JPS604902A - Manufacture of optical star coupler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of manufacturing an optical distribution circuit (optical star coupler) that distributes a light beam propagating through an optical fiber to a plurality of optical fibers.

[Background of the invention]

With the rapid progress of optical fiber transmission technology, optical CAT
Research and development of V-networks, optical local area networks, optical computer links, etc., has become active. In configuring these systems, an optical star coupler is an essential device that can mix optical signals from multiple input optical fibers and distribute them evenly and with low loss to multiple output optical fibers. be.

Conventionally, for this type of optical fiber coupling, a large number of optical fibers were bundled together in one place, twisted and fused while being heated, and distributed by forming a tapered region in the center. There is.

However, since the tapered narrow region is stretched by heating and melting until its outer diameter is approximately equal to the outer diameter of a single optical fiber, the central portion tends to become distorted, resulting in a lack of reliability.

Furthermore, since such a narrow diameter stretching technique requires skill, the manufacturing yield is poor and the method is not suitable for mass production. As a method for solving these problems, there is an optical star coupler using a slab waveguide, but there is a problem in that it is difficult to manufacture a slab waveguide with low loss and high dimensional accuracy. Further, in order to reduce distribution variations, the dimensional structure has to be large, and there is also the problem that insertion loss also increases.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing an optical star coupler that has low loss, little distribution variation, and can be mass-produced with high yield.

[Summary of the Invention] The present invention utilizes a gas phase chemical reaction to form a core glass layer with a refractive index higher than that of the glass tube on the inner wall surface of a hollow glass tube containing 8102 as a main component. A glass thin layer, which serves as a cladding with a refractive index lower than the refractive index of the glass, is stretched near the longitudinal center of the glass tube in which one or more sets are formed, so that the cross section of the glass tube in the center becomes dense. The hollow glass tube is constructed in a tapered shape so that it is solid, and the outer diameter of the central core is circular and equal to or larger than the core diameter of the optical fiber, and the circumference at both ends of the hollow glass tube is The present invention relates to a method of manufacturing an optical star coupler in which optical fibers are arranged (anchored) in a circumferential manner around a core glass layer portion formed in a shape.

As described above, in the present invention, since a glass layer through which light propagates is formed using a gas phase chemical reaction, it is possible to realize an optical star coupler with extremely low absorption loss. Since the part interface is formed uniformly, scattering loss is also extremely small.

The biggest feature is that the cross-sectional shape of the central part, which is tapered, gradually transforms from a cylindrical shape to a cylindrical shape, and then gradually returns to a cylindrical shape, and it has a completely symmetrical structure. Therefore, the light emitted from each input optical fiber is mixed with very good uniformity in this portion, and then spreads in the circumferential direction to be evenly distributed and propagated into each output optical fiber. In the conventional method of twisting and fusing an optical fiber bundle to form a tapered region in the center, each optical fiber has a different cross-sectional shape in the cross section of the tapered part, and the cross-sectional shape is different from that of the other. Since the optical fibers have a uniform shape, the optical coupling between the optical fibers also becomes non-uniform, resulting in large distribution variations. In addition, an optical star coupler in which a plurality of optical fibers are coupled to both ends of a slab waveguide has a drawback in that the length 9 width of the slab waveguide must be increased in order to suppress distribution variations as small as possible. Therefore, the present invention is the most suitable optical star coupler structure that can minimize distribution variations.

[Embodiments of the invention]

The first embodiment of the optical star coupler manufacturing method of the present invention is described in the first embodiment.
Illustrated in the figure. Figure (a) is an overview of the optical star coupler.
(b) is a radial cross-sectional view of the portion indicated by arrows A, B, and C in (a), and (C) is an arrow A of the optical waveguide section 2 in (a).

