JPH01154006A - Production of optical fiber coupler - Google Patents

Abstract

PURPOSE:To enable simultaneous production of plural optical fiber couplers having uniform characteristics by inserting plural optical fibers into low- refractive index glass tubes to constitute coupler units and inserting these tubes into a quartz tube, then heating and stretching the fibers in this state from the outside, thereby welding and stretching the plural optical fibers. CONSTITUTION:The quartz tube 4 is reduced in the inside diameter and the respective low-refractive index glass tubes 2 constituting the respective coupler units 3 are reduced in the inside diameter as well when the quartz tube 4 inserted with the plural coupler units 3 is heated from the outside and is stretched. Since the optical fibers 1 inserted therein adhere tightly to each other, the welded and stretched parts 21 to constitute the coupling parts are formed by the subsequent stretching. The respective low-refractive index glass tubes 2 are respectively internally heated uniformly and, therefore, the welding and stretching conditions of the respective optical fibers 1 are uniformized. The plural optical fiber couplers having uniform branching ratios are thus produced by one time of stretching operation.

Description

[Detailed Description of the Invention] Summary: A method for manufacturing an optical fiber coupler made by fusing and drawing optical fibers, in which a plurality of optical fiber couplers having uniform characteristics are simultaneously manufactured.
A plurality of optical fibers are inserted into a low refractive index glass tube having a refractive index smaller than the refractive index of these claddings to form a coupler unit, and a plurality of said coupler units are inserted into a quartz tube. By heating and stretching the quartz tube from the outside in this state, a plurality of optical fibers in each low refractive index glass tube are fused and stretched.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber coupler by fusing and stretching optical fibers.

In the field of optical communications that uses optical fibers as transmission paths, it is necessary to distribute transmitted optical signals to multiple devices, or to introduce multiple channels of wavelength-multiplexed signal light into a single optical fiber. , a photocoupler is used. An optical coupler basically includes an input section and an output section for connecting to an optical fiber, and a functional section for branching an input signal at a predetermined ratio. Practical optical couplers are required to (a) be easy to manufacture, (b) have small variations in characteristics such as branching ratio and excess loss, and (c) be suitable for miniaturization. etc.

Conventional technology Conventionally, optical couplers include micro-optical system types constructed using optical elements such as lenses and half mirrors, waveguide types, and optical couplers that fuse multiple (for example, two) optical fibers together.・Fiber fused types made by stretching are mainly used. Especially when the optical transmission line is a single mode optical fiber, it is a micro-optical system type or a waveguide type.
Since there is a large loss when converting the light beam or when connecting to the optical transmission line, it is said that an optical fiber coupler that can be directly connected to the optical transmission line is advantageous in such cases.

FIG. 4 is a diagram showing the general configuration of an optical fiber coupler 30, which includes input sections 31, 32,
It consists of an output section 33, 34 and a fusing/stretching section 35. The optical power from the input section 31 or 32 is P. When an optical signal of 111 is input, optical signals of optical powers P and P2 are outputted from the output sections 33 and 34 at respective predetermined branching ratios.

According to such a configuration, insertion loss is small because it can be directly connected to a single mode optical fiber, and since the only component is an optical fiber, it can be said that reliability against temperature, humidity, etc. is high. In addition, P/P
, P /Po or Pl :P2 is the outer diameter and length of the fused/stretched portion 35 and the fused/stretched portion 35.
It is known that the refractive index is determined depending on the refractive index of the cladding part of the extension part 35 and its surroundings.

FIG. 5 is an explanatory diagram of a conventional manufacturing method of an optical fiber coupler. By forming a twisted part 43 in the part of the optical fiber 41, 42 where the fused/stretched part is to be formed, and heating and fusing this twisted part 43 with a burner 44, and stretching it in the direction C in the figure, This forms a fused/stretched part. Here, the twisted portion 43 is formed by optical fibers 41 and 42.
This is to make the fusion bond easier by bringing the materials into close contact with each other. The optical fiber coupler manufactured in this manner is usually housed in a case together with a resin having a predetermined refractive index in order to stabilize the branching ratio and improve mechanical strength.

Problems to be Solved by the Invention However, the optical fiber coupler manufactured by the conventional method described above has a method of achieving a desired branching ratio by performing fusing and stretching operations while monitoring the output light relative to the input light of a predetermined wavelength. Therefore, even if a plurality of optical fiber couplers are made from the same component, there is a problem in that the branching ratio of each optical fiber coupler varies.

In addition, when manufacturing a large number of optical fiber bacculers, it is necessary to perform the above monitoring on all of them.
Another problem was that it was complicated.

Furthermore, when a large number of optical fiber couplers are used in the same device, there is a problem in that a large amount of space is required.

The present invention was created in view of these problems, and aims to make it possible to simultaneously manufacture a plurality of optical fiber couplers having uniform characteristics, and thereby to achieve miniaturization of the device.

Means for Solving the Problems The method for manufacturing an optical fiber coupler of the present invention, which was made to solve the problems of the prior art described above, consists of a plurality of optical fibers having a refractive index smaller than the refractive index of their claddings. A coupler unit is formed by inserting the coupler units into a low refractive index glass tube having a Fusion and splicing of multiple optical fibers
It is meant to be stretched.

1-1-■ When a quartz tube into which multiple coupler units are inserted is heated from the outside and stretched, the inner diameter of the quartz tube decreases, and along with this, the inner diameter of the low refractive index glass tube that makes up each coupler unit also decreases. Decrease. As the inner diameter of the low refractive index glass tube decreases,
Since the optical fibers inserted into each interior are brought into close contact with each other, a fused/stretched portion that becomes a coupling portion is formed by subsequent stretching. At this time, since the inside of each low refractive index glass tube is uniformly heated, the conditions for fusing and drawing each optical fiber are uniform. Therefore, it is possible to manufacture a plurality of optical fiber couplers having a uniform branching ratio by one drawing operation.

