Optical fiber light source

Abstract

To provide an optical fiber that is in a single transverse mode, has a high degree of wavelength spectrum freedom, and can perform CW incoherent output.SOLUTION: An optical fiber light source 10A includes a first end 111 for emitting light, a second end 112 positioned in an opposite side of the first end 111, and a taper part 113 positioned between the first end 111 and the second end 112, and also has an optical fiber 11 as a single-mode fiber, a wavelength conversion part 15 in contact with the taper part 113, a light source 20A for exciting the wavelength conversion part 15, and a support part 17 in contact with the wavelength conversion part 15. The first end 111 outputs radiation light from the excited wavelength conversion part 15, the taper part 113 includes a constriction part 113a in which a diameter is minimized, a first taper area in which the diameter becomes smaller, and a second taper area in which the diameter becomes larger, and a diameter D1 of the constriction part 113a is smaller than the diameter of the first end 111 and the diameter of the second end 112, and is equal to or smaller than a size of the wavelength of the radiation light.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to Optical fiber light source .

Background Art

[0002] Fiber output type light sources using optical fibers in the output section have been developed in various types and are widely used in industrial, research, etc. applications due to the convenience of routing and the portability of the device. However, in light sources that output incoherent light, usually multimode fibers are used in the output section, and as a result, the light diffuses and the quality of the transverse mode deteriorates. Also, in methods such as rare earth doped fibers where the core of the optical fiber itself emits light, only light of the emission wavelength of the dopant is extracted, and the degree of freedom of the wavelength spectrum is low. For this reason, an incoherent optical fiber light source that can output with good transverse mode quality and high wavelength spectrum degree of freedom is desired. Among them, for example, research on nanoscale optical fibers is progressing as in Non-Patent Document 1.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In one aspect of the disclosure, an object is to provide an optical fiber light source or an optical fiber structure that can output incoherent light with a single transverse mode, high wavelength spectrum degree of freedom, and continuous wave (CW).

Means for Solving the Problems

[0005] In one aspect of the disclosure, the optical fiber light source is An optical fiber having a first end that emits light, a second end located on the opposite side of the first end, and a tapered portion located between the first end and the second end, and being a single-mode fiber, A wavelength conversion portion in contact with the tapered portion, A light source that excites the wavelength conversion portion, A support portion in contact with the wavelength conversion portion, and having, The first end outputs the emitted light from the excited wavelength conversion portion, The tapered portion includes a constricted portion where the diameter is minimized, a first tapered region where the diameter decreases from the second end side toward the constricted portion, and a second tapered region where the diameter increases from the constricted portion toward the first end side, The diameter of the constricted portion is smaller than the diameters of the first end and the second end, and is less than or equal to the wavelength of the emitted light.

[0006] In one aspect of the disclosure, the optical fiber structure includes, An optical fiber having a first end that emits light, a second end located on the opposite side of the first end, and a tapered portion located between the first end and the second end, and being a single-mode fiber, A wavelength conversion portion in contact with the tapered portion, A support portion in contact with the wavelength conversion portion, and having, The first end outputs the emitted light from the excited wavelength conversion portion, The tapered portion includes a constricted portion where the diameter is minimized, a first tapered region where the diameter decreases from the second end side toward the constricted portion, and a second tapered region where the diameter increases from the constricted portion toward the first end side, The diameter of the constricted portion is smaller than the diameters of the first end and the second end, and is less than or equal to the wavelength of the emitted light.

Advantages of the Invention

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

[0008]

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[0009] In the embodiment, an optical fiber light source that satisfies three conditions, namely, "single transverse mode," "high wavelength spectrum flexibility," and "CW incoherent light source," is provided. 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 large in the center and small on the periphery. Light in a single transverse mode has high focusing and straightness.

[0010] "High wavelength spectrum freedom" 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 and interference is unlikely to occur. In this respect, it differs from lasers that output coherent light with a uniform 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. Also, since the distribution of phase and amplitude fluctuates randomly, almost no wave interference occurs. As incoherent light sources with high condensing or directivity, there are superluminescent diodes and amplified spontaneous emission (ASE) light sources, but the wavelength of the output light is fixed and the degree of freedom of the wavelength spectrum is low. That is, a light source that satisfies all of "single transverse mode", "high degree of freedom of wavelength spectrum", and "CW incoherent light source" has not been realized yet.

