WO2004066007A1

WO2004066007A1 - Optical fiber, light amplifier, and light source

Info

Publication number: WO2004066007A1
Application number: PCT/JP2004/000141
Authority: WO
Inventors: Koji Seo; Nishimura Naoya
Original assignee: The Furukawa Electric Co., Ltd
Priority date: 2003-01-10
Filing date: 2004-01-13
Publication date: 2004-08-05
Also published as: JP4330017B2; JPWO2004066007A1

Abstract

A coated optical fiber which comprises a coating material covering the outer surface of an optical fiber and is capable of transmitting a high power light is characterized in that heating-up of the coating material caused by absorbing lights leaking out of the optical fiber is suppressed by using a transparent ultraviolet-curing resin as the coating material. A light transmission method is characterized in that a fiber fuse propagation threshold value, which is the minimum optical power necessary for propagation of a fiber fuse, is found and the power of the transmitted light is controlled so that it is smaller than the fiber fuse propagation threshold value.

Description

Specification

Optical fiber, optical amplifier and light source

The present invention relates to an optical fiber used in an optical communication system, an optical amplifier such as a Raman amplifier and a rare-earth doped optical amplifier, and an optical source. Background art

In recent years, in the field of optical communication, there has been a demand for higher transmission capacity due to higher communication speed and WDM communication technology.

Particularly in WDM communication technology, the need for a broadband optical amplifier that can amplify a broadband signal light at a time is increasing. For this broadband optical amplifier, for example, a Raman amplifier and a rare-earth-doped fiber amplifier are considered to be amplifiers that meet the requirements. The Raman amplifier uses the stimulated Raman scattering effect to amplify signal light. In order to generate the stimulated Raman scattering effect of this Raman amplifier efficiently, high-output pump light is required.

To amplify a broadband signal light in a Raman amplifier, it is common to use pump light obtained by multiplexing laser lights of a plurality of wavelengths. For this reason, the multiplexed pump light output from the optical amplifier may become high-output light. In the future, an optical amplifier capable of collectively amplifying over a wide band will be required in order to cope with a wider communication band, but a higher power pump light will be required to satisfy this requirement. In other words, higher-power pump light is output from the optical amplifier. It is also important that this optical amplifier is designed so that the band of the signal light to be amplified has a flat gain. Although the Raman amplifier has been described above, the same can be said for a propagated signal light and a rare earth-doped fiber amplifier such as an EDFA. In other words, high output light is propagated. For example, even weak light such as signal light may become high power if it is multiplexed with a multiplexer such as an AWG. Also, even in the case of a laser element used in combination with an EDFA, its output may be increased. In such an environment of high output power of transmitted light, more problems have also arisen. The first problem is that the coating material of the optical fiber is burned. In the optical communication system, while the output of light is increasing, the necessity of mounting optical components at a high density for the purpose of further downsizing optical amplifiers and light sources is increasing. In order to realize this, it has become necessary to bend and store the optical fiber with an arbitrary small curvature in consideration of the downsize of the optical amplifier and light source. Specifically, for high-density packaging and downsizing of optical devices, high-power light must be propagated with optical fibers housed more compactly. However, if the optical fiber is bent with such a small radius of curvature, the transmitted light leaks from the core to the outside of the optical fiber through the cladding and the covering material. At this time, as described above, as the power of the propagated light increases, there may be a problem that cannot occur with the conventional light intensity.

For example, in an optical fiber, a coating material covering an outer peripheral portion thereof absorbs hyper light leaked from a core and generates heat. For this reason, the small curvature diameter portion of the optical fiber is used at high temperatures. As a result, the coating material may deteriorate faster than before, and the optical fiber may be easily broken.

Accordingly, one object of the present invention is to solve the above-described conventional problems and to provide a high-output light In an optical fiber that propagates light, even if it is bent with a small radius of curvature, there is no problem such as deterioration of the coating material due to the optical power leaking from the core of the optical fiber through the cladding and the coating material. Another object of the present invention is to provide an optical fiber that can transmit high-output light without any problem. The second problem associated with increasing the output power of optical power is a problem related to a so-called fiber fuse.

In the state where the optical energy density in the optical fiber serving as the transmission line is higher than a certain threshold, that is, in the state where the optical energy density is high, when various factors that induce core melting such as heating are added, the central portion of the optical fiber becomes First, it melts locally. Then, this melting phenomenon causes self-transmission toward the light source, that is, a so-called fiber fuse phenomenon occurs.

In this case, it is known that, for example, in the case of SMF (Single Mode Fiber), the melting phenomenon of the optical fiber occurs in a cross-sectional area having the same diameter as the core (about Ι Ομπι).

