JP2023038453A - Optical diffusion fiber and optical device having the same - Google Patents

Abstract

To provide an optical diffusion fiber which offers high light extraction efficiency.SOLUTION: An optical diffusion fiber 10 comprises a first core 11 and a second core 12 with light diffusion capability provided to be in contact with and cover the first core 11. The second core 12 includes second core bodies 121 having a refractive index greater than that of the first core 11.SELECTED DRAWING: Figure 1A

Description

The present invention relates to a light diffusing fiber and an optical device using the same.

Light diffusing fibers are used in applications such as illumination. For example, Patent Literature 1 discloses a light diffusing fiber comprising a core having a scattering structure, and a clad, a secondary coating, and a jacket provided concentrically from the inside so as to cover the core. there is

Japanese Patent No. 6483095

An object of the present invention is to provide a light diffusing fiber with high light extraction efficiency.

The present invention is a light diffusing fiber comprising a first core and a second core having a light scattering function provided so as to contact and cover the first core, wherein the second core is the It includes a second core body having a higher refractive index than the first core.

The present invention is an optical device having the light diffusing fiber of the present invention.

According to the present invention, the second core having a light scattering function provided so as to contact and cover the first core includes a second core body having a higher refractive index than the first core. Extraction efficiency can be obtained.

1 is a cross-sectional view of a light diffusing fiber according to an embodiment; FIG. 1 is a vertical cross-sectional view of a light diffusing fiber according to an embodiment; FIG. It is a figure which shows the structure of a linear light source. It is the 1st figure which shows the structure and operation|movement of the 1st modification of a linear light source. It is the 2nd figure which shows the structure and operation|movement of the 1st modification of a linear light source. It is a figure which shows the structure of the 2nd modification of a linear light source. It is a figure which shows the structure of a transmissive optical fiber stress sensor. It is a figure which shows the structure of the 1st modification of a transmissive optical fiber stress sensor. FIG. 10 is a diagram showing the configuration of a second modification of the transmission type optical fiber stress sensor; It is a figure which shows the structure of a reflection type optical fiber stress sensor. FIG. 2 illustrates spatial light collection and coupling using a light diffusing fiber according to an embodiment; It is a graph which shows the relationship between the spread angle of incident light of an Example model, and the amount of scattered light. 7 is a graph showing the relationship between the spread angle of incident light and the amount of scattered light in Comparative Example Model 1. FIG. 10 is a graph showing the relationship between the spread angle of incident light and the amount of scattered light in Comparative Example Model 2. FIG. It is a graph which shows the relationship between the position of the length direction of an Example model, and scattered light intensity. 7 is a graph showing the relationship between the position in the longitudinal direction of Comparative Example Model 1 and the scattered light intensity. 10 is a graph showing the relationship between the position in the length direction of Comparative Example Model 2 and the scattered light intensity. 7 is a graph showing the relationship between the scattered light emission angle and the scattered light intensity of the example model. 7 is a graph showing the relationship between the scattered light emission angle and the scattered light intensity of Comparative Example Model 1. FIG. 10 is a graph showing the relationship between the scattered light emission angle and the scattered light intensity of Comparative Example Model 2. FIG.

Embodiments will be described below.

1A and B show a light diffusing fiber 10 according to embodiments. This light diffusing fiber 10 is an optical component that emits scattered light from the side surface of the fiber.

A light diffusing fiber 10 according to an embodiment includes a first core 11, a second core 12, a clad 13, and a coating layer 14. As shown in FIG.

A first core 11 is provided at the center of the fiber. The cross-sectional shape of the first core 11 is circular. The diameter of the first core 11 is, for example, 10 μm or more and 2000 μm or less. The first core 11 is preferably made of a glass material. Examples of the glass material include pure quartz, quartz doped with fluorine (F) or germanium (Ge) to adjust the refractive index, and the like. The first core 11 may be made of a resin material such as acrylic resin.

The second core 12 is provided so as to contact and cover the first core 11 . The cross-sectional shape of the second core 12 is annular. The outer diameter of the second core 12 is, for example, 100 μm or more and 10000 μm or less. The second core 12 includes a matrix second core body 121 having a higher refractive index than the first core 11 and light scatterers 122 dispersed in the second core body 121 .

