JP2003315588A - Method for manufacturing glass hollow optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide such a method that a hollow fiber adaptive not only in an IR wavelength region but in a wide wavelength region can be manufactured at a low cost. <P>SOLUTION: In the method for manufacturing a hollow optical fiber by heating, fusing and drawing a glass tube, the thickness of the glass is controlled by using the interference effect of light in the glass of the optical fiber, so as to obtain an optical fiber showing low loss property in the wavelength region of the purpose. Preferably, a metal layer is added to the outer surface of the glass hollow optical fiber. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hollow fiber for optical transmission.

[0002]

2. Description of the Related Art A thin metal film is formed on the inner surface of a glass or resin tube to improve the reflectance on the inner surface of the tube.
Furthermore, a low-loss hollow fiber with a dielectric material such as a polymer or an inorganic material deposited on its surface and the internal reflectance further increased by the optical interference effect in the dielectric thin film is used for infrared lasers such as carbon dioxide laser and erbium yag. Is being developed as a transmission line for the. Moreover, since this hollow fiber uses air or gas as the core, the possibility of end face destruction is low, and since there is no reflection at the end face, it is suitable for transmission of large optical power. Even in the wavelength range where can be used, applications are being developed in various fields.

On the other hand, the fact that the refractive index of a certain type of oxide glass is smaller than 1 in a specific wavelength region of infrared and shows a high reflectance at the interface with air is utilized to draw an oxide glass. A method of manufacturing a hollow optical fiber by processing it into a tube has been proposed.

However, in the former method of forming a plurality of thin films on the inner surface of the tube, the manufacturing process is complicated and thus the manufacturing cost is high. Further, since a liquid or the like is introduced into the tube to form the thin films, There was also a problem in the production of hollow fibers with higher flexibility and small diameter.

On the other hand, in the latter method, since the glass drawing method is used, there are advantages that the manufacturing cost is kept low and a fiber having an extremely small diameter can be manufactured, but the wavelength band that can be transmitted is determined by the material. Because,
There was a limit to the degree of freedom in wavelength selection. It is possible to shift the corresponding wavelength range by mixing several kinds of glass, but due to the absorption coefficient that exists even in the region where the real part of the complex refractive index is less than 1, absorption loss occurs and perfect reflection is not possible. It won't. Therefore, it was difficult to obtain a sufficiently high fiber transmission efficiency, and it was not possible to put it into practical use.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to realize a method capable of manufacturing a hollow fiber which can be adapted to a wide wavelength range including an infrared wavelength range at a low cost.

[0007]

In order to achieve the above-mentioned object, the present invention provides a method for producing a hollow optical fiber by heating and melting a glass tube and drawing the optical fiber inside the glass. A glass hollow optical fiber manufacturing method characterized by adjusting the glass wall thickness of the optical fiber so that an optical fiber exhibiting low loss in a target wavelength band can be obtained by utilizing the interference effect of.

A method for manufacturing a glass hollow optical fiber may be characterized in that a metal layer is loaded on the outer surface of the hollow optical fiber.

A method of manufacturing a glass hollow optical fiber may be characterized in that a dielectric multilayer film is formed on the outer surface of the hollow optical fiber.

A method for manufacturing a glass hollow optical fiber may be characterized in that a dielectric multilayer film is formed on the outer surface of the hollow optical fiber, and a metal layer is loaded on the outer surface.

According to the method for manufacturing a hollow optical fiber of the present invention as described above, a low loss property is exhibited with respect to light having a wide range of wavelengths from ultraviolet to infrared, and flexibility is small and a diameter is small. Hollow optical fibers can be manufactured at low cost.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described in detail. First, the glass tube that is the base material must have a sufficiently low absorption coefficient in the wavelength range to be applied. Quartz glass, which has high transparency at all wavelengths of ultraviolet, visible, and infrared, is one of the preferable materials. In addition, Pyrex glass and soda glass, which have a low glass softening temperature, can be melted even in a simple furnace, so they are desirable materials from the viewpoint of low-cost manufacturing. On the other hand, if glass with high transparency in the mid-infrared wavelength range such as chalcogenide glass is used, it is possible to manufacture a fiber with high transmittance even in the long-wavelength range of 3 μm or more.

Hollow fibers are manufactured by melting and softening a preform glass tube in a high-temperature atmosphere such as a tubular electric furnace, and then applying tension to draw it. When the wire is drawn in a normal state, the ratio of the outer diameter of the base material to the glass thickness matches that of the fiber to be drawn, so it is desirable to use a base material with a shape close to the design value. In addition, the wall thickness of the drawn fiber can be controlled by applying tension to the inside and outside of the tube by applying pressure to the inside of the base material.