This fiber fuse phenomenon proceeds at a speed of about lmZs and continues as long as the optical transmission from the optical amplifier and the light source is stopped or the optical energy density in the optical fiber does not fall below a certain threshold. After the optical fiber has been transmitted by the fused portion, a transmission mark (cavity) is formed in the core, and the light is not transmitted. Fiber fuse is a phenomenon that is most likely to occur when high-power light is transmitted with a light energy density above a certain threshold or is locally heated. For this reason, fiber fuses do not necessarily occur even if the area around the core is locally heated. Moreover, it occurs only when certain conditions are satisfied, and its occurrence probability is extremely low.

Once the fiber fuse has been generated, the optical amplifier and light source side As the fiber fuse progresses, there is a possibility that the fiber ruptures over part or the entire length of the optical fiber. Furthermore, when the fiber fuse reaches the optical component or optical device connected to the optical fiber, the optical device may be destroyed, and the optical transmission line may be destroyed. Therefore, another object of the present invention is to solve the above-mentioned conventional problems and to enable transmission of a high-power optical signal without generating or transmitting a fiber fuse phenomenon in an optical fiber. The purpose of the present invention is to provide an optical signal transmission method and a control method. Disclosure of the invention

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, in order to achieve the above object, as a first embodiment of the optical fiber of the present invention, by using a coating material that absorbs less leaked light in an optical fiber that propagates high output light. However, even if the optical fiber is bent with a small radius of curvature, an optical fiber that can stably transmit high-output light without damaging the optical fiber has been found.

In the present embodiment, by using a transparent UV-curable resin as a material for the coating, it is possible to prevent the coating material of the optical fiber from deteriorating due to absorption of leaked light even when bent at a minimum diameter of about 1 Omm. It is possible to prevent disconnection and the like. Further, as another embodiment of the optical fiber of the present invention, the coating layer of the optical fiber is composed of a primary coating layer, a secondary coating layer, and a coloring layer made of an ultraviolet curable resin, and the coloring layer has a surrounding layer. We also found an optical fiber that was intermittent in some directions and did not cover the secondary coating layer. Also, by forming this colored layer in a stripe shape, We also found an optical fiber that does not cover a part of the colored layer, and an optical fiber that does not cover a part of the colored layer by forming the colored layer in a helical strip.

In addition, the present inventors have found optical devices (optical amplifiers and light sources) using the above optical fibers and optical fiber cables connected to optical devices using the above optical fibers.

Disconnection of the optical fiber due to deterioration of the coating, which is a problem of the prior art, and ignition of the coating layer are further caused on the outer periphery of the optical fiber coated with the primary coating layer and the secondary coating layer made of the ultraviolet curing resin. When a colored layer is applied, it is considered that the energy of the leaked light that reaches the coating layer through the glass clad layer does not pass through the colored layer but is reflected and absorbed in the coating layer to generate heat.

Therefore, according to the above-described embodiment, a part of the colored layer on the secondary coating layer is removed, and the leaked light is released to the outside of the coated fiber, whereby the coated optical fiber that guides high output light of 50 OW or more is guided. In this case, even if the bending diameter is reduced, a reliable transmission system can be provided without causing any problems.o In addition, the present inventor has performed various analyzes and experiments to determine whether fiber fuse transmission can occur. The required minimum optical power P _th (W) (fiber fuse transmission threshold) was found. We also found the relationship between this minimum optical power P _th and the wavelength of light (Spectra), the type of optical fiber, the type of dopant, and the MFD (Mode Field Diameter).

The power P (W) of the propagating light can be controlled using the minimum optical power P _th that is found.

That is,

p <P _th

If the light is propagated in the range where the relationship holds, no fiber fuse will be generated. Even if a fiber fuse is generated due to a sudden trigger, there is no risk of transmission to the optical amplifier and light source, and high-output light can be transmitted. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing an outline of a bending test apparatus for an optical fiber of the present invention and a conventional optical fiber.

FIG. 2 is a diagram showing a change in outer surface degree in a bending test of the optical fiber of the present invention and a conventional optical fiber.

FIG. 3 is a table showing bending test results of the optical fiber of the present invention and a conventional optical fiber.

FIG. 4 is a diagram showing an outline of a measuring device for measuring a fiber fuse transmission threshold value P _th (W).

FIG. 5 is a diagram comparing the measurement results of the fiber fuse transmission threshold value P _th (W) of the SMF, DSF, and DCF.

FIG. 6 is a diagram showing the relationship between the fiber fuse transmission threshold value P _th (W) and the MFD.

FIG. 7 is a diagram showing a configuration diagram of an embodiment of a high-power wavelength-division multiplexing pump light source used for Raman amplification.

FIG. 8 is a flowchart showing a signal light transmission method for controlling the total output power P to be smaller than the fiber fuse transmission threshold _Pth .

