JP2003055003A - Optical fiber for transmission of uv ray and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber for transmission of UV rays in which proceeding of deterioration by UV rays is highly suppressed and to provide a method for manufacturing the fiber. SOLUTION: The method includes a process of heating a quartz optical fiber preform 1 formed to have resistance against UV rays to draw into an optical fiber 2 (process A) and a process of applying a coating layer 3 on the peripheral surface of the optical fiber 2 immediately after drawn (process B) to obtain the optical fiber F for transmission of UV rays. The coating layer 3 can make the temperature decrease of the optical fiber 2 just after drawn slower than that in natural cooling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silica-based optical fiber provided with ultraviolet light resistance for transmitting ultraviolet light.

[0002]

2. Description of the Related Art With the increase in the density of integrated circuits, steppers and the like for forming the circuit patterns are required to perform finer drawing with higher resolution.
Therefore, it is necessary to irradiate an ultraviolet laser beam having a shorter wavelength, and a KrF excimer laser device (wavelength 248 nm), an ArF excimer laser device (wavelength 193 nm), or the like is used as a laser light source.

In some cases, the object to be processed is irradiated with the ultraviolet laser light emitted from these light source devices through an optical fiber. Also, when analyzing the ultraviolet rays emitted by the processed object when excited by the irradiation light and monitoring which layer the etching has reached, the optical fiber is used as the transmission path from the processed object to the photodetector. There are cases.
As described above, the importance of an optical fiber capable of favorably transmitting high-energy ultraviolet rays among ultraviolet rays is increasing.

However, when transmitting high-energy ultraviolet rays using a silica-based optical fiber, structural defects occur in the silica-based glass due to the transmitted ultraviolet rays themselves, unlike the case of transmitting visible light or infrared rays. Phenomenon in which a defect absorbs light of a specific wavelength and deteriorates transmission characteristics (UV deterioration)
Becomes noticeable. Especially, the defect called E'center is
Since it exhibits absorption in a relatively wide wavelength range with a peak near a wavelength of 215 nm, it is a major obstacle to the transmission of high-energy ultraviolet light having a wavelength of 248 nm or 193 nm.

The E'center is a defect bond of silicon, and the cause of the E'center is that the bond between silicon and hydrogen formed in the fiber is broken by high-energy ultraviolet light. It is being appreciated. It is known that this bond between silicon and hydrogen often occurs when a core glass preform containing a large amount of hydrogen is drawn.

In order to reduce the occurrence of E'center,
Japanese Patent Application Laid-Open No. 7-35733 discloses a technique for drawing a wire using a core glass base material having a low hydrogen content,
Further, it is described that hydrogen charging is performed after drawing to improve damage.

[0007]

However, when the inventors of the present invention investigated the degree of ultraviolet deterioration of an optical fiber using a core glass preform having a reduced hydrogen content as described above, the inventors found that However, it was found that the deterioration of ultraviolet rays (in particular, the increase in absorption near the wavelength of 215 nm) could not be sufficiently suppressed without the hydrogen charge after drawing. In addition, the hydrogen-charged material has a temporary effect of suppressing the deterioration of ultraviolet rays, and if it is left for a long time (about 3 months), "release" of the charged hydrogen occurs, and the absorption near the wavelength of 215 nm is also caused. Is known to increase.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide an optical fiber for ultraviolet ray transmission that further suppresses the progress of ultraviolet ray deterioration and a method for manufacturing the same.

[0009]

The present invention has the following features. (1) An optical fiber main body drawn from a silica-based optical fiber preform manufactured to have ultraviolet resistance, and the temperature drop of the optical fiber main body immediately after drawing at room temperature on the outer peripheral surface of the optical fiber main body. And a coating layer formed so as to delay the temperature drop caused by natural cooling.

