Optical fiber, medical device, illumination device, and probe

Abstract

To provide an optical fiber which offers a wide irradiation range and superior tensile strength and is capable of emitting less yellowish white light, and to provide a medical device, an illumination device, and an ophthalmic surgery illumination probes using the same.SOLUTION: An optical fiber comprises a core and cladding, in which a light transmission loss at 525 nm is 2,500 dB / Km or less and a yield point stress coefficient represented by the following formula is 40 or greater. The core contains a polymer 1 having a glass transition temperature Tg of 137°C or higher and 147°C or lower and a refractive index of 1.55 or greater. Expression: yield point stress coefficient=yield point stress (N) / (fiber diameter (mm))2.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an optical fiber and a medical device, a lighting device, and an ophthalmic surgical lighting probe using the optical fiber. [Background technology]

[0002] In endoscopic surgery and ophthalmic surgery, a common method is to observe the affected area by irradiating light from one end of an optical fiber and irradiating it from the exit end. Since the larger the irradiation angle of the light, the wider the area around the affected area can be observed, optical fibers with a large numerical aperture are preferably used.

[0003] In general, in order to increase the numerical aperture of an optical fiber, it is effective to combine a core with a high refractive index and a cladding with a low refractive index. As an example of such a core-cladding combination, optical fibers using polycarbonate resin or norbornene resin for the core have been disclosed (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 61-210303 [Patent Document 2] JP 2000-275448 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the optical fiber disclosed in Patent Document 1 has a low viscosity and a low spinning temperature, and therefore has a problem in productivity, such as low strength and the tendency for the fiber to break during continuous spinning.

[0006] Furthermore, the optical fiber disclosed in Patent Document 2 has a problem that it is not suitable for medical use because it has a large transmission loss in the low wavelength region and the emitted light is colored yellow.

[0007] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide an optical fiber that has a wide irradiation range, excellent tensile strength, and is capable of emitting white light with little yellowness. [Means for solving the problem]

[0008] The present invention for solving the above problems is as follows. (1) An optical fiber having a core and a cladding, The transmission loss at 525 nm is 2,500 dB / km or less, The yield stress coefficient represented by the following formula is 40 or more, The optical fiber, wherein the core comprises a polymer 1 having a glass transition temperature Tg of 137° C. or more and 147° C. or less and a refractive index of 1.55 or more.

[0009] Formula: Yield stress coefficient = Yield stress (N) / (fiber diameter (mm)) 2 (2) The optical fiber according to (1) above, wherein the polymer 1 is polycarbonate. (3) the clad in contact with the core comprises polymer 2; The optical fiber according to (1) or (2)2, wherein the refractive index of the polymer 2 is smaller than the refractive index of the core by 0.18 or more. (4) the clad in contact with the core comprises polymer 2; The optical fiber according to any one of (1) to (3), wherein the polymer 2 contains 35% by weight or less of vinylidene fluoride as a copolymerization component. (5) The polymer 2 is Hexafluoropropylene 10-35% by weight Tetrafluoroethylene 45-75% by weight Vinylidene fluoride 5-35% by weight Perfluoroalkyl vinyl ether 1-15% by weight The optical fiber according to any one of (1) to (4) above, which contains as a copolymerization component. (6) The optical fiber according to any one of (1) to (5), wherein the cladding has a multilayer structure. (7) The optical fiber according to any one of (1) to (6) above, wherein the outermost cladding layer contains a polymer 3 containing ethylene as a copolymerization component. (8) A medical device comprising the optical fiber according to any one of (1) to (7). (9) A lighting device comprising the optical fiber according to any one of (1) to (7). (10) A probe for illumination in ophthalmic surgery, comprising the optical fiber according to any one of (1) to (7) above. Effect of the Invention

[0010] According to the present invention, it is possible to provide an optical fiber that has a wide irradiation range, excellent tensile strength, and is capable of emitting white light with little yellowness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the optical fiber, medical device, lighting device, and ophthalmic surgical lighting probe according to the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be modified in various ways depending on the purpose and application.

