JP2003054979A - Method for manufacturing optical fiber for ultraviolet transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber for UV transmission which largely suppresses the progress of deterioration due to UV. SOLUTION: A quartz-base optical fiber preform 1 formed in such a way as to impart UV resistance is heated and drawn to an optical fiber body 2 (drawing step A) and the optical fiber body 2 after drawing is heated at a heating temperature between room temperature and the drawing temperature (heating step B) so that the temperature drop of the optical fiber body 2 is made slower than a temperature drop due to spontaneous cooling at room temperature to obtain the objective optical fiber F for UV transmission.

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.

An object of the present invention is to solve the above problems and to provide a manufacturing method capable of manufacturing an optical fiber for ultraviolet ray transmission in which the progress of ultraviolet ray deterioration is more highly suppressed.

[0009]

The present invention has the following features. (1) The drawing step of heating the silica-based optical fiber preform formed to have ultraviolet resistance and drawing it to the optical fiber main body, and the temperature drop of the optical fiber main body after the drawing are controlled by natural cooling at room temperature. To delay more than descent,
And a heating step of heating the optical fiber main body at a heating temperature between room temperature and a drawing temperature.

(2) The production according to (1) above, wherein the silica optical fiber preform is an optical fiber preform having at least a core preform made of silica glass having a hydrogen content of 10 ¹⁸ molecules / cm ³ or less. Method.

(3) The heating in the heating step is performed by disposing one or more heaters along the traveling path of the optical fiber main body which is drawn and extends. The manufacturing method described.

(4) The manufacturing method according to (3) above, wherein the number of heaters arranged is one and the heating temperature is 700 ° C to 1500 ° C.

(5) A plurality of the above heaters are arranged along the traveling path of the optical fiber main body, and each heater is set so that the heating temperature by each heater gradually decreases as the optical fiber main body advances. (3) The manufacturing method as described.

(6) The number of heaters arranged is 2 to 10, the heating temperature by the heater for first heating the optical fiber main body is 700 ° C to 1500 ° C, and the heating temperature by the heater for final heating is 100 ° C to 500 ° C. The production method according to (5) above, wherein the production method is C.

(7) The drawing step is a step of heating the quartz optical fiber preform to 2000 ° C. to 2400 ° C. and drawing at a drawing speed of 1 m / min to 300 m / min. The manufacturing method according to any one of the above (1) to (6), wherein a heater for heating first is arranged at a position of 100 mm to 5000 mm from the end of the quartz optical fiber preform.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The manufacturing method of the present invention will be described below. The room temperature referred to in the present invention is 5 to 35 ° C. as specified in JIS K 0050. However, the room temperature in the actual production process is usually controlled to about 15 ° C to 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.
The manufacturing method uses a silica-based optical fiber preform (hereinafter also referred to as “ultraviolet-resistant optical fiber preform”) 1 formed to have ultraviolet resistance, as schematically shown by A in FIG. There is a drawing step of heating and drawing to the optical fiber main body 2, and the optical fiber main body 2 drawn and extending is drawn between room temperature and the drawing temperature, as schematically shown by B in the figure. And a heating step of heating at the heating temperature. The heating in the heating step is performed so as to delay the temperature drop of the optical fiber main body 2 after the drawing (more preferably immediately after the drawing) from the natural drop.

As described above, a heating step is provided after the drawing step, and the cooling is performed more slowly than the natural fall, whereby ultraviolet deterioration (particularly due to the occurrence of E'center 2
It is possible to obtain an optical fiber for transmitting ultraviolet light in which the deterioration (absorption near 15 nm) is suppressed. This is considered to be because the cooling process after drawing is a preferable slow cooling process for the silica glass.

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 fall 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, A heating process is added to reduce the degree of temperature drop.

(Delaying the temperature drop of the optical fiber main body after drawing after the natural drop) makes the time to reach room temperature longer as compared with the case of rapid cooling such as natural drop. Means that. In the drawing step, the silica-based optical fiber preform is heated and melted, and the lower end portion of the preform becomes an optical fiber main body and extends slenderly, and advances in the room air (room temperature) like a belt conveyor. A rapid natural fall. In the present invention, a heating step is provided in the portion of this rapid free fall, so that the free fall is relaxed and the time required to reach room temperature is longer as a result.

