JPH0359403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for splicing single mode fibers while detecting cladding mode leakage light.

[Conventional technology] Single-mode fibers (hereinafter referred to as SM fibers) are attracting attention for their ability to transmit large amounts of information, but their core diameter is extremely small at 5 to 10 μm, and advanced technology is required for connection. has been done.

Examples of connection methods for SM fibers include optical power monitoring method and clad mode leakage light detection method. The former optical power monitoring method uses light (λ = 0.85 μm or
In this method, the optical waveguide mode (light propagating through the core) that enters the SM fiber (1.3 μm) and exits from the end of the other SM fiber is connected by aligning the axes to maximize the output. It is necessary to guide the output back to the connection point using a multimode fiber, which is not only extremely troublesome, but also economically disadvantageous in cases where the fiber length is 1 km or more.

Therefore, the other SM fiber was held between the roll (or guide) and the sensor in the middle of the other SM fiber (near the connection point) and bent with a gentle curvature, allowing the light that was propagating through the core from that part to be bent. An optical fiber connection method has been proposed in which the leaked light is measured by a sensor and the axis is aligned to maximize the output (Japanese Patent Application Laid-Open No. 154814-1989).
Publication No.). However, bending not only SM fibers but also optical fibers is not preferable in terms of mechanical strength, and there is a problem in that work efficiency becomes worse because the work of attaching and detaching the SM fibers between the roll and the sensor increases.

For this reason, the latter cladding mode leakage light detection method has recently begun to be adopted (Japanese Patent Application Laid-Open No.
59-187305). The principle difference between the cladding leakage light detection method and the optical power monitoring method is as follows.
While the optical power monitoring method connects the other SM fiber in a state where the light propagating through its core is at its maximum, the cladding leakage light detection method
The point is to connect the fiber in such a way that the light leaking from the fiber cladding to the outside is minimized.

FIG. 2 is an explanatory diagram showing the principle of the cladding mode leakage light detection method. 1 and 2 are SM fibers, and the outer periphery of the glass fiber consisting of cores 13 and 23 and claddings 14 and 24 is coated with primary coats 15 and 25 of silicone resin, buffer layers 16 and 26 of silicone resin, and nylon or Teflon or the like. A sheath consisting of jackets 17 and 27 is provided.

Light is input into the SM fiber 1 from a light source such as a semiconductor laser, and the light is emitted from the end face of the core 13, which is separated by a distance of gap G.
The light is radially incident on the end faces of the core 23 and cladding 24 of the SM fiber 2.

At this time, if the cores 13 and 23 are axially misaligned, the cladding mode leakage light 9 leaks out of the jacket 27 in accordance with the amount of axial misalignment, and the sensor 8 can detect the output. Note that since the SM fiber 1 and the SM fiber 2 are separated by the gap G, cladding mode leakage light can be detected as shown in FIG. 3 even when there is no axis misalignment. Therefore, as shown in FIG. 3, if the connection is made when the output of the cladding mode leakage light 9 is minimum,
There is no axis misalignment between the core 13 and the core 23.

[Problems to be Solved by the Invention] However, most of the light emitted from the core 13 propagates to a long distance while being confined within the core 23, cladding 24, and primary coat 25, so the output of the cladding mode leakage light 9 is The output becomes smaller as the connection point gets further away from the light source. That is, if the lower detection limit of the sensor 8 is a in FIG. 3, there is no problem in the curve A, but in the curve B, it becomes impossible to detect the cladding mode leakage light near the axis deviation O. Therefore, the distance between the conventional connection point and the light source is 20
Km is the limit, and in order to lower the detection limit a, a sensitive and expensive sensor is required.

Further, due to variations in the materials of the primary coat and jacket, as well as variations in manufacturing conditions, the amount of leaked light for each fiber varies significantly, resulting in problems such as requiring a long time for connection work.

Note that if the optical fiber is bent as in the optical power monitoring method described above, the light propagating through the core will leak, making it impossible to detect only the cladding mode leakage light, so there is no way to bend the optical fiber. , cannot be adopted.

[Object of the Invention] In view of the above-mentioned problems of the prior art, an object of the present invention is to improve the detection sensitivity of cladding mode leakage light so that the connection work of single mode fibers can be easily and quickly performed. The object of the present invention is to provide a method for connecting single-mode fibers that can significantly increase the possible distance.

