JP2011053636A - Optical fiber, optical fiber preform, clad material and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber which has an excellent transmittance of ultraviolet light which propagates in the optical fiber without performing a hydrogen processing or an oxide processing, and to provide a clad material used for the manufacturing the optical fiber. <P>SOLUTION: The optical fiber is made of quartz glass and internal transmissivity per 1 m of light transmission in the optical fiber is 65% or larger for the light having the wavelength of 193 nm and 25% or larger for the light having the wavelength of 180 nm, and a mean H<SB>2</SB>density ≤1×10<SP>16</SP>pieces/cm<SP>3</SP>is satisfied. The clad material is made of a tube-shaped quartz glass, and a mean OH density ≤10 ppm, mean F density ≥7,000 ppm, mean O<SB>2</SB>density ≤1×10<SP>16</SP>pieces/cm<SP>3</SP>, mean H<SB>2</SB>density ≤1×10<SP>16</SP>pieces/cm<SP>3</SP>, mean ODC(I) density ≤1×10<SP>13</SP>pieces/cm<SP>3</SP>, mean ODC(II) density ≤1×10<SP>12</SP>pieces/cm<SP>3</SP>, mean NBOHC density ≤2×10<SP>14</SP>pieces/cm<SP>3</SP>and mean E'center density ≤2×10<SP>14</SP>pieces/cm<SP>3</SP>are satisfied. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical fiber for high-power optical transmission or ultraviolet light transmission, in particular, an optical transmission fiber that transmits ultraviolet light having a wavelength of 300 nm or less, a cladding material used for manufacturing the optical fiber, an optical fiber preform, and the like It relates to the manufacturing method.

Conventionally, optical fibers are used for information communication and the like, and are also used for medical equipment, semiconductor manufacturing apparatuses, and the like, and are also used for transmission of excimer laser light used in lithography in semiconductor manufacturing processes.
The optical fiber is made of synthetic silica glass or the like and is provided with a cladding having a low refractive index on the outer periphery of the core having a high refractive index. The core is doped with germanium, phosphorus, etc. to increase the refractive index. Is doped with boron, F or the like in order to lower the refractive index.

Excimer lasers such as ArF lasers and KrF lasers emit high-energy ultraviolet light with wavelengths of 193 nm and 248 nm. These high-energy ultraviolet light, that is, deep ultraviolet light having a wavelength of 200 to 300 nm, or vacuum ultraviolet light having a wavelength of 200 nm or less is absorbed by H ₂ O or O ₂ when propagating in the air. Large transmission was impossible. For this reason, an exposure apparatus using an excimer laser has become a large-scale apparatus because it requires a vacuum state or an optical path filled with an inert gas with respect to ultraviolet light or deep ultraviolet light. In order to reduce the size of an exposure apparatus using such an excimer laser, an optical fiber capable of handling these lights has been required.

Optical fibers are also used for the propagation of high-intensity lasers for processing and welding. As processing speeds have increased, there has been a demand for a high-power optical transmission fiber with good light resistance so as to propagate higher energy. Here, the high-power optical transmission fiber means a high-energy light such as a high-intensity laser having a laser peak power of 50 KW / cm ² or more, preferably 500 KW / cm ² or more, more preferably 5 MW / cm ² or more. A transmission fiber.

There is an excimer lamp as a device using deep ultraviolet light or vacuum ultraviolet light. Excimer lamps, for example, Xe ₂ lamps, KrCl lamps, and XeCl lamps emit deep ultraviolet light and vacuum ultraviolet light of 172 nm, 222 nm, and 308 nm, respectively. Such excimer lamps are used in surface cleaning equipment that optically decomposes and removes dirt adhering to the surface of semiconductor wafers and liquid crystal display glass by ultraviolet light irradiation. In surface cleaning equipment using excimer lamps, However, for the same reason as in the exposure apparatus, there has been a demand for the application of an optical fiber that is downsized and easy to handle.

In order to meet these demands, an optical fiber for ultraviolet light transmission whose core is made of silica glass containing 100 to 1000 ppm of F is disclosed (see Patent Document 1).
However, the optical fiber for ultraviolet light transmission described in Patent Document 1 has the following problems to be solved.

  [Problem 1] The F-doped optical fiber in the invention of Patent Document 1 is remarkably superior in terms of transmittance of deep ultraviolet light or vacuum ultraviolet light and durability against ultraviolet light irradiation compared to the previous optical fiber. It came to show performance. However, it has been found that there is a problem that the transmittance in the deep ultraviolet region is lowered on the longer wavelength side than the wavelength expected from the glass transmission spectrum of the preform before spinning into the optical fiber. This is because the absorption end of the optical fiber after spinning is not the intrinsic absorption end (arback end) of the preform, but oxygen deficiency defects (Oxygen-Defective Center (I), hereinafter referred to as “ODC (I) This is because it is shifted to the long wavelength side.

[Problem 2] In a thin fiber having a fiber diameter of about 200 μm, there is a problem in that the transmittance decreases and the durability deteriorates depending on the spinning conditions. This is because, as will be described later, oxygen deficiency defects (Oxygen-Defective Center (II), hereinafter referred to as “ODC (II)”) and E ′ center are generated by heating and drawing during the spinning process.
By applying hydrogen treatment to the F-doped silica glass fiber containing such defects, the E ′ center can be eliminated, but ODC (II) cannot be eliminated.
The F-doped silica glass fiber containing ODC (II) has a drawback that its transmittance is deteriorated by irradiation with ultraviolet light such as ArF excimer laser.

In order to solve the problem 1, Patent Document 2 is an optical fiber having a core made of quartz glass having an F content of 100 to 1000 ppm, and a clad having a refractive index lower than that of the core around the core. An optical fiber for ultraviolet light transmission in which the concentration of oxygen deficiency defects (ODC (I)) in the optical fiber is 10 ¹² / cm ³ or less is disclosed. The optical fiber for ultraviolet light transmission disclosed in Patent Document 2 is said to be an optical fiber for ultraviolet light transmission having excellent durability that hardly causes deterioration due to ultraviolet light irradiation. In the optical fiber for ultraviolet light transmission described in Patent Document 2, the optical fiber is subjected to hydrogen treatment in a temperature range of 500 ° C. to 900 ° C., and the concentration of (ODC (I)) is set to 10 ¹² pieces / cm ³ or less.

  In order to solve the problem 2, Patent Document 3 discloses a core made of quartz glass containing a predetermined amount of F, and a clad made of quartz glass provided on the core and containing a predetermined amount of F or boron. An optical fiber for deep ultraviolet light transmission, which includes a fiber having a protective coating layer provided on the clad and is subjected to oxygen treatment and hydrogen treatment, is disclosed. Thereby, it is said that ODC (II) can be eliminated in the F-doped silica glass fiber, and a deep ultraviolet light transmission fiber with almost no deterioration in transmittance can be obtained.

JP 2002-214454 A Japanese Patent Laid-Open No. 2006-45012 JP 2005-266645 A

However, the optical fibers for ultraviolet light transmission described in Patent Documents 2 and 3 have the following problems.
In Patent Document 2, since it is necessary to perform the hydrogen treatment of the optical fiber at a high temperature of 500 ° C. or more, it is necessary to remove the protective layer coated on the outer periphery of the clad before spinning before spinning. On the other hand, in Patent Document 3, since the hydrogen treatment is performed at 150 ° C. or lower, deterioration of the protective layer coated on the outer periphery of the cladding can be avoided, and it is not necessary to remove the coating. The rate has not been obtained.

  In Patent Document 2, high-temperature hydrogen treatment is performed after the spinning process, and in Patent Document 3, both hydrogen treatment and oxygen treatment are performed after the spinning process, so that the E ′ center, ODC (I), ODC (II), etc. In this case, each defect generates a Si—H bond. The Si—H bond is easily broken and becomes an E ′ center when irradiated with an ArF excimer laser. The E ′ center has a large absorption cross-section at 193 nm compared to other defects, so that the change in transmittance when the ArF excimer laser is continuously irradiated becomes large, and it is difficult to obtain a stable transmittance. It was.

  In addition, the hydrogen molecules contained in the optical fiber by the above hydrogen treatment diffuse out of the optical fiber when the optical fiber is stored at room temperature or high temperature for a long time, and there is a problem that the usable period of the optical fiber is short. there were.

  In order to solve the above-mentioned problems of the prior art, the present invention provides an optical fiber excellent in the transmittance of ultraviolet light transmitted through the optical fiber without subjecting the optical fiber to hydrogen treatment or oxygen treatment, and its production It is an object of the present invention to provide an optical fiber preform suitable for the above and a method for manufacturing the same, and a clad material used for the optical fiber preform and a method for manufacturing the same.

  The present invention is an invention having the following gist.

<1> An optical fiber made of quartz glass, and the internal transmittance per 1 m of optical fiber of light transmitted through the optical fiber is 65% or more for light having a wavelength of 193 nm and 25% or more for light having a wavelength of 180 nm, An optical fiber having an average H ₂ concentration ≦ 1 × 10 ¹⁶ / cm ³ .

<2> Optical fibers each having a core and a clad made of quartz glass, wherein the average OH concentration of the core is ≦ 10 ppm, the average F concentration is ≦ 1000 ppm, the average OH concentration of the clad is ≦ 10 ppm, and the average F concentration is ≧ 7000 ppm The average ODC (II) concentration of the optical fiber ≦ 1 × 10 ¹² pieces / cm ³ , the average NBOHC concentration ≦ 5 × 10 ¹² pieces / cm ³ , and the average E ′ center concentration ≦ 1 × 10 ¹² pieces / cm ³ <1>.

  <3> An optical fiber for high power optical transmission or ultraviolet light transmission, comprising the optical fiber according to <1> or <2>.

<4> A tubular clad material made of quartz glass, which is used for manufacturing an optical fiber preform, and has an average OH concentration ≦ 10 ppm, an average F concentration ≧ 7000 ppm, and an average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average H ₂ concentration ≦ 1 × 10 ¹⁶ cells / cm ³ , average ODC (I) concentration ≦ 5 × 10 ¹⁵ cells / cm ³ , average ODC (II) concentration ≦ 5 × 10 ¹⁴ cells / cm ³ , average NBOHC A clad material having a concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ and an average E ′ center concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ .

  <5> The average OH concentration in a region 20 μm deep from the inner wall surface of the cladding material is 10 ppm or less, and the average OH concentration in a region 10 μm deep from the inner wall surface of the cladding material is 50 ppm or less. Clad material.

<6> An optical fiber preform having the following core and the following cladding each made of quartz glass.
Core: average OH concentration ≦ 10 ppm, average F concentration ≦ 1000 ppm, average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average ODC (I) concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³
Cladding: average OH concentration ≦ 10 ppm, average F concentration ≧ 7000 ppm, average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average ODC (I) concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ , average NBOHC concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , average E ′ center concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ .

<7> The optical fiber preform according to <6>, wherein the core contains F at a concentration satisfying the following formula.
x ≦ 2.8 × 10 ⁶ − {(y−2.8 × 10 ⁶ ) ² + 3.5 × 10 ¹⁰ } ^1/2
(In the formula, y is the average F concentration (ppm) of the cladding, and x is the average F concentration (ppm) of the core.)

<8> In the range of ± 20 μm from the interface between the core and the clad, the average OH concentration ≦ 100 ppm, the average ODC (I) concentration ≦ 5 × 10 ¹⁷ / cm ³ , and the average ODC (II) concentration ≦ 1 × 10 ¹⁶ / The optical fiber preform according to <6> or <7>, which is cm ³ .

<9> In the range of ± 10 μm from the interface between the core and the clad, the average OH concentration ≦ 200 ppm, the average ODC (I) concentration ≦ 1 × 10 ¹⁸ / cm ³ , and the average ODC (II) concentration ≦ 5 × 10 ¹⁶ / The optical fiber preform according to any one of <6> to <8>, which is cm ³ .

<10> The method for producing a clad material according to <4>, wherein SiO ₂ glass fine particles obtained by flame hydrolysis of a glass forming raw material are deposited and grown on a base material to form a porous SiO ₂ glass body And a step of heat-treating the obtained porous SiO ₂ glass body at 1000 ° C. or higher in an atmosphere containing F-containing gas, oxygen, and a rare gas to obtain an F-doped porous SiO ₂ glass body. And a step of heat-treating the obtained F-doped porous SiO ₂ glass body in an atmosphere containing oxygen and a rare gas at 500 ° C. or higher to obtain an F-doped porous SiO ₂ glass body after the oxygen treatment; And a step of obtaining a clad material from the obtained oxygen-treated F-doped porous SiO ₂ glass body as a transparent glass body having a density of 2.0 to 2.3 g / cm ^3. To manufacture clad material Law.