[0012] In an embodiment, by taking the light obtained by wavelength conversion into an optical fiber, an optical fiber light source that satisfies the above three conditions is realized. As a light source that utilizes the nonlinear optical effect of an optical fiber, there is a supercontinuum (SC) light source, but the SC light source is a pulsed light source that outputs strong coherent pulses with aligned phases. The optical fiber light source of the embodiment is an incoherent light source that has the same straightness and condensing property as a laser beam and has a high degree of freedom of wavelength spectrum. The optical fiber light source of the embodiment having such characteristics is applicable to spot illumination of a microscope, a light source for exciting a fluorescent marker used in an endoscope, etc., and is highly useful.

[0013] FIG. 1 is a diagram for explaining the principle of the optical fiber light source 10 of the embodiment. In the following embodiments, the same components may be denoted by 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 that excites the wavelength conversion portion 15, and the radiation light L RAD emitted from the excited wavelength conversion portion 15 is taken into the optical fiber 11 and output from the first end portion 111.

[0014] The optical fiber 11 is a single-mode fiber. More specifically, the target radiation light L RADIt is an optical fiber that operates in single mode with respect to the wavelength. A tapered portion 113 is provided between the first end portion 111 of the optical fiber 11 and the second end portion 112 located on the opposite side of the first end portion. As the material of the optical fiber 11, glass, plastic, single crystal, etc. can be used. Also, from the viewpoint of ease of manufacture, it is desirable that the optical fiber 11 be a standard single mode fiber with a clad diameter of several hundred μm and a core diameter of about several μm.

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

[0016] The tapered portion 113 can be obtained, for example, by heating and stretching a part of the single mode fiber to reduce the diameter to equal to or less than the target wavelength. In the constricted portion 113a and its vicinity, the core 101 and the clad 102 of the optical fiber 11 are integrated, and the entire optical fiber 11 functions as a core. The medium surrounding the constricted portion 113a and its vicinity functions as a clad. In this sense, the material of the optical fiber 11 is preferably one with as high a refractive index as possible, and particularly preferably one with a refractive index of 1.6 or more.

[0017] In the constriction 113a whose diameter is narrowed to be below the wavelength, since the optical propagation mode is distributed up to the outside (i.e., the cladding) of the optical fiber 11, the light emission from the cladding part propagates along the optical fiber 11 as part of the propagation mode. Since the wavelength conversion part 15 arranged in contact with the tapered part 113 also functions as the cladding of the constriction 113a, it has a refractive index lower than that of the optical fiber 11.

[0018] Emitted light L RAD is generated by irradiating the wavelength conversion part 15 with the excitation light L PUMP . Since it is sufficient to be able to irradiate the wavelength conversion part 15 with the excitation light L PUMP , the excitation light L PUMP may be incident from the second end part 112 of the optical fiber 11, or the wavelength conversion part 15 may be directly irradiated from the outside of the optical fiber 11.

[0019] The wavelength conversion part 15 is formed of any material that generates the emitted light L PUMP with a wavelength different from that of the excitation light L PUMP by the irradiation of the excitation light L RAD . As an example, it contains a fluorescent substance and is formed of a material having a refractive index lower than that of the optical fiber 11. By selecting the type of the fluorescent substance and the wavelength of the excitation light that excites the fluorescent substance, the wavelength of the emitted light L RAD can be designed to a desired wavelength. As the fluorescent substance, a phosphor, a rare earth ion, a quantum dot, etc. can be used. When the wavelength conversion part 15 contains a phosphor as the fluorescent substance, the diameter of the phosphor is preferably about several μm to several tens of μm, specifically, 1 μm or more and 50 μm or less is preferable because the options of the phosphor that can be used are widened.

[0020] The fluorescence emitted from the fluorescent substance by the irradiation of the excitation light L PUMP is incoherent light containing waves with various phases and amplitudes. This incoherent light is taken into the optical fiber 11 by the propagation mode of the optical fiber 11 that spreads to the outside of the constriction 113a, and propagates through the optical fiber 11 as the emitted light L RAD . More precisely, the emitted light L RADis mainly confined to the core 101, and a part of it oozes 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 collimated single transverse-mode CW incoherent light. Despite being incoherent light, it propagates over a long distance with suppressed diffusion. In order to further enhance the collimation of the output light, a collimating lens 19 may be disposed at the first end portion 111 of the optical fiber 11. When the collimating lens 19 is disposed, the light can be irradiated onto a minute spot. Further, by using the collimating lens 19 as an achromatic lens, the light L RAD included in the light can be made into uniform parallel light for various wavelengths. Also, a wavelength filter that transmits only a specific wavelength component included in the emitted light L RAD may be disposed to output monochromatic light, or only a specific wavelength component may be cut to output a specific combination of wavelengths.

