JP2003026437A - Method of manufacturing optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of manufacturing an optical waveguide having a high UV transmittance. SOLUTION: This method comprises heating and melting a preform 2 having a core section consisting of quartz glass incorporated with fluorine and a clad section consisting of the quartz glass and drawing the optical waveguide 8 from this preform 2. When the preform is heated and melted at about <=1,800 deg.C, the dislocation of the fluorine added to the core section of the preform is sufficiently prevented. The formation of the glass defect within the core of the optical waveguide is suppressed in the manner described above and therefore the UV transmittance is enhanced.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical waveguide, and more particularly to a method for manufacturing an optical waveguide for transmitting ultraviolet light. [0002] Ultraviolet light having a wavelength of 300 nm or less has recently been used for photolithography, laser processing, sterilization,
The utility value is increasing in fields such as disinfection. In particular, with the miniaturization of semiconductor chips, technology for transmitting shorter wavelength ultraviolet light has been developed. Currently 248nm
KrF excimer laser light having a wavelength of 1.9 nm is mainly used, but an ArF excimer laser light having a wavelength of 193 nm and an F ₂ laser light having a wavelength of 157 nm are expected to become mainstream in the future. A typical example of an optical waveguide for transmitting ultraviolet light is an optical fiber, which is actually used in fields such as medical treatment and fine processing. As an optical fiber for transmitting ultraviolet light, a silica-based optical fiber having silica glass as a core is generally used.
The transmittance of a silica-based optical fiber for ultraviolet light is lower than the transmittance for light having a wavelength of 1.3 μm or 1.55 μm used in optical communication, and the transmittance decreases as the wavelength of transmitted light decreases. Lower. It is said that the low ultraviolet light transmittance of a silica-based optical fiber is caused by a bonding defect of glass. In the present specification, the bonding defect of glass is a state in which a part of the glass network structure is completely cut, or a part of the network is distorted and the bonding distance is greatly extended, so that the glass is extremely cut. It means that it is in an easy state. FIG. 2 shows several examples of the currently reported glass defects of quartz glass. Among them, oxygen-deficient defects such as {Si. (E 'center)} and {Si-Si} are typical ones that absorb light in the ultraviolet region. It is believed that the E 'center defect absorbs light in a wavelength region centered at 215 nm, and the Si-Si bond absorbs light in a wavelength region centered at 163 nm. It is considered that these defects existing in the core of the silica-based optical fiber absorb ultraviolet light, resulting in a decrease in ultraviolet light transmittance. [0005] Various techniques have been proposed for increasing the ultraviolet light transmittance of quartz glass. For example, US Pat.
No. 679125 discloses that fluorine is added to quartz glass in order to eliminate ultraviolet light absorption caused by glass defects and to secure high transmittance. [0006] With the shortening of the wavelength of transmission light, there is a demand for a further increase in ultraviolet light transmittance.
Accordingly, in order to obtain an optical waveguide having a high ultraviolet light transmittance, it is necessary to optimize an optical waveguide manufacturing technique. The present invention has been made in view of the above, and has as its object to provide a method capable of manufacturing an optical waveguide having a high ultraviolet light transmittance. The present invention is directed to a first method for heating and melting a preform having a core portion made of quartz glass to which fluorine is added and a clad portion made of quartz glass.
A second step of drawing an optical waveguide from the preform;
And a method for manufacturing an optical waveguide for ultraviolet light transmission comprising the steps of: The “optical waveguide” refers to a circuit or a line for transmitting light by confining light in a core, and includes an optical fiber and a bundle fiber having a structure in which a plurality of optical fibers are bundled. In the present invention, in the first step, the preform is heated and melted at a temperature of about 1800 ° C. or less. By heating the preform at a temperature lower than the conventional heating temperature of 2000 ° C., the escape of fluorine added to the core is prevented. This suppresses the generation of glass defects in the core of the optical waveguide to be drawn, and increases the transmittance of ultraviolet light. [Embodiment 1] Hereinafter, an optical waveguide manufacturing method according to a first embodiment of the present invention will be specifically described with reference to FIG. Here, FIG. 1 schematically shows a configuration of a drawing apparatus 1 used in the method of the present embodiment. In the present embodiment, ArF excimer laser light (wavelength 193 nm) output from an ArF excimer laser light source
Manufactures optical fibers designed to transmit light. In this embodiment, an optical fiber is drawn from the preform 2 using the drawing apparatus 1. The preform 2 has a substantially cylindrical core portion and a substantially tubular clad portion which is in close contact with the side surface of the core portion and concentrically surrounds the core portion. The core and the clad are made of quartz glass, and the clad has a lower refractive index than the core. In the present embodiment, the core portion contains 1% by weight of fluorine, and the cladding portion contains 3% by weight of fluorine. As described above, fluorine added to quartz glass reduces ultraviolet light absorption due to glass defects and increases the ultraviolet light transmittance of quartz glass. The preform 2 is heated by a heating furnace 4. As a result, the tip of the preform 2 melts and the viscosity decreases. The glass with reduced viscosity gradually decreases in diameter in the heating furnace to have a substantially constant diameter and exits the heating furnace. The quartz glass that has come out of the heating furnace is cooled and becomes an optical fiber 8. Thus, the optical fiber 8 is drawn. As indicated by the arrow 9, the optical fiber 8 moves downward along its longitudinal direction, passes through the coating die 10 after its outer diameter is measured by the outer diameter measuring device 6. When the optical fiber 8 passes through the coating die 10, the first and second ultraviolet curable resins are applied collectively with a predetermined thickness. Thereafter, the optical fiber 8 is irradiated with ultraviolet rays by a curing device 12 such as a high-pressure mercury lamp, and the first and second ultraviolet curable resins are cured together. Thus, the resin coating of the optical fiber 8 is completed, and an optical fiber having the inner coating made of the first ultraviolet-curable resin and the outer coating made of the second ultraviolet-curable resin, that is, the optical fiber 14 is obtained. The optical fiber 14 is taken up by a capstan 16 and wound up by a winding drum 20 via a guide roller 18. Optical fiber 8
A predetermined tension is applied to the optical fiber 14 by the capstan 16. An outer diameter control device 22 is connected to the outer diameter measuring device 6 and the capstan 16.