The silica-based optical fiber preform (preform) used as a material for drawing in the present invention has a core preform made of silica-based glass formed to have ultraviolet resistance for ultraviolet transmission. I wish I had.
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 . The optical fiber preform made of silica-based glass with the hydrogen content reduced in this way and the gradual cooling by the heating step in the present invention have a remarkable effect of suppressing the ultraviolet deterioration associated with the generation of the E ′ center. It is possible to obtain a preferable optical fiber for transmitting ultraviolet light in which the increase in absorption around 215 nm is highly suppressed. It is considered that this is because the optical fiber main body is formed in such a manner that the properties of the base material (that is, the property that the bond between silicon and hydrogen is small) are inherited as much as possible.

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

The heating step may be provided at any temperature position of the optical fiber main body which is extended while being lowered in temperature after drawing, as long as the temperature drop of the optical fiber main body after drawing is delayed more than the natural drop. Any heating temperature may be used. However, from the viewpoint of reducing the bond between silicon and hydrogen generated in the fiber, it is preferable to provide a high temperature heating step during the higher temperature stage to mitigate the sudden temperature drop. Specifically, it is preferable that the optical fiber main body is heated to a temperature between room temperature and the drawing temperature while the optical fiber main body is cooled down to 700 ° C. after the drawing, so as to alleviate the spontaneous drop. Also, if the heating process is provided at a high temperature stage,
At least the initial heating temperature immediately after drawing is also preferably high, 700 ° C or higher, and more preferably 700 ° C-
It is 1500 ° C, particularly preferably 900 ° C to 1200 ° C.

The heating temperature is the temperature of the heat released from the heating heat source when measured near the surface of the optical fiber body. The temperature of the heating heat source itself may be higher than that, and the distance may be adjusted or obstacles may be appropriately arranged so as to obtain a desired heating temperature.

Although the heating temperature and the temperature of the optical fiber main body when heated are not necessarily the same, in order to reduce the temperature drop of the optical fiber main body smoothly and gently,
It is more preferable that the two temperatures are close to each other. Further, if the temperature drop of the optical fiber body is monotonically reduced, it is sufficient to further add the condition of (heating temperature ≦ temperature of the optical fiber body when heated).

The heating method in the heating step is not limited, but as shown in FIGS. 1 and 2, it is preferable to arrange one or more heaters along the traveling path of the optical fiber body which is drawn and extends. According to this aspect, the temperature drop curve can be freely controlled by changing the arrangement pattern such as the temperature and the position of the heater. This aspect will be described below.

In the example of FIG. 1, the heater H is used as the heating step.
1 is placed. Optical fiber body 2 immediately after drawing
By passing near the heater H1, the temperature drop becomes gentler than in the case of natural drop. The heating temperature by the heater H1 is 700 ° C. or higher, preferably 7 ° C. or higher, as described above as the first heating temperature immediately after drawing.
00 ° C to 1500 ° C, particularly preferably 900 ° C to 120
It is 0 ° C.

In the example of FIG. 2, a plurality of heaters (5 in total, H1 to H5 in the figure) are arranged in the heating step, and the heating temperature by each heater is gradually lowered as the optical fiber body advances. Is set to. The heating temperature may be set appropriately by setting the temperature of the heater itself, setting the distance from the optical fiber body, setting obstacles, and the like. With this mode, the rate of temperature drop can be controlled more finely and gently than in the mode of FIG.

In the conventional manufacturing method, the temperature of the optical fiber body is rapidly lowered to room temperature by a natural drop, but in the embodiment shown in FIG. 1, the heater H1 slows down the temperature by one step during the temperature drop and eases it. To be done. Furthermore, FIG.
In this mode, the temperature drop is relaxed in a plurality of stages, and the first heater H1 reduces the difference between the heating temperature and the temperature of the optical fiber main body, while the last heater H5 reduces the temperature difference between the heating temperature and the room temperature. Can be made smaller. That is, in the mode of FIG. 2, the high temperature optical fiber main body immediately after drawing is received at the high heating temperature and sent out from the low heating temperature to the room, so that the optical fiber main body does not undergo a sudden temperature change and is smoother. It becomes possible to lead to room temperature.

