JP2554776B2 - Reinforcing method of optical fiber connection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION “Industrial field of application” The present invention relates to an optical fiber using an amorphous carbon re-coating device for a fused splicing portion of a fused silica fused optical fiber coated with an amorphous carbon film. The present invention relates to a method of reinforcing a connection part.

"Prior Art" Generally, a glass optical fiber such as quartz glass is often used as an optical fiber. If the surface of the optical fiber made of glass is damaged or the like, when the tensile force is applied to the fiber in the longitudinal direction, the damage may grow and further break. Further, if water adheres to the surface of the fiber, there is a problem that the mechanical strength of the water adhering portion decreases with time.
Further, if the optical fiber is exposed to a hydrogen atmosphere, hydrogen gas diffuses into the fiber, and there is a problem that the diffused hydrogen causes a large optical absorption loss of the optical fiber. In addition, hydrogen reacts with structural defects of glass to form SiOH groups, which causes a problem of increasing transmission loss.

As a method for solving these various problems, various methods have been proposed in which the surface of the optical fiber is covered with a highly airtight coating to prevent the optical fiber from being damaged and from being contacted with hydrogen ions, water and the like. For example, on the surface of an optical fiber, an amorphous carbon film (hereinafter simply referred to as a carbon film) having a characteristic of not permeating water that reduces the mechanical strength of the optical fiber or hydrogen that increases transmission loss is formed. There is a method of coating a few 100 to 1000 angstroms. In the optical fiber 1 coated with the carbon coating, a carbon coating 4 is coated as a hermetic coating on the surface of a glass optical fiber normally composed of a core 2 and a cladding 3 as shown in FIG. It is known that a synthetic resin coating 5 is laminated on top of 4.

By the way, since an optical fiber has a finite length in practical use, when laying it over a long distance, it is necessary to connect and use an optical fiber of a finite length as needed. As a method for connecting the optical fibers in this way, there are a connector method, a fusion splicing method, etc., but as the permanent connection method, generally, the end portions of the optical fibers are butted against each other,
A fusion splicing method of melting and connecting in an arc discharge is used. To apply this fusion splicing method to the optical fiber coated with the carbon coating described above, first remove the coating such as the synthetic resin coating at the end of each optical fiber to be spliced,
The ends are butted against each other and melted and connected in an arc discharge. However, in the heating process by the arc discharge, the carbon coated on the surface of the optical fiber burns and disappears. For this reason, the optical fiber surface of the fusion spliced portion is exposed in a bare state, and the exposed fusion spliced portion of the optical fiber surface is further adhered with water or hydrogen gas to cause fusion. There is a possibility that the mechanical strength in the vicinity of the connection portion may be reduced, or that the light transmission loss may be increased.

The following methods have been considered to solve the above problems. This method, after fusion splicing the optical fiber coated with Servoun coating, introduce the exposed fusion spliced portion of the optical fiber surface into the atmosphere of the raw material gas for coating the carbon coating, and the fusion spliced portion Is a method of irradiating a radiant heat ray (for example, a laser beam) having a constant intensity from a radiant heat source while moving the varnish and heating the radiant heat source to re-coat the fusion-spliced portion with the carbon film.

[Problems to be Solved by the Invention] However, when the carbon coating is recoated on the fusion-spliced portion by the conventional method, the focal point of the radiant heat ray is the fusion of the heating target when the portion to be recoated is moved. It may deviate from the joint, which makes it difficult to keep the surface temperature of the fused joint to be recoated constant. Therefore, it is also difficult to apply a uniform carbon coating to the fusion-spliced portion, and sometimes a portion of the recoated carbon coating has an extremely thin portion, or
Further, there is a possibility that a portion where the carbon coating is not formed may occur, and therefore the above method still has a point to be improved in terms of how to make the thickness of the carbon coating uniform.