What makes the refractive index of the low refractive index glass tube smaller than that of the optical fiber cladding is the formed wA.
This is to prevent light from leaking outside from the attachment/stretching section and increase loss, and to stabilize the branching ratio. This eliminates the need to fill each fused/stretched portion with a resin having a predetermined refractive index, making it possible to downsize the device.

On the other hand, if the shape of the fused and stretched portion of each optical fiber is the same as the conventional shape to obtain the desired branching ratio, the overall outer diameter will increase by the amount of the low refractive index glass tube and quartz tube. Therefore, the mechanical strength increases. As a result, not only are protective forms such as resin and cases reduced or unnecessary, but changes in the branching ratio due to undesirable curvature of the fused/stretched part are prevented, and the branching ratio during multiple production is reduced. Variability is reduced.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an optical fiber manufactured by applying the present invention. FIG. 2 is a front view showing the arrangement of each member in the iba couple before heating the quartz tube. 4 is, for example, a quartz tube with an inner diameter of 5 mm and an outer diameter of 7 mm, and a plurality (four in this embodiment) of low refractive index glass tubes 2 are inserted inside this quartz tube 4. . Inside each of the low refractive index glass tubes 2, a plurality of (
In this embodiment, two optical fibers 1 are inserted in each case. The inner diameter of the low refractive index glass tube 2 is, for example, approximately 1 mm.
The outer diameter is approximately 2 tm, and the relative refractive index difference with the cladding of the optical fiber 1 is, for example, 0.5%.

FIG. 2 is an explanatory diagram showing the state in which the above-mentioned members are heated and stretched. In order to monitor the branching ratio, prior to heating and stretching, an LD (semiconductor laser) light source 11 is connected to one end of one of the optical fibers 1 in one of the low refractive index glass tubes 2, and the optical fiber is A photodiode 12.1 at the other end of the optical fiber 1 and the other optical fiber 1, respectively.
Optical power meters 14 and 15 are connected via 3. 02-H for heating the quartz tube 4 from the outside
2 burners 16 are relatively large (e.g. 20 m)
The quartz tube 4 can be heated uniformly.

When heating the quartz tube 4 with the 02-H2 burner 16 to form the extended portion 20 approximately in the center thereof, for example, the quartz tube 4 is rotated in the direction shown in the figure to uniformly heat the quartz tube 4. It is best to gradually stretch it in the 8 directions in the figure. At this time, the light introduced from the LD light source 11 is branched at a predetermined branching ratio depending on the state of fusion/stretching of the optical fiber, and is incident on each photodiode 12. The stretching operation can be performed while comparing the measured values of 15 until a desired branching ratio is achieved.

FIG. 3 is a sectional view of the extension section 20. A fused/stretched part 21 between optical fibers is formed, and this is covered with a low refractive index glass part 22 and a quartz tube covering part 23 in this order. Here, the fused/stretched portion 21 is formed without twisting the optical fibers together as in the past, because the quartz tube 4 and the low refractive index glass tube 2 are formed during stretching.
The inner diameter of decreases and this force becomes light? This is because it acts in the direction of bringing the bis into close contact with each other.

Generally, in optical fiber couplers that utilize field coupling of surface wave (evanescent wave) energy around the core, the optical power is transferred through the electric field superimposed between the cores, and the surface wave energy is transferred to the core. Since the distance decreases exponentially with the distance from the core, it is required that the cores be extremely close to each other. wA by the method of the present invention
In the manufactured optical fiber bacable, the splicing/stretching part 2
As the cross-sectional area of the core 1 is reduced, the electric field of the surface wave spreads far from the core, and the claddings fuse together, bringing the cores closer together, achieving good optical coupling. As stated above, the branching ratio, which indicates the degree of optical coupling, is determined according to the outer diameter and quality of the fused/stretched part, and the refractive index of the cladding part of the fused/stretched part and its surroundings. However, according to the present invention, these parameters can be made uniform for each fused/stretched part, so it is possible to simultaneously manufacture a plurality of optical fiber couplers having branching ratios with little variation. .

Effects of the Invention As detailed above, according to the method of the present invention, a plurality of optical fiber couplers having uniform characteristics can be manufactured at the same time, and the manufacturing work can be simplified and the equipment can be made smaller. play.

[Brief explanation of the drawing]

Fig. 1 is an embodiment of the present invention, and is a front view showing the Rn state of each member before heating the quartz tube, Fig. 2 is a manufacturing method explanatory diagram showing an embodiment of the present invention, and Fig. 3 4 is a diagram illustrating the structure and operation of a conventional optical fiber coupler, and FIG. 5 is a diagram illustrating a method of manufacturing a conventional optical fiber coupler. DESCRIPTION OF SYMBOLS 1... Optical fiber, 2... Low refractive index glass tube, 3... Coupler unit, 4... Quartz tube, 20
... Stretching part, 21... Fusion/stretching part. 20: Clam extension (1 Meat A column Figure 3 A Hikimai A column Figure 4 A Hikimai A column Eye figure 5

Claims (1)

[Claims] A plurality of optical fibers (1) are inserted into a low refractive index glass tube (2) having a refractive index smaller than the refractive index of these claddings to form a coupler unit (3). With the coupler unit (3) inserted into the quartz tube (4), by heating and stretching the quartz tube (4) from the outside, a plurality of A method for manufacturing an optical coupler, which comprises fusing and stretching an optical fiber (1).