FIG. 9A is a diagram showing damage to the end face of the optical fiber.

FIG. 9B is a diagram showing damage to the end face of the optical fiber.

FIG. 9C is a diagram showing damage to the end face of the optical fiber.

FIG. 10 is a table showing the results of a damage test on the end of the optical fiber.

FIG. 11 is a diagram showing the effect of the high-power transmission on the coating layer. Fig. 12 is a diagram showing the results of an experiment in which a 5-minute wire test was performed in a high-power transmission experiment.

FIG. 13 is a cross-sectional view showing a conventional optical fiber whose entire surface is covered with a colored layer. FIG. 14 is a cross-sectional view showing an optical fiber having an intermittent colored layer according to the present invention. FIG. 15 is a side view showing an optical fiber having a striped colored layer. FIG. 16 is a side view showing an optical fiber having a spiral-stripe colored layer. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Optical fiber that does not burn coating material)

First, a description will be given of an embodiment of an optical fiber capable of transmitting an excitation light or a hyper-optical signal without causing deterioration, damage, or the like even when bent at a small curvature diameter.

(Optical fiber using transparent UV curable resin)

In conventional optical fibers, urethane acrylate, epoxy acrylate, silicon-based UV-curable resin compositions (hereinafter referred to as UV-curable resins), nylon resins, etc. are used as the coating material. The coating is colored for optical fiber identification. Accordingly, when the optical fiber is bent with a small radius of curvature, the coating absorbs the optical power that tends to leak to the outside through the core and clad of the optical fiber, and generates heat. Previously, low propagating optical power did not generate enough heat to cause problems. In the future, due to the higher output of signal light and pumping light to be propagated, the coloring of the coating material absorbs the power of the leaked light of the transmitted signal light and generates heat, which generates heat and damages the coating material. As a result, the optical fiber may be broken. On the other hand, in the present invention, a transparent uv resin is used as a material for coating the optical fiber. Accordingly, when transmitting high-power light, the optical fiber is bent with a small radius of curvature, and even if leakage light occurs due to this bending, the amount of optical power absorbed by the coating material is greatly reduced. . Therefore, this coating material is not damaged by heat generation, and can continue to transmit high-output light as it is. Here, in order to confirm the reproducibility of the optical fiber of the present invention, a test was conducted in which high-power light was propagated in a state where the optical fiber was bent to an arbitrary curvature diameter together with a conventional optical fiber.

FIG. 1 shows an outline of an apparatus for a bending test performed on the optical fiber of the present invention and a conventional optical fiber. The optical fiber for the test includes an optical fiber coated with the transparent UV-curable resin of the present invention, and three types of optical fibers coated with white, blue, and green UV-curable resins, respectively, as conventional optical fibers. And a total of four types of optical fibers covered with a white nib.

In general, an optical fiber coated with a UV curable resin is used in an optical device, and an optical fiber coated with a nylon is often used as an optical fiber connecting optical devices. The outer diameter of the optical fiber is 250 m for the optical fiber coated with the UV curable resin, and the outer diameter for the optical fiber coated with nylon is 900 μm.

In the test, a laser light source was connected to each test optical fiber, and then a part of the optical fiber was bent one turn. Then, by changing the intensity of the input light and the curvature 柽 of the bending, the degree of deterioration of the coating material of the optical fiber due to the leaked light in each case was observed.

In the test, the output P (unit: W) of a laser light source having a wavelength of 148 O nm was changed in three stages of 1 W, 2 W, and 3 W. In addition, the output of each laser The bending diameter A (unit: mm) was changed in five steps of 30 mm, 2 O mm, 15 mm, 1 O mm, and 5 mm, and the state of degradation of the coating material was observed.

At the same time, the temperature change of the outer surface of the optical fiber was measured with a thermocouple. The temperature change was measured under the most severe conditions, with the output P of the laser source set to a maximum of 3 W and the bending diameter A of the optical fiber set to 3 mm. Figure 2 shows the results of the temperature measurement. The optical fiber coated with the transparent UV curable resin of the present invention and the conventional optical fiber coated with a white UV curable resin were measured. Here, the vertical axis of the graph is temperature (unit: C), and the horizontal axis is time (unit: minute).

In both optical fibers, the temperature rises rapidly about 1 minute after passing through, and in about 2 to 3 minutes, the heat generated by the leaked light and the heat radiation from the outer surface are balanced, and the temperature is in an equilibrium state It has become. The surface temperature of an optical fiber coated with a conventional white UV curable resin reached about 100 ° C., whereas the optical fiber coated with a transparent UV curable resin according to the present invention has a surface temperature of about 100 ° C. The temperature settled around 60-65 ° C. Considering the heat resistant temperature of the coating material, this temperature difference is considered to have a very large effect.

