JPS617436A - Method for measuring connection loss of optical fiber - Google Patents

Abstract

PURPOSE:To measure the connection loss of optical fibers only at the connecting point, by providing bending parts at two places in one optical fiber to be connected, arranging a light receiving device at the far bending part, and comparing the amounts of received light beam from the connecting points before and after the connection. CONSTITUTION:Optical fibers 4-1 and 4-2 are connected at a connecting point 4-3. Bending parts are provided at two places in one optical fiber 4-2. A light receiving device 4-4 is arranged at the part 4-6 far from the connecting point. A lighting device 4-9 is arranged at the connecting point 4-3. Light is projected under the state the end surfaces of the optical fibers 4-1 and 4-2 are sufficiently separated before the connection. The light is also projected after the connection. The amounts of the light beams 4-8, which are inputted to the light receiving device 4-4, are compared. Owing to the presence of the first bending part 4-5, the light in a clad mode is removed, and only the light in a propagating mode is measured by the light receiving device 4-4. Thus the connection loss of the optical fibers can be accurately measured. The connection loss can be measured only in the vicinity of the connecting point.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for measuring splice loss during an optical fiber splicing process only at splicing points.

(Prior art) Conventionally, as shown in Fig. 1, a light source 1-3 emits light from the end of one of the two optical fibers 1-1, 1-2 connected together, which is remote from the connection point of one 1-1. The light enters the receiver 1- at the connection point.
After measuring the received light level by step 4 [Fig. 1(a)], temporarily connect optical fibers 1-1 and 1-2 at temporary connection point 1-5, and connect the other optical fiber 1-2 to the connection point. The received light level is measured by the light receiver 1-4 at the end far from the first
(b)], by cutting at a position approximately 1 m away from the connection point 1-5 in the direction of light propagation, and measuring the received light level with the light receiver 1-4 at that position [Fig. 1 (c)]. After measuring the transmission loss of the rear optical fiber, connect optical fiber 1 again.
-1.1-2, and measure the light reception level at the end of the rear optical fiber 1-2 with the receiver 1-4 [Fig. 1(d)] to measure the splice loss. Ta. For this reason, a light source and a receiver are required at both ends of the optical fiber to be connected in addition to the connection point, and during field work, workers are dispersed to these three far apart locations, resulting in poor work efficiency and poor communication between each other. It was a complicated process, requiring measurements to be taken while taking measurements. Furthermore, since the work place is divided into three locations, there is a drawback that many workers and measuring instruments are required, which increases the cost. Furthermore, since light sources are usually fixed at locations such as telephone offices, when connecting multiple optical fibers in series, they must be connected in order from the light source, which greatly reduces work efficiency. There was a downside to it being bad.

(Objective of the Invention) In order to solve these drawbacks, the present invention irradiates the connection point with light, injects the light into the optical fiber, and bends and radiates the light that has propagated through the optical fiber near the connection point. An object of the present invention is to provide an optical fiber splice loss measuring method that can easily and highly accurately measure splice loss only at splicing points by receiving the light.

(Principle of the Invention) The present invention will be described in detail below.8 The basic principle of the present invention is to utilize the scattering of light caused by the structural deformation of the optical fiber at the optical fiber connection point. FIG. 2 is an enlarged conceptual cross-sectional view of the connecting portion of the optical fiber 2-1. When an axis shift or deformation of the core 2-2 occurs at the connection point 2-5, the light 2-3 propagating through the core 2-2 is scattered at the connection point 2-5, and a part of it becomes the leakage light 2.
-4 leaks out of the core 2-2. This leaked light 2-
4 is the connection loss at this connection point 2-5. Obviously, a part of this leaked light 2-4 leaks out from the cladding part of the optical fiber 2-1, and therefore, at a connection point having a loss, a part of the propagating light 2-3 is transferred to compensate for the loss. Optical fiber 2-
It can be observed outside of 2. The present invention is based on the reverse process of this phenomenon.

