JPH10316445A - Treatment of optical fiber before use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical fiber having improved electromagnetic wave resistant characteristics. SOLUTION: This method for treating an optical fiber used under a condition exposed to the irradiation with electromagnetic waves including a light transmitted in the core, before using the optical fiber comprises a step for previously measuring the strength of the electromagnetic wave suffering at the condition to be used, a step for irradiating the optical fiber with electromagnetic waves for previous treatment, having a strength higher than the previously measured strength, and a step for immersing in the atmosphere comprising hydrogen gas. The electromagnetic waves for the previous treatment can be radiated so that the electromagnetic waves for the previous treatment may have the total amount of the converted energy larger than the calculated total amount of the converted energy by calculating the total amount of the electromagnetic waves converted into the energy. The electromagnetic waves are γ-rays, X-rays, laser rays, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating an optical fiber, and more particularly, to an optical fiber for transmitting light in an electromagnetic wave irradiation environment including light propagating through a core, which has excellent initial transmission characteristics and increases transmission loss. And a method for treating an optical fiber before use.

[0002]

2. Description of the Related Art The use of optical fibers has recently increased in various fields such as communication, image transmission, and energy transmission because of their advantages such as low loss, light weight, small diameter, and non-induction. As one of them, for example, there is a use in an environment exposed to electromagnetic waves such as a nuclear field, a medical field, a fine processing field, etc., and an optical fiber mainly composed of quartz glass (SiO ₂ ) is considered to be most suitable. However, even in the case of a silica glass fiber, there is a problem that glass deteriorates and transmission loss increases under an electromagnetic wave irradiation environment, and various reports have been made on improvement of electromagnetic wave exposure resistance.

For example, Japanese Patent Application Laid-Open No. 5-147966 (referred to as a document) discloses a technique for reducing the deterioration of quartz-based glass by ultraviolet irradiation, when the OH group content in a pure quartz core is 10 to 1000 ppm, and F (fluorine) is used. 50 to 50%
It has been proposed to obtain an optical fiber having excellent initial transmission characteristics with respect to ultraviolet light by adjusting the Cl (chlorine) content to 5000 ppm and substantially zero, and having reduced ultraviolet irradiation deterioration by containing a specific amount of fluorine. .

[0004] Further, although not directly aimed at improving the deterioration of ultraviolet irradiation, there are known several techniques for improving the radiation resistance of a fiber for transmitting visible light and near infrared light. For example, Japanese Unexamined Patent Publication No. Sho 60-90853 (referred to as a document) discloses that any one of a glass soot molding, a transparent glass preform, and a glass molding (optical fiber) is treated in a hydrogen atmosphere to eliminate defects in the glass. Thus, a processing method for improving the radiation resistance of an optical fiber has been proposed.

On the other hand, Eastmon, Nagasawa, et al., "Improvement of radiation resistance of optical fiber by hydrogen treatment and gamma irradiation", Showa
Proceedings of the IEICE National Conference on Semiconductors and Materials Division, Vol. 1, pp. 1-213, published by The Institute of Electronics, Communication and Engineers in 1985. As a method for suppressing an increase in light absorption at a wavelength of 630 nm (visible light), a hydrogen treatment is performed on an optical fiber as a first step, and then a gamma ray is irradiated as a second step, thereby seeding defects in glass ( (Precursor) into a defect causing the 2 eV band, and by chemically bonding hydrogen and the defect previously diffused into the fiber in the previous process to improve the radiation resistance in the visible light region. It has been reported.

[0006] US Pat. No. 5,574,820 (reference) discloses a means for reducing an increase in loss in a visible light region when a pure silica core fiber is used in a radiation environment as an image fiber for transmitting visible light. By irradiating a pure silica core fiber with a large dose of radiation of 10 ⁵ Gy or more in advance, even if the radiation is subsequently irradiated, light whose loss increase in the visible light region of a wavelength of 400 to 700 nm does not exceed 30 dB / km. Fibers and their production have been proposed.

[0007] Further JP-A-5-288942 discloses (referred document), the image as a way to improve the radiation resistance of the fibers, melt-spun ¹⁰⁷ to the image fiber ⁹ for transmitting visible light as well as the literature It has been proposed to irradiate a large dose of γ-ray called X-ray (10 ⁵ to 10 ⁷ Gy) and then heat it in a hydrogen atmosphere.