(2) The ultraviolet light as described in (1) above, wherein the silica-based optical fiber base material is an optical fiber base material having at least a core base material made of silica-based glass having a hydrogen content of 10 ¹⁸ molecules / cm ³ or less. Optical fiber for transmission.

(3) The optical fiber for ultraviolet transmission according to (1) or (2), wherein the coating layer is a layer made of a metal having a melting point of 220 ° C. or higher.

(4) The ultraviolet transmitting optical fiber as described in (3) above, wherein the metal is aluminum.

(5) The ultraviolet transmitting optical fiber as described in (1) or (2) above, wherein the coating layer is a carbon layer.

(6) A step of heating a quartz optical fiber preform formed to have ultraviolet resistance and drawing it to the optical fiber main body, and a temperature drop of the optical fiber main body immediately after drawing are controlled by natural cooling at room temperature. A method for producing an optical fiber for ultraviolet ray transmission, comprising a step of forming a coating layer capable of delaying the temperature drop more than immediately after drawing on the outer peripheral surface of the optical fiber body.

(7) The production according to (6) above, wherein the silica-based optical fiber preform is an optical fiber preform having at least a core preform made of silica-based glass having a hydrogen content of 10 ¹⁸ molecules / cm ³ or less. Method.

(8) The material of the coating layer is a metal having a melting point of 220 ° C. or higher, and in the step of forming the coating layer, the molten metal is passed through the optical fiber main body immediately after drawing. The production method according to (6) or (7) above, which includes processing to form the coating layer.

(9) The method according to (8) above, wherein the metal is aluminum.

(10) The coating layer is a carbon layer, and the step of forming the coating layer includes a process of forming a carbon film on the optical fiber body immediately after drawing at a temperature of 1000 ° C. or higher. 6) The production method according to 7).

(11) In the drawing step, the quartz optical fiber preform is heated to 2000 ° C to 2400 ° C,
In the step of drawing at a drawing speed of 1 m / min to 300 m / min, the step of forming the coating layer is performed at a temperature of 220 ° C. or higher at a position of 100 mm to 5000 mm from the end of the silica-based optical fiber preform. The method according to any one of (6) to (10) above, which is a step of forming a coating layer by means of the above method.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of the ultraviolet transmission optical fiber of the present invention obtained by the method will be described below while explaining the manufacturing method of the present invention. Room temperature in the present invention means
5 to 35 as specified in JIS K 0050
℃. However, the actual room temperature of the production process is 15 ℃ ~
It is usually controlled at about 25 ° C. In the following description, the temperature drop due to natural cooling at room temperature is also abbreviated as “natural drop”.

FIG. 1 is a diagram schematically showing a process of processing an ultraviolet transmission optical fiber according to the manufacturing method of the present invention.
In the manufacturing method, as schematically shown by A in FIG.
A silica-based optical fiber preform formed to have ultraviolet resistance (hereinafter, also referred to as "ultraviolet-resistant optical fiber preform") 1
Of heating and drawing the optical fiber body 2 (hereinafter,
(Also simply referred to as “drawing step”), and as schematically shown by B in the figure, the coating layer 3 that can delay the temperature drop of the optical fiber main body 2 immediately after drawing from the natural drop is provided immediately after drawing. Step of forming on the outer peripheral surface of the optical fiber body (hereinafter,
(Also referred to as “coating step”).

The optical fiber obtained by the manufacturing method is the ultraviolet transmitting optical fiber according to the present invention, and the optical fiber drawn from the ultraviolet resistant optical fiber preform 1 as shown in the step after B of FIG. An optical fiber F for transmitting ultraviolet light, which has a fiber body 2 and a coating layer 3 formed on the outer peripheral surface of the optical fiber body 2 so as to delay the temperature drop of the optical fiber body immediately after drawing from the natural drop.
Is.

By adding the above-mentioned coating step B to the drawing step A, as will be described later, the cooling step immediately after drawing becomes a preferable gradual cooling step for the silica glass, and ultraviolet deterioration (particularly due to the occurrence of E'center). 215nm
It is possible to obtain an optical fiber for transmitting ultraviolet light in which deterioration (absorption in the vicinity) is suppressed.

