; and a support part. The first end outputs radiant light emitted from the excited wavelength conversion part. The tapered part includes: a constricted part; a first tapered region in which a diameter gradually decreases from the second end side toward the constricted part; and a second tapered region in which a diameter gradually increases from the constricted part toward the first end side. The constricted part has a diameter smaller than those of the first and second ends, and has a size of the wavelength or less of the radiant light. The wavelength conversion part is composed of liquid or gas and is disposed so as to surround at least an outer periphery of the constricted part of the tapered part. The light source simultaneously excites the outer peripheral portion surrounding the wavelength conversion part.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to fiber optic light sources. [Background technology]

[0002] Fiber-output light sources using optical fibers in the output section have been developed in various types due to their ease of routing and portability, and are widely used in industrial and research applications. However, light sources that output incoherent light typically use multimode fibers in the output section, resulting in light diffusion and poor transverse mode quality. Furthermore, methods that illuminate the optical fiber core itself, such as rare-earth doped fibers, extract only light at the dopant's emission wavelength, resulting in limited wavelength spectrum flexibility. For this reason, there is a demand for optical fiber light sources that can output incoherent light with high transverse mode quality and high wavelength spectrum flexibility. In this context, research into nano-optical fibers is progressing, as seen in Non-Patent Document 1, for example. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] NEW GLASS Vol.31 No.118 2016 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one aspect of the disclosure is to provide an optical fiber light source or an optical fiber structure that has a single transverse mode, a high degree of wavelength spectrum flexibility, and is capable of outputting incoherent continuous waves (CW). [Means for solving the problem]

[0005] In one aspect of the disclosure, the fiber optic light source comprises: an optical fiber that is a single mode fiber and has a first end that emits light, a second end that is located opposite to the first end, and a tapered portion that is located between the first end and the second end; a wavelength converting portion in contact with the tapered portion; a light source that excites the wavelength conversion unit; a support portion in contact with the wavelength converting portion; and the first end outputs the emitted light from the excited wavelength converting portion; the tapered portion includes a narrowed portion having a minimum diameter, a first tapered region in which the diameter decreases from the second end side toward the narrowed portion, and a second tapered region in which the diameter increases from the narrowed portion toward the first end side, The diameter of the constriction is smaller than the diameter of the first end and the diameter of the second end, and is equal to or smaller than the wavelength of the emitted light.

[0006] In one aspect of the disclosure, the optical fiber structure comprises: an optical fiber that is a single mode fiber and has a first end that emits light, a second end that is located opposite to the first end, and a tapered portion that is located between the first end and the second end; a wavelength converting portion in contact with the tapered portion; a support portion in contact with the wavelength converting portion; and the first end outputs the emitted light from the excited wavelength converting portion; the tapered portion includes a narrowed portion having a minimum diameter, a first tapered region in which the diameter decreases from the second end side toward the narrowed portion, and a second tapered region in which the diameter increases from the narrowed portion toward the first end side, The diameter of the constriction is smaller than the diameter of the first end and the diameter of the second end, and is equal to or smaller than the wavelength of the emitted light. [Effects of the Invention]

[0007] It is possible to provide an optical fiber light source or an optical fiber structure that has a single transverse mode, a high degree of wavelength spectrum flexibility, and is capable of CW incoherent output. [Brief explanation of the drawings]

[0008] [Figure 1] 1A and 1B are diagrams illustrating the principle of an optical fiber light source according to an embodiment. [Figure 2] FIG. 1 is a diagram illustrating a first configuration example of an optical fiber light source. [Figure 3] FIG. 10 is a diagram illustrating a second configuration example of an optical fiber light source. [Figure 4] 1A and 1B are diagrams illustrating a first example of an optical fiber structure including a wavelength converting portion and a supporting portion. [Figure 5] 10A and 10B are diagrams illustrating a second example of an optical fiber structure including a wavelength converting portion and a supporting portion. [Figure 6] 10A and 10B are diagrams illustrating a third example of an optical fiber structure including a wavelength converting portion and a supporting portion. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the embodiment, an optical fiber light source is provided that satisfies three conditions: "single transverse mode," "high wavelength spectrum flexibility," and "CW incoherent light source." 00 It is a Gaussian distribution type propagation mode in which the intensity distribution in the cross section of the light beam (cross section perpendicular to the optical axis) is high in the center and low in the periphery. Light in a single transverse mode has high focusing and straightness.