[0008]

According to the method of the above-mentioned document, an optical fiber having excellent initial transmission characteristics of ultraviolet light is obtained. However, there is a limit in improving the ultraviolet light transmission characteristics by this method. Not much effect. Conversely, in some cases, the absorption derived from the ultraviolet absorption end is increased, and it has been quite difficult to adjust the optimum amount of addition. On the other hand, the literature on improvement of radiation resistance characteristics in transmission of visible light and near-infrared light, for example, is not effective for irradiation deterioration due to ultraviolet rays, or when applied to optical transmission fibers, will deteriorate the optical fiber coating. Some were difficult to put into practical use.

In view of the above-mentioned situation, the present invention provides an excellent electromagnetic wave resistant material which has excellent initial transmission characteristics and has no increase in transmission loss even when used for a long time by treating an optical fiber used in an electromagnetic wave exposure environment before use. It is an object of the present invention to provide a method for treating an optical fiber which can be used as an explosive optical fiber before use. Another object of the present invention is to provide a method for treating an optical fiber before use, in which not only the glass fiber but also its coating when applied to an optical fiber is not deteriorated by irradiation with electromagnetic waves.

[0010]

According to the present invention, there is provided a method for treating an optical fiber before use, which is used in an environment which is exposed to electromagnetic waves including light propagating in a core. Then, the intensity of the electromagnetic wave received in the use environment is determined in advance, and the optical fiber is irradiated with an electromagnetic wave for pretreatment having an intensity greater than the intensity, and then immersed in an atmosphere made of hydrogen gas. The processing method,
(2) This is a processing method before using an optical fiber used in an environment that is exposed to electromagnetic waves including light propagating in the core, and the total amount of electromagnetic waves received in the operating environment converted to energy is calculated in advance. The method according to the above (1), wherein the optical fiber is irradiated with an electromagnetic wave for pretreatment so as to have a total energy conversion amount larger than the total amount, and then immersed in an atmosphere composed of hydrogen gas. The method according to the above (1) or (2), wherein γ-rays are used as the pretreatment electromagnetic waves, and (4) X-rays are used as the pretreatment electromagnetic waves. The processing method according to claim 1 or 2. (5) The processing method according to (1) or (2), wherein a laser beam having a wavelength of 400 nm or less is used as the pretreatment electromagnetic wave, and (6) the treatment electromagnetic wave is applied at a dose of 10 to 10. The treatment method according to the above (3) or (4), wherein the irradiation is performed within a range of ⁴ Gy.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, an optical fiber is first irradiated with an electromagnetic wave for pretreatment and then subjected to a hydrogen treatment. [W / m ² ]. Further, it is preferable to make the total energy amount larger than the total energy amount [J / m ² ] of the electromagnetic wave received in the irradiation environment later. As a result, the optical fiber is no longer deteriorated in the environment where the electromagnetic wave is subsequently irradiated.

The reason why irradiation does not cause deterioration due to electromagnetic wave irradiation in the use environment due to such processing is currently under study. However, according to the present inventors, the cause of the increase in loss is as follows. And glass defects such as the E 'center schematically shown in FIG. There are two types of glass defects: those that are present from the beginning and those that are formed by breaking a bond that is easily broken by irradiation of high-energy electromagnetic waves. When hydrogen treatment is performed, hydrogen atoms are bonded to such defects to prevent an increase in loss. Initial state (Fig. 1
When (a)] is subjected to hydrogen treatment from the beginning as in the conventional method, the defect disappears immediately after the hydrogen treatment as shown in (d) of Fig. 1, but the bond that is easily broken by the subsequent exposure to electromagnetic waves A new defect is generated by cutting (Fig. 1 (e)),
Loss increases. On the other hand, when the hydrogen treatment is performed after the bond which is easily exposed and broken by being exposed to an electromagnetic wave exceeding the exposure amount in the later use environment [FIG. 1 (b)] as shown in FIG. As shown in (c), the bonds that are potentially susceptible to defects are also replaced by hydrogen atoms, so if new defects do not occur even after subsequent exposure to electromagnetic waves (for example, electromagnetic waves irradiated during use). Conceivable.

The method of the present invention will be specifically described. First,
In the present invention, the electromagnetic radiation exposure environment means an environment exposed to ultraviolet light, vacuum ultraviolet light, X-rays, γ-rays, and the like. Included in the environment exposed to electromagnetic waves. The electromagnetic wave transmitted by the optical fiber of the present invention is not particularly limited, and includes infrared light, near infrared light, visible light, ultraviolet light, and vacuum ultraviolet light.