Also, based on this temperature rise data, if high-power light is allowed to propagate for 5 minutes, the state of equilibrium has already been reached, and it is considered that the damage state due to the temperature change of the coating material can be sufficiently understood. Therefore, in the comparison test of each optical fiber described below, we decided to observe the damage state after propagating the power light for 5 minutes. The table in FIG. 3 shows the relationship between the optical fiber of the present invention (UV (transparent)) and four types of conventional optical fibers (UV (white), UV (blue), UV (green), and Nylon (white)). It shows the results of the comparative test. For input light intensity P of 1 W, 2 W, and 3 W, bending diameter A is 30 mm, 2 O mm, 15 mm, 10 mm, and 5 m for each optical fiber. The observation result in the case of m is shown.

When the input light intensity P was 1 W, the optical fiber coated with the transparent UV curable resin of the present invention did not cause any damage at any bending diameter.

On the other hand, when the bending diameter of all three colors of the optical fiber coated with the UV curable resin is 15 mm or less, the coating material absorbs the leaked light and is damaged, and the optical fiber becomes hazy (deformed). ).

In the case of a nylon-coated optical fiber, if the bending diameter is 15 mm or less, the covering material absorbs the leaked light and is damaged, causing the optical fiber to be damaged. The material was dissolved, and the optical fiber itself was exposed. When the input light intensity P was 2 W, the optical fiber coated with the transparent UV-curable resin of the present invention did not cause any damage up to a bending diameter of 1 Omm. When the bending diameter was 5 mm or less, the coating material turned brown.

When the bending diameter of all three colors of the optical fiber coated with the colored UV curable resin became 15 mm or less, the coating material absorbed the leaked light and was damaged, causing the optical fiber to become distorted. When the bending diameter was 5 mm or less, the coating material turned brownish in all three colors.

When the bending diameter of the optical fiber is less than 15 mm, the covering material absorbs the leaked light and is damaged, and the fiber is damaged by the optical fiber, and the bending diameter is 5 mm or less. Then, the coating material broke.

When the input light intensity P was 3 W, the optical fiber coated with the transparent UV curable resin of the present invention did not cause any damage when the bending diameter was 1 O mm or more. When the bending diameter of the optical fiber was 5 mm or less, the material discolored brownish. For optical fibers coated with colored UV curable resin, if the bending diameter of white or blue optical fibers is 15 mm or less, the coating material will absorb the leaked light and be damaged, causing damage to the optical fibers. Was attached. Green fiber has a bend diameter of 20 m At less than m, the cladding absorbed the leaked light and was damaged, resulting in a hazy optical fiber. When the bending diameter was 5 mm or less, the coating material changed color for all three colors. In the case of a nylon-coated optical fiber, if the bending diameter is 15 mm or less, the covering material absorbs the leaked light and is damaged, causing the optical fiber to be damaged.In addition, if the bending diameter is 5 mm or less, The coating broke.

Summarizing the above results, the optical fiber coated with the transparent UV-curable resin of the present invention has a high power of up to 3 W without any damage if the bending diameter is 1 O mm or more. Light could be transmitted.

On the other hand, for optical fibers coated with colored UV-cured resin, even if the input light has a power of 1 W, the coating material will be damaged if the bending diameter is less than 15 mm, so that it can be used practically. It turned out to be impossible. However, there was no clear difference in the difference in damage due to the difference in color.

Even with the same conventional optical fiber, the optical fiber coated with nylon was more severely damaged, and if the bending diameter was reduced to 5 mm or less, the coating material was melted or disconnected.

From this experiment, it has been proved that the optical fiber of the present invention has much better performance than the conventional optical fiber with respect to the damage resistance performance due to leakage light generated by bending.

(Semi-transparent UV-curable resin is used.)

In the above test, an optical fiber coated with a transparent UV-curable resin was used, but an optical fiber coated with a translucent UV-curable resin could be used instead. There is a great difference from the fiber, and it has been found that the fiber has a damage resistance equivalent to that of an optical fiber coated with a transparent UV curable resin.

Further, when the optical fiber having the coating material made of the transparent UV-curable resin described above is bent and installed in an optical device, a functional unit that absorbs leaked light outside the optical fiber is used. Goods may be arranged. For example, when an optical fiber is wound in a bobbin or the like and placed in the optical device, a light-absorbing package member is placed so as to cover the outside of the pobin. In this case, the package member may be provided with a light-absorbing film on at least the inner surface thereof. As described above, when an optical fiber having a coating material made of a transparent UV curable resin is housed in a package member, light leaking outside the optical fiber without being absorbed by the coating material is absorbed by the package member. It does not adversely affect the optical amplifier and light source. If necessary, the package member may be provided with a temperature adjustment function.

