JP2005215632A - Hollow fiber for laser energy transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser energy transmission hollow fiber which is used to transmit laser light beams having high peak power over a long distance. <P>SOLUTION: The core is made into a hollow region in the laser energy transmission hollow fiber. The fiber is provided with a hollow core 12 having a diameter that is equal to one hundred times the propagation light beam wavelength or larger, and a solid section 11 which surrounds the hollow core 12. A plurality of air holes 13 is formed in the solid section 11 and extended along the fiber longitudinal direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a transmission medium suitable for transmission of high-power, short-pulse laser light, and more particularly to a hollow fiber for laser energy transmission.

  Development of various applications using laser energy with high peak power has become active due to higher output and shorter pulses of semiconductor lasers and solid-state lasers. In particular, it has attracted attention in the fields of display, processing of substrates in the field of semiconductors, laser knife and chemical analysis in the fields of medicine and biotechnology.

  As shown in FIG. 5, conventionally, a large-diameter silica-based optical fiber 50 has been used to transmit high-power laser light. This is because, like an optical fiber used for optical communication, a solid core region 52 having a relatively high refractive index by adding a doping material such as germanium, and a clad having a refractive index lower than that of the core region 52 The optical power is concentrated and transmitted to the core region 52 while satisfying the total reflection condition at the boundary with the region 51. Such a silica-based optical fiber 50 can transmit laser light having a wavelength of approximately 2 μm or less over a long distance with low loss. The difference from a normal optical communication optical fiber is that there is no need for single mode transmission, and the power density of laser light to be transmitted is lowered by using a core with a large diameter of about 100 to 200 μm.

  When laser light is confined and transmitted in a certain region, a transmission path is generally formed in which a region having a high refractive index and a region having a low refractive index surrounding it are formed and guided by total reflection.

  However, the leaky waveguide 60 as shown in FIG. 6 (see Non-Patent Document 1) developed by the present inventors or a dielectric-incorporated metal hollow as shown in FIG. There is a waveguide 70 (see Non-Patent Document 2).

  The leaky waveguide 60 is composed of a ring-shaped dielectric layer 61 surrounding the hollow core region 62. By optimizing the thickness of the dielectric layer 61, low-loss transmission of laser energy becomes possible.

The dielectric-embedded metal hollow waveguide 70 includes a ring-shaped dielectric layer 71 and a metal layer 72 that surrounds the outer periphery thereof, and a hollow core region 73 is formed inside the dielectric layer 71. The thickness of the dielectric layer 71 is optimized depending on the wavelength of the laser beam to be transmitted, and it is sufficient that the thickness of the metal layer 72 as the lossy medium is equal to or greater than the skin depth of the laser beam. Thus, even in a hollow waveguide in which the dielectric layer 71 having an appropriate thickness is housed inside the metal layer 72 having a large complex refractive index, low loss transmission of laser energy is possible. The dielectric-embedded metal waveguide 70 has been demonstrated to transmit high-power laser energy with relatively low loss, and is mainly used as a transmission path for a CO ₂ laser and an Er-YAG laser for laser processing and medical use. It has been developed for the purpose of laser scalpels.

  The leaky waveguide 60 and the dielectric-incorporated metal waveguide 70 are mainly intended for transmission in an infrared wavelength band where a silica-based optical fiber cannot be used.

Japanese Patent Laid-Open No. 9-159845 JP 2000-35521 A Miyagi et al., “Transmission Characteristics of Dielectric Tube Leaky Waveguide”, I Triple E, Transaction on Microwave Theory and Technics (IEEE, Trans. Microwave Theory Tech.), 1980 June, 28, 6, 536-541 Miyagi et al. “Transmission Characteristics of Germanium Thin-Films-coated Metallic Hollow Waveguides for High-Powered CO2 Laser Light”, Eye Triple E, J. Quantum Electrin. (IEEE, J.Quantum Electrin.), September 1990, Vol. 28, No. 9, p. 1510-1515

  In general, a silica-based optical fiber can perform low-loss transmission with respect to light having a wavelength of 2 μm or less.

  However, even in the case of a short wavelength laser such as an Nd-YAG laser having a wavelength of 1.06 μm or a semiconductor laser having a wavelength of 0.85 μm, the peak power is spatially or temporally high in the case of a high output, short pulse laser beam. When it becomes very large, the self-focusing action of the laser energy works due to the nonlinear optical effect, and the core region is destroyed. Further, when a foreign substance adheres to the fiber end face, end face destruction occurs.

