Plastic optical fiber and medical sensor device

Abstract

The present invention provides a plastic optical fiber, wherein the plastic optical fiber has excellent noise suppression effect.　This plastic optical fiber comprises a core and a cladding, a light-shielding agent being included in a first cladding adjacent to the core, and the content of the light-shielding agent being in the range of 100-10000 ppm, and the plastic optical fiber preferably further comprises a second cladding on the outside of the first cladding. The plastic optical fiber is also suitable for use in a medical sensor device.

Description

Plastic optical fiber and medical sensor devices

[0001] The present invention relates to a plastic optical fiber and a medical sensor device.

[0002] Plastic optical fibers are superior to glass-based optical fibers in terms of processability, handling, and manufacturing costs, and are therefore used in applications such as short-distance optical signal transmission, light guides, and sensors.

[0003] A plastic optical fiber is usually composed of two layers: a core and a first cladding. The core is generally made of a polymer with excellent transparency and weather resistance, such as polymethyl methacrylate (hereinafter abbreviated as PMMA). On the other hand, the cladding must have a lower refractive index than the core in order to confine light inside the core, and fluorine-containing polymers are widely used. The condition for total reflection of light inside the core is when the propagation angle θ is equal to or smaller than the critical angle (total reflection angle) θ. ０ The critical angle (total reflection angle) θ ０ is the refractive index of the core n1 and the refractive index of the cladding n2, ０ On the other hand, the critical angle θ ０ The larger light penetrates into the cladding. The light that penetrates into the cladding is proportional to the refractive index of the cladding (n2) and the refractive index of air (n3) as sinθ １ = n3 / n2 Critical angle (total reflection angle) θ １ The total reflection occurs when the propagation angle is less than θ. The totally reflected light does not have a critical angle because the core refractive index n1 is greater than the cladding refractive index n2, and returns to the core. In general, when an optical fiber is used in a sufficiently long state for communication purposes, the light returning to the core via the cladding will reach the critical angle (total reflection angle) θ due to light scattering within the cladding or bending of the fiber. １This is not a major problem because the light propagating through the cladding is gradually attenuated as it enters the air layer. However, when used in a length of a few meters or less, such as for sensor applications, the light propagating through the cladding is detected without attenuation, which becomes noise, which has been an issue. As a plastic optical fiber that reduces this noise, an optical fiber has been proposed in which a resin layer with a higher refractive index than the first cladding layer adjacent to the core is formed as the second cladding layer (see, for example, Patent Document 1).

[0004] It has also been proposed to add a light-blocking agent to the second cladding (see, for example, Patent Document 2).

[0005] Furthermore, it has been proposed that the refractive index of the first cladding be greater than that of the second cladding, and that a light-blocking agent be added to the second cladding (for example, Patent Document 3).

[0006] JP 2003-227976 A International Publication No. 2022 / 009653 JP 2002-98864 A

[0007] However, in the method described in Patent Document 1, the refractive index of the second cladding is made larger than the refractive index of the first cladding, eliminating the critical angle (total reflection angle) between the first and second claddings, and light propagation through the first cladding is reduced. However, the second cladding has a lower refractive index than the second cladding, and being sandwiched between the first cladding and an air layer creates a problem in that a new light propagation route is created through the second cladding.

[0008] In addition, in the method described in Patent Document 2, the refractive index of the second cladding is smaller than the refractive index of the first cladding. Therefore, a critical angle (total reflection angle) exists at the interface between the second cladding and the first cladding. Light larger than the critical angle penetrates the second cladding. Because the second cladding contains a light-blocking agent, the light that penetrates the second cladding is gradually attenuated. For light smaller than the critical angle, some is absorbed by the light-blocking agent on the surface of the second cladding, but the majority of the light is totally reflected.

[0009] Furthermore, in the method described in Patent Document 3, the refractive index of the second cladding is made larger than that of the first cladding, eliminating the critical angle (total reflection angle) between the first and second claddings. As a result, light propagation through the first cladding is reduced, and light that penetrates into the second cladding is gradually attenuated. However, even with this method, noise was not completely eliminated. This suggests that when fibers are generally formed by melt spinning, a miscible layer of several tens to several hundreds of nanometers exists between each layer. Therefore, even if the refractive index of the second cladding is larger than that of the first cladding, light does not completely penetrate from the first cladding to the second cladding, and some light is reflected between the second cladding and the first cladding.

[0010] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a plastic optical fiber and a medical sensor device that are excellent in suppressing noise generated by light propagation through the cladding.

[0011] The present invention has the following configuration.

[0012] (1) A plastic optical fiber consisting of a core and a clad, wherein the first clad adjacent to the core contains a light-blocking agent, and the content of the light-blocking agent is in the range of 100 to 10,000 ppm.

[0013] (2) The plastic optical fiber according to (1), wherein the light-shielding agent contained in the first cladding is carbon black.

[0014] (3) A plastic optical fiber according to (1) or (2), further comprising a second cladding outside the first cladding.

[0015] (4) The plastic optical fiber according to (3), wherein the refractive index of the second cladding is greater than the refractive index of the first cladding.

