PERIPHERAL SURFACE-EMITTING LINEAR LIGHT GUIDE AND  METHOD FOR MANUFACTURING THE SAME

A peripheral surface-emitting linear light guide is provided with an optical fiber including a core, an outer peripheral surface of which is exposed from a cladding at one end in a longitudinal direction, and a light-scattering member that covers an entire periphery of the outer peripheral surface of the core in an exposed portion over a predetermined axial length range. The light emitted from the outer peripheral surface of the core is scattered and radiated by the light-scattering member. The light-scattering member includes a light transmissive base material having a higher refractive index than the core and light-scattering particles that scatter the light incident on the base material, and the light-scattering particles are dispersed and mixed in a certain proportion throughout the base material. At least a portion of the light-scattering member in the longitudinal direction is an increasing portion whose thickness increases gradually toward a tip side of the core.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on Japanese patent application No. 2022-188340 filed on Nov. 25, 2022, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a peripheral surface-emitting linear light guide with an optical fiber and a light-scattering member, and a method for manufacturing the same.

BACKGROUND OF THE INVENTION

Conventionally, e.g., catheter treatment is performed by inserting an optical fiber catheter equipped with an optical fiber into a luminal organ such as the esophagus or intestine of the human body, or into a blood vessel or heart of the human body, and treating the affected site with light emitted from the core of the optical fiber. The applicant has proposed a peripheral surface-emitting linear light guide for such catheter therapy, as described in Patent Literature 1.

The peripheral surface-emitting linear light guide described in Patent Literature 1 has an optical fiber including a cladding that is removed to expose a core, and a light-scattering member in which light-scattering particles are dispersedly mixed into a light-transmissive base material having a higher refractive index than the core, and an outer peripheral surface of the exposed core is covered by the light-scattering member. The light-scattering member consists of a plurality of layers with different mixing ratios of light-scattering particles to the base material to enhance the homogeneity of light intensity in the axial direction, and the plurality of layers overlap at least partially in the radial direction of the core. In forming this light-scattering member, multiple types of liquids with different mixing ratios of light-scattering particles are prepared, and the step of adhering these liquids to the outer periphery of the core and curing them is repeated.

CITATION LIST

SUMMARY OF THE INVENTION

Optical fiber catheters used for catheter treatment (i.e., catheterization) are disposable, and there is a need to reduce the cost of catheters. The outer peripheral surface-emitting linear light guide configured as described above required many man-hours and long processing time to form a light-scattering member having multiple layers with different mixing ratios of light-scattering particles, making it difficult to reduce the cost.

Therefore, it is an object of the present invention to provide a peripheral surface-emitting linear light guide with a configuration that enables cost reduction while increasing the homogeneity of light intensity, and a method for manufacturing the peripheral surface-emitting linear light guide.

For the purpose of solving the above problem, one aspect of the present invention provides a peripheral surface-emitting linear light guide, comprising:an optical fiber including a core, an outer peripheral surface of which is exposed from a cladding at one end in a longitudinal direction; anda light-scattering member that covers an entire periphery of the outer peripheral surface of the core in an exposed portion over a predetermined axial length range,wherein light emitted from the outer peripheral surface of the core is scattered and radiated by the light-scattering member,wherein the light-scattering member comprises a light transmissive base material having a higher refractive index than the core and light-scattering particles that scatter the light incident on the base material, and the light-scattering particles are dispersed and mixed in a certain proportion throughout the base material, andwherein at least a portion of the light-scattering member in the longitudinal direction is an increasing portion whose thickness increases gradually toward a tip side of the core.

Further, for the purpose of solving the above problem, another aspect of the present invention provides a method for manufacturing the peripheral surface-emitting linear light guide as described above, comprising:processing the optical fiber to expose the outer peripheral surface of the core from the cladding;preparing a liquid to be used as the light-scattering member;immersing the exposed core in the liquid;pulling-up the core from the liquid by moving the core and the liquid relative to each other in a vertical direction; andcuring the liquid adhered to the core,wherein, in the pulling-up step, when forming the incremental portion of the light-scattering member, a pulling-up speed is varied to gradually increase a thickness of the liquid adhering to the outer peripheral surface of the core.

