JPH0356603B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for connecting optical fibers while aligning their axes by observing the end faces of the optical fibers.

(Prior Art) Conventionally, alignment of optical fibers in this type of connection direction has been performed as follows. That is, as shown in FIG. 4, an abutting plate 3 having a mirror 4 formed on its upper part is inserted between the end faces of two optical fibers 1 and 2 to be connected, and a microscope 5 is placed on the upper part of the abutting plate 3.
At the same time, illumination light 6 is applied to the end faces of optical fibers 1 and 2 from the microscope 5 side via mirror 4, and from the difference in light intensity of reflected light 7 caused by the difference in refractive index on the end faces. The optical fibers 1 and 2 were aligned while observing the core positions of the optical fibers 1 and 2 using a microscope 5. This axis alignment moves the cores of both optical fibers 1 and 2 to positions equidistant from the apex of the mirror 4 within the field of view of the microscope 5.
Next, both optical fibers 1,
This is done by moving 2.

However, optical fibers that are connected in this way usually have a small core diameter and a very small refractive index difference of about 0.004 between the core and the cladding.
The method described above was extremely difficult to find the axis of the core and was not practical.

There is a method shown in FIG. 5 as an example of an improvement on the above-mentioned method. This is done by applying illumination light 6 from the side of the optical fibers 1 and 2 at a position away from the connecting end surfaces of the optical fibers 1 and 2, propagating the scattered light 8 into the core, and directing the scattered light 8 to the butt. This is a method of identifying the core by observing it with a microscope 5 through a mirror 4 of a plate 3.

However, this method requires a lamp of several tens of W as a light source,
When the optical fiber is coated with colored nylon, there is a drawback that sufficient observation cannot be made.

Furthermore, in observing the birefringence axis of a stress-applied polarization-maintaining optical fiber, etc., none of the above-mentioned methods can be used because the refractive index of the stress-applying portion is close to the refractive index of the cladding.

Another method is to chemically treat the end face of the optical fiber to be connected to form a convex part on the end face, and then align the center of the core while observing the convex shape. -Disclosed in Publication No. 91415.

However, this method requires a mixed solution of HF and HN ₄ F, which are extremely reactive and powerful chemicals, as an etching solution for the end face of the optical fiber, so a very dangerous pretreatment process is required when connecting the optical fiber. In addition to this, there are always problems with the possession and storage of this powerful drug, and there is a drawback that a series of connection processes cannot be integrated into a device.

(Object of the Invention) In view of the above-mentioned conventional drawbacks, the present invention has been developed by making it possible to clearly identify the core axis, birefringence axis, etc. through a series of steps and without using powerful chemicals. The purpose of this invention is to realize low-loss, low-mode return connections of optical fibers.

(Structure of the Invention) In order to achieve the above object, the present invention arranges a plurality of optical fibers to be connected to face each other with a predetermined interval between their end faces, and heats each optical fiber end face to a temperature lower than the melting temperature of the cladding portion. After deforming the end face of each optical fiber by preheating it so that The optical fiber end face is melted and connected by heating at a temperature higher than the melting temperature of the clad part.

In other words, the melting temperature of the core portion and stress-applying portion (hereinafter referred to simply as the shaft portion) containing the dopant is lower than that of the pure quartz cladding portion, so even a slight amount of heating deforms the shaft portion at the end face of the optical fiber. Focusing on this, the present invention is characterized in that when observing the end face of the optical fiber, the deformation is caused by preheating so that the shaft portion can be clearly identified.

(Embodiment) FIGS. 1a to 1c show embodiments of the present invention, in which the same components of the conventional example are denoted by the same reference numerals. First, before observing the end surfaces 1a and 2a of the optical fibers 1 and 2 to be connected, as shown in FIG. jig 1
0 and 11, and both end surfaces 1a and 2a are heat-treated by discharge heating using discharge electrodes 20 and 21. This heating should be to a level that does not adversely affect the fusion splicing of the optical fibers 1 and 2, which will be described later. In other words, the discharge time is about 0.05 to 0.1 seconds,
The cladding part of pure quartz is hardly melted, and only the core part and the stress-applying part are melted and deformed.
After that, as shown in Figure b, the distance between the end surfaces 1a and 2a of both optical fibers 1 and 2 is widened a little, the abutment plate 3 is inserted between them, and the microscope 5 is positioned above it, and the microscope 5 side is The illumination light 6 is transmitted through the mirror 4 to the end surfaces 1a and 2 of the optical fibers 1 and 2.
a, and the optical fibers 1 and 2
As described in the conventional example, the optical fibers 1 and 2 are aligned while observing the position of the core with the microscope 5. FIG. 2 shows how the shape of the optical fiber end face changes due to preheating, which is a feature of the present invention, and how it is improved when observing the end face using a microscope.