[0016] (5) The plastic optical fiber according to (3) or (4), wherein the second cladding contains a light-shielding agent, and the content of the light-shielding agent is in the range of 100 to 10,000 ppm.

[0017] (6) A plastic optical fiber according to (5), wherein the transmittance t1 of light having a wavelength of 650 nm through the thickness of the first cladding and the transmittance t2 of light having a wavelength of 650 nm through the thickness of the second cladding satisfy the relationship t1>t2.

[0018] (7) The plastic optical fiber according to (5) or (6), wherein the light-shielding agent contained in the second cladding is carbon black.

[0019] (8) A plastic optical fiber according to any one of (5) to (7), wherein the light-shielding agent contained in the first cladding and the light-shielding agent contained in the second cladding are made of the same material, and the light-shielding agent content D1 of the first cladding and the light-shielding agent content D2 of the second cladding satisfy the relationship D1 < D2.

[0020] (9) A plastic optical fiber according to any one of (4) to (8), wherein the plastic optical fiber forming thickness T1 of the first cladding and the plastic optical fiber forming thickness T2 of the second cladding have a relationship of T1<T2.

[0021] (10) A plastic optical fiber according to any one of (1) to (9), wherein the core is made of polymethyl methacrylate, and the numerical aperture NA of the core and the first cladding is 0.65 or less.

[0022] (11) A medical sensor device having the plastic optical fiber according to any one of (1) to (10).

[0023] According to the present invention, it is possible to provide a plastic optical fiber that has an excellent effect of suppressing noise generated through the cladding. This noise suppression effect is also excellent in plastic optical fibers used for lengths of a few meters or less, such as those used in sensors, where light propagation through cracks is not sufficiently attenuated in the past and tends to become noise.

[0024] Therefore, the present invention makes it possible to provide a plastic optical fiber suitable for industrial sensors such as those used in semiconductor manufacturing equipment and automobile manufacturing equipment, and for medical sensors such as those used to measure blood oxygen levels.

[0025] Below, we will specifically explain preferred embodiments of the plastic optical fiber and the plastic optical fiber cord containing the same according to the present invention, but the present invention is not limited to the following embodiments and can be implemented with various modifications depending on the purpose and application.

[0026] A plastic optical fiber according to an embodiment of the present invention has, in that order, a core and a first cladding adjacent to the core. The first cladding is adjacent to the core and is provided to surround it. A second cladding layer may be provided on the outside of the first cladding layer, and a coating layer may be provided on the outside of the first cladding layer, or, if necessary, on the outside of the second cladding layer provided on the outside of the first cladding layer. It is preferable that the core layer, the first cladding layer, and the second cladding layer and coating layer, which are provided if necessary, are substantially concentric from the viewpoint of optical axis centering when connecting to a sensor connector.

[0027] When the plastic optical fiber of the present invention is used as a multi-core fiber, it is preferable that the first cladding adjacent to the core has a uniform thickness. Specifically, in the method for measuring the thickness of the first cladding described below, three arbitrary points on the first cladding at the interface between the first cladding and air (or the second cladding, or the coating layer described below), i.e., three arbitrary points on the outer periphery of the first cladding (three points whose central angle of the arc is in the range of 120°±10°), are selected, and the shape is preferably such that a circle can be drawn through the three points. The thickness of the first cladding is half the value obtained by subtracting the core diameter from the diameter of the drawn circle, and the core diameter is measured by the method described below. When a second cladding is present outside the first cladding, in the case of a three-layer single core, it is preferable that the second cladding also has a uniform thickness. Specifically, the shape is preferably such that a circle can be drawn by extracting any three points on the interface between the second cladding and the air (or the coating layer described below), i.e., any three points on the outer periphery of the second cladding (three points whose central angle is within the range of 120°±10°). Alternatively, the core may be a three-layer multi-core in which the second cladding layer exists outside the first cladding layer in a sea-like state. In this case, the thickness of the second cladding layer is defined as the thickness of its thinnest part.

[0028] (Core) From the viewpoint of transmittance, the core material of the plastic optical fiber of the present invention is preferably a (co)polymer containing methyl methacrylate (hereinafter sometimes abbreviated as MMA) as the main copolymerization component. Specifically, it includes polymethyl methacrylate (hereinafter sometimes abbreviated as PMMA) or a copolymer in which MMA accounts for 70% by weight or more of the copolymerization components, and examples thereof include copolymers of (meth)acrylic acid esters, (meth)acrylic acid, (substituted)styrenes, and (N-substituted)maleimides, or modified polymers such as glutaric anhydride and glutarimide obtained by polymer reaction of these. The above (co)polymer refers to both polymers and copolymers. Similarly, (meth)acrylic acid esters refer to both acrylic acid esters and methacrylic acid esters. Examples of (meth)acrylic acid esters include methyl acrylate, ethyl acrylate, ethyl methacrylate, butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, phenyl methacrylate, bornyl methacrylate, and adamantyl methacrylate. Examples of substituted styrenes include methylstyrene and α-methylstyrene. Examples of N-substituted maleimides include N-isopropylmaleimide, N-cyclohexylmaleimide, N-methylmaleimide, N-ethylmaleimide, and N-o-methylphenylmaleimide. A plurality of these copolymerization components may be used, or small amounts of other components may be used. Furthermore, stabilizers such as antioxidants may be included in an amount that does not adversely affect light transmittance.

