JP2011164318A - Hollow optical fiber and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hollow optical fiber that can transmit long wavelength laser light at a low loss and can be formed into a long fiber through a relatively simple process, and to provide a method for manufacturing the optical fiber. <P>SOLUTION: The hollow optical fiber 1 includes: a glass tube 2 having a coefficient A1 of linear expansion and a softening point T1; and a metal layer 3 formed on the inner circumference face of the glass tube, having a coefficient A2 of linear expansion slightly greater than A1, and having a melting point T2 close to the T1. The metal layer 3 is formed on the inner circumference face of the glass tube by: blowing gas to an aerosol container to change fine particle raw material into an aerosol; supplying the fine particle raw material in the aerosol state together with the gas into the glass tube 2 having the coefficient A1 of linear expansion, which is almost equal to or slightly smaller than the A2, and having the softening point T1 close to T2; and heating the glass tube 2 from the outer circumference of the glass tube 2 while evacuating the inside of the glass tube 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hollow optical fiber capable of propagating a long transmission path with low loss and a method for manufacturing the same.

  In recent years, long-wavelength laser light has been used for surgery, incision surgery, or for hemostasis of blood during surgery, and in dental treatment. The wavelength of long-wavelength laser light used in such medical fields is 1 μm or more (2 μm band, 3 μm band, 10.6 μm band), and laser light sources of these various wavelength bands and the laser light are transmitted with low loss. The development of optical fibers has become an important issue.

As a therapeutic laser light source in the medical field, a Ho: YAG laser having a wavelength of 2.1 μm, an Er: YAG laser having a wavelength of 2.94 μm, and a CO ₂ laser having a 10.6 μm have already been put into practical use.
On the other hand, as an optical fiber aiming at application in the medical field, development of a hollow optical fiber in which a core portion for propagating light is made of air or an inert gas is underway. As an example, there is a hollow optical fiber of 10.6 μm band in which a silver coating is formed on the inner peripheral surface of a glass capillary tube to form a cladding, and light is transmitted by reflection on the surface of the silver coating (non-patent document) 1).

In fields other than medicine, for example, in fields such as semiconductor microfabrication and surface modification of materials, processing using a laser with a short wavelength is actively performed. For processing, for example, ArF laser (oscillation wavelength 193 nm), F ₂ laser (oscillation wavelength 157 nm), KrF laser (oscillation wavelength 248 nm), excimer laser (oscillation wavelength 266 nm), etc. are used to transmit these laser beams. Hollow optical fibers have been developed (see Non-Patent Document 2 and Patent Documents 1 to 5).

Japanese Patent Laid-Open No. 2003-114344 Japanese Patent Laid-Open No. 2003-315588 Japanese Unexamined Patent Publication No. 2006-243306 JP 2009-198728 JP 2009-204683 A

Hongo, Koike, Suzuki, "Development of medical infrared hollow fiber", Hitachi Cable, No.24, 2005-1, pp.7-12 Matsuura, "Study on hollow fiber type optical transmission line for vacuum ultraviolet and soft X-ray", The Murata Science Foundation, Annual Report, No.18, 2004, pp.265-268

However, the above-described hollow optical fiber has the following problems.
A hollow optical fiber with a silver coating as the cladding has a refractive index of the core (air) lower than the refractive index of the cladding (silver coating), so light at the boundary between the core and the cladding, that is, the surface (inner peripheral surface) of the silver coating. There is a loss in the reflection. In order to reduce the loss, it is necessary to maintain the surface of the silver coating in a mirror state and increase the reflectance on the surface of the silver coating. However, when a silver coating is formed by a silver mirror reaction, it is difficult to keep the surface of the silver coating in a mirror state, and the structural loss on the surface of the silver coating causes a significant increase in scattering loss. Therefore, we have devised to increase the reflectance by forming a dielectric film on the surface of the silver film, but the process of forming the dielectric film is complicated, and a film with a uniform composition is formed with a uniform film thickness. Difficult to do.

  In the conventional hollow optical fiber, a method of forming a metal thin film such as a silver coating using an MOCVD apparatus is also employed. However, the MOCVD apparatus is very expensive and causes an increase in manufacturing cost. Conventionally, since a hollow optical fiber is manufactured by forming a silver coating on the inner peripheral surface of a short glass capillary tube having a length of about 2 m by a silver mirror reaction, it is made long (several tens of meters). It is difficult. Furthermore, since it is a single item production, it has been difficult to realize a low cost and a high yield production.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a hollow optical fiber that can transmit long-wavelength laser light with low loss and can be made long by a relatively simple process, and a method for manufacturing the same.

  The hollow optical fiber and the manufacturing method thereof according to the present invention have been made in order to solve the above-described problems, and in particular, have been made for the purpose of realizing a stable structure that is not easily subjected to unnecessary stress and strain. Is.

Specifically, the hollow optical fiber according to the first invention of the present application is:
a) a glass tube with a linear expansion coefficient of A1 and a softening point of T1,
b) a first metal layer formed on the inner peripheral surface of the glass tube and having a linear expansion coefficient value A2 slightly larger than A1 and a melting point T2 close to T1. To do.
Here, “slightly larger value A2 than A1” means that A2 is larger than A1 and about 1.2 times A1. Further, “value T2 close to T1” means that T2 is about T1 ± 300 ° C.

  According to a second invention, in the first invention, a second metal layer made of the same metal as the first metal layer is further formed on the outer peripheral surface of the glass tube.

  According to a third invention, in the first invention or the second invention, the linear expansion coefficient is a value A3 smaller than A1 and the melting point between the inner peripheral surface of the glass tube and the first metal layer. A buffer layer having a value T3 close to T1 is formed.

  In the first invention or the second invention, it is preferable that the glass tube is formed from a hard glass tube, and the first metal layer is formed from any one of gold, silver, and aluminum.

  In the third invention, the glass tube is formed from a hard glass tube or a Pyrex (registered trademark) glass tube, the buffer layer is formed from Si or SiN, and the first metal layer is any one of gold, silver, and aluminum. It is preferable to form from.