<11> A method for producing a clad material according to <5>,
A step of depositing and growing SiO ₂ glass fine particles obtained by flame hydrolysis of a glass forming raw material on a substrate to form a porous SiO ₂ glass body;
A step of heat-treating the obtained porous SiO ₂ glass body at 1000 ° C. or higher in an atmosphere containing F-containing gas, oxygen, and a rare gas to obtain an F-doped porous SiO ₂ glass body;
The resulting F-doped porous SiO ₂ glass body, and obtaining the oxygen and heat-treated at 500 ° C. or higher is F-doped after oxygen treatment in an atmosphere containing a rare gas porous SiO ₂ glass body, The step of converting the obtained F-doped porous SiO ₂ glass body after oxygen treatment into a transparent glass body having a density of 2.0 to 2.3 g / cm ³ , and the obtained transparent glass body into a tube shape A step of cutting into a tube-shaped glass body, a step of precisely polishing the obtained tube-shaped glass body to obtain a glass tube, and a step of precisely cleaning the obtained glass tube to obtain a clad material The manufacturing method of the clad material characterized by including these.

<12> According to the production method described in <11>, average OH concentration ≦ 10 ppm, average F concentration ≧ 7000 ppm, average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average ODC (I) concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ , average NBOHC concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , average E The center concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , the average OH concentration in the region 20 μm deep from the inner wall surface of the clad material ≦ 10 ppm, and the average OH concentration in the region 10 μm deep from the inner wall surface of the clad material ≦ 50 ppm for obtaining a clad material, average OH concentration ≦ 10 ppm, average F concentration ≦ 1000 ppm, average O ₂ concentration ≦ 1 × 10 ¹⁶ / cm ³ , average ODC (I) concentration ≦ 5 × 10 ¹⁵ / cm ^3, the average ODC Obtaining a core material of the outer peripheral surface of the quartz glass rod is II) concentration ≦ 5 × 10 ¹⁴ atoms / cm ³ by precision grinding and precision cleaning, after inserting the core material into the clad material by a rod-in-tube method A method of manufacturing an optical fiber preform, comprising the steps of: grinding an outer periphery, and further precision polishing and cleaning to obtain an optical fiber preform.

<13> The optical fiber preform according to <12>, wherein the core material subjected to precision polishing and precision cleaning and the clad material subjected to precision polishing and precision cleaning satisfy the following (1) to (3), respectively: Production method.
(1) The surface roughness Ra of the treated surface is 10 nm or less.
(2) No particles having a size of 50 μm or more are present on the treated surface.
(3) There is no scratch having a width of 11 μm or more on the treated surface.

  <14> The method for producing an optical fiber preform according to <12> or <13>, wherein a difference between an outer diameter of the core material and an inner diameter of the clad material is set to 2 mm or less.

  <15> A method for producing an optical fiber, comprising: obtaining an optical fiber preform by the production method according to any one of <12> to <14>, and spinning the optical fiber preform to obtain an optical fiber.

<16> A method for producing an optical fiber made of quartz glass doped with hydrogen,
The internal transmittance of light transmitted through the optical fiber per meter of optical fiber is 65% or more for light with a wavelength of 193 nm and 25% or more for light with a wavelength of 180 nm, and the average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ^3. The optical fiber is held in a hydrogen atmosphere at a temperature of less than 400 ° C. for a certain time, and the internal transmittance per 1 m of the optical fiber of the light transmitted through the optical fiber is 65% or more and the wavelength of 180 nm. A method for producing a hydrogen-doped optical fiber, comprising obtaining an optical fiber that is 30% or more of light.

  <17> The method for producing a hydrogen-doped optical fiber according to <16>, wherein the hydrogen treatment is performed by holding in a hydrogen-containing atmosphere of 15 to 400 ° C. and 0.2 to 15 MPa for 15 hours or more.

<18> ArF excimer laser having an internal transmittance of 65% or more for light having a wavelength of 193 nm and 30% or more for light having a wavelength of 180 nm, and an energy density of ² mJ / cm ² for light transmitted through the optical fiber. Is a hydrogen-doped optical fiber having a transmission energy density of 0.6 or more after irradiation with 5 × 10 ⁶ pulses with respect to the transmission energy density immediately after irradiation.

  According to the present invention, an optical fiber having a low transmission loss when transmitting ultraviolet light can be obtained without performing hydrogen treatment or oxygen treatment.

FIG. 1 is a graph showing transmittance spectra of the clad materials of Examples 1 and 2. FIG. 2 is a graph showing transmittance spectra of the optical fibers of Examples 7 to 9. FIG. 3 is a graph showing transmittance spectra of the optical fibers of Examples 10 to 12. FIG. 4 is a graph showing optical fiber transmittance spectra of Examples 9, 13, and 14. FIG. 5 is a graph showing the relationship between the number of irradiation pulses and the normalized transmission energy density in the optical fibers of Examples 10 and 11. FIG. 6 is a graph showing the relationship between the number of irradiation pulses and the normalized transmission energy density in the optical fibers of Examples 10 and 11. FIG. 7 is a graph showing the relationship between the number of irradiation pulses and the normalized transmission energy density in the optical fibers of Examples 10 and 12.

  In the present specification, unless otherwise specified, ppm represents mass ppm.

<Optical fiber>
In the optical fiber of the present invention, the internal transmittance per 1 m of the optical fiber of light transmitted through the optical fiber is 65% or more for the light having a wavelength of 193 nm. If it is less than 65%, absorption becomes a problem when used for light having a wavelength of 193 nm such as ArF laser light. More preferably, it is 70% or more. On the other hand, it is usually difficult to make it 75% or more, and hydrogen treatment or oxygen treatment is required. Therefore, in an optical fiber not subjected to hydrogen treatment, the internal transmittance of light at 193 nm is generally less than 75% per meter.

  In the optical fiber of the present invention, the internal transmittance per 1 m of the optical fiber of light transmitted through the optical fiber is 25% or more for light having a wavelength of 180 nm. If it is less than 25%, when vacuum ultraviolet light is incident on the optical fiber, problems such as inducing defects and deteriorating transmittance occur. More preferably, it is 26% or more, further preferably 30% or more, and particularly preferably 50% or more. On the other hand, it is usually difficult to make it 70% or more, and hydrogen treatment or oxygen treatment is required. Therefore, in an optical fiber that is not subjected to hydrogen treatment, the internal transmittance of light at 180 nm is generally less than 70% or less than 65% per meter.

The optical fiber of the present invention has an average H ₂ concentration of 1 × 10 ¹⁶ pieces / cm ³ or less. As described in Patent Documents 2 and 3, the high internal transmittance can be obtained by treating an optical fiber with hydrogen. However, there is a problem that the hydrogen molecules incorporated in the optical fiber by hydrogen treatment diffuse out of the optical fiber when the optical fiber is stored for a long time at room temperature or high temperature, and the usable period of the optical fiber is short. Therefore, by achieving the above transmittance without performing hydrogen treatment, it is possible to obtain a high-power optical transmission fiber or an ultraviolet transmission optical fiber that can withstand long-term use and has excellent ultraviolet light durability. . In the optical fiber of the present invention, the average H ₂ concentration is preferably 1 × 10 ¹⁵ atoms / cm ³ or less, and particularly preferably substantially free of hydrogen molecules.

The optical fiber of the present invention has a core and a clad each made of quartz glass, the average OH concentration of the core is ≦ 10 ppm, the average F concentration is ≦ 1000 ppm, the average OH concentration of the clad is ≦ 10 ppm, and the average F concentration is ≧ 7000 ppm. The average ODC (II) concentration of the fiber ≦ 1 × 10 ¹² pieces / cm ³ , the average NBOHC concentration ≦ 5 × 10 ¹² pieces / cm ³ , and the average E ′ center concentration ≦ 1 × 10 ¹² pieces / cm ^3. preferable. Here, the average OH concentration and the average F concentration are average concentrations of the core and the clad, respectively, and hardly include the influence of the interface.

In the optical fiber of the present invention, when the average OH concentration of the core and the clad is 10 ppm or less, high energy light (hereinafter, simply referred to as “high energy light”) having a laser peak power of 50 KW / cm ² or more. .) Refractive index change accompanying volume reduction of quartz glass during irradiation and ultraviolet light irradiation can be reduced, and high power light transmission or ultraviolet light with excellent durability that hardly causes deterioration due to both light irradiations It can be set as the optical fiber for transmission. The mechanism of volume change of quartz glass during irradiation with high energy light and ultraviolet light is not clearly understood, but the OH group in quartz glass is subject to a high electric field such as a laser used as high energy light or ultraviolet light. It is considered that rearrangement occurs and a refractive index change accompanied by volume reduction occurs. In the optical fiber of the present invention, the average OH concentration of the core and the clad is more preferably 8 ppm or less, and particularly preferably 4 ppm or less. It is preferable that OH is not substantially contained.

  In the optical fiber of the present invention, a structure that becomes a precursor of defects such as E ′ center and NBOHC (Non-Bridging Oxygen Hole Center, non-bridging oxygen radical) by setting the average F concentration of the clad material to be 7000 ppm or more. It is possible to reduce the occurrence of defects when spinning and spinning to produce an optical fiber. In addition, since the Si-F structure is formed in the quartz glass constituting the cladding, the durability of the optical fiber when irradiated with high energy light or ultraviolet light is improved. In the optical fiber of the present invention, the average F concentration of the clad is more preferably 9000 ppm or more, further preferably 10,000 ppm or more, and particularly preferably 14,000 ppm or more. In the optical fiber of the present invention, the average F concentration of the clad is more preferably 30000 ppm or less. If it exceeds 30000 ppm, oxygen deficiency defects tend to occur.

In the optical fiber of the present invention, the average Cl concentration in the core and the clad is preferably 50 ppm or less. When chlorine is contained, the light resistance during ultraviolet irradiation is deteriorated. The average Cl concentration in the core and the clad is more preferably 10 ppm or less, further preferably 1000 ppb or less, particularly preferably 10 ppb or less, and most preferably substantially free of chlorine. The average chlorine concentration can be measured by fluorescent X-rays or SIMS (Secondary Ion Mass Spectrometer). The limit of measurement of chlorine by these methods is 5 ppm. As a more accurate measurement method, there is a charged particle activation analysis. The measurement limit of chlorine by this method is about 10 ppb. In the case where quartz glass is produced using a raw material containing chlorine, such as silicon tetrachloride, as a raw material, it may contain chlorine below the measurement limit. Therefore, in order to produce an optical fiber composed of a core and a clad that do not substantially contain chlorine, a raw material that does not contain chlorine, for example, R _n Si (OR ′) _4-n (R and R ′ are hydrogen atoms, Or a preform made of quartz glass produced using an alkoxysilane represented by (an alkyl group having 1 to 4 carbon atoms). Moreover, although the raw material containing chlorine is used in the Example mentioned later, when the raw material containing chlorine is used, a chlorine concentration can be made into 10 ppb or less by baking soot under reduced pressure.

For the same reason as described for the cladding, the core of the optical fiber of the present invention preferably also contains F. However, if the average F concentration of the core is increased, the light refractive index of the core is lowered, so that the average F concentration of the cladding needs to be increased accordingly. When the average F concentration of the clad becomes high, it becomes difficult to set the average ODC (II) concentration of the optical fiber ≦ 1 × 10 ¹² pieces / cm ³ . Therefore, the average F concentration of the core of the optical fiber of the present invention is preferably 1000 ppm or less, more preferably 800 ppm or less, and particularly preferably 500 ppm or less. The average F concentration of the core of the optical fiber of the present invention is preferably 100 ppm or more. If it is less than 100 ppm, problems such as an increase in OH concentration and a failure to reduce the number of structures serving as precursors of defects may occur. More preferably, it is 200 ppm or more, Most preferably, it is 300 ppm or more.

If oxygen-deficient defects are present in the core and cladding of the optical fiber, E ′ centers may be generated from the oxygen-deficient defects when irradiated with high energy light or ultraviolet light. The average ODC (II) concentration of the optical fiber of the present invention is preferably 1 × 10 ¹² pieces / cm ³ or less. As a result, oxygen-deficient defects and E 'centers existing in the optical fiber are extremely reduced, and durability for high-power light transmission or ultraviolet light transmission is excellent. Optical fiber. The occurrence of the E ′ center causes a decrease in the transmittance of the optical fiber, an increase in the absolute refractive index, a change in the refractive index distribution, and generation of fluorescence. In the optical fiber of the present invention, the average ODC (II) concentration in the optical fiber is more preferably 5 × 10 ¹¹ pieces / cm ³ or less, and particularly preferably 2 × 10 ¹¹ pieces / cm ³ or less. For the same reason, the average ODC (I) concentration is preferably 1 × 10 ¹³ atoms / cm ³ or less.