[0029] Other polymers that can form the core, such as cycloolefin polymer (COP), cycloolefin copolymer (COC), polystyrene, polycarbonate, fluorene-containing polyester, and polymethylpentene, can also be preferably used in combination with the core and first cladding so long as the fiber numerical aperture (NA) does not exceed 0.65. If the NA exceeds 0.65, the plastic optical fiber of the present invention is prone to exhibiting high noise (S / N ratio). The S / N ratio here refers to the maximum light intensity (S) in the area inside θm / 10 from the maximum light output angle θm calculated from the fiber numerical aperture (NA) on one side, divided by the maximum light intensity (N) in the area inside θm / 10 from the maximum light output angle ±θm / 10. For example, if the maximum light emission angle is 40°, the maximum light intensity (S) in the area 4° inward from the maximum light emission angle, i.e., the area from 0 to 36°, is calculated by dividing the maximum light intensity (N) in the area from 36 to 44°.

[0030] The core diameter of the plastic optical fiber of the present invention is preferably 100 to 3000 μm. A core diameter of 100 μm or more is preferable because a sufficient amount of light can be obtained as the plastic optical fiber of the present invention. Furthermore, a core diameter of 3000 μm or less is preferable because it is a suitable size for use in sensors.

[0031] The light amount referred to here refers to the optical fiber transmission loss (dB / km) calculated by the cutback method.

[0032] (First Cladding) The plastic optical fiber of the present invention has a cladding in addition to a core, and the cladding adjacent to the core is referred to as the first cladding. When the core material is PMMA (refractive index 1.48 to 1.50), the cladding material used for the first cladding is preferably a low-refractive fluororesin from the viewpoint of NA. The fluororesin is not particularly limited, but preferred are copolymers of vinylidene fluoride units and trifluoroethylene units (refractive index 1.39 to 1.41), fluorinated acrylate polymers (refractive index 1.35 to 1.37), which have a lower refractive index than that, good adhesion to PMMA, and excellent processability, polyperfluorobutyl methacrylate (refractive index 1.36), polyperfluoroisopropyl methacrylate (refractive index 1.37), and polyhexafluoro-2-propyl methacrylate (refractive index 1.38). Furthermore, a dopant such as a fluorine-based material, such as magnesium fluoride, may be added to further lower the refractive index.

[0033] Other materials for forming the cladding include, for example, cycloolefin polymer (COP), cycloolefin copolymer (COC), polystyrene, polycarbonate, fluorene-containing polyester, and polymethylpentene. In combination with the cladding, PMMA can also be used as a resin other than fluororesin, as long as the NA does not exceed 0.65. If the core material is PMMA with a refractive index of approximately 1.49, the refractive index difference between the core and cladding is preferably in the range of 0.03 to 0.15. If the core material is a cycloolefin polymer with a refractive index of approximately 1.54, the refractive index difference between the core and cladding is preferably in the range of 0.03 to 0.15. If the core material is a fluorene-containing polyester with a refractive index of approximately 1.64, the refractive index difference is preferably in the range of 0.03 to 0.14.

[0034] The first cladding of the plastic optical fiber of the present invention is characterized by containing a light-blocking agent. Both organic and inorganic pigments can be used as the light-blocking agent, such as carbon black and titanium black. Carbon black is particularly preferable. The light to be blocked here is assumed to have a wavelength of 650 to 1000 nm, which is generally used in sensors, but this is not necessarily the case. By containing a light-blocking agent, noise propagating through the first cladding can be suppressed.

[0035] In the plastic optical fiber of the present invention, the first cladding adjacent to the core preferably contains carbon black as a light-shielding agent. The content of the light-shielding agent such as carbon black in the cladding material is preferably in the range of 100 to 10,000 ppm. When the content of the light-shielding agent such as carbon black is 100 ppm or more, noise detection is suppressed, and when the content is 10,000 ppm or less, a sufficient amount of light is emitted from the core.

[0036] The carbon black content in the cladding of an optical fiber can be identified by SEM observation. Observing the cross section of an optical fiber using an SEM allows the resin (cladding material) that makes up the cladding to be distinguished from the carbon black, allowing the area ratio of the resin and carbon black that make up the cladding to be calculated. Multiplying this area by the specific gravity of each material allows the weight ratio to be calculated. To avoid variations, it is preferable to prepare SEM samples with different cross sections and calculate the average of measurements from 10 specimens. This content identification method can be applied not only to carbon black, but also to other organic and inorganic pigments.

