JPH0193706A - Manufacturing method of optical fiber coupler - Google Patents

Abstract

PURPOSE:To provide an optical fiber coupler which is small in insertion loss, has a stable branching ratio and is easy to handle by inserting plural optical fibers into a covering tube having the low refractive index part lower in refractive index than the clads of the fibers and heating the covering tube from the outside. CONSTITUTION:The covering tube 2 constituted by forming a low refractive index glass layer on the inside surface of an ordinary quartz tube to be used for production of optical fibers is used. Plural, for example, two pieces, of the optical fibers 1 are inserted into the covering tube 2 and the covering tube 2 is heated from the outside, by which the optical fibers 1 are welded and stretched together with the covering tube 2. For example, the covering tube 2 is stretched in a direction B in the state of heating the covering tube 2 and the optical fibers 1 in a direction A. Then, the inside diameter of the covering tube 2 decreases and, therefore, the optical fibers 1 are welded to each other. The reason for providing the low refractive index part to the covering tube 2 is to prevent the leakage of the light from the welded and stretched part and the consequent increase in the insertion loss.

Description

[Detailed Description of the Invention] Overview The purpose of the present invention is to provide an optical fiber coupler that has low insertion loss, stable branching ratio, and is easy to handle, regarding a method for manufacturing an optical fiber coupler made by fusing and stretching optical fibers. In a method for manufacturing an optical fiber coupler in which a plurality of optical fibers arranged in parallel are fused and stretched together, the plurality of optical fibers are placed in a cladding tube having a refractive index portion lower than the refractive index of the cladding. The optical fiber is inserted and heated from the outside of the cladding tube to fuse and stretch the optical fiber together with the cladding tube.

INDUSTRIAL APPLICATION FIELD The present invention relates to a method of manufacturing an optical fiber coupler formed by FJIAi drawing of an optical fiber.

In the field of optical communications using optical fibers as transmission paths, in order to distribute transmitted optical signals to multiple devices, or to introduce multiple channels of wavelength-multiplexed signal light into a single optical fiber, An optical coupler 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 have (a) low insertion loss, that is, a small rate of decrease in output optical power relative to input optical power, and (b) ease of handling and reliability under usage environmental conditions. It is said that it is high.

Conventional technology Conventionally, optical couplers include micro-optical type ones constructed using optical elements such as lenses and half mirrors, waveguide type ones, and optical couplers that fuse multiple (for example, two) optical fibers together.・Fiber-fused type 4, which is made by stretching, is mainly used. Especially when the optical transmission line is a single mode optical fiber, if it is a micro-optical type or a waveguide type, there will be a large loss when connecting to the optical transmission line and when converting the light beam, so in such cases It is said that an optical fiber coupler that can be directly connected to an optical transmission line is advantageous.

FIG. 5 is a diagram showing the general configuration of an optical fiber coupler, and this optical fiber coupler 40 includes input sections 41, 42,
It is composed of output parts 43 and 44 and a fusing/stretching part 45. The optical power from the input section 41 or 42 is P. When the optical signals of P1 . The optical signals of P, , are output.

According to such a configuration, insertion loss is small because it can be directly connected to a single mode optical fiber, and since the component is an optical fiber (), temperature and temperature fluctuations can be reduced. ! i!
It can be said that the reliability with respect to degrees etc. is high. In addition, P
The branching ratio represented by /P, P2/Po or P2:P2 is determined according to the outer diameter and length of the fused/stretched part 45 and the refractive index of the cladding part of the fused/stretched part 45 and its surroundings. It is known that

FIG. 6 is an explanatory diagram of a conventional manufacturing method of an optical fiber coupler. By forming a twisted portion 53 in a portion of the optical fiber 51, 52 where a fused/stretched portion is to be formed, and heating and fusing this twisted portion 53 with a burner 54, and stretching in the C direction in the figure, This forms a fused/stretched part. Here, the twisted portion 53 is formed by optical fibers 51 and 52.
This is to make the fusion bond easier by bringing the materials into close contact with each other.

Problems to be Solved by the Invention However, optical fiber absorbers manufactured by conventional manufacturing methods have problems in that they are easily damaged and difficult to handle because the outer diameter of the fused/stretched portion is as small as several tens of micrometers. was there. In addition, if there are minute parts as mentioned above, when this optical fiber coupler is housed in a case, etc., the minute parts may curve undesirably, increasing insertion loss, or changing the branching ratio to the set value. There was an inconvenience that the result would be different.

The present invention was developed in view of these circumstances! The purpose of the optical fiber coupler is to provide an optical fiber coupler that has low insertion loss, stable branching ratio, and is easy to handle.

To achieve the 4th point - Fig. 1 is an explanatory diagram of the principle of the present invention, and this manufacturing method can be applied to an optical fiber coupler in which a plurality of optical fibers arranged in parallel are fused and stretched to each other. It is something that can be done.

First, as shown in Figure (a), multiple (two in the figure)
An optical fiber 1 is inserted into a cladding tube 2 having a portion with a refractive index lower than the refractive index of these claddings.

The optical fiber 1 is then fused and stretched together with the cladding tube 2 by heating the cladding tube 2 from the outside.

Operation In FIG. 1, for example, when the cladding tube 2 and the optical fiber 1 are heated in the A direction and the cladding tube 2 is stretched in the B direction,
Since the inner diameter of the cladding tube 2 is reduced, the optical fibers 1 inserted into the cladding tube 2 are fused together. Therefore, the optical fibers 1 can be stretched in the B direction without being twisted together in advance. Assuming that the outer diameter of the fused/stretched portion of the optical fibers 1 thus formed is the same as that of the conventional structure for obtaining the desired branching ratio, the overall outer diameter of the cladding tube 2 is Since the amount of feces increases, the strength of the fused/stretched portion increases, and a decrease in insertion loss and variation in branching ratio due to curvature of this portion are prevented.

