JPS63264718A - Method for switching and connecting optical fiber - Google Patents

Abstract

PURPOSE:To safely and surely switch and connect optical fibers to each other at a high speed with a simple constitution, by practically using a light guiding sleeve, to which an optical fiber reinforcing function and leaking light condensing function are additionally added, to optical fibers in advance. CONSTITUTION:Light guiding sleeves 3a-3c having a refractive index which is equivalent to or higher than that of the clad sections of optical fibers and a function which highly efficiently guides leaking light in optical fibers 10a-10c are previously put on both sides 10a and 10b of the point of the exposed part of the optical fibers, at which they are cut off, and on the end 10c of the optical fiber 10c which is another switching destination, and alignment when the current fibers 1a-1c are cut off and reconnected is carried out while the leaking light in the optical fibers 10a-10c is monitored through the sleeves 3a-3c. Since the light guiding members cover the optical fibers in almost cylindrical states and have guidewave structures made principally of a low-loss glass material having an appropriate refractive index, most of the leaking light produced at the connecting point can be caught and efficiently guided to photoreceptor elements 7a-7c. At the same time, the stress cutting, movement, and alignment of the optical fibers can be controlled accurately by grasping the light guiding sleeves 3a-3c.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is capable of directly mechanically switching an existing fiber line in service to a broken fiber line in a short time when relocating a section of an optical fiber communication line. Regarding how to connect.

(Conventional technology) Optical fiber communication lines transmit an order of magnitude more information than conventional metal communication lines, so it is important to have a technology that can quickly switch to the new line in the event of a problem with the service line. .

However, since an optical fiber is a waveguide transmission line made of a glass material, switching using a simple branching and connecting method as in the case of a metal core wire is impossible. The most effective switching method is to disconnect the current core line (currently in communication) and then quickly connect to the new core line. In this case, the time during which communication is interrupted due to switching must naturally be short, and
It is desirable to keep it below Qms.

The switching connection procedure according to the prior art will be explained using FIG. 2. As shown in FIG. 2(A), the covering of a part of the optical fiber core 1 is removed in advance to expose the optical fiber 10, and the optical fiber 10 is set in the core wire holders 5a/ and 5b/. At the same time, the ends of separate optical fiber cores 1c are also juxtaposed at 6b'. Next, the scratching blade 9 is pressed against the part of the optical fiber 10 to be cut to scratch the surface of the optical fiber. After that, pull the fiber holder 6a' to the left in the figure and insert the optical fiber 10.
5a as shown in FIG. 2(B).
/ to the bottom of the diagram at high speed and connect the optical fibers lOa and tOC.
Connect oppositely.

Alignment between optical fibers 10a and 100 is the most difficult technique. In particular, in the case of a single mode optical fiber, it is necessary to align the center of the core rather than the outer periphery of the optical fiber cladding, so a method is used to align the axis by monitoring changes in light propagating through the core.

A typical conventional monitoring method, as shown in FIG. 3, is a method of detecting leakage light components (Tararad mode, etc.) caused by imperfections such as axis misalignment and gaps between cores at connection points. The guided mode of the optical fiber 10a undergoes mode conversion at the connection point and excites a leakage light component in IOc.

The leaked light component is captured by the coating 11c having a refractive index higher than the refractive index of the cladding portion, and is detected by the light receiving element 7c/ through the matching oil 30. When the output of the light receiving element is minimum, the core axes between the optical fiber 10a and the IOC match.

The conventional methods outlined above have the following problems. 1st
In addition, the coating 11 of the optical fiber is a soft resin that requires a buffering effect, so if the coating of the core wire is fixed to the holder and the optical fiber is stress-cut as shown in Fig. 2, the coating may shift. It is not possible to control the correspondence between the amount of movement of the core fiber holder 6a/ and the distance between the optical fiber end faces at the cutting point. Therefore, the optical fiber 10a after cutting.

Advanced operations such as controlling the propagation loss between 10b and 10b are impossible, and even when moving to the opposing arrangement of 10a and IOC, a large deviation occurs in the amount of monitored light. Furthermore, during stress cutting, there is a large deviation in the time required for the fiber to break, so it is difficult to adapt the method to the case where the fiber is switched to the new fiber side at the same time at two distant locations. To avoid this problem, optical fiber 10. Core wire holders 6a', 6b' up to the ioc part
A method of fixing it is being considered. However, when a bare fiber is mechanically gripped, minute scratches occur on the fiber surface.

The strength of the portion 10c is significantly reduced, and even when cutting, there are cases where the material breaks at an unspecified location other than the location where it should be cut.

