JPH02271306A - Production of optical fiber coupler - Google Patents

Abstract

PURPOSE:To produce the multimode optical fiber coupler which is stable in the degree of coupling by previously heating and stretching two pieces of multimode optical fibers and fusing or elongating the two optical fibers in the heated and stretched part, thereby controlling the length of the fused part. CONSTITUTION:Two pieces of the multimode optical fibers 21a, 21b are previously stretched by heating and a part of the stretched part is used as the coupler by forming a standing wave mode in the stretched parts 22a, 22b. Namely, the central part of the stretched parts 22a, 22b is heated and fused and the output light from the two fibers 21a, 21b is measured. While the degree of the optical coupling is monitored, the light is coupled by adjusting the length and shape of the fused part 33 and a part of the stretched parts is used as the coupler. Even if a mode conversion is generated by a bending or side pressure in the input optical fiber, the fluctuating mode is once converted to the standing wave mode by reducing the core diameter to a tapered shape just before the optical fiber coupler and thereafter, the optical coupling is executed and, therefore, the stable coupling is obtd. as far as the tapered parts of the cores are fixed to a substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a multimode optical fiber coupler used for branching optical signals in communication systems, sensors, and the like.

<Prior art> In optical transmission systems such as subscriber systems, optical signals propagating through one transmission path are branched into multiple propagation paths, or optical signals from multiple transmission paths are split into one transmission path. The number of requests to be superimposed on transmission lines is rapidly increasing.

One component that performs this function is a fused and drawn optical fiber coupler. Optical fiber couplers have the characteristics of low loss, excellent connectivity with optical fibers that are light transmission lines, and low cost.

A conventional multimode optical fiber coupler is realized by fusing and stretching parts of two optical fibers, as shown in FIG. 7(a), where lla and llb are multimode optical fibers, and 12 is a multimode optical fiber. The fused portion 13 is a stretched portion.

A conventional multimode optical fiber coupler is shown in Fig. 7(b).
Multimode optical fibers lla, llb as shown in
They were simply fused together and then stretched. In a multimode optical fiber, there is coupling between modes due to bending and lateral pressure, and this causes speckle noise and causes fluctuations in light intensity. If it is in standing wave mode, there will be no light intensity fluctuation, but if there is irregular bending or lateral pressure during mounting, such as in an optical fiber coupler, mode conversion will occur and the degree of coupling of the optical fiber coupler will fluctuate. For this reason, conventional multimode optical fiber couplers are unreliable and cannot be applied to optical transmission systems or optical fiber sensors.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for manufacturing a multimode optical fiber coupler with a stable degree of coupling.

(Means for Solving the Problems) The present invention provides the following features when producing a multimode optical fiber coupler:
Two multimode optical fibers are drawn in advance, and a standing wave mode is created in the drawing section, with a part of the drawing section serving as a coupler.

In the present invention, even if mode conversion occurs in the input optical fiber of the optical fiber coupler due to bending or lateral pressure, the changing mode can be converted into a standing wave mode by tapering the core diameter just before the optical fiber coupler. After conversion, try to perform optical coupling. As long as the core taper portion is fixed to the substrate, mode conversion does not occur, so stable coupling can be obtained.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

Example 1 FIG. 1 is a pre-stretched diagram of a multimode optical fiber that is the principle of the present invention, and FIG. 2 is a diagram of the pre-stretched multimode optical fiber shown in FIG. 1 fused and stretched. 21&
, 21b is a multimode optical fiber, 22a and 22b are extension parts, 31a and 31b are multimode optical 7 fibers, 32
32a and 32b are stretched parts, and 33 is a fused part.

Relative refractive index Δ=1%, core diameter 50 μm 1 cladding diameter 125
As shown in Figure 1, a μm multimode optical fiber is heated and stretched with an oxyhydrogen flame burner until the cladding has an outer diameter of 40 μm and a length of 15 mm, and then the center of the stretched portion is fused to increase the degree of bonding. So that it becomes 50% at a wavelength of 1.3 μm,
The length of the fused part and the shape of the fused part were adjusted. In this case, the cross-sectional shape of the fused portion is approximately circular as shown in FIG. 3, and the length of the fused portion is approximately 5 mm. In this case, since it is not stretched, there is almost no tapered shape in the fused portion.

41a and 41b are cores, 42a and 42b are claddings, and 43 is a fused portion. The loss of this optical fiber coupler was 0.25 dB at a wavelength of 1.3 μm. Extension part 22
a, 22b.