In the optical fiber of the present invention, the average NBOHC concentration of the optical fiber is preferably 5 × 10 ¹² pieces / cm ³ or less, more preferably 2 × 10 ¹² pieces / cm ³ or less. The occurrence of NBOHC causes a decrease in the transmittance of the optical fiber, an increase in the absolute refractive index, a change in the refractive index distribution, and the generation of fluorescence.

In the optical fiber of the present invention, the average E ′ center concentration in the optical fiber is preferably 1 × 10 ¹² pieces / cm ³ or less, more preferably 5 × 10 ¹¹ pieces / cm ³ or less.

The method for measuring the average ODC (II) concentration in the optical fiber is as follows. The transmission spectrum of the optical fiber is measured by the cutback method, and is obtained from the absorption coefficients of 163 nm and 245 nm by the following equation.
Average ODC (II) concentration [piece / cm ³ ] = absorption coefficient of 245 nm [cm ⁻¹ ] / 45 × 10 ⁻¹⁸ [piece ⁻¹ cm ² ]
When the internal transmittance per 1 m of the optical fiber transmitted through the optical fiber is 65% or more for light having a wavelength of 193 nm and 25% or more for light having a wavelength of 180 nm, the average ODC (I) concentration is 1 × 10 6. It is estimated that it is ¹³ pieces / cm ³ or less.

Moreover, the measuring method of the average NBOHC density | concentration and average E 'center density | concentration in an optical fiber is as follows. After measuring the transmittance T% of the optical fiber by the cutback method and converting it to an absorption coefficient α [cm ⁻¹ ] = − 1/100 × ln (T / 100), the following equation is obtained from the absorption coefficients of 258 nm and 214 nm. Ask for.
Average NBOHC concentration [pieces / cm ³ ] = 258 nm absorption coefficient [cm ⁻¹ ] /5.3×10 ⁻¹⁸ [pieces ⁻¹ cm ² ]
Average E ′ center concentration [piece / cm ³ ] = 214 nm absorption coefficient [cm ⁻¹ ] / 25 × 10 ⁻¹⁸ [piece ⁻¹ cm ² ]

The average OH concentration and average H ₂ concentration in the optical fiber of the present invention can be measured in the same manner as the cladding material measurement method described later, except that micro-infrared spectroscopy and micro-Raman spectroscopy are used. On the other hand, the average F concentration is measured by the following method. A Raman spectrum of the fiber cross section is measured using a microscopic Raman spectroscope, and the peak intensity around 950 cm ⁻¹ due to SiF is evaluated. That is, quantitative evaluation is performed by the value I950 / I800 obtained by dividing the peak intensity I950 due to SiF at 950 cm ⁻¹ by the peak intensity I800 due to the fundamental vibration of the bond between the silicon atom and the oxygen atom at 800 cm ⁻¹ . A calibration curve for obtaining F concentration from I950 / I800 is prepared using quartz glass with known F concentration, and F concentration is obtained from I950 / I800 of the measured fiber.

  The optical fiber of the present invention is preferably used as an optical fiber for high power light transmission or ultraviolet light transmission.

<Clad material>
The clad material of the present invention is a tube-shaped clad material made of quartz glass used for optical fiber preforms, and has an average OH concentration ≦ 10 ppm, an average F concentration ≧ 7000 ppm, and an average O ₂ concentration ≦ 1 × 10 ¹⁶ / cm ³ , average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average ODC (I) concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ , average The NBOHC concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ and the average E ′ center concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ .

  The average OH concentration of the clad material of the present invention is 10 ppm or less. For the same reason as in the description of the optical fiber, 8 ppm or less is more preferable, and 4 ppm or less is particularly preferable. It is preferable that OH is not substantially contained.

  The average F concentration of the clad material of the present invention is 7000 ppm or more. For the same reason as in the description of the optical fiber, 9000 ppm or more is more preferable, 10,000 ppm or more is more preferable, and 14000 ppm or more is particularly preferable. Moreover, it is more preferable that it is 30000 ppm or less.

The average O ₂ concentration of the clad material of the present invention is 1 × 10 ¹⁶ pieces / cm ³ . When the average O ₂ concentration of the clad material is high, oxygen excess defects may occur. When oxygen-excess defects exist in the clad, there is a possibility that non-bridging oxygen radicals (NBOHC) are generated from the oxygen-excess defects when a preform produced from the clad is spun to produce an optical fiber. The occurrence of NBOHC causes a decrease in the transmittance of the optical fiber, an increase in the absolute refractive index, a change in the refractive index distribution, and the generation of fluorescence. 1 × 10 ¹⁵ pieces / cm ³ or less is preferable.

The average H ₂ concentration of the clad material of the present invention is 1 × 10 ¹⁶ pieces / cm ³ or less. For the same reason as in the description of the optical fiber, it is preferably 1 × 10 ¹⁵ pieces / cm ³ or less, and particularly preferably substantially free of hydrogen molecules.

The average ODC (I) concentration and the average ODC (II) concentration of the clad material of the present invention are 5 × 10 ¹⁵ pieces / cm ³ or less and 5 × 10 ¹⁴ pieces / cm ³ or less, respectively. For the same reason as in the description of the optical fiber, the average ODC (I) concentration is preferably 1 × 10 ¹⁵ pieces / cm ³ or less. The average ODC (II) concentration is preferably 2 × 10 ¹⁴ atoms / cm ³ or less.

The average NBOHC concentration of the clad material of the present invention is 5 × 10 ¹⁵ pieces / cm ³ or less. The generation of NBOHC causes a decrease in the transmittance of the optical fiber and the generation of fluorescence. 1 × 10 ¹⁵ pieces / cm ³ or less is preferable.
The average E ′ center concentration of the clad material of the present invention is 5 × 10 ¹⁵ pieces / cm ³ or less. The E ′ center causes a decrease in the transmittance of the optical fiber, an increase in the absolute refractive index, a change in the refractive index distribution, and generation of fluorescence. 1 × 10 ¹⁵ pieces / cm ³ or less is more preferable, and 5 × 10 ¹⁴ pieces / cm ³ or less is more preferable.

  The OH concentration of the clad material can be measured using a known method. For example, the measurement can be performed with an infrared spectrophotometer, and the OH concentration can be obtained from the absorption peak at a wavelength of 2.7 μm (JP Williams et. Al., American Ceramic Society Bulletin, 55 (5), 524, 1976). . The detection limit by this method is 0.1 mass ppm.

  The F concentration of the clad material can be measured using a known method. For example, it can be measured by the following procedure. A part of the cladding material is heated and melted with anhydrous sodium carbonate, and distilled water and hydrochloric acid are added to the obtained melt one by one in a volume ratio with respect to the melt to prepare a sample solution. The electromotive force of the sample solution was used as a fluorine ion selective electrode and a reference electrode. 945-220 and no. 945-468, respectively, are measured with a radiometer, and the fluorine content is obtained based on a calibration curve prepared in advance using a fluorine ion standard solution (The Chemical Society of Japan, 1972 (2), 350). The detection limit by this method is 10 ppm.

The measuring method of the O ₂ concentration of the clad material is as follows. Excitation is performed with a laser having a wavelength of 1064 nm or 765 nm, and emission of a 1272 nm peak is measured. Measurement is performed using a detector capable of measuring light having a wavelength of 1272 nm (L. Skuja and B. Guttler, ^'' Detection of Interstitial Oxygen Molecules in SiO ₂ Glass by a Direct Photoexcitation of the Infrared Luminescence of Singlet O ₂ ^” Physical Review Letters, (USA), 1996, Vol. 77, No. 10, P.2093-2096)).

Since the oxygen concentration is proportional to the peak intensity I of the emission spectrum, the average O ₂ concentration can be calculated from the ratio to the emission peak intensity of a standard sample whose oxygen concentration is known in advance. When there is no standard sample, the Raman intensity peak intensity I _{R of} Raman shift: 490 cm ⁻¹ is constant regardless of the sample, and the ratio I of the emission spectrum peak intensity I to the Raman peak intensity I _R From / I _R , the average O ₂ concentration can be calculated by the relational expression of average O ₂ concentration≈5 × 10 ¹⁷ I / I _R [cm ⁻³ ].

The H ₂ concentration of the clad material is measured as follows. A Raman spectroscopic measurement is performed, and a scattering peak intensity I _{4135 of 4135} cm ⁻¹ in the laser Raman spectrum and a scattering peak intensity I ₈₀₀ of ₈₀₀ cm ⁻¹ which is a fundamental vibration between silicon and oxygen are obtained. The hydrogen molecule concentration (molecules / cm ³ ) is determined from the intensity ratio (= I ₄₁₃₅ / I ₈₀₀ ) (VSKhotimchenko et.al., Zhurnal Prikladnoi Spektroskopii, Vol. 46, No. 6, 987 to 997, 1986). .

The measuring method of the average ODC (I) concentration and the average ODC (II) concentration of the clad material is as follows.
First, a transmittance spectrum T [%] is measured using a spectrophotometer, and this is converted into an absorption coefficient α = −1 / D × ln (T / 100) [cm ⁻¹ ] (D is the sample thickness). (expressed in cm).
Next, for ODC (I), the value obtained by dividing the peak intensity α [cm ⁻¹ ] of the absorption band having a peak at 163 nm by 75 × 10 ¹⁸ [cm ² / piece] is defined as the average ODC (I) concentration. .
For ODC (II), a value obtained by dividing the peak intensity α [cm ⁻¹ ] of an absorption band having a peak at 245 nm by 45 × 10 ¹⁸ [cm ² / piece] is defined as the average ODC (II) concentration.

When the average ODC (I) concentration is 10 ¹³ pieces / cm ³ or less, it is preferable to use the following measuring method. Lamp light having a peak at 163 nm perpendicular to the 15 mm × 15 mm mirror surface is incident on a measurement sample, specifically, a sample having dimensions of 15 mm × 15 mm × 100 mm and a 15 mm × 15 mm surface being a double-sided mirror surface. As the lamp light, it is preferable to use a deuterium lamp having a power of 150 W or more because light intensity sufficient to detect a slight difference in transmittance can be obtained. This lamp light is made incident on the half mirror through a light chopper (80 kHz). One of the light split by the half mirror is incident on the photomultiplier tube I, the other is transmitted through the sample, and then incident on the photomultiplier tube II, and the output voltages thereof are compared. Since the light intensity-voltage characteristics of the photomultiplier tubes I and II do not usually match, the average ODC (I with high sensitivity can be obtained by comparing with the ratio when a sample having a known ODC (I) concentration is measured under the same conditions. ) The concentration can be measured.

When the average ODC (II) concentration is 10 ¹² / cm ³ or less, it is preferable to use the following measuring method. A measurement sample, specifically, a sample having a dimension of 15 mm × 15 mm × 30 mm and a mirror surface is irradiated with light such as ArF laser (wavelength 193 nm), KrF laser (wavelength 248 nm), and the sample comes out. The emission intensity near 280 nm is measured. At this time, the average ODC (II) concentration can be measured with high sensitivity by comparing the emission intensity when a sample having a known ODC (II) concentration is measured under the same conditions.

Moreover, the measuring method of the average NBOHC density | concentration of a clad material and an average E 'center density | concentration is as follows. First, the glass to be measured is cut into a thickness of 1.5 cm, for example, and both surfaces are mirror-polished, and then the transmittance T% is measured using a spectrophotometer. However, the absorption coefficients of 258 nm and 214 nm obtained by direct conversion from the transmittance T% are values including reflection loss at the entrance surface and the exit surface of the sample, and do not reflect the internal transmittance itself. For this reason, the absorption coefficient α [cm ⁻¹ ] = − 1 / D × ln ((T−3) / 100) at each wavelength is obtained from the value obtained by subtracting the reflectance loss from 3% and the transmittance T%. (D is the sample thickness in cm, so in this case D = 1.5). The average NBOHC concentration and the average E ′ center concentration are obtained by the following equations.
Average NBOHC concentration [pieces / cm ³ ] = 258 nm absorption coefficient [cm ⁻¹ ] /5.3×10 ⁻¹⁸ [pieces ⁻¹ cm ² ]
Average E ′ center concentration [piece / cm ³ ] = 214 nm absorption coefficient [cm ⁻¹ ] / 25 × 10 ⁻¹⁸ [piece ⁻¹ cm ² ]
The detection limit of the average NBOHC concentration and the average E ′ center concentration obtained by this method is 2 × 10 ¹⁴ pieces / cm ³ .