The method for producing a hollow optical fiber of the fourth invention of the present application is as follows:
A fine particle raw material with a submicron particle size of a metal having a linear expansion coefficient of A2 and a melting point of T2 is aerosolized, and the aerosolized fine particle raw material has a linear expansion coefficient substantially equal to or slightly smaller than A2 and is softened. Into a glass tube with a point T1 close to T2,
A hollow optical fiber is manufactured by forming the first metal layer made of the fine particle raw material on the inner peripheral surface of the glass tube by heating the glass tube from the outer peripheral direction of the glass tube while exhausting the inside of the glass tube. It is characterized by.

  The method for producing a hollow optical fiber according to a fifth aspect of the present application is the method according to the fourth aspect, further comprising: aerosolizing a fine particle material having a submicron particle size of the same metal as the first metal layer on the outer peripheral surface of the glass tube. The second metal layer made of the fine particle raw material is formed by spraying.

  In the fourth or fifth aspect of the invention, it is preferable that a container for aerosolizing the particulate raw material is provided so that exhaust from the glass tube is returned to the container.

In the method for manufacturing a hollow optical fiber according to the sixth invention of the present application, a fine particle raw material having a submicron particle diameter of a metal having a linear expansion coefficient of A2 and a melting point of T2 is aerosolized, and the aerosolized fine particle raw material has a linear expansion coefficient. The glass tube is heated from the outer peripheral direction of the glass tube while being sent to the glass tube having a value A1 that is substantially equal to or slightly smaller than A2 and the softening point is a value T1 close to T2, and evacuating the glass tube. Forming a first metal layer made of the fine particle raw material on the inner peripheral surface of the glass tube to produce a hollow optical fiber preform tube;
A step of melting the tip of the hollow optical fiber preform tube while keeping the inside of the hollow optical fiber preform tube in an inert atmosphere, and drawing the optical fiber by drawing at a constant speed.

In addition, in the method for manufacturing a hollow optical fiber according to the seventh invention of the present application, a fine particle raw material having a submicron particle diameter of a metal having a linear expansion coefficient of A2 and a melting point of T2 is aerosolized, and the aerosolized fine particle raw material is linearly expanded. The coefficient is almost equal to or slightly smaller than A2, and the glass tube is heated from the outer peripheral direction of the glass tube while feeding the glass tube having the softening point T1 close to T2 and evacuating the glass tube. Forming a first metal layer made of the fine particle raw material on the inner peripheral surface of the glass tube,
The second metal layer made of the fine particle material is formed on the outer peripheral surface of the glass tube by aerosolizing and spraying the fine particle material having the same metal submicron particle size as the first metal layer on the outer peripheral surface of the glass tube. And the process of creating a hollow optical fiber preform tube,
A step of melting the tip of the hollow optical fiber preform tube while keeping the inside of the hollow optical fiber preform tube in an inert atmosphere, and drawing the optical fiber by drawing at a constant speed.

  Furthermore, in the method for manufacturing a hollow optical fiber according to the eighth invention of the present application, in the sixth invention or the seventh invention, before the first metal layer is formed on the inner peripheral surface of the glass tube, the linear expansion coefficient is increased. A buffer layer having a value T3 smaller than A1 and having a melting point close to T1 is provided by a preliminary step of forming a buffer layer by a gas phase chemical reaction using a silane-based gas or a silane-based gas and a nitrogen-based gas. .

In the manufacturing methods of the sixth and seventh inventions described above, it is preferable that the glass tube is made of a hard glass tube and the first metal layer is made of any one of gold, silver, and aluminum.
In the eighth invention, the glass tube is formed from a hard glass tube or a Pyrex glass tube, the buffer layer is formed from Si or SiN, and the first metal layer is formed from any one of gold, silver, and aluminum. Is preferred.

  In the hollow optical fiber of the present invention, since the linear expansion coefficient A2 of the first metal layer is slightly larger than the linear expansion coefficient A1 of the glass tube, the first metal layer is formed on the inner peripheral surface of the glass tube. It is difficult to apply unnecessary stress. Further, since the softening point T1 of the glass tube and the melting point T2 of the first metal layer are substantially equal, a high-purity metal layer can be easily formed on the inner peripheral surface of the glass tube.

  Further, if the second metal layer of the same metal as the first metal layer formed on the inner peripheral surface is formed on the outer peripheral surface of the glass tube, the glass tube and the first metal layer have different linear expansion coefficients. The strain based on the asymmetric structure can be reduced. Moreover, it can suppress that unnecessary stress and distortion are added to a hollow optical fiber by the change of environmental temperature.

  Further, if a buffer layer having a linear expansion coefficient value A3 smaller than A1 and a melting point T3 close to T1 is interposed between the glass tube and the metal layer, the material of the glass tube and the metal layer can be further increased. It is possible to select from a wide range, and it is possible to realize an optical fiber with a lower loss and higher strength. Moreover, since the buffer layer and the metal layer have a two-layer structure, it is possible to prevent the optical signal propagating through the hollow from leaking out from the outer periphery of the hollow optical fiber.

  In addition, according to the method for producing a hollow optical fiber of the present invention, since the first metal layer is formed by feeding the metal aerosolized fine particle raw material into the glass tube by the so-called aerosolized gas deposition method, the crystal structure is very dense. A metal layer having a uniform particle size can be formed on the inner peripheral surface of the glass tube. For this reason, an optical signal can be uniformly reflected by the first metal layer, and a hollow optical fiber with a small scattering loss can be obtained. Moreover, in the hollow optical fiber obtained by the manufacturing method of the present invention, the linear expansion coefficient A2 of the first metal layer is slightly larger than the linear expansion coefficient A1 of the glass tube. It is difficult to apply unnecessary stress when forming the first metal layer. Further, since the softening point T1 of the glass tube and the melting point T2 of the metal layer are substantially equal, a high-purity metal layer can be easily formed on the inner peripheral surface of the glass tube.