The second core body 121 is made of a material with a higher refractive index than the first core 11 . The second core body 121 is preferably made of a resin material. Examples of resin materials include silicone-based resins, fluorine-based resins (polytetrafluoroethylene (PTFE) resin, tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA) resin, ethylene-tetrafluoroethylene copolymer (ETFE ) resin, etc.), polyamide-based resin (nylon resin, etc.), and the like. Silicone-based resin has a high affinity with various light scatterers 122, so that the light scatterers 122 can be uniformly dispersed. Silicone-based resins have high heat dissipation properties, so they can suppress deterioration of the light scatterers 122 that are weak against heat, such as polymethyl methacrylate (PMMA) resins and polystyrene (PS) resins. Since the silicone-based resin has high adhesion to quartz, high adhesion can be obtained between the first core 11 and the second core 12 when the first core 11 is made of a glass material. Since the silicone-based resin has high light transmittance, high resistance to laser light can be obtained. For these reasons, the second core body 121 is preferably made of a silicone-based resin. When the first core 11 is formed of a glass material, following the drawing of the first core 11, the second core 12 is formed on the surface thereof, and from the viewpoint of obtaining high mass productivity and reproducibility, the More preferably, the two-core main body 121 is made of a thermosetting or ultraviolet-curing silicone resin. The second core body 121 may be made of a glass material such as pure quartz, or quartz doped with fluorine (F) or germanium (Ge) to adjust the refractive index.

The light scatterer 122 may be composed of particles of an inorganic material, an organic material, a ceramic material, or a metal material. Examples of inorganic materials include quartz. Examples of organic materials include PMMA and PS. Ceramic materials include, for example, light-transmitting TiO ₂ and the like. Metal materials include, for example, aluminum (Al) and gold (Au). The particulate light scatterer 122 may have a multi-layered structure with an air layer inside. The light scatterer 122 may be composed of fine air bubbles. The light scatterer 122 is preferably composed of one or more of these. When the second core body 121 is made of a silicone resin, the transparency is high and the light absorption is low. , from the viewpoint of good dispersibility, it is more preferable to be composed of particulates of an organic material. The light scatterer 122 having optical transparency may have a refractive index different from that of the second core body 121, and may be higher or lower.

The particle size of the light scatterer 122 is, for example, 0.1 μm or more and 30 μm or less. The particle size distribution of the light scatterer 122 may be either monodisperse with uniform particle size or polydisperse with wide particle size distribution. When the particle size distribution of the light scatterer 122 is monodisperse, the characteristic of the scattered light changes when the wavelength of the propagating light changes. Changes in characteristics can be suppressed. When the light scatterers 122 are particulate, the content of the light scatterers 122 in the second core 12 is, for example, 0.01% by mass or more and 30% by mass or less with respect to the content of the second core body 121. From the viewpoint of absorption of light by the scatterer 122 and suppression of bias in the amount of scattered light in the length direction, the content is preferably 3% by mass or less.

The second core 12 may contain a fluorescent material and/or a phosphorescent material in addition to the light scatterer 122 . The diameter, particle size distribution, and content of the phosphor and phosphor are the same as those of the light scatterer 122 . For example, when the propagating light is blue light having a wavelength of about 440 nm, the second core 12 contains a phosphor (for example, Y ₃ Al ₅ O ₁₂ :Ce ³⁺ (YAG)) that emits yellow light using this blue light as excitation light. If it is included, it is possible to obtain quasi-white light emission in which blue scattered light and yellow fluorescence are mixed. Further, if the second core 12 contains a phosphorescent body, even if the propagating light stops, phosphorescent light emission can be obtained for a while, and it can be used for evacuation display. For example, when the wavelength of the propagating light is 405 nm, the second core 12 uses a phosphorescent material (strontium aluminate (SrAl ₂ O ₄ ) system, zinc sulfide (ZnS)) that emits green light using this as excitation light. Core 12 may include.