  In the cladding material of the present invention, the average OH concentration in the region 20 μm deep from the inner wall surface of the cladding material is 10 ppm or less, and the average OH concentration in the region 10 μm deep from the inner wall surface of the cladding material is 50 ppm or less. Is preferred. As will be described later on the method for producing the clad material, the clad material of the present invention is produced by precision polishing and precision cleaning without using flame polishing. For this reason, the clad material of the present invention, the average OH concentration, the average ODC (I) concentration, and the average ODC (II) concentration in the vicinity of the surface can be lowered.

The measurement method of the average OH concentration in the 20 μm deep region and the 10 μm deep region from the inner wall surface of the clad material is to examine the H ₂ concentration distribution in the cross section of the clad material using the TOF-SIMS analysis method. This is carried out by calculating the average in the region having a depth of 20 μm and the region having a depth of 10 μm from the inner wall surface. In this analysis method, it is possible to measure the average H ₂ concentration from the surface layer to a depth of about 10 μm with good spatial resolution and sensitivity, but it is not obvious whether the concentration of H ₂ corresponds to the concentration of OH groups. Therefore, by obtaining the spatial distribution of the OH concentration near the surface layer using a microscopic Fourier transform infrared spectrophotometer (FT-IR), the concentration distribution of the OH group is obtained, and consistency with the result of the TOF-SIMS analysis is obtained. It is necessary to confirm. The absorption coefficient of the absorption peak due to the OH group at 3670 cm ⁻¹ was determined using FT-IR spectroscopy, and the following formula: OH group concentration [ppm] = absorption coefficient [cm ⁻¹ ] /1.05×100
From this, the concentration of OH groups can be determined. However, in FT-IR spectroscopy, since the spatial resolution is not as high as that of TOF-SIMS analysis, an accurate distribution of OH groups cannot be obtained. Therefore, the exact concentration distribution of OH groups is determined by TOF-SIMS analysis.

<Preform>
The preform of the present invention has the following core and the following cladding each made of quartz glass.
Core: average OH concentration ≦ 10 ppm, average F concentration ≦ 1000 ppm, average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average ODC (I) concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³
Cladding: average OH concentration ≦ 10 ppm, average F concentration ≧ 7000 ppm, average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average ODC (I) concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ , average NBOHC concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , average E ′ center concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ .

  Since the preform of the present invention has an extremely low average OH concentration of the core and the clad of 10 ppm or less, as described above, there is little change in the refractive index accompanying the volume reduction of the quartz glass when irradiated with high energy light and ultraviolet light. Thus, the optical fiber for high power light transmission or ultraviolet light transmission excellent in durability that hardly causes deterioration with respect to both light irradiations is obtained. In the preform of the present invention, the average OH concentration of the core and the clad is preferably 0 to 8 ppm, and more preferably 0 to 4 ppm.

If the average O ₂ concentration in the preform core and cladding is high, oxygen-excess defects may occur. If oxygen excess defects exist in the preform core and cladding, non-crosslinked oxygen radicals (NBOHC) may be generated from the oxygen excess defects when spinning to produce an optical fiber. The occurrence of NBOHC causes a decrease in the transmittance of the optical fiber, an increase in the absolute refractive index, a change in the refractive index distribution, and the generation of fluorescence.

In the preform of the present invention, the average O ₂ concentration of the core is 10 ¹⁶ pieces / cm ³ or less and the average O ₂ concentration of the clad is 10 ¹⁶ pieces / cm ³ or less. The occurrence of defects is suppressed. In addition, when an optical fiber is produced by spinning, generation of oxygen excess defects in the core and the clad is suppressed. As a result, in the optical fiber manufactured using the preform, the oxygen excess defects and NBOHC existing in the core and the clad are extremely reduced, and durability is hardly deteriorated with respect to high energy light irradiation or ultraviolet light irradiation. It becomes an excellent optical fiber for high power light transmission or ultraviolet light transmission.

Also, if the average O ₂ concentration in the preform core and clad is high, bubbles may be generated at the interface between the core and the clad. Bubbles generated at the interface between the core and the clad cause problems such as strength deterioration in an optical fiber produced by spinning the preform.

Furthermore, it is known that the absorption edge of quartz glass shifts red when the O ₂ concentration is high (K. Awazu and H. Kawazoe, ^'' Gaseous species and their photochemical reaction in SiO ₂ ^'' Journal of Non- Crystalline Solids, (USA), 1994, Vol. 179, No. 2, pages 214-225).

The center of the absorption peak is near 150 nm, but the bottom of the absorption also affects the wavelength region of 190 nm or less. Further, when O ₃ is generated from O ₂ by irradiation with high energy light or ultraviolet light, an absorption peak of O ₃ appears at 259 nm and the transmittance is reduced, so that resistance to high energy light or ultraviolet light is deteriorated.

Since the preform of the present invention has an extremely low average O ₂ concentration in the core and the clad, generation of bubbles at the interface between the core and the clad is prevented. As a result, an optical fiber manufactured using the preform is an excellent optical fiber for high power light transmission or ultraviolet light transmission that has no bubbles at the interface between the core and the clad.

In the preform of the present invention, the average O ₂ concentration of the core is preferably 1 × 10 ¹⁵ pieces / cm ³ or less, and more preferably 1 × 10 ¹⁴ pieces / cm ³ or less. The average O ₂ concentration of the cladding is preferably 1 × 10 ¹⁵ pieces / cm ³ or less, more preferably 1 × 10 ¹⁴ pieces / cm ³ or less, and further preferably 1 × 10 ¹³ pieces / cm ³ or less.

The method for measuring the average O ₂ concentration is as follows. Excitation is performed with a laser having a wavelength of 1064 nm or 765 nm, and emission of a 1272 nm peak is measured. Measurement is performed using a detector capable of measuring light having a wavelength of 1272 nm (L. Skuja and B. Guttler, ^'' Detection of Interstitial Oxygen Molecules in SiO ₂ Glass by a Direct Photoexcitation of the Infrared Luminescence of Singlet O ₂ ^” Physical Review Letters, (USA), 1996, Vol. 77, No. 10, P.2093-2096)).

Since the O ₂ concentration is proportional to the peak intensity I of the emission spectrum, the average O ₂ concentration can be calculated from the ratio with the emission peak intensity of a standard sample whose O ₂ concentration is known in advance. When there is no standard sample, the Raman intensity peak intensity I _{R of} Raman shift = 490 cm ⁻¹ is constant regardless of the sample, and the ratio I of the emission spectrum peak intensity I and the Raman peak intensity I _R From / I _R , the average O ₂ concentration can be calculated by the relational expression of average O ₂ concentration≈5 × 10 ¹⁷ I / I _R [cm ⁻³ ].

  When the average concentration of oxygen-deficient defects (ODC (I), ODC (II)) in the preform core and cladding is high, oxygen-deficient defects (ODC) in the core and cladding of optical fibers manufactured using the preform are obtained. The concentration of (I) and ODC (II) is increased. If oxygen-deficient defects are present in the core and cladding of the optical fiber, E ′ centers may be generated from the oxygen-deficient defects when irradiated with high energy light or ultraviolet light. The occurrence of the E ′ center causes a decrease in the transmittance of the optical fiber, an increase in the absolute refractive index, a change in the refractive index distribution, and generation of fluorescence. Further, when producing the optical fiber by spinning the preform, there is a possibility that an E ′ center generated from the oxygen deficiency defect may occur.

In the preform of the present invention, the average ODC (I) concentration and the average ODC (II) concentration in the core and the clad are extremely low at 5 × 10 ¹⁵ pieces / cm ³ or less and 5 × 10 ¹⁴ pieces / cm ³ or less, respectively. In an optical fiber manufactured using the preform, the oxygen deficiency defect and the E ′ center existing in the core and the clad are extremely reduced, and durability is hardly deteriorated with respect to high energy light irradiation or ultraviolet light irradiation. It becomes an excellent optical fiber for high power light transmission or ultraviolet light transmission. In the preform of the present invention, the average ODC (I) concentration of the core and the clad is preferably 1 × 10 ¹⁵ pieces / cm ³ or less. In the preform of the present invention, the average ODC (II) concentration of the core and the clad is preferably 2 × 10 ¹⁴ pieces / cm ³ or less.

A method for measuring the average ODC (I) concentration and the average ODC (II) concentration of the preform is as follows.
First, a transmittance spectrum T [%] is measured using a spectrophotometer, and this is converted into an absorption coefficient α = −1 / D × ln (T / 100) [cm ⁻¹ ] (D is the sample thickness). (expressed in cm).
Next, for ODC (I), the value obtained by dividing the peak intensity α [cm ⁻¹ ] of the absorption band having a peak at 163 nm by 75 × 10 ¹⁸ [cm ² / piece] is the average ODC (I) concentration. .
For ODC (II), a value obtained by dividing the peak intensity α [cm ⁻¹ ] of an absorption band having a peak at 245 nm by 45 × 10 ¹⁸ [cm ² / piece] is defined as the average ODC (II) concentration.

The preform of the present invention has an average NBOHC concentration of the clad of 5 × 10 ¹⁵ pieces / cm ³ or less. NBOHC causes a decrease in transmittance of the optical fiber and generation of fluorescence. 1 × 10 ¹⁵ or less is more preferable.

The preform of the present invention has an average E ′ center concentration of the clad of 5 × 10 ¹⁵ pieces / cm ³ or less. The E ′ center causes a decrease in the transmittance of the optical fiber and the generation of fluorescence. 1 × 10 ¹⁵ pieces / cm ³ or less is more preferable, and 5 × 10 ¹⁴ pieces / cm ³ or less is more preferable.

When the average F concentration of the core is increased, the light refractive index of the core is lowered, so that the average F concentration of the cladding needs to be increased accordingly. For this reason, when a core contains F, it is necessary for the average F density | concentration of a core to satisfy | fill following formula (1).
x ≦ A − ((y−A) ² + B) ^1/2 formula (1)
(Where y is the average F concentration (ppm) of the cladding, x is the average F concentration (ppm) of the core, and A = 2.8 × 10 ⁶ , B = 3.5 × 10 ¹⁰ )
Equation 1 was derived by the following method.
It is assumed that the refractive indexes n _core and n _clad of the _core and the _clad satisfy the following formula (2), respectively, and are represented by the following formulas (3) and (4), respectively.
n = aF + b Formula (2)
n _core = aF _core + b Formula (3)
n _clad = aF _clad + b Equation (4)
Here, a and b are both functions of wavelength.

NA is a defining formula,
NA = n ² _core -n ² _clad equation (5)
Substituting Equation (3) and Equation (4) into and solving for F _core ,
F _core = −b / a − {(F _clad + b / a) ² + (NA / a) ² } ^1/2 formula (6)
When −b / a in the formula (6) is A and (NA / a) ² is B,
F _core = A − {(F _clad −A) ² + B} ^1/2 formula (7)
It becomes.

Here, literature (K. Tsukuma, 4 others, ^'' Refractive index, dispersion and absorption of fluorine-doped silica glass in the deep UV region ^'' Journal of Non-Crystalline Solids, (USA), 1991, 127th. Vol. 2, No. 2, P. 191-196 and W. Fleming, DL Wood, ^'' Refractive index dispersion and related properties in fluorine doped silica ^'' Applied Optics, (USA), 1983, Vol. 22, No. 19 , P. 3102-3104), when a and b are obtained by applying Equation (2) for a wavelength of 237.8 nm and a wavelength of 365.0 nm, the values shown in Table 1 are obtained.

  Therefore, when NA = 0.1, the relationship between A and B in Equation 7 is obtained as shown in Table 2.

When these values are extrapolated to obtain the value at 173 nm, A is about 2.8 × 10 ⁶ and B is about 3.5 × 10 ^10. Therefore, A and B at 173 nm are did.
According to the above formula, when an optical fiber having NA = 0.12 and an average F concentration of 15,000 ppm for the clad is manufactured, the average F concentration of the core may be 5000 ppm or less. However, when the F concentration of the core is increased, the F concentration of the cladding needs to be increased. Since it is difficult to introduce a high concentration of F without generating oxygen deficiency defects, the average F concentration of the core is preferably 1000 pmm or less.