The silica-based optical fiber base material (preform) used as a material for drawing in the present invention has a core base material made of silica-based glass formed to have ultraviolet resistance for ultraviolet transmission. I wish I had it.
As a quartz glass formed so as to have resistance to ultraviolet rays, it is known that the content of OH, F, B and Cl is controlled in the process of depositing particulate SiO ₂ and forming synthetic quartz glass. What has reduced the content,
It is particularly effective in suppressing the deterioration of the ultraviolet rays associated with the generation of the E'center.

When using a silica glass having a reduced hydrogen content, the hydrogen content is preferably 10 ¹⁸ molecules / cm ³ or less, and particularly preferably 10 ¹⁵ to 10 ¹⁸ molecules / cm ³ . An optical fiber preform made of silica glass with a reduced hydrogen content,
Combined with the slow cooling by forming the coating layer in the present invention, the effect of suppressing the generation of E'center becomes remarkable, and
It is possible to obtain a preferable optical fiber for transmitting ultraviolet light in which the increase in absorption at around 15 nm is highly suppressed.

As a method for forming the quartz optical fiber preform, a known method such as VAD method or plasma method may be used. For a method for reducing the hydrogen content of the silica-based optical fiber preform, known techniques such as Japanese Patent Laid-Open No. 2000-159545 may be referred to.

The silica-based optical fiber preform may have only the core part or may have a core part and a clad part. In the case of only the core portion, the clad portion is covered during drawing. As the material of the clad portion, silica glass having a lower refractive index than that of the core portion is used, but it is preferable that the hydrogen content is similar to that of the core portion.

In the conventional manufacturing process of an optical fiber for transmitting ultraviolet rays, natural cooling is performed at room temperature immediately after drawing (about 2000 ° C. to 2400 ° C.), but the natural decrease immediately after drawing is gradual cooling. Was considered. On the other hand, in the present invention, it has been found that the spontaneous drop immediately after drawing is a rapid cooling in the sense that defects are generated in the silica-based glass, so that the optical fiber main body is not allowed to spontaneously drop (quickly cool) immediately after drawing, The coating layer is formed at a high temperature stage to achieve preferable slow cooling. At the same time, the coating layer shall be formed at a high temperature so that the act of forming the coating layer itself does not rapidly cool the optical fiber body, and a coating layer material that can be formed at such a high temperature is selected. ing. For example, conventionally, a mode is known in which the plastic material is coated when the temperature naturally drops to about 100 ° C. However, this is a rapid quenching, which is not preferable. In the present invention, as the coating layer material, for example, a high melting point material such as aluminum is selected and coating is performed at a temperature equal to or higher than the melting point to avoid quenching due to the coating process itself.

It is considered that by forming the coating layer, the temperature drop immediately after drawing is gradually cooled more than the natural drop, and defects such as E'center are less likely to occur. In particular, when an optical fiber preform having a low hydrogen content is used, the properties of the preform (that is, the property that the bond between silicon and hydrogen is small)
It is considered that the optical fiber body is formed by taking over as much as possible.

(Delaying the temperature drop of the optical fiber main body immediately after drawing rather than the natural drop) means that the time and distance to reach room temperature are more effective than the case of rapid cooling such as natural drop. It means to lengthen. However, the temperature of the optical fiber body whose temperature drop has been delayed need not always be higher than the temperature that spontaneously drops from the high temperature immediately after drawing to room temperature, and it is temporarily higher than the natural drop. It may include a portion where the temperature drops quickly. For example, when the coating formation is started by passing through a die containing aluminum melted at about 730 ° C. at the time of spontaneous fall to 1000 ° C. after drawing, the coating is limited to the start time of the coating, as compared with the case of the natural fall. It will quickly fall to the temperature of formation. However, during coating formation, the optical fiber body is maintained at a temperature of 730 ° C. of the molten aluminum in the die, which can result in a slower temperature drop than in the case of spontaneous drop. Further, in this case, the temperature of 730 ° C. is transmitted from the die filled with the molten aluminum to the downstream through the coating layer, so that the temperature drop rate may be slowed down.
After drawing, when the temperature naturally drops to 650 ° C, 680 ° C
When the aluminum is coated with, the temperature drop is naturally delayed as compared with the case of spontaneous drop because of reheating. Further, when the carbon coating layer is formed by vapor deposition at 1000 ° C. immediately after drawing, the carbon layer may function as a heat retaining layer.