ADVANTAGEOUS EFFECTS OF THE INVENTION

According to the outer peripheral surface-emitting linear light guide and the manufacturing method thereof according to the present invention, it is possible to reduce costs while increasing the homogeneity of light intensity.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment

FIG.1is a schematic diagram showing a treatment device using a peripheral surface-emitting linear light guide according to an embodiment of the present invention as a catheter, together with a patient to be treated. The treatment device1includes a main body2, and a peripheral surface-emitting linear light guide3, in which a tip of the peripheral surface-emitting linear light guide3is inserted into the body of patient P. The main body2includes a light source21that emits laser light, and the laser light emitted by the light source21enters a base end (i.e., proximal end) of the peripheral surface-emitting linear light guide3.

Configuration of the Outer Peripheral Surface-Emitting Linear Light Guide

FIG.2is a schematic diagram showing an end portion of the peripheral surface-emitting linear light guide3inserted into the body of patient P. InFIG.2, a portion of patient P's blood vessel P1is cut out to show the end portion of the peripheral surface-emitting linear light guide3inserted into blood vessel P1. The laser light Lr scattered and emitted from the peripheral surface-emitting linear light guide3irradiates the treatment site P2and reacts with the drug previously contained in the treatment site P2. This results in intravascular laser therapy.

FIG.3Ais a perspective view of one end of the peripheral surface-emitting linear light guide3.FIG.3Bis a cross-sectional view of the peripheral surface-emitting linear light guide3along the axial direction. The peripheral surface-emitting linear light guide3includes an optical fiber4that guides the laser light emitted by the light source21to the treatment site P2, and a light-scattering member5provided at one end of the optical fiber4. The optical fiber4includes a core41, a cladding42, and a sheath43. At one end of the optical fiber4in the longitudinal direction, an outer peripheral surface42aof the cladding42is exposed from the sheath43, and an outer peripheral surface41aof the core41is also exposed from the cladding42. InFIGS.3A and3B, the thickness of the light-scattering member5is exaggerated for clarity of explanation.

The light-scattering member5covers the entire outer peripheral surface41aof the core41in the portion exposed from the cladding42over a predetermined axial length range. The axial length of the core41in the portion covered by the light-scattering member5is, e.g., 3 to 7 cm. A longitudinal portion of the core41is an uncovering portion410that is not covered by either the cladding42or the light-scattering member5.

The optical fiber4in the present embodiment is a quartz glass optical fiber in which the core41is made of quartz glass and the cladding42is made of polymer. The sheath43is made of fluoropolymer, more specifically, ETFE (ethylene tetrafluoroethylene copolymer). The diameter of the core41is, e.g., 200 μm. The refractive index of the core41is higher than that of the cladding42, and light propagating in the core41in the cladding42is totally reflected off the interface with the cladding42.

The light-scattering member5scatters and radiates the light emitted from the outer peripheral surface41aof the core41. The light-scattering member5includes a light transmissive base material50having a higher refractive index than the core41, and a number of light-scattering particles500that scatter the light incident on the base material50, and the light-scattering particles500are dispersed and mixed in a certain proportion throughout the base material50. Here, dispersion-mixed at a constant ratio means that the light-scattering particles500are mixed so that the light-scattering particles500are evenly dispersed throughout the base material50so that the distribution of the light-scattering particles500is not biased to a part within the base material50. In the present embodiment, the base material50is a thermosetting resin. The light-scattering particles500are so fine that they cannot be recognized by the naked eye, but the size of the light-scattering particles500is exaggerated inFIG.3B.

The base material50has a higher refractive index than the core41, and light emitted from the outer peripheral surface41aof the core41enters the light-scattering member5. In this embodiment, the base material50is silicone resin and its refractive index is, e.g., 1.52. The refractive index of the core41is, e.g., 1.46. The light-scattering particles500are metal particles that reflect light incident on the light-scattering member5. In this embodiment, titanium oxide (TiO2) is used as the light-scattering particles500. However, the present invention is not limited thereto, and fine powders of aluminum oxide (alumina), or fine metallic powders of silver, copper, iron, or alloys thereof may also be used as the light-scattering particles500.

The light-scattering member5has an incremental portion51whose thickness gradually increases toward a tip side (i.e., distal end side) of the core41, an annular thin-walled portion52provided on the tip side of the core41relative to the incremental portion51, and a tip-covering portion53provided around the tip surface41bof the core41. The annular thin-walled portion52is formed in a thin-walled circular-cylindrical shape, and the tip-covering portion53is hemispherical. The annular thin-walled portion52is interposed between the incremental portion51and the tip-covering portion53, and the length of the annular thin-walled portion52in the longitudinal direction of the core41is shorter than the length of the incremental portion51in the same direction.