The second issue concerns monitor efficiency. In the case of the configuration shown in Figure 3, the collection efficiency of the leaked light component is extremely low, so a cooled PD (photodiode) with a large light receiving area and low noise is used, and a low-noise preamplifier is used. It is finally detectable. For this reason, when the light receiving element is attached to a holder or the like, it is difficult to achieve the target switching time because it is not possible to downsize or use high-speed signals.

(Problems to be Solved by the Invention) The present invention enables fine control of the distance between the optical fiber end faces at the cutting point, reinforces the exposed portion of the optical fiber, and significantly improves the efficiency of the leakage light monitor. Our goal is to provide new means to make this possible.

(Means for Solving the Problems) The method of the present invention provides a method in which a refractive index equal to that of the optical fiber cladding is applied to both sides of the exposed portion of the optical fiber to be cut and to the end of the optical fiber to be switched to another destination. A light guide member having a large refractive index and a function of efficiently guiding leakage light in the optical fiber is installed, and while monitoring the leakage light in the optical fiber through the light guide member, Perform axis alignment when disconnecting and changing connections.

The above-mentioned conventional technology enables fine control of the distance between the optical fiber end faces at the cutting point by attaching a light guiding member to the exposed portion of the optical fiber in advance, reinforces the exposed portion of the optical fiber, and monitors leakage light. The difference is that the efficiency has been significantly improved. In the method of the present invention, the light guide member covers the optical fiber in a substantially cylindrical shape and has a waveguide structure mainly made of a low-loss glass material with an appropriate refractive index, so that the leakage light generated at the connection point is large. The part can be captured and efficiently guided to the light receiving element. At the same time, stress cutting, movement, and alignment can be accurately controlled by gripping the light guide member.

The relationship between the distance between the optical fiber end faces at the cutting point and the splice loss is shown in FIG. Optical fiber is single-wire for wavelength 1゜3μm.
It is a single optical fiber, the parameter n9 is the refractive index of the medium between the end faces, and no is the refractive index of the optical fiber core.

For the purpose of the present invention, it is desirable to maintain the line without deteriorating the transmission quality in the process of cutting the existing core line. By limiting the line disconnection time during switching to only the travel time for connection switching, the above goal can be easily achieved. To achieve this, it is necessary to suppress the splice loss immediately after cutting to about 0.5 CIB or less, and as shown in Figure 4, the distance between the optical fiber end faces should be about 60 μm or less (when nqζ00) or about 20 μm or less (when n, = 1). need to be controlled. This control is extremely difficult with the conventional method as shown in FIG. Since in the present invention the light guiding member acts as an effective reinforcing member: control of said spacing is easy.

The improvement of the leakage light collection efficiency by the method of the present invention is as follows. The incident optical power to the optical fiber connection point is P. , the propagating light component after passing through the connection point is Pl, the leakage light component is P2, the received power of the leakage light component is P3, the power transfer coefficient at the connection point is α(α”p+/po), and the collection of leakage light components is If the optical efficiency is k (k=P3/P2), the received light power is P3
=P, (1-α)k. 101o101o (d
B) as a parameter, the connection loss knee between optical fibers is
0101o (dB) and received light power/incident light power: 1
The relationship with 01101o/Pa (dB) is shown in FIG.

The conventional configuration shown in Figure 3 has low light collection efficiency.
K-20 to -30 dB. Note that the main type of optical fiber is single mode optical fiber. In a normal optical fiber line, Po is at most -30
dBm, and the sensitivity of the light-receiving element is limited to about -70 dBm. Therefore, in the case of a connection loss of 0.5 dB or less, it is difficult to receive light with a stable S/N ratio using the conventional method. As will be described later, for the purpose of the present invention, it is necessary to suppress the connection loss to about 0.5 dB or less in order to prevent transmission quality from deteriorating when the current core wire is cut. In contrast, in the configuration of the present invention, the leaked light component can be efficiently guided to the light receiving element by the light guiding sleeve.
It is possible to increase the light collection efficiency K to about -5 dB.

That is, K is improved by about 20 dB compared to the conventional method.

(Embodiment) FIGS. 1(A) to 1(F) are diagrams showing the procedure of an embodiment of the present invention. la, lb, lc are optical fiber cores, 2a, 2b are coating removal blades, 3a, 3b, 3
c is a light guide sleeve, 4a, 4b, 4c is a transparent adhesive (cured state), 5a, 5b, 5c is a transparent adhesive (uncured), 6a, 6b, 6a', 6b' is a core wire holder, 7a, 7b and 7c are light receiving elements, 8 is an alignment controller,
10, 10a, 10b, 10c are optical 7 fibers, 11
is a covering.

