JP2619130B2 - Single Mode Optical Fiber Interconnection Method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber interconnection method that enables single-mode optical fibers having different core diameters to be connected with low loss.

(Prior Art) A single mode optical fiber widely used in optical communication generally has a relative refractive index difference Δ between a core and a clad of about 0.3%. In this case, if the optical fiber is bent with a small radius of curvature, the amount of light leaking from the core to the clad increases, and the loss increases.Therefore, when wiring using an optical fiber, the bending radius is usually about 20 mm or more. It is used in.

On the other hand, when it is necessary to bend at a smaller radius of curvature or when it is necessary to increase the energy density of light in the fiber, a single mode optical fiber having a higher Δ and a smaller core diameter may be used. . Increasing Δ allows the fiber to bend with a smaller radius of curvature for the same loss, but with a smaller spot size than a normal single mode optical fiber.

Even when such a small-diameter core optical fiber is used in an optical circuit, it is necessary to connect a general single-mode optical fiber in a portion for extracting an optical signal to the outside.

At this time, for example, as shown in FIG. 5, a normal single mode optical fiber 12 comprising a core 12a and a clad 12b is used.
When the small-diameter core optical fiber 11 composed of the small-diameter core 11a and the small-diameter core 11b is directly butt-connected, a large connection loss occurs because the spot sizes of the two optical fibers 11, 12 are discontinuous at the connection points. . FIG. 6 shows measured values of connection loss when a normal single-mode optical fiber is connected to a small-diameter core optical fiber having a spot size of about half using a normal PC optical connector. The optical connector used can provide a connection loss value of about 0.1 dB if ordinary single-mode optical fibers are connected to each other.However, because of the discontinuous spot size described above, an average of 2.
The loss is as large as 6 dB.

Single mode optical fibers with different core diameters
Directly connecting the optical fibers 11 and 12 in principle causes a large loss. Therefore, when trying to connect the optical fibers 11 and 12 with low loss, for example, as shown in FIG.
A method of connecting using two lenses 31 and 32 conforming to is adopted.

(Problems to be Solved by the Invention) However, as compared with a method in which optical fibers are directly joined to each other, this method requires a much more complicated assembling process, is large, and is expensive.

The present invention has been made in view of the above-described prior art, and when connecting two single mode optical fibers having different core diameters, it is possible to connect with low loss even using a normal optical connector or fusion splicing technology. It is an object to provide a method of interconnecting optical fibers that is possible.

(Means for Solving the Problems) According to the present invention, two single-mode optical fibers having different core diameters are doped silica-based optical fibers, and one of the two optical fibers having a smaller core diameter is used. In a temperature range where the doping agent diffuses but the optical fiber does not melt, the core diameter in the vicinity of the heated portion is enlarged by heating locally in the temperature range in which the doping agent diffuses but the optical fiber does not melt. After breaking, the two optical fibers are connected to each other.

(Function) According to the present invention, a portion having a uniform enlarged core diameter can be formed over a certain section by heating an intermediate portion of the optical fiber, and furthermore, the portion is stress-ruptured at this portion for connection. The change rate of the spot size of both optical fibers to be connected can be made equal at the connection point.

(Embodiment) FIGS. 1 and 2 are views showing an example of a method for interconnecting single mode optical fibers having different core diameters according to the present invention, wherein 1 is a small diameter core whose core diameter is locally enlarged at an end face. 1a shows a core, 1b shows a cladding, 2 shows a normal single mode optical fiber, 2a shows a core, and 2b shows a cladding. In order to connect two optical fibers by directly abutting each other in this manner, (a) a method by fusion splicing (FIG. 1), (b) a method by mechanical splice, and (c) a method by optical connector (No. 2). In FIG. 2, 3 is a ferrule, and 4 is a split sleeve. According to the present invention, when the ordinary single mode optical fiber 2 and the small-diameter core optical fiber 1 are connected, any of the methods (a), (b), and (c) can be used.
The connection loss close to the original ability value by each connection technique can be realized.

FIG. 3 is an example of measured values of connection loss when a normal single-mode optical fiber 2 and a small-diameter core optical fiber 1 are connected by an optical connector using the present invention. By using the present invention, the connection loss can be significantly reduced as compared with the case where the connection is made without increasing the core diameter as shown in FIG.