  The average F concentration of the core is preferably 100 ppm or more, more preferably 200 ppm or more, further preferably 300 ppm or more, and particularly preferably 500 ppm or more. If it is less than 100 ppm, the OH concentration increases, and there is a possibility that the structure serving as a defect precursor cannot be reduced.

  In order to measure the refractive index difference between the core and the clad in the preform, the refractive index distribution in the preform may be measured with a preform analyzer (for example, P104 manufactured by York Technology Ltd.).

  Since the preform of the present invention has a low average ODC (I) concentration, average ODC (II) concentration, and average E ′ center concentration in the core and cladding, it propagates long-wavelength laser light as high energy light or ultraviolet light. In this case, the probability that the harmonics of the laser beam are absorbed by these defects is small. Therefore, even if the intensity of the laser beam is increased, a new defect generation due to absorption and a change in refractive index accompanied by a volume decrease are unlikely to occur. That is, an optical fiber manufactured using the preform of the present invention having a low defect concentration is less likely to cause transmission loss even for a long wavelength laser beam.

  In addition, introduction of F into quartz glass lowers the fictive temperature of the glass and stabilizes the glass structure. The three-membered and four-membered rings found in quartz glass structures at high fictive temperatures are structures that are energetically weak and break relatively easily when irradiated with high-energy light or ultraviolet light, inducing structural defects. . When F is introduced into quartz glass, F selectively reacts with a weak bonding portion such as a three-membered ring or a four-membered ring. Therefore, high resistance to high energy light or ultraviolet light can be expected by introducing F into quartz glass. That is, it is considered that an optical fiber having a high F concentration exhibits high resistance to high energy light or ultraviolet light.

The average OH concentration, average F concentration, average H ₂ concentration, average NBOHC concentration, and average E ′ center concentration in the preform of the present invention can be measured in the same manner as the cladding material measurement method.

<Manufacturing method of clad material>
The clad material of the present invention can be manufactured by the following procedure.
(A) Porous SiO ₂ glass body forming step SiO ₂ glass fine particles obtained by flame hydrolysis of Si precursor as a glass forming raw material are deposited and grown on a substrate to form a porous SiO ₂ glass body. The glass forming raw material is not particularly limited as long as it is a gasifiable raw material. Examples of the Si precursor include chlorides such as SiCl ₄ , SiHCl ₃ , SiH ₂ Cl ₂ and SiH ₃ Cl, fluorides such as SiF ₄ , SiHF ₃ and SiH ₂ F ₂ , bromides such as SiBr ₄ and SiHBr ₃ , and SiI. halogenated silicon compounds such as iodides such as _{4, R n Si (OR)} 4-n (R is selected from the same or different an alkyl group having 1 to 4 carbon atoms .n is an integer of from 0 to 3.) The alkoxysilane represented by these is mentioned. However, when a raw material containing C is used, oxygen deficiency defects such as ODC (I) and ODC (II) are likely to be generated. Therefore, chlorides such as SiCl ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , SiH ₃ Cl, and SiF ₄ , fluorides such as SiHF ₃ and SiH ₂ F ₂ are preferably used.

  As the base material, a seed rod made of quartz glass (for example, a seed rod described in Japanese Patent Publication No. 63-24973) can be used. Moreover, you may use not only rod shape but a plate-shaped base material.

Further, since the porous SiO ₂ glass body is difficult to handle as it is, it is preferable to hold the porous SiO ₂ glass body at a temperature of 1000 ° C. or higher for a certain period of time while being deposited on the base material. Particularly, in the case of using a chloride such as SiCl ₄ as a raw material, by heat treating the porous SiO ₂ glass body, it is possible to reduce the chlorine concentration of the porous SiO ₂ glass body. Although the atmosphere is not particularly limited, oxygen deficiency defects are easily generated in a reduced pressure atmosphere or a reducing atmosphere, and oxygen excess defects are easily generated in an oxygen atmosphere. The holding time is preferably 3 hours or more and 96 hours or less. If it is less than 3 hours, the retention effect may not be obtained, and if it is 96 hours or more, oxygen excess defects may be easily generated.

(B) F-doping step By heat-treating the obtained porous SiO ₂ glass body at 1000 ° C. or higher in an atmosphere containing F-containing gas, oxygen, and a rare gas, the F-doped porous SiO ₂ glass body is obtained. obtain.

When the porous SiO ₂ glass body is heat-treated in an atmosphere containing only F-containing gas, the inventors of the present application dope a large amount of F, and the densification progresses due to a decrease in viscosity, so that bubbles are generated in the glass. I found it. In order to prevent this, it is necessary to dilute with a gas other than the F-containing gas in order to reduce the concentration of the F-containing gas. When diluted with only a rare gas, oxygen deficiency defects are likely to be generated. It was found that excessive defects are easily generated. For this reason, in the method for producing a clad material of the present invention, it is effective to perform the treatment in an atmosphere in which an F-containing gas, oxygen, and a rare gas are present.

As the F-containing gas, SiF ₄ , SF ₆ CHF ₃ , CF ₄ , C ₂ F ₆ , C ₃ F ₈ , and F ₂ can be used, but SiF ₄ is preferable in order to suppress generation of oxygen-deficient defects. As the rare gas, helium is preferable because the diffusion coefficient is increased and homogeneous and high concentration F is introduced. When the diffusion coefficient is small, the gas does not diffuse into the porous SiO ₂ glass body, and there is a possibility that a difference in F concentration occurs between the inside and the outer surface.

  The concentrations of the F-containing gas, oxygen, and rare gas are preferably 10% by volume or more, 10% by volume or more, and 20% by volume or more, respectively. More preferably, the F-containing gas is 15% to 60% by volume, oxygen is 20% to 60% by volume, and the rare gas is 20% to 60% by volume.

The heat treatment temperature is preferably 800 ° C. or higher, more preferably 1000 ° C. or higher. Moreover, 1250 degrees C or less is preferable.
The heat treatment time is preferably 2 hours or longer, and more preferably 4 hours or longer.
The treatment temperature and treatment time can be set according to the amount of F to be doped into the porous SiO ₂ glass body.

(C) Oxygen treatment step The obtained F-doped porous SiO ₂ glass body is heat-treated at 500 ° C. or higher in an atmosphere containing oxygen and a rare gas, so that the F-doped porous SiO ₂ after the oxygen treatment is obtained. A glass body is obtained.

  When diluted with only a rare gas, oxygen deficiency defects are likely to be generated, and when diluted with only oxygen, oxygen excess defects are likely to be generated. Therefore, the treatment is performed in an atmosphere in which oxygen and a rare gas exist. The heat treatment temperature is preferably 800 ° C. or higher, more preferably 1000 ° C. or higher. Moreover, it is preferable to set it as 1300 degrees C or less. If it exceeds 1300 ° C, it may start to be densified.

As the rare gas, helium is preferable. Helium has a large diffusion coefficient, so even if closed pores are generated, it is difficult to form bubbles. The concentration of oxygen is preferably 0.5% by volume or more, and more preferably 2% by volume or more. Moreover, 30 volume% or less is preferable.
The concentration of the rare gas is preferably 70% by volume or more, and more preferably 90% by volume or more. Moreover, 99.5 volume% or less is preferable.
The heat treatment time is preferably 2 hours or longer, more preferably 4 hours or longer, and particularly preferably 15 hours or longer.

(D) Vitrification step The obtained oxygen-doped F-doped porous SiO ₂ glass body is made into a transparent glass body having a density of 2.0 to 2.3 g / cm ³ . Heat treatment is preferably performed at 1200 ° C. or higher for 2 hours or more in a helium atmosphere or a reduced-pressure atmosphere.

(E) Tube process The obtained transparent glass body is cut into a tube shape to obtain a tube-shaped glass body.

(F) Polishing step The obtained tube-shaped glass body is polished to obtain a glass tube. As a polishing method, it is preferable to perform precision polishing described later.

(G) Cleaning step The obtained glass tube is cleaned. As a cleaning method, it is preferable that precision cleaning described later is performed.

The core material is produced by the following steps: a porous SiO ₂ glass body containing F by holding in an atmosphere containing an F compound gas at room temperature without performing heat treatment in steps (b) and (c). The manufacturing procedure of the clad material of the present invention is substantially the same except that it is obtained. As the core material used for producing the preform of the present invention, the average OH concentration ≦ 10 ppm, the average F concentration ≦ 1000 ppm, the average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , and the average ODC (I) concentration ≦ 5 × It is preferable that 10 ¹⁵ pieces / cm ³ and the average ODC (II) concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ .

  In addition to the above-described methods, there are known VAD, ODV, MCVD, and PCVD methods as methods for manufacturing the core material and the clad material, but the conventional method achieves a predetermined defect concentration and gas component concentration. I could not. In the present invention, a clad material satisfying a predetermined defect concentration and gas component concentration could be produced by producing glass by the procedures of (a) to (g). In particular, (d) before the vitrification step, (b) the F-doping step and (c) the oxygen treatment step are performed separately, and by limiting the type of gas used and the amount of gas, a predetermined defect concentration, gas component Concentration could be achieved.

Here, the precision polishing and the precision cleaning refer to a surface polishing method and a surface cleaning method other than flame polishing that are performed in order to make the inner wall surface of the clad material and the outer peripheral surface of the core material have the required surface properties. Specifically, a surface polishing method and a surface cleaning method that can satisfy the following conditions (1) to (3) are preferable.
(1) The surface roughness Ra of the treated surface is 10 nm or less.
(2) No particles having a size of 50 μm or more are present on the treated surface.
(3) There is no scratch having a width of 11 μm or more on the treated surface.

  If one or both of the core and the clad does not satisfy the conditions (1) to (3), a preform is produced, and bubbles and foreign matters are generated at the interface between the core and the clad, thereby reducing the strength of the fiber. There is a possibility that problems such as deterioration and deterioration of fiber characteristics may occur.

The surface roughness Ra of the inner wall surface of the clad material and the outer peripheral surface of the core material is preferably 5 nm or less, and more preferably 1 nm or less.
More preferably, no particles having a size of 10 μm or more are present on the treated surface.
More preferably, there is no scratch having a width of 5 μm or more on the treated surface.

  The surface roughness Ra of the inner wall surface of the clad material and the outer peripheral surface of the core material is measured along the outer peripheral surface of the core and the inner peripheral surface of the clad using an ultra-precision three-dimensional measuring instrument, for example, UAP3 (manufactured by Panasonic). It can be determined by measuring a surface roughness Ra of 10 mm in each direction and circumferential direction.

  Particles and scratches on the inner wall surface of the clad material and the outer peripheral surface of the core material can be observed by confirming light scattering due to defects caused by the particles and scratches using a high-intensity light source (50,000 lux).

Here, in order to eliminate scratches, it is preferable to gradually reduce the size of the abrasive grains. Specifically, by changing the size of the abrasive grains to # 240, # 400, # 600, # 800, # 1000, and then mirror polishing with cerium oxide, a scratch-free mirror surface can be obtained. . Even if the size of the abrasive grains is not reduced gradually, for example, even if it is changed to # 240, # 600, or # 1000, it can be made into a mirror surface by subsequent mirror polishing, but latent scratches may exist. Examples of the polishing include precision polishing (mechanical polishing) performed on an optical surface of an optical member such as a lens surface.
In order to precisely polish the inner wall surface of the clad material and the outer peripheral surface of the core material, a jig suitable for the outer diameter and inner diameter is prepared, and the shape is gradually adjusted by combining the abrasive grains and the jig, and the surface. It is preferable to obtain a core material (core rod) or a clad material (clad tube) with high precision by precision polishing by the work of increasing smoothness.

As precision cleaning, wet cleaning methods include solvent cleaning using an alkaline solvent, functional water cleaning using ozone water, electrolytic ion water, hydrogen water, etc., ultrasonic cleaning, microbubble cleaning, HF cleaning, and the like. . Examples of dry cleaning methods include etching gas cleaning using an etching gas such as CF ₄ and C ₄ F ₈ , excimer lamp cleaning, plasma cleaning, and ion cleaning.

  By removing the foreign matter on the inner wall surface of the clad material and the outer peripheral surface of the core material and performing the above-mentioned precision polishing and precision cleaning instead of flame polishing for the purpose of improving flatness, the clad material near the inner wall surface Volatilization of F, and oxygen deficiency defects (ODC (I), ODC (II)) and the structure serving as a precursor thereof are thereby prevented. In addition, problems such as an increase in OH concentration in the vicinity of the outer peripheral surface of the core material and generation of a structure serving as a defect precursor are prevented.

