JPH04202029A - Method for reinforcing optical fiber juncture - Google Patents

Abstract

PURPOSE:To allow the coating of a fusion spliced part where optical fiber surfaces are exposed with a carbon film of a uniform film thickness by heating the optical fibers while moving the fibers in a longitudinal direction, then controlling the output of a radiation type heat source so as to maintain the specified surface temp. of the heated part. CONSTITUTION:A CO2 laser beam 4 is first oscillated from an oscillator 1. The oscillated laser beam is passed through a quarter lambda plate 2 and is then passed through an EOM 5, by which the intensity of the CO2 laser beam 4 is controlled. The laser beam 4 after the passage through the EMO 5 is guided by reflected mirror, etc., onto the surface of a parabolic mirror 9. The laser beam 4 guided to the parabolic mirror 9 is condensed to one point on the surface of the optical fiber 12 in a chamber 7 and only this one point rises to a high temp. The atmosphere of the gaseous raw materials introduced from a gas introducing device 8 is maintained in the chamber 7 at this time. Then, the gaseous raw materials react on the optical fiber surfaces of the above- mentioned high-temp. part and the fiber surfaces are coated with the carbon film. The above-mentioned optical fibers are moved longitudinally by a traverser 13 in order to apply the uniform film on the surfaces thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention provides an optical fiber recoating system using an apparatus for recoating amorphous carbon at a fusion spliced part in which fused silica glass optical fibers coated with amorphous carbon are spliced. The present invention relates to a method for reinforcing fiber joints.

"Prior Art" Generally, optical fibers made of glass such as quartz glass are often used as optical fibers. If there is damage to the surface of the glass optical fiber, the damage may grow and even break when tension is applied to the fiber in the longitudinal direction. Further, when moisture adheres to the fiber surface, there is a problem in that the mechanical strength of the portion to which the moisture adheres decreases over time. Furthermore, when an optical fiber is exposed to a hydrogen atmosphere, hydrogen gas diffuses into the fiber, and the diffused hydrogen increases the optical absorption loss of the optical fiber. Furthermore, hydrogen reacts with structural defects in the glass to form 5iOH groups, which has the problem of increasing transmission loss.

As a method to solve these problems, various methods have been considered to protect the optical fiber from damage and contact with hydrogen ions, water, etc. by applying a highly airtight coating to the surface of the optical fiber. For example, an amorphous carbon coating (hereinafter simply abbreviated as carbon coating) on the surface of an optical fiber has the characteristic that it does not transmit moisture, which reduces the mechanical strength of the optical fiber, or hydrogen, which increases transmission loss.
There is a method of forming a film with a thickness of several 100 to 1000 angstroms. The optical fiber 1 coated with the above-mentioned carbon film is usually produced by coating the surface of a glass optical fiber consisting of a core 2 and a cladding 3 with a carbon film 4 as a hermetic coat, as shown in FIG. It is known that a synthetic resin film 5 is laminated on top of the film 4.

Incidentally, optical fibers have a finite length in practice, so when laying them over long distances, it is necessary to connect optical fibers of finite lengths as needed.

Methods for connecting optical fibers include the connector method and the fusion splicing method, but the permanent connection method generally involves butting the ends of the optical fibers together and melting them in an arc discharge. The fusion splicing method is used. To apply this fusion splicing method to the carbon-coated optical fibers mentioned above, first remove the synthetic resin coating or other coating from the ends of each optical fiber to be spliced, and then butt the ends together. Connect by melting in arc discharge. However, in the heating process by arc discharge,
The carbon coated on the surface of the optical fiber burns and disappears. As a result, the surface of the optical fiber at the fusion spliced portion is exposed in a bare state, and furthermore, moisture may adhere to the exposed fusion spliced portion of the optical fiber surface, or hydrogen gas may come into contact with the fusion spliced portion. There is a fear that the mechanical strength near the connection portion may decrease or the optical transmission loss may increase.

The following methods have been considered to solve the above problem. In this method, after fusion splicing an optical fiber coated with a carbon film, the exposed fusion spliced portion on the surface of the optical fiber is introduced into an atmosphere of raw material gas for coating the carbon film, and the fusion spliced portion is In this method, the fusion spliced portion is recoated with a carbon film by heating it by irradiating it with radiant heat rays (for example, laser light) of a constant intensity from a radiant heat source while moving the fusion spliced portion.

