JP2012118560A - Multi-core optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-core optical fiber which is high in mechanical reliability for achieving lateral irradiation in a long range, and for obtaining desired light quantity distribution in a longitudinal direction, and for achieving manufacturing with simple working.SOLUTION: A multi-core optical fiber 1H includes, at its top end, a top end working section 11 in which a plurality of groove sections 12, 13 and so on going around its periphery with cross-sections almost V-shaped are formed. The groove sections 12 and 13 and so on include: vertical faces 12a, 13a and so on formed almost vertically to cores 1d on which at least a portion of the plurality of cores 1d are opened; and inclined faces 12b, 13b and so on configured to reflect the rays of light emitted from the cores 1d opened on the first faces to the outside of a multi-core optical fiber 1H. The respective groove sections 12, 13, and so on are formed so that at least a portion of the cores 1d can be opened, the cores 1d which being arranged at the more central side of the multi-core optical fiber 1H than the cores 1d opened on the vertical faces of the groove sections adjacent to the groove sections at the rear end side of the top end working section 11 among the plurality of cores 1d.

Description

  The present invention relates to a multi-core optical fiber having a plurality of cores.

  Photodynamic therapy (PDT: Photodynamic Therapy), in which photosensitivity substance with tumor affinity is administered into the body, and then photochemical reaction is caused by irradiating the tumor tissue with a laser beam to cause metastasis and necrosis of the tumor tissue. It attracts attention as a new treatment method for cancer and the like (see, for example, Patent Document 1).

  In PDT, laser light is guided using an optical fiber, and laser light is emitted from the tip of the optical fiber to irradiate the tumor tissue. Generally, a front irradiation type optical fiber is used to irradiate light to a tumor tissue. However, for example, when the tumor tissue is in a stenosis, it may be difficult to irradiate the target tumor tissue.

  Therefore, various optical fibers processed so that light can be emitted to the side of the optical fiber have been proposed. For example, a technique is known in which a scatterer is provided on the side surface of the tip portion of a single core (monocore) optical fiber and light is scattered by the scatterer to irradiate the optical fiber in the entire lateral direction.

  In addition, the tip of the mono-core optical fiber is obliquely cut and mirrored, and the technology that enables side illumination in one direction, and the tip of the mono-core optical fiber is polished conically to enable side-by-side irradiation. The technique is also known (for example, refer nonpatent literature 1).

Japanese Patent No. 2882818

Seiko Giken Co., Ltd., “Various processed optical fibers”, [online], [Search April 3, 2007], Internet <URL: http://www.seikoh-giken.co.jp/business/fiber.html >

  In the optical fiber using the above-mentioned scatterer, since a scatterer which is a separate part is attached, complicated processing is required, and mechanical reliability is low.

  In addition, in the above-described optical fiber in which the tip is cut obliquely and mirrored, or the optical fiber in which the tip is polished into a conical shape, a mono-core optical fiber is used, so that the side irradiation is limited to a short range. . Furthermore, the light amount distribution in the longitudinal direction of the optical fiber cannot be adjusted, and a desired light amount distribution cannot be obtained.

  The present invention has been made in view of the above, and realizes a long-range side irradiation, a desired light quantity distribution in the longitudinal direction, and can be manufactured by simple processing, and has high mechanical reliability. An object is to provide an optical fiber.

  In order to achieve the above object, an invention according to claim 1 is a multi-core optical fiber having a plurality of cores, a common cladding surrounding the plurality of cores, and a jacket tube covering the periphery of the common cladding. The multi-core optical fiber includes a tip processing portion formed with a plurality of substantially V-shaped grooves that circulate around the periphery of the multi-core optical fiber, and the grooves are formed substantially perpendicular to the core. Each groove portion has a first surface in which at least a part of the core is open, and a second surface that reflects the light emitted from the core opened in the first surface toward the outside of the multi-core optical fiber. Is arranged on the center side of the multi-core optical fiber from the core opened in the first surface of the groove part adjacent to the groove part on the rear end side of the tip processed part among the plurality of cores It is formed so as to open at least part of the A.

  According to a second aspect of the present invention, in the multi-core optical fiber according to the first aspect, the core, the clad, and the jacket tube are made of glass.

  According to a third aspect of the present invention, in the multi-core optical fiber according to the first or second aspect of the present invention, the multicore optical fiber further includes a transparent protective portion provided so as to cover the periphery of the tip processed portion.