[0010] "High wavelength spectrum flexibility" refers to a configuration that can generate and output light of any desired wavelength, not just light of a single wavelength. A "CW incoherent light source" is a light source that continuously oscillates incoherent light. Incoherent light is light in which the phases and amplitudes of multiple waves fluctuate independently, making interference unlikely. In this respect, it differs from lasers that output coherent light with a consistent phase, but by realizing a "single transverse mode," it is possible to output incoherent light with the same focusing and straightness as laser light.

[0011] Incoherent light has a broad spectral distribution, like sunlight or LED light. In addition, because the phase and amplitude distributions fluctuate randomly, there is almost no wave interference. Superluminescent diodes and amplified spontaneous emission (ASE) light sources are incoherent light sources with high focusing or directivity, but the wavelength of the output light is fixed and the degree of freedom of the wavelength spectrum is low. In other words, a light source that satisfies all of the following requirements has not yet been realized: a single transverse mode, a high degree of wavelength spectrum freedom, and a CW incoherent light source.

[0012] In the embodiment, an optical fiber light source that satisfies the above three conditions is realized by incorporating light obtained by wavelength conversion into an optical fiber. A supercontinuum (SC) light source is a light source that utilizes the nonlinear optical effect of optical fibers. An SC light source is a pulsed light source that outputs strong coherent pulses with a consistent phase. The optical fiber light source of the embodiment is an incoherent light source that has the same linearity and focusing properties as laser light and a high degree of freedom in wavelength spectrum. The optical fiber light source of the embodiment, which has these characteristics, is highly useful and can be applied to spot illumination in microscopes and light sources for exciting fluorescent markers used in endoscopes.

[0013] FIG. 1 is a diagram illustrating the principle of an optical fiber light source 10 according to an embodiment. In the following embodiments, the same components are given the same reference numerals, and redundant explanations may be omitted. The optical fiber light source 10 includes an optical fiber 11 having a tapered portion 113, a wavelength conversion portion 15 in contact with the tapered portion 113, and a light source 20 for exciting the wavelength conversion portion 15. The excited wavelength conversion portion 15 emits radiated light L RAD is taken into the optical fiber 11 and output from the first end 111.

[0014] The optical fiber 11 is a single-mode fiber. More specifically, the desired radiation light L RADThe optical fiber 11 is an optical fiber that operates in a single mode for a wavelength of 100 μm. A tapered portion 113 is provided between a first end portion 111 of the optical fiber 11 and a second end portion 112 located opposite the first end portion. The optical fiber 11 can be made of a material such as glass, plastic, or single crystal. From the viewpoint of ease of manufacture, the optical fiber 11 is preferably a standard single-mode fiber with a cladding diameter of several hundred μm and a core diameter of several μm.

[0015] The tapered portion 113 includes a narrowed portion 113a having a minimum diameter, a first tapered region 113b whose diameter decreases from the second end 112 side toward the narrowed portion 113a, and a second tapered region 113c whose diameter increases from the narrowed portion 113a toward the first end 111. The diameter of the narrowed portion 113a is smaller than the diameters of the first end 111 and the second end 112, and the emitted light L RAD Here, the magnitude of the radiation L RAD The wavelength of the narrowed portion 113a refers to the wavelength of the light to be output. For example, if near-infrared light with a wavelength in the 1 μm band is to be output, the diameter of the narrowed portion 113a is set to about 500 nm. If white light is to be output, the diameter of the narrowed portion 113a is set to about 230 nm.

[0016] The tapered portion 113 can be obtained, for example, by heating and stretching a portion of a single-mode fiber to reduce the diameter to a value equal to or less than the target wavelength. At the narrowed portion 113a and its vicinity, the core 101 and cladding 102 of the optical fiber 11 are integrated, and the entire optical fiber 11 functions as the core. The narrowed portion 113a and the medium surrounding its vicinity function as the cladding. In this sense, it is preferable that the material of the optical fiber 11 has as high a refractive index as possible, and a refractive index of 1.6 or higher is particularly preferable.