[0012] In the present invention, the term "not less than" means that the value is the same as or larger than the indicated value, and the term "not more than" means that the value is the same as or smaller than the indicated value.

[0013] The optical fiber of the present invention has a core and a cladding. By combining the core having the function of transmitting light with the cladding surrounding it according to the required characteristics, the optical characteristics, mechanical characteristics, etc. can be adjusted to the desired range. The number of cores in the optical fiber of the present invention is not particularly limited, and it may be either an embodiment having only one core or an embodiment having multiple cores with claddings around them, but an embodiment having only one core is preferable because it allows the irradiation angle to be large.

[0014] The optical fiber of the present invention has a transmission loss at 525 nm of 2,500 dB / km or less. The optical fiber of the present invention has a transmission loss at 525 nm of preferably 2,100 dB / km or less, more preferably 1,800 dB / km or less, so that it can emit white light with little yellowness. The smaller the transmission loss at 525 nm, the better, and there is no particular lower limit, but from the viewpoints of versatility of materials and cost, the lower limit is thought to be about 100 dB / km.

[0015] The transparency of the core can reduce the light transmission loss of the optical fiber. To achieve this, for example, a highly transparent material is selected for the core, the glass transition temperature of the core is reduced, the melt flow rate is improved, and the spinning temperature is appropriately set, thereby making it possible to obtain an optical fiber with high transparency and low light transmission loss.

[0016] The optical fiber of the present invention preferably has a transmission loss of 1,200 dB / km or less at 650 nm. By having a transmission loss of 1,000 dB / km or less, more preferably 800 dB / km or less, the optical fiber can emit strong light even when used for a long period of time. From the viewpoints of versatility of materials and cost, a transmission loss of 100 dB / km or more is preferable.

[0017] In the optical fiber of the present invention, the ratio of the light transmission loss at 525 nm to the light transmission loss at 650 nm (light transmission loss at 525 nm) / (light transmission loss at 650 nm) is preferably 3.0 or less. By making it 3.0 or less, more preferably 2.5 or less, it is possible to emit white light with little yellowness.

[0018] Here, the light transmission loss of an optical fiber complies with Section 7 of JIS C 6823:2010. For example, parallel halogen light (incident NA=0.25) is incident on an optical fiber wound in a skein state, and the light intensity A (dBm) at a position 10 m from the incident point and the light intensity B (dBm) at a position 5 m from the incident point are measured, and the light transmission loss C (dB / km) can be calculated from (BA) / ((10-5) / 1000).

[0019] The optical fiber of the present invention has a yield stress coefficient, represented by the following formula, of 40 or more.

[0020] Formula: Yield stress coefficient = Yield stress (N) / (fiber diameter (mm)) 2 Here, the fiber diameter refers to the long diameter of the optical fiber core excluding the protective layer, etc. The yield stress coefficient of the optical fiber of the present invention is preferably 48 or more, more preferably 56 or more, to improve productivity and handleability. The higher the yield stress coefficient, the better, and there is no particular upper limit, but a value of about 160 is considered to be within the range that can be actually manufactured.

[0021] The stress coefficient at yield point of an optical fiber can be improved, for example, by increasing the glass transition temperature of the core, decreasing the melt flow rate, and further performing a drawing process during manufacturing.

[0022] Here, the yield stress of the optical fiber can be measured using a tensile tester on a sample of optical fiber having a length of 10 cm in accordance with Section 5 of JIS C 6821:2022.

[0023] The numerical aperture (NA) of the optical fiber is preferably 0.7 or more. If the numerical aperture is 0.7 or more, more preferably 0.8 or more, it is possible to suppress the light transmission loss and increase the irradiation range even in a long optical fiber of several meters, such as in an endoscope, an ophthalmic surgical illumination, or a catheter.