The clad 13 is provided so as to contact and cover the second core 12 . The coating layer 14 is provided so as to contact and cover the clad 13 . Both the clad 13 and the coating layer 14 have annular cross-sectional shapes. The outer diameters of the clad 13 and the coating layer 14 are, for example, 200 μm or more and 20000 μm. The clad 13 and the coating layer 14 are preferably made of a resin material. Examples of resin materials include silicone-based resins, fluorine-based resins, acrylic-based resins, and polyamide-based resins. The resin material forming the clad 13 and the coating layer 14 is preferably a silicone-based resin or a fluorine-based resin from the viewpoint of resistance to transmission of high-power laser light, heat resistance, and outdoor weather resistance. The resin material forming the clad 13 and the coating layer 14 may have crystallinity. The refractive index of the cladding 13 is preferably lower than that of the second core body 121 , but may be higher than that of the second core body 121 . The refractive index of the coating layer 14 may be either higher or lower than that of the clad 13 . The cladding 13 and coating layer 14 may contain the same or different light scatterer as the second core 12 .

According to the light diffusing fiber 10 according to the embodiment having the above configuration, the second core 12 having a light scattering function provided so as to cover and contact the first core 11 has a refractive index higher than that of the first core 11. By including the second core main body 121 having a high .DELTA., the propagating light of the first core 11 is easily guided to the second core 12 and emitted to the outside as scattered light, so that high light extraction efficiency can be obtained. .

By the way, in a light diffusing fiber in which a high refractive index core is coated with a low refractive index clad containing a light scatterer, it is necessary to let the light propagating through the core leak into the clad and guide the light to the light scatterer for scattering. be. Therefore, it is necessary to increase the content of the light scatterers in the clad and increase the content of the light scatterer in the clad to make the interface between the core and the clad have an uneven refractive index and structure. Means are taken to turn the propagating light of the core into a radiation mode by forming a uniform portion.

However, the former method has a problem that it is necessary to prepare a dedicated light source that emits light with a large spread angle. The latter method has a problem that the amount of scattered light is uneven in the length direction of the light diffusing fiber because the amount of light absorbed by the light scatterer is large and the influence of the non-uniform portion tends to be excessive.

On the other hand, in the light diffusing fiber 10 according to the embodiment, the second core body 121 has a higher refractive index than the first core 11, and the propagating light of the first core 11 is easily guided to the second core 12. , there is no need to use a dedicated light source that emits light with a large divergence angle in order to leak light propagating through the first core 11 to the second core 12, and the high refractive index core contains a light scatterer and has a low refractive index. Unlike a clad-coated light diffusion fiber, there is no need to include many scatterers in the clad and form a non-uniform portion of refractive index or structure near the interface with the core. In the diffusion fiber 10, the content of the light scatterers 122 in the second core 12 can be made small. As a result, absorption of light by the light scatterer 122 can be suppressed, and the influence of non-uniform portions of the refractive index and structure can be reduced, so that unevenness in the amount of scattered light in the length direction can be suppressed. Moreover, since there is no restriction on the minimum content of the light scatterers 122 for the purpose of forming a non-uniform portion, a high degree of freedom in designing the light diffusing fiber 10 can be obtained.

In the light diffusing fiber 10 according to the embodiment, restrictions on the angle of light from the first core 11 to the light scatterer 122 are relaxed, and the emission angle of the scattered light fluctuates as the light propagating through the first core 11 fluctuates. Therefore, by utilizing this characteristic, it can be used for various light sources such as illumination and display, and optical devices such as optical fiber sensors.

FIG. 2 shows a linear light source 20 as an example of an optical device.

This linear light source 20 has the light diffusion fiber 10 according to the embodiment and the original light source 21 connected to one end thereof.

In this linear light source 20, the emission angle of the scattered light is controlled by changing the spread angle of the light from the original light source 21, and the scattered light is emitted as desired in the range between the solid line arrow and the broken line arrow shown in FIG. can be guided and emitted in the direction of

Here, as a method of changing the spread angle of light from the original light source 21, for example, a method of switching a plurality of original light sources 21 with different spread angles of emitted light, or a method of changing the spread angle of light using an optical component such as a lens. A method, a method of changing the incident angle from the original light source 21 to the light diffusion fiber 10, a method of connecting the original light source 21 and the light diffusion fiber 10 with another optical fiber, and applying external stress and heat to the optical fiber to change the light propagation characteristics. A method of changing the intensity, a method of applying an external stress to the light diffusing fiber 10 itself, and the like can be mentioned.