When arranging a plurality of heaters along the traveling path of the optical fiber main body, the number of the heaters is not limited, but considering the cost, the arrangement space, and the effect obtained thereby, it is about 2 to 10, particularly 4 to. 6 is preferable.

When a plurality of heaters are arranged along the traveling path of the optical fiber main body, the heating temperature by the heater on the most upstream side (high temperature side) is 700 ° C. or more as the first heating temperature immediately after drawing, More preferably 70
The temperature is preferably 0 ° C to 1500 ° C, particularly 900 ° C to 1200 ° C. Further, the heating temperature by the heater on the most downstream side (low temperature side) is preferably about 100 ° C to 500 ° C, although it varies depending on the number of heaters arranged.

The width of decrease in heating temperature (step difference) by each heater may be appropriately determined according to the first and last heating temperatures, the number of heaters arranged, and the like, but heaters having the same heating temperature may be continuously arranged. Good. Also, the heating temperature by each heater does not necessarily have to monotonically decrease monotonically as the optical fiber body progresses, and according to a specific decrease curve, and if necessary, the heating temperature of the downstream side The heating temperature may be set higher than the heating temperature on the upstream side.

The drawing speed differs depending on the outer diameter of the ultraviolet transmitting optical fiber to be manufactured. For example, the ultraviolet resistant optical fiber base material, particularly the core base material having a low hydrogen content as described above, is used, and the cladding layer is used. Outer diameter 70 μm to 2500 μ
When forming an optical fiber body of m
~ 2400 ° C, drawing speed 1m / min ~ 300
It is preferably m / min. Although the installation position of the first heater in the heating step is not limited, it is preferably from the end (drawing start end) of the ultraviolet resistant optical fiber preform to 5000 mm, more preferably from 100 mm to 5000 m.
m, especially 100 mm to 3000 mm is preferable. The total length of the heating step is preferably up to 5000 mm, particularly up to 3000 mm.

The heater used in one heating position is
It is preferable to heat from one side of the optical fiber main body and to balance it from the other side, rather than heating from only one side. Moreover, it is preferable that the shape is such that the entire outer circumference of the optical fiber body can be heated uniformly. Specific examples of the heater include a heating wire and a gas burner.

On the outer side of the optical fiber main body, a coating layer made of resin (a known resin material, and preferably an ultraviolet curable material) may be formed for the purpose of protection and reinforcement. The coating layer may be formed at a temperature higher than room temperature, such as 50 ° C. to 70 ° C., after the gradual cooling effect by the heating step is sufficiently obtained. When forming the coating layer,
It is preferable not to give a rapid temperature change to the optical fiber body. A known technique may be referred to for a method of forming the coating layer.

[0038]

EXAMPLE 1 In this example, as shown in FIG. 1, only one heater was provided in the heating step, and the ultraviolet transmitting optical fiber of the present invention was actually manufactured. 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.

As shown in FIG. 1, as the drawing step A,
In order to draw the base material 1 from the lower end of the ultraviolet resistant optical fiber base material 1 by its own weight, the base material 1 is drawn in a drawing furnace S1 at 2200 ° C.
Set to. The drawing speed is about 60 m / min. Further, as the heating step B, a heater H1 using a heating wire
Was placed directly below the drawing process. Heating temperature is 700 ℃
From the lower end 1a (drawing start end) of the base material,
The distance to the heater entrance was set to about 3000 mm. After the heating step, the temperature was naturally lowered to room temperature.

Example 2 In this example, as shown in FIG. 2, the ultraviolet transmitting optical fiber of the present invention was manufactured in the same manner as in Example 1 except that five heaters were provided in the heating step. did.

The specifications of the heaters H1 to H5 are that the respective heating temperatures are H1; 700 ° C., H2; 500 ° C., H3; 300.
C., H4; 200.degree. C., H5; 100.degree. C., and the total length from the inlet of the heater H1 to the outlet of the heater H5 is 2000 mm.