  Therefore, the solid core laser energy transmission optical fiber 50 is used in a range in which the core diameter is increased and the optical fiber breakdown threshold is not exceeded, and the laser energy transmission capacity and transmission distance are limited. is there.

  In addition, the leaky waveguide 60 as shown in FIG. 6 has a low loss in theory, but since the thickness of the solid portion 61 is as thin as a wavelength and is not a structure capable of maintaining mechanical strength, it is practically realized. Strict.

  Furthermore, the dielectric-embedded metal hollow waveguide 70 as shown in FIG. 7 uses a metal as a part of the material, and a manufacturing method based on a drawing technique such as a normal silica-based optical fiber cannot be applied. The length that can be transmitted is only a few meters.

  Accordingly, an object of the present invention is to provide a hollow fiber for laser energy transmission that solves the above-described problems and enables long-distance transmission of laser light having high peak power.

  In order to achieve the above object, an invention according to claim 1 is an energy transmission hollow fiber comprising a hollow core having a diameter of 100 times or more of a transmission light wavelength, and a solid portion surrounding the hollow core. It is a hollow fiber for laser energy transmission in which a plurality of holes extending in the longitudinal direction of the fiber are formed.

  The invention according to claim 2 is the hollow fiber for laser energy transmission according to claim 1, wherein the holes are provided on a circumference centered on the center of the hollow core.

  The invention according to claim 3 is the hollow fiber for laser energy transmission according to claim 1 or 2, wherein the holes are formed at equal intervals on a circumference centered on the center of the hollow core.

  The invention according to claim 4 is the hollow fiber for laser energy transmission according to any one of claims 1 to 3, wherein the holes are formed on two or more concentric circles centered on the center of the hollow core.

  The invention according to claim 5 is the hollow fiber for laser energy transmission according to claim 4, wherein the inner and outer holes formed on concentric circles having different diameters are aligned in the radial direction.

  The invention according to claim 6 is characterized in that adjacent inner and outer holes formed on concentric circles having different diameters are aligned at radial positions passing through the middle between adjacent holes in the circumferential direction. The hollow fiber for laser energy transmission according to claim 4.

In the invention of claim 7, the distance δ _s between the hollow core side in the radial direction of the holes arranged on the same circumference and the outer periphery of the hollow core is expressed as follows: n _s is the refractive index of the solid part, λ is the wavelength of the propagating light , Where m is an integer greater than or equal to 0,

  The hollow fiber for laser energy transmission according to claim 1, wherein:

In the invention of claim 8, when the distance δ _ss between adjacent holes inside and outside the concentric circles is λ, the wavelength of the propagating light is λ, the refractive index of the solid part is n _s , and m is an integer of 0 or more,

  The hollow fiber for laser energy transmission according to any one of claims 4 to 7, wherein:

In the invention of claim 9, when the hole has a radial width δ ₀ of a circle centered on the center of the hollow core, the wavelength of propagating light is λ, and m is an integer greater than or equal to 0,

  The hollow fiber for laser energy transmission according to claim 1, wherein:

  A tenth aspect of the present invention is the hollow fiber for laser energy transmission according to any one of the first to ninth aspects, wherein the hole has a circular, oval or polygonal cross-sectional shape.

  The invention of claim 11 is the laser energy transmitting hollow fiber according to any one of claims 1 to 10, wherein the material forming the solid portion is quartz.

  According to the present invention, an excellent effect that high-power, short-pulse light can be transmitted over a long distance is exhibited.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1A is a cross-sectional view showing a laser energy transmission hollow fiber 10 according to a first embodiment of the present invention, and FIG. 1B is a refractive index distribution diagram thereof.

  As shown in FIG. 1A, a hollow fiber 10 for laser energy transmission is formed with a cylindrical solid portion 11 made of pure quartz so as to surround a cylindrical hollow core 12, and the solid portion 11 A plurality of holes 13 are formed in the vicinity of the hollow core 12 side. The air holes 13 are arranged on the circumference centered on the center O of the hollow core and at equal intervals in the circumferential direction, extend in the fiber longitudinal direction, and have a circular cross-sectional shape.