[0024] The major axis of the optical fiber is preferably 0.1 to 2.0 mm. If it is 1.0 mm or less, more preferably 0.5 mm or less, the influence on the affected area can be suppressed, so that it can be suitably used for medical purposes. Here, the major axis of the optical fiber can be measured using a micrometer.

[0025] [core] (Polymer 1) In the optical fiber of the present invention, the core contains polymer 1. Here, polymer 1 is a polymer having a glass transition temperature Tg of 137° C. or more and 147° C. or less and a refractive index of 1.55 or more.

[0026] Since the core is composed of multiple components including polymer 1, when polymer 1 is separated from the core, polymer 1 can be eluted from the core using gel permeation chromatography (GPC) and then various measurements can be performed.

[0027] The glass transition temperature Tg of polymer 1 is 137°C or higher and 147°C or lower, but is preferably 137°C or higher, and more preferably 140°C or higher, so that the light transmission loss at 650 nm can be reduced. Furthermore, an optical fiber with a high yield point stress can be obtained. The glass transition temperature Tg of polymer 1 is 147°C or lower, and is more preferably 145°C or lower, so that the flowability is improved and the spinning temperature can be reduced, and therefore the light transmission loss at 525 nm can be reduced.

[0028] The glass transition temperature in the present invention is a value obtained by measuring under the following conditions using a DSC (differential scanning calorimeter) in a nitrogen atmosphere in accordance with JIS K 7121:2012. First, the temperature is raised from -40°C at a heating rate of 10°C / min, and after reaching 200°C, it is held for 5 minutes. Then, the temperature is lowered to -40°C and held for 5 minutes, and then the temperature is raised again to 200°C at a heating rate of 10°C / min. The change point of the calorific value obtained during the second heating process is taken as the glass transition temperature. As a differential scanning calorimeter, for example, Diamond DSC manufactured by Perkin Elmer, etc. can be mentioned. When it is difficult to collect a core and directly measure the glass transition temperature, if the composition of the core is known, a core of the same composition can be prepared and the glass transition temperature can be measured.

[0029] The refractive index of polymer 1 is 1.55 or more. By having a refractive index of 1.55 or more, an optical fiber with a high numerical aperture can be obtained. Although there is no particular upper limit to the refractive index of polymer 1, from the viewpoints of versatility of materials and cost, the upper limit is considered to be about 1.65.

[0030] The refractive index in the present invention can be measured in accordance with JIS K 7142:2014 using an Abbe refractometer for a test piece of 20 mm x 8 mm x 1.4 mm in an atmosphere of room temperature 25 ° C. If it is difficult to collect a core and directly measure the refractive index, the collected core can be heated at 210 ° C. for 5 minutes using a press molding machine, then cooled to room temperature to prepare a test piece molded to 20 mm x 8 mm x 1.4 mm, and the refractive index can be measured. In addition, if the composition of the core is known, a test piece can be similarly prepared from the known composition and the refractive index can be measured.

[0031] Polymer 1 preferably has a melt flow rate (hereinafter sometimes abbreviated as MFR) of 70 g / 10 min or more and 160 g / 10 min or less under conditions of a temperature of 300° C. and a load of 1.2 kg. By setting the lower limit of the melt flow rate to more preferably 100 g / 10 min or more, the fluidity is improved and the spinning temperature can be reduced, thereby reducing the light transmission loss at 525 nm. Furthermore, by setting the upper limit of the melt flow rate to more preferably 145 g / 10 min or less, an optical fiber with a high yield point stress can be obtained.

[0032] As the polymer 1, for example, it is preferable that it has a cyclic structure such as an aromatic ring or a cycloalkyl group, or a structure with a large atomic refraction, and for example, cycloolefin polymer (COP), cycloolefin copolymer (COC), polystyrene, polycarbonate, fluorene-containing polyester, polymethylpentene, etc. Among these, polycarbonate is particularly preferable as the polymer 1 because it can achieve both a high refractive index and a glass transition point.

[0033] The core may further contain small amounts of stabilizers such as antioxidants and other additives as long as they do not affect the light transmittance.