<Preform manufacturing method>
The preform of the present invention is manufactured by inserting a core material (core rod) into a clad material (clad tube) using a rod-in-tube method.
The preform of the present invention uses a core material and a clad material that have been subjected to precision polishing and precision cleaning, instead of flame polishing that is usually performed in the preform manufacturing process.

  When a preform is manufactured by the rod-in-tube method, flame polishing is usually performed for the purpose of removing foreign matters on the surface of the core material (core rod) and the surface of the clad material (cladding tube) and improving the flatness. Since there is no mechanical equipment to precisely polish the outer circumference of the core material (core rod) and the inner wall surface of the clad material (clad tube), it usually takes time to finish with high precision such as roundness and linearity. In general, a core material (core rod) or a clad material (clad tube) with high accuracy is obtained by flame polishing. The same applies to cleaning, and in particular, foreign matter adhering to the inner wall surface of the clad material (clad tube) is difficult to remove by cleaning, and it is common to remove foreign matter by flame polishing.

  However, when glass containing F is heated in an atmosphere containing moisture, F is volatilized from the glass surface. When performing flame polishing, since it is usually performed with an oxyhydrogen flame, heating is performed in an atmosphere containing a lot of moisture, and the F concentration on the glass surface becomes smaller than that inside. As a result, the F concentration of the core material is reduced near the interface between the core and the cladding, and when the preform is formed, the refractive index near the interface between the core and the cladding becomes higher than that in the core, and the output light In addition to distortion of the wavefront shape, there may be a problem that propagation loss increases.

  Therefore, in order to precisely polish the outer peripheral surface of the core material (core rod) and the inner wall surface of the cladding material (clad tube), a jig suitable for the outer diameter and inner diameter is prepared, and the abrasive grains and the jig are combined. It is preferable to obtain a core material (core rod) or a clad material (clad tube) with high precision by precision polishing by gradually adjusting the shape and increasing the surface smoothness.

  During flame polishing, F is volatilized in the vicinity of the inner wall surface and the outer peripheral surface of the clad material (clad tube). Of these, the inner wall surface of the clad material (clad tube) forms the interface between the core and the clad when the preform is formed, so that the volatilization of F from the vicinity of the inner wall surface of the clad material (clad tube), and this Oxygen deficiency defects (ODC (I), ODC (II)) due to the formation of a structure serving as a precursor thereof are particularly problematic. The vicinity of the inner wall surface of the clad material refers to a portion from the inner wall surface of the clad material (clad tube) to a depth of about 20 μm.

  In the present invention, since the core material (core rod) does not contain F or has a low F concentration, the problems caused by the volatilization of F as described above are unlikely to occur. In the vicinity of the outer peripheral surface of the core material (core rod), problems such as an increase in OH concentration and generation of a defect precursor structure occur. The vicinity of the outer peripheral surface of the core material (core rod) refers to a portion from the outer peripheral surface of the core material (core rod) to a depth of about 20 μm.

  Also, when a preform is formed using the rod-in-tube method, heat is applied to the core material and the clad material, so that F is volatilized and oxygen deficiency defects (ODC (I), ODC (II)) and their A structure that becomes a precursor may be generated. Therefore, in order to lower the heating temperature when performing the rod-in tube and shorten the heating time, the difference between the outer diameter of the core material (core rod) and the inner diameter of the cladding material (cladding tube) is preferably within 2 mm. , More preferably within 1.5 mm, and even more preferably within 1 mm. When the difference between the outer diameter of the core rod and the inner diameter of the clad tube is large, the amount of heat applied to the clad tube in the rod-in-tube process increases, which may cause oxygen deficiency defects in the preform.

  In addition, it is preferable to provide a dedicated cleaning facility for precision cleaning, and to remove foreign substances by using ultrasonic cleaning or the like. In particular, since the clad material (clad tube) is difficult to circulate the chemical solution, it is difficult to reduce the number of particles on the inner wall of the clad material (clad tube) by a normal cleaning method. Therefore, it is preferable to use immersion in an acidic aqueous solution for cleaning the clad material (clad tube). After washing, immerse in isopropyl alcohol (IPA) and dry. When subjected to a high-temperature heat process such as a rod-in tube with moisture or alcohol adhering to the glass surface, F reacts with hydroxyl groups and volatilizes as HF to form defects. Is preferably reduced as much as possible. Therefore, the drying is finally performed at 100 ° C. or higher.

  In the preform manufacturing method of the present invention, in the rod-in tube process, the cladding tube is heated from the outside with an oxyhydrogen flame, and therefore it is preferable to grind the outside of the preform by at least 1 mm. Polishing is preferably performed after grinding to form a preform. At this time, it is preferable that the surface of the preform has a C level or higher in the Mil-O-13830A standard. It is preferable that no scratches having a width of 25 μm or more exist on the preform surface, more preferably 21 μm or more, further preferably 16 μm or more, particularly preferably 11 μm or more. For the outer periphery grinding of the preform, a well-known grinding method can be adopted. For example, the preform can be mounted on a lathe, ground with a diamond grindstone, and the abrasive grain size of the grindstone can be gradually reduced. In order to eliminate a scratch having a large line width, it is preferable to polish by a known method. For example, the preform can be attached to a lathe and polished while supplying a cerium oxide slurry. Like the outer periphery of the core material (core rod), it is more preferable to perform precision polishing.

In the preform of the present invention, in the region of ± 10 μm from the interface between the core and the clad, the average OH concentration is preferably 200 ppm or less, more preferably 50 ppm or less, and further preferably 10 ppm or less. Preferably has an average ODC (I) concentration is 1 × 10 ¹⁸ / cm ³ or less, more preferably 1 × 10 ¹⁷ / cm ³ or less, more preferably 1 × 10 ¹⁶ / cm ³ or less, 5 × 10 ¹⁵ pieces / cm ³ or less are particularly preferred, and 1 × 10 ¹⁵ pieces / cm ³ or less are most preferred. The average ODC (II) concentration is preferably 5 × 10 ¹⁶ pieces / cm ³ or less, more preferably 1 × 10 ¹⁶ pieces / cm ³ or less, further preferably 1 × 10 ¹⁵ pieces / cm ³ or less, and 5 × 10 ¹⁴ pieces / cm ³ or less is particularly preferable. The boundary between the core and the clad is an interface, and the core side from the interface is indicated by a positive value, and the clad side is indicated by a negative value. ± 20 μm from the interface indicates a region extending to 20 μm on both the core side and the cladding side, and ± 10 μm indicates a region extending from the interface to 10 μm on both the core side and the cladding side.

In the preform of the present invention, in the region of ± 20 μm from the core / cladding interface, the average OH concentration is preferably 100 ppm or less, more preferably 20 ppm or less, and even more preferably 10 ppm or less. The average ODC (I) concentration is preferably 5 × 10 ¹⁷ pieces / cm ³ or less, more preferably 5 × 10 ¹⁶ pieces / cm ³ or less, further preferably 5 × 10 ¹⁵ pieces / cm ³ or less, and 1 × 10 ¹⁵ pieces / cm ³ or less is particularly preferable. The average ODC (II) concentration is preferably 1 × 10 ¹⁶ pieces / cm ³ or less, more preferably 1 × 10 ¹⁵ pieces / cm ³ or less, and further preferably 5 × 10 ¹⁴ pieces / cm ³ or less.

The average ODC (I) concentration and the average ODC (II) concentration in the region of ± 20 μm and the region of ± 10 μm from the interface between the core and the clad are measured by, for example, elemental analysis of the cross section of the preform using the TOF-SIMS analysis method. And the average ODC (I) concentration and the average ODC (II) concentration in the ± 20 μm region and the ± 10 μm region are obtained from the obtained F and hydrogen cross-sectional concentration distributions. When flame polishing is performed, an increase in the amount of hydrogen due to an increase in OH groups and a decrease in F occur, but the decrease in F suggests that the Si-F bond was broken and F was volatilized from the surface. It is considered that the bond deficient portion becomes a defect such as ODC (I) or ODC (II). The average concentration of the average ODC (I) concentration and the average ODC (II) concentration can be determined from the absorption coefficients at 163 nm and 245 nm by the following equation by measuring the transmission spectrum.
Average ODC (I) concentration [pieces / cm ³ ] = 163 nm absorption coefficient [cm ⁻¹ ] / 75 × 10 ⁻¹⁸ [pieces ⁻¹ cm ² ]
Average ODC (II) concentration [piece / cm ³ ] = absorption coefficient of 245 nm [cm ⁻¹ ] / 45 × 10 ⁻¹⁸ [piece ⁻¹ cm ² ]
However, since these defects generated by flame polishing exist only near the surface, in order to determine the concentration of defects near the surface, the absorption coefficient of the above equation is used to determine the thickness of the F defect layer obtained from TOF-SIMS analysis. Convert from.

The average OH concentration in the ± 20 μm region and the ± 10 μm region from the core / cladding interface is determined by examining the H ₂ concentration distribution in the cross section of the preform using the TOF-SIMS analysis method. This is performed by calculating the average in the region of ± 10 μm. In this analysis method, it is possible to measure the average H ₂ concentration from the surface layer to a depth of about 10 μm with good spatial resolution and sensitivity, but it is not obvious whether the concentration of H ₂ corresponds to the concentration of OH groups. Therefore, by obtaining the spatial distribution of the OH concentration near the surface layer using a microscopic Fourier transform infrared spectrophotometer (FT-IR), the concentration distribution of the OH group is obtained, and consistency with the result of the TOF-SIMS analysis is obtained. It is necessary to confirm. The absorption coefficient of the absorption peak due to the OH group at 3670 cm ⁻¹ is obtained using FT-IR spectroscopy, and the concentration of the OH group can be obtained from the following formula.

OH group concentration [ppm] = absorption coefficient [cm ⁻¹ ] /1.05×100 [cm ⁻¹ ppm ⁻¹ ]
However, in FT-IR spectroscopy, since the spatial resolution is not as high as that of TOF-SIMS analysis, an accurate distribution of OH groups cannot be obtained. Therefore, the exact concentration distribution of OH groups is determined by TOF-SIMS analysis.

  Note that the SIMS analysis method, which is excellent in terms of spatial resolution and measurement accuracy, is used for the concentration distribution measurement of the ODC (I) concentration, ODC (II) concentration, and OH concentration of the core and clad alone.

  In the preform manufacturing method of the present invention, both the core rod and the clad tube are precision-polished and precision-cleaned, and then preformed by the rod-in-tube method. Regarding the method of performing the rod-in tube after the precision polishing and precision cleaning, it is disclosed in Japanese Patent Application Laid-Open No. 2003-238184, but the inventors of the present application, as described above, the precision polishing method, the precision cleaning method, It has been found that the preform of the present invention can be obtained by improving all of the rod-in-tube methods.

<Optical fiber manufacturing method>
The preform of the present invention produced by the above procedure is heated and melted in a spinning furnace while adjusting the speed of the take-up machine so that the outer diameter becomes a predetermined value. A transmission optical fiber can be manufactured. By inserting the core material (core rod) into the clad material (cladding tube) and inserting it into the electric furnace, the core and the clad can be integrated and then the fiber can be drawn simultaneously. In this case, appropriate fiber spinning conditions Since it is difficult to achieve appropriate rod-in-tube conditions in the same electric furnace at the same time, it is preferable to perform spinning in a separate step after integrating the core and the clad with the rod-in tube.

  According to the present invention, it is possible to obtain an optical fiber for high power light transmission or ultraviolet light transmission which has low transmission loss when transmitting ultraviolet light and excellent durability without performing hydrogen treatment. The treated fiber may be treated with hydrogen. It may be possible to further improve the transmittance by performing hydrogen treatment.

  A hydrogen-doped optical fiber can be obtained by holding the optical fiber of the present invention in a hydrogen atmosphere at a temperature of less than 400 ° C. for a certain period of time. As a result, the internal transmittance per 1 m of the optical fiber transmitted through the optical fiber is 65% or more for light having a wavelength of 193 nm and 30% or more for light having a wavelength of 180 nm. It is maintained even when irradiated with ultraviolet light.

The hydrogen treatment conditions are preferably 15 hours or longer under a hydrogen atmosphere of 15 to 400 ° C. and 0.2 to 15 MPa.
If it is less than 15 ° C., it takes time for hydrogen treatment, so it is difficult to dope hydrogen into the interior. More preferably, it is 50 degreeC or more, Most preferably, it is 100 degreeC or more. When hydrogen treatment is performed at a temperature higher than 400 ° C., Si—H bonds are formed, and when irradiated with an ArF excimer laser, an E ′ center is formed, which may cause a change in transmittance. The hydrogen treatment temperature is preferably less than 200 ° C, more preferably less than 150 ° C, particularly preferably less than 120 ° C, and most preferably less than 90 ° C.