[0017] In the narrowed portion 113a, which is narrowed to a diameter equal to or smaller than the wavelength, the propagation mode of light is distributed to the outside of the optical fiber 11 (i.e., the cladding), and therefore, the light emitted from the cladding propagates along the optical fiber 11 as part of the propagation mode. The wavelength converting portion 15, which is disposed in contact with the tapered portion 113, also functions as a cladding for the narrowed portion 113a, and therefore has a refractive index lower than that of the optical fiber 11.

[0018] Synchrotron radiation L RAD The wavelength conversion unit 15 is excited by the excitation light L PUMP The wavelength conversion unit 15 is irradiated with the excitation light L PUMP Since it is sufficient to irradiate with the excitation light L PUMP The light may be incident on the second end 112 of the optical fiber 11, or may be directly irradiated onto the wavelength converting portion 15 from the outside of the optical fiber 11.

[0019] The wavelength conversion unit 15 converts the excitation light L PUMP By irradiating the excitation light L PUMP and radiation L RAD As an example, the optical fiber 11 is made of a material that contains a fluorescent substance and has a lower refractive index than the optical fiber 11. By selecting the type of fluorescent substance and the wavelength of the excitation light that excites the fluorescent substance, the emitted light L RAD The wavelength can be designed to a desired wavelength. Phosphors, rare earth ions, quantum dots, etc. can be used as the fluorescent material. When wavelength converting section 15 contains a phosphor as the fluorescent material, the diameter of the phosphor is preferably about several μm to several tens of μm, and specifically, a diameter of 1 μm or more and 50 μm or less is preferable because this widens the options for usable phosphors.

[0020] Excitation light L PUMP The fluorescence emitted from the fluorescent material by irradiation with the light is incoherent light containing waves of various phases and amplitudes. This incoherent light is taken into the optical fiber 11 by the propagation mode of the optical fiber 11 that extends to the outside of the narrowed portion 113a, and is converted into emitted light L RAD More precisely, the emitted light L RADis mainly confined to the core 101, and a part of it penetrates into the cladding 102 and propagates through the optical fiber 11, and is emitted from the first end portion 111.

[0021] The light output from the first end portion 111 of the optical fiber 11, which is a single-mode fiber, is a single transverse-mode CW incoherent light with condensing properties. Despite being incoherent light, it propagates over a long distance with suppressed diffusion. In order to further enhance the condensing property of the output light, a collimating lens 19 may be arranged at the first end portion 111 of the optical fiber 11. When the collimating lens 19 is arranged, light can be irradiated onto a minute spot. Further, by using the collimating lens 19 as an achromatic lens, the light RAD included in the radiation light L can be made into uniform parallel light for lights of various wavelengths. Also, a wavelength filter that transmits only a specific wavelength component included in the radiation light L RAD may be arranged to output monochromatic light, or only a specific wavelength component may be cut to output a specific wavelength combination.

[0022] <The first configuration example> FIG. 2 is a schematic diagram of the optical fiber light source 10A of the first configuration example. In the first configuration example, a method of propagating the excitation light in the optical fiber 11 is adopted. The optical fiber light source 10A includes an optical fiber 11 having a tapered portion 113, a wavelength conversion portion 15 in contact with the tapered portion 113, a light source 20A that excites the wavelength conversion portion 15, and a support portion 17 in contact with the wavelength conversion portion 15. The light source 20A is, for example, a laser diode (LD) that injects the excitation light L PUMP into the second end portion 112 of the optical fiber 11. The optical fiber structure 110 is formed in the portion of the optical fiber light source 10A excluding the light source 20A.

[0023] The diameter D1 of the constricted portion 113a of the tapered portion 113 of the optical fiber 11 is smaller than the diameters D2 of the second end portion 112 and the first end portion 111 of the optical fiber 11 (D1 < D2), and is smaller than the wavelength of the radiation light L RAD The excitation light L incident from the second end portion 112 of the optical fiber 11 PUMPis distributed as evanescent light in the narrowed portion 113a and its vicinity in the wavelength converting portion 15. The wavelength converting portion 15 is excited by this evanescent light and emits light with a high degree of freedom in wavelength spectrum.