As shown in FIGS. 3A and 3B, the linear light source 20 may have a configuration in which a first source light source 211 and a second source light source 212 are connected to one end of the light diffusion fiber 10 and the other end, respectively. In this linear light source 20, as shown in FIG. 3A, the propagating light from the first primary light source 211 is emitted as scattered light, and as shown in FIG. It is possible to further emphasize the attractiveness by properly using the case where the light is emitted.

As shown in FIG. 4, the linear light source 20 may have a configuration in which the light diffusing fiber 10 is provided with a function imparting structure 22 that bends or restricts the propagating light. As a result, it is possible to obtain the effect of flickering light, the effect of increasing the attractiveness, and the like in the portion where the function-imparting structure 22 is provided.

In the above linear light source 20, since the light diffusion fiber 10 is excellent in flexibility, the light diffusion fiber 10 can be bent into an arbitrary shape and arranged. It is also possible to configure a surface light source or a three-dimensionally stacked three-dimensional light source. Furthermore, when used as display lighting, the direction of light irradiation to the exhibit can be changed without changing the installation position of the light source. When used as lighting for growing plants in agriculture, the direction of light irradiation can be changed to illuminate shadowed areas such as the undersides of leaves that are not exposed to light. When used as a guide display, a highly eye-catching display can be achieved by changing the direction of light emission. The light emitted from the primary light source 21 and the first and second primary light sources 211 and 212 may be any of visible light, infrared light, and ultraviolet light, but visible light is preferable for guidance display. .

FIG. 5 shows a transmissive optical fiber stress sensor 30, which is an example of an optical device.

This optical fiber stress sensor 30 includes a light source 31, an optical fiber 32 including a sensing section 321 having one end connected to the light source 31, a light diffusion fiber 10 according to the embodiment connected to the other end, and a light diffusion fiber 10 and a photodetector 33 provided at the output side portion of the device.

In this optical fiber stress sensor 30, the light from the light source 31 enters and propagates through the optical fiber 32, and then enters and propagates through the light diffusion fiber 10. Detect the outgoing angle distribution of the scattered light from. Then, when an external force F (lateral pressure, bending, temperature, etc.) acts on the sensing portion 321 of the optical fiber 32, the spread angle of the light propagating through the optical fiber 32 changes, and this change causes the scattered light to emerge from the light diffusion fiber 10. It appears as a change in the angular distribution, and the photodetector 33 detects the emitted angular distribution of the scattered light whose divergence angle has changed. Therefore, the external force F acting on the sensing part 321 can be measured based on the change in the emission angle distribution of the scattered light from the light diffusion fiber 10 detected by the photodetector 33 . In the same type of conventional optical fiber stress sensor, the sensing part is made of a different structure and material than the optical fiber, making optical connection difficult, and the need for a special light source according to the sensor function. There is However, this optical fiber stress sensor 30 does not have such a problem. Moreover, unlike the conventional optical fiber stress sensor, it is not necessary to form a special structure in the sensing portion. The sensing unit 321 may be provided in the vicinity of the optical fiber 32 and the light diffusion fiber 10 with a structure and arrangement that facilitates transmission of the external force F. Further, the optical fiber 32 and the light diffusion fiber 10 may be laid so as to receive the external force F directly without providing a specific structure as the sensing section 321 . In the former case, detection at a specific position is possible, and in the latter case, detection is possible in a wide area where the cable is laid. For example, the former case is effective for sensing a specific site in a living body, sensing joints of a robot, and the like. In the latter case, it is effective for sensing topographical changes in a wide area of a collapse danger zone.

Note that the sensing section 321 may be provided on the light diffusion fiber 10 . Moreover, as shown in FIG. 6A, a plurality of sensing portions 321 may be provided, and the entire length of the optical fiber 32 may constitute the sensing portion 321 . Furthermore, as shown in FIG. 6B, multiple units of the optical fiber 32, the light diffusion fiber 10, and the photodetector 33 may be connected in series.

FIG. 7 shows a reflective optical fiber stress sensor 30 as an example of an optical device.

This optical fiber stress sensor 30 includes a light source 31, a light diffusion fiber 10 according to an embodiment having one end connected to the light source 31, an optical fiber 32 including a sensing part 321 connected to the other end, and a light diffusion fiber It has first and second photodetectors 331 and 332 respectively provided at the output side portion and the incident side portion of 10 and a reflecting mirror 34 provided at the output end of the optical fiber 32 .