[0022] <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 for exciting 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 configured 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 emitted light L RAD The excitation light L incident from the second end portion 112 of the optical fiber 11 PUMPIn the vicinity of the constriction 113a, it is distributed to the wavelength conversion section 15 as evanescent light. The wavelength conversion section 15 is excited by this evanescent light and emits light with a high degree of freedom in the wavelength spectrum.

[0024] Excitation light L PUMP The light generated in the wavelength conversion section 15 by the irradiation of the excitation light L is CW incoherent light containing waves of various phases and amplitudes. This CW incoherent light is captured by the propagation mode of the optical fiber 11 in the vicinity of the constriction 113a and propagates through the optical fiber 11 as the radiated light L RAD and propagates through the optical fiber 11 as the radiated light L RAD is emitted as single transverse mode light from the first end portion 111 of the optical fiber 11 which is a single mode fiber.

[0025] With the configuration of FIG. 2, a CW incoherent light source with a single transverse mode and a high degree of freedom in the wavelength spectrum is realized.

[0026] <Second Configuration Example> FIG. 3 is a schematic diagram of the optical fiber light source 10B of the second configuration example. In the second configuration example, the wavelength conversion section 15 is irradiated and excited from the outside by a light source 20B provided outside the optical fiber 11 without the excitation light L PUMP being incident from the second end portion 112 of the optical fiber 11. The optical fiber light source 10B includes an optical fiber 11 having a tapered portion 113, a wavelength conversion section 15 in contact with the tapered portion 113, a light source 20B for exciting the wavelength conversion section 15, and a support portion 17 in contact with the wavelength conversion section 15. The light source 20B is, for example, a laser diode (LD) or a light emitting diode (LED) arranged at a position where the wavelength conversion section 15 can be irradiated with light. An optical fiber structure 110 is formed by the portion of the optical fiber light source 10B excluding the light source 20B.

[0027] In the second configuration example, at least the radiated light L RADIt is sufficient that the portion from the tapered portion 113 into which light is incident to the first end portion 111 is a single-mode fiber. However, from the perspective of the manufacturing method of 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 is smaller than the wavelength of the radiated light L RAD is smaller than the wavelength of.

[0028] The wavelength conversion unit 15 in contact with the tapered portion 113 is directly irradiated with the excitation light L PUMP from the light source 20B. By irradiating the excitation light L PUMP , the wavelength conversion unit 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 unit 15.

[0029] In the configurations of FIGS. 2 and 3, the support portion 17 in contact with the wavelength conversion unit 15 is made of epoxy resin, silicon resin, rubber, etc., and supports the tapered portion 113 and the wavelength conversion unit 15. From the viewpoint of strength, it is preferable that the thickness of the support portion 17 is equal to or greater than the thickness of the wavelength conversion unit 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 unit 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. However, in the configuration of FIG. 2, it is not particularly limited and does not necessarily need to transmit light. Since the diameter D1 of the narrow portion 113a of the tapered portion 113 is very small, the strength is improved by being supported by the support portion 17. Further, 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 by the wavelength conversion unit 15 is taken into the propagation mode of the optical fiber 11 in the narrow portion 113a and its vicinity, and the radiated light L RADIt is emitted from the first end portion 111 of the optical fiber 11. Also with the configuration of FIG. 3, a CW incoherent light source having a single transverse mode and a high degree of freedom in wavelength spectrum is realized.

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

[0032] The wavelength conversion film 151 contains a fluorescent substance. The type of fluorescent substance contained in the wavelength conversion film 151 may be one type, or a plurality of types of fluorescent substances may be mixed. Thereby, the spectrum of the emitted light can be freely designed. By mixing a fluorescent substance that emits fluorescence of a desired wavelength into a low refractive index base material such as an acrylic resin or an 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 transparent to the excitation light L PUMP and the emitted light L RAD and preferably transmits 70% or more, preferably 80% or more, and more preferably 90% or more of the excitation light L PUMP or the emitted light L RAD .

[0033] The wavelength conversion film 151 is preferably arranged so as to cover the tapered portion 113, but it is not necessarily applied to cover the entire circumference of the tapered portion 113. The coating range is not limited as long as it is in contact with the constricted portion 113a and its vicinity. Also, the thickness of the wavelength conversion film 151 is preferably several tens of μm to several hundreds of μm because it is easy to manufacture.