  Further, the glass tube and the first metal layer are formed by aerosolizing and spraying a fine particle material having a submicron particle size of metal on the outer peripheral surface of the glass tube to form a second metal layer similar to the first metal layer. The distortion caused by the asymmetrical coefficient of linear expansion can be reduced. For this reason, it can prevent that the obtained hollow optical fiber deform | transforms by the change of environmental temperature.

  Further, by utilizing a gas phase chemical reaction using a silane-based gas or a silane-based gas and a nitrogen-based gas, a buffer layer having a high purity and a uniform structure is interposed between the glass tube and the first metal layer. The surface (inner peripheral surface) of the first metal layer can be in a uniform mirror surface state. For this reason, a further low-loss hollow optical fiber can be manufactured.

  In the method for producing a hollow optical fiber of the present invention, a hollow optical fiber preform tube obtained by forming a first metal layer on the inner peripheral surface of a glass tube by an aerosolized gas deposition method is used. Thus, a long hollow optical fiber having a length of 1 km or more can be easily manufactured because it is drawn and drawn in a heating furnace maintained in an inert atmosphere. Moreover, since the structural irregularity on the inner peripheral surface of the first metal layer as the interface between the core and the clad can be extremely reduced by drawing and drawing, it is possible to obtain a hollow optical fiber that is further low in loss and strong in bending. it can.

It is a schematic block diagram of the hollow optical fiber which concerns on Example 1 of this invention, (a) is a cross-sectional view, (b) is a longitudinal cross-sectional view. Manufacturing process drawing of a hollow optical fiber. The figure for demonstrating the method of forming a metal layer in the internal peripheral surface of a glass tube. The manufacturing process figure suitable for a long hollow optical fiber. The figure for demonstrating the method of drawing-drawing a fiber preform pipe | tube. The equivalent figure of FIG. 1 of the hollow optical fiber which concerns on Example 2 of this invention. FIG. The figure for demonstrating the method of forming a metal layer in the outer peripheral surface of a glass tube. FIG. FIG. 1 is a view corresponding to FIG. 1 of a hollow optical fiber according to a third embodiment of the present invention. FIG. The figure for demonstrating the method of forming a buffer layer in the internal peripheral surface of a glass tube. The figure for demonstrating the 1st modification of this invention and explaining another example of the method of forming a metal layer in the internal peripheral surface of a glass tube. The figure for showing the 2nd modification of this invention and explaining another example of the method of forming a metal layer in the internal peripheral surface of a glass tube. The figure for showing the 3rd modification of this invention and explaining another example of the method of forming a metal layer, after forming a buffer layer in the internal peripheral surface of a glass tube. The figure for demonstrating the 4th modification of this invention, and explaining the economical method of forming a metal layer in the internal peripheral surface of a glass tube.

  Hereinafter, specific examples of the present invention will be described.

  FIG. 1 shows a hollow optical fiber according to Embodiment 1 of the present invention. FIG. 2A is a transverse sectional view along the radial direction of the hollow optical fiber, and FIG. 2B is a longitudinal sectional view taken along the line X1-X1. The hollow optical fiber 1 includes a glass tube 2 and a metal layer 3 formed on the inner peripheral surface thereof. If the linear expansion coefficient of the glass tube 2 is A1 and the softening point is T1, the metal layer 3 is made of a metal whose linear expansion coefficient is a value A2 slightly larger than A1 and whose melting point is a value T2 close to T1. ing. The hollow optical fiber 1 is composed of a thin glass tube 2, and a metal layer 3 formed on the inner peripheral surface of the glass tube 2 functions as a cladding. Therefore, as shown by an arrow 5 in FIG. 1, the signal incident into the hollow optical fiber 1 is reflected by the surface of the metal layer 3 and is transmitted through the hollow portion 4 of the glass tube 2.

The outer diameter of the hollow optical fiber 1 is selected according to the power of the optical signal to be transmitted, the beam spot size, and the size of the object to be irradiated. For example, when transmitting infrared light, the hollow optical fiber 1 is generally set to have a small outer diameter of about 150 μm and a large one of about 1000 μm. However, if necessary, the hollow optical fiber 1 having an outer diameter other than the above can be manufactured.
In general, the hollow optical fiber 1 has a small inner diameter of about 80 μm and a large inner diameter of about 800 μm.

The thickness of the metal layer 3 need only be sufficiently larger than the optical skin depth of the optical signal to be transmitted, and does not need to be precisely controlled. However, in order to maintain the uniformity of the film thickness and the mirror state during film formation A range of 0.5 μm to 5 μm is preferred. On the other hand, if the metal layer 3 is too thin, the uniformity as the reflecting surface is deteriorated. On the other hand, if the metal layer 3 is too thick, excessive stress is applied to the glass tube 2 due to a slight difference in the linear expansion coefficient.
In order to make the hollow optical fiber 1 easy to bend and handle, it is preferable to coat a resin such as a silicone resin, a nylon resin, a UV resin, and a polyimide resin on the outer periphery of the glass tube 2.

Next, the manufacturing method of the said hollow optical fiber 1 is demonstrated using FIGS. First, an example of a manufacturing method suitable for the short hollow optical fiber 1 will be described with reference to FIGS.
The step indicated by S1 is a step of cleaning the inner peripheral surface of the small-diameter glass tube 2 serving as a starting material for the hollow optical fiber 1 with a cleaning gas. As the cleaning gas, CF ₄ , C ₂ F ₆ gas, or the like can be used. A cleaning gas is sent into the glass tube 2 together with the inert gas to clean the inner peripheral surface of the glass tube 2. If the cleaning process is performed while the outer periphery of the glass tube 2 is heated in the range of 200 ° C. to 500 ° C., the inner peripheral surface of the glass tube 2 is etched with the cleaning gas. The resulting structural irregularities can be reduced.