In this optical fiber stress sensor 30, the light from the light source 31 enters the light diffusion fiber 10 and propagates in the traveling direction, enters the optical fiber 32, propagates, and is reflected by the reflecting mirror 34. After that, after propagating through the optical fiber 32 in the backward direction, the light is incident on the light diffusion fiber 10 and propagated, and the first photodetector 331 detects the scattered light of the light from the light source 31 propagating in the advancing direction. Along with detecting the emission angle distribution, the second photodetector 332 detects the emission angle distribution of scattered light from the optical fiber 31 propagating in the backward direction. When an external force F (lateral pressure, bending, temperature, etc.) acts on the sensing portion 321 of the optical fiber 32, the spread angle of the propagating light of the optical fiber 32 changes, and this change causes the light diffusion fiber of the light propagating backward. The second photodetector 332 detects the emission angle distribution of the scattered light whose divergence angle has changed. On the other hand, the first photodetector 331 detects the emission angle distribution of the light source 31 itself, which is not affected by the external force F. The external force F acting on the sensing part 321 can be measured based on the difference in the emission angle distribution of the scattered light. The propagating light of the optical fiber 32 propagates back and forth in the traveling direction and the backward traveling direction, and is greatly affected by the external force F acting on the sensing section 321 . As a result, high detection sensitivity for the external force F can be obtained. A plurality of sensing units 321 may be provided in this reflection type optical fiber stress sensor 30 as well. Also, the entire area of the entire length of the optical fiber 32 may constitute the sensing section 321 .

Since the light diffusing fiber 10 according to the embodiment has a wide range of emission angles of scattered light, it is easy to condense and combine spatial light as shown in FIG. has a structure with high coupling efficiency, and couples and emits the condensed spatial light. Therefore, by constructing and using a planar structure in which the light diffusion fibers 10 are arranged two-dimensionally, a three-dimensional structure in which the light diffusion fibers 10 are arranged three-dimensionally, or an arbitrary curved surface structure utilizing flexibility, An efficient optical coupling device can be constructed. The lights from the plurality of light diffusion fibers 10 can be combined using optical components such as optical couplers, lenses, and mirrors. Moreover, the spatial light may be any of visible light, infrared light, and ultraviolet light.

In the above embodiment, the single first core 11 having a circular cross-sectional shape is provided at the center of the fiber. It may be polygonal or the like, a plurality of first cores may be provided, and the first cores may be provided eccentrically from the center of the fiber.

In the above embodiment, the second core 12 is configured to include the light scatterer 122, but is not particularly limited to this. It may be formed of a resin material having crystallinity such as resin and have a light scattering function.

A simulation performed using optical design analysis software (Zemax OpticStudio manufactured by Zemax) will be described.

A light diffusing fiber in which a first core, a second core, and a clad are provided concentrically in order from the inside, wherein the second core has a higher refractive index than the first core, and the light scatterer is uniform in the second core body. The example model was the one with a configuration in which the components were dispersed. In the light diffusing fiber of the example model, the diameter of the first core is 100 μm and the refractive index is 1.45, the outer diameter of the second core is 200 μm and the refractive index of the second core body is 1.50, and the outer diameter of the clad is 700 μm and a refractive index of 1.40, and the particle size of the light scatterer was 2 μm and a refractive index of 1.49.

The refractive index of the second core body is 1.40, so that the refractive index of the second core body is lower than that of the first core, and the doping concentration of the light scatterer is increased so that 25% of the refractive index of the first core is Comparative Example Model 1 was a light diffusing fiber having the same configuration as that of the Example Model except that the light scatterers were unevenly distributed at the interface between the first core and the second core so as to be in contact with .

A light diffusing fiber having the same configuration as the example model except that the refractive index of the second core body is 1.40, and thus the refractive index of the second core body is lower than that of the first core, is used as a comparative model. 2.

In the simulation, we simulated incident visible light having a unimodal Gaussian-shaped intensity distribution in both the horizontal and vertical directions for the light diffusion fiber of each model. The amount and intensity of light scattered sideways from the diffusion fiber and the angle of emergence were analyzed. The simulation was performed when the content of the light scatterer in the second core was changed in three levels of content A to C (A<B<C), and when the divergence angle of the incident light was changed.