(Optical fiber with intermittent coloring layer)

Next, an embodiment of an optical filter having an intermittent coloring layer in which the coloring layer does not cover the entire secondary coating layer will be described.

Tight bending of optical fibers is not allowed due to long-term reliability, but short-term bending may be added in actual system installation. Severe bending causes light to leak from the core to the coating, and in high-power environments, the light leaks and generates heat, which in turn can lead to degradation of the coating. The present inventors conducted the following tests on coating damage when bending is applied for a short period in a high-power environment.

The optical fiber used in the experiment of the present invention is a single mode fiber based on ITU-T G.625, and the coating layer of the optical fiber is composed of a primary coating layer and a secondary coating layer made of an ultraviolet curable resin. Of two-layer coating.

Normally, a soft resin with a Young's modulus of about 0.5 to 1 OMPa at room temperature is used for the primary coating layer of the optical fiber to prevent the influence of external force from being transmitted to the glass. For protection, a hard resin having a Young's modulus at normal temperature of 100 to 100 MPa is used for protection. Other properties include T g (glass transition temperature) A material with a temperature of 20 to 10 ° C is used as the coating material and a temperature of 60 to 120 ° C is used as the secondary coating material. The refractive index of the coating layer is preferably used in a combination that increases from the glass clad to the primary coating layer and the secondary coating layer toward the outer periphery. The ultraviolet-curable resin used in the present invention is a polyether-polyurethane acrylate-based ultraviolet-curable resin, has a thickness of 200 / zm, and is evaluated in a sheet at a UV irradiation amount of 500 mJm2 in air under air. For the primary coating layer, a resin having a Young's modulus of 1. OMPa, Tg-5 and a refractive index of 1.49 was used. The secondary coating layer was made of a resin having a Young's modulus of 8 O OMPa, Tg of 90 ° C, and a refractive index of 1.53.

Optical fiber used in the present invention is a single mode off Aipa glass diameter 125 Myuitaiota, the primary coating layer diameter 195 Myupaiiota, whereas Oh ο in the secondary coating layer diameter ₂₄₅ μ πι, colored layer Not It is formed by adding various pigments or dyes to a cured ultraviolet-curable resin liquid, applying the pigment or dye uniformly to the coated fiber, and curing by UV irradiation. At this time, the greater the amount of the pigment or dye added, the deeper the color and color tone of the colored layer and the more easily distinguishable the color. Will decrease. The transmittance of the colored layer can be measured with an ultraviolet spectrophotometer by preparing a colored ultraviolet curable resin film having the same thickness as the colored layer using a spin coater or the like. It can be obtained as a percentage (12 / 11X100) of the intensity I 1 of the light incident on the film and the intensity 12 of the light passing through it.

Usually, the colored layer is formed as a thin film having a thickness of 3 to 10 microns, but the diphotoinitiator used for the colored ultraviolet curing resin is a diphenylketone or aminoketone compound, and the absorption wavelength is It is approximately 330-420 nm. In that area, a colored resin having a thickness of 10 microns and a transmittance of 5% or more is usually used. The colored ultraviolet curable resin in the present invention is a clear resin containing no pigment, and has a normal temperature Young's modulus in sheet evaluation at a UV irradiation dose of 500 mJ / cm2 under air at a thickness of 40 / zm. A resin having characteristics of 1100 MPa and TglO 0 ° C was used. The coloring of the coloring resin used in the experiment of the present invention is blue and green, and the transmittance of each colored resin is 5% or more.

The colored core wire constituting the present invention has a structure in which a colored layer having a thickness of 5 μπι is applied to the outer periphery of the optical fiber according to each of Examples and Comparative Examples.

In the present invention, the ratio of the colored layer of the colored optical fiber core to the optical fiber is preferably 30 to 80%, more preferably 40 to 70% of the outer peripheral surface area of the optical fiber. If it is lower than 30%, it will be difficult to identify, and if it is higher than 80%, deformation will occur due to the effect of light leakage.

(Example 1)

Example 1 was applied to a stripe at three places on the circumference of the optical fiber so that the coloring was alternated with the non-colored layer at about 50% of the outer surface area of the optical fiber. (See FIGS. 14 and 15.) For comparison, FIG. 13 shows a cross-sectional view of a conventional optical fiber having a colored layer on the entire surface.

(Example 2)

Coloring was applied on the stripe at three places on the circumference of the optical fiber hatch wire so as to alternate with the non-colored layer at about 50% of the outer surface area of the optical fiber. In addition, the optical fiber was twisted at the time of coloring so that the stripe became spiral. (See Fig. 16.) The method of twisting is the same as the method of twisting an optical fiber while drawing to improve PMD characteristics. At the position after passing through the UV lamp, twisting is applied to form a striped spiral. The state formed.