[0037] The thickness of the first cladding of the plastic optical fiber of the present invention is preferably 5 to 50 μm. A thickness of 5 μm or more ensures sufficient cladding functionality. Furthermore, a thickness of 50 μm or less provides a preferable size without excessive cladding thickness. (Second Cladding) The plastic optical fiber of the present invention may further include a second cladding outside the first cladding. If a second cladding is included, it is preferable that the refractive index of the second cladding be higher than that of the first cladding. This allows the second cladding to not only protect the first cladding, but also, by having a refractive index higher than that of the first cladding layer, eliminate reflection at the interface between the first and second claddings and allow light within the first cladding layer to escape to the second cladding, thereby suppressing light propagation through the first cladding. However, as mentioned above, a compatibility layer of several tens to several hundreds of nanometers formed by melt spinning exists between the first and second claddings, so light penetration from the first cladding to the second cladding layer is not 100%. The refractive index of the resin forming the second cladding is not particularly limited as long as it is larger than that of the resin forming the first cladding, but if the first cladding is a fluororesin, a resin such as PMMA or a fluororesin having a refractive index larger than that of the fluororesin forming the first cladding can be used. Also, if the first cladding is a PMMA resin, a resin such as cycloolefin or polycarbonate having a refractive index larger than that of PMMA can be used.

[0038] In principle, there is no problem if the difference in refractive index between the second cladding and the first cladding is larger than that of the second cladding, but it is preferable that it is 0.01 or more, because the refractive index of the last three digits varies depending on the raw material lot, and there is a possibility that the refractive index difference will disappear.

[0039] The second cladding of the plastic optical fiber of the present invention preferably contains a light-shielding agent. As the light-shielding agent, either an organic pigment or an inorganic pigment can be used, such as carbon black or titanium black. Of these, carbon black is preferably used.

[0040] Of the light that penetrates the second cladding, light that is less than the critical angle between the second cladding and air is reflected at the air interface, which has a lower refractive index than the second cladding. Furthermore, of this reflected light, light that is less than the critical angle between the first cladding and the second cladding is again reflected at the first cladding interface, which has a lower refractive index than the second cladding. In this way, noise due to light propagation through the cladding may occur even within the second cladding. Therefore, a light-blocking agent such as carbon black can absorb this light. Usable light-blocking agents include those exemplified as the light-blocking agent contained in the first cladding. The amount of light-blocking agent such as carbon black added is preferably in the range of 100 to 10,000 ppm. A content of 10,000 ppm or less improves the dispersibility of the light-blocking agent such as carbon black, making it possible to maintain a good fiber diameter of the plastic optical fiber.

[0041] In the plastic optical fiber of the present invention, it is preferable that the light-blocking agent contained in the first cladding and the light-blocking agent contained in the second cladding are made of the same material, and that the light-blocking agent content D1 of the first cladding and the light-blocking agent content D2 of the second cladding satisfy the relationship D1 < D2. A high carbon black content D1 in the first cladding improves the noise suppression effect, but there is a trade-off in that the amount of emitted light is reduced due to absorption by the carbon black. Therefore, it is easier to achieve both the noise suppression effect and the amount of emitted light by making the carbon black content D2 in the second cladding higher than D1. Furthermore, since the second cladding also plays a role in blocking external disturbance light, a higher concentration of carbon black improves the ability to block external disturbance light.

[0042] In addition, it is preferable that the plastic optical fiber forming thickness T1 of the first cladding of the plastic optical fiber of the present invention and the plastic optical fiber forming thickness T2 of the second cladding have the relationship T1<T2. This is because if the thickness T1 of the first cladding is thick, light scattering occurs within the first cladding, resulting in a large loss of light intensity. Therefore, if a second cladding is present, it is more effective to make the thickness of the first cladding as thin as possible and to make the thickness of the second cladding thick so that more noise can be absorbed by the second cladding.

[0043] Furthermore, it is preferable that the transmittance t1 of light with a wavelength of 650 nm through the thickness of the first cladding of the plastic optical fiber of the present invention and the transmittance t2 of light with a wavelength of 650 nm through the thickness of the second cladding satisfy the relationship t1 > t2. Here, the transmittance through the cladding thickness refers to the transmittance when each material used for the cladding is made into a film with the same thickness as the cladding. Since it is actually difficult to produce a film with the same thickness as the cladding, a 100 μm film is formed and the transmittance is measured with a spectrophotometer. The transmittance through the cladding thickness is calculated from the transmittance through the 100 μm film. If the transmittance t1 of light with a wavelength of 650 nm through the thickness of the first cladding is low, the noise suppression effect is improved, but there is a trade-off in that the amount of emitted light is reduced due to absorption by the light-blocking agent. Therefore, it is easier to achieve both the noise suppression effect and the amount of emitted light by making the transmittance t2 of light with a wavelength of 650 nm through the thickness of the second cladding lower than t1. Furthermore, the second cladding also plays a role in blocking external disturbance light, and therefore the lower the transmittance, the better the ability to block external disturbance light.

[0044] The transmittance of the cladding of an optical fiber can be directly measured using, for example, the following method. That is, an optical fiber is embedded in epoxy resin and a measurement sample is collected. For this measurement sample, a cross section perpendicular to the longitudinal direction is polished until the longitudinal length of the optical fiber is 100 μm. Using a high-definition microspectrometer, a light beam with a wavelength of 650 nm is irradiated longitudinally from the cross section to measure the transmittance of the cladding portion. This allows the transmittance of a cladding portion with a thickness of 100 μm to be obtained. The transmittance at the cladding thickness is calculated based on the obtained transmittance at the 100 μm thickness.