  According to a fourth aspect of the present invention, in the multi-core optical fiber according to the third aspect, the protective portion is made of a material having a refractive index higher than that of the tip processed portion.

  According to a fifth aspect of the present invention, in the multi-core optical fiber according to the third or fourth aspect, the protection part includes a scatterer for scattering light emitted from the tip processing part.

  A sixth aspect of the present invention is the multicore optical fiber according to any one of the third to fifth aspects, wherein the surface of the protection portion is processed to scatter light emitted from the tip processing portion. Is given.

  A seventh aspect of the present invention is the multicore optical fiber according to any one of the third to sixth aspects, further comprising a front irradiation preventing unit that does not transmit light and is provided in front of the distal end processing unit in the distal direction. .

  According to the present invention, it is possible to provide a multi-core optical fiber that realizes a long-range side irradiation, can obtain a desired light amount distribution in the longitudinal direction, can be manufactured by simple processing, and has high mechanical reliability. Can do.

1 is a side view showing a multicore optical fiber according to a first embodiment of the present invention. (A) is AA sectional drawing in FIG. 1, (b) is an enlarged view which shows the core arrangement | sequence in the multi-core optical fiber shown in FIG. It is a figure which shows an example of the method of forming the twist process part of the multi-core optical fiber shown in FIG. It is a side view which shows an example of the multi-core optical fiber in which the twist pitch in the twist process part is changing. (A) is the side view which shows an example of the multi-core optical fiber in which the central axis of the twist in the twist process part is changing, (b) is the figure which looked at the multi-core optical fiber shown in (a) from the front end side. It is a partial cross section side view which shows the multi-core optical fiber which concerns on the modification 1 of the 1st Embodiment of this invention. It is a partial cross section side view which shows the multi-core optical fiber which concerns on the modification 2 of the 1st Embodiment of this invention. (A) is the side view which shows the multi-core optical fiber which concerns on the 2nd Embodiment of this invention, (b) is the figure which looked at the multi-core optical fiber shown in (a) from the front end side. It is a partial cross section side view which shows the multi-core optical fiber which concerns on the modification of the 2nd Embodiment of this invention. It is a side view which shows the multi-core optical fiber which concerns on the 3rd Embodiment of this invention. It is a side view which shows the multi-core optical fiber which concerns on the 4th Embodiment of this invention.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(First embodiment)
1 is a side view showing a multi-core optical fiber according to a first embodiment of the present invention, FIG. 2 (a) is a cross-sectional view taken along line AA in FIG. 1, and FIG. 2 (b) is shown in FIG. It is an enlarged view which shows the core arrangement | sequence in a multi-core optical fiber.

  As shown in FIG. 1, the multi-core optical fiber 1 according to the first embodiment of the present invention has a twisted portion 2 formed at the tip thereof to which a twist is applied around its central axis.

  As shown in FIG. 2A, the multi-core optical fiber 1 includes an image circle 1a made of, for example, quartz glass, and a jacket tube 1b made of, for example, quartz glass provided so as to cover the periphery of the image circle 1a. Furthermore, it is comprised from the resin-made coating 1c provided so that the circumference | surroundings of this jacket pipe | tube 1b might be covered. The outer diameter of the multi-core optical fiber 1 is about 0.1 mm to 5 mm.

  As shown in FIG. 2B, the image circle 1a includes a large number of cores 1d and a common cladding 1e surrounding them. Each of the many cores 1d independently transmits light.

  In the twisted portion 2, the coating 1c in this portion is removed, and the cladding 1e including the core 1d and the jacket tube 1b are in a state in which twisting is applied around the central axis. In the twisted portion 2, the position of each core 1 d is displaced by twisting, and has a spiral shape in the longitudinal direction. The length of the twisted portion 2 can be set to about 10 mm, for example.

  In the present invention, the length of one rotation (360 °) when the multi-core optical fiber is twisted is defined as the twist pitch. Here, the twist pitch of the twisted portion 2 is preferably about 10 mm / 360 ° to 20 mm / 360 °. By setting the torsion pitch in this range, at least a part of the multiple cores 1d can radiate the transmitted light as a radiation mode to the outside of the core.