In the present invention, the spontaneous fall after drawing is regarded as a rapid cooling, which is alleviated. However, it is particularly preferable to delay the natural fall at a high temperature immediately after drawing from the viewpoint of suppressing ultraviolet deterioration. Specifically, it is preferable to form a coating layer after the drawing to drop the temperature of the optical fiber main body to 700 ° C., preferably to 800 ° C., to reduce the spontaneous fall. The coating layer forming temperature at that time is 220 to 1
It is preferably 500 ° C, particularly 600 to 800 ° C. The temperature of the optical fiber body at the time of forming the coating layer and the condition temperature for forming the coating layer do not necessarily have to be the same, but in order to prevent a sudden change in the glass, the temperatures of the two are close. Is preferred.

As the material of the coating layer which can be formed as a coating layer in the above temperature range and which can delay the temperature drop of the optical fiber main body from the natural drop,
Examples thereof include carbon and metals having a melting point of 220 ° C. or higher. As the metal, aluminum (melting point 66
0 ° C), nickel (melting point 1453 ° C), gold (melting point 106
3 ° C.), silver (melting point 961.9 ° C.), copper (melting point 1084.
9 ° C.), zinc (420 ° C.), tin (231.9 ° C.) and the like are preferable.

When the material of the coating layer is a metal, the coating layer is preferably formed by passing the molten metal through the optical fiber main body immediately after drawing to form a coating layer.
As a specific device, there is a die having a melting tank for storing metal in a molten state and having a through hole at the bottom thereof. The melting point of aluminum is 660 ° C,
The melting temperature for coating is preferably about 660 ° C to 750 ° C. Regarding the metal coating technique itself at high temperature, the metal coating technique for imparting heat resistance and mechanical strength in a general optical fiber for infrared / visible light transmission may be referred to.

When the coating layer is a carbon layer, the coating layer is formed on the optical fiber body immediately after drawing by 1000 times.
Processing (for example, a chemical decomposition method etc.) which decomposes | disassembles hydrocarbon of a raw material and deposits carbon at 1000 degreeC or more, Preferably it is 1000 degreeC-1800 degreeC, and forms a film. Regarding the carbon layer coating technique itself, a conventionally known coating technique for an optical fiber for infrared / visible light transmission may be referred to.

The drawing speed differs depending on the outer diameter of the ultraviolet transmitting optical fiber to be manufactured. For example, a silica optical fiber preform for ultraviolet resistance, particularly a core preform having a low hydrogen content as described above is used. , Clad layer outer diameter 70 μm to 2
When forming a 500 μm optical fiber main body, 2
It is preferable to heat to 000 ° C to 2400 ° C and set the drawing speed to 1 m / min to 300 m / min. Also in that case,
5 from the end of the quartz optical fiber preform (starting end of drawing)
Area up to 000 mm, especially 100 mm to 5000 mm
It is preferable to arrange the above-mentioned coating step in the area of.

The thickness of the coating layer is not limited, but considering the flexibility and strength of the fiber, the thickness of the coating layer made of metal is preferably about 10 μm to 50 μm, and the thickness of the coating layer made of carbon is 1 nm to about 1 nm. About 50 nm is preferable. The thickness of the coating layer can be controlled by selecting a value from the drawing speed (fiber entry temperature into the die portion), the molten metal temperature (viscosity control), and the coating die size, and combining them.