[0024] Excitation light L PUMP The light generated in the wavelength conversion unit 15 by irradiation with the radiation is CW incoherent light containing waves of various phases and amplitudes. This CW incoherent light is taken into the propagation mode of the optical fiber 11 at and near the narrowed portion 113a, and is converted into radiated light L RAD The radiation L propagates through the optical fiber 11 as RAD is emitted as light in a single transverse mode from the first end 111 of the optical fiber 11, which is a single mode fiber.

[0025] The configuration shown in Figure 2 realizes a CW incoherent light source with a single transverse mode and high degree of wavelength spectrum flexibility.

[0026] <Second configuration example> 3 is a schematic diagram of an optical fiber light source 10B according to a second example of the configuration. PUMP In this embodiment, instead of light being incident on the second end 112 of the optical fiber 11, a light source 20B provided outside the optical fiber 11 irradiates and excites the wavelength converting portion 15 from the outside. The optical fiber light source 10B includes the optical fiber 11 having a tapered portion 113, the wavelength converting portion 15 in contact with the tapered portion 113, the light source 20B that excites the wavelength converting portion 15, and a support portion 17 in contact with the wavelength converting portion 15. The light source 20B is, for example, a laser diode (LD) or a light emitting diode (LED) that is placed in a position where it can irradiate the wavelength converting portion 15 with light. The optical fiber structure 110 is made up of the portion of the optical fiber light source 10B excluding the light source 20B.

[0027] In the second configuration example, at least the radiation light L RADFrom the tapered portion 113 into which it is incorporated to the first end portion 111, it may be a single-mode fiber, but from the viewpoint of the method of manufacturing the tapered portion 113, it may be a single-mode fiber as a whole, similar to the first configuration example. The diameter D1 of the narrow portion 113a of the tapered portion 113 is smaller than the diameters D2 of the second end portion 112 and the first end portion 111 of the optical fiber 11 (D1 < D2), and the emission light L RAD is smaller than the wavelength of.

[0028] The wavelength conversion portion 15 in contact with the tapered portion 113 is directly irradiated by the excitation light L PUMP from the light source 20B. By the irradiation of the excitation light L PUMP , the wavelength conversion portion 15 emits light having a wavelength different from that of the excitation light L PUMP . The emitted light is CW incoherent light including waves of various phases and amplitudes. The wavelength of this CW incoherent light can be designed with a high degree of freedom by appropriately selecting the material used for the wavelength conversion portion 15.

[0029] In the configurations of FIGS. 2 and 3, the support portion 17 in contact with the wavelength conversion portion 15 is made of an epoxy resin, a silicone resin, rubber, etc., and supports the tapered portion 113 and the wavelength conversion portion 15. From the viewpoint of strength, it is preferable that the thickness of the support portion 17 is not less than the thickness of the wavelength conversion portion 15 and not more than twice the diameter D2 of the second end portion 112 and the first end portion 111 of the optical fiber 11. In the configuration of FIG. 3, it is preferable that the support portion 17 in contact with the wavelength conversion portion 15 transmits 70% or more, preferably 80% or more, more preferably 90% or more of the excitation light L PUMP from the light source 20B, but in the configuration of FIG. 2, it is not particularly limited and may not transmit light. Since the diameter D1 of the narrow portion 113a of the tapered portion 113 is very small, the strength is improved by supporting it with the support portion 17. Also, when manufacturing the optical fiber light sources 10A and 10B, movement of the optical fiber 11 is suppressed, and the manufacturing of the optical fiber light sources 10A and 10B becomes easy.

[0030] The CW incoherent light generated in the wavelength conversion portion 15 is taken into the propagation mode of the optical fiber 11 in the narrow portion 113a and its vicinity, and the emission light L RADThe light is emitted as such from the first end 111 of the optical fiber 11. The configuration of Fig. 3 also realizes a CW incoherent light source with a single transverse mode and a high degree of freedom in wavelength spectrum.

[0031] <Configuration example of optical fiber structure including wavelength conversion portion and support portion> 4 to 6 show a configuration example of an optical fiber structure 110A including a wavelength converting portion 15 and a supporting portion 17. The optical fiber structure 110A of FIG. 4 uses a solid wavelength converting portion 15A. The wavelength converting portion 15A is a wavelength converting film 151 formed on at least the outer periphery of the tapered portion 113 of the optical fiber 11. The wavelength converting film 151 can be formed by an appropriate method such as a coating method, a spray method, or a dip coating method. The supporting portion 17A is formed in contact with the wavelength converting film 151 and can be formed by an appropriate method such as a dipping method or ultraviolet curing method.