FIG. 1 is a sectional view showing an embodiment of a fiber manufactured by the method for manufacturing a hollow optical fiber of the present invention. In this example, a metal layer is formed on the outer surface of the drawn fiber in order to improve the transmittance of the fiber. In addition, by adding a metal layer, it is possible to remove the influence of the light transmitted through the fiber from the environment outside the fiber and improve the strength of the fiber. As a material for the metal layer, a material exhibiting a high reflectance in the applicable wavelength range is desirable, and aluminum in the ultraviolet range, silver in the visible range, silver, gold, molybdenum, nickel in the infrared range are suitable. As a method of adding a metal layer, a plating method, a vacuum deposition method, a sputtering method, a method of depositing molten metal, or a combination thereof is preferable. Since the strength of glass may deteriorate after drawing, it is desirable to place a metal layer forming device directly below the drawing furnace so that a metal layer can be added immediately after drawing.

FIG. 2 shows theoretical calculation values of the transmission loss of a fiber obtained by drawing quartz glass and a fiber having a silver layer added to its outer surface. The assumed fiber inner diameter is 2
The transmission loss of HE11 mode, which is 80 micron and is the lowest mode of the circular hollow fiber, is shown as a function of the glass thickness of the fiber.

The glass thickness d giving the low loss property is the refractive index of glass in the case of a fiber having no metal layer added.
If n and the wavelength to be applied are λ, they are given by the following formula.

[0017]

[Equation 1]

On the other hand, the optimum glass thickness d when the metal layer is added is given by the following equation.

[0019]

[Equation 2]

If the thickness of the glass layer is extremely small, the strength of the fiber will decrease, and if it is too large, the effect of absorption loss in the glass will increase. Therefore, the thickness of the glass layer is about 5 to 20 microns, and it is desirable to satisfy the conditions of the above formula. The optimum film thickness is given by the above equation, and an error of about 10% from the optimum value is allowed when actually manufacturing the fiber.

When the thickness of the metal layer is extremely small, the light transmitted through the fiber cannot be shielded from the environment outside the fiber, so that a thickness of 0.1 micron or more is required. Further, in order to give sufficient mechanical strength to the fiber, it is desirable that the thickness of the metal layer be 10 microns or more, but an extremely thick metal layer reduces the flexibility of the fiber, It is desirable that the thickness is 200 microns or less. In addition, after forming a metal film of 0.1 micron or more that functions optically to increase the reflectance,
It is also possible to add another protective layer to give mechanical strength to the fiber. Metal, resin, etc. are suitable as the material of the protective layer.

Further, by forming a multi-layered film of a dielectric material on the outer surface of the drawn glass hollow fiber, it is possible to improve the low loss property and give the fiber wavelength selectivity. In that case, if the number of layers of the multilayer film is small, the transmission efficiency can be improved by adding a metal layer to the outer surface of the multilayer film.

[0023]

In summary, according to the present invention, the following excellent effects are exhibited.

It is possible to manufacture a hollow fiber having a low loss property applicable to a wide wavelength range from ultraviolet to infrared.

It is possible to manufacture a flexible fiber having a small diameter and at a low cost.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram showing the result of theoretical calculation showing the effect of the present invention.

[Explanation of symbols]

1 hollow fiber 2 glass layers 3 metal layers 4 protective layer 5 Hollow area 6 Quartz glass hollow fiber 7 Silica glass hollow fiber with added silver layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mitsunobu Miyagi             Aoba, Aoba-ku, Sendai City, Miyagi Prefecture             Shi) Tohoku University (72) Inventor Takashi Katagiri             Aoba, Aoba-ku, Sendai City, Miyagi Prefecture             Shi) Tohoku University F-term (reference) 2H050 AA06 AB02Y AB67Y AC36                       AC64

Claims (4)

[Claims] 1. A method for manufacturing a hollow optical fiber by heating and melting a glass tube and drawing the glass tube, utilizing the interference effect of light inside the glass of the optical fiber, and exhibiting low loss in a target wavelength band. A method for producing a glass hollow optical fiber, characterized in that the glass wall thickness of the optical fiber is adjusted so that an optical fiber can be obtained. 2. The method for producing a glass hollow optical fiber according to claim 1, wherein a metal layer is added to the outer surface of the hollow optical fiber. 3. The method for producing a glass hollow optical fiber according to claim 1, wherein a dielectric multilayer film is added to the outer surface of the hollow optical fiber. 4. The method for producing a glass hollow optical fiber according to claim 1, wherein a dielectric multilayer film is formed on the outer surface of the hollow optical fiber, and a metal layer is added to the outer surface.