This figure shows the circular refractive index distribution in the radial cross section of the portions indicated by B and C. 1 is an input optical fiber bundle, 4 is an output optical fiber bundle, 3 is a tapered part of the optical waveguide 2, and this part is a region where light is mixed and divided into two parts, 5 is a 5j02't
:'Glass tubes as main components (e.g. quartz glass tubes,
A Vycor glass tube or a glass tube with a cladding glass layer formed on the inner wall of the glass tube, and this portion functions as a cladding layer. ), 6 is a light propagation glass layer (
The thickness of the glass layer is determined by the thickness of each optical fiber in the input optical fiber bundle 1 (one optical fiber in the bundle is designated as 1') in order to reduce loss at the connection part. It is set to a value approximately equal to the core diameter of. Reference numeral 7 denotes a thin glass layer for cladding having a refractive index lower than that of the core layer 6, and its thickness is selected from a range of several μm to 20-odd μm. Numeral 8 is a cladding portion, and numeral 9 is a core portion for light propagation, which has a solid rondo shape. This core portion is circular and its diameter is equal to or larger than the core diameter of the optical fiber. This diameter and the length of the region of the tapered portion 3 are important parameters for equally distributing light. That is, the smaller the diameter and the longer the tapered area, the more effective it is.

Reference numeral 10 denotes a cladding portion obtained by solidifying and stretching the thin glass layer 7 for cladding, and the diameter thereof is set to be a few micrometers or less, preferably a few micrometers in diameter. 4' is one optical fiber in the output optical fiber bundle 4. Next, the operation of this optical star coupler will be explained. The light emitted from the optical fiber (for example, 1') in the input optical fiber bundle 1 enters the core layer 6 of the optical waveguide 2 and propagates in the axial direction of the optical waveguide 2 (from the left side in the figure). right direction). The light then propagates within the core portion 9 as it propagates from the tapered portion to the central portion. Then, conversely, as the light propagates from the central part to the tapered part, the light spreads evenly in the circumferential direction, propagates within the core layer 6, and obtains an optical signal that is evenly distributed to each output optical fiber. It will be done. Similarly, the light emitted from the other input optical fibers is equally distributed. The reason why it is distributed equally in this way is that it is continuously deformed from a cylindrical shape to a cylindrical shape, and then continuously deformed from a cylindrical shape to a cylindrical shape again. Moreover, these deformations are performed completely symmetrically, and the resulting structure is also symmetrical.

FIG. 2 shows an embodiment of the method for manufacturing the optical waveguide section 2. As shown in FIG. The same figure (a) is a stage before heating and stretching the glass tube 11 on which the glass layer 6.7 is formed, (b) is a side sectional view of the glass tube 11, (C) is heating the glass tube 11,
The figure shows the shape after stretching.

The glass layer 6.7 can be formed on the inner wall surface of the glass tube by a conventional optical fiber base material manufacturing method (internal CVD method). That is, a glass tube is mounted on a glass lathe and rotated, and Ar is introduced into the tube from one end of the glass tube while heating it with a heat source that moves back and forth along the axial direction of the glass tube.

A glass layer can be deposited by introducing frit gas together with 02. First, in (a), while heating the glass tube 11 with a heating source 13 (usually a resistance heating furnace, high frequency induction heating furnace, oxyhydrogen burner, propane, city gas φ burner) Stretch by applying tensile force in one direction or in both directions simultaneously. As a result, it is possible to create an optical waveguide 2 having a tapered region 3 near the center as shown in (C).

FIG. 3 shows another embodiment of the optical waveguide section of the present invention. (a) is a glass tube on which glass layers 6 and 7 are formed 1), (b) is a cross-sectional view of an optical waveguide obtained by heating the central part 14 of the glass tube and stretching it into a tapered shape, (C)
2 shows the radial refractive index distribution in the cross section taken along arrows A, B, and C of the optical waveguide in FIG. A feature of this optical waveguide is that, as shown in FIG. 1(b), there is no cladding portion (10 in FIG. 1(b)) at the center of the radial cross section near arrow B. As a result, uniform light distribution is realized. To make this optical waveguide, (a
), the cladding glass layer 7 may be formed so that the thickness of the glass layer becomes gradually thinner from both ends of the glass tube toward the center portion 14. These two methods of formation are easily achieved by conventional internal CVD methods.

FIG. 4 shows another embodiment of Mitsuo Moto's optical star coupler. (a) is an axial cross-sectional view of the optical star coupler, (b) is a radial direction of the portions indicated by arrows A, B, and C in (a),
Vr plane view, (C) shows arrows A and B of the optical waveguide in (a).

This figure shows the radial cross-sectional circular refractive index distribution of the portion indicated by C. This connects the optical fiber to the first core glass 116
This optical star coupler has a structure in which 20 optical star couplers are arranged concentrically on the top and 12 on the second core glass layer 15. 7 is a first cladding glass layer, 16 is a second cladding glass layer, and their refractive indexes are set, for example, as shown in (C).