[0032] The wavelength conversion film 151 contains a fluorescent material. The type of fluorescent material contained in the wavelength conversion film 151 may be one type, or multiple types of fluorescent materials may be mixed. This allows the spectrum of the emitted light to be freely designed. By mixing a fluorescent material that emits fluorescence of a desired wavelength into a base material with a low refractive index such as acrylic resin or epoxy resin to form the wavelength conversion film 151, the light emission characteristics of the wavelength conversion film 151 can be adjusted. The base material is made of a material that can be used to adjust the light emission characteristics of the wavelength conversion film 151. PUMP and synchrotron radiation L RAD It is transparent to the excitation light L PUMP or synchrotron radiation L RAD It is preferable that 70% or more, preferably 80% or more, and more preferably 90% or more of the total light transmitted through the optical fiber is transmitted through the optical fiber.

[0033] The wavelength conversion film 151 is preferably disposed so as to cover the tapered portion 113, but it is not necessarily required to coat the entire circumference of the tapered portion 113, and the coating area is not limited as long as it is in contact with the narrowed portion 113a and its vicinity. In addition, the thickness of the wavelength conversion film 151 is preferably several tens of μm to several hundreds of μm, as this facilitates manufacturing.

[0034] The excitation light may be incident from the second end 112 of the optical fiber 11 as shown in Fig. 2, or may be irradiated directly onto the wavelength conversion film 151 from outside the tapered portion 113 as shown in Fig. 3. The configuration of the wavelength conversion unit in Fig. 4 is advantageous in terms of portability and assembly because the wavelength conversion unit 15A is fixed to the single-mode optical fiber 11. Furthermore, by providing a support 17A in contact with the wavelength conversion unit 15A, the tapered portion 113 of the optical fiber 11 and the wavelength conversion unit 15A are stably held.

[0035] In FIG. 5, an optical fiber structure 110B is used, which includes a liquid wavelength converting portion 15B and a supporting portion 17B. The wavelength converting portion 15B is, for example, a wavelength converting liquid 152 contained in a container 5. The wavelength converting liquid 152 is a liquid obtained by mixing a fluorescent substance with a solvent such as distilled water or a fluorine-based inert liquid. The supporting portion 17B is preferably made of a material with a refractive index lower than that of the optical fiber 11, since this can reduce the influence on the propagation mode. Furthermore, the supporting portion 17B is preferably made of a material with a refractive index similar to that of the wavelength converting liquid 152, since this can further reduce the influence on the propagation mode. For example, the supporting portion 17B is a plate-shaped member made of a low-refractive acrylic resin, epoxy resin, or the like. From the viewpoints of compactness and strength, it is preferable that the width and height are 3 cm to 7 cm, and the thickness is 1 mm to 10 mm, but this is not limiting. The first tapered region 113b, the narrowed portion 113a, and the second tapered region 113c are fixed to the support portion 17B with a fixing material 154 such as epoxy resin whose refractive index is close to that of the wavelength converting liquid 152. The optical fiber 11 is immersed in the wavelength converting liquid 152 while being fixed to the support portion 17B. The entire optical fiber 11 does not need to be immersed in the wavelength converting liquid 152, as long as at least the tapered portion 113 including the narrowed portion 113a is immersed in the wavelength converting liquid 152. In the example of Fig. 5, the extended tapered portion 113 is folded back in a U-shape and immersed in the wavelength converting liquid 152, but the tapered portion 113 may be placed in a sealed container filled with the wavelength converting liquid 152 without being folded back. Alternatively, the tapered portion 113 may be made to meander in the sealed container filled with the wavelength converting liquid 152. By appropriately determining the arrangement pattern of the tapered portion 113 on the support portion 17B, at least the tapered portion 113 can be immersed in the wavelength converting liquid 152.

