JPS6151287B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for connecting optical fibers used in optical communications.

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 using 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 from the temporary connection point 4 where the influence of the radiation mode can be ignored is connected to the receiving side optical fiber 5, and the output is measured using the power meter 3 at the connection point. Measure the emitted 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=-10logP ₃ P ₄ /P ₁ P ₂ (dB) ...(1) However, since the optical fibers 2 and 5 to be connected have a length of several hundred meters to several kilometers, 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 monitor 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), this method bends the light-receiving fiber 5 after the connection point 9 in order to simplify the connection work, and the optical power emitted from this bent portion 10 and measured by the optical power meter 3 is maximized. The connecting device 8 is adjusted so that the connection is made. 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.

The present invention aims to eliminate such drawbacks, shorten connection work time, simplify work and reduce costs, and provide an optical fiber connection method with low transmission loss. In this method, a light source is connected to a light source side optical fiber, and the output light power _P1 from the light source side optical fiber is measured at the connection point with the light receiving side optical fiber, and then the radiation mode generated at the connection point is measured. Temporarily connect the light receiving side optical fiber with the light source side optical fiber, the bending portion of which is set at a distance 2l, which is twice the distance l, where the power of the waveguide mode becomes negligible when the power propagates this distance. At the same time, the output light power P ₂ from the bent portion is measured, and the receiving side optical fiber is cut at a distance l from the temporary connection point, and the output light power at this cutting point is measured.
P ₃ is measured, and finally, the light-receiving optical fiber that is at a distance of l from the temporary connection point is removed, and the light-receiving optical fiber whose bent portion is now located at a distance of l from the cutting point is removed. The output light power P ₄ from the bent portion connected to the light source side optical fiber is measured, and the loss given by each output light power P ₁ to P ₄ obtained in each step is −10logP ₃ P ₄ /P ₁ P
₂ (dB) is as minimum as possible, the two optical fibers are aligned and connected.

Hereinafter, an optical fiber connecting method according to the present invention will be explained based on the embodiment shown in FIG.

First, the light source 1 is connected to the light source side optical fiber 1, and the output light power _P1 from the light source side optical fiber 2 is measured with an optical power meter 3 at the connection point with the light receiving side optical fiber 5 (FIG. 3a). In the connection method according to the present invention, in order to measure the output light power from the temporary connection to the actual connection at the connection point, the bent portion 10 of the light-receiving side optical fiber 5 is moved from the temporary connection point 4 to the point 2.
The key is to set the distance to l. Here, l is the distance at which the power of the radiation mode generated at the connection point becomes negligible compared to the power of the guided mode when propagated over this distance,
Generally, it will be in the range of 0.5m to 1.5m. Therefore, when making a temporary connection, the optical power meter 3 can be placed very close to the connection point, and when the optical fiber is aligned with the connection device 8, it is possible to do so while looking at the optical power meter 3. Become. After temporarily connecting both optical fibers 2 and 5 at the temporary connection point, the bent portion 1
The optical power P ₂ emitted from 0 is the optical power meter 3
(Figure 3b). Next, the receiving optical fiber 5 is cut at a distance l from the temporary connection point 4, and the output light power P3 at a distance l from the temporary connection point is measured by the optical power meter ₃ (FIG. 3d). When the output light power P ₃ at a distance of l from the temporary connection point is measured, the receiving side optical fiber 5 remaining temporarily connected to the light source side optical fiber 2 at a distance of l is removed;
Both optical fibers 2 and 5 are connected by a connection device 8 at a main connection point 10 . At this time, the bent portion 10 provided on the light-receiving side optical fiber 5 is located at a distance l from the main connection point 9. Therefore,
When the output power P ₄ from the bent part 10 is measured with the optical power meter 3, the loss α in the final connection is
can be determined using equation (2) (Fig. 3d).

α= _-10logP3P4 / _P1P2 ( _{dB )} ...(2) As explained above based on the embodiment shown in the drawings, according to the connection method according to the present invention, the connection loss In addition to being able to precisely measure the power at the connection point, it also allows the connection device to be operated while monitoring the transmitted optical power at the connection point, which is not only useful for submarine optical cables where it is not possible to monitor the optical power at the receiving end of the optical fiber. Unlike conventional methods, a special data transmission device is not required to monitor connection loss, making it possible to perform connections with extremely high workability and economic efficiency.

Finally, to explain the detection sensitivity of the output power at the bent portion 10, using a single mode optical fiber, which is said to be the most difficult to detect, as an example, the relative refractive index difference is 0.3%, the core diameter is 10 μm, and the normalized operating frequency is 2.4.If the bending radius is 2cm, the bending loss is
10 ^-4 dB/cm. If an optical power of -5 dBm can be input into the optical fiber, the output power at the bent portion 10 is -51 dBm. The detection sensitivity of the optical power meter is -70 dBm, which is a sufficient dynamic range. Furthermore, if the light from the light source is modulated intermittently at a constant frequency using a chopper or the like, and the power meter is also phase-locked to this frequency, the dynamic range can be further expanded.

In addition, the optical powers P ₁ to _{P 4} measured in Fig. 3 a to d
In order to obtain the connection loss using equation (2), it is necessary to keep the shape of the bent portion 10 constant in steps a to d. This can be easily achieved by using a jig that presses and fixes the optical fiber against the cylinder. Furthermore, in order for Equation (2) to represent the splice loss, the optical loss at the cutting length l must be zero. Generally the loss of optical fiber is 0.001d
B/m or less, and the optical loss at the cutting length l can be ignored. In addition, if it is not possible to have a large curvature at the bent portion 10 due to the reliability of the fiber,
By making the wavelength of the light source longer and reducing the normalized operating frequency, it is possible to increase the output power with a small curvature that does not affect reliability.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams of a conventional connection method in which connections are made while measuring loss at connection points, and Figure 3 is an explanatory diagram of a connection method in the present invention in which connections are made while measuring loss at connection points. It is. 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 main connection point, 10 is a light receiver This is the bent part of the side optical fiber.

Claims (1)

[Claims] 1. Connect a light source to a light source side optical fiber, determine the output light power P ₁ from the light source side optical fiber at the connection point with the light receiving side optical fiber, and then determine the output power P 1 of the light generated at the connection point. A distance 2 l that is twice the distance l at which the power of the radiation mode becomes negligible compared to the power of the guided mode when the power of the radiation mode propagates this distance.
The light-receiving side optical fiber, which has a bent portion set at , is temporarily connected to the light source-side optical fiber, the output light power P ₂ from the bent portion is measured, and the light-receiving side optical fiber is connected at a distance l from the temporary connection point. Cut the fiber and measure the output light power P ₃ at this cutting point.Finally, remove the light-receiving optical fiber at a distance l from the temporary connection point and insert the bent portion at a distance l from the cutting point. The optical fiber on the light receiving side, which has become curved, is connected to the optical fiber on the light source side, and the output light power from the bent portion is adjusted.
Measure P ₄ and obtain each output light power in each process.
Loss given by P ₁ to _{P 4} - 10log P ₃ P ₄ /P ₁ P ₂ (d
A method for connecting optical fibers, characterized in that the two optical fibers are aligned and connected so that B) is minimized as much as possible.