The process indicated by S <b> 2 is a process for forming the metal layer 3 on the inner peripheral surface of the glass tube 2. Here, the metal layer 3 is formed on the inner peripheral surface of the glass tube 2 by the aerosolized gas deposition method. That is, first, a fine particle raw material 14 having a submicron particle diameter of a metal having a linear expansion coefficient of A2 and a melting point of T2 is put in an aerosol container 13. Then, the particulate raw material 14 that sends the inert gas through the valve 16 into the aerosol container 13 from the transport pipe 17a is aerosolized. Ar, He, N ₂ or the like can be used as the inert gas. The method for aerosolizing the fine particle raw material 14 is not limited to the above-described preparation conditions. For example, a method of heating an aerosol container to make it easy to be aerosolized may be used.

  The aerosolized fine particle raw material 14 is sent into the transfer pipe 17b from the container 13 together with the inert gas. The conveyance tube 17b is inserted into the glass tube 2 from one end, and an outlet 17c is provided at the tip. Therefore, the inert gas containing the aerosolized fine particle raw material 14 fed into the transport pipe 17b is blown into the glass tube 2 from the outlet 17c as indicated by an arrow 14a. At the start of the formation of the metal layer 3, the outlet 17c of the transfer tube 17b is located near the other end of the glass tube 2, and then the glass tube 2 is gradually moved in the direction indicated by the arrow 11, thereby The position of the outlet 17c in the pipe 2 moves from the other end to one end. Further, the glass tube 2 is heated by the heating source 10 from the outer periphery thereof, and the inert gas containing the fine particle raw material blown into the glass tube 2 is exhausted from the other end as indicated by an arrow 18.

As the heating source 10, an electric furnace, a high frequency furnace, an oxyhydrogen burner, or the like can be used.
Moreover, a hard glass tube can be mentioned as a glass tube, Gold, silver, aluminum, copper etc. can be mentioned as a fine particle raw material with a submicron particle diameter of a metal. The heating temperature for forming the metal layer from these fine metal particles is preferably in the range of 150 ° C to 400 ° C. When the metal layer is formed in this temperature range, there is no evaporation process for producing nanoparticles, so that a desired metal layer can be formed without causing a change in material composition.

As a result, the metal layer 3 is formed on the entire inner peripheral surface of the glass tube 2 by the metal fine particle raw material 14 blown into the glass tube 2, and thus the hollow optical fiber 1 is manufactured. In particular, since the metal layer 3 is formed by the aerosolized gas deposition method in this embodiment, the metal layer 3 having a dense crystal structure and a uniform particle size can be formed on the inner peripheral surface of the glass tube 2. As a result, it is possible to realize a good reflecting surface for the signal light.
In addition, when the formation process of the metal layer 3 is performed while rotating the glass tube 2 in the direction indicated by the arrow 12, the metal layer having a uniform film thickness in the circumferential direction and the longitudinal direction on the inner peripheral surface of the glass tube 2 3 can be formed.

  In addition, since the linear expansion coefficient A2 of the metal layer 3 is slightly larger than the linear expansion coefficient A1 of the glass tube 2, the hollow optical fiber 1 is formed when the hollow optical fiber 1 is formed by forming the metal layer 3. Unnecessary stress and strain are not easily applied. Further, since the softening point T1 of the glass tube 2 and the melting point T2 of the metal layer 3 are substantially equal, the high-purity metal layer 3 can be easily formed on the inner surface of the glass tube 2.

A specific manufacturing example of the short hollow optical fiber 1 using the manufacturing method described above will be shown below.
As the glass tube 2, a hard glass tube having a length of 2 m, an outer diameter of 800 μm, and an inner diameter of 600 μm is prepared, and the particle diameter is 1 μm or less in a transport tube 17 b inserted into the hard glass tube 2 from one end. The submicron-sized gold fine particle raw material 14 is aerosolized with Ar gas (100 cc / min (= 1 × 10 ⁻⁴ m ³ / min) and then sent into the glass tube 2 while exhausting from the other end. The outer periphery of the glass tube 2 is heated to 200 ° C. by the heating source 10 and the glass tube 2 is moved at a speed of 0.5 mm / sec in the direction from one end to the other end while the glass tube 2 is moved at 15 rpm (15 / is rotated at 60s ^-1). As a result, the gold layer 3 having a thickness of approximately 0.5μm is formed on the inner peripheral surface of the glass tube 2, the desired hollow optical fiber 1 is obtained.

Next, the manufacturing method of the long hollow optical fiber 1 is demonstrated using FIG.4 and FIG.5.
The manufacturing method of the long hollow optical fiber 1 includes a first step (S2 ′) in which a metal layer is formed on the inner peripheral surface of the glass tube 2 to create a hollow fiber preform tube 21, and the fiber preform tube 21. A hollow-shaped optical fiber 1 is manufactured by inserting the melted fiber preform tube 21 at a constant speed into a drawing furnace 23 maintained in an inert atmosphere while keeping the interior in an inert atmosphere, and stretching the lower end of the molten fiber preform tube 21 at a constant speed. And the second step (S3).
The first step is substantially the same as the step indicated by S2 in FIG. Although not shown in FIG. 4, a cleaning process may be performed before the first process, as in the manufacturing process of the short hollow optical fiber 1.

  In the second step, the fiber preform tube 21 is in an inert atmosphere in a state where an inert gas flows as indicated by an arrow 22a, or in a state where the inside of the fiber preform tube 21 is maintained in an inert atmosphere. Is inserted into the drawing furnace 23 kept at a constant speed vp. And the hollow optical fiber 1 is manufactured by extending | stretching the lower end of the fiber preform pipe | tube 21 fuse | melted in the drawing furnace 23 with the constant speed vf, and winding up with the drum 30. FIG.

Here, when the diameter d of the hollow optical fiber 1 is D, the diameter of the optical fiber preform tube 21 is D
d = D (vp / vf) ^1/2
Given in.