The optical fiber targeted by the method of the present invention is an optical fiber made of quartz glass. There is no particular limitation on the method for producing the quartz glass material itself as a raw material before the step of the present invention. In the present invention, high-purity quartz glass means quartz glass containing no transition metals such as Fe, Cu, and Ni, and impurities such as alkalis and alkaline earth metals.
It must be less than B order. As a specific material, quartz (SiO ₂ ) is a main component.
The following are preferred. OH group content 2000ppm
The term “approximately” means an almost upper limit of the OH group concentration that can be added to glass by a general method for producing quartz glass such as a soot method or a direct method. In some cases, it may be preferable to contain about 1% by weight of fluorine (F). No dopant other than F that changes the refractive index is included. It is particularly preferable that the core contains no more than 1 ppm of Cl. On the other hand, the material of the region through which ultraviolet rays do not pass, such as the cladding of an optical fiber, is not limited to the above-described material, and a dopant that reduces the refractive index may be added. The optical fiber may be any of mono-core, multi-core, single mode, and multi-mode, and may be a bundle fiber.

First, the optical fiber is irradiated with a pre-treatment electromagnetic wave, and the pre-treatment electromagnetic wave of the present invention is 3.5 eV to 3.5 eV.
Electromagnetic wave can be mentioned having a quantum energy of 1.33 MeV, the upper limit value is equal to the value of the industrially widely utilized ⁶⁰ Co of γ-ray energy as γ-ray source, a practical value determined. An electromagnetic wave of less than 3.5 eV is not practical because it takes a long time to obtain an effect. The electromagnetic waves of the present invention include ultraviolet rays (400 to 160 nm) and vacuum ultraviolet rays (less than 160 to 1 nm) such as laser light such as an excimer laser, X-rays (several tens to 0.01 nm), and γ rays (0.01 nm or less). Is used.

A feature of the present invention is that the intensity A _{1 of} an electromagnetic wave irradiated in a later use environment is obtained in advance, and when the intensity of the electromagnetic wave in the pre-processing is set to A ₀ , the intensity A ₁ is set so that A ₀ > A _1. Treatment irradiation, followed by hydrogen treatment. In the present invention, to previously obtain the energy conversion amount E ₁ of the electromagnetic wave used is emitted in the environment after, when the energy conversion amount of the electromagnetic wave of the pretreatment and E _0, E _0> E ₁ become as It is particularly preferable to irradiate the pretreatment with an electromagnetic wave. The unit of the intensity and the total amount is [W / m ² ] as the intensity and [J / m ² ] as the total amount with respect to the laser beam.
For γ-rays and X-rays, the absorbed dose rate [Gy /
s], [Gy] can be used as the total amount. The irradiation dose is 10 to 10 ⁴ as the absorbed dose in the case of gamma rays or the like.
Gy, preferably 10 ² to 10 ³ Gy, and sufficient electromagnetic wave resistance can be obtained with such a low dose.
As a specific irradiation means, in the case of γ-ray, ⁶⁰ Co, ¹³⁷
An X-ray tube targeting W (tungsten), Cu or the like in the case of Cs or X-ray, a deuterium lamp in the case of ultraviolet or vacuum ultraviolet, a KrF excimer laser beam (248 nm),
ArF excimer laser light (193 nm), synchrotron orbital radiation, or the like is used.

The thermosetting silicone is used for the primary coating of the optical fiber.
Or UV-curable urethane acrylate is used,
Nylon is often used for the secondary coating.
Higher elongation after irradiation on primary coating
It is preferable to use UV-curable urethane acrylate.
New Fig. 2 shows the absorbed dose of radiation (Gy) and the residual resin extension.
Ratio (fraction of elongation at break after irradiation to elongation at break before irradiation)
In the figure, the dose is 10^FiveBeyond Gy
When the irradiation condition of the present invention is 10 ^FourGy
The following clearly shows that there is substantially no coating deterioration.

After the electromagnetic wave irradiation treatment, a hydrogen treatment is performed. The “atmosphere made of hydrogen gas” of the present invention means that the partial pressure of hydrogen gas is about 0.1 to 10 atm, preferably 0.5 to 1 atm.
0 atmosphere of pure hydrogen gas or a mixed atmosphere of hydrogen gas and nitrogen gas and / or inert gas. The basis of the limitation of the atmospheric pressure range is that in the range of 0.5 to 10 atmospheric pressures, it is possible to obtain almost the same effect as the diffusion rate of hydrogen in the glass, and this gas pressure is easy to use in actual production, If the pressure exceeds 10 atm, high pressure gas will be handled, legal regulations will be strict, and it will not be economical. Although there is no difference in effect even at about 0.1 atm, it is practically difficult to handle. Note that the same effect can be obtained by using deuterium gas as the hydrogen gas. The temperature at the time of the hydrogen treatment is not particularly limited, but it takes about 7 days at room temperature to reach the center of the fiber with 1 atm of hydrogen.
Since the temperature is 80 ° C. for one day and 200 ° C. for about 2 hours, the temperature may be higher than room temperature. In the case of optical fiber, the upper limit temperature is substantially determined by the heat resistance of the fiber coating,
It is about 0 to 200 ° C. Note that 80 ° C. is near the upper limit temperature of heat resistance of the ultraviolet curable acrylate resin, and 200 ° C. is the upper limit temperature of heat resistance of the silicone resin. The processing time varies depending on the processing temperature, but if it is 80 ° C. or higher, hydrogen diffuses into the optical fiber within about 2 to 3 days, and the processing is completed.