  Here, an example of a method for forming the twisted portion 2 will be described with reference to FIG. As shown in FIG. 3, the coating 1c of the multi-core optical fiber 1 is partially removed to expose the jacket tube 1b. And this exposed part used as the twist process part 2 is heated with heating sources 3, such as an oxyhydrogen flame burner. Then, the exposed portion softened by heating is twisted around the central axis C, then cooled, and one end side of the exposed portion is cut. As a result, the twisted portion 2 is formed at the tip of the multi-core optical fiber 1.

  In the multi-core optical fiber 1 shown in FIG. 1, at least a part of incident light incident on each core 1d from the rear end side shifts from the propagation mode to the radiation mode in the spiral core 1d of the twisted portion 2, Radiated out of the core from the side surface of the core 1d. Thereby, light is radiated from the side surface of the twisted portion 2 in the entire circumferential direction.

  As described above, according to the multicore optical fiber 1 according to the first embodiment, the twisted portion 2 radiates transmission light as a radiation mode from the side surface of the spiral core 1d. Light can be emitted over the entire longitudinal direction, and a long range of side illumination can be realized.

  Further, since the necessary processing is only torsion processing, the processing is easy, and there is no connection of other parts, so that the mechanical reliability is high.

  Moreover, the light quantity distribution of the emitted light in a longitudinal direction can be made into a desired light quantity distribution by changing the twist pitch in the twist process part 2 along the longitudinal direction of a multi-core optical fiber.

  For example, when the twist pitch in the twisted portion 2 is constant from the torsion start portion to the torsion end portion, a lot of light is emitted on the rear end side (light incident side) of the twisted portion, and is emitted as it advances toward the front end side. The amount of light decreases. For this reason, the light amount distribution is such that the light amount decreases as it goes to the tip.

Therefore, by making the twist pitch of the twisted portion 2 smaller on the front end side than on the rear end side, it is possible to approach a uniform light amount distribution. An example of such a multi-core optical fiber is shown in FIG. In the multi-core optical fiber 1A shown in FIG. 4, the pitch P ₁ twist the tip end of the twisting process portion 2A, it is made smaller than the pitch P ₂ torsion of the rear end side. Since light is more likely to be emitted as a radiation mode when the twisting pitch is smaller, the light amount distribution of the emitted light from the twisted portion 2A is made closer to a uniform light amount distribution in the longitudinal direction by performing as shown in FIG. be able to.

  Moreover, if the twist pitch in the twist processing part 2 is changed variously along the longitudinal direction of the multi-core optical fiber, various light quantity distributions can be obtained.

  Moreover, you may make it change the center axis | shaft of the twist in the twist process part 2 along the longitudinal direction of a multi-core optical fiber. If twisting is applied coaxially when the twisted portion 2 is formed, the core positioned near the center of the multi-core optical fiber is hardly twisted. Thus, the transmission light incident on the core that is hardly deformed does not enter the radiation mode and is emitted forward from the tip of the twisted portion 2.

  Therefore, when the twisted portion 2 is formed, the core in the vicinity of the center can be deformed by applying torsion while changing the central axis of the twist along the longitudinal direction, that is, generating shearing deviation. An example of the multi-core optical fiber formed in this way is shown in FIGS. FIG. 5A is a side view showing an example of a multi-core optical fiber in which the central axis of twisting in the twisted portion changes along the longitudinal direction, and FIG. 5B shows the multi-core shown in FIG. It is the figure which looked at the optical fiber from the front end side.

  In the twisted portion 2B of the multi-core optical fiber 1B shown in FIGS. 5A and 5B, the central axis of the twist changes along the longitudinal direction of the twisted portion 2B, which is sufficient for the core near the center. A torsion is added. Thereby, the transmission light of the core near the center can also be set to the radiation mode, and unnecessary light emitted forward can be reduced.

  Note that the jacket tube 1b may be removed from the twisted portions 2, 2A, 2B. Thereby, it can prevent that the light radiated | emitted from the core 1d is reflected by the jacket tube 1b, and can improve irradiation efficiency.

  Further, the multi-core optical fiber 1 is not limited to a silica-based fiber, and may be configured by a multicomponent glass fiber, a plastic fiber, or the like.

(Modification 1)
FIG. 6 is a partial cross-sectional side view showing a multicore optical fiber according to Modification 1 of the first embodiment. In FIG. 6, the same components as those of the multi-core optical fiber 1 shown in FIG.