  The hydrogen treatment time is preferably 15 hours or longer. When the hydrogen treatment time is short, hydrogen does not reach the inside of the optical fiber, and the effect of the hydrogen treatment is difficult to be exhibited. The hydrogen treatment time is more preferably 50 hours or more, and particularly preferably 100 hours or more.

  The hydrogen treatment pressure is preferably 0.2 MPa or more. When the hydrogen treatment pressure is low, hydrogen does not reach the inside of the optical fiber and the effect of the hydrogen treatment is difficult to be exhibited. The hydrogen treatment pressure is more preferably 0.3 MPa or more, further preferably 0.5 MPa or more, particularly preferably 1 MPa or more, and most preferably 5 MPa or more. On the other hand, if it exceeds 15 MPa, there is a possibility that embrittlement of the apparatus and piping used for the hydrogen treatment becomes remarkable. More preferably, it is 10 MPa or less.

The hydrogen-doped optical fiber of the present invention, when irradiated with an ArF excimer laser having an energy density of ² mJ / cm ² at a frequency of 1 kHz, has a transmission energy density after irradiation of 5 × 10 ⁶ pulses with respect to the transmission energy density immediately after irradiation. However, it is preferably 0.6 or more, more preferably 0.8 or more, and particularly preferably 0.9 or more.

  Here, the energy density and transmission energy density of the laser light irradiated to the optical fiber are obtained as follows. The light incident on the optical fiber is made into a spot that is approximately 10% larger than the core diameter of the optical fiber by inserting an iris in front of the incident end. The light in this spot is received by a power meter (for example, LASERSTAR made by OPHIR), the energy intensity is obtained, and the energy density of the irradiated laser light is obtained by dividing by the area of the iris. On the other hand, the transmission energy density is obtained by irradiating an optical fiber with a laser beam, receiving the laser beam emitted from the emission end, and measuring it.

As in the optical fiber for ultraviolet light transmission described in Patent Document 3, there is known a fiber in which the optical fiber is doped with hydrogen to improve the transmittance and thereby improve the durability. In such an optical fiber, there is little decrease in transmittance even when irradiated with high energy density ultraviolet laser light. However, when the laser beam with low energy density is irradiated for a long time, especially when the laser beam with a high repetition frequency of 1 kHz or more is irradiated for a long time of 10 ⁶ pulses or more, the transmittance gradually decreases, and stable for a long time. Problems arise with use. Since the optical fiber of the present invention exhibits excellent transmittance without hydrogen treatment, it exhibits excellent durability in a hydrogen-doped optical fiber.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples. Examples 1, 4, 7, and 10 are examples, and examples 2, 3, 5, 6, 8, 9, and 11-14 are comparative examples.
In Tables 3 to 7 below, the abbreviations have the following meanings.
OH: Average OH concentration (ppm), F: Average F concentration (ppm), O ₂ : Average O ₂ concentration (pieces / cm ³ ), H ₂ : Average H ₂ concentration (pieces / cm ³ ), ODC (I) : mean ODC (I) concentration (number ^{/ cm 3), ODC (II} ): mean ODC (II) concentration (number / cm ^3), NBOHC: mean NBOHC concentration (pieces / cm ^3), E'center: mean E 'Center concentration (pieces / cm ³ ).

[Example 1] (Clad material production)
A porous SiO ₂ glass body was obtained by depositing and growing SiO ₂ glass fine particles obtained by heating hydrolysis (flame hydrolysis) of SiCl ₄ as a glass forming raw material in an oxyhydrogen flame on a substrate (( a) Step). Since the obtained porous SiO ₂ glass body was difficult to handle as it was, it was kept in the atmosphere at 1300 ° C. for 6 hours and then removed from the substrate.

The obtained porous SiO ₂ glass body was held at 1080 ° C. for 5 hours in an atmospheric pressure atmosphere of 35% by volume of SiF _4, 35% by volume of oxygen and 30% by volume of helium, and F-doped porous SiO ₂ glass. A body was obtained (step (b)).
The obtained F-doped porous SiO ₂ glass body was held at 1150 ° C. for 5 hours in an atmospheric pressure atmosphere of 5 volume% oxygen and 95% helium volume, and F-doped porous SiO after oxygen treatment. _Two glass bodies were obtained (step (c)).

The obtained oxygen-doped F-doped porous SiO ₂ glass body was held under reduced pressure at 1150 ° C. for 24 hours, then heated to 1370 ° C. in 5 hours, held at 1370 ° C. for 2 hours, A transparent glass body having a density of about 2.2 g / cm ³ was obtained (step (d)).
The obtained transparent glass body was held at 1700 ° C. for 2 hours and formed into a block shape. Then, it cut into the tube shape with the outer periphery grinding machine and the cylindrical grinding machine, and obtained the tube-shaped glass body ((e) process).

  After polishing the obtained tube-shaped glass body with a slurry of abrasive grains GC # 240, GC # 400, FO # 600, FO # 800, FO # 1000 (all are trade names of Fujimi Corporation) The glass tube was obtained by carrying out precision polishing without using an oxyhydrogen flame using a miracle (trade name, manufactured by Mitsui Kinzoku Co., Ltd.) containing cerium oxide as a main component (step (f)). The obtained glass tube had an outer diameter of 24 mm and an inner diameter of 18 mm. Further, the non-circularity was 2 or less, the roughness was φ0.1 μm or less, and the scratch was 11 μm in width.

  The obtained glass tube was immersed in an aqueous nitric acid solution for 12 hours as a pretreatment, then ultrasonically cleaned with pure water, and ultrasonically cleaned in an IPA cleaning tank as a posttreatment, and dried at 100 ° C. Obtained (step (g)). The inner wall surface of the obtained clad material had a surface roughness Ra of 10 nm or less, no particles having a size of 50 μm or more, and no scratch having a width of 11 μm or more.

[Example 2] (Production of clad material)
An example except that instead of the steps (a) to (e), the glass obtained by the PCVD method was cut into a tube shape by a peripheral grinding machine and a cylindrical grinding machine to obtain a tubular glass body. A clad material was obtained in the same manner as in method 1.

[Example 3] (Production of clad material)
The clad material of Example 2 was subjected to flame polishing using an oxyhydrogen flame to obtain a clad material. Flame polishing was performed by a method in which an oxygen gas was allowed to flow inside the cladding material and the outside was blown with an oxyhydrogen burner. It was 2000 degreeC when the temperature rise of the clad material in a flame grinding | polishing process was measured with the radiation thermometer (the Laytec make, marathon MM-model G5H).

  The physical properties of the clad materials of Examples 1 and 2 were measured and shown in Table 3. The transmittance spectra of the clad materials of Examples 1 and 2 sliced 15 mm from the surface were measured and are shown in FIG.

The cladding material of Example 1 has an average OH concentration ≦ 10 ppm, an average F concentration ≧ 7000 ppm, an average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , an average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , an average ODC ( I) Concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , Average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ , Average NBOHC concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ , Average E ′ center concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ .

  The OH concentration on the inner wall surface of the cladding material of Example 1 and the cladding material of Example 3 was measured. Table 4 shows the average OH concentration in a region 20 μm deep from the surface and the average OH concentration in a region 10 μm deep from the surface. Since the inner wall surface of the cladding material of Example 1 is not subjected to flame polishing, the average OH concentration in the region 20 μm deep from the surface ≦ 10 ppm, and the average OH concentration in the region 10 μm deep from the surface of the cladding material ≦ 50 ppm there were.

[Example 4] (Preform preparation)
Quartz glass AQX (trade name, manufactured by Asahi Glass Co., Ltd., average OH concentration = 4 ppm, average F concentration = 200 ppm, average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , average H ₂ concentration ≦ 1 × 10 ¹⁵ pieces / cm ³ , The average ODC (I) concentration ≦ 1 × 10 ¹³ pieces / cm ³ and the average ODC (II) concentration ≦ 1 × 10 ¹² pieces / cm ³ ) were cut into a rod shape by an outer peripheral grinding machine.

  Then, after polishing the outer periphery with a slurry of abrasive grains GC # 240, GC # 400, FO # 600, FO # 800, and FO # 1000, precision polishing is performed using a miracle mainly composed of cerium oxide. A glass rod was obtained. The obtained glass rod had an outer diameter of 17.2 mm, a non-circularity of 2 or less, a diameter of φ0.1 μm or less, and a scratch of 11 μm in width.

The obtained glass rod is immersed in an aqueous nitric acid solution for 12 hours as a pretreatment, then ultrasonically cleaned with pure water, and ultrasonically cleaned in an IPA cleaning tank as a posttreatment, and dried at 100 ° C. Obtained. The inner wall surface of the obtained core material had a surface roughness Ra of 10 nm or less, no particles having a size of 50 μm or more, and no scratch having a width of 11 μm or more.
A preform was produced by the rod-in-tube method using the produced core material and the clad material of Example 1.

[Example 5] (Preform preparation)
A preform was produced by the rod-in-tube method using the core material produced in the same manner as in Example 4 and the clad material in Example 2.

[Example 6] (Preform preparation)
The core material produced in the same manner as in Example 3 was subjected to flame polishing using an oxyhydrogen flame. It was 2000 degreeC when the temperature rise of the core material in a flame grinding | polishing process was measured with the radiation thermometer (The Raytec make, Marathon MM-model G5H).
A preform was produced by a rod-in-tube method using the flame-polished core material and the clad material of Example 3.

Table 5 shows the OH concentration, O ₂ concentration, ODC (I) concentration, and ODC (II) concentration in portions sufficiently distant from the interfaces of the core material and the clad material used in the preparation of the preforms of Examples 4 to 6. The preform of Example 4 has low defect concentration and gas component concentration of the core material and the clad material used.

Expected measurement values of average OH concentration, average ODC (I) concentration, average ODC (II) concentration, and average F concentration in the regions of ± 10 μm and ± 20 μm from the core-cladding interface in the preforms of Examples 4 to 6 Is shown in Table 6. In Example 4, since flame polishing was not performed, the average OH concentration ≦ 100 ppm, the average ODC (I) concentration ≦ 5 × 10 ¹⁷ pieces / cm ³ , and the average ODC (II) in the range of ± 20 μm from the core / cladding interface. The concentration is ≦ 1 × 10 ¹⁶ pieces / cm ³ , and the average OH concentration ≦ 200 ppm, the average ODC (I) concentration ≦ 1 × 10 ¹⁸ pieces / cm ³ , and the average ODC (± 10 μm from the core / cladding interface) II) Concentration ≦ 5 × 10 ¹⁶ / cm ³ is expected.

[Example 7] (Fabrication of optical fiber)
Using the preform of Example 4, an optical fiber having a core diameter of 400 μm and a cladding diameter of 440 μm was spun.

[Example 8] (Fabrication of optical fiber)
Using the preform of Example 5, an optical fiber having a core diameter of 400 μm and a cladding diameter of 440 μm was spun.

[Example 9] (Production of optical fiber)
Using the preform of Example 6, an optical fiber having a core diameter of 400 μm and a cladding diameter of 440 μm was spun.

The transmittances of the optical fibers of Examples 7 to 9 are shown in FIG. The average OH concentration and average F concentration in the core and the clad are estimated values from the core material and the clad material. As shown in FIG. 2, in the optical fiber of Example 7, the internal transmittance per 1 m of the optical fiber transmitted through the optical fiber is 65% or more for light with a wavelength of 193 nm and 25% or more for light with a wavelength of 180 nm. The average H ₂ concentration was 10 ¹⁶ pieces / cm ³ or less.

Also, as shown in Table 7, the optical fiber of Example 7 has an average OH concentration of the core ≦ 10 ppm, an average F concentration ≦ 1000 ppm, an average OH concentration of the cladding ≦ 10 ppm, and an average F concentration ≧ 7000 ppm. The average ODC (II) concentration ≦ 1 × 10 ¹² pieces / cm ³ , the average NBOHC concentration ≦ 5 × 10 ¹² pieces / cm ³ , and the average E ′ center concentration ≦ 5 × 10 ¹² pieces / cm ³ . Further, from the result of the average internal transmittance of the optical fiber, it is estimated that the ODC (I) concentration of Example 7 ≦ 1 × 10 ¹³ pieces / cm ³ .

[Example 10]
The optical fiber of Example 7 was left to stand in a 100% hydrogen atmosphere at 80 ° C. and 0.98 MPa for 7 days to perform hydrogen treatment.