The outer diameter of the incremental portion51gradually increases from the small diameter end portion511, which is the end on the cladding42-side in the incremental portion51, to the large diameter end portion512, which is the end on the tip side of the core41. The large diameter end portion512is the thickest part where the thickness of the incremental portion51is the thickest in the direction perpendicular to the central axis C of the core41. The outer peripheral surface51aof the incremental portion51is a tapered surface inclined to the central axis C of the core41without steps. Here, “step” refers to an annular stepped shape formed by a step change in the outer diameter of the light-scattering member5.

The annular thin-walled portion52is formed thinner in thickness than the large diameter end portion512of the incremental portion51. The annular thin-walled portion52is substantially constant in thickness and is formed so that the outer peripheral surface52ais parallel to the central axis C of the core41. A circularly stepped surface51bis formed between the outer peripheral surface51aof the incremental portion51and the outer peripheral surface52aof the annular thin-walled portion52.

FIGS.4A and4Bare cross-sectional views of the peripheral surface-emitting linear light guide3in a cross-section perpendicular to the central axis C of the core41.FIG.4Ashows a cross-section of the small diameter end portion511of the incremental portion51, andFIG.4Bshows a cross-section of the large diameter end portion512of the incremental portion51.

The diameter D of the core41is, e.g., 200 μm. The thickness T1of the light-scattering member5at the small diameter end portion511is 2 μm as an example, while the thickness T2of the light-scattering member5at the large diameter end portion512is 3 μm as an example. The length L of the incremental portion51in the axial direction parallel to the central axis C of the core41(seeFIG.3B) is 55 mm as an example. In this case, the taper angle θ of the outer peripheral surface51aof the incremental portion51is 0.001 degrees (=Tan−1(0.001/55)). The thickness of the annular thin-walled portion52is, e.g., 0.5 μm.

In this embodiment, when the central axis C of the core41is straight, the angle (taper angle θ) of the outer peripheral surface51aof the incremental portion51in a direction parallel to this central axis C is substantially constant, except for minute irregularities. However, the incremental portion51need not necessarily have a constant taper angle θ, as long as the thickness of the incremental portion51increases monotonically and gradually toward the tip side of the core41.

Method for Manufacturing the Peripheral Surface-Emitting Linear Light Guide3

Next, the manufacturing method of the peripheral surface-emitting linear light guide3will be described. The method for manufacturing the peripheral surface-emitting linear light guide3includes the following steps: an optical fiber-processing step of exposing the outer peripheral surface41aof the core41from the cladding42; a preparation step of preparing a liquid to serve as the light-scattering member5; an immersion step of immersing a predetermined axial length range of the core41exposed from the cladding42into the liquid; and a pulling-up step of raising the core41and the liquid from the liquid by moving the core41and the liquid relative to each other in a vertical direction; and a curing step of curing the liquid adhered to the core41.

The liquid prepared in the preparation step has a lower viscosity at higher temperatures. When the core41is immersed in the liquid in the immersion step and when the core41is pulled up in the pulling-up step, the temperature of the liquid is adjusted in such a manner that an appropriate amount of the liquid adheres to the core41depending on the viscosity of the liquid. The viscosity of the liquid may also be adjusted with an organic solvent (e.g., toluene, acetone) for dilution.

FIGS.5A to5Care cross-sectional views showing the optical fiber-processing step. In this step, an optical fiber4having a core41, cladding42, and sheath43is prepared as shown inFIG.5A, and the sheath43is removed over a predetermined length range as shown inFIG.5B. Then, as shown inFIG.5C, the cladding42of the portion exposed from the sheath43is removed over a predetermined length range to expose the core41from the cladding42, and a portion of the exposed core41is cut. The core41can be cut by, e.g., scratching a part of the core41using a cutting tool6and folding the core41at the scratched point. The tip surface41bof the cut core41is a plane perpendicular to the longitudinal direction of the optical fiber4.