As a method for keeping the drawing furnace 23 in an inert atmosphere, gas introduction nozzles 24a and 24b are provided above and below the drawing furnace 23, and an inert gas is fed into these nozzles 24a and 24b as indicated by arrows. At this time, the inert gas sent into the nozzles 24a and 24b flows in the drawing furnace 23 as indicated by arrows 25a and 25b, and as indicated by 26a, 26b, 26c and 26d outside the drawing furnace 23. Make it flow.
Thus, by drawing and drawing in the drawing furnace 23 maintained in the inert atmosphere while keeping the inside of the optical fiber preform tube 21 in the inert atmosphere, the oxidation of the metal layer can be prevented.

A specific manufacturing example of the long hollow optical fiber 1 using the manufacturing method described above will be shown below.
A hard glass tube having an outer diameter of 20 mm, an inner diameter of 17 mm, and a length of 80 cm is used as the glass tube 2, and a 30 μm thick gold layer is formed as an aerosol gas gas as the metal layer 3 formed on the inner peripheral surface of the glass tube 2. Form by the position method. The linear expansion coefficient of the hard glass tube is 8.5 × 10 ⁻⁶ / K and the softening point is 785 ° C., whereas the linear expansion coefficient of the gold layer is 9 × 10 ⁻⁶ / K and the melting point is 1063 ° C. Both have similar physical properties. For this reason, a gold layer can be formed on the inner peripheral surface of the hard glass tube by the aerosolized gas deposition method, and as a result, a hollow fiber preform tube can be produced.
Next, the obtained fiber preform tube is heated and drawn in a heating furnace having a temperature close to about 1000 ° C. kept in an inert atmosphere while keeping the inside of the fiber preform tube in an inert atmosphere. As a result, a long hollow optical fiber of about 1 km could be manufactured. This long hollow optical fiber 1 had an outer diameter of 500 μm, an inner diameter of about 425 μm, and a gold layer thickness of about 0.75 μm.

  In the hollow optical fiber 1 described above, since the linear expansion coefficient of the hard glass tube and the linear expansion coefficient of the metal layer are close to each other, excessive stress occurs when the fiber preform tube is drawn and stretched. Can be prevented as much as possible. Moreover, the obtained hollow optical fiber 1 was difficult to cause practical problems such as cracks, extreme strains, and breakage due to bending during handling.

The obtained hollow optical fiber 1 has a length of 10 m, and CO ₂ laser light having a wavelength of 10.6 μm (output 60 W, beam spot diameter 180 μm) is incident on the hollow portion 4 as infrared light, and a CO ₂ laser at the exit end. The light output was measured. As a result, it was found that about 80% of the incident light propagates. The reason why the low loss characteristic is obtained in this way is considered to be that the structural irregularity between the core and the cladding interface can be extremely reduced by drawing.

  FIG. 6 shows a hollow optical fiber according to Embodiment 2 of the present invention. FIG. 4A is a transverse sectional view along the radial direction of the optical fiber, and FIG. 4B is a longitudinal sectional view in the X2-X2 line direction of FIG. The hollow optical fiber 6 of Example 2 is different from the hollow optical fiber 1 of Example 1 in that a metal layer 7 made of the same metal as the metal layer 3 formed on the inner peripheral surface is formed on the outer peripheral surface of the glass tube 2. . In the following description, the metal layer formed on the inner peripheral surface of the glass tube 2 is referred to as a first metal layer 3, and the metal layer formed on the outer peripheral surface is referred to as a second metal layer 7.

Also in the hollow optical fiber 6 of the second embodiment, as shown by the arrow 5, the optical signal incident in the hollow optical fiber 6 is reflected by the surface of the first metal layer 3 and transmitted through the hollow portion 4 of the glass tube 2. To do.
In the structure in which the metal layer 3 is formed only on the inner peripheral surface of the glass tube 2, distortion occurs due to asymmetry due to the difference in the linear expansion coefficient between the glass tube 2 and the metal layer 3, but the inner peripheral surface and the outer periphery of the glass tube 2. In a structure in which a metal layer made of the same metal is formed on both surfaces, the occurrence of such strain can be reduced. Thereby, it can suppress that unnecessary stress and distortion are added to the hollow optical fiber 6 by the change of environmental temperature.

  Since the second metal layer 7 does not contribute to the reflection of the optical signal, the film thickness can be set regardless of the optical skin depth. However, the above-described distortion can be reduced, the optical signal can be prevented from leaking, and the damage can be prevented. The thickness is preferably set in consideration of preventing the above, and the thickness is preferably in the range of 0.3 μm to 5 μm. If the thickness of the metal layers 3 and 7 formed on the inner peripheral surface and the outer peripheral surface of the glass tube 2 is 5 μm or less, the present inventor has no practical problem even if the hollow optical fiber 6 is bent with a bending radius of 50 mm. I have confirmed that.

  A method for manufacturing the hollow optical fiber 6 will be described with reference to FIGS. First, an example of a manufacturing method suitable for the short hollow optical fiber 6 will be described with reference to FIGS. The manufacturing method of the short hollow optical fiber 6 is different from the manufacturing method shown in FIG. That is, after the first metal layer 3 is formed on the inner peripheral surface of the small-diameter glass tube 2 that is the starting material of the hollow optical fiber 6 (S2), the outer peripheral surface of the glass tube 2 is also the same as the first metal layer 3 A second metal layer 7 made of metal is formed (S4).

  FIG. 8 shows an apparatus used in the second metal layer 7 formation step (S4). Since the apparatus of FIG. 8 is substantially the same apparatus as the apparatus shown in FIG. 3, the same parts as those of the apparatus shown in FIG. First, when the inert gas 15 is sent into the aerosol container 13 from the transfer pipe 17a through the valve 16 and the metal fine particle raw material 14 having a submicron particle size is aerosolized, the aerosolized fine particle raw material 14 together with the inert gas is transferred to the transfer pipe. 17d and blown out from the outlet 17e of the transfer pipe 17d.