[0045] (Core Material) Furthermore, the core material of the plastic optical fiber of the present invention is most preferably polymethyl methacrylate, and the numerical aperture NA of the core and first cladding is most preferably 0.65 or less. While the present invention aims to suppress noise by containing a light-blocking agent in the cladding, there is a concern that the light absorption by the light-blocking agent may increase transmission loss, so polymethyl methacrylate, which has the highest transmittance, is preferred as the core material. Furthermore, from the viewpoint of noise suppression, if the numerical aperture exceeds 0.65, that is, if the light spread exceeds ±40.5°, the range in which noise is judged will widen, so it is preferable that the NA be 0.65 or less.

[0046] The type and amount of the light-shielding agent and the thickness of each clad layer may be adjusted depending on the required level of noise suppression, and it is also possible to adjust the thickness by combining these means.

[0047] (Method of Manufacturing Plastic Optical Fiber) A preferred method of manufacturing a plastic optical fiber is, for example, a composite spinning method in which raw materials for forming the core material, raw materials for forming the first cladding material, and materials for forming the optional second cladding material are each thoroughly dried under vacuum at 50 to 90°C, and then extruded from a composite spinneret for concentric composite in a heated, molten state at 200 to 300°C to form a two- or three-layer core-sheath structure of core / first cladding / second cladding (optional component). Subsequently, in order to improve mechanical properties such as breaking strength, a stretching process of about 1.2 to 3 times is generally performed to produce a plastic optical fiber.

[0048] (Cord Coating) The plastic optical fiber according to the embodiment of the present invention may have at least one coating layer on the outer layer of the aforementioned plastic optical fiber. Examples of materials for forming the coating layer include polyethylene, polypropylene, copolymers or blends thereof, olefin-based polymers containing organosilane groups, polyamide resins such as ethylene-vinyl acetate, polyvinyl chloride, polyvinylidene fluoride, nylon 12, polyester resins, nylon elastomers, polyester elastomers, urethane resins, fluororesins, and rubbers such as EPM and EPDM. The coating layer may be single-layered or multi-layered. In the case of multi-layered coatings, tension members such as "Kevlar" (registered trademark) may be inserted between the coating layers. These coating layers may contain stabilizers such as flame retardants, antioxidants, anti-aging agents, and UV stabilizers. The coating layer can be preferably formed by a conventional method, such as melt extrusion molding using a crosshead die, after first forming the plastic optical fiber by composite melt spinning.

[0049] (Plastic Optical Fiber) The plastic optical fiber of the present invention thus obtained has an excellent effect of suppressing noise propagating through the cladding. As described above, even if the plastic optical fiber does not have a length sufficient to attenuate this noise, for example, a plastic optical fiber of several meters or less, it has an excellent effect of suppressing noise generated by light propagation through the cladding, and therefore can be suitably used as a plastic optical fiber for industrial sensors such as those used in semiconductor manufacturing equipment and automobile manufacturing equipment, and for medical sensors such as those used to measure blood oxygen levels.

[0050] The present invention will be described in more detail below with reference to examples. Evaluations in each example and comparative example were carried out by the following methods.

[0051] (1) Core Diameter / First Cladding Thickness / Second Cladding Thickness The core diameter / first cladding thickness / second cladding thickness can be measured by cutting five randomly selected locations from a plastic optical fiber perpendicular to the drawing direction, polishing the cross section so that the core / first cladding / second cladding interfaces can be observed, and then observing the cross section under magnification 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 fits within the field of view and the interfaces can be observed. On the cross section, three points are selected on the boundary circle formed by the core and first cladding interface so that the central angle of each arc is within the range of 120°±10°, and the diameter of the circle drawn through the three points is defined as the core diameter. Three arbitrary points on the first cladding at the interface between the first cladding and air (or second cladding) (three points where the central angle of the arc is in the range of 120°±10°) were extracted, and the thickness of the first cladding was half the value obtained by subtracting the core diameter from the diameter of the drawn circle. Three arbitrary points on the interface between the second cladding and air (three points where the central angle of the arc is in the range of 120°±10°) were extracted, and the thickness of the second cladding was half the value obtained by subtracting the cladding diameter from the diameter of the drawn circle.

[0052] (2) Refractive Index Test pieces of 10 mm x 10 mm x 3 mm were prepared from the materials used in each of the Examples and Comparative Examples by injection molding at 250°C, and the refractive indexes were measured using an Abbe refractometer in an atmosphere at room temperature of 25°C.

[0053] (3) Numerical Aperture NA The numerical aperture was calculated from the refractive index measured by the above-mentioned method using the following formula.

[0054] Numerical aperture of core / first cladding = ((refractive index of core) ２ - (refractive index of first cladding) ２ ) １／２ .