FIG.6is an explanatory diagram showing the immersion step. In the immersion step, the core41is immersed in the liquid7prepared in the preparation step with the core41hanging vertically. The liquid7is a liquid base material70, which is liquid at room temperature, in which the light-scattering particles500are dispersed and mixed. The liquid base material70is thermosetting and cured upon heating to become the solid base material50. The liquid7is contained in a bottomed cylindrical syringe81, and a heating jig82is arranged around the syringe81. The heating jig82retains the liquid7at a predetermined temperature via the syringe81in such a manner that the liquid7has a viscosity suitable for the immersion and pulling-up steps. This predetermined temperature is, e.g., 40° C.

As shown inFIG.6, the liquid surface7aof the liquid7is lower than a top surface81aof the syringe81and a top surface82aof the heating jig82, and the amount of liquid7, the height of the syringe81and the height of the heating jig82should be adjusted in such a manner that the distance between the liquid surface7aof the liquid7and the top surface81aof the syringe81in the vertical direction is greater than the length of the core41in the portion exposed from the cladding42. This means that the air in the space810in the syringe81that touches the liquid7is also heated by the heating jig82, which prevents the liquid7from being cooled from the liquid surface7a.The concentration of the light-scattering particles500in the liquid7is equivalent to the concentration of the light-scattering particles500in the light-scattering member5. This concentration is, e.g., 1 mg/mL.

FIG.7is an explanatory diagram of the pulling-up step. When forming the incremental portion51of the light-scattering member5in the pulling-up step, the pulling-up speed is varied to gradually increase the thickness of the liquid7adhering to the outer peripheral surface41aof the core41. The thickness of the adhered liquid7can be calculated by the following formula (1):

where the notations in the formula are h: thickness (m) of the liquid7adhering to the core41, η: viscosity (Pa·s) of the liquid7, U: pulling-up speed (m/s) of the core41, γ: surface tension (mn/m) of the liquid7, ρ: density (kg/m3) of the liquid7, and g: gravitational acceleration (m/s2).

As is clear from the above formula (1), the thickness of the liquid7adhering to the core41varies with the pulling-up speed of the core41, and the faster the pulling-up speed, the thicker the liquid7adhering to the core41. In this method, the core41is immersed in the liquid7with the core41hanging vertically so that the tip surface41bof the core41is vertically downward, and the core41is gradually pulled up, so the pulling-up speed is gradually increased when forming the incremental portion51of the light-scattering member5in the pulling-up step. When forming the annular thin-walled portion52and the tip-covering portion53, the pulling-up speed is reduced and the core41is raised at a lower speed.

FIGS.8A and8Bshow the results of measuring the relationship between the position of the core41, which is the reference position (0 mm) at the start of the pulling-up step, the pulling-up speed (mm/s), and the thickness (μm) of the adhered liquid7. At the time of this measurement, the pulling-up speed was 0.05 mm/s when forming the small diameter end portion511of the incremental portion51and the pulling-up speed was 0.07 mm/s when forming the large diameter end portion512, and the incremental portion51of the light-scattering member5was formed by gradually increasing the pulling-up speed from 0.05 mm/s to 0.07 mm/s. The light-scattering member5was formed by increasing the pulling speed gradually from 0.05 mm/s to 0.07 mm/s. In the pulling-up step, the pulling-up speed of core41was set at 0.002 mm/s at the 55 to 58 mm position to form the annular thin-walled portion52. As shown in this graph, by varying the pulling-up speed of core41, it is possible to control the thickness of the liquid7adhering to core41and thus the thickness of light-scattering member5.

Configuration of a Peripheral Light-Emitting Linear Light Guide3A in a Comparative Example

FIG.9shows a cross-sectional view of a peripheral light-emitting linear light guide3A in a comparative example. This peripheral surface-emitting linear light guide3A, like the peripheral surface-emitting linear light guide3in the above embodiment, includes an optical fiber4in which outer peripheral surface41aof the core41is exposed from the cladding42, and the entire outer peripheral surface41aof the core41is covered by a light-scattering member5A over a predetermined axial length range. The configuration of the light-scattering member5A is different from that of the light-scattering member5of the above embodiment.

In the peripheral surface-emitting linear light guide3A in the comparative example, the thickness of the light-scattering member5A covering the outer peripheral surface41aof the core41is constant throughout the entire axial direction. The light-scattering member5A has a number of light-scattering particles500dispersed and mixed in the base material50in the same concentration as in the above embodiment. The mixing ratio of the light-scattering particles500to the base material50in the light-scattering member5A is homogeneous throughout the entire axial direction.