As shown in FIG. 1B, the refractive index distribution in the radial line r passing from the center O of the hollow core 12 to the center of the hole 13 becomes a distribution line 17, and the hollow core 12 and the hole 13 are Since it is air, its refractive index n ₀ is approximately 1, and since the solid part 11 is made of pure quartz, its refractive index n _s is approximately 1.48.

In FIG. 1B, δ _s is the distance between the hollow core outer periphery (boundary between the hollow core 12 and the solid part 11) 14 and the radial direction of the hollow core 13 (the hollow core outer periphery 14 and the void). Represents the shortest distance from the outer periphery 15), and δ ₀ represents the diameter of the hole 13.

  The diameter 2R of the hollow core region 12 may be at least 100 times the wavelength λ of the transmitted light. In the present embodiment, since the light propagating through the hollow fiber 10 is emitted from the Nd-YAG laser having a wavelength of 1.06 μm, the diameter of the hollow core region 12 is 200 μm.

The distance δ _s between the hollow core outer periphery 14 and the hole 13 substantially satisfies the following equation (1) when the propagation light wavelength λ and the refractive index of the solid portion 11 are n _s (hereinafter “substantially satisfy” is: It shall be within ± 10% of the value).

In the present embodiment, the propagation light wavelength λ is 1.06 μm, the refractive index n _s of the solid portion 11 is 1.48, m = 0, and δ _s is 0.24 μm from Equation (1).

The hole diameter (diameter) δ ₀ substantially satisfies the following expression (2).

  In this embodiment, the propagation light wavelength λ is 1.06 μm, m = 2, and the hole diameter is 1.3 μm from the equation (2).

  The operation of the present embodiment will be described.

  The hollow fiber 10 is a fiber having a leak structure in which the core (hollow core 12) that confines light has a refractive index much smaller than that of the clad (solid portion 11), and interference reflection between the hollow core outer periphery 14 and the hole outer periphery 15 occurs. Light transmitted by repetition is confined in the hollow core 12, and the hollow core 12 is used as a propagation region.

When the diameter of the hollow core 12 is sufficiently larger than the wavelength of light to be transmitted, when the distance δ _s substantially satisfies the equation (1) in the radial line r, the hollow core outer periphery 14 and the hole outer periphery 15 When the phase of the light reflected to the 12 side interferes, it is in phase. At this time, the intensity of light reflected by the hollow core 12 is maximized (reflectance is maximized). Therefore, the light confinement effect in the hollow core 12 is maximized, and low-loss transmission of light propagating through the hollow core 12 is enabled.

  In the hollow fiber 10 of the present embodiment, since most of the laser energy propagates through the hollow core 12, self-focusing is performed on a high-power, short-pulse laser beam having a very large spatial or temporal peak power. There is no destruction of the core due to action or foreign matter adhesion, and the destruction threshold is much higher than that of a solid core optical fiber.

  In addition, the solid portion 11 surrounding the hollow core 12 is formed only of a dielectric such as quartz. However, since the solid portion 11 has a structure having a sufficient thickness to maintain mechanical strength, it is damaged by an external force. Can be prevented.

  Furthermore, since a silica-based material is used, a drawing technique used when manufacturing a silica-based optical fiber for long-distance communication can be applied, and a long laser energy transmission hollow fiber can be easily manufactured. Therefore, long-distance transmission of high-power, short-pulse laser light is possible.

  All the loss in the hollow fiber 10 is converted into heat, but the solid part 11 of the hollow fiber 10 is formed of pure quartz having a very high melting point of 1000 ° C. or higher, and thus has excellent heat resistance.

  Next, the laser energy transmission hollow fiber according to the second embodiment will be described.

  As shown in FIG. 2A, the hollow fiber 20 for laser energy transmission has an outer peripheral side of a hole 13 formed on the circumference in addition to the configuration of the hollow fiber 10 of the first embodiment. In addition, a plurality of holes 23 are formed.

  The holes 13 are formed at equal intervals on the circumference centered on the center O of the hollow core 12 in the solid portion 21, and the holes 23 are arranged at equal intervals in the circumferential direction on a concentric circle on the outer peripheral side thereof. It is formed to be.

  Furthermore, the holes 13 and the holes 23 formed on concentric circles having different diameters are aligned at radial positions passing through the middle between adjacent holes in the circumferential direction.