[0055] (4) Light Transmission Loss of Plastic Optical Fiber For the optical fiber in a skein state obtained in each Example and Comparative Example, a sample was cut to a length of 5 m, and parallel halogen light (wavelength 650 nm, incident NA = 0.25) was incident on one end, and the amount of light A (dBm) emitted from the other end was measured. Next, this 5 m sample was cut to a length of 2 m, and the same parallel light was incident on the other end, and the amount of light B (dBm) emitted from the other end was measured, and the light transmission loss C (dB / km) was calculated from (B - A) / (5-2).

[0056] (5) Noise S / N Ratio The skein-wound optical fiber obtained in each example and comparative example was cut to a length of 2 m, and laser light (wavelength 650 nm, incident NA = 0.65) was incident on the end. The spot diameter was adjusted to be the fiber diameter. The light emitted from one end of the fiber was irradiated onto a LaserView-LHB (manufactured by Kokyo Co., Ltd.) screen from a position of 2.5 mm, and the light intensity distribution was measured. The maximum light intensity (S) was determined in the area from 0° to (0.9 x θm) relative to the maximum emission angle θm of the fiber NA. Meanwhile, the maximum light intensity (N) was determined in the area from 0.9 x θm to 1.1 x θm.

[0057] The S / N ratio was calculated as 1 x 10 ３ If it was above that, it was considered a pass.

[0058] (6) Materials used in Examples and Comparative Examples Material A: Acrylic polymer (PMMA) (trade name "GH-1000S", manufactured by Kuraray Co., Ltd.) The refractive index measured after injection molding was 1.49. Material B: Cycloolefin polymer (trade name "K26R", manufactured by Zeon Corporation) The refractive index measured after injection molding was 1.54. Material C: Copolymer of 74.5 wt% vinylidene fluoride / 25.5 wt% tetrafluoroethylene. The refractive index measured after injection molding was 1.40. Material D: Copolymer of 18 wt% vinylidene fluoride / 62 wt% tetrafluoroethylene / 16 wt% hexafluoropropylene / 4 wt% perfluoropropyl vinyl ether. The refractive index measured after injection molding was 1.35.

[0059] (7) Dispersion of Carbon Black Material E: Using a twin-screw extrusion melt kneader, material A and carbon black were kneaded in a ratio of 96:4 (mass ratio). Material F: Using a twin-screw extrusion melt kneader, material C and carbon black were kneaded in a ratio of 96:4 (mass ratio). Material G: Material C and material F were blended in a ratio of 39:1 (mass ratio), resulting in a carbon black content of 1,000 ppm. Material H: Material C and material F were blended in a ratio of 19:1 (mass ratio), resulting in a carbon black content of 2,000 ppm. Material I: Material C and material F were blended in a ratio of 9:1 (mass ratio), resulting in a carbon black content of 4,000 ppm. Material J: Material C and material F were blended in a ratio of 1:1 (mass ratio), resulting in a carbon black content of 20,000 ppm. Material K: Material A and Material E were blended in a ratio of 19:1 (by mass), resulting in a carbon black content of 2000 ppm. (8) Carbon Black Content In this example, the carbon black content was calculated based on the amount of raw material used. When measuring the carbon black content in the cladding using an optical fiber, the method described above was used. (9) Transmittance Measurement Each material containing carbon black was processed into a 100 μm film using a heat press, and the transmittance t100 at 650 nm was measured using a spectrophotometer UV3510 (manufactured by Hitachi, Ltd.). From this transmittance t100, the absorbance A100 at a 100 μm film thickness was calculated using the formula A = -LOG10(t100). Absorbance A follows the Beer-Lambert law, which is proportional to the optical path length, and for example, absorbance A10 at 10 μm can be calculated as A10 = A100 / 10 (when the thickness is n μm, An = A100 / (100 / n)). From this absorbance A10, transmittance t10 at a film thickness of 10 μm can be calculated as t10 = 10 to the power of -A10. Note that when measuring the transmittance of a cladding using an optical fiber, the method described above can also be used.

[0060] [Example 1] Material A as the core material and material H as the first cladding material were supplied to a composite spinning machine and subjected to core-sheath composite melt spinning at a temperature of 250°C to obtain a plastic optical fiber 1 having a fiber diameter of 260 μm (core diameter: 240 μm, first cladding thickness: 10 μm) and a theoretical numerical aperture of 0.5. Material H was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 4.8%. From this transmittance, the transmittance for a first cladding thickness of 10 μm was calculated to be 73.8%. The transmission loss of the obtained plastic optical fiber was 250 dB / km, which was good. The S / N ratio was 1.3×10 ４ It was good.

[0061] [Example 2] Material A was supplied as the core material and material I as the first cladding material to a composite spinning machine, and core-sheath composite melt-spinning was performed at a temperature of 250°C to obtain a plastic optical fiber 2 having a fiber diameter of 260 μm (core diameter: 240 μm, first cladding thickness: 10 μm) and a theoretical numerical aperture of 0.5. Material I was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 0.2%. From this transmittance, the transmittance for a first cladding thickness of 10 μm was calculated to be 54.5%. The transmission loss of the obtained plastic optical fiber was 450 dB / km, which was favorable. The S / N ratio was 3.5×10 ５ It was good.