[0036] The excitation light may be incident on the second end 112 of the optical fiber 11 as shown in FIG. 2, or may be irradiated onto the wavelength conversion liquid 152 from outside the container 5. When the wavelength conversion liquid 152 is excited from outside the container 5, the container 5 is formed of a material that is transparent to the excitation light. The configuration of the wavelength conversion unit in FIG. 5 makes it easy to replace the wavelength conversion liquid 152 and to output light of the desired wavelength. When the container 5 is a sealed container, it is easy to carry and assemble. By providing the support part 17B in contact with the wavelength conversion part 15B, the tapered part 113 of the optical fiber 11 can be stably held within the wavelength conversion part 15B, facilitating the manufacture of the optical fiber structure 110B.

[0037] FIG. 6 illustrates an optical fiber structure 110C including a gaseous wavelength converting portion 15C and a supporting portion 17C. The wavelength converting portion 15C is, for example, a wavelength converting gas 153 sealed in a sealed container 6. The wavelength converting gas 153 contains alkali metal gases such as rubidium and cesium, molecules such as iodine, and ions of alkaline earth metals, which act as fluorescent substances. The supporting portion 17C is preferably made of a material with a refractive index lower than that of the optical fiber 11, since this can minimize the influence on the propagation mode. For example, it is a plate-shaped member made of a low-refractive index acrylic resin or epoxy resin. From the viewpoints of compactness and strength, it is preferable that the width and height are 3 cm to 7 cm, and the thickness is 1 mm to 10 mm, but this is not limiting. The first tapered region 113b, the narrowed portion 113a, and the second tapered region 113c are fixed to the supporting portion 17C with a fixing material 154 such as acrylic resin or epoxy resin. The optical fiber 11 is fixed to the support portion 17C and sealed in the sealed container 6. It is not necessary that the entire optical fiber 11 is sealed in the sealed container 6, as long as at least the tapered portion 113 including the narrowed portion 113a is disposed in the sealed container 6.

[0038] The sealed container 6 is formed with holes 61 and 62 through which the optical fiber 11 passes, and is sealed with a sealing material such as a vacuum device filler with the optical fiber 11 passed through. The holes 61 and 62 do not necessarily have to be located on both sides of the sealed container 6, and may be located on the same side.

[0039] 2, the excitation light may be incident on the second end 112 of the optical fiber 11, or the wavelength-converted gas 153 may be irradiated from outside the sealed container 6. When the wavelength-converted gas 153 is excited from outside the sealed container 6, the sealed container 6 is made of a material that transmits 70% or more of the excitation light, preferably 80% or more, and more preferably 90% or more. By providing the support part 17C in contact with the wavelength converting part 15C, the tapered part 113 of the optical fiber 11 can be stably held within the wavelength converting part 15C, facilitating the manufacture of the optical fiber structure 110C.

[0040] <Selection of output wavelength> In the optical fiber light source 10 of the embodiment, light of various wavelengths can be output by selecting the fluorescent material contained in the wavelength conversion portion 15 and the wavelength of the excitation light that excites the fluorescent material. Even when a solid wavelength conversion film 151 is used as shown in Figure 4, it is possible to output light of different wavelengths by changing the wavelength of the excitation light. Instead of forming the wavelength conversion film 151 around the tapered portion 113 of the optical fiber 11, the tapered portion 113 of the optical fiber 11 can also be mounted on a substrate on which the wavelength conversion film 151 is formed, so that emitted light can be taken into the optical fiber and output from the first end portion 111, allowing the output wavelength to be freely selected.

[0041] When a phosphor is used as the fluorescent material, one example of a combination of phosphor and excitation light is, for example, to generate blue-green light with a full width at half maximum (FWHM) of about 30 nm, europium-doped barium silicon oxynitride (BaSi2O2N2:Eu 2+ ) may be used, and a gallium nitride laser diode (GaN-LD) with an emission wavelength of 405 nm may be used as the excitation light source. 2+ When CaSi2O2N2:Eu is used, green light with a wider FWHM is obtained, and when CaSi2O2N2:Eu is used, green light with a wider FWHM is obtained. 2+ When using a 1000-kJ / s laser, yellow-green radiation with a wider FWHM can be obtained.

[0042] When YAG is used as the yellow-emitting phosphor, yellow light with a FWHM of about 100 nm can be obtained by using a GaN-LD with an emission wavelength of 450 nm as the excitation light source. White light can also be generated by mixing multiple phosphors. For example, a red-emitting SCASN ((Sr,Ca)AlSiN3) and a green-emitting β-sialon (Si 6-z Al z O z N 8-z ) and blue emitter JEM(LaAl(Si 6-z Al z )N 10-z O z ) and excited by a GaN-LD with an emission wavelength of 405 nm, white light can be generated.