Light Intensity Distribution of the Peripheral Surface-Emitting Linear Light Guide3According to the Embodiment and the Peripheral Surface-Emitting Linear Light Guide3A According to the Comparative Example

FIG.10is an explanatory diagram showing a measurement method for measuring the light intensity distribution in the axial direction of the peripheral surface-emitting linear light guide3according to the above-mentioned embodiment and the peripheral surface-emitting linear light guide3A according to the comparative example. InFIG.10, the state at the time of measurement of the peripheral surface-emitting linear light guide3is shown as an example, and the light intensity distribution is measured in the same way for the peripheral surface-emitting linear light guide3A in the comparative example.

In this measurement method, the laser light Lr emitted by the light source21is incident on the incident surface41cof the core41, and the optical power meter9, which measures the intensity of the light radiated from the light-scattering members5,5A in the radial direction of the core41, is moved in the X direction parallel to the core41to measure the light intensity at multiple X direction positions.

FIG.11is a graph showing the intensity of light radiated in the radial direction of the core41from the incremental portion51of the light-scattering member5of the peripheral surface-emitting linear light guide3of the above embodiment as a solid line, and the intensity of light radiated in the radial direction of the core41from the light-scattering member5A of the peripheral surface-emitting linear light guide3A of the comparative example as a broken line. The horizontal axis of this graph shows the position in the X-direction with the above reference position (the position of the end portion of the cladding42-side of the light-scattering member5,5A) as 0. As shown inFIG.11, the homogeneity of light intensity in the axial direction of the core41is enhanced in the peripheral surface-emitting linear light guide3according to the embodiment, compared to the peripheral surface-emitting linear light guide3A according to the comparative example. This is due to the following reasons.

The light that is emitted from the core41and enters the light-scattering members5,5A, but does not hit the light-scattering particles500and is not scattered, is reflected at the outer peripheral surface of the light-scattering members5,5A (interface with the outside) and the outer peripheral surface of the core41(interface with the light-scattering members5,5A) while propagating within the base material50. This is because the light coming from the light source21propagating through the core41has a shallow angle to the axial direction of the core41. However, when the light incident on the light-scattering members5,5A hits the light-scattering particles500, the light-scattering particles500reflect this light diffusely and the reflected light hits the outer peripheral surface of the light-scattering members5,5A at a relatively large angle. As a result, the light reflected by the light-scattering particles500is more likely to be radiated outward from the light-scattering members5,5A.

In the peripheral surface-emitting linear light guide3A of the comparative example, the thickness of the light-scattering member5A and the mixing ratio of the light-scattering particles500are homogeneous throughout the entire axial direction. The light in the core41gradually becomes weaker due to dissipation to the outside as it approaches the tip side, and the light incident on the light-scattering member5A also gradually becomes weaker. Therefore, the intensity of light radiated from the light-scattering member5A also gradually decreases toward the tip side of the core41. In other words, in the peripheral surface-emitting linear light guide3A, the light intensity distribution is such that the light intensity gradually decreases toward the tip side of the core41.

On the other hand, in the peripheral surface-emitting linear light guide3, the thickness of the incremental portion51, which is the essential portion of the light-scattering member5, increases gradually toward the tip side of the core41, so that light incident on the light-scattering member5easily returns to the core41near the small diameter end portion511, and the light incident on the light-scattering member5is easily radiated outward near the large diameter end portion512. In other words, in the peripheral surface-emitting linear light guide3, a balance between the intensity of light in the core41and the case of radiation to the outside of the light-scattering member5results in a flat overall light intensity distribution.

In the peripheral surface-emitting linear light guide3, the annular thin-walled portion52is formed by slowly pulling the core41away from the liquid surface7aof the liquid7by decreasing the pulling speed near the tip portion of the core41in the pulling-up step. This prevents a large amount of liquid7from adhering to the periphery of the tip surface41bof the core41and forming a large hemispherical resin ball due to surface tension. If a large resin ball is formed on the tip surface41bof the core41, this resin ball will contain a large amount of light-scattering particles500. If this is the case, the light intensity may become locally stronger at the resin ball, and the homogeneity of the light intensity distribution may be reduced. In other words, the annular thin-walled portion52has the function of suppressing the decrease in homogencity of light intensity.

