JPH04335303A - Method for splicing optical fiber - Google Patents

Abstract

PURPOSE:To perform the operation in a short time, to improve the reliability, and to reduce the connection loss by fusing and drawing a fusion-spliced connection part formed by arc discharging while matching the outer peripheries of clads with each other. CONSTITUTION:One eccentric core optical fiber 1 and the other single-mode optical fiber 2 are positioned on the basis of the outer peripheries of their clads 1a and 2a as reference positions and they are fused and spliced by the arc discharging. The positioning operation is carried out by a normal image process and the fusion-splicing connection operation is performed similarly to a multi-mode optical fiber. In this state, both the cores 1b and 2b shift in position at the connection point 3, so the connection point 3 is heated and the optical fibers 1 and 2 are drawn in opposite directions in a half-fused state to draw the periphery of the connection point 3. Consequently, the core diameters decreases as well as the fiber external diameter of the periphery. The mold field diameter of propagated light, therefore, increases and the quantity of axis deviation between the cores 1b and 2b also decreases, so the connection loss is reduced as the fibers are drawn.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for splicing single-mode optical fibers, and in particular improves workability and reliability in splicing eccentric core optical fibers, and also aims to reduce splice loss. It is something.

0002

2. Description of the Related Art One type of single mode optical fiber is an eccentric core optical fiber whose core is largely eccentric. This eccentric core optical fiber is being researched and developed as a fiber sensor, for example, as an oil leak detection sensor. When an eccentric core optical fiber is used as a sensor, a normal single mode optical fiber is often connected to both ends or one end in order to efficiently and stably input or receive light.

Conventionally, in order to connect an eccentric core optical fiber to a normal single mode optical fiber, a fusion splicer is used to manually align the cores and then perform fusion splicing. Normally, fusion splicing machines perform image analysis, automatically align the core position using a microcomputer, and perform fusion splicing by melting the joint using arc discharge.
If image processing is not possible for some reason, or if you want to make a splice with very low loss, you can enter the light from one end of the fiber, monitor the optical power output from the other end, and perform a fusion splice by aligning the fiber. Sometimes it is done.

0004

[Problems to be Solved by the Invention] However, image processing may not be possible with an eccentric core optical fiber whose core is extremely far from the center of the cladding, and in that case, it is necessary to manually connect the two fibers. It was necessary to shift the cores so that they overlapped each other, which took a very long time to align. Furthermore, during fusion bonding, the arc discharge must be weakened to prevent the joint surfaces from completely melting in order to prevent the combined cores from shifting due to surface tension. For this reason, there were reliability problems such as low connection strength and easy breakage of connection points. Therefore, an object of the present invention is to improve workability and improve workability when fusion splicing single mode optical fibers with eccentric cores, such as eccentric core optical fibers.
The object of the present invention is to obtain a connection method that is highly reliable and can reduce connection loss.

[0005]

[Means for solving the problem] This problem can be solved by aligning the outer circumferences of the claddings of the optical fibers to be connected, performing fusion splicing by arc discharge, and then melting and drawing the joint. .

[0006] This invention will be explained in detail below. FIG. 1 shows an example of the connection method of the present invention in which one optical fiber is an eccentric core optical fiber 1 and the other optical fiber is an ordinary single mode optical fiber 2. first,
As shown in FIG. 1A, both optical fibers 1 and 2 are aligned using the outer circumferences of their claddings 1a and 1b as reference positions, and then fusion spliced by arc discharge. The alignment here can be performed by normal image processing, and the fusion splicing can also be performed by a conventional method, and this work can be performed in the same way as the fusion splicing of multimode optical fibers.

However, in this state, since the positions of both cores 1b and 1b are shifted as shown in FIG. 1(B) at the connection point 3, the connection loss becomes quite large. Therefore, the connection point 3 is heated to a semi-molten state, and in this semi-molten state, the optical fibers 1 and 2 are slightly pulled in opposite directions to stretch the connection point 3 and its surroundings. As a result of this stretching, the outer diameter of the fiber around the connection point 3 decreases, as shown in FIG. 1(C), and the core diameter also decreases.