The present invention has been made in view of the above circumstances. When the optical fibers coated with a carbon film are heated and fused and connected, the carbon coated on the surface of the optical fiber burns and disappears to expose the surface of the optical fiber. It is an object of the present invention to provide a method for reinforcing an optical fiber splicing part, which can coat a carbon film having a uniform thickness on the fusion spliced part.

"Means for Solving the Problem" The above-mentioned problem is to radiate a furnace for heating the fusion-bonded portion after fusion-splicing the ends of the carbon-coated optical fiber to each other. A cover for shutting off the fusion-spliced portion from the outside air, and an apparatus having a mechanism for introducing a raw material gas into the cover is used to re-spray the fusion-spliced portion with carbon by fusion-splicing of an optical fiber. In the method of reinforcing the part, the problem is solved by heating the optical fiber while moving in the longitudinal direction and controlling the output of the radiant heat source so that the surface temperature of the optical fiber in the heated part is kept constant.

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

 Hereinafter, the present invention will be described in detail.

The method for reinforcing an optical fiber splicing part of the present invention is, after fusion splicing an optical fiber, heating the fusion splicing part in a source gas atmosphere by a radiation type heat source to apply a carbon coating to the fusion splicing part. At this time, it is a method of re-coating a uniform carbon film by controlling the reaction temperature of the carbon film formation to be constant.

The apparatus for performing the above method, a radiant heat source for heating the fusion splicing portion, and a cover for shielding the fusion splicing portion of the glass optical fiber from the outside air, and a mechanism for introducing the raw material gas into this covering, At the time of the carbon coating formation reaction, a light receiver for measuring the light intensity of the light generated from the surface of the optical fiber to be coated, or a thermometer for measuring the temperature of the carbon coating formation portion during the carbon coating formation reaction. From the mechanism that feeds back information indicating the state of the carbon film formation portion obtained at these times to the radiant heat source, and the controller that adjusts the output of the radiant heat source based on this fed back information. It is configured.

As the radiant heat source, it is desirable to use a CO ₂ laser which is an infrared ray, and to uniformly irradiate the surface of the optical fiber through an optical means having a reflection mirror, a lens, and a radiation surface mirror. External power adjustment of the laser by an electro-optic modulator is desirable.

Next, an example of the method for reinforcing the optical fiber connection portion of the present invention will be described in more detail with reference to the drawings. FIG. 2 shows an example of an apparatus preferably used in this method. This apparatus emits from a carbon dioxide gas laser oscillator, a 1/4 λ plate 2, and a carbon film formation site during carbon film formation. PID that controls the laser light 4 emitted from the oscillator 1 when passing through a CdTe (cadmium tellurium) EOM (hereinafter simply abbreviated as EOM) 5 according to the information from the light receiver 3 and the received light Controller (proportional differential integration controller) 6 and chamber 7 for shutting off the reaction system from the outside air
And a gas introduction device 8 for introducing the raw material gas into the chamber 7.
It is composed of

In order to recoat the optical fiber connection portion with the carbon coating using the apparatus having the above-described configuration, first, the oscillator 1 emits the carbon dioxide laser light 4. The oscillated laser light 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 light 4 after passing through the EMO 5 is guided onto the surface of the parabolic mirror 9 by reflected light or the like. The reflecting mirror and parabolic mirror 9 are provided with slits 10 and 11 for passing an optical fiber. Parabolic mirror 9
Laser light 4 guided to the optical fiber in the chamber 7
12 It is focused on one point on the surface, and only this one point becomes hot. At this time, the inside of the chamber 7 is in the 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 coat the carbon film. The optical fiber is moved in the longitudinal direction by the traverser 13 in order to apply a uniform coating on the surface thereof. As the raw material gas used at this time, linear hydrocarbons, benzene, chlorofluorocarbon, etc. are suitable.

Further, the control of the laser light intensity is performed by using the light emitted from the coating film forming portion 14 when the carbon coating film is formed.
The light is received by the PID controller 6, the information on the light intensity is sent to the PID controller 6, and the PID controller 6 controls the EOM 5 to perform the operation. Further, as the optical fiber coated with the carbon film by this method, not only the fusion-spliced portion,
It is also possible to apply locally to the part where the carbon coating is not applied.