[0034] As described above, the core contains polymer 1. Although the content thereof is not particularly limited, it is preferable that the core essentially consists of polymer 1, that is, the core contains 95 to 100% by weight, more preferably 99 to 100% by weight, and even more preferably 100% by weight of polymer 1 in 100% by weight of the core.

[0035] [Clad] The optical fiber of the present invention has a cladding.

[0036] (Polymer 2) In the optical fiber of the present invention, the cladding in contact with the core preferably contains polymer 2. Here, polymer 2 is the polymer that is contained in the largest amount (by weight) in the cladding in contact with the core.

[0037] The polymer 2 is preferably a polymer having a refractive index smaller than that of the core by 0.18 or more. The refractive index of the polymer 2 is preferably smaller than that of the core by 0.18 or more, more preferably by 0.20 or more, thereby making it possible to obtain an optical fiber with a high numerical aperture. The absolute value of the refractive index of the polymer 2 and the core is preferably 1.40 or less, more preferably 1.38 or less.

[0038] Since the clad is composed of multiple components including polymer 2, when polymer 2 is separated from the clad, polymer 2 can be eluted from the clad using gel permeation chromatography (GPC) and then various measurements can be performed.

[0039] Here, the refractive index of the clad and polymer 2 can be measured in the same manner as the refractive index of the core. If it is difficult to collect the clad or polymer 2 and directly measure the refractive index, the collected clad can be heated at 210°C for 5 minutes using a press molding machine, cooled to room temperature, and molded into a test piece measuring 20 mm x 8 mm x 1.4 mm, and the refractive index can be measured. If the composition of the clad is known, a test piece can be similarly prepared from the known composition, and the refractive index can be measured.

[0040] As the polymer 2, a fluorine-containing polymer such as vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer or vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer is preferable. By using a fluorine-containing polymer as the polymer 2, the flexibility of the cladding in contact with the core can be improved. As the polymer 2, two or more of these may be used. Among these, the polymer 2 preferably contains 35% by weight or less of vinylidene fluoride as a copolymerization component. By containing 35% by weight or less of vinylidene fluoride as a copolymerization component, the refractive index of the cladding in contact with the core is reduced, and an optical fiber with a high numerical aperture can be obtained. Furthermore, by improving the transparency of the cladding in contact with the core, an optical fiber with excellent light transmission can be obtained.

[0041] Furthermore, polymer 2 is preferably a copolymer containing hexafluoropropylene, tetrafluoroethylene, vinylidene fluoride, and perfluoroalkyl vinyl ether as copolymerization components, and the copolymerization components preferably contain 10% by weight or more and 35% by weight or less, preferably 30% by weight or less, 45% by weight or more and 75% by weight or less, 5% by weight or more and 35% by weight or less, preferably 10% by weight or more and 35% by weight or less, and perfluoroalkyl vinyl ether, preferably 1% by weight or more and 15% by weight or less, preferably 10% by weight or less. By using such a copolymer as polymer 2, an optical fiber having high light transmittance, low refractive index, and excellent flexibility can be obtained.

[0042] The perfluoroalkyl vinyl ether, which is a copolymerization component of the polymer 2, preferably has a perfluoroalkyl group having a linear structure, a branched structure, and / or a cyclic structure. Examples of perfluoroalkyl vinyl ethers include perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether), perfluoro(butyl vinyl ether), perfluoro(hexyl vinyl ether), and perfluoro(octyl vinyl ether). Two or more of these may be used. Among these, perfluoro(propyl vinyl ether) is preferred.

[0043] The MFR of the polymer 2 under the conditions of a temperature of 265° C. and a load of 5 kg is preferably 10 g / 10 min or more and 60 g / 10 min or less.

[0044] As mentioned above, it is preferable that the clad in contact with the core contains polymer 2. Although the content is not particularly limited, it is preferable that the clad in contact with the core essentially consists of polymer 2, that is, the clad in contact with the core contains 95 to 100 wt%, more preferably 99 to 100 wt%, and even more preferably 100 wt% of polymer 2 in 100 wt% of the clad in contact with the core.