FIG. 3 is a conceptual diagram showing a state in which the connecting portion 2-5 of the optical fiber 2-2 is irradiated with light from the surroundings. When the light 3-4 is irradiated from the outside of the optical core fiber 3-1 to the connection point 3-5 having a loss, the propagating light 3-3 inside the core 3-2 just leaks to the outside of the optical fiber 3-1. Following the reverse process,
A part of the irradiated light 3-4 from the outside is transmitted through the core as propagated light 3-3. The intensity of this propagating light 3-3 is
If the intensity of the irradiated light 3-4 from the outside is constant, the value corresponds to the connection loss, and the higher the loss, the stronger it is, and the lower the loss, the weaker. In this way, the propagating light 3-3 having an optical intensity corresponding to the connection loss can be generated at the connection point 3-5, and the intensity of this propagating light 3-3 can be changed to a light source near the connection part 3-5. By measuring without destroying the fiber, splice loss can be measured only at the splice location. The propagation light intensity is measured by bending the optical fibers 2-1 and 3-1 and receiving the light emitted from the bent portion to the outside of the optical fiber.

(Structure and operation of the invention) Next, the measurement method will be described.

FIG. 4 is a conceptual diagram for explaining the measurement method of the present invention, 4-1 and 4-2 are optical fibers, 4-3 is a connection point,
4-4 is the light receiver, 4-5 is the first bending part, 4-6 is the second bending part, 4-7 is the light emitted at the first bending part, and 4-8 is the light emitted at the second bending part. 4-9 represents the illuminator, and 4-10 represents the light irradiated to the connection point.

To determine the splice loss θ1j, first heat the end faces of the optical fibers 4-1 and 4-2 sufficiently before connecting the illuminator 4-1.
9 irradiates the end portions of the optical fibers 4-1 and 4-2 with light, and the light 4-8 emitted from the second bending portion 4-6 is transmitted to the receiver 4.
Receives light at -4. The sufficiently heated state means that in the second track when the optical fibers are connected, the light reception value at section 4-6 is the fifth.
As shown in the figure, this refers to a state in which the end face spacing is set to be approximately constant. In the example shown in Figure 5, the end face spacing is 0.5w.
This is an area greater than or equal to ux. The light reception value in this state is used as the reference value of the measurement system.

Next, after the connection, the illuminator 4-9 is used again to connect the connection part 4-
3 is irradiated with light, and the light is received by the second bent portion 4-6. At this time, it is necessary to measure under the same conditions as when measuring the reference value, and the first bent part 4-5 and the second bent part 4-6 are kept fixed during the measurement, and the illuminator 4-9. Receiver 4-4
Also keep it fixed. According to the above-described principle, when light is irradiated onto the connection portion 4-3, light 4-10 corresponding to the connection loss is incident into the core of the optical fiber 4-1.4-2. However, in addition to the propagation mode light necessary for measurement, cladding mode light is also generated within the optical fiber 4-1.4-2.
It propagates within 2 for tens of meters to several meters. No, connection point 4
Even if the intensity of the light propagating within the optical fibers 4-1 and 4-2 is measured near the optical fibers 4-3 and 4-2, it is not possible to accurately measure the splice loss. Remove this cladding mode.

In order to measure only the light in the propagation mode corresponding to the connection loss, the -th bending section 4-5 is prepared.

FIG. 6 shows the optical fiber 4-5 at the bending portion 4-5.
2 shows the measured values of the bending diameter of No. 2, the transmittance of the propagation mode light, and the transmittance of the cladding mode light generated in the optical fiber by the illuminator 4-9 (here, a xenon discharge tube is used). The optical fiber 4-2 is bent once into a semicircular shape. As you can see from this diagram, the diameter of the song is 5
When M, the transmittance of cladding mode light is 1/14 of that of propagation mode light. Although the propagation mode light intensity is also reduced to about 1/3, the cladding mode light is reduced to about 1/40 and can be almost completely eliminated.

In this way, after the cladding mode is removed at the first bending section 4-5, propagation mode light is emitted by bending radiation at the second bending section 4-6. This light is received by the light receiver 4-4.