  As shown in FIG. 6, the multicore optical fiber 1 </ b> C according to the modified example 1 is different from the multicore optical fiber 1 shown in FIG. 1 in that the protective portion 4 is coated around the twisted portion 2 and the tip of the twisted portion 2. It is the structure which added the front irradiation prevention part 5 provided in the direction front.

  A material that is transparent at the wavelength used is used for the protection unit 4 so as to transmit light emitted from the twisting unit 2. Further, in order to prevent the light emitted from the twisted portion 2 from being reflected by the protective portion 4, the protective portion 4 includes a material (a material constituting the jacket tube 1b, the core 1d, and the cladding 1e in the twisted portion 2). For example, a material having a higher refractive index than that of quartz glass is used. As such a material, for example, a resin having a high refractive index such as silicone or epoxy is used for the protective portion 4.

  Further, in order to improve the scattering of the light emitted from the torsion processing portion 2, a scatterer may be mixed in the protection portion 4 or a process for making the surface of the protection portion 4 uneven.

  The front irradiation prevention unit 5 prevents light emitted from the front end surface 2a of the torsion processing unit 2 from being irradiated forward, and is configured by an opaque resin, a mirror, an optical thin film, or the like at a used wavelength. .

  By doing in this way, while being able to prevent damage to the twist process part 2, it can prevent irradiating light to an unnecessary place.

(Modification 2)
FIG. 7 is a partial cross-sectional side view showing a multi-core optical fiber according to Modification 2 of the first embodiment. In FIG. 7, the same components as those of the multi-core optical fiber 1 shown in FIG.

  As shown in FIG. 7, the multicore optical fiber 1 </ b> D according to the modified example 2 is different from the multicore optical fiber 1 shown in FIG. 1 in that the protection portion 6 made of a pipe material that houses the twisted portion 2 and the twisted portion 2. This is a configuration in which a front irradiation prevention unit 7 provided at the front end of the protection unit 6 is added to face the front end surface 2a.

  The protective part 6 is a material that is transparent at the used wavelength and has a higher refractive index than the torsion processed part 2 (for example, a resin having a high refractive index such as silicone or epoxy), as in the protective part 4 of the first modification. May be mixed with a scatterer or may be processed to make the surface uneven.

  The front irradiation prevention unit 7 has a function similar to that of the front irradiation prevention unit 5 of the first modification, and is made of an opaque resin, a mirror, an optical thin film, or the like at the used wavelength.

  Even if it does in this way, the effect similar to the said modification 1 is acquired.

  In the first and second modifications, the jacket tube 1b of the twisted portion 2 may be removed, and the twist pitch and the central axis of the twist in the twisted portion 2 are along the longitudinal direction of the multicore optical fiber. It may be changed.

(Second Embodiment)
FIG. 8A is a side view showing a multi-core optical fiber according to the second embodiment of the present invention, and FIG. 8B is a view of the multi-core optical fiber shown in FIG. It is. 8A and 8B, the same components as those of the multi-core optical fiber 1 shown in FIG.

  As shown in FIGS. 8 (a) and 8 (b), the multi-core optical fiber 1E according to the second embodiment of the present invention is twisted around its central axis, and its outer diameter decreases as it advances toward the tip side. A twisted portion 8 having a conical shape is formed at the tip.

  The torsion processing portion 8 grinds the tip portion to which the twist is applied by the method described with reference to FIG. 3 in the first embodiment to a conical shape, and polishes the side surface (taper surface) by etching or the like. It is formed by doing.

  In the twisted portion 8, the position of each core 1 d is displaced by twisting and has a spiral shape extending in the longitudinal direction, and is open to the side surface of the twisted portion 8, and the rear end side of the twisted portion 8 ( As it progresses from the light incident side to the tip side, the outer core 1d is opened in order from the inner core 1d.

  The torsion pitch in the torsion processing portion 8 may be, for example, about 10 mm / 360 ° to 0.001 mm / 360 °. Thereby, the core 1d can be opened on the side surface of the twisted portion 8.

  In the multi-core optical fiber 1 </ b> E shown in FIG. 8, incident light incident on each core 1 d from the rear end side is emitted from the opening surface of each core 1 d on the side surface of the twisted portion 8. Since each of the twisted cores 1d is open toward the outer peripheral direction, light is radiated in a spiral shape from the side surface of the twisted portion 8.

  As described above, according to the multi-core optical fiber 1E according to the second embodiment, since light is emitted from the opening surface of each core 1d opened on the side surface of the twisted portion 8, the entire longitudinal direction of the twisted portion 8 is obtained. Light can be emitted over a long range, and a long range of side illumination can be realized.

