JPS6218882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber splicing method capable of detecting splice loss at a spliced portion.

Generally, an optical communication line is constructed by connecting a plurality of short cables, but in order to construct a highly reliable and high quality line, it is necessary to reduce the connection loss between the cables as much as possible. Therefore, conventionally, connections have been made while strictly measuring the loss at the connection point in a four-step procedure as shown in FIG. That is, first, the light source 1 is connected to the light source side optical fiber 2, and at the connection point, the output light power _P1 from the light source side optical fiber 2 is measured with the optical power meter 3 (FIG. 1a). Next, the receiving side optical fiber 5 and the light source side optical fiber 2 to be connected are fixed to the connecting device 8 and connected at the temporary connection point 4, and the output light power of the receiving side optical fiber 5 at this time is
P ₂ is measured with an optical power meter 6 on the receiving side. In addition,
7 is a monitor device for reading the indicated value of the power meter 6 at the connection point 4, and is used especially when the connection device 8 has a function of aligning the axes of the optical fibers 2 and 5 to be connected. Figure 1 b). When the temporary connection is completed, in order to measure the splice loss at the temporary connection point 4, a fiber length that allows the influence of the radiation mode from the temporary connection point 4 to be ignored is set on the receiving side optical fiber 5, and the power meter 3 at the connection point is used to measure the connection loss. Measure the output light power _P3 (Fig. 1c). Finally, connect the optical fibers 2 and 5 again at the main connection point 9, measure the output light power P ₄ from the receiving side optical fiber 5 with the optical power meter 6, and use the following equation (1) to connect the main connection point 9. The loss α at is calculated (Fig. 1d).

α= _-10logP3P4 / _P1P2 ( _dB )...(1) However, since the optical fibers 2 and 5 to be connected are several hundred meters to several kilometers long, the connection points 4 _and 9
It is necessary to perform the work in separate manholes for the light receiving point and the light receiving point, and as shown in Figure 1, in addition to two optical power meters 3 and 6 and a special monitoring device 7, an extra worker is required on the light receiving side. There were problems in terms of work time and costs.

Furthermore, Fig. 2 shows another conventional method of connecting optical fibers (Patent Application No. 1983).
-48463 (Japanese Unexamined Patent Publication No. 57-164706)), this method bends the light-receiving fiber 5 after the connection point 9 in order to simplify the connection work, and this bent portion 1
The connection device 8 is adjusted and connected so that the optical power emitted from the optical power meter 3 becomes maximum. Therefore, while there is an advantage in that the work only needs to be done at the connection point and only one power meter is required, there is a major disadvantage in that the loss at the connection point 9 cannot be determined.

In order to overcome these drawbacks of the method shown in Fig. 2, there is a method that combines the method shown in Fig. 2 and the method shown in Fig. 1 to measure splice loss (Japanese Patent Application No. 57-44702). In either case, it is necessary to perform the connection twice in order to measure the connection loss, which poses a major problem in terms of working time. In addition, in order to shorten the work time, there is a method of estimating the splice loss from the change in monitor power before and after fusion in one heat fusion, but the loss after splicing can only be estimated statistically, and there is a limit. be. For example, all connection losses are 0.05dB
The following is almost impossible with conventional methods.

The present invention attaches a liquid that burns or evaporates during thermal fusion between the end faces of fibers to be connected, and highly accurately estimates the loss after splicing only from changes in optical power monitor values before and after thermal fusion. The present invention provides a method for quickly performing connection work with low loss, thereby making it possible to realize a high-quality optical line, shorten connection work time, and reduce connection work costs.

Below, the connection method of the present invention will be explained in detail based on the drawings.

FIG. 3 shows an outline of the connection method of the present invention. In the figure, a connection point 9 where optical fibers 2 and 5 are connected
A pair of electrodes 11 are arranged with the electrodes 11 in between. The electrode 11 is an electrode that heat-seals the end faces of the optical fibers 2 and 5 by arc discharge, and 13 is the discharge arc. In the conventional connection, as shown in a, the fibers 2 and 5 to be connected are abutted at a preheating interval, the axis of the core is aligned, and then heat fusion is performed. However, in the method of passing light through a fiber and monitoring it in order to align the axis, if a semiconductor laser or the like is used as the light source, the light that is multiplely reflected between the fiber end faces feeds back to the light source, resulting in an increase in the output of the light source. This causes power fluctuations and, together with interference effects, causes large fluctuations in the optical power monitor value. It has been experimentally confirmed that this fluctuation range extends to more than ±dB. The advantage of using a semiconductor laser as a light source is that it is possible to bend the fiber just after the connection point and monitor the optical power radiated from it, and the monitor for axis alignment is provided only at the connection point. That's enough. Therefore, in the present invention, a matching liquid 12 is applied between the fiber end faces in order to eliminate the multiple reflection effect that occurs between the fiber end faces.
Attach. The matching liquid 12 is a mixture of glycerin and ethyl alcohol, and is almost completely burned by the heat of the arc discharge. Furthermore, by appropriately changing the content of ethyl alcohol, the refractive index can be made to match the group refractive index of the optical fiber.