[0019]

EXAMPLES The present invention will be described below with reference to examples.
The method of measuring the amount of transmission in each of the examples and comparative examples is as follows. It is assumed that the wavelength dependency of the light source and the light receiver has been corrected. Measurement of the amount of transmission at a wavelength of 0.85 μm or 1.5 μm: The amount of light on the emission side is measured with the signal light incident on the fiber. With the incident side fixed, the fiber is cut at about 1 m from the incident side, and the light amount on the exit side (about 1 m) is measured again. The difference between the two measurements is the loss due to the cut fiber. The length of the fiber used for the measurement is about 1 km. Measurement of transmission amount at a wavelength of 248 μm: Cutback is not performed at 248 μm because a bundle fiber was used. The measurement light is incident on the bundle fiber, and the light quantity is measured on the emission side of the fiber. In the first measurement, it is assumed that the transmittance in a region where absorption is not seen from the wavelength characteristics (the region where the light amount is flat without depending on the wavelength) is 100%, and the transmittance in the other wavelength region and the second and subsequent times are assumed. Calculate the transmittance of the measurement. Therefore, the error is larger than the cutback. The length of the fiber used for the measurement is 2 m.

Example 1 A pure silica core optical fiber (bundle fiber) was irradiated with a KrF excimer laser beam (wavelength: 248 nm) having an output of 200 mW / cm ² for 10 hours, and thereafter, a H ₂ atmosphere at 80 ° C. and 3 atm was used. Left for 24 hours. The transmission amount at a wavelength of 248 nm of the optical fiber 2 m after the treatment was 90%. Then, 2mW / cm
^When irradiation with the excimer laser light (wavelength 248 nm) of No. ² was continued, the transmission amount hardly changed to 88% until 1000 hours, and the transmission amount gradually decreased after 1000 hours, and decreased to 50% after 1500 hours. became.

[0021] Example 2 ⁶⁰ to the optical fiber of the silica core
Irradiation with Co γ-rays was performed at 3 × 10 ⁻¹ Gy / s for 1 hour, and then left standing at 80 ° C. in an H ₂ atmosphere at 3 atm for 24 hours. The transmission loss of the treated optical fiber is 1.55 μm.
m was 0.20 dB / km. Then 3 × 10 ^-4
When the transmission loss (at a wavelength of 1.55 μm) of this optical fiber was measured under a Gy / s gamma ray exposure environment,
It does not increase so much to 0.30dB / km until 000 hours,
If the time exceeds 1000 hours, the loss increase becomes large, and
At 0 hours, it was 0.85 dB / km.

[0022] Comparative Example 1 ⁶⁰ to the optical fiber of the silica core
Irradiation with Co γ-rays was performed at 3 × 10 ⁻³ Gy / s for 1 hour, and then allowed to stand at 80 ° C. and 3 atm in a H ₂ atmosphere for 24 hours. The transmission loss of the treated optical fiber is 1.55 μm.
Was 0.20 dB / km. Then, 6 × 10 ^-3 G
When the transmission loss (at a wavelength of 1.55 μm) of this optical fiber was measured in an environment exposed to y / s gamma rays, the loss increased from the beginning.
It has deteriorated to 90 dB / km.

[Embodiment 3] A ⁶⁰ % pure silica core optical fiber was used.
Irradiation with Co γ-rays was performed at 3 × 10 ⁻¹ Gy / s for 1 hour, and then left at 80 ° C. in a hydrogen atmosphere at 3 atm for 24 hours. The transmission loss of the treated optical fiber is 0.85 μm.
Was 2.50 dB / km. Then, 3 × 10 ^-4 G
When the transmission loss of this fiber was measured in a y / s gamma ray exposure environment, it was 2.60 dB / km up to 100 hours.
After 100 hours, the increase in loss became large, and after 200 hours, the loss was 3.95 dB / km.