  The transport pipe 17d is arranged at a certain distance from the outer peripheral surface of the glass tube 2, and the outlet 17e of the transport pipe 17d is located near the other end of the glass tube 2 when the formation of the metal layer 7 is started. Thereafter, the glass tube 2 is gradually moved in the direction indicated by the arrow 11, whereby the position of the outlet 17e with respect to the outer peripheral surface of the glass tube 2 is moved from the other end portion to one end portion. At this time, the glass tube 2 is rotated in the direction indicated by the arrow 12. As a result, the second metal layer 7 made of the metal fine particle raw material 14 is uniformly formed on the outer peripheral surface of the glass tube 2 in the circumferential direction and the longitudinal direction.

FIG. 9 shows a method for manufacturing a long hollow optical fiber 6. This manufacturing method includes a first step (S2 ′) of forming a first metal layer on the inner peripheral surface of the glass tube 2, and forming a second metal layer on the outer peripheral surface of the glass tube 2 to form a hollow optical fiber preform tube. An intermediate step (S4 ′) for forming the preform, and the lower end of the melted preform tube is inserted at a constant speed into a drawing furnace maintained in an inert atmosphere while maintaining the inside of the optical fiber preform tube at a constant speed. And a second step (S3) for producing a hollow optical fiber by drawing.
The first step and the intermediate step are substantially the same as the step indicated by S2 and the step indicated by S4 in FIG. Further, the second step is substantially the same as the second step in FIG.

  FIG. 10 shows a hollow optical fiber according to Embodiment 3 of the present invention. FIG. 2A is a transverse sectional view along the radial direction of the optical fiber, and FIG. 2B is a longitudinal sectional view in the X3-X3 line direction of FIG. In the hollow optical fiber 8 of Example 3, the buffer layer 9 between the inner peripheral surface of the glass tube 2 and the metal layer 3 has a linear expansion coefficient A3 smaller than A1 and a melting point T3 close to T1. Is different from the hollow optical fiber 1 of the first embodiment. By interposing the buffer layer 9, the material of the glass tube 2 and the metal layer 3 constituting the hollow optical fiber 8 can be selected from a wider range. For example, a Pyrex glass tube or a hard glass tube can be used for the glass tube 2, and gold, silver, aluminum, copper, or the like can be used for the metal layer 3.

  By selecting from these materials, a uniform metal layer 3 can be formed on the inner peripheral surface of the glass tube 2 using a metal fine particle raw material having a submicron particle diameter. For this reason, a favorable reflecting surface for infrared light can be realized, and a hollow optical fiber with even lower loss can be realized.

  Further, since the buffer layer 9 and the metal layer 3 have a two-layer structure, it is possible to prevent infrared light propagating in the hollow portion 4 from leaking from the outer periphery of the hollow optical fiber 8 to the outside. Therefore, for example, infrared light with a wavelength of 10.6 μm is extremely dangerous light if it is accidentally applied to the human body, but leakage from the optical fiber 8 can be prevented even when such infrared light is used. A hollow optical fiber that is safe in use can be realized.

  Further, a buffer layer is provided to prevent infrared light propagating through the hollow portion 4 from leaking from the outer periphery of the hollow optical fiber 8 to the outside. By adopting a two-layer structure of the buffer layer 9 and the metal layer 3, it is possible to provide a high-strength hollow optical fiber that is not easily damaged. Moreover, since the roughness of the inner peripheral surface of the glass tube 2 is reduced by the buffer layer by using the two-layer structure, and the metal layer 3 is formed thereon, the structural irregularity of the cladding surface can be greatly reduced as a result. Thus, it becomes possible to obtain an optical fiber with even lower loss.

  Since the buffer layer 9 is provided for the purpose of relaxing the mechanical and physical connection between the glass tube 2 and the metal layer 3, Si or SiN can be used as a candidate for the material. The thickness of the buffer layer 9 is desirably thinner than the thickness of the metal layer 3, and is preferably in the range of 0.1 μm to 2 μm.

A hard glass tube can be used as the material of the glass tube 2 constituting the hollow optical fiber 8, and Si or SiN can be used as the material of the buffer layer 9. The linear expansion coefficient of hard glass is 8.5 × 10 ⁻⁶ / K, the softening point is 785 ° C., the linear expansion coefficient of Si is 4.2 × 10 ⁻⁶ / K, and the linear expansion coefficient of SiN is 2.2 × 10 ⁻⁶ / K. It is. As the metal layer 3, a gold layer (linear expansion coefficient is 9 × 10 ⁻⁶ / K), a silver layer (linear expansion coefficient is 19 × 10 ⁻⁶ / K), an Al layer (linear expansion coefficient is 23.2 × 10 ^−6). / K). By using these materials, a buffer layer 9 having a smaller linear expansion coefficient than either the glass tube 2 or the metal layer 3 between the hard glass tube 2 having a high linear expansion coefficient and the metal layer 3 having a higher linear expansion coefficient. Will intervene. For this reason, a mechanically stable optical fiber structure can be realized. Further, a metal layer having a higher reflectance can be selected as the metal layer 3.

  A specific manufacturing example will be described. First, a hard glass tube having an outer diameter of 20 mm, an inner diameter of 17 mm, and a length of 80 cm is used as the glass tube 2, and the inner peripheral surface of the glass tube is gasified using silane-based gas or silane-based gas and nitrogen-based gas. A buffer layer 9 made of a SiN layer is formed to a thickness of about 20 μm by a phase chemical reaction method. Thereafter, a metal layer 3 made of a gold layer was formed to a thickness of about 30 μm on the surface of the buffer layer 9 by an aerosolized gas deposition method, thereby obtaining a hollow optical fiber preform tube.

Next, the hollow optical fiber preform tube is heated in a drawing furnace having an inert atmosphere at a temperature close to about 1000 ° C. while being kept in an inert atmosphere, and is drawn and drawn to make a long hollow optical fiber 8 having a length of about 1 km. (The outer diameter is 500 μm, the inner diameter is about 425 μm, the thickness of the buffer layer is about 0.5 μm, and the thickness of the gold layer is about 0.75 μm).
This hollow optical fiber 8 is cut to a length of 10 m, and CO ₂ laser light having a wavelength of 10.6 μm (output 60 W, beam spot diameter 180 μm) is incident on the hollow part 4 in the hollow optical fiber 8 as infrared light. The output of the CO ₂ laser beam was measured at the exit end of the hollow optical fiber 8. As a result, it was found that nearly 80% of light propagated.