The reason why the cladding tube 2 is provided with a low refractive index portion is to prevent light from leaking out from the fused/stretched portion and increase insertion loss.

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

FIG. 2 is a perspective view of a cladding tube that can be used in the practice of the present invention. This cladding tube 11 has a low refractive index glass layer 13 on the inner surface of an ordinary quartz tube 12 used for manufacturing optical fibers. It forms. The low refractive index glass layer 13 can be obtained, for example, by forming a SiO2 glass film doped with an additive such as F or 8203 by a normal internal CVD method. Incidentally, the cladding tube 11 may be used after forming the low refractive index glass layer 13 and then being stretched to an appropriate length. In this embodiment, the outer diameter of the quartz tube 12 is approximately 2 ms, and the inner diameter is approximately 1jIl11 low refractive index glass wr11.
3 has a thickness of approximately 0.2#llI.

FIG. 3 is an explanatory diagram of a method of manufacturing an optical fiber coupler.

The figure shows a state in which stretching is being carried out while monitoring the branching ratio, but prior to this, each member is first arranged as follows.

A 0.511I11 outer diameter optical fiber core is completely stripped of its coating (nylon, silicone rubber, etc.) over a length of approximately 5 ctn and this section is cleaned. Next, a bare optical fiber 2 with an outer diameter of 125 μm is
1.22 are inserted into the cladding tube 11 so that they are arranged in parallel. Then, an LD (semiconductor laser) light source 24 is connected to one end of one optical fiber, for example, the optical fiber 21, and both Optical power meters 2 are connected to the other ends of the optical fibers 21 and 22 via photodiodes 25 and 26, respectively.
Connect 7°28. By doing so, the branching ratio can be monitored by comparing the measured values of the optical power meters 27 and 28.

Once each member is arranged in this manner, the fused/stretched portion 30 can be formed by heating the approximately central portion of the cladding tube 11 from the outside using, for example, the 02-H2 burner 23. At this time, the light introduced from the LD light source 24 is
! The signals are branched at a predetermined branching ratio depending on the coupling state in the first extension section 30 and are incident on the photodiodes 25 and 26, respectively, so that the power meters 27 and 28
The stretching operation can be performed to obtain a desired branching ratio while comparing the measured values.

FIG. 4 is a cross-sectional view of the fusion/stretching section 30.

The optical fibers 21 and 22 are fused and stretched to form a coupling portion 31, which is covered with a low refractive index glass portion 32 and a covering portion 33 made of quartz in this order. The reason why the coupling portion 31 is formed without intentionally twisting the optical fibers 21 and 22 is as follows.
This is because the inner diameter of the cladding tube 11 decreases during stretching, and this force acts in a direction that brings the optical fibers 21 and 22 into close contact with each other.

Generally, surface wave energy (Evan
In optical fiber couplers that utilize field coupling of
The two cores must be very close together because they travel through a perpendicular electric field and the surface wave energy decreases exponentially with distance from one core.

Optical fiber coupler (fourth
), the cores 31a, 3 of the coupling part 31 are
By reducing the cross-sectional area of 1b, the electric field of the surface wave spreads far from the core, and by fusing the cladding of the coupling part 31, the core 31a.

31b are close to each other, good optical coupling is achieved.

When a 1:1 (3 dB) coupler was manufactured by the method of the present invention, the outer diameter of the covering portion 33 was approximately 1.7 mm, the diameter of the low refractive index glass portion 32 was approximately 1 mm, and the outer diameter of the coupling portion 31 was approximately 1 mm. The thickness was approximately 20 μm. Considering that the outer diameter of the converging/stretching part consisting only of the force-twisting part in the past was several tens of μm, the optical fiber coupler manufactured by the method of the present invention does not have such a minute part. It can be said that the mechanical strength has improved and handling has become easier. Further, since there is no reduction in insertion loss or fluctuation in branching ratio due to low mechanical strength, it becomes possible to easily manufacture an optical fiber coupler with good characteristics (for example, insertion loss is 1 dB or less).

In the above description, the number of optical fibers in each cladding tube is two, but it goes without saying that the present invention is not limited to this.

Effects of the Invention As detailed above, the l! According to method 43a, it is possible to provide an optical fiber coupler that has a small insertion loss, a stable branching ratio, and is easy to handle.

Further, by using a cladding tube, there is no possibility that impurities will be mixed into the coupling part during fusion bonding and stretching, so it is possible to prevent an increase in loss due to the mixing of impurities.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is a perspective view of a cladding tube that can be used to implement the present invention, and Fig. 3 is an explanation of a method for manufacturing an optical fiber coupler showing an embodiment of the present invention. 4 is a cross-sectional view of the fusion/stretching part shown in FIG. 3, FIG. 5 is a diagram for explaining the conventional general optical fiber coupler (QIN configuration and operation, 1.21.22... Optical fiber, 2.11... Coated tube, 12... Quartz tube, 13.
...Low refractive index glass layer, 30...Fusion/stretching part, 3
1...Coupling part. 1 foot in the row (refer to Figure 5).

Claims (1)

[Claims] In a method for manufacturing an optical fiber coupler in which a plurality of optical fibers arranged in parallel are fused and stretched to each other, the plurality of optical fibers (1) have a refractive index lower than that of their cladding. An optical fiber characterized in that the optical fiber (1) is inserted into a cladding tube (2) having a cladding tube (2) and heated from the outside of the cladding tube (2) to fuse and stretch the optical fiber (1) together with the cladding tube (2). A method of manufacturing fiber couplers.