[0037]

EXAMPLE In this example, the optical fiber for ultraviolet transmission of the present invention was actually manufactured according to the manufacturing process shown in FIG. As the ultraviolet resistant optical fiber base material, a material made of quartz glass having a hydrogen content of about 10 ¹⁸ (molecules / cm ³ ) was used. The base material has a core portion and a fluorine-doped clad portion. The coating layer material was aluminum.

As shown in FIG. 1, as the drawing step A,
The preform 1 was set in a drawing furnace S1 at 2200 ° C. so that the lower end of the ultraviolet resistant optical fiber preform 1 was drawn. The drawing speed is about 60 m / min. Further, as the coating step B, the aluminum coating die S2 was arranged immediately below the drawing step. The distance from the lower end 1b of the base material (starting end of drawing) to the molten surface of aluminum is set to about 3 so that coating is performed at a high temperature immediately after drawing.
It was set to 000 mm.

The aluminum coating die S2 has a melting tank S20 which can be heated by a heater (not shown),
Molten aluminum S21 maintained at 720 to 730 ° C. is housed in the melting tank. The optical fiber main body 2 immediately after drawing was passed through the molten aluminum S21, and was drawn out downward through a through hole at the bottom of the melting tank to obtain an ultraviolet transmission optical fiber F on which the aluminum coating layer 3 was formed. After forming the coating layer, the temperature was naturally lowered to room temperature. The temperature at which the optical fiber body rushed into the molten aluminum was about 400 ° C to 600 ° C.

Comparative Example A UV-resistant optical fiber preform similar to that of the above-described example except that the coating step was not provided, and the same processing steps were used.
A conventional optical fiber for transmitting ultraviolet rays (without coating) was manufactured.

(Evaluation) Ultraviolet rays having a wavelength of 400 nm or less were continuously transmitted for 13 hours to each of the optical fibers for transmitting ultraviolet rays manufactured by the examples and comparative examples, and what kind of absorption occurred in which wavelength range with time. Was measured with an ultraviolet light source and an ultraviolet spectroscope to examine the degree of ultraviolet deterioration.

The measurement result of the example product is shown in FIG. 2, and the measurement result of the comparative example product is shown in FIG. 3, respectively. The graphs of FIGS. 2 and 3 both show the relationship between the “wavelength” (horizontal axis) and the “change in transmittance” (vertical axis) after transmitting ultraviolet rays for 13 hours. “Transmittance change” means the ratio of the transmittance after the ultraviolet ray has been transmitted for a certain time (13 hours in this example) to the initial transmittance (the transmittance when measured at 0 hour of the ultraviolet ray transmission) ( %). Since the initial transmittance is 100% over all wavelengths, the graph shown in the graph is a completely flat straight line.

First, as is apparent from the graph in FIG. 3, the conventional optical fiber for transmitting ultraviolet light of the comparative example shows strong absorption having a peak near a wavelength of 215 nm due to transmission of ultraviolet light for 13 hours. The change in transmittance at the apex of the peak is 10 to 50% of the initial value, which is greatly deteriorated from the initial state. On the other hand, in the ultraviolet transmission optical fiber of the example, even when 13 hours have passed after the start of transmission, the absorption having a peak near the wavelength of 215 nm is very small, and the transmittance change at the apex of the absorption peak is 90.
% Or more, a value in which deterioration is sufficiently suppressed as compared with the conventional deterioration degree is shown.

From the above, even if the optical fiber preform subjected to the same hydrogenation is used, if the temperature drop after drawing is simply lowered naturally, defects such as E'center will be generated by the ultraviolet transmission and the ultraviolet deterioration will occur. However, it has been found that the deterioration of ultraviolet rays can be suppressed by forming a coating layer at a high temperature stage and further gradually cooling according to the present invention.