[Example 11]
The optical fiber obtained by the same method as in Example 8 was left to stand in a 100% hydrogen atmosphere at 80 ° C. and 0.98 MPa for 14 days for hydrogen treatment.

[Example 12]
The optical fiber obtained by the same method as in Example 9 was left to stand in a 100% hydrogen atmosphere at 80 ° C. and 0.98 MPa for 14 days for hydrogen treatment.

[Example 13]
The optical fiber obtained by the same method as in Example 9 was left in an oxygen atmosphere at 150 ° C. and 15 MPa for 7 days for oxygen treatment. This corresponds to L8 in FIG.

[Example 14]
The optical fiber obtained by the same method as in Example 9 was allowed to stand for 7 days in an oxygen atmosphere at 150 ° C. and 15 MPa. After oxygen treatment, the optical fiber was further left in a hydrogen atmosphere at 15 MPa and 150 ° C. for 2 days. Processed. This corresponds to L9 in FIG.

  The transmittance spectra of the optical fibers of Examples 10 to 12 are shown in FIG. In Example 10, although the hydrogen treatment time is shorter than in Examples 11 and 12, the internal transmittance per 1 m of the optical fiber of light transmitted through the optical fiber is 65% or more for light with a wavelength of 193 nm and a wavelength of 180 nm. It became the outstanding physical property of 30% or more about light.

The transmittance spectra of the optical fibers of Examples 13 and 14 are shown in FIG.
It can be seen that Example 7 was able to obtain the same internal transmittance without hydrogen treatment and Example 10 without oxygen treatment.

The optical fibers of Examples 10 and 11 having a length of 1.5 m were prepared, and this was irradiated with an ArF excimer laser having an energy density of ² mJ / cm ² at a frequency of 1 kHz. FIG. 5 shows changes in the transmission energy density normalized by the initial transmission energy density when the number of irradiation pulses is increased. The transmission energy density normalized by the initial transmission energy density (hereinafter simply referred to as “normalized transmission energy density”) is the ratio of the transmission energy density after irradiation with a predetermined amount of pulses to the transmission energy density immediately after irradiation. .
From FIG. 4, in Example 11, the normalized transmission energy density greatly decreases as the number of irradiation pulses increases, whereas in Example 10, the normalized transmission energy density averages 1 even when the number of irradiation pulses increases. As a result, the physical properties of the standardized transmission energy density were not deteriorated.

The optical fibers of Examples 10 and 11 having a length of 1.5 m were prepared, and this was irradiated with an ArF excimer laser having an energy density of 5 mJ / cm ² at a frequency of 1 kHz. The normalized transmission energy density when the number of irradiation pulses is increased is shown in FIG. From FIG. 6, in Example 11, the normalized transmission energy density greatly decreases as the number of irradiation pulses increases, whereas in Example 10, the decrease in normalized transmission energy density is small even when the number of irradiation pulses increases. After irradiation with 1 × 10 ⁶ pulses, excellent physical properties such as a high value of 0.8 were obtained.

The optical fibers of Examples 10 and 12 having a length of 1 m were prepared, and irradiated with light of the fourth harmonic (266 nm) of an Nd: YVO4 laser having an energy density of 16 mJ / cm ² at a frequency of 50 kHz. did. FIG. 7 shows the normalized transmission energy density when the number of irradiation pulses is increased. From FIG. 7, in Example 12, the normalized transmission energy density decreases significantly as the number of irradiation pulses increases, whereas in Example 10, the decrease in normalized transmission energy density is small even when the number of irradiation pulses increases. It was an excellent physical property that it was almost constant with the initial value.

  The optical fiber of the present invention is excellent in the transmittance of ultraviolet light transmitted through the optical fiber. Such an optical fiber of the present invention is suitably used, for example, in the field of medical equipment, semiconductor manufacturing equipment, etc., in addition to being used for information communication and the like.

Claims (18)

It is an optical fiber made of quartz glass, and the internal transmittance per 1 m of optical fiber of light transmitted through the optical fiber is 65% or more for light with a wavelength of 193 nm and 25% or more for light with a wavelength of 180 nm, and the average H ₂ An optical fiber having a concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ . An optical fiber having a core and a clad each made of quartz glass,
The average OH concentration of the core ≦ 10 ppm, the average F concentration ≦ 1000 ppm,
The average OH concentration of the clad ≦ 10 ppm, the average F concentration ≧ 7000 ppm,
The average ODC (II) concentration of the optical fiber ≦ 1 × 10 ¹² pieces / cm ³ , the average NBOHC concentration ≦ 5 × 10 ¹² pieces / cm ³ , and the average E ′ center concentration ≦ 1 × 10 ¹² pieces / cm ^3. The optical fiber according to 1.   An optical fiber for high power light transmission or ultraviolet light transmission comprising the optical fiber according to claim 1 or 2. A tubular clad material made of quartz glass used in the manufacture of optical fiber preforms,
Average OH concentration ≦ 10 ppm, average F concentration ≧ 7000 ppm,
Average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , Average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ ,
Average ODC (I) concentration ≦ 5 × 10 ¹⁵ / cm ³ ,
Average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ ,
Average NBOHC concentration ≦ 5 × 10 ¹⁵ / cm ³ ,
A clad material having an average E ′ center concentration ≦ 5 × 10 ¹⁵ pieces / cm ³ .   The clad material according to claim 4, wherein an average OH concentration in a region 20 μm deep from the inner wall surface of the clad material is 10 ppm or less, and an average OH concentration in a region 10 μm deep from the inner wall surface of the clad material is 50 ppm or less. An optical fiber preform having the following core and the following cladding, each of which is made of quartz glass.
Core: average OH concentration ≦ 10 ppm, average F concentration ≦ 1000 ppm,
Average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , Average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ ,
Average ODC (I) concentration ≦ 5 × 10 ¹⁵ / cm ³ ,
Average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ .
Cladding: average OH concentration ≦ 10 ppm, average F concentration ≧ 7000 ppm,
Average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , Average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ ,
Average ODC (I) concentration ≦ 5 × 10 ¹⁵ / cm ³ ,
Average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ ,
Average NBOHC concentration ≦ 5 × 10 ¹⁵ / cm ³ ,
Average E ′ center concentration ≦ 5 × 10 ¹⁵ / cm ³ . The optical fiber preform according to claim 6, wherein the core contains F at a concentration satisfying the following formula.
x ≦ 2.8 × 10 ⁶ − {(y−2.8 × 10 ⁶ ) ² + 3.5 × 10 ¹⁰ } ^1/2
In the formula, y is the average F concentration (ppm) of the cladding, and x is the average F concentration (ppm) of the core. In the region of ± 20 μm from the interface between the core and the cladding, the average OH concentration ≦ 100 ppm, the average ODC (I) concentration ≦ 5 × 10 ¹⁷ pieces / cm ³ , and the average ODC (II) concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ The optical fiber preform according to claim 6 or 7. In the range of ± 10 μm from the core / cladding interface, the average OH concentration ≦ 200 ppm, the average ODC (I) concentration ≦ 1 × 10 ¹⁸ / cm ³ , and the average ODC (II) concentration ≦ 5 × 10 ¹⁶ / cm ³ The optical fiber preform according to any one of claims 6 to 8. It is a manufacturing method of the clad material according to claim 4,
A step of depositing and growing SiO ₂ glass fine particles obtained by flame hydrolysis of a glass forming raw material on a substrate to form a porous SiO ₂ glass body;
A step of heat-treating the obtained porous SiO ₂ glass body at 1000 ° C. or higher in an atmosphere containing F-containing gas, oxygen, and a rare gas to obtain an F-doped porous SiO ₂ glass body;
The resulting F-doped porous SiO ₂ glass body, and obtaining the oxygen and heat-treated at 500 ° C. or higher is F-doped after oxygen treatment in an atmosphere containing a rare gas porous SiO ₂ glass body,
A step of obtaining a clad material by using the obtained oxygen-doped F-doped porous SiO ₂ glass body as a transparent glass body having a density of 2.0 to 2.3 g / cm ³ ;
A method for producing a clad material comprising: It is a manufacturing method of the clad material according to claim 5,
A step of depositing and growing SiO ₂ glass fine particles obtained by flame hydrolysis of a glass forming raw material on a substrate to form a porous SiO ₂ glass body;
A step of heat-treating the obtained porous SiO ₂ glass body at 1000 ° C. or higher in an atmosphere containing F-containing gas, oxygen, and a rare gas to obtain an F-doped porous SiO ₂ glass body;
The resulting F-doped porous SiO ₂ glass body, and obtaining the oxygen and heat-treated at 500 ° C. or higher is F-doped after oxygen treatment in an atmosphere containing a rare gas porous SiO ₂ glass body,
A step of converting the obtained F-doped porous SiO ₂ glass body after the oxygen treatment into a transparent glass body having a density of 2.0 to 2.3 g / cm ³ ;
Cutting the obtained transparent glass body into a tube shape to form a tube-shaped glass body;
A step of precisely polishing the obtained tubular glass body to obtain a glass tube;
A step of precisely cleaning the obtained glass tube to obtain a clad material;
A method for producing a clad material comprising: According to the manufacturing method of claim 11,
Average OH concentration ≦ 10 ppm, average F concentration ≧ 7000 ppm,
Average O ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ , Average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ³ ,
Average ODC (I) concentration ≦ 5 × 10 ¹⁵ / cm ³ ,
Average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ ,
Average NBOHC concentration ≦ 5 × 10 ¹⁵ / cm ³ ,
Average E ′ center concentration ≦ 5 × 10 ¹⁵ / cm ³
Obtaining a clad material having an average OH concentration ≦ 10 ppm in a region 20 μm deep from the inner wall surface of the clad material and an average OH concentration ≦ 50 ppm in a region 10 μm deep from the inner wall surface of the clad material;
Average OH concentration ≦ 10 ppm, average F concentration ≦ 1000 ppm,
Average O ₂ concentration ≦ 1 × 10 ¹⁶ / cm ³ ,
Average ODC (I) concentration ≦ 5 × 10 ¹⁵ / cm ³ ,
Precision polishing and precision cleaning of the outer peripheral surface of a quartz glass rod having an average ODC (II) concentration ≦ 5 × 10 ¹⁴ pieces / cm ³ to obtain a core material;
After inserting the core material into the clad material by the rod-in-tube method, grinding the outer periphery, further precision polishing and precision cleaning to obtain an optical fiber preform,
The manufacturing method of the optical fiber preform characterized by including. The method for producing an optical fiber preform according to claim 12, wherein the core material subjected to precision polishing and precision cleaning and the clad material subjected to precision polishing and precision cleaning satisfy the following (1) to (3), respectively.
(1) The surface roughness Ra of the treated surface is 10 nm or less.
(2) No particles having a size of 50 μm or more are present on the treated surface.
(3) There is no scratch having a width of 11 μm or more on the treated surface.   The method for producing an optical fiber preform according to claim 12 or 13, wherein a difference between an outer diameter of the core material and an inner diameter of the clad material is set to 2 mm or less.   An optical fiber manufacturing method comprising: obtaining an optical fiber preform by the manufacturing method according to any one of claims 12 to 14; and spinning the optical fiber preform to obtain an optical fiber. A method for producing an optical fiber made of hydrogen-doped quartz glass,
The internal transmittance of light transmitted through the optical fiber per meter of optical fiber is 65% or more for light with a wavelength of 193 nm and 25% or more for light with a wavelength of 180 nm, and the average H ₂ concentration ≦ 1 × 10 ¹⁶ pieces / cm ^3. And holding the optical fiber in a hydrogen atmosphere at a temperature below 400 ° C. for a certain period
Hydrogen doped light characterized by obtaining an optical fiber having an internal transmittance per 1 m of optical fiber of light transmitted through the optical fiber of 65% or more for light having a wavelength of 193 nm and 30% or more for light having a wavelength of 180 nm Fiber manufacturing method.   17. The method for producing a hydrogen-doped optical fiber according to claim 16, wherein the hydrogen treatment is performed under a hydrogen-containing atmosphere of 15 to 400 ° C. and 0.2 to 15 MPa for 15 hours or more. The internal transmittance per 1 m of the optical fiber transmitted through the optical fiber is 65% or more for light with a wavelength of 193 nm and 30% or more for light with a wavelength of 180 nm,
When an ArF excimer laser with an energy density of ² mJ / cm ² is irradiated at a frequency of 1 kHz, the transmission energy density after irradiation with 5 × 10 ⁶ pulses with respect to the transmission energy density immediately after irradiation is 0.6 or more. Optical fiber.

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