At the connection point 3, the mode field diameter of the propagating light increases as the core diameter decreases, and the cores 1b and 2b
The amount of axis misalignment also decreases, so the connection loss decreases as the wire is stretched. FIG. 2 shows the results of calculating the increase in the mode field diameter as the core diameter decreases according to the New Peterman definition. At this time, the cutoff value when the core diameter was 8.1 microns was set to 1.1 microns, Δ was set to 0.3%, and the wavelength of the propagated light was set to 1.3 microns. Next, FIG. 3 shows the relationship between the core diameter and the connection loss calculated using the relational expression (1) between the core axis misalignment amount and the connection loss. However, it was assumed that the initial axis deviation amount was 50 microns and that the mode field diameters of each fiber were equal. From this result, it is calculated that if the core diameter is stretched to 2.8 microns or less, the connection loss will decrease to 1.0 dB or less.

[0009]

[Math 1]

In the formula, αd is the connection loss, d is the amount of core deviation, and W1 and W2 are the respective mode field diameters.

[0011] Furthermore, the amount of stretching (stretching length) is proportional to the amount of core misalignment between core 1b and core 2b, and as the amount of core misalignment increases, the amount of stretching should be increased; this is based on experience. Alternatively, a method may be adopted in which light is input from one open end of an optical fiber and the optical fiber is stretched while monitoring the optical power emitted from the other open end. The melt drawing used here is an established technique for manufacturing optical fiber couplers, and can be performed with high precision and high reproducibility. The method of reinforcing the connection point 3 after melt-stretching can also be adapted from the method of reinforcing the fiber optic coupler by using a shrink tube or resin coating.

Furthermore, the connection method of the present invention can naturally be applied to the connection of general single-mode optical fibers, and in this case, since the amount of core deviation is slight, extremely low loss can be achieved with a slight amount of stretching. Connection is now possible. Examples are shown below to clarify the effects.

(Example 1) General single mode optical fiber for 1.3 microns (core diameter 8.1 microns, cladding diameter 125 microns, △0.3%, cutoff value 1.1
micron) and an eccentric core optical fiber whose core is 50 microns away from the center of the cladding (core diameter 8 microns, cladding diameter 126 microns, △0.3%, cutoff value 1.
The connection method according to the invention was carried out using 1 micron). As a result, a connection loss of 2.5 dB was obtained with a stretching amount of 10 mm.

(Example 2) General single mode optical fiber for 1.55 microns (core diameter 10 microns, cladding diameter 125 microns, △0.3%, cutoff value 1.5
The connection method according to the present invention was carried out using a single-mode optical fiber (core diameter 3 microns, cladding diameter 126 microns, Δ0.9%, cutoff value 1.1 microns) doped with erbium ions. As a result, the connection loss, which was 1.0 dB immediately after connection, decreased to 0.1 dB after stretching 2 mm.

[0015]

[Effects of the Invention] As explained above, in the optical fiber splicing method of the present invention, the outer peripheries of the claddings of the optical fibers to be spliced are aligned, fusion splicing is performed by arc discharge, and then the spliced portion is Since it is melt-stretched, it is possible to perform fusion splicing with high workability and excellent reliability, and to reduce splicing loss.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the connection method of the present invention in the order of steps.

FIG. 2 is a graph showing the relationship between core diameter and mode field diameter.

FIG. 3 is a graph showing the relationship between core diameter and connection loss.

[Explanation of symbols]

1... Eccentric core optical fiber, 2... Single mode optical fiber, 1a, 2a... Clad, 1b, 2b... Core, 3... Connection point

Claims (2)

[Claims] [Claim 1] When fusion splicing single-mode optical fibers, the outer circumferences of the claddings of the optical fibers to be spliced are matched, fusion splicing is performed by arc discharge, and then the spliced portion is melt-stretched. Optical fiber connection method. 2. The method for connecting optical fibers according to claim 1, wherein one of the single mode optical fibers is an eccentric core optical fiber.