[0045] The thickness of the clad in contact with the core is not particularly limited, but is preferably 2 to 20 μm.

[0046] Here, the thickness of the cladding in contact with the core can be measured by cutting five randomly selected locations from the plastic optical fiber perpendicular to the longitudinal direction, polishing the cross section so that the core / cladding interface can be observed, and then magnifying and observing the cross section using a digital microscope VHX-7000 (manufactured by Keyence). The magnification for magnification observation is between 10 and 200 times, and a range is selected in which the entire cross section is within the field of view and the interface can be observed. In the cross section, the thickness of the thinnest part of the cladding in contact with the core is measured, and this is taken as the thickness of the cladding in contact with the core. The thickness of the cladding in contact with the core is measured for each of the five cross sections, and the average value is taken as the thickness of the cladding in contact with the core.

[0047] (Polymer 3) The optical fiber of the present invention has a cladding around the core, and although the number of layers in the cladding is not particularly limited, it is preferable that the cladding has a laminated structure. By forming the cladding into a laminated structure, the yield stress of the fiber can be improved. In this case, it is preferable that the cladding in contact with the core is formed from a material with a low refractive index, and the irradiation range of the light emitted from the optical fiber can be widened, making it suitable for use in medical device components such as endoscopes, ophthalmic surgery lighting, and catheters.

[0048] In the case of having a laminated clad, it is preferable that the clad of the outermost layer contains a polymer 3 containing ethylene as a copolymerization component. By containing ethylene as a copolymerization component in the polymer 3, it is possible to improve the scratch resistance and further improve the yield stress of the optical fiber while maintaining the flexibility of the clad of the outermost layer. As the polymer 3, an ethylene / tetrafluoroethylene / hexafluoropropylene copolymer (a polymer containing ethylene, tetrafluoroethylene, and hexafluoropropylene as copolymerization components) is more preferable. When an ethylene / tetrafluoroethylene / hexafluoropropylene copolymer is used as the polymer 3, it is preferable that the copolymerization components contain 10 to 35% by weight of ethylene, 45 to 69% by weight of tetrafluoroethylene, and 20 to 45% by weight of hexafluoropropylene. When the ethylene, which is a copolymerization component of the polymer 3, is 10% by weight or more in the polymer 3 in the clad of the outermost layer, molding stability is improved. When it is 35% by weight or less, crystallinity can be reduced and transparency is improved. The proportion of ethylene, which is a copolymerization component of polymer 3, is preferably 11 to 30% by weight. When tetrafluoroethylene, which is a copolymerization component of polymer 3, is 45% by weight or more, molding stability is improved. When it is 69% by weight or less, crystallinity can be reduced and transparency is improved. When hexafluoropropylene, which is a copolymerization component of polymer 3, is 20% by weight or more, flexibility is improved and light transmission loss in a bent state can be further reduced. When it is 45% by weight or less, adhesion is reduced and processability when coating with a coating layer is improved.

[0049] The polymer 3 preferably further has a carbonyl group-containing functional group, which can improve the solvent resistance. The polymer 3 may have the carbonyl group-containing functional group at the polymer chain end or in the side chain.

[0050] Examples of the carbonyl-containing functional group include a carbonate group having a bond of -OC(=O)O-, and a carboxylic acid halide group having a structure of -COY [Y is a halogen element]. Among these, a carbonate group is preferable. The carbonyl-containing functional group preferably has fluorine, and a fluorine-containing carbonate group (-RF-OC(=O)-RF'-) and a carboxylic acid fluoride group (-C(=O)F) are preferable. Here, RF and RF' represent a group having fluorine, such as an alkyl fluoride group or a vinylidene fluoride group.