As shown in FIGS. 2 (b) and 2 (c), the refractive index distributions in the radial lines r1 and r2 passing from the hollow core center O through the holes 13 and 23, respectively, are distribution lines 27 and 28, respectively. hollow core 12, the holes 13 and 23 the refractive index because it is air substantially 1, and the refractive index n _s of a solid portion 21 is substantially 1.48.

The distance δ _s1 between the hollow core outer periphery 14 and the holes 13 arranged on the inner circumference is the value of δ _s when m = 0 in the equation (1), and the refractive index n _{s of the} solid portion 21. Is 1.48 and the transmission light wavelength λ is 1.06 μm, δ _s1 is 0.24 μm. The distance δ _s2 between the outer periphery 14 of the hollow core 14 and the holes 23 arranged on the outer circumference is the value of δ _s when m = 1 in the equation (1), and the refraction of the solid portion 21 the rate n _s 1.48, when the propagation light wavelength λ was 1.06 .mu.m, [delta] _s2 is 0.73 .mu.m.

The hollow fiber 20 has the same effect as the hollow fiber 10 of the first embodiment. Further, since the hole 23 is formed outside the hole 13, the light radiated from the solid part 21 between the adjacent holes 13, 13 is emitted from the boundary surface between the hole 23 and the solid part (hole outer periphery 25. ), And the distance δ _s2 between the holes substantially satisfies the formula (1), so that the phase of the light reflected to the hollow core side interferes in the same phase, and the light confinement effect on the hollow core 22 is obtained. Enlarge. Therefore, the loss of light propagating through the hollow core 22 can be extremely reduced.

  Next, the laser energy transmission hollow fiber according to the third embodiment will be described.

  As shown in FIG. 3A, the laser energy transmission hollow fiber 30 is obtained by changing the arrangement of the holes of the laser energy transmission hollow fiber 20 of the second embodiment.

  In the solid portion 31, the holes 13 formed on the inner concentric circles and the holes 33 formed on the outer concentric circles are arranged in the same number at equal intervals in the circumferential direction. 13 and 33 are formed aligned in the radial direction of concentric circles.

As shown in FIG. 3B, the refractive index distribution in the radial line r passing through the hollow holes 13 and 33 from the hollow core center O becomes a distribution line 37, and the hollow core 32 and the hollow holes 13 and 33 are obtained. Is significantly lower than the refractive index of the solid portion 31. The distance δ _s between the hollow core outer periphery 14 and the inner hole 13 substantially satisfies the expression (1), and the distance δ _ss between the hollow core outer periphery 14 and the outer hole 33 approximately satisfies the following expression (3). .

δ _s and δ _ss may have the same thickness, and may have an odd multiple relationship with each other as long as both δ _s and δ _ss substantially satisfy Expression (1) and Expression (3).

The hollow fiber 30 has the same effect as the hollow fiber 10 of the first embodiment. Further, since total reflection does not occur at the boundary surface between the hole 13 and the solid portion 31, the hole 33 is formed outside the hole 13, so that the light emitted without being reflected can be emitted from the hole 33. And the solid portion can be reflected at the boundary surface (hole outer periphery 35). In addition, since the inter-hole distance δ _ss substantially satisfies the expression (3), the phase of the light reflected to the hollow core side interferes in the same phase on the outer periphery of the hollow core, and the light confinement effect on the hollow core 31 is greatly increased. To do. Therefore, the loss of light propagating through the hollow core 12 can be greatly reduced.

  The hollow fibers 20 and 30 of the second and third embodiments are formed by forming the holes 13 and 23 (33) on two concentric circles having different diameters, but there are two concentric circles forming the holes. Not limited to that, it may be more.

  Next, a laser energy transmission hollow fiber according to a fourth embodiment will be described.

  As shown in FIG. 4, the laser energy transmitting hollow fiber 40 is different from the hollow fiber 10 of the first embodiment in the cross-sectional shape of the holes.

  In the solid portion 41, a plurality of holes 43 are formed at equal intervals on a circumference centered on the center O of the hollow core 12. The cross section of the air hole 43 has an oval shape, the major axis direction is aligned on the circumference, and the area of the air hole outer periphery 45 is larger than that of the circular hole 13.

The hole 43 is formed at a position where the distance δ _s between the hollow core outer periphery 14 and each hole 43 substantially satisfies the expression (1), and the radial width δ _{0 of} each hole 43 approximately satisfies the expression (2). It is formed in a size that fills.