This hollow optical fiber 8 was easier to bend than the hollow optical fiber 1 of Example 1.
Further, as another prototype example of Example 3, a structure using a glass tube 2 made of a Pyrex glass tube instead of a hard glass tube was also examined. It was found that an optical fiber having

  Next, the manufacturing method of the said hollow optical fiber 8 is demonstrated using FIG.11 and FIG.12. Here, a manufacturing method suitable for the long hollow optical fiber 8 will be described as an example. This manufacturing method differs from the manufacturing method shown in FIG. 4 in that it has a preliminary step (PS1) for forming the buffer layer 9 before forming the metal layer 3 on the inner peripheral surface of the glass tube 2.

In the preliminary process, first, the glass tube 2 is attached to the glass lathe 20 and rotated in the circumferential direction as indicated by an arrow 12, and SiH ₄ gas and N ₂ gas as raw material gases are introduced into the glass tube 2 from one side thereof. (Or NH ₄ gas) is sent in with the carrier gas.
Here, the glass tube 2 preferably has a diameter of 15 mm to 40 mm, and a longer optical fiber can be produced as the diameter increases. Further, the thickness of the glass tube 2 is preferably in the range of 1 mm to 4 mm, and a longer optical fiber can be produced as the thickness is increased. Further, the gas flow rates of SiH ₄ gas and N ₂ gas (or NH ₄ gas) are preferably in the range of 50 cc / min to 1000 cc / min, and are selected in consideration of the desired refractive index of the buffer layer 9. The film forming rate can be increased as the flow rate of the source gas is increased. Ar or N ₂ is preferably used as the carrier gas, and the gas flow rate is preferably the same as or slightly less than the flow rate of the entire source gas. If the flow rate of the carrier gas is small, the film formation rate decreases, but the film uniformity improves. Conversely, if the carrier gas flow rate is large, the film formation rate increases, but the film thickness uniformity decreases.

  Next, the glass tube 2 is heated in the range of 400 ° C. to 600 ° C. using the heating source 10 from the outer peripheral direction of the glass tube 2 while evacuating from the other side of the glass tube 2 as indicated by an arrow 19a. For the heating source 10, an electric furnace, an oxyhydrogen burner, or the like can be used.

  And the SiN layer 9 is formed in the inner peripheral surface of the glass tube 2 of the heated area | region by moving the heating source 10 to the direction shown by the arrow 11b toward the other side from the one side of the glass tube 2, and this heating When the source 10 reaches the other end, the heating source 10 is moved in the direction indicated by the arrow 11a and returned to the first position on the one end side, and the same method of forming the SiN layer 9 as above is repeated a plurality of times. The SiN layer 9 is formed into a plurality of layers to obtain a hollow fiber preform tube.

  The hollow fiber preform tube obtained by this manufacturing method is composed of uniform ultrafine particles because the SiN layer is formed on the inner peripheral surface of the glass tube 2 by a gas phase chemical reaction using a thermal decomposition reaction. In addition, the buffer layer 9 (SiN layer) can be formed in the glass tube 2 with a uniform thickness and good adhesion. For this reason, the metal layer 3 to be formed thereafter can also be formed in a mirror surface state with a uniform thickness. As a result, the metal layer 3 can transmit the inside of the hollow part 4 in the glass tube 2 by efficiently reflecting, for example, infrared light. In addition, a uniform SiN layer with very few impurities can be formed. Furthermore, since the reaction described above is performed in a closed system, it is possible to suppress the entry of impurities from the outside, so that it is possible to form a more uniform SiN layer, extremely low unnecessary scattering, and low loss. Can be obtained.

Note that SiH ₂ Cl ₂ may be used instead of the SiH ₄ gas. Using SiH ₂ Cl ₂ instead of the SiH ₄ gas, utilizing a gas phase chemical reaction on the inner wall surface of the glass tube 2 at a SiH ₄ temperatures above about 300 ° C. than in the case of gas (ranging from 700 ° C. to 800 ° C.) Thus, a more uniform SiN layer can be formed.

In addition, this invention is not limited to an above-described Example, A suitable change is possible.
FIG. 13 shows another example of a method of vertically placing the glass tube 2 and forming the metal layer 3 on the inner peripheral surface of the glass tube 2. In the vertically placed glass tube 2, a transfer tube 17b is inserted upward from the lower end thereof. An aerosol of the metal fine particle raw material 14 having a submicron particle diameter is flowed to the transport pipe 17b together with an inert gas, and blown out from the outlet 17c at the tip as indicated by an arrow 14a.

FIG. 14 shows another example of a method for forming the metal layer 3 on the inner peripheral surface of the glass tube 2. In this example, the aerosolized metal fine particle raw material 14 is blown out together with an inert gas from the outlet 17c of the transport pipe 17b arranged near the inlet of the glass tube 2 as indicated by an arrow, and the inner peripheral surface of the glass tube 2 Then, the metal layer 3 is sequentially formed in the longitudinal direction. According to this method, even when the glass tube 2 is thin and long, the metal fine particle material 14 having an aerosolized submicron particle diameter is supplied into the glass tube 2 together with the inert gas to form the metal layer. 3 can be formed. In this method, the glass tube 2 may be rotated in the circumferential direction when the metal layer 3 is formed.
FIG. 15 shows an example in which the metal layer 3 is formed after the buffer layer 9 is formed on the inner peripheral surface of the glass tube 2 by the method shown in FIG. The method shown in FIG. 15 can provide the same operations and effects as the method shown in FIG.