[0024] Comparative Example 2 ⁶⁰ to the optical fiber of the silica core
Irradiated with Co γ-ray at 3 × 10 ⁻⁴ Gy / s for 1 hour, then left at 80 ° C. in a hydrogen atmosphere at 3 atm for 24 hours. The transmission loss of the treated optical fiber is 0.85 μm.
Was 2.50 dB / km. Then, 6 × 10 ^-4 G
When the transmission loss (0.85 μm) of this fiber was measured in a y / s gamma-ray exposure environment, the loss increased from the beginning, and it became 4.15 dB / km by irradiation for 15 minutes.

Table 1 summarizes the results of the above examples and comparative examples.

[0026]

[Table 1]

Comparative Example 3 An optical fiber (bundle fiber) having a pure silica core was placed in a hydrogen atmosphere at 80 ° C. and 3 atm.
Left for 4 hours. Then, within 24 hours, gamma rays of ⁶⁰ Co were irradiated at 3 × 10 ^-1 Gy / s for 1 hour. The transmittance at a wavelength of 248 nm of the optical fiber (2 m) having undergone the above steps was 85%, and the increase in loss was suppressed at this time.
Thereafter, an excimer laser beam of ² mW / cm ² (wavelength 24
8 nm), 50% in 100 hours,
In 2000 hours, the transmission amount decreased to 20%, which was remarkable.

[0028]

According to the present invention, the amount of electromagnetic waves (intensity or total energy) that an optical fiber (including a bundle fiber) is exposed to in its use environment is calculated in advance, and the intensity or total energy is larger than this amount. By performing hydrogen treatment after previously irradiating an electromagnetic wave to the optical fiber, the optical fiber no longer causes deterioration of electromagnetic wave irradiation in a later use environment, so that an optical fiber with extremely improved electromagnetic wave resistance can be provided. The processing steps are simple, for example, γ
Line irradiation can process a large number of fibers at once. Further, if the present invention is carried out at a relatively low dose, there is no problem of coating deterioration of the optical fiber, which is practically advantageous. In the conventional ultraviolet region fiber, it was necessary to transmit light under a vacuum condition at a wavelength of 160 nm to 200 nm (for this reason, this region is referred to as a vacuum ultraviolet region). However, according to the present invention, 300 to
It can be used not only in the ultraviolet region of 160 nm but also in the vacuum ultraviolet region without applying vacuum. Further, in the vacuum ultraviolet region, the optical fiber according to the present invention has an advantage that light transmittance is better than that in the atmosphere, and since it has flexibility, excimer laser light,
Equipment utilizing ultraviolet light sources such as deuterium lamps and halogen lamps, especially processing equipment, such as laser processing, photoresist, fiber curing radiation source, adhesive curing radiation source, processing of various micro parts, Sr (synchrotron) light generation radiation It can be used as a source optical transmission fiber.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating the operation of the present invention and a conventional method in comparison.

FIG. 2 is a graph showing the relationship between the absorbed dose of radiation (Gy) and the residual elongation (%) of the coating resin.

Continued on the front page (72) Inventor Masaharu Mogi 1st Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Inside Sumitomo Electric Industries, Ltd. Inside Yokohama Works

Claims (6)

[Claims] 1. A method for treating an optical fiber used in an environment exposed to electromagnetic waves including light propagating in a core before use, wherein the intensity of the electromagnetic waves received in a use environment is determined in advance, and The above-mentioned processing method, wherein the optical fiber is irradiated with an electromagnetic wave for pretreatment having an intensity higher than the above intensity, and then immersed in an atmosphere made of hydrogen gas. 2. A method for treating an optical fiber used in an environment exposed to electromagnetic waves including light propagating in a core before use, wherein a total amount of the electromagnetic waves received in the environment used is converted into energy in advance. 2. The processing method according to claim 1, wherein the optical fiber is irradiated with an electromagnetic wave for pretreatment so that the total amount of energy of the optical fiber becomes larger than the total amount, and then the optical fiber is immersed in an atmosphere made of hydrogen gas. 3. The processing method according to claim 1, wherein gamma rays are used as the pre-processing electromagnetic waves. 4. The processing method according to claim 1, wherein X-rays are used as the pre-processing electromagnetic waves. 5. The method according to claim 5, wherein the electromagnetic wave for pretreatment has a wavelength of 400.
3. The processing method according to claim 1, wherein a laser beam having a wavelength of not more than nm is used. 6. The method according to claim 1, wherein the pre-treatment electromagnetic wave is irradiated with a dose of 10 to 10.
^The method according to claim 3, wherein the irradiation is performed within a range of ⁴ Gy.