As described above, the reference value is determined before connection using the same measurement system, and the light reception value corresponding to the connection loss is determined again after connection. After this connection, normalize the measured value with the reference value.
Okay, first bending part 4-5. One-on-one with loss, unaffected by the state of the second bending part 4-6, the arrangement of the illuminator 4-9 and receiver 4-4, and the color and structure of the optical fiber coating. You can get the corresponding value. Find the relationship between this normalized value and the connection loss in advance, and
It is possible to determine the connection loss based on that relationship.

Figure 7 shows an example of measurement. The normalized value obtained using this method is shown for the connection loss obtained by measurement using the conventional power monitoring method. A xenon discharge tube is used as the illuminator 4-9, and a photoamplifier tube is used as the receiver 4-4. The second track is the result of measuring the diameters in 5 order for both sections 4-6. As can be seen from this figure, a high loss measurement accuracy of about ±0.05 dB can be obtained for a low loss connection of 0.5 dB or less.

In the above example, only an example in which a xenon discharge tube is used as the illuminator 4-9 has been described, but a strobe light emitting bulb or a pulse laser used for photography etc. can also be used. It is possible to use an APD in addition to a photoamplifier tube for the light receiver 4-4. In the above example, the third bending portion 4-5.
Although only an example in which the bending diameter of the second bending portion 4-6 is set to 5N has been described, there is a concern that mechanical damage to the optical fiber due to bending may occur.

To avoid this, the bending diameter may be increased and bends may be provided at several locations. It is clear that by doing this, it is possible to eliminate the cladding mode as described above and bend the propagation mode to emit radiation without damaging the optical fiber.

(Effects of the Invention) As explained above, the present invention irradiates the connection point with light, prepares two bent portions near the connection point, and
This method removes unnecessary light for measurement at the bending part, emits light corresponding to the loss at the second bending part, and receives that light, so it is possible to measure connection loss with high accuracy and high speed only in the vicinity of the connection point. There are benefits that can be measured.

In addition, there is no need for temporary connections, and there is no need for a worker's measuring device or the like at a location other than the connection point, so the cost required for measurement can be significantly reduced. Furthermore, this method has the advantage that it is extremely easy to integrate the loss measuring device and the optical fiber connecting device.

[Brief explanation of drawings]

Fig. 1 is a layout diagram for explaining the conventional splice loss measurement method, Fig. 2 is a schematic vertical cross-sectional view showing the state in which propagating light leaks from the optical fiber connection, and Fig. 3 is a diagram illustrating the basic principle of the present invention. 4 is a layout diagram showing an embodiment of the present invention, FIG. 5 is a characteristic diagram showing the relationship between the end face spacing and the amount of light received during measurement before connection, and FIG. A characteristic diagram showing the measurement results of the relationship between the diameter and the transmittance of steady mode light and the transmittance of cladding mode light. Figure 7 shows the measured values (standard values) according to the present invention and those measured by the conventional transmitted light monitoring method. FIG. 3 is a characteristic diagram showing correspondence with connection loss values. 1-1...Optical fiber in front of the connection point, 1-2...After the connection point "0 light 7"6p."-3°゛°light."-"
°°Reception (.) Optical device, 1-5...Temporary connection point, 1-6
...Connection point, 2-1...Hikari 7 eyeball, 2-2...
Core, 2-3... Propagation 2-5... Connection point,
゛3-1...Optical fiber, 3-2...Core, 3-3
... Propagation 4-3... Connection point, 4-4... Light receiver,
4-5...First bending part, 4-6...Second bending part,
4-7...Light emitted at the -th bend (d) part, 4
-8...Light emitted at the second bending part, 4-9...Illuminator, 4-10...Light irradiated to the connection part.

Claims (1)

[Claims] One of the pair of optical fibers to be connected is provided with two bent portions, a light receiver is placed at the bent portion farther from the connection point, and an illuminator is fixedly placed at the connection work point, The illuminator irradiates the end of the optical fiber before connection with light, and after the amount of light received by the light receiver and the pair of optical fibers are interconnected, the illuminator irradiates the connection part of the interconnection with light again. An optical fiber splice loss measuring method for measuring splice loss of the pair of optical fibers by comparing the amount of light received by the light receiver.