  As shown in FIG. 4B, the refractive index distribution in the radial line r passing from the hollow core center O through the holes 43 is as a distribution line 47, and the refractive indexes of the hollow core 42 and the holes 43 are solid portions. It is much lower than the refractive index of 41.

  The hollow fiber 40 has the same effect as that of the first embodiment. Furthermore, by increasing the hole outer periphery 45 of the holes 43 formed on the same circumference, the reflection area of light radiated to the outside of the fiber is increased, and the effect of confining light in the hollow core 22 is increased. . Therefore, the loss of light propagating through the hollow core can be greatly reduced.

In the first to fourth embodiments, the cross-sectional shape of the holes formed in the solid portion is a circle or an oval. However, the shape is not limited to these, and may be an ellipse or a polygon. At that time, it is preferable that the width δ _{0 of} the formed hole in the radial direction of the hollow fiber substantially satisfies the expression (2). In addition to the circular shape, the cross-sectional shape of the hollow core may be a polygonal shape such as a hexagon.

  As described above, the hollow fiber for laser energy transmission according to the present embodiment can provide a very useful transmission line in various fields using laser energy.

(A) shows sectional drawing of the fiber for laser energy transmission of 1st embodiment which concerns on this invention, (b) shows the refractive index distribution of radial direction. (A) shows sectional drawing of the fiber for laser energy transmission of 2nd embodiment, (b), (c) shows the refractive index distribution of radial direction. (A) shows sectional drawing of the fiber for laser energy transmission of 3rd embodiment, (b) shows the refractive index distribution of radial direction. (A) shows sectional drawing of the fiber for laser energy transmission of 4th embodiment, (b) shows the refractive index distribution of radial direction. (A) shows a cross-sectional view of a conventional laser energy transmission fiber having a solid core as a propagation region, and (b) shows a refractive index distribution in the radial direction. (A) shows sectional drawing of the conventional leaky waveguide, (b) shows the refractive index distribution of radial direction. (A) shows a sectional view of a conventional dielectric-incorporated metal hollow waveguide, and (b) shows a refractive index distribution in the radial direction.

Explanation of symbols

10 Hollow Fiber for Laser Energy Transmission 11 Solid Part 12 Hollow Core 13 Hole 14 Hollow Core Outer

Claims (11)

  A hollow fiber for laser energy transmission having a hollow core as a hollow region, comprising: a hollow core having a diameter of 100 times or more of the propagation light wavelength; and a solid portion surrounding the hollow core, wherein the solid portion includes a plurality of voids extending in the fiber longitudinal direction. A hollow fiber for laser energy transmission, wherein holes are formed.   The hollow fiber for laser energy transmission according to claim 1, wherein the holes are provided on a circumference centered on a center of the hollow core.   The hollow fiber for laser energy transmission according to claim 1 or 2, wherein the holes are formed at equal intervals on a circumference centered on the center of the hollow core.   The hollow fiber for laser energy transmission according to any one of claims 1 to 3, wherein the holes are formed on two or more concentric circles centered on the center of the hollow core.   5. The hollow fiber for laser energy transmission according to claim 4, wherein the inner and outer holes formed on concentric circles having different diameters are aligned in the radial direction.   5. The laser according to claim 4, wherein the adjacent inner and outer holes formed on concentric circles having different diameters are aligned at a radial position passing between the adjacent holes in the circumferential direction. Hollow fiber for energy transmission. The distance δ _s between the hollow core side in the radial direction of the holes arranged on the same circumference and the outer circumference of the hollow core is such that n _s is the refractive index of the solid part, λ is the wavelength of propagating light, and m is an integer of 0 or more. When

The hollow fiber for laser energy transmission according to claim 1, wherein: When the distance δ _ss between adjacent holes inside and outside the concentric circle is λ for the wavelength of propagating light, n _{s for} the refractive index of the solid part, and m is an integer of 0 or more,

The hollow fiber for laser energy transmission according to claim 4, wherein: When the hole has a radial width δ ₀ of a circle centered on the center of the hollow core, the wavelength of propagating light is λ, and m is an integer of 0 or more,

The hollow fiber for laser energy transmission according to claim 1, wherein:   The hollow fiber for laser energy transmission according to any one of claims 1 to 9, wherein a cross-sectional shape of the hole is a circle, an ellipse, or a polygon. The hollow fiber for laser energy transmission according to claim 1, wherein the material forming the solid portion is quartz.

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