  FIG. 16 shows a third modification of the present invention, and the point that the gas exhausted from the other end side of the glass tube 2 is superimposed on the inert gas introduced into the aerosol container 13 is the above-described first to first embodiments. Different from 3. According to Modification 3 having such a configuration, the metal fine particles having a submicron particle diameter contained in the exhaust gas can be effectively used, and a hollow optical fiber can be manufactured economically.

Furthermore, the hollow optical fiber of the present invention is used for transmitting an infrared signal of 2.1 μm in a Ho: YAG laser, and for transmitting a 2.94 μm Er: YAG laser in addition to an optical fiber that transmits an optical signal in the infrared region of a wavelength of 10.6 μm. The same can be applied to the case. In addition to the infrared region, the present invention can also be applied to transmission of optical signals in the ultraviolet region, for example, Q-switched Nd: YAG laser fourth harmonic (wavelength 266 nm). If this laser is used to transmit through the hollow optical fiber of the present invention, effective treatment of soft tissue and hard tissue can be expected. In addition, in microfabrication of semiconductors and surface modification of materials, the hollow of the present invention is also used for processing using an ArF laser (oscillation wavelength 193 nm), F ₂ laser (oscillation wavelength 157 nm), or even an excimer laser (oscillation wavelength 266 nm). An optical fiber can be applied.

1, 6, 8 ... hollow optical fiber 2 ... glass tube 3 ... metal layer (metal layer on the inner peripheral surface of the glass tube)
4 ... hollow part 7 ... metal layer (metal layer on the outer peripheral surface of the glass tube)
9 ... Buffer layer 10 ... Heat source 13 ... Aerosol container 14 ... Metal fine particle raw material

Claims (13)

a) a glass tube with a linear expansion coefficient of A1 and a softening point of T1,
b) A hollow optical fiber formed on the inner peripheral surface of the glass tube and comprising a first metal layer having a linear expansion coefficient value A2 slightly larger than A1 and a melting point value T2 close to T1.   The hollow optical fiber according to claim 1, wherein a second metal layer made of the same metal as the first metal layer is formed on an outer peripheral surface of the glass tube.   A buffer layer having a linear expansion coefficient A3 smaller than A1 and a melting point T3 close to T1 is provided between the inner peripheral surface of the glass tube and the first metal layer. Item 3. The hollow optical fiber according to Item 1 or 2.   The hollow optical fiber according to claim 1 or 2, wherein the glass tube is made of a hard glass tube, and the first metal layer is made of any one of gold, silver, and aluminum.   The glass tube is made of a hard glass tube or a Pyrex (registered trademark) glass tube, the buffer layer is made of Si or SiN, and the first metal layer is made of any one of gold, silver, and aluminum. The hollow optical fiber according to claim 3, wherein: A fine particle raw material with a submicron particle size of a metal having a linear expansion coefficient of A2 and a melting point of T2 is aerosolized, and the aerosolized fine particle raw material has a linear expansion coefficient substantially equal to or slightly smaller than A2 and is softened. Into a glass tube with a point T1 close to T2,
A method of manufacturing a hollow optical fiber by forming the first metal layer made of the fine particle raw material on the inner peripheral surface of the glass tube by heating the glass tube from the outer peripheral direction of the glass tube while exhausting the inside of the glass tube .   The second metal layer made of the fine particle material is formed on the outer peripheral surface of the glass tube by aerosolizing and spraying a fine particle material having the same metal submicron particle size as the first metal layer. The method for producing a hollow optical fiber according to claim 6.   The method for producing a hollow optical fiber according to claim 6 or 7, further comprising a container for aerosolizing the particulate raw material, wherein exhaust from the glass tube is returned to the container. A fine particle raw material with a submicron particle size of a metal having a linear expansion coefficient of A2 and a melting point of T2 is aerosolized, and the aerosolized fine particle raw material has a linear expansion coefficient substantially equal to or slightly smaller than A2 and softened. Into a glass tube with a point T1 close to T2,
A hollow optical fiber preform tube is formed by heating the glass tube from the outer peripheral direction of the glass tube while evacuating the glass tube to form a first metal layer made of the fine particle raw material on the inner peripheral surface of the glass tube. Creating a process;
A hollow optical fiber comprising a step of melting the tip of the hollow optical fiber preform tube while keeping the inside of the hollow optical fiber preform tube in an inert atmosphere, drawing the optical fiber by drawing at a constant speed Manufacturing method. A fine particle raw material with a submicron particle size of a metal having a linear expansion coefficient of A2 and a melting point of T2 is aerosolized, and the aerosolized fine particle raw material has a linear expansion coefficient substantially equal to or slightly smaller than A2 and softened. The glass tube is fed into the glass tube whose value is T1 close to T2, and the glass tube is heated from the outer peripheral direction of the glass tube while exhausting the inside of the glass tube. Forming a metal layer;
The second metal layer made of the fine particle material is formed on the outer peripheral surface of the glass tube by aerosolizing and spraying the fine particle material having the same metal submicron particle size as the first metal layer on the outer peripheral surface of the glass tube. And the process of creating a hollow optical fiber preform tube,
A hollow optical fiber comprising a step of melting the tip of the hollow optical fiber preform tube while keeping the inside of the hollow optical fiber preform tube in an inert atmosphere, drawing the optical fiber by drawing at a constant speed Manufacturing method.   Before forming the first metal layer on the inner peripheral surface of the glass tube, a buffer layer having a linear expansion coefficient A3 smaller than A1 and a melting point T3 close to T1 is set to silane-based gas or silane-based gas. The method for producing a hollow optical fiber according to any one of claims 6 to 10, further comprising a preliminary step of forming by a gas phase chemical reaction using a nitrogen-based gas.   The method for producing a hollow optical fiber according to any one of claims 6 to 10, wherein the glass tube is formed of a hard glass tube, and the first metal layer is formed of any one of gold, silver, and aluminum. .   The glass tube is made of a hard glass tube or a Pyrex glass tube, the buffer layer is made of Si or SiN, and the first metal layer is made of any one of gold, silver, and aluminum. Item 12. A method for producing a hollow optical fiber according to Item 11.

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