(Comparative Example 1) Comparative Example 1 was made by uniformly applying coloring on the outer periphery of the optical fiber. (Experiment)

Fig. 11 is a diagram of an experimental device for the effect of high power transmission on the coating layer. The output of the laser light source was P [W] and the bending diameter was A [ram]. A light source with a center wavelength of 1480 nm and a maximum of 3 W was used.

Using this high-power experimental system, a 5-minute pass test was performed on the examples and comparative examples. The experimental results after 5 minutes are shown in the table in FIG. It was confirmed that there was no problem in both the comparative example and the example when the diameter was 30 mm or more, but a remarkable effect was observed in the example when the diameter was 20 mm or less.

In Comparative Example 1, when the diameter was 2 Omm and the power was 3 W, deformation of the UV coating layer of the green fiber core wire (a state in which the habit was not restored) was observed. At diameters of 10 and 15 mm, deformation of the UV coating layer was observed for both the blue and green core wires at 2 W or more. On the other hand, in Example 1, no change was observed at a diameter of 15 mm or more. However, at a diameter of 1 O mm, deformation of the UV coating layer was observed for both the blue and green core wires.

In Example 2, no change was observed under all conditions. It is thought that if the stripe coloring is made spiral, the intermittent coloring is uniform in both the radial and length directions of the surface of the strand, and it is considered that deformation becomes difficult.

As described above, even if the transmission light leaks due to sudden bending of the fiber during handling of high-power light during transmission, etc., since the colored layer is striped, the leaked light escapes outside the coating layer. However, deterioration of the fiber coating can be suppressed, and problems such as disconnection and ignition can be completely prevented.

Optical transmission method that does not generate an _L over's)

Next, high-output light can be reduced without generating or transmitting fiber fuses. An embodiment of a fully propagating transmission method will be described.

Considering the fact that the optical power has been increasing in recent years, this fiber-fuse phenomenon has occurred.For example, the optical power due to contamination such as dust adhered to the connection end face of the connector built into the optical transmission line has been considered. In situations that can easily occur due to absorption, optical absorption based on tissue defects in optical fibers or guided multilayer filters, and optical energy density enrichment due to multiple reflections due to bending or bending of optical fibers. Has become.

Therefore, assuming that the optical power will be further increased in the future, it is necessary to prevent the occurrence of the above-described fiber fuse phenomenon and, if it occurs, to prevent the optical amplifier and the light source from proceeding. In other words, it is absolutely necessary to take measures to prevent the occurrence and progress of fiber fuses and to prevent damage to expensive optical amplifiers, light sources, optical components, and optical devices.

As represented by pumping light used in Raman amplifiers, the output of propagating signal light and pumping light is increasing, and the possibility of fire perfuse is increasing. In the present embodiment, the relationship between the minimum optical power required for fiber fuse transmission (fiber fuse transmission threshold value P _th ), the wavelength of the light source, the type of optical fiber, the type of dopant, and the MFD has been found. In other words, if the power of the propagating light is P, p <p _th

By propagating in a range in which the relationship is satisfied, it is possible to prevent occurrence of fiber fuse and transmission of fiber fuse.

Figure 4, shows the outline of a measuring device for measuring the full multiplexing fuse propagation闘値P _th. A light source that generates a maximum power of 5 W at a wavelength of 1664 nm or 1467 nm is connected to the optical fiber to be measured. Then, the power of the input light is increased, the optical fiber is locally heated, and a fiber fuse is generated at the heated portion. After that, when the power of the light source was lowered and the firefuse was extinguished, 0141

17 The optical power was set as the fiber fuse transmission threshold P. Therefore, this value is a value on the very safe side, and it is considered that firefighting is unlikely to occur with light having a power less than this value.

Figure 5 shows the single mode fiber (SMF), dispersion shifted fiber (DSF), and dispersion compensation fiber (DCF) fiber transmission at wavelengths of 1064 nm and 1467 nm. The result of measuring the value of the threshold value P _th (W) is shown. The vertical axis of the graph is the threshold (unit: ¾), and the horizontal axis is the wavelength (unit: nm).

It is considered that there is a linear function or a correlation approximate to the linear function between the wavelength and the fire-puffuse transmission threshold. Figure 5 shows that the relationship between this wavelength and the fiber fuse transmission threshold is determined by the type of optical fiber. The MFD (Mode Field Diameter) of the SMF is around 前後 Ομπι, the MFD of the DSF is around 7 to 8 μΐη, and the MFD of the DCF is around 4 to 5 μπι. In other words, MFD is smaller in the order of SMF, DSF, and DCF. According to FIG. 5, the fiber fuse transmission threshold value P _th is in the order of SMF, DSF, and DCF.