[0062] [Example 3] Material A was used as the core material, material H as the first cladding material, and material A as the second cladding material. A composite spinning machine was used to perform core-sheath composite melt spinning at a temperature of 250°C, resulting in a plastic optical fiber 3 having a fiber diameter of 280 μm (core diameter: 240 μm, first cladding thickness: 10 μm, second cladding thickness: 10 μm) and a theoretical numerical aperture of 0.5. Material H was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 4.8%. From this transmittance, the transmittance at a first cladding thickness of 10 μm was calculated to be 73.8%. Material A was formed into a 100 μm film using a heat press machine, and the transmittance was 99.3%. From this transmittance, the transmittance at a second cladding thickness of 10 μm was calculated to be 99.9%. The resulting plastic optical fiber had a good transmission loss of 250 dB / km. The S / N ratio was 7.5×10 ３ It was good.

[0063] [Example 4] Material A was used as the core material, material H as the first cladding material, and material K as the second cladding material. A core-sheath composite melt spinning process was performed at a temperature of 250°C to obtain a plastic optical fiber 4 having a fiber diameter of 280 μm (core diameter: 240 μm, first cladding thickness: 10 μm, second cladding thickness: 10 μm) and a theoretical numerical aperture of 0.5. Material H was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 4.8%. From this transmittance, the transmittance at a first cladding thickness of 10 μm was calculated to be 73.8%. Material K was formed into a 100 μm film using a heat press machine, and the transmittance was 20.0%. From this transmittance, the transmittance at a second cladding thickness of 10 μm was calculated to be 85.1%. The resulting plastic optical fiber had a good transmission loss of 250 dB / km. The S / N ratio was 1.5×10 ６ It was good.

[0064] [Example 5] Material B as the core material and material K as the first cladding material were supplied to a composite spinning machine and subjected to core-sheath composite melt spinning at a temperature of 250°C to obtain a plastic optical fiber 5 having a fiber diameter of 260 μm (core diameter: 240 μm, first cladding thickness: 10 μm) and a theoretical numerical aperture of 0.3. Material K was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 20.0%. From this transmittance, the transmittance for a first cladding thickness of 10 μm was calculated to be 85.1%. The transmission loss of the obtained plastic optical fiber was 650 dB / km, which was good. The S / N ratio was 5.3 × 10 ４ It was good.

[0065] [Example 6] Material A was used as the core material, material G as the first cladding material, and material K as the second cladding material. A core-sheath composite melt spinning process was performed at a temperature of 250°C to obtain a plastic optical fiber 4 having a fiber diameter of 280 μm (core diameter: 240 μm, first cladding thickness: 10 μm, second cladding thickness: 10 μm) and a theoretical numerical aperture of 0.5. Material G was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 21.9%. From this transmittance, the transmittance at a first cladding thickness of 10 μm was calculated to be 85.9%. Material K was formed into a 100 μm film using a heat press machine, and the transmittance was 20.0%. From this transmittance, the transmittance at a second cladding thickness of 10 μm was calculated to be 85.1%. The resulting plastic optical fiber had a transmission loss of 200 dB / km, which was the best value. The S / N ratio was 2.5×10 ６ It was good.

[0066] [Example 7] Material A was used as the core material, material H as the first cladding material, and material K as the second cladding material. A core-sheath composite melt spinning process was performed at a temperature of 250°C to obtain a plastic optical fiber 4 having a fiber diameter of 280 μm (core diameter: 240 μm, first cladding thickness: 5 μm, second cladding thickness: 15 μm) and a theoretical numerical aperture of 0.5. Material H was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 4.8%. From this transmittance, the transmittance at a first cladding thickness of 5 μm was calculated to be 85.9%. Material K was formed into a 100 μm film using a heat press machine, and the transmittance was 20.0%. From this transmittance, the transmittance at a second cladding thickness of 15 μm was calculated to be 78.6%. The resulting plastic optical fiber had a good transmission loss of 250 dB / km. The S / N ratio was 7.5×10 ６ It was the best.

[0067] Comparative Example 1 Material A as the core material, material C as the first cladding material, and material D as the second cladding material were supplied to a composite spinning machine and subjected to core-sheath composite melt spinning at a temperature of 250°C to obtain a plastic optical fiber 6 having a fiber diameter of 280 μm (core diameter: 240 μm, first cladding thickness: 10 μm, second cladding thickness: 10 μm) and a theoretical numerical aperture of 0.5. Material C was formed into a 100 μm film using a heat press machine and the resulting transmittance was 98.0%. From this transmittance, the transmittance at a first cladding thickness of 10 μm was calculated to be 99.8%. Material D was formed into a 100 μm film using a heat press machine and the transmittance was 99.1%. From this transmittance, the transmittance at a second cladding thickness of 10 μm was calculated to be 99.9%. The resulting plastic optical fiber had a good transmission loss of 200 dB / km. The S / N ratio was 2.6×10 ２ So it was a no-go.