Here, there are the following methods for locally increasing the spot size. As shown in FIG. 4, by heating the optical fiber 1 with the flame of the burner 21, the dopant contained in the core 1a of the optical fiber 1 diffuses into the cladding, and the core diameter of the optical fiber 1 is locally enlarged. be able to. Also, in an optical fiber having a structure in which the core is made of pure quartz and the cladding 1b contains a doping agent that lowers the refractive index, the core diameter is similarly enlarged by diffusing the doping agent from the cladding 1b to the core 1a by heating. be able to. Further, as a method of locally heating, in addition to the method using a flame as described above, a method of irradiating a laser beam, a method of resistance heating, and the like can be considered.

In order to connect the small core optical fiber 1 having the enlarged core 1a to the ordinary single mode optical fiber 2, there are the following methods. First, during the heat treatment, the burner 21 is moved in the axial direction of the optical fiber 1 to produce the small-diameter core optical fiber 1 having a uniform enlarged core diameter over a certain length. Stress rupture. Next, the end and the ordinary single mode optical fiber 2 prepared separately are fusion-spliced, or mechanical splicing is performed using a V-groove or the like. Alternatively, the ferrule 3 is bonded to a position where the end face slightly protrudes after the small-diameter core optical fiber 1 having a uniform enlarged core diameter over a certain length as described above is stress-ruptured at the center of the heat-treated portion. Is polished to form an optical connector, and the connector is connected to a separately prepared connector butted single mode optical fiber 2.

In this case, the core diameter is continuously increased in the vicinity of the end face of the small-diameter core optical fiber which has been subjected to the heat treatment and stress-ruptured. Also, by moving the burner during heating, the core enlarged part is secured uniformly for a certain length, so stress breakage at the center of the heat treated part or polishing only the part with uniform enlarged core after ferrule bonding Even when the manufactured small-diameter core optical fiber end is directly connected to a normal single-mode optical fiber and connected, a shape in which the spot size changes continuously can be expected, and low-loss connection can be expected.

Even if only the end face of the small-diameter core optical fiber 1 is heat-treated, it is difficult to obtain a core diameter distribution that smoothly leads to the spot size of the normal single-mode optical fiber 2. In addition, if only the end is heated, the end face is likely to be drooped or bent, which makes it difficult to handle. Therefore, in order to increase the core diameter according to the present invention, it is preferable to heat not the end but the middle of the small-diameter core optical fiber.

(Effects of the Invention) As described above, according to the present invention, an intermediate portion of a small-diameter core optical fiber is locally heated to enlarge the core diameter, the enlarged portion is stress-ruptured, and then connected. By doing
The rate of change of the spot size of both optical fibers to be connected can be made equal at the connection point, so that single mode optical fibers having different core diameters can be connected with extremely low loss without passing through a lens or the like. This is extremely advantageous for improving the performance, miniaturization, and cost reduction of an optical component using a small-diameter core optical fiber.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a method of interconnecting single mode optical fibers having different core diameters according to the present invention, and FIG. 2 is another example of an interconnecting method of single mode optical fibers having different core diameters according to the present invention. FIG. 3 is a cross-sectional view, FIG. 3 is a distribution diagram showing an example of a connection loss obtained by the optical fiber interconnection method according to the present invention, and FIG. 4 illustrates an example of a method for producing a core-enlarged optical fiber used in the present invention. Figure, fifth
The figure illustrates a state in which single mode optical fibers with different core diameters are connected according to the conventional technology. FIG. 6 shows an example of connection loss when single mode optical fibers with different core diameters are interconnected according to the conventional technology. FIG. 7 is a diagram for explaining a method of connecting single mode optical fibers having different core diameters with low loss according to the conventional technique. In the figure, 1 ... a small core optical fiber, 2 ... a normal single mode optical fiber, 1a, 2a ... a core, 1b, 2b ... a clad, 21 ... a burner, 3 ... a ferrule, 4 ... a split sleeve.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhiro Ando 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Hiroaki Hanafusa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Telegraph and Telephone Corporation (56) References JP-A-61-117508 (JP, A) JP-A-57-24906 (JP, A)

Claims (1)

(57) [Claims] A single-mode optical fiber having a core diameter different from each other is a doped silica-based optical fiber, and a part of the two optical fibers having a smaller core diameter has an intermediate portion. In a temperature range where the doping agent diffuses but the optical fiber does not melt, the core diameter near the heated portion is enlarged by locally heating, and the optical fiber in the enlarged portion is stress-ruptured. A method for interconnecting single-mode optical fibers, comprising: connecting optical fibers to each other.