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

[0035] In FIG. 5, an optical fiber structure 110B including a liquid wavelength conversion section 15B and a support section 17B is used. The wavelength conversion section 15B is, for example, a wavelength conversion liquid 152 accommodated in a container 5. The wavelength conversion liquid 152 is a liquid obtained by mixing a solvent such as distilled water or a fluorine-based inert liquid and a fluorescent substance. The support portion 17B is preferably made of a material having a refractive index lower than that of the optical fiber 11 because the influence on the propagation mode can be suppressed. Further, the support portion 17B is preferably made of a material having a refractive index approximately the same as that of the wavelength conversion liquid 152 because the influence on the propagation mode can be further suppressed. For example, it is a plate-like member made of a low refractive index acrylic resin, epoxy resin, or the like. It is preferably 3 cm to 7 cm in width and height and 1 mm to 10 mm in thickness from the viewpoints of miniaturization and strength, but is not limited thereto. The first tapered region 113b, the constricted portion 113a, and the second tapered region 113c are fixed to the support portion 17B with a fixing material 154 such as an epoxy resin having a refractive index close to that of the wavelength conversion liquid 152. The optical fiber 11 is immersed in the wavelength conversion liquid 152 in a state where it is fixed to the support portion 17B. Even if not all of the optical fiber 11 is immersed in the wavelength conversion liquid 152, it is sufficient that at least the tapered portion 113 including the constricted portion 113a is immersed in the wavelength conversion 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 conversion liquid 152, but it may be arranged in a sealed container filled with the wavelength conversion liquid 152 without folding back the tapered portion 113. Alternatively, the tapered portion 113 may be meandered in a sealed container filled with the wavelength conversion 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 conversion liquid 152.

[0036] The excitation light may be incident from the second end portion 112 of the optical fiber 11 as shown in FIG. 2, or the wavelength conversion liquid 152 may be irradiated from the outside of the container 5. When the wavelength conversion liquid 152 is excited from the outside of the container 5, the container 5 is formed of a material having translucency with respect to the excitation light. The configuration of the wavelength conversion section in FIG. 5 allows for easy replacement of the wavelength conversion liquid 152 and can output light of a desired wavelength. When the container 5 is a sealed container, it is also easy to carry and assemble. By providing the support portion 17B in contact with the wavelength conversion portion 15B, the tapered portion 113 of the optical fiber 11 can be stably held in the wavelength conversion portion 15B, facilitating the manufacture of the optical fiber structure 110B.

[0037] In Fig. 6, an optical fiber structure 110C including a gas wavelength conversion section 15C and a support section 17C is used. The wavelength conversion section 15C is, for example, a wavelength conversion gas 153 enclosed in a sealed container 6. The wavelength conversion gas 153 contains alkali metal gases such as rubidium and cesium, molecules such as iodine, and ions such as alkaline earth metals, and these act as fluorescent substances. The support section 17C is preferably made of a material having a refractive index lower than that of the optical fiber 11 because it can suppress the influence on the propagation mode. For example, it is a plate-like member made of a low refractive index acrylic resin or epoxy resin. It is preferable from the viewpoints of miniaturization and strength that the width and height are 3 cm to 7 cm and the thickness is 1 mm to 10 mm, but it is not limited thereto. The first taper region 113b, the constriction 113a, and the second taper region 113c are fixed to the support section 17C with a fixing material 154 such as an acrylic resin or an epoxy resin. The optical fiber 11 is sealed in the sealed container 6 in a state where it is fixed to the support section 17C. Even if not all of the optical fiber 11 is sealed in the sealed container 6, it is sufficient that at least the taper section 113 including the constriction 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 filler for a vacuum device in a state where the optical fiber 11 passes through. The holes 61 and 62 do not necessarily have to be disposed on both sides of the sealed container 6, and may be disposed on the same side.

[0039] The excitation light may be incident from the second end 112 of the optical fiber 11 as shown in Fig. 2, or the wavelength conversion gas 153 may be irradiated from the outside of the sealed container 6. When the wavelength conversion gas 153 is excited from the outside of the sealed container 6, the sealed container 6 is formed of a material that transmits 70% or more, preferably 80% or more, and more preferably 90% or more of the excitation light. By providing the support section 17C in contact with the wavelength conversion section 15C, the taper section 113 of the optical fiber 11 can be stably held in the wavelength conversion section 15C, and the manufacture of the optical fiber structure 110C becomes easy.

[0040] <Selection of Output Wavelength> In the optical fiber light source 10 of the embodiment, by selecting the fluorescent material included in the wavelength conversion unit 15 and the wavelength of the excitation light that excites the fluorescent material, light of various wavelengths can be output. Even when using the solid wavelength conversion film 151 as shown in FIG. 4, by changing the wavelength of the excitation light, there is a possibility of outputting light of different wavelengths. Instead of forming the wavelength conversion film 151 around the tapered portion 113 of the optical fiber 11, by mounting the tapered portion 113 of the optical fiber 11 on a substrate on which the wavelength conversion film 151 is formed, the emitted light can be taken into the optical fiber and output from the first end portion 111, so that the output wavelength can be freely selected.