[0051] Moreover, the polymer 3 preferably contains a fluorovinyl compound represented by the following general formula (1) as a copolymerization component. CH2=CX 1 (CF2)nX 2 (1) In the above general formula (1), X 1 represents a fluorine atom or a hydrogen atom, and X 2 represents a fluorine atom or a hydrogen atom, and n is an integer of 1 to 10.

[0052] Examples of the fluorovinyl compound represented by the above formula (1) include CH2=CF(CF2)3H, CH2=CH(CF2)3H, CH2=CF(CF2)4H, CH2=CH(CF2)4H, CH2=CF(CF2)3CH3, CH2=CF(CF2)3C2H5, and CH2=CH(CF2)3F. Two or more of these may be used. Among these, perfluoro(1,1,5-trihydro-1-pentene) represented by the following structural formula (2) is preferred, and is excellent in productivity, cost, environmental friendliness, and transmission characteristics of plastic optical fibers.

[0053] CH2=CF(CF2)3H (2) The outermost clad preferably contains polymer 3. Although the content is not particularly limited, it is preferable that the outermost clad consists essentially of polymer 3, that is, 100% by weight of the outermost clad contains 95 to 100% by weight of polymer 3, more preferably 99 to 100% by weight, and even more preferably 100% by weight.

[0054] The melting point of the polymer 3 is preferably 150 to 200° C. The refractive index of the polymer 3 is preferably 1.37 to 1.41.

[0055] The thickness of the outermost clad layer is preferably 2 to 20 μm.

[0056] [Manufacturing method / Application] As a method for manufacturing an optical fiber, for example, when the optical fiber has a core and a cladding of a laminated structure (two layers), a composite spinning method is preferably used, in which the core and the cladding are extruded from a composite spinneret for concentric composite in a heated and molten state to form a three-layer core-sheath structure of the core / the cladding in contact with the core / the outermost cladding. If the spinning temperature is too high, the optical fiber will be colored, and if it is too low, yarn unevenness will occur, both of which cause the light transmission loss to increase, so it is necessary to set appropriate temperature conditions. Next, a drawing process is generally performed. A drawing process of 1.2 times or more is preferable because it is possible to obtain an optical fiber with a large yield point stress due to the orientation of the polymer, and a drawing process of 3 times or less is preferable because it is possible to obtain an optical fiber with a small light transmission loss due to the suppression of the orientation of the polymer.

[0057] The optical fiber of the present invention can be suitably used in medical devices, lighting devices, and ophthalmic surgical lighting probes. That is, the medical device of the present invention is a medical device having the optical fiber of the present invention, the lighting device of the present invention is a lighting device having the optical fiber of the present invention, and the ophthalmic surgical lighting probe of the present invention is a ophthalmic surgical lighting probe having the optical fiber of the present invention. Examples of medical devices include endoscopes, ophthalmic surgery, laparoscopic surgery, catheters, and the like. As for lighting devices, the optical fiber of the present invention can be used as lighting in the medical device in combination with the above-mentioned medical devices. EXAMPLES

[0058] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these.

[0059] Clad composition ratio (wt%): The clads used in the examples and comparative examples were 19 The composition ratio (wt%) was determined using F-NMR (AVANCE NEO 400 manufactured by Bruker) and FT-IR (FT-IR manufactured by Bio-Rad Digilab).

[0060] Refractive index (-) of core and clad (polymer 2): Test pieces measuring 20 mm × 8 mm × 1.4 mm were prepared from the core and clad (polymer 2) used in each of the Examples and Comparative Examples, and the refractive index was measured at room temperature (25°C) using an Abbe refractometer.

[0061] Long diameter of optical fiber (μm): For the optical fibers obtained in each of the examples and comparative examples, the diameter of the optical fiber was measured using a micrometer.

[0062] Theoretical numerical aperture of optical fiber (-): The numerical aperture was calculated from the refractive index measured by the above-mentioned method using the following formula.

[0063] Numerical aperture = ((refractive index of core)) 2 - (Refractive index of the cladding adjacent to the core) 2 ) 1 / 2 .