FIG. 1(A) shows a method of exposing the optical fiber by removing the coating from a part of the existing core wire prior to the process of the present invention. First, a cut is made in the coating in the axial direction (not shown), and then a cut is made in the circumferential direction by the coating removal blades 2a and 2b, and then the coatings 2a and 2b are moved in the direction of the arrow in the figure.

The coating 11 is made of ultraviolet (tlV) curable resin and has a two-layer structure of a soft inner layer and a hard outer layer, so that it can be removed by cutting the outer layer.

In FIG. 1(B), light guide sleeves 3a, 3b', 3c are provided at the exposed portion of the current fiber 1 and the optical fiber end of the switched fiber 1c.
Shown with the . FIG. 1(C) is a side view in two directions, taking the core wire la side as an example (the holder portion is excluded). The light guiding sleeve is a sleeve made of a low-loss glass material mainly made of synthetic quartz, similar to optical fibers. As is clear from the figure, the structure has a U-shaped groove along the axis, allowing the optical fiber to be accommodated loosely. After the optical fiber is set in the U-shaped groove, the gap is filled with a transparent UV curing adhesive, the adhesive is cured by irradiation with t+V light, and the optical fiber is fixed to the light guide sleeve. The refractive index n2 of the light guide sleeve 3 is set to be slightly (about 2%) higher than the refractive index n of the optical fiber cladding part, and the adhesive 4 is transparent, and its refractive index na is set to n, <n.・,<n
2, most of the leaked light in the optical fiber is guided into the light guiding sleeve. The end surface of the light guide sleeve is a reflective surface set obliquely to the axis, as shown in Figure 1 (
C) As shown on the right, the leaked light that has traveled through the light guide sleeve is emitted toward the light receiving element.

Figure 1 (B) also shows that after scratching the middle part of the optical fiber 1o with a carbide blade, transparent UV light is applied to the scratched area.
A state in which a cured adhesive 5a is attached is shown. Similarly, adhesive 5b is also attached to the tip end of the optical fiber 10c to which switching is made. In this state, the light receiving element 7a,
No signals are output from 7b and 7c (see Figure 1 (
In B), the receiving electrical system is omitted).

FIG. 1(D) is a step subsequent to FIG. 1(B), and shows a state in which the optical fiber 10 is stress-cut by pulling the core fiber holder 6a to the left. Assume that the signal light on the current core is propagating from the left to the right. The output signals from the light receiving elements 7b and 7c are input to the alignment controller 8, and changes therein are monitored. Since leakage light is excited in the optical fiber 10b at the same time as the optical fiber 10 is cut, the output of the light receiving element 7b increases rapidly as shown by the dotted line in FIG. 1(G). The alignment controller precisely controls the position of the core wire holder 6a so that the output signal level does not exceed a reference level that has been calibrated and set in advance. At this time, the transparent adhesive 5a is attached to the optical fiber 1.
0a.

Since it fills the space between the end faces of 10b and acts as a refractive index matching agent, n, ζn, and the Fresnel reflection loss of the end face is 0.
．． 3dB can be excluded. In addition, the relative position of the optical fiber and core holder is maintained accurately through the light guide sleeve.
Since no axis misalignment is caused between the optical fibers 10a and 10b, even if the end face spacing is widened to about 50 μm, the transmission quality of the line will not be affected in this process. In the cutting process, due to the reinforcing effect of the light guide sleeve, the timing of applying tensile stress can be accurately controlled, and failures such as breakage at unspecified locations do not occur.

Next, the core wire holder 6a is moved in parallel at high speed, and as shown in FIG.
). If the output of the light receiving element 7C is detected at this time, the output will increase rapidly at the moment the optical fibers 10a and 10c are opposed to each other. The output change is measured by the alignment controller 8.
Based on this, the position of the core fiber holder 6a is finely adjusted to achieve precise alignment between the optical fibers 10a and TOC. Immediately after parallel movement, 5μ due to the limit of machine accuracy.
There is an axial misalignment of about m, and in addition to the loss due to the spacing shown in FIG. 4, there is an axial misalignment connection loss of about 4 dtl. On the other hand, the output change of the light receiving element 7C is detected at high speed, and the core wire holder 6a is placed at the position where the output takes the minimum value.
It is to adjust. An example of the change in the output of the light receiving element 7C in this step is shown by the solid line in FIG. 1(G). The time between the last peak of the dotted line and several peaks of the solid line is the time during which the transmission quality of the line is degraded due to switching, and is suppressed to about 1Qms. After alignment, the fiber holder 6a is moved to the right to reduce the distance between the end faces of the optical fibers 10a and toc, and abut them against each other. Therefore, when the adhesive 5b is irradiated with a spot of UV light and cured, the connection of the optical fibers is almost completed. At this time, the output of the light receiving element 7C converges to a constant value corresponding to a slight connection loss. By comparing this value with a reference level that has been calibrated and set in advance, it is possible to roughly estimate the connection loss and determine the success or failure of switching. An average connection loss of about 0.15 dB was obtained.

