JP2969602B2 - Optical fiber fusion splicing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for fusion splicing an optical fiber by a direct core viewing method.

[0002]

2. Description of the Related Art A conventional fusion splicing method using a core direct view method will be briefly described. As shown in FIG. 2A, the optical fiber 10 is fixed to the V-groove block 20. Optical fiber 1
The parallel light beam 22 is applied to 0, and the enlarged optical fiber image 12 is obtained on the TV monitor 30 by the objective lens 26 and the TV camera 28. Two dark lines 14 arranged close to each other near the central axis of the optical fiber image 12 indicate the core portion. 24 is a mirror.

The optical fiber image 12 is image-processed by a control device 32 and the fine movement device 3 is adjusted so that the dark lines 14 coincide with each other.
4, the position of the V-groove block 20 is adjusted. After that, as shown in FIG.
The optical fiber 10 is fusion spliced. Prior to the above alignment, the fiber is cleaned by a weak discharge to remove dust.

[0004]

One type of surface-reinforced fiber, for example, a Ti-doped fiber has a residual compressive stress on its surface. If residual compressive stress exists on the fiber surface as in this Ti-doped fiber and the refractive index distribution of the fiber is different from that of a normal non-doped fiber, the core position of the fiber image obtained by the core direct viewing method may And different. For this reason, misalignment occurs, the axis shifts, and the connection loss increases.

[0005] This phenomenon is considered to occur when an unstable state occurs in the relationship between tension and cooling in the spinning process, and a non-uniform residual compressive stress is generated in the circumferential direction. Therefore, there is variation depending on the fiber, and the situation is not always the same. This phenomenon will become an inevitable problem as mass production progresses in the future.

[0006]

The residual compressive stress of the optical fiber is released by a heat treatment, and thereafter, the fusion splicing is performed by the above-mentioned core direct-view method.

[Explanation] The residual compressive stress existing in the fiber changes the refractive index and causes misalignment. Therefore, it is sufficient to release the residual compressive stress and return the refractive index distribution to a normal one. . The release of residual stress is by heat treatment, such as annealing in metal and annealing in plastic. For the heat treatment, a weak discharge conventionally used for cleaning the fiber before the main discharge is used.

What is heated by the weak discharge is the tip of the optical fiber 10. The spark due to the weak discharge has some extent, but it is necessary to move the electrode 36 along the longitudinal direction of the optical fiber due to the magnitude of the residual stress. If the residual stress is small, there is no need to move, but only a weak discharge at a certain position. The current value of the weak discharge may be approximately the same as that at the time of cleaning, but differs depending on the magnitude of the residual stress. The discharge time is, for example, about 0.2 seconds. It is better to perform the discharge in a plurality of times.

After the release of the residual compressive stress, fusion splicing is performed by the above-described core direct view method as in the past. However, the cleaning of the optical fiber is also performed at the same time by the weak discharge for releasing the stress, so that it is not necessary to perform the fiber cleaning before the main discharge again.

[0010]

A precise optical fiber image 12 (the dark line 14 indicating the core is at the correct position) is obtained by releasing the residual compressive stress on the optical fiber surface. Therefore, the alignment using the optical fiber image 12 is accurately performed.

[0011]

[Experimental example] Fig. 1 shows an experimental result that the centering error is reduced by the weak discharge. -The discharge current is, for example, 15 to 16 mA. -The discharge time is, for example, 0.2 seconds.・ The pause time is random. Weak discharge is performed under the above conditions, and the relationship between the number of discharges and the alignment error is obtained.

This relationship changes depending on the type of optical fiber and the magnitude of the residual stress. Therefore, the residual compressive stress can be released by appropriately selecting the discharge power, the discharge time, the interval, the number, and the like of the weak discharge by experiments, and the fusion splicing can be performed with low loss without misalignment.

[0013]

Since the residual compressive stress of the optical fiber is released by the heat treatment, an accurate optical fiber image 12 (the dark line 14 indicating the core is at the correct position) can be obtained in the subsequent direct core viewing method. . Therefore, a surface-reinforced fiber such as a Ti-doped fiber can be fusion-spliced with low loss.

In addition to the surface-reinforced fiber, low-loss fusion splicing can be performed with the above-described method not only on a surface-reinforced fiber, but also on other fibers in which a residual stress exists in the fiber due to an increase in drawing speed or the like. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the number of weak discharges for stress relaxation and alignment error.

FIG. 2 is an explanatory diagram of an incoming connection method using a core direct view method common to the present invention and the prior art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical fiber 12 Optical fiber image 14 Dark line 20 V groove block 22 Parallel light 24 Mirror 26 Objective lens 28 TV camera 30 TV monitor 32 Control device 34 Fine movement device 36 Electrode

Continuation of the front page (56) References JP-A-59-24815 (JP, A) JP-A-1-282509 (JP, A) JP-A-2-7005 (JP, A) JP-T3-502839 (JP) , A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6/255

Claims (1)

(57) [Claims] 1. An optical fiber having a surface having a residual compressive stress is fusion-spliced by a core direct-view method, the residual compressive stress of the optical fiber is released by heat treatment.
Thereafter, fusion splicing of the optical fiber is performed by fusion splicing by the core direct view method.