[0045]

As described above, according to the manufacturing method of the present invention, a preferable gradual cooling effect can be obtained immediately after drawing, and an optical fiber for ultraviolet ray transmission in which the progress of ultraviolet ray deterioration is further suppressed can be obtained. .

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a process of processing an optical fiber for transmitting ultraviolet light according to a manufacturing method of the present invention.

FIG. 2 is a graph showing evaluation of an optical fiber for transmitting ultraviolet light obtained in an example.

FIG. 3 is a graph showing evaluation of an ultraviolet transmission optical fiber obtained by a comparative example.

[Explanation of symbols] 1 UV resistant optical fiber base material 2 Optical fiber body 3 coating layer A wire drawing process B coating process F Ultraviolet transmission optical fiber

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 12, 2001 (2001.12.
12)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

In order to reduce the occurrence of E'center ,
The hydrogen content using a depressed core glass preform drawing technique is disclosed, additionally, because of damage improvement, it is disclosed that performs a hydrogen charging after drawing.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahisa Sugihara             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Tohru Funabashi             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Takeshi Satake             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Kunihiro Hattori             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Kenzo Cicada             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Tokuharu Hayashi             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works F-term (reference) 4G060 AA01 AB00 AC01 AD12 AD22                       AD30 AD53 CA16 CA20

Claims (11)

[Claims] 1. An optical fiber main body drawn from a silica-based optical fiber preform formed to have ultraviolet resistance, and a temperature drop of the optical fiber main body immediately after drawing on the outer peripheral surface of the optical fiber main body at room temperature. And a coating layer formed so as to delay the temperature drop due to the natural cooling of the optical fiber for ultraviolet transmission. 2. The silica based optical fiber preform contains hydrogen.
Quantity 10¹⁸Molecule / cm ³Core made of the following quartz glass
An optical fiber preform having at least a preform.
The optical fiber for transmitting ultraviolet light described. 3. The optical fiber for ultraviolet transmission according to claim 1, wherein the coating layer is a layer made of a metal having a melting point of 220 ° C. or higher. 4. The metal according to claim 3, which is aluminum.
The optical fiber for transmitting ultraviolet light described. 5. The coating layer is a carbon layer.
Alternatively, the optical fiber for transmitting ultraviolet light according to the item 2. 6. A step of heating a silica-based optical fiber preform formed to have ultraviolet resistance and drawing it into an optical fiber main body, and a temperature drop of the optical fiber main body immediately after drawing is controlled by natural cooling at room temperature. A method of manufacturing an optical fiber for ultraviolet ray transmission, comprising a step of forming a coating layer that can be delayed more than the descent on the outer peripheral surface of the optical fiber body immediately after drawing. 7. The silica-based optical fiber preform contains hydrogen.
Quantity 10¹⁸Molecule / cm ³Core made of the following quartz glass
7. An optical fiber preform having at least a preform.
The manufacturing method described. 8. The material of the coating layer is a metal having a melting point of 220 ° C. or higher, and in the step of forming the coating layer, the molten metal is passed through an optical fiber main body immediately after drawing, 7. A process for forming a coating layer is included.
Or the manufacturing method according to 7. 9. The method of claim 8, wherein the metal is aluminum.
The manufacturing method described. 10. The coating layer is a carbon layer, and the step of forming the coating layer includes a process of forming a carbon film on the optical fiber body immediately after drawing at a temperature of 1000 ° C. or higher. Or the manufacturing method according to 7. 11. The drawing step is a step of heating the silica-based optical fiber preform to 2000 ° C. to 2400 ° C. and drawing at a drawing speed of 1 m / min to 300 m / min to form a coating layer. The manufacturing method according to any one of claims 6 to 10, wherein the step of forming is a step of forming a coating layer at a temperature of 220 ° C or higher at a position of 100 mm to 5000 mm from an end of the quartz optical fiber preform. .