Comparative Example An optical fiber for ultraviolet ray transmission (conventional product) was manufactured in the same manner as in Example 1 except that the heating step was not provided.

(Evaluation) Each of the optical fibers for transmitting ultraviolet light manufactured according to Examples 1 and 2 and the comparative example has a wavelength of 200 nm to
The degree of ultraviolet deterioration was investigated by continuously transmitting ultraviolet rays of 360 nm for 13 hours and measuring what kind of absorption occurs in which wavelength range over time using an ultraviolet light source and an ultraviolet spectroscope. The measurement results of the optical fibers according to Examples 1 and 2 are shown in FIGS. 3 and 4, respectively, and the measurement results of the comparative example products are shown in FIG. Each graph shows the relationship between the “wavelength” (horizontal axis) and the “transmission change” (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 clear from the graph of FIG. 5, 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 about 10% of the initial value, which is greatly deteriorated from the initial state.

On the other hand, in the optical fiber for transmitting ultraviolet light of Example 1, as is clear from the graph of FIG. 3, even when 13 hours have passed after the start of transmission, the absorption peaking at around the wavelength of 215 nm is very small. As a result, the change in transmittance at the apex of the absorption peak is 30% of the initial value, which is a value suppressed compared to the conventional deterioration degree. Furthermore, as is clear from the graph of FIG. 4, the ultraviolet transmission optical fiber of Example 2 has a change in transmittance at the apex of the absorption peak having a peak near the wavelength of 215 nm even 13 hours after the start of transmission. Is 40% of the initial value, and the deterioration degree is further suppressed as compared with the optical fiber of Example 1.

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 was found that UV deterioration can be suppressed by providing a heating step and gradually cooling.

[0047]

As described above, according to the manufacturing method of the present invention, a preferable gradual cooling effect can be obtained 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 diagram schematically showing a preferred embodiment of a processing step of an optical fiber for transmitting ultraviolet light according to the manufacturing method of the present invention.

3 is a graph showing deterioration characteristics of the optical fiber for transmitting ultraviolet light obtained in Example 1. FIG.

FIG. 4 is a graph showing deterioration characteristics of the optical fiber for transmitting ultraviolet light obtained in Example 2.

FIG. 5 is a graph showing deterioration characteristics of the optical fiber for transmitting ultraviolet light obtained in a comparative example.

[Explanation of symbols]

1 UV resistant optical fiber base material 2 Optical fiber body H1 heater A wire drawing process B heating process F Ultraviolet transmission optical fiber

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[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 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 Tatsuya Nishioki             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) 4G021 HA01 HA05

Claims (7)

[Claims] 1. A drawing step of heating a silica-based optical fiber preform formed to have ultraviolet resistance and drawing it to an optical fiber body, and a temperature drop of the optical fiber body after drawing is naturally cooled at room temperature. And a heating step of heating the optical fiber main body at a heating temperature between room temperature and a drawing temperature so as to delay the temperature drop due to. 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 manufacturing method described. 3. The heating in the heating step is performed along the traveling path of the optical fiber main body which is drawn and extends.
The manufacturing method according to claim 1 or 2, which is performed by disposing the above heater. 4. The manufacturing method according to claim 3, wherein the number of heaters arranged is 1, and the heating temperature is 700 ° C. to 1500 ° C. 5. A plurality of the heaters are arranged along the traveling path of the optical fiber main body, and the heating temperature by each heater is gradually lowered as the optical fiber main body advances.
The manufacturing method according to claim 3, wherein each heater is set. 6. The number of heaters arranged is 2 to 10,
The manufacturing method according to claim 5, wherein the heating temperature by the heater that first heats the optical fiber main body is 700 ° C to 1500 ° C, and the heating temperature by the heater that finally heats the optical fiber body is 100 ° C to 500 ° C. 7. 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.
The heating step is performed from the end of the quartz optical fiber preform 1
The manufacturing method according to any one of claims 1 to 6, wherein a heater for heating first is arranged at a position of 00 mm to 5000 mm.