  Moreover, you may change the twist pitch in the twist process part 8 along the longitudinal direction of the multi-core optical fiber 1E. Thereby, similarly to 1st Embodiment, the light quantity distribution of the emitted light in a longitudinal direction can be made into a desired light quantity distribution.

  Moreover, you may make it change the center axis | shaft of the twist in the twist process part 8 along the longitudinal direction of the multi-core optical fiber 1E. As in the first embodiment, when the twisted portion 8 is formed, twisting is performed while changing the central axis of the twist along the longitudinal direction of the multi-core optical fiber 1E, and the core near the center is also deformed. Unnecessary light emitted forward can be reduced by the core which is hardly deformed.

(Modification)
FIG. 9 is a partial cross-sectional side view showing a multi-core optical fiber according to a modification of the second embodiment. In FIG. 9, the same components as those of the multi-core optical fiber 1E shown in FIG. 8 and the multi-core optical fiber 1D shown in FIG.

  As shown in FIG. 9, the multi-core optical fiber 1F according to this modification is different from the multi-core optical fiber 1E shown in FIG. 8 in the same manner as the multi-core optical fiber 1D shown in FIG. 7 is provided.

  By doing in this way, while being able to prevent the damage of the twist process part 8, it can prevent irradiating light to an unnecessary place.

  Similar to the multi-core optical fiber 1C shown in FIG. 6, the twisted portion 8 may be protected by coating the twisted portion 8 with a transparent resin or the like at the used wavelength.

(Third embodiment)
FIG. 10 is a side view showing a multi-core optical fiber according to the third embodiment of the present invention. In FIG. 10, the same components as those of the multi-core optical fiber 1 shown in FIG.

  As shown in FIG. 10, the multi-core optical fiber 1G according to the third embodiment of the present invention is formed with a tip processing portion 10 having a conical shape whose outer diameter becomes smaller toward the tip side.

  The tip processing portion 10 is formed by grinding the tip portion of the multi-core optical fiber into a conical shape and polishing the side surface (tapered surface) by etching or the like. In the multi-core optical fiber 1G having the tip processing portion 10 formed in this way, each core 1d is open to the side surface (tapered surface) of the tip processing portion 10, and the rear end side (light (Opening side) from the outer peripheral side to the inner peripheral side 1d in order from the leading end side.

  The tip angle θ of the tip processing portion 10 is 80 to 80 so that the transmitted light of the core 1d reflected by the side surface (tapered surface) of the tip processing portion 10 is reflected in a direction substantially perpendicular to the longitudinal direction of the core 1d. 90 degrees is preferable.

  In the multi-core optical fiber 1G shown in FIG. 10, incident light incident on each core 1d from the rear end side is substantially perpendicular to the longitudinal direction of the core 1d by the side surface of the front end processed portion 10 and goes toward the center of the multi-core optical fiber 1G. Reflected in the direction. Thereby, light is radiated | emitted from the front-end | tip process part 10 to the perimeter direction.

  As described above, according to the multi-core optical fiber 1G according to the third embodiment, the transmission light of each core 1d opened on the side surface of the tip processing unit 10 is reflected by the side surface of the tip processing unit 10, thereby processing the tip processing. Light can be emitted over the entire longitudinal direction of the portion 10, and a long range of side illumination can be realized.

  In addition, like the multi-core optical fiber 1F shown in FIG. 9, the protection part 6 and the front irradiation prevention part 7 may be provided to protect the tip processing part 10. Further, similarly to the multi-core optical fiber 1C shown in FIG. 6, the tip processed portion 10 may be protected by coating the tip processed portion 10 with a transparent resin or the like at the used wavelength.

(Fourth embodiment)
FIG. 11 is a side view showing a multi-core optical fiber according to the fourth embodiment of the present invention. In FIG. 11, the same components as those of the multi-core optical fiber 1 shown in FIG.

  As shown in FIG. 11, a multi-core optical fiber 1H according to the fourth embodiment of the present invention has a tip processing portion 11 having a plurality of substantially V-shaped grooves 12, 13,. ing.

  Each of the groove portions 12, 13,... Is formed around the tip processed portion 11, and is formed to be substantially perpendicular to the longitudinal direction of the multi-core optical fiber 1H, and the vertical surfaces 12a, 13a,. , 13a,... And inclined surfaces 12b, 13b,.