[Summary of the Invention] The gist of the present invention is to make the end faces of two single mode fibers face each other so that light is incident on one single mode fiber and propagated to the other single mode fiber. In a method of connecting a mode fiber while detecting clad mode leakage light leaking out of the sheath of the mode fiber with a sensor, the other single mode fiber, which is closer to the connection part than the sensor, is held by a compression jig without bending, and the sheath is The objective is to increase the cladding mode leakage light output by scattering the light propagating inside the fiber layer or primary coat to the outside of the jacket through compressive deformation.

[Example] Hereinafter, an example of the present invention will be described based on FIG. 1.

The arrangement of the SM fibers 1 and 2 is similar to that shown in FIG. 2, and their core end faces are separated by a gap G. A compression jig 30 is installed between the end face of the SM fiber 2 and the sensor 8, and when pressure is applied to an extent that does not break the fiber, only the sheath is deformed, and the light 10 that was propagating inside the primary coat 25 is removed from the jacket. The light leaks out of the cladding mode 27 and is detected by the sensor 8 together with the cladding mode leakage light 9 before being compressed and deformed.

Therefore, the output of the cladding mode leakage light is significantly increased compared to the conventional method, and it becomes possible to perform long-distance connections that were not possible in the conventional method.

Example 1 A compression jig was grounded at a position approximately 100 mm from the core end face of the SM fiber 2, and a sensor was installed at a position approximately 3 mm behind it.

The SM fiber has a buffer layer diameter of 0.5 mm and a Teflon jacket diameter of 0.8 mm, and when the SM fiber was deformed by 50% using a compression jig, cladding mode leakage light was obtained that was approximately 35 dB lower than the transmitted power.

Since the light source output is -12 dbm and the minimum detection sensitivity of the sensor is -65 db, it was confirmed that connections with a connection interval of 30 km are possible if the fiber loss is 0.6 db/Km.

In addition, conventional methods that do not deform the fiber can only obtain cladding mode leakage light that is approximately 50 dB lower than the transmitted power, and the possible connection length is greatly limited.

In addition, in Example 1, there is only one compression deformation part, but by providing another compression jig at a position approximately 10 mm closer to the connection part, the scattering of the cladding mode is further promoted, and the leakage light output is reduced. was confirmed to be significantly improved.

As described above, as a result of conducting experiments on connecting SM fibers using the method of the present invention, the number of connection points was 100,
The average connection loss was 0.07db, and the connection was equivalent to the optical power monitor method currently in use.
Further, since the amount of axis deviation can be detected near the connection part, the work is easy and connection can be made in a short time.

Note that the shape of the compression jig 30 is preferably such that it does not damage the fiber, and one side may be used as a fixed plate and compression may be performed from the other side.

In this case, since the compression jig itself serves as a means for fixing the fiber, the attachment and detachment of the fiber is no different from the conventional method, and is extremely easy to operate.

[Effects of the Invention] As explained in detail above, the present invention provides the following remarkable effects.

(1) Since the amount of axis misalignment can be detected near the connection part, it is economical as it does not require a feedback circuit like the optical power monitor method. (2) It is easy to work and can be connected in a short time. It is.

(3) By clamping the SM fiber with a compression jig and compressing and deforming only the sheath without bending the vicinity of the connection, it is possible to significantly increase the cladding mode leakage light output without adversely affecting the glass fiber. Yes, relay section 30km
The above connections are fully possible.

(4) Since the sensor and compression jig are small and can be integrated, they can be easily attached to a conventional fusion splicer.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a conventional example, and FIG. 3 is an explanatory diagram showing the relationship between the amount of axis deviation and cladding mode leakage light. 1, 2: SM fiber, 8: sensor, 9: cladding mode leakage light, 10: light, 13, 23: core, 14, 24: cladding, 15, 25: primary coat, 16, 26: buffer layer, 17,
27: Jacket, 30: Compression jig.

Claims (1)

[Claims] 1. Two single mode fibers each having a sheath on the outer periphery of a glass fiber consisting of a core and a cladding are made to face each other so that light is incident on one single mode fiber and propagated to the other single mode fiber. , the cladding mode leakage light leaking out of the sheath of the other single mode fiber is detected by a sensor provided on the outside of the other single mode fiber, and when the cladding mode leakage light is minimized, the two A method for connecting single mode fibers, characterized in that the other single mode fiber closer to the connection part than the sensor is held by a compression jig without bending, and the sheath is compressively deformed. Method.