Next, Fig. 6 shows the relationship between the fiber fuse transmission threshold _Pth and the MFD. Data was measured using SMF, DSF, DCF, and other fibers with large MFD. As an example of a fiber having a large MFD, there is a thermal-diffused expanded core fiber (hereinafter referred to as 1 EC fiber). The TEC fiber is a fiber in which the MFD (mode field diameter) of the optical fiber is locally enlarged by heat diffusion technology. Here, the vertical axis of the graph is the threshold (unit: W), and the horizontal axis is the MFD (unit: μπι). Although not shown in the graph, the experimental results show that the fiber fuse transmission threshold P _th of the optical fiber is most affected by the size of the MFD. Other factors affecting the light transmission threshold _Pth include: 0141

18 Types and amounts of punts are conceivable.

As shown in FIG. 6, the measurement data of Faibafuyu one's transmission threshold P _th in a wide MFD range up 30 jum longitudinal it did not exist until now. From the measurement data of the fiber fuse transmission threshold P _th in the narrow range where the MFD is 10 jum or less, the relationship between the firefuse transmission threshold P _th and the MFD has a quadratic approximation correlation. However, as shown in Fig. 6, based on the measurement results when the MFD is 20 μm and 30 μπι, the relationship between the two is a linear function; the Pth-O-ISX optical fiber MFD (μ ΐη ) Or a similar correlation.

By using the data shown in FIGS. 5 and 6, a predetermined fiber fuse transmission threshold value P _th can be obtained based on the type and specification of the optical fiber as the transmission path and the wavelength of the signal light and the pump light to be transmitted.

Next, a description will be given of an optical amplifier in which the power P of the propagated light is controlled within the range where the relationship of P < _Pth is satisfied with respect to the fiber fuse transmission threshold value _Pth . Fig. 7 shows a configuration diagram of a high-power wavelength-division multiplexed pump light source used for Raman amplification. This high-power wavelength-division multiplexing pump light source includes a total of seven laser elements of five types of wavelengths. The wavelength of this laser device is stabilized by an FBG, a multilayer filter, and the like. The pump light generated from these laser elements is subjected to polarization synthesis and wavelength synthesis in a multiplexer to obtain a high-output pump light. This Raman amplifier can obtain a flat gain-wavelength characteristic by changing the output power of each wavelength.

This figure shows a backward pumping system, in which the connection parts A and B are connected to the signal light transmission line, and the above-described high-power pump light is propagated to the signal light transmission line via a WDM force bra. In addition, a part of the high-power pumping light is branched into a small amount by a tapping force brazer on the way, and transmitted to the output power monitor. With this output power monitor, the total output power of The monitor is monitored and the monitored value is fed back to the drive control circuit. The drive control circuit functions to control the output of the laser element so as to generate signal light and pump light of a predetermined output.

This control method is shown in the flowchart of FIG. As described above, the total output power P of the pump light unit is monitored. Then, a comparison is made with a fiber fuse transmission threshold value P _th for various parameters set in advance. If the total output power P is smaller than the fiber fuse transmission threshold value P _th , the power to maintain the power as it is \ power is increased.

If the total output power P is larger than the fiber fuse transmission threshold P, a fiber fuse may be generated, and control to reduce the power P is performed. In this case, it is important that the power be reduced while maintaining a flat gain-wavelength characteristic.

The Raman amplifier can obtain a flat gain-wavelength characteristic by controlling the output power of the pump light of each wavelength.However, when reducing the total power, if the power of a specific wavelength is reduced, However, the flatness of the gain-wavelength characteristic is lost, and the performance cannot be fully exhibited. In particular, since the gain spectrum generated by the pump light on the short wavelength side tends to have ripples, it is usually necessary to perform control such as reducing the number of multiplexes to reduce the gain per wavelength.

Therefore, appropriate power reduction control is required to reduce the power of the pump light of each wavelength little by little so as not to generate ripples and lose the flatness of the gain-wavelength characteristic.

With the above control, it is possible to always transmit high-power signal light and pump light with stable gain-wavelength characteristics without fear of fiber fuse generation or transmission. 4 000141

20 As described above, when propagating high-power pumping light and signal light of several watts, according to the present invention, even if bent at a small diameter of 1 Omm, the propagation continues without damage. Optical fiber can be provided. Therefore, it is possible to sufficiently satisfy the demands for higher power of transmission signal light and pumping light accompanying the ever-increasing transmission capacity and miniaturization of optical devices used in optical communication systems. Also, troubles caused by accidents and mistakes can be prevented.