FIG. 2a shows an observed state of the end face of the single mode optical fiber before preheating. In the figure, 1b is the clad part,
1c is the core portion. In this state, since the relative refractive index difference of the core is as small as about 0.3%, the core portion 1c shown by the broken line can hardly be observed in reality. FIG. 2b is a side view showing the vicinity of the end face after preheating. As shown in the figure, it has been confirmed through experiments that only the core portion 1c is melted by preheating and becomes slightly convex. FIG. 2c shows the appearance of the end face when observed after preheating. Illumination light is scattered in the deformed core part 1c, and it can be clearly distinguished from the bright cladding part 1b. After alignment, fusion splicing using conventionally known discharge electrodes 20 and 21 as shown in FIG. 1c can be performed.

FIG. 3 shows how a polarization-maintaining optical fiber having a stress applying portion 1d is improved. Figure 3a shows the state of observation of the end face before preheating, in which 1b is the cladding part, 1c is the core part, and 1d is the core part.
is the stress applying part. In this state, the refractive index difference is
The core part 1c is indicated by a broken line because it is small at about 0.3%.
And the stress-applying portion 1d can hardly be observed in reality. FIG. 3b is a side view showing the vicinity of the end surface after preheating. As shown in the figure, only the core portion 1c and the stress-applying portion 1d are particularly melted by the preheating, and have a slightly convex surface. This has also been confirmed through experiments. FIG. 3c shows the appearance of the end face when observed after preheating. Illumination light is scattered in the deformed core part 1c and the stress applying part 1d, so that they can be clearly distinguished from the bright round rod part 1b. The birefringence axis in the polarization-maintaining optical fiber is located at the stress applying portion 1d or in a direction perpendicular thereto, and is in the x and y directions shown in FIG.
According to the observation method described above, the birefringence axis can be clearly known. The reason why the birefringence axes of both optical fibers are aligned and connected is that the propagation mode with an electric field component in the x-direction and the propagation mode with an electric field component in the y-direction have different phase velocities. This is because mode conversion occurs when the birefringence axis is tilted.

(Effects of the Invention) As explained above, according to the present invention, a plurality of optical fibers to be connected are made to face each other with a predetermined end face interval, and each optical fiber end face is heated to a temperature lower than the melting temperature of the cladding portion. After deforming the end face of each optical fiber by preheating it so that Since the optical fiber end face is melted and connected by heating at a temperature higher than the melting temperature of the cladding part, the shaft part such as the core part and stress applying part has a lower melting temperature than the pure quartz cladding part. deformation, which scatters the illumination light and makes it clearly distinguishable from the bright cladding. Therefore,
Without having to propagate light in two optical fibers to be connected and monitor the optical power as in the conventional case, the shaft parts of the cores etc. can be easily aligned just by the connection point. In particular, when aligning the birefringent axes of polarization-maintaining optical fibers, there is a 50% probability that the stress-applying parts of two optical fibers that are connected can be aligned using a method that monitors the power of propagating light. If the parts are not aligned, the connection and strength properties will deteriorate. In the method of the present invention, the stress-applying parts can be aligned 100%, so a more reliable connection is possible.

In addition, since there is no need to use highly reactive powerful drugs, it is highly safe, and troublesome problems such as possession and storage of powerful drugs can be avoided.Furthermore, it can be manufactured in a series of steps without going through a pre-treatment process. .

[Brief explanation of drawings]

Figures 1a to 1c are process explanatory diagrams showing an embodiment of the present invention, Figure 2a is a diagram showing the observed state of the end face of a single mode optical fiber before preheating, and Figure 2b is an end face after preheating. Figure 2c is a side view showing the vicinity, Figure 2c is a diagram showing the state of the end face when observed after preheating, and Figure 3a is the end face of a polarization maintaining optical fiber with a stress applying section before preheating. Observation state diagram, Figure 3b
is a side view showing the vicinity of the end surface after preheating, FIG. 3c is a diagram showing the state of the end surface when observed after preheating, and FIGS. It is an explanatory view of axis alignment of an optical fiber. 1, 2... optical fiber, 1a, 2a... end face,
1b... Clad part, 1c... Core part (shaft part).

Claims (1)

[Claims] 1. A plurality of optical fibers to be connected are placed facing each other with a predetermined distance between their end faces, and the end faces of each optical fiber are preheated to a temperature lower than the melting temperature of the cladding portion. After deforming the end faces of the optical fiber, the end faces are irradiated with light, and the shafts of the optical fiber end faces are aligned while being observed through an optical system such as a mirror, until the temperature is higher than the melting temperature of the cladding part. 1. A method for connecting optical fibers, which comprises heating the optical fibers to melt the end faces of the optical fibers and connect them.