That is, it only needs to be lower than the refractive index of the core glass layer, and may be equal to or different from the refractive index of the glass tube 5. In the radial cross section of the portion indicated by the arrow B in FIG. 3(b), the optical fiber has a stepped optical fiber configuration consisting of a core portion 18 and a cladding portion 17.

Then, for example, one of the input optical fiber bundles 1
The light emitted from the main optical fiber 1' is equally distributed into each optical fiber of the output optical fiber bundle 4. Similarly 1"
The light emitted from the optical fiber is also equally distributed into the output optical fiber. It can be seen that by arranging optical fibers in multiple concentric circles in this manner, an optical star coupler with a large distribution number can be realized with a small size and simple structure.

As described above, since the optical star coupler manufactured by the manufacturing method of the present invention has a cylindrical or cylindrical shape that allows light to propagate most easily, mixing and distribution conversion of light can be easily performed. Therefore, there is almost no distribution variation. In addition, it is easy to mass-produce without the poor manufacturing yield and difficulty of processing unlike conventional optical star couplers obtained by adding a screw υ to an optical fiber, fusing it, and stretching it. Furthermore, it can be significantly smaller than conventional slab waveguide type optical star couplers, and is also superior in terms of distribution variation and insertion loss.

The invention is not limited to the above embodiments. For example, the glass tube 5 may be a multi-component glass tube (eg, Bilex). The refractive index of the core portion and the cladding portion may have a gentle distribution other than a flat characteristic. Hollow part 1 of hollow glass tube
9 may be filled with any material (for example, glass, polymeric material, metal, etc.) and made solid. The numbers of input and output optical fibers may not be equal.

Furthermore, in FIGS. 1 and 4, if the central part indicated by arrow B is cut in the radial direction and an optical fiber is connected to the cut surface of the cut optical waveguide section 2, 1 pair n (n; output light (number of fibers) can be made into an optical coupler.

〔Effect of the invention〕

The method of the present invention has the following effects.

(1) The cross-sectional shape of the central part, which is tapered, is gradually converted from a cylindrical shape to a cylindrical shape, and then gradually returns to the cylindrical shape each time, and it has a completely symmetrical structure. , the light emitted from within each input optical fiber is evenly distributed into each output optical fiber.

(2) Since a glass layer through which light propagates is formed using a gas phase chemical reaction, an optical star coupler with extremely low absorption loss and low scattering loss can be realized.

(3) Compared to conventional methods, it is smaller, simpler, and easier to process;
It is also easy to mass produce.

[Brief explanation of drawings]

No. 11, FIG. 4 is an embodiment of the optical star coupler of the present invention,
FIG. 2 shows an actual example of the method for using the optical waveguide section of the optical star coupler of the present invention, and FIG. 3 shows another embodiment of the optical waveguide section of the optical star coupler of the present invention. 1... Input optical fiber bundle, 2... Optical waveguide, 3.
3'...Tapered part of optical waveguide section, 4...Output optical fiber bundle, 5...Hollow glass tube, 6.15...Glass layer for core, 7.16...Glass for cladding layer, 8, 1
0.17...Clad part, 9.18...Core part, 1
1... Hollow glass tube with a glass layer formed, 12.1
2'...Direction of applying tension, 13...Heating source, 14...Central part of hollow glass tube, 1', 1"4'
, 4//...-271 Figure 22 Qλn (b) 3rd mouth A.

Claims (1)

[Claims] A glass layer that serves as a core with a refractive index higher than that of the glass tube on the inner wall surface of a hollow glass tube whose main component is 1.5IOz, and a glass layer that serves as a cladding with a refractive index lower than that of the glass layer on top of that glass layer. An optical star cube characterized in that a glass tube having one set or a plurality of layers formed thereon is tapered so that the longitudinal center portion of the glass tube is extended so that the cross section of the glass tube at the center portion is solid. 2. Manufacturing method. 2. In the method for manufacturing an optical star coupler according to claim 1, the thickness of the glass layer is gradually reduced from both ends of the hollow glass tube toward the center. A method for manufacturing an optical star coupler, characterized in that it is formed as follows. 3. A method of manufacturing an optical star coupler, which comprises cutting the tapered central portion of the optical star coupler described in claim 1 and connecting an optical fiber to the cut portion.