9A to 9C show the relationship between the spread angle of incident light and the amount of scattered light in the example model and comparative example models 1 and 2, respectively.

According to FIG. 9A, in the example model, even if the divergence angle of the incident light changes, the amount of scattered light changes little in any of the contents A to C of the light scatterers, especially when the divergence angle is small. It can also be seen that a stable amount of scattered light can be obtained. For this reason, if the light diffusing fiber has the same configuration as the embodiment model, it is necessary to prepare a light source that emits light with a large divergence angle exceeding the critical angle of the interface between the first core and the second core. Also, there is no need to add a light scatterer in high concentration to form a non-uniform portion of refractive index or structure at the interface between the first core and the second core.

According to FIG. 9B, in Comparative Example Model 1, when the divergence angle of incident light changes, the amount of scattered light also changes greatly.

According to FIG. 9C, even in Comparative Example Model 2, when the divergence angle of incident light changes, the amount of scattered light also changes greatly. I know you can't.

FIGS. 10A to 10C show the relationship between the position in the longitudinal direction and the scattered light intensity of the example model and comparative example models 1 and 2, respectively.

According to FIG. 10A, in the embodiment model, the scattered light intensity increases along the length direction from the light source 32 side regardless of the spread angle of the incident light. This indicates that light gradually leaks from the first core to the second core along the length direction and scattered light is emitted, thereby making the scattered light intensity uniform along the length direction. be.

According to FIG. 10B, it can be seen that in Comparative Example Model 1, the scattered light intensity is high in the range of 150 mm to 300 mm from the light source. It is presumed that the uneven portion of the interface between the first core and the second core excessively affects the waveguide mode of the first core.

According to FIG. 10C, it can be seen that the scattered light intensity is high in the range of 150 mm to 200 mm from the light source even in the comparative example model 2. In addition, in the comparative example model 2, it can be seen that it is necessary to use incident light with a large divergence angle.

11A to 11C show the relationship between the scattered light emission angle and the scattered light intensity of the example model and comparative example models 1 and 2, respectively. In addition, the emission angle of the scattered light is the angle from the direction perpendicular to the length direction. In addition, the output angle from about 88° to 90° is mainly the transmission mode angle of the propagating light of the first core.

According to FIG. 11A, in the example model, regardless of the spread angle of the incident light, scattered light exists in a width of about 30° from the minimum output angle of 60°, and when the spread angle of the incident light changes, , the component distribution of the emission angle of the scattered light changes. Specifically, when the divergence angle of incident light is small, there are many components with large output angles, but when the divergence angle of incident light is large, components with small output angles increase. The variable width of the emission angle can be adjusted by adjusting the refractive index and size of the first and second cores, the particle size of the light scatterer, and the like.

According to FIG. 11B, even in the comparative example model 1, when the divergence angle of the incident light changes, the component distribution of the emission angle of the scattered light changes, but the variable range is smaller than in the example model.

According to FIG. 11C, in the comparative example model 2, even if the spread angle of the incident light changes, the component distribution of the emission angle of the scattered light hardly changes.

INDUSTRIAL APPLICABILITY The present invention is useful in the technical field of light diffusion fibers and optical devices using the same.

10 Light Diffusion Fiber 11 First Core 12 Second Core 121 Second Core Body 122 Light Scattering Body 13 Cladding 14 Coating Layer 20 Linear Light Source (Optical Device)
21 original light source 211 first original light source 212 second original light source 22 function imparting structure 30 optical fiber stress sensor (optical device)
31 light source 32 optical fiber 321 sensing unit 33 photodetector 331 first photodetector 332 second photodetector 34 reflecting mirror

Claims (5)

A light diffusing fiber comprising a first core and a second core having a light scattering function provided so as to contact and cover the first core,
The light diffusing fiber, wherein the second core includes a second core body having a higher refractive index than the first core. The light diffusing fiber according to claim 1,
A light diffusing fiber, wherein the second core includes light scatterers dispersed in the second core body. In the light diffusion fiber according to claim 1 or 2,
A light diffusing fiber further comprising a clad provided to contact and cover the second core. In the light diffusion fiber according to any one of claims 1 to 3,
A light diffusion fiber, wherein the first core is made of a glass material and the second core is made of a resin material. An optical device comprising the light diffusing fiber according to any one of claims 1 to 4.

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