[0043] By introducing the generated light into the fiber from the narrowed portion 113a of the tapered portion 113 of the optical fiber 11 and its vicinity, CW incoherent light with a high degree of freedom in wavelength spectrum in a single transverse mode can be output from the first end 111.

[0044] The optical fiber light source 10 emits incoherent light with high focusing and linearity, making it suitable for use as spot illumination for microscopes and excitation light for fluorescent markers in endoscopes. Furthermore, the wavelength spectrum has a high degree of freedom, and by appropriately selecting the fluorescent material and excitation light, the emission wavelength and linewidth can be designed with a high degree of freedom.

[0045] The optical fiber light source 10 is not limited to the above-described exemplary configuration, and modifications, substitutions, etc. are possible within the scope of the invention. The combination of the phosphor used in the wavelength conversion unit and the wavelength of the excitation light is not limited to the above-described example, and can be selected appropriately depending on the application. The optical fiber light source 10 of the embodiment may be arranged in a single package and used as a light source module. In this case, at least a portion of the optical fiber 11 may be wound around a reel and housed in the package. When the excitation light is irradiated from outside the optical fiber 11, as shown in FIG. 3, the excess portion of the optical fiber 11 on the second end 112 side may be removed.

[0046] The wavelength conversion unit 15 may be a member having a wavelength conversion film 151 formed on its surface, which is replaceably disposed in the package. A laser diode (LD) or a light emitting diode (LED) may be used as the excitation light source 20. The optical characteristics of the light emitted from the optical fiber light source 10 may be adjusted by combining the material of the wavelength conversion unit 15 with the wavelength of the excitation light output from the light source 20. [Explanation of symbols]

[0047] 10, 10A, 10B Fiber Optic Light Source 5 containers 6. Airtight containers 15, 15A~15C Wavelength conversion unit 151 Wavelength conversion film 152 Wavelength conversion liquid 153 Wavelength conversion gas 154 Fixed materials 11 Optical Fiber 111 First end 112 Second end 113 Tapered section 113a Stenosis 113b First tapered region 113c Second taper region 17, 17A~17C Support part 20, 20A, 20B light source 110, 110A to 110C Optical fiber structure

Claims

1. an optical fiber that is a single mode fiber and has a first end that emits light, a second end that is located opposite to the first end, and a tapered portion that is located between the first end and the second end; a wavelength converting portion in contact with the tapered portion; a light source that excites the wavelength conversion unit; a support portion in contact with the wavelength converting portion; and the first end outputs the emitted light from the excited wavelength converting portion; the tapered portion includes a narrowed portion having a minimum diameter, a first tapered region in which the diameter decreases from the second end side toward the narrowed portion, and a second tapered region in which the diameter increases from the narrowed portion toward the first end side, a diameter of the constriction portion is smaller than a diameter of the first end and a diameter of the second end, and is equal to or smaller than a wavelength of the emitted light; the wavelength converting portion is a liquid or a gas, and is disposed so as to surround at least an outer periphery of the narrowed portion of the tapered portion, The light source is an optical fiber light source that simultaneously excites the portion of the wavelength converting portion that surrounds the outer periphery.

2. The optical fiber light source of claim 1 , wherein the light source inputs excitation light of a desired wavelength into the optical fiber from the second end.

3. 2. The optical fiber light source according to claim 1, wherein the light source irradiates the wavelength converting portion with excitation light of a desired wavelength from outside the optical fiber.

4. a container in which the wavelength converting unit is placed, the light source irradiates the wavelength conversion unit with excitation light of a desired wavelength from outside the container; The optical fiber light source according to claim 1 , wherein the container is made of a material that transmits 70% or more of the excitation light.

5. a container in which the wavelength converting unit is placed, 5. The optical fiber light source according to claim 1, wherein the container seals the wavelength converting portion.

6. 6. The optical fiber light source according to claim 1, wherein the radiation light output from the optical fiber is incoherent light.

7. the wavelength converting portion includes a phosphor, 7. The optical fiber light source according to claim 1, wherein the diameter of the phosphor is 1 μm or more and 50 μm or less.

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