32a and 32b, all modes are excited, and even if the ambient temperature changes from -10℃ to 80℃, the L
Even when OG impact was applied, the degree of bonding varied within 1%.

Example 2 FIG. 5 shows another embodiment of the present invention, 61a.

61b is a multimode optical fiber, 62a and 62b are stretching parts, and 63 is a fused/stretched part I. As shown in Figure 1, a multimode optical fiber with a relative refractive index Δ=1%, a core diameter of 50 μm, and a cladding diameter of 125 μm is stretched until the cladding has an outer diameter of 40 μm and a length of 15 mm, and then a part of the center of the stretched portion is drawn. were fused at a lower temperature than in Example 1, and the degree of bonding was 1.3μ at the wavelength.
The fused portion was further stretched so that the length was 50%. In this case, the cross-sectional shape of the fused portion is approximately 80-shaped, as shown in FIG. 4, and the fused portion is shallower than that in FIG. 3.

Further, the length of the extended portion is approximately 3 mm. 51a and 51b are cores, 52a and 52b are claddings, and 53 is a fused portion.

This optical fiber coupler has wide wavelength characteristics as shown in Figure 6, and its loss is 0.15 dB at a wavelength of 1.3 μm, and the coupling degree is low against IOG impact at ambient temperatures of -10°C to 80°C. The fluctuation was within 1%, and the loss fluctuation was 0.02 (fB).

In this example, the coupling between the multimode optical fibers is 50
%, but the degree of bonding is 0 to 100.
It can be arbitrarily selected between %. 0-50% in actual application
An optical fiber coupler for coupling may be used. Especially in the case of an optical tap, an optical fiber coupler with 0 to 20% coupling is required.

In this case, the stretch will be much shorter than a 50% coupling optical fiber coupler. In fact, in an optical fiber coupler with 10% coupling, the length of the stretched portion after fusion was approximately 1.5 mm at a wavelength of 1.3 μm.

(Effects of the Invention) As described above, in the method for manufacturing an optical fiber coupler of the present invention, by pre-stretching a multimode optical fiber, no matter what mode is excited in the multimode optical fiber before the stretching part, Since the standing wave mode is excited in the extended portion, a stable degree of coupling can be obtained.

In conventional multimode optical fiber couplers, the coupling degree varies depending on the coherency of the light source or by bending or applying lateral pressure to the optical fibers at both ends of the optical fiber coupler. problems like this are solved.

[Brief explanation of drawings]

Figure 1 is a pre-stretched view of the multimode optical fiber that is the principle of the present invention, Figure 2 is a diagram of the pre-stretched multimode optical fiber shown in Figure 1 fused and stretched, and Figure 3 is the stretched state. FIG. 4 is a cross-sectional view of two stretched multimode optical fibers that are deeply fused together; FIG. 5 is a cross-sectional view of two stretched multimode optical fibers that are shallowly fused together; FIG. FIG. 6 is a diagram showing wavelength characteristics of an optical fiber coupler obtained by the manufacturing method of the present invention, and FIGS. 7(a) and (b) are explanatory diagrams of a conventional method for manufacturing a multimode optical fiber coupler. 11a, flb...multimode optical fiber 12...
Fusion part 13...stretching part 21&, 21b
...Multimode optical fibers 22a, 22b - extension parts 311, 31b...Multimode optical fibers 32a, 3
2b...Stretched part 33...Fused part 41a, 4
1b.:lA 42a, 42b-...Clad 43...Fusion part 51a, 51b...
Cores 52a, 52b...Clad 53...Fusion parts 61a, 61b...Multimode optical fiber 62a
, 62b...Stretching part 63...Fusion/stretching part FIG. 1, FIG. 3, 2fa, 21b---'1it-do i77, l'7'5
22a, z2b-yi Shinichi β Fig. 4 Fig. 2 Fig. 5 Fig. 5 32a, 32f) ---Ikami Iku 3.3 ---Issa Part 1

Claims (1)

[Claims] One or two multimode optical fibers are stretched by heating in advance, the central part of the stretched part is heated and fused, and the output light from both optical fibers is measured to monitor the degree of optical coupling. A method for manufacturing an optical fiber coupler, characterized in that both optical fibers are fused together by heating and the length of the fused portion is varied. 2. Two multimode optical fibers are stretched by heating in advance, the central part of the stretched part is heated to fuse and stretch, and the output light from both optical fibers is measured and the degree of optical coupling is monitored while heating. 1. A method for producing an optical fiber coupler, which comprises stretching both optical fibers and varying the stretching length.