Further, according to the present invention, it is possible to propagate high-power pump light and signal light without fear of generating or transmitting a fiber fuse. In particular, according to the transmission method of the present invention, it is possible to control the power of pumping light and signal light propagating without impairing the flat gain-wavelength characteristic of a Raman amplifier and the like, which is increasingly important in the future. And stable propagation of high-power pump light and signal light becomes possible.

Further, by using the optical fiber and the method for transmitting high-power pumping light and signal light of the present invention, it is possible to provide various optical devices and optical communication systems compatible with high-power light.

(Damage of optical fiber end)

Next, damage to the end of the optical fiber will be described.

With the increase in the output power of the optical power, the end face of the optical fiber is damaged as shown in Figs. 9A to 9C. At present, damage to optical connectors is sometimes reported. The test is performed using a light source that has a peak wavelength in 1480im, which is the same wavelength band as the pump light of the optical amplifier. Test samples can be prepared by mating the connectors with a force impurity that damages the end face of the FC connector. Then, a 2 W laser beam was input to the optical system, and changes in the test sample were observed. FIG. 10 shows the test conditions and test results. 04 000141

21 As a result of the test, test samples according to the standard (without scratching the core layer of commonly available SMF) did not change as expected.

Secondly, the test samples that were scratched with less appropriate polishing conditions did not show any further damage. Also, for the test samples that were very severely scratched with a 5 / m file, the temperature increased but no other damage was seen. No changes were seen in the test samples with the highly transparent impurities. For the test sample with the index matching oil with bubbles, the temperature increased but this was probably due to splice loss.

In the case of test samples containing light-absorbing impurities such as metals and black components, even if the splice loss is small, the ends of the test sample may be damaged and fiber fuses may occur. In particular, in the case of phosphor bronze, the edge was damaged even with a power of only 50 mW.

The above tests show that only the impurities that readily absorb the light output directly damage the end of the optical fiber. Therefore, it is desirable to avoid scratches in the core layer because there is a risk of trapping this impurity. Similarly, it is better to avoid using index-matching oils in high-power environments because they can easily trap bubbles and impurities.

Note that widening the MFD by using a GRIN lens or a heat dissipation technique can reduce the energy output density at the end, and thus has the effect of increasing durability. On the other hand, cleaning the edges to remove impurities is the most effective way to address this problem. If the end breaks, the problem can be solved by regrinding or replacing the damaged connector. As described above, various embodiments of the present invention have been described. However, aspects of the present invention are not limited to the above-described aspects, and various other aspects can be considered.

Claims

Claims A coated optical fiber whose outer periphery is covered with a coating material, wherein the coating material uses a transparent ultraviolet curable resin to prevent light leaked from the optical fiber to the outside by the coating material. 2. A coating light capable of transmitting output light, characterized in that it absorbs and suppresses generation of heat. 4. A translucent ultraviolet-curable resin is used for the coating material instead of a transparent material. An optical fiber filter capable of transmitting high-output light as described in the item. A coated optical fiber whose outer periphery is covered in the order of a primary coating layer made of an ultraviolet-curable resin, a secondary coating layer made of an ultraviolet-curable resin, and a colored layer, wherein the colored layer is outside the secondary coated layer Coating light capable of transmitting high-output light characterized by covering a part of the surface: The colored layer having a stripe shape covers a part of the outer surface of the secondary covering layer. 4. The coated optical fiber according to claim 3, which is capable of transmitting high output light. 4. The coated light capable of transmitting high output light according to claim 3, wherein the colored layer having a helical stripe shape covers a part of an outer surface of the secondary coating layer. fiber. A high output light of 50 O mW or more is transmitted. 6. A coated optical filter capable of transmitting high-output light according to any one of items 1 to 5.

7. The coated optical fiber capable of transmitting high-output light according to any one of claims 1 to 6 is housed in a package member having a light absorbing layer on the inner surface. Optical fiber package.

8. An optical device using the coated optical fiber capable of transmitting high-output light according to any one of claims 1 to 6.

9. A fiber fuse transmission threshold, which is the minimum light output required for fiber fuse transmission, is obtained, and output control is performed so that the output of light to be transmitted becomes smaller than the fiber fuse transmission threshold. Light transmission method.

10. A step of monitoring a part of the output light of the optical amplifier by branching it by a very small amount;

Comparing a preset fiber fuse transmission threshold with a monitored value (monitored value);

If the monitor value is smaller than the fiber fuse transmission threshold, a command is issued to maintain or increase the output of the optical amplifier, and if the monitor value is equal to or greater than the fiber perfuse transmission threshold, the light is output. Issuing a command to lower the output of the amplifier;

A method for controlling an optical amplifier, comprising:

11 1. When lowering the output of the optical amplifier, 10. The method for controlling an optical amplifier according to claim 10, wherein the optical output is gradually reduced.