Finally, as shown in FIG. 1(F), new adhesive 5C is filled into the gap between the light guide sleeves 3a and solidified. For further reinforcement, use the light guide sleeve 3a.

An effective method is to integrally cover the coated portions of the optical fibers 3C and the coated optical fibers 1a and lc with a half sleeve (not shown), fill the gap with adhesive, and solidify the adhesive. In addition, in the above procedure, if the signal light in the optical fiber core 1 is propagating from the right to the left, only the change in the output of the light receiving element 7a is detected and the same control as described above is performed. It will be easily understood that exactly the same switching connection can be made by

(Effects of the Invention) As explained above, the method of the present invention utilizes a light guiding sleeve for an optical fiber, which has both the function of reinforcing the optical fiber and the function of concentrating leaked light, and is simple and safe. , it has the advantage of being able to perform reliable and high-speed switching connections. A light guide sleeve that can stably monitor minute leakage light is left at the connection after switching and connection, so it can be effectively used for line signal monitoring, core fiber comparison, etc. during subsequent maintenance of the optical fiber line.

[Brief explanation of drawings]

FIGS. 1(A) to (F) are diagrams showing the procedure of an embodiment of the present invention, FIG. 1(G) is a diagram showing the relationship between the outputs of the light receiving elements 7b and 7c and time, and FIG. A) and (B) are diagrams showing the conventional method, Figure 3 is a diagram (not shown) of the conventional method of detecting leakage light at the connection point, and Figure 4 is a diagram showing the relationship between the optical fiber end face spacing and splice loss. FIG. 5 is a diagram showing the relationship between splice loss and received light power using light collection efficiency as a parameter. 1, 1a, lb, IC...optical fiber line 2a, 2
b... Cover removal blade 3a, 3b, 3c... Light guide sleeve 4a, 4b, 4c... Transparent adhesive 5
a, 5b, 5c...transparent adhesive 6a, 5b, 5a
' , 6b ', ... Core holders 7a, 7b, 7
c... Light receiving element 8... Alignment controller 9... Scratching blades 10, 10a, 10b, lQc... Optical fiber 1
1.11C...Coating 30...Matching oil-N
PS
1lAn: *Risukura rf# /Qα, tob-... 1t7pl Figure 1 (G) (F) 5cm---Esu , 7-P3/enter tlf 尤/gu7-F4 (d
B) N loss (dB)

Claims (1)

[Claims] 1. Remove the coating from a part of the optical fiber core to expose the optical fiber, and cut the optical fiber at the exposed part to divide it into first and second optical fiber ends. However, in a method of reconnecting one optical fiber end to a third optical fiber end which is the end of an individual optical fiber core wire, both sides of the exposed portion to be cut and the third optical fiber end are connected to each other. a step of attaching to the fiber end a light guide member having a refractive index higher than the refractive index of the optical fiber cladding portion and having a function of guiding leaked light in the optical fiber to the inside thereof, and fixing the light guide member to the optical fiber; While monitoring the leakage light in the optical fiber through the light guide member, stress-cut the exposed portion to be cut, detect changes in the leakage light, and cut one end of the split optical fiber. Optical fiber core wire switching connection characterized in that the connection is changed using the procedure of aligning the axes between both optical fiber ends by arranging the ends of the optical fibers to face each other and detecting a change in leakage light. Method. 2. In the optical fiber core wire switching and connecting method according to claim 1, the light guide member is fixed to the optical fiber via a transparent adhesive, and the optical fiber cladding portion, the transparent adhesive,
A method for switching and connecting optical fibers, characterized in that the relationship n_1≦n_a≦n_2 is established, where the refractive indices of the light guide members are n_1, n_a, and n_2, respectively. 3. In the optical fiber core wire switching and connecting method according to claim 1, the location where the exposed portion is to be cut and the third
An optical fiber core wire switching and connecting method characterized in that an uncured transparent adhesive is applied in advance to the tip of the optical fiber end.