[0068] [Comparative Example 2] Material A as the core material, material C as the first cladding material, and material K as the second cladding material were supplied to a composite spinning machine and subjected to core-sheath composite melt spinning at a temperature of 250°C to obtain a plastic optical fiber 7 having a fiber diameter of 280 μm (core diameter: 240 μm, first cladding thickness: 10 μm, second cladding thickness: 10 μm) and a theoretical numerical aperture of 0.5. Material C was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 98.0%. From this transmittance, the transmittance at a first cladding thickness of 10 μm was calculated to be 99.8%. Material K was formed into a 100 μm film using a heat press machine, and the transmittance was 20.0%. From this transmittance, the transmittance at a second cladding thickness of 10 μm was calculated to be 85.1%. The resulting plastic optical fiber had a good transmission loss of 200 dB / km. The S / N ratio was 8.2 × 10 ２ So it was a no-go.

[0069] [Comparative Example 3] Material B as the core material and material D as the first cladding material were supplied to a composite spinning machine and subjected to core-sheath composite melt spinning at a temperature of 250°C to obtain a plastic optical fiber 8 having a fiber diameter of 260 μm (core diameter: 240 μm, first cladding thickness: 10 μm) and a theoretical numerical aperture of 0.74. Material D was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 99.1%. From this transmittance, the transmittance for a first cladding thickness of 10 μm was calculated to be 99.9%. The transmission loss of the obtained plastic optical fiber was 650 dB / km, which was good. The S / N ratio was 3.7×10 １ So it was a no-go.

[0070] Comparative Example 4: Material B as the core material, material A as the first cladding material, and material H as the second cladding were supplied to a composite spinning machine and subjected to core-sheath composite melt spinning at a temperature of 250°C, resulting in a plastic optical fiber 9 having a fiber diameter of 280 μm (core diameter: 240 μm, first cladding thickness: 10 μm, second cladding thickness: 10 μm) and a theoretical numerical aperture of 0.39. Material A was formed into a 100 μm film using a heat press machine, and the resulting transmittance was 99.3%. From this transmittance, the transmittance at a first cladding thickness of 10 μm was calculated to be 99.9%. Material H was formed into a 100 μm film using a heat press machine, and the transmittance was 4.8%. From this transmittance, the transmittance at a second cladding thickness of 10 μm was calculated to be 73.8%. The resulting plastic optical fiber had a good transmission loss of 670 dB / km. The S / N ratio was 5.4×10 ２ So it was a no-go.

[0071] Comparative Example 5: Material A was used as the core material and Material J as the first cladding material. A composite spinning machine was used to perform core-sheath composite melt spinning at a temperature of 250°C, resulting in a plastic optical fiber 10 with a fiber diameter of 260 μm (core diameter: 240 μm, first cladding thickness: 10 μm) and a theoretical numerical aperture of 0.5. Material J was formed into a 100 μm film using a heat press machine, and the transmittance was measured, but it was at the lower limit of measurement. Therefore, since the theoretical transmittance of Material H at 100 μm and the transmittance of Material J at 10 μm are theoretically the same, the transmittance of Material H at 100 μm (4.8%) was set as the transmittance at a first cladding thickness of 10 μm (4.8%). The resulting plastic optical fiber had a transmission loss of 3000 dB / km, which was unacceptable. The S / N ratio was undetectable.

[0072]

Claims

1. A plastic optical fiber comprising a core, a first cladding adjacent to the core, and a second cladding on the outside of the first cladding, wherein the first cladding and the second cladding contain a light-blocking agent, the content of the light-blocking agent contained in the first cladding is in the range of 100 to 10,000 ppm, and the transmittance t1 of light with a wavelength of 650 nm through the thickness of the first cladding and the transmittance t2 of light with a wavelength of 650 nm through the thickness of the second cladding satisfy the relationship t1 > t2.

2. 2. The plastic optical fiber according to claim 1, wherein the light-shielding agent contained in the first cladding is carbon black.

3. 3. The plastic optical fiber according to claim 1, wherein the refractive index of said second cladding is greater than the refractive index of said first cladding.

4. 3. The plastic optical fiber according to claim 1, wherein the content of the light-shielding agent contained in the second cladding is in the range of 100 to 10,000 ppm.

5. 3. The plastic optical fiber according to claim 1, wherein the light-shielding agent contained in the second cladding is carbon black.

6. 3. A plastic optical fiber according to claim 1, wherein the light-shielding agent contained in the first cladding and the light-shielding agent contained in the second cladding are made of the same material, and the light-shielding agent content D1 of the first cladding and the light-shielding agent content D2 of the second cladding satisfy the relationship D1 < D2.

7. 3. The plastic optical fiber according to claim 1, wherein a thickness T1 of the first cladding formed with a plastic optical fiber and a thickness T2 of the second cladding formed with a plastic optical fiber satisfy the relationship T1<T2.

8. 3. The plastic optical fiber according to claim 1, wherein the core is made of polymethyl methacrylate, and the numerical aperture NA of the core and the first cladding is 0.65 or less.

9. A medical sensor device comprising the plastic optical fiber according to claim 1 or 2.