[0064] Optical fiber transmission loss (dB / km): For the optical fiber in a skein state obtained in each of the Examples and Comparative Examples, parallel halogen light (wavelengths 525 nm and 650 nm, incident NA = 0.25) was incident, and the light quantity A (dBm) at a position 10 m from the incident point and the light quantity B (dBm) at a position 5 m from the incident point were measured, and the transmission loss C (dB / km) was calculated from (BA) / ((10-5) / 1000).

[0065] Yield stress (N): For the optical fibers obtained in each of the examples and comparative examples, a 10 cm sample was taken and measured using a bench-top precision universal testing machine (Autograph AGS-10kNX, manufactured by Shimadzu Corporation).

[0066] Yield stress coefficient (N / mm 2): The yield stress coefficient was calculated from the yield stress measured by the above-mentioned method and the major axis of the optical fiber according to the following formula.

[0067] Formula: Yield stress coefficient = Yield stress (N) / (fiber diameter (mm)) 2 The materials used in each of the examples and comparative examples are shown below.

[0068] Core A: Polycarbonate (product name "HL8002", manufactured by Mitsubishi Engineering Plastics Corporation), Tg: 141°C, MFR: 141g / 10min Core B: Polycarbonate (product name "HL7001", manufactured by Mitsubishi Engineering Plastics Corporation), Tg: 143°C, MFR: 113g / 10min Core C: Polycarbonate (product name "LC1202", manufactured by Idemitsu Kosan Co., Ltd.), Tg: 135°C, MFR: 150g / 10min Core D: polycarbonate (product name "TX0301", manufactured by Sumika Polycarbonate Co., Ltd.), Tg: 149°C, MFR: 29g / 10min Clad A: 74.5% by weight vinylidene fluoride / 25.5% by weight tetrafluoroethylene copolymer Clad B: 40% by weight vinylidene fluoride / 40% by weight tetrafluoroethylene / 20% by weight hexafluoropropylene copolymer Clad C: 20% by weight vinylidene fluoride / 60% by weight tetrafluoroethylene / 20% by weight hexafluoropropylene copolymer Clad D: 18% by weight vinylidene fluoride / 62% by weight tetrafluoroethylene / 16% by weight hexafluoropropylene / 4% by weight perfluoropropyl vinyl ether copolymer Clad E: 20% by weight ethylene / 55% by weight tetrafluoroethylene / 25% by weight hexafluoropropylene [Example 1] The core A and the clad A as the clad in contact with the core were fed to a composite spinning machine, and the core and the clad were subjected to core-sheath composite melt spinning at a temperature of 245° C. to obtain an optical fiber having a fiber diameter of 250 μm (core diameter: 246 μm, clad thickness: 4 μm) and a theoretical numerical aperture of 0.71. The obtained optical fiber was evaluated by the above-mentioned method, and the results are shown in Table 1.

[0069] [Example 2] An optical fiber was produced in the same manner as in Example 1, except that the core was changed to B, and the results of evaluation by the above-mentioned method are shown in Table 1.

[0070] [Example 3] An optical fiber was produced in the same manner as in Example 1, except that the cladding was changed to B, and the results of evaluation by the above-mentioned method are shown in Table 1. Since the refractive index of the cladding B was smaller than the refractive index of the core by 0.18 or more, the numerical aperture was high and good.

[0071] [Example 4] An optical fiber was produced in the same manner as in Example 1, except that the cladding was changed to C, and the results of evaluation by the above-mentioned method are shown in Table 1. Since the cladding C contained 35% by weight or less of vinylidene fluoride as a copolymerization component, the optical fiber had good light transmittance.

[0072] [Example 5] Except for changing the cladding to D, an optical fiber was produced in the same manner as in Example 1, and the results of evaluation by the above-mentioned method are shown in Table 1. Cladding D contained 10 to 35% by weight of hexafluoropropylene, 45 to 75% by weight of tetrafluoroethylene, 5 to 35% by weight of vinylidene fluoride, and 1 to 15% by weight of perfluoroalkyl vinyl ether as copolymerization components, and therefore had better light transmittance.