The procedure of the present invention is to first match a pair of optical fibers 2 and 5 to be connected at a preheating interval (FIG. 3a). Next, the matching liquid 12 is applied and interposed between the end faces of the optical fibers 2 and 5, and the optical fibers 2 and 5 are aligned so that their axes are aligned (FIG. 3b). Subsequently, light is passed through the optical fibers 2 and 5 with the matching liquid 12 interposed, and a monitored value _P1 of the optical power passing through the abutted portion of both end faces is measured (FIG. 3c). Next, with the matching liquid 12 interposed, the distance between the optical fiber end faces is adjusted to the preheating interval, and the end faces of the optical fibers are melted and fused together by the discharge arc 13 of the electrode 11 (FIG. 3d). After fusion splicing, light is passed through the optical fibers 2 and 5, and a monitored value _P2 of the optical power passing through the connection point 9 is measured (Fig. 3e).

Above in Fig. 3, change ΔP in optical power monitor value before and after fusion splicing by fusion splicing having processes a to e.
= 10log(P ₁ /P ₂ ), the loss α _s after fusion splicing can be estimated with high accuracy. FIG. 4 shows the relationship between ΔP and actual splice loss α _s . As is clear from the figure, the relationship between ΔP and α _s is α _s = (ΔP +
0.02) ±0.01 (dB). The reason why the loss after fusion splicing can be estimated with an accuracy of ±0.01 dB is that the splice loss before fusion splicing in Figure 3c is 0.02 ±
This is because it becomes 0.01 dB. This is because in the conventional connection method that does not use a matching liquid, if the end surface of the optical fiber 2 to be connected is formed at an inclined angle as shown in FIG. When it exits into the air, it is refracted, propagates toward the other optical fiber 5, and enters the other optical fiber. At this time, as can be seen from FIG. 5a, the positions of the optical fibers that pass through the connection point and reach the maximum optical power entering the optical fiber 5 do not necessarily match and shift due to the refraction of the monitor light. . If the optical fibers are fused in this state, the cores of the optical fibers will be misaligned with each other.

Furthermore, if there is any irregularity in the end face of the optical fiber, the monitor light will be scattered there, resulting in large variations in the butt loss after core alignment.

However, if a liquid having a refractive index equal to the refractive index of the optical fiber, that is, a matching liquid 12, is attached between the end faces of the optical fiber as in the present invention, even if the end face is inclined, as shown in FIG. Since there is no refractive index difference between the fiber and the matching liquid 12, the monitor light is not refracted at the end face.

Therefore, the monitor light travels straight through the connection interface of the optical fibers, and the core axes of the optical fibers coincide regardless of the irregularity of the end surfaces. The variation in connection loss before welding with matching liquid applied is ±
This is why it is as small as 0.1 dB. The reason why the average loss is 0.02 dB is because we use a matching liquid that completely burns or evaporates when heated, so no residue remains and the attached connection part is a normal optical fiber waveguide. structure (structure consisting of core and cladding),
This is because loss occurs due to structural imperfections due to the lack of core-clad refractive index.
0.02dB means its average loss.

As explained above, according to the present invention, the splicing loss after fusion splicing can be estimated with extremely high accuracy by applying a matching liquid between the end faces of the fibers to be spliced, and from the change in the optical power monitor value before and after fusion splicing. It becomes possible to configure a high-quality optical path. Also,
Since the splice loss can be estimated with high precision only from the change in the optical power monitor value that has passed through the splice point, it is also useful for splicing methods such as bending the fiber immediately after the splice point and monitoring the radiated power. The invention is applicable and enables economical connection work with low connection loss and short working time compared to conventional connection methods.

[Brief explanation of the drawing]

Fig. 1 a, b, c, d and Fig. 2 are explanatory diagrams showing the conventional connection method, Fig. 3 a, b, c, d, e
is an explanatory diagram showing the splicing method of the present invention, FIG. 4 is a graph showing the relationship between the estimated splice loss and the actual measured splice loss according to the present invention, and FIGS. FIG. 3 is a cross-sectional explanatory diagram of a main part for explaining light emission and incidence conditions at the end face of a dual-optical fiber in the conventional connection method and the connection method of the present invention. In the drawing, 1 is a light source, 2 is an optical fiber on the light source side, 3
is an optical power meter for connection point measurement, 4 is a temporary connection point, 5 is an optical fiber on the light receiving side, 6 is an optical power meter on the light receiving side, 7 is a monitor device, 8 is a connection device, 9 is a connection point, 10 is on the light receiving side Bending part of optical fiber, 11
is the discharge electrode, 12 is the matching liquid, 13 is the discharge arc, α _s is the connection loss after fusion, and ΔP is the change value of the optical power monitor before and after fusion.

Claims (1)

[Claims] 1. In connecting optical fibers, the end faces of the optical fibers are placed opposite each other, and a matching liquid that burns or evaporates by heating is interposed between these end faces, and then light is propagated through the optical fiber and the light that passes through both end faces is interposed between these end faces. After measuring the power monitor value P ₁ and then connecting the end faces of the optical fibers by heat-sealing, the light is further propagated and the monitor value P ₂ of the optical power that has passed through the connection portion is _measured . , P ₂ , and detecting the splice loss based on the amount of change ΔP based on P 2 .