Example The carbon coating was applied to the fusion spliced portion of the optical fiber using the apparatus shown in FIG. A carbon dioxide gas laser with an output of 20 W was used as the radiant heat source. The oscillation wavelength of the laser light was 10.6 μm. Laser light of this wavelength is very well absorbed by quartz glass,
Efficient heating is possible. The laser light intensity was controlled by the light receiver 3, the EOM 5, and the PID controller 6 so that the reaction light intensity detected by the light receiver 3 was constant. In addition, a mixed gas prepared by diluting benzene to a concentration of 10% with Ar gas is introduced into the chamber 7 in advance, and an optical fiber for coating is further focused on the portion where the carbon coating is to be applied. It was set inside the chamber 7 so as to be exposed to light. The optical fiber in the chamber 7 is a traverser 13
Was moved at a speed of 10 mm / min.

Under the above conditions, 20 samples were prepared by fusion-splicing the end portions of the optical fibers as a sample, and the fusion-spliced portion was coated with a carbon film, and the film thickness was about 100.
An angstrom amorphous carbon coating was applied.

(Comparative Example) The same device as that used in the above example is used so that the intensity of the laser beam is always constant (output 20 W) without controlling the laser beam by the light receiver 3, EOM5, PID controller 6, etc. The same operation was performed under the same conditions except that, 20 samples were prepared by fusion splicing the end portions of the optical fiber, and the fusion spliced portion was coated with an amorphous carbon film. Some samples had uneven thickness, and some samples were not coated.

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

[Advantages of the Invention] As described above, according to the reinforcing method for the optical fiber connecting portion of the present invention, the optical fiber is heated while moving in the longitudinal direction, and at this time, the temperature of the optical fiber surface of the heated portion is constant. Since the mechanism for controlling the output of the radiant heat source is used so as to keep the temperature constant, it is possible to recoat the carbon film having a uniform film thickness at the connecting portion of the optical fiber. Therefore, the mechanical strength of the fusion spliced part is generally improved uniformly, and since water and hydrogen do not pass through the carbon coating and contact the glass part of the optical fiber, the mechanical strength of the optical fiber is reduced and Can effectively prevent the transmission loss.

Further, since the control mechanism of the radiant heat source is a mechanism for measuring the light intensity emitted at the time of carbon generation and feeding back this to the radiant heat source output to control the heat source output, the optical fiber connection by the radiant heat source is connected. Since the degree of heating of the portion can be adjusted accurately, the uniformity of the carbon coating described above is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an optical fiber coated with a carbon film, and FIG. 2 is a schematic view showing an example of an apparatus preferably used in the method for reinforcing an optical fiber connecting portion of the present invention. 1 ... laser light oscillator, 3 ... photoreceiver, 4 ... laser light, 5 ... EOM, 6 ... PID controller, 7 ... chamber, 8 ... gas introducing device, 12 ... optical fiber, 14 …… Film formation site, 15 …… Optical fiber, 18 …… Carbon film.

Claims (2)

(57) [Claims] 1. A radiation-type furnace for fusion-splicing the ends of an optical fiber coated with amorphous carbon and then heating the fusion-splicing portion, and the fusion-splicing portion of the optical fiber from the outside air. In a method of reinforcing an optical fiber splicing part for re-coating the fusion spliced part and amorphous carbon by using a device having a cover for shutting off and a mechanism for introducing a raw material gas into the cover, A method for reinforcing an optical fiber connecting portion, which comprises heating while moving in the longitudinal direction, and controlling the output of a radiant heat source so as to keep the temperature of the optical fiber surface of the heated portion constant. 2. The control of the radiant heat source is performed by measuring the intensity of light emitted when amorphous carbon is produced and controlling the radiant heat source output by field-backing this to the radiant heat source. The method for reinforcing an optical fiber connecting portion according to claim 1.