[Problem to be Solved by the Invention J] However, when the carbon coating is recoated on the fusion spliced part by the above-mentioned conventional method, when moving the part to be recoated, the focus of the radiant heat rays is focused on the fusion spliced part to be heated. There is a possibility of deviation from the spliced portion, making it difficult to maintain a constant surface temperature of the fusion spliced portion to be recoated. Therefore, it is difficult to apply a uniform carbon film to the above-mentioned fusion spliced parts, and sometimes the re-coated carbon film may have extremely thin parts, or even a carbon film may be formed. Therefore, the above method still has some points to be improved in terms of how to make the thickness of the carbon film uniform.

The present invention was developed in view of the above circumstances, and when carbon-coated optical fibers are connected by heat fusion, the carbon coated on the surface of the optical fiber burns and disappears, exposing the surface of the optical fiber. It is an object of the present invention to provide a method for reinforcing an optical fiber spliced portion, which can cover a fusion spliced portion with a carbon film having a uniform thickness.

"Means for Solving the Problem" The above problem consists of a radiation-type furnace that heats the fusion-spliced portion after fusion-splicing the ends of carbon-coated optical fibers, and Fusion splicing of optical fibers in which the fusion spliced part is recoated with carbon using a device having a cover for shielding the fusion spliced part from the outside air and a mechanism for introducing source gas into the cover. In the method of reinforcing the part, heating the optical fiber while moving it in the longitudinal direction,
At this time, the problem can be solved by controlling the output of the radiant heat source so as to keep the surface temperature of the optical fiber at the heated portion constant.

Further, in controlling the radiant heat source, it is desirable to measure the intensity of light emitted when carbon is generated, and feed this back to the radiant heat source to control the output of the radiant heat source.

The present invention will be explained in detail below.

The method for reinforcing an optical fiber joint of the present invention includes fusion splicing optical fibers, heating the fusion spliced portion in a source gas atmosphere using a radiant heat source, and applying a carbon film to the fusion spliced portion. In this method, a uniform carbon film is recoated by controlling the reaction temperature for carbon film formation to be constant.

The apparatus for carrying out the above method includes a radiant heat source that heats the fusion spliced part, a cover that isolates the fusion spliced part of the glass optical fiber from the outside air, and a mechanism that introduces the source gas into the cover. A light receiver for measuring the intensity of light emitted from the surface of the optical fiber to be coated during the above carbon film formation reaction, or a thermometer for measuring the temperature of the carbon film forming part during the carbon film formation reaction. , a mechanism that feeds back information indicating the state of the carbon film forming part at the time of carbon film formation to the radiant heat source, and a control device that adjusts the output of the radiant heat source based on this feedback information. It is configured.

As the radiation type heat source, it is preferable to use an infrared C○2 laser and uniformly irradiate the surface of the optical fiber through an optical means having a reflecting mirror, a lens, and a parabolic mirror. External output adjustment of the laser by ROM (electro-optic modulator) is desirable.

Next, an example of the method for reinforcing an optical fiber connection portion of the present invention will be described in more detail with reference to the drawings. Figure 2 shows an example of a device suitably used in illegal activities. The laser beam 4 emitted from the oscillator 1 is converted into a CdTe laser using a photoreceiver 3 that receives light and information from the photoreceiver 3.
(cadmium telluride) EOM (hereinafter simply abbreviated as EOM) 5; a PID controller (proportional differential integral controller) 6 for controlling when passing through; a chamber 7 for isolating the reaction system from outside air; It is composed of a gas introduction device 8 that introduces raw material gas.

In order to recoat the optical fiber connection portion with the carbon film using the apparatus configured as described above, first, the oscillator 1 oscillates the carbon dioxide laser beam 4 . The oscillated laser beam 4 is 1/4
After passing through the λ plate 3, it passes through the EOM 5, and the intensity of the carbon dioxide laser beam 4 is controlled. The laser beam 4 after passing through the EMO 5 is guided onto the surface of a parabolic mirror 9 by reflected light or the like, and this reflecting mirror or parabolic mirror 9 has a slit 10 for passing the optical fiber. 11 are provided. The laser beam 4 guided by the parabolic mirror 9 is focused on one point on the surface of the optical fiber 12 in the chamber 7, and only this point becomes high temperature. Further, at this time, the inside of the chamber 7 is in an atmosphere of the raw material gas introduced from the gas introduction device 8.

Therefore, the raw material gas reacts on the surface of the optical fiber in the high-temperature portion to form a carbon film. The optical fiber is also moved longitudinally by a traverser 13 in order to apply a uniform coating on its surface. Note that the raw material gases used at this time include linear hydrocarbons, benzene,
Freon or the like is suitable.