A reflective film made of a metal with high reflectivity, such as gold or silver, may be formed on the tip surface41bof the core41, e.g., by sputtering. A black paint may also be applied to the tip surface41bof the core41. In this case, the annular thin-walled portion52and the tip-covering portion53may not be formed on the light-scattering member5. In other words, the light-scattering member5need only have at least one portion in the longitudinal direction of the core41as the incremental portion51.

FIG.12shows an example of the results of calculating the homogeneity of emission distribution, which is an index value indicating the homogeneity of the intensity of light radiated in the radial direction of the core41from the outer peripheral surface51abetween the small diameter end portion511and the large diameter end portion512of the incremental portion51, by changing the taper angle θ of the outer peripheral surface51aof the incremental portion51by increasing or decreasing the thickness of the large diameter end portion512of the incremental portion51. Here, the homogencity of emission distribution (i.e., the emission distribution homogeneity) (%) is a value obtained by multiplying the quotient obtained by dividing the minimum value of light intensity measured by an optical power meter9by the maximum value in the measurement method shown inFIG.10by 100. For example, if a liquid7with a concentration of light-scattering particles500of 1 mg/mL is used and the target value of homogeneity of emission distribution is set at 70% or more, this target can be achieved within a taper angle θ of 0.0006 degrees or more and 0.0014 degrees or less. For example, if the target value of emission distribution homogeneity is set at 75% or more, this target can be achieved within a taper angle θ of 0.0008 degrees or more and 0.0012 degrees or less.

Functions and Effects of the Embodiment

According to the embodiment described above, it is possible to increase the homogeneity of the intensity of the light radiated from the light-scattering member5A compared to the case where the thickness of the light-scattering member5A is constant, as in the case of the peripheral surface-emitting linear light guide3A in the comparative example. In addition, by adjusting the pulling-up speed of the core41in the pulling-up step, it is possible to form the incremental portion51whose thickness gradually increases toward the tip side of the core41in a single raising, thus enabling lower cost compared to the method of forming a light-scattering member having multiple layers with different light-scattering particle mixing ratios.

Summary of the Embodiments

Next, the technical concepts that can be grasped from the above-described embodiment will be described with the aid of the codes, etc. in the embodiment. However, each code in the following description does not limit the members in the scope of claims to the parts, etc. specifically shown in the embodiment.

According to the first feature, a peripheral surface-emitting linear light guide3having an optical fiber4including a core41, an outer peripheral surface41aof which is exposed from a cladding42at one end in a longitudinal direction, and a light-scattering member5, which covers an entire periphery of the outer peripheral surface41aof the core41in an exposed portion over a predetermined axial length range. The light emitted from the outer peripheral surface41aof the core41is scattered and radiated by the light-scattering member5. The light-scattering member5has a light transmissive base material50having a higher refractive index than the core41and light-scattering particles500that scatter the light incident on the base material50. The light-scattering particles500are dispersed and mixed in a certain proportion throughout the base material50. At least a portion of the light-scattering member5in the longitudinal direction is an increasing portion51whose thickness increases gradually toward a tip side of the core41.

According to the second feature, in the peripheral surface-emitting linear light guide3as described in the first feature, the outer peripheral surface51aof the incremental portion51is a tapered surface inclined to a central axis C of the core41without steps.

According to the third feature, in the peripheral surface-emitting linear light guide3described in the first feature, the light-scattering member3has, on the tip side of the core41from the incremental portion51, an annular thin-walled portion52which is thinner than a thickest portion (large diameter end portion)512of the incremental portion51.

According to the fourth feature, a method for manufacturing the peripheral surface-emitting linear light guide3according to any one of the first to third features, includes an optical fiber-processing step of exposing the outer peripheral surface41aof the core41from the cladding42; a preparation step of preparing a liquid7to be used as the light-scattering member5; an immersion step of immersing the exposed core41in the liquid7; a pulling-up step of pulling-up the core41from the liquid7by moving the core41and the liquid7relative to each other in a vertical direction; and a curing step of curing the liquid7adhered to the core41. In the pulling-up step, when forming the incremental portion51of the light-scattering member5, a pulling-up speed is varied to gradually increase a thickness of the liquid7adhering to the outer peripheral surface41aof the core41.

The above-described embodiments of the invention are not limiting the invention as claimed in the claims. It should also be noted that not all of the combinations of features described in the embodiment are essential to the solution of the technical problem of the invention.