[0041] When using a phosphor as the fluorescent substance, as an example of the combination of the phosphor and the excitation light, for example, when generating blue-green light with a full width at half maximum (FWHM) of about 30 nm, as the phosphor, europium-doped barium silicon oxynitride (BaSi2O2N2:Eu 2+ ) can be used, and a gallium nitride LD (GaN-LD) with an emission wavelength of 405 nm can be used as the excitation light source. When using SrSi2O2N2:Eu 2+ as the phosphor, green light with a wider FWHM can be obtained, and when using CaSi2O2N2:Eu 2+ as the phosphor, yellow-green emitted light with an even wider FWHM can be obtained.

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

[0043] By taking in the generated light into the fiber from the constricted 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 portion 111.

[0044] Since the optical fiber light source 10 is incoherent light but has high condensing property and straight traveling property, it can be used as spot illumination for a microscope and fluorescence marker excitation light for an endoscope. Also, since the degree of freedom in the wavelength spectrum is high, by appropriately selecting a fluorescent material and excitation light, the emission wavelength and line width can be designed with a high degree of freedom.

[0045] The optical fiber light source 10 is not limited to the above-described configuration example and can be deformed, replaced, etc. within a range not departing from the gist of the invention. The combination of the phosphor used in the wavelength conversion section and the wavelength of the excitation light is not limited to the above-described example and can be appropriately selected according to the application. The optical fiber light source 10 of the embodiment may be arranged in one package and used as a light source module. In that case, at least a part of the optical fiber 11 may be wound around a reel and accommodated in the package. When irradiating the excitation light from the outside of the optical fiber 11 as shown in FIG. 3, the surplus portion on the second end portion 112 side of the optical fiber 11 may be removed.

[0046] As the wavelength conversion section 15, a member having a wavelength conversion film 151 formed on its surface may be disposed in the package so as to be replaceable. As the excitation light source 20, a laser diode (LD) or a light emitting diode (LED) may be used. The optical characteristics of the emitted light from the optical fiber light source 10 may be adjusted by the combination of the material of the wavelength conversion section 15 and the wavelength of the excitation light output from the light source 20.

Explanation of Reference Numerals

[0047] 10, 10A, 10B Optical fiber light source 5 Container 6 Sealed container 15, 15A to 15C Wavelength conversion section 151 Wavelength conversion film 152 Wavelength conversion liquid 153 Wavelength conversion gas 154 Fixing material 11 Optical fiber 111 First end 112 Second end 113 Taper section 113a Narrow section 113b First taper region 113c Second taper region 17, 17A - 17C Support part 20, 20A, 20B Light source 110, 110A - 110C Optical fiber structure

Claims

1. An optical fiber, which is a single-mode fiber, having a first end portion that emits light, a second end portion located on the opposite side of the first end portion, and a tapered portion located between the first end portion and the second end portion. A wavelength conversion portion in contact with the tapered portion. A light source that excites the wavelength conversion portion. A support portion in contact with the wavelength conversion portion. And having The first end portion outputs the radiation light from the excited wavelength conversion portion. The tapered portion includes a constricted portion where the diameter is minimized, a first tapered region where the diameter decreases from the second end portion side toward the constricted portion, and a second tapered region where the diameter increases from the constricted portion toward the first end portion side. The diameter of the constricted portion is smaller than the diameters of the first end portion and the second end portion, and is of a size equal to or less than the wavelength of the radiation light. The wavelength conversion portion is a solid and is arranged to surround at least the outer periphery of the constricted portion of the tapered portion. The light source is an optical fiber light source that simultaneously excites the portion surrounding the outer periphery of the wavelength conversion portion.

2. The wavelength conversion portion is formed of a material having a refractive index lower than that of the optical fiber and includes a phosphor, a rare earth ion, or a quantum dot as a fluorescent substance. The optical fiber light source according to claim 1.

3. The light source is an optical fiber light source according to claim 1 or 2, wherein excitation light of a desired wavelength is incident on the optical fiber from the second end portion.

4. The light source is an optical fiber light source according to claim 1 or 2, wherein the wavelength conversion portion is irradiated from the outside of the optical fiber.

5. The radiation light output from the optical fiber is incoherent light. The optical fiber light source according to any one of claims 1 to 4.

6. The wavelength conversion portion contains a phosphor. The diameter of the phosphor is 1 μm or more and 50 μm or less, and the optical fiber light source according to any one of claims 1 to 5.

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