The outer diameter control device 22 controls the rotation speed of the capstan according to the measured outer diameter of the optical fiber 8 so that the optical fiber 8 has a predetermined outer diameter. In the conventional drawing of a silica-based optical fiber, the temperature in the heating furnace is set to about 2000 ° C., whereas in the present embodiment, the temperature in the heating furnace 4 is set to about 1800 ° C. or less. When the preform 2 is heated at a high temperature in the heating furnace 4, the fluorine in the preform 2 is easily diffused to the outside.
When fluorine escapes from the core portion of the preform 2, glass defects are easily generated there, and as a result, the ultraviolet light transmittance of the optical fiber 14 obtained by drawing becomes low. Therefore, in the present embodiment, the diffusion and escape of fluorine are prevented by making the temperature inside the heating furnace 4 relatively low. Thereby, the ultraviolet light transmittance of the obtained optical fiber is increased. According to the knowledge of the present inventor, an optical fiber having a sufficiently high initial transmittance for ArF excimer laser light (wavelength: 193 nm) can be manufactured by heating and melting a preform at a temperature of about 1800 ° C. or less. . The lower limit of the temperature in the heating furnace 4 is a temperature at which the preform 2 can be melted and softened to such an extent that drawing can be performed, and is about 1700 ° C. in the present embodiment. The drawing speed is about 1800 ° C. in the heating furnace 4.
At about 6.5 m / min. When the heating temperature is set lower, drawing can be performed without cutting the optical fiber by lowering the drawing speed. The temperature of the heating furnace and the ultraviolet light transmittance of the obtained optical fiber are shown below. Here, the wavelength of the ultraviolet light used for measuring the transmittance is 193 nm, and the length of the optical fiber is 1 m. Heating furnace temperature Ultraviolet light transmittance 2000 ° C. 17% 1800 ° C. 27% 1700 ° C. 30% As described above, the present invention has been specifically described based on the embodiments, but the present invention is limited to the above embodiments. Various modifications are possible without departing from the gist of the invention. For example, in the above embodiment, an optical fiber is manufactured, but other optical waveguides that can be manufactured by drawing can be manufactured similarly. The refractive index distribution structure of the optical waveguide is not particularly limited, and may be any of a monocore, a multicore, a single mode, and a multimode. According to the present invention, the core of the optical waveguide is formed by heating the preform at a lower temperature than in the prior art and performing drawing at a higher drawing speed than in the prior art. Prevents fluorine from escaping from the constituent quartz glass.
This suppresses the generation of glass defects in the core of the optical waveguide, so that an optical waveguide having a high ultraviolet light transmittance can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a configuration of a drawing apparatus used in the present embodiment. FIG. 2 is a diagram showing an example of a bonding defect of glass together with a normal glass structure and a stable structure in which hydrogen is fixed to the defect. [Description of Signs] 2 ... Preform, 4 ... Heating furnace, 6 ... Outer diameter measuring device, 8 ...
Optical fiber, 10: coating die, 12: curing device, 14: optical fiber, 16: capstan, 18
... guide roller, 20 ... winding drum, 22 ... outer diameter control device.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Shihiko Shimohiko             Sumitomo Electric, 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd.Yokohama Works F term (reference) 4G021 HA01 HA02 HA04 HA05

Claims (1)

Claims: 1. A first step of heating and melting a preform having a core portion made of quartz glass to which fluorine is added and a clad portion made of quartz glass, and forming an optical waveguide from the preform. A second step of drawing,
A method of manufacturing an optical waveguide for ultraviolet light transmission, comprising: heating the preform at a temperature of about 1800 ° C. or less to melt the preform.