In addition, the control of the laser beam intensity is performed by directing the light emitted from the film forming part 14 to the light receiver 3 during carbon film formation.
Information on this light intensity is sent to the PID controller 6, and this PID controller 6 further controls the EOM 5.

Further, the optical fiber coated with a carbon film by this method can be applied not only to the fusion spliced portion but also to a portion where the carbon film is not locally coated.

"Example" Using the apparatus shown in FIG. 2 described above, a carbon film was coated on a fusion spliced portion of an optical fiber. A carbon dioxide laser with an output of 20 W was used as a radiant heat source. Further, the oscillation wavelength of the laser beam was set to 10.6 μm. Note that since laser light of this wavelength is extremely well absorbed by silica glass, efficient heating is possible. Further, the laser light intensity was controlled by the light receiver 3, the EOM 5, and the PID controller 6 so that the intensity of the reaction light detected by the light receiver 3 was constant.

In addition, a mixed gas in which benzene is diluted to a concentration of 10% with Ar gas is introduced in advance into the chamber 7, and a laser beam is focused on the part of the optical fiber to be coated with a carbon coating. It was set inside chamber 7 so as to be exposed to light. Further, the optical fiber in the chamber 7 was moved by the traverser 13 at a speed of 10 mm 7 minutes.

Under the above conditions, we prepared 20 samples of optical fibers with their ends fused together, and coated the fusion spliced parts with a carbon film.
A 0 angstrom amorphous carbon film was applied.

(Comparative example) A device similar to that used in the above example was used as the light receiver 3.
, the same operation was performed under the same conditions except that the laser light was not controlled by the EOM5, PID controller 6, etc. and the intensity of the laser light was always constant (output 20W), and the ends of the optical fibers were When we prepared 20 samples with fusion spliced and coated the fusion spliced parts with an amorphous carbon film, we found that some samples had uneven carbon film thickness and some samples were not coated. Ta.

20 samples of the above example and sample 2 of the comparative example
The average tensile strength, standard deviation of tensile strength, and static fatigue coefficient were measured for each sample. The results are shown in Table 1 below.

Table 1 in the margin below: "Effects of the Invention" As explained above, according to the method for reinforcing an optical fiber connection part of the present invention, the optical fiber is heated while moving in the longitudinal direction, and at this time, the light of the heated part is Since a mechanism is used to control the output of the radiant heat source to keep the fiber surface temperature constant, the connecting portion of the optical fiber can be recoated with a carbon film of uniform thickness. Therefore, the mechanical strength of the fusion spliced part is increased evenly and overall, and water and hydrogen do not pass through the carbon coating and come into contact with the glass part of the optical fiber, which prevents a decrease in the mechanical strength of the optical fiber and transmission loss can be effectively prevented.

In addition, the control mechanism for the radiant heat source is a mechanism that measures the light intensity emitted during carbon generation and feeds this back to the radiant heat source output to control the heat source output.
Since the degree of heating of the optical fiber connecting portion by the radiant heat source can be accurately adjusted, the uniformity of the carbon coating is improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an optical fiber coated with a carbon film, and FIG. 2 is a schematic diagram showing an example of a device suitably used in the method for reinforcing an optical fiber connection portion of the present invention. DESCRIPTION OF SYMBOLS 1... Laser beam oscillator, 3... Light receiver, 4... Laser beam, 5... EOM, 6... PID controller, 7... Chamber, 8... Gas introduction device, 12. ...Optical fiber, 14... Film generation site, 15... Optical fiber, 18... Carbon film.

Claims (1)

[Claims] 1. A radiation-type furnace that heats the fusion-spliced portion after fusion-splicing the ends of amorphous carbon-coated optical fibers, and the fusion-spliced portion of the optical fiber. In a method for reinforcing an optical fiber spliced portion, the fusion spliced portion is recoated with amorphous carbon using a device having a cover for shielding the fiber from the outside air and a mechanism for introducing raw material gas into the cover, A method for reinforcing an optical fiber joint, which comprises heating the optical fiber while moving it in the longitudinal direction, and controlling the output of a radiant heat source so as to keep the surface temperature of the optical fiber constant at the heated portion. 2. A claim characterized in that the radiant heat source is controlled by measuring the intensity of light emitted when amorphous carbon is generated, and feeding this back to the radiant heat source to control the output of the radiant heat source. 1. The method for reinforcing an optical fiber connection portion according to 1.