  The core 1d located on the outer peripheral side is opened on the vertical surface 12a of the groove 12 formed at the rear end of the tip processed portion 11, and the vertical surface 12a is formed on the vertical surface 13a of the groove 13 adjacent to the groove 12. The core 1d on the inner peripheral side is open relative to the core 1d that is open to the center. Similarly, on the vertical surface 14 a of the groove portion 14 adjacent to the groove portion 13, the core 1 d on the inner peripheral side with respect to the core 1 d opened on the vertical surface 13 a is opened, and on the vertical surface 15 a of the groove portion 15 adjacent to the groove portion 14. The core 1d on the inner peripheral side is opened relative to the core 1d opened in the vertical surface 14a. As described above, the outer peripheral side core 1d is opened in order from the outer peripheral side core 1d toward the front end side of the front end processed portion 11.

  The tip portion of the tip processing portion 11 is ground into a conical shape. The tip angle θ of the tip processing portion 10 is preferably 80 to 90 degrees as in the third embodiment.

  In the multi-core optical fiber 1H shown in FIG. 11, incident light incident from the rear end side on each core 1d opening in the vertical surfaces 12a, 13a,... Is emitted from the vertical surfaces 12a, 13a,. The light emitted from the vertical surfaces 12a, 13a,... Is reflected by the inclined surfaces 12b, 13b,... In a direction substantially perpendicular to the longitudinal direction of the core 1d and toward the outside of the multicore optical fiber 1H.

  Further, the light incident on the core 1d located near the center of the multi-core optical fiber 1H is substantially perpendicular to the longitudinal direction of the core 1d and is centered on the multi-core optical fiber 1H by the tapered surface 16 of the tip portion of the tip processing portion 11. Reflected in the direction to go.

  As described above, according to the multicore optical fiber 1H according to the fourth embodiment, the inclined surfaces 12b, 13b,... Of the plurality of grooves 12, 13,. By reflecting the transmission light of each core 1d toward the outside of the multi-core optical fiber 1H, it is possible to realize long-range side irradiation.

  In the above description, the case where four groove portions are formed in the tip processing portion 11 has been described, but the number of groove portions is not limited thereto.

  Further, similarly to the multi-core optical fiber 1F shown in FIG. 9, the tip processing portion 11 may be protected by providing the protection portion 6 and the front irradiation prevention portion 7. Further, similarly to the multi-core optical fiber 1C shown in FIG. 6, the tip processing portion 11 may be protected by coating the tip processing portion 11 with a transparent resin or the like at the used wavelength.

1, 1A to 1H Multi-core optical fiber 2, 2A, 2B, 8 Torsion processing part 4, 6 Protection part 5, 7 Front irradiation prevention part 10, 11 Tip processing part

Claims (7)

A multi-core optical fiber having a plurality of cores, a common cladding surrounding the plurality of cores, and a jacket tube covering the periphery of the common cladding,
At the tip of the multi-core optical fiber, it is provided with a tip processing portion in which a plurality of groove portions having a substantially V-shaped cross section that circulates around the periphery of the multi-core optical fiber are formed.
The groove is formed substantially perpendicular to the core, and a first surface where at least a part of the plurality of cores opens, and light emitted from the core opened in the first surface of the multi-core optical fiber. A second surface that reflects outward,
Each of the grooves is disposed on the center side of the multi-core optical fiber with respect to the core that is open on the first surface of the groove adjacent to the groove on the rear end side of the tip processed portion among the plurality of cores. A multi-core optical fiber formed so as to open at least a part of a core.   The multi-core optical fiber according to claim 1, wherein the core, the clad, and the jacket tube are made of glass.   The multi-core optical fiber according to claim 1, further comprising a transparent protective portion provided so as to cover the periphery of the tip processed portion.   The multi-core optical fiber according to claim 3, wherein the protective part is made of a material having a refractive index higher than that of the tip processed part.   The multi-core optical fiber according to claim 3 or 4, wherein the protection part includes a scatterer for scattering light emitted from the tip processing part.   6. The multi-core optical fiber according to claim 3, wherein the surface of the protection part is processed to scatter light emitted from the tip processing part. 7.   The multi-core optical fiber according to any one of claims 3 to 6, further comprising a front irradiation preventing portion that does not transmit light and is provided in front of the tip processing portion in the tip direction.