[0073] [Example 6] The core A, clad D as the clad in contact with the core, and clad A as the outermost clad were shared in a composite spinning machine, and the core and clad were subjected to core-sheath composite melt spinning at a temperature of 245°C to obtain an optical fiber with a fiber diameter of 250 μm (core diameter: 242 μm, clad thickness in contact with the core: 4 μm, outermost clad thickness: 4 μm). The optical fiber obtained was evaluated by the above-mentioned method, and the results are shown in Table 1. Since the clad had a laminated structure, the yield stress coefficient was high and good.

[0074] [Example 7] An optical fiber was produced in the same manner as in Example 6, except that the outermost cladding was changed to E, and the results of evaluation by the above-mentioned method are shown in Table 1. Since cladding E contains ethylene as a copolymerization component, the yield stress coefficient was better.

[0075] [Examples 8 to 12] Except for changing the core and cladding as shown in Table 1, optical fibers were produced in the same manner as in Example 6. The results of evaluation by the above-mentioned method are shown in Table 1.

[0076] [Comparative Example 1] Except for changing the core to C, an optical fiber was produced in the same manner as in Example 1, and the results of evaluation by the above-mentioned method are shown in Table 1. Since the Tg of Core C was less than 137°C and the yield stress coefficient was less than 40, continuous spinning was difficult.

[0077] [Comparative Example 2] Except for changing the core to D, an optical fiber was produced in the same manner as in Example 1, and the results of evaluation by the above-mentioned method are shown in Table 1 (the light transmission loss at 525 nm was not measurable due to the small amount of light). Since the Tg of core D was higher than 147°C, the light transmission was poor.

[0078] [Comparative Example 3] An optical fiber was produced in the same manner as in Example 1, except that the core was changed to D and the spinning temperature was changed to 260°C, and the results of evaluation by the above-mentioned method are shown in Table 1. Since the Tg of Core D was higher than 147°C and the spinning temperature was high, the light transmittance at 525 nm was poor and the emitted light was yellowish.

[0079] [Table 1]

[0080] In the table, "refractive index difference" means the difference between the refractive index of the cladding and the refractive index of the core.

Claims

1. An optical fiber having a core and a cladding, The transmission loss at 525 nm is 2,500 dB / km or less, The yield stress coefficient represented by the following formula is 40 or more, The optical fiber, wherein the core contains a polymer 1 having a glass transition temperature Tg of 137° C. or higher and 147° C. or lower and a refractive index of 1.55 or higher. Formula: Yield stress coefficient = Yield stress (N) / (Fiber diameter (mm)) ２

2. The optical fiber of claim 1 , wherein said polymer 1 is a polycarbonate.

3. the clad in contact with the core comprises polymer 2; 2. The optical fiber according to claim 1, wherein the refractive index of said polymer 2 is smaller than the refractive index of the core by at least 0.

18.

4. the clad in contact with the core comprises polymer 2; 2. The optical fiber according to claim 1, wherein said polymer 2 contains 35% by weight or less of vinylidene fluoride as a copolymerization component.

5. The polymer 2 is 10 to 35% by weight of hexafluoropropylene 45 to 75% by weight of tetrafluoroethylene Vinylidene fluoride 5 to 35% by weight Perfluoroalkyl vinyl ether 1 to 15% by weight 5. The optical fiber according to claim 4, comprising as a copolymerization component:

6. The optical fiber of claim 1 , wherein the cladding is of a layered construction.

7. 7. The optical fiber according to claim 6, wherein the outermost cladding layer contains a polymer 3 containing ethylene as a copolymerization component.

8. A medical device comprising the optical fiber according to any one of claims 1 to 7.

9. A lighting device comprising the optical fiber according to any one of claims 1 to 7.

10. A probe for illumination in ophthalmic surgery, comprising the optical fiber according to any one of claims 1 to 7.