JP2006039080A - Optical branch waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical splitter having a small loss over a broadband to be used for FTTH, etc. and a constant branch ratio without going through complicated production processes. <P>SOLUTION: Optical branch elements having refractive index different from a core are provided inside the core of the tapered optical waveguide, using an optical waveguide 10 and two optical guides 20 connected in Y with an optical branch waveguide through a tapered optical guide 30. This optical branch elements are preferably a triangule 52, a rectangule 53, a polygon, a round shape 54, or oval islands separated from one another or a island 55 all connected together. A multistep optical branch waveguide can be obtained by connecting those optical branch waveguides in multiple stages. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical waveguide used in the field of optical communication, and more particularly to a branched optical waveguide that branches light propagating through one optical waveguide into a plurality of optical waveguides.

  In the optical communication field, an optical splitter that is an optical element that splits the power of light propagating in one optical path into a plurality of optical paths is required. Conventionally, an optical fiber splitter in which two or more optical fibers are fused is used, but an optical splitter using a flat optical waveguide is also known. As this optical waveguide type splitter, as shown in FIG. 5, a Y-branch type (FIG. 5A) using a Y-shaped optical waveguide, a directional coupler type (FIG. 5B), a multimode An interference type ((c) in the figure) has been proposed.

  In general, the directional coupler type and the multimode interference type are highly wavelength dependent. Therefore, the loss is kept small over the entire band (1.26 to 1.56 μm) of the communication wavelength used for optical communication between the station and the subscriber, so-called fiber-to-the-home (FTTH), It is difficult to keep the branching ratio constant. On the other hand, the Y-branch type can provide a splitter that is small in wavelength dependency and suitable for FTTH.

  In the Y-branch type, as shown in FIG. 6A, one optical waveguide 10 is branched into two optical waveguides 20 via a tapered optical waveguide 30, but the branching angle θ is made as small as possible. If possible, the loss can be reduced and the wavelength dependence can be reduced. However, it is difficult to reproduce the narrow and sharp shape of the branching clad tip 22, and in fact, it becomes a blunt tip 24 as shown in FIG. 6B, and this shape also tends to vary. For this reason, the occurrence of a certain amount of loss is inevitable, and it is difficult to make the branching ratio constant among a plurality of elements.

As a method for reducing this loss, the following methods (A) to (D) are proposed, and the effect of reducing the loss is obtained.
(A) A multi-mode waveguide is provided at the branch (see, for example, Patent Document 1).
(B) A mode coupling is introduced into the branching section (see, for example, Patent Document 2).
(C) A phase accelerator is provided at the branch (see, for example, Patent Document 3).
(D) A diffraction grating is provided at the branch (see, for example, Patent Document 4).
JP-A-9-212244 JP-A-9-265018 JP-A-8-327836 Japanese Patent Laid-Open No. 9-325226

  However, the wavelength dependency is increased by introducing the methods (A) to (D). Therefore, these means cannot solve the problems of improving the uniformity of the branching ratio and reducing the loss and the problem of reducing the wavelength dependence at the same time, and are insufficient for FTTH using a wide wavelength band.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a splitter having a low loss and a constant branching ratio over a wide band without a complicated manufacturing process.

  In the present invention, a branched optical waveguide in which one optical waveguide and two optical waveguides are connected in a Y shape by a tapered optical waveguide is used. Different light splitting structures are provided.

  By introducing the light splitting structure, it is possible to prevent an increase in loss affected by the shape of the tip of the branching clad and to reduce the variation in the branching ratio. Further, since this means utilizes the effect of refraction, the wavelength dependency is small and it can be used in a wide wavelength range.

It is preferable that the light splitting structure has a triangular shape, a quadrangular shape, a polygonal shape, a circular shape, or an elliptical shape that are separated from each other or connected to each other.
The shape of the light splitting structure is not particularly limited. However, with the above shape, the traveling direction of the light beam is simple, and the structure design of the optical waveguide is facilitated.

The branch optical waveguide can be connected in multiple stages.
According to the present invention, a Y-branch optical waveguide with low loss and small variation in branching ratio can be obtained. Therefore, even when this is connected in multiple stages to form a multi-branch optical waveguide, a large number of loss is small and the branching ratio is stable. A branched optical waveguide can be provided.

  Since the means of the present invention is based on the refraction phenomenon, a branching optical waveguide having a uniform branching ratio and a small insertion loss over a wide wavelength range can be realized, and a splitter using this can be provided.

Embodiments of the present invention will be described below.
FIG. 1 shows the basic principle of the present invention. A light beam 100 traveling in a medium having a constant refractive index n1 causes a light splitting structure 50 (hereinafter abbreviated as a structure) having a refractive index n2 different from the medium to be inclined with respect to its end face. When passing, refraction occurs due to the difference in refractive index between the medium and the structure. By appropriately disposing the structure with respect to the traveling direction of the light beam, the traveling direction of the light beam can be divided into two on both sides of the structure. FIG. 1A shows an example of arrangement of structures when n1> n2, and FIG. 1B shows an example of arrangement of structures when n1 <n2. In any case where there is a difference in refractive index, the traveling direction of the light beam can be divided into two.

  In the present invention, the above principle is applied, and a light splitting structure having an effect of dividing the propagating light into two is arranged in the tapered waveguide 30 of the Y branch optical waveguide as shown in FIG. Since the optical waveguide is originally composed of a core and a clad having different refractive indexes, it is easy to introduce a structure having a refractive index different from that of the core. Due to the presence of this structure, even if “blunt” occurs at the tip of the branch cladding, it does not lead to an increase in loss, and a low-loss Y-branch optical waveguide can be obtained.

  In general, in order to reduce wavelength dependency and temperature dependency, optical waveguides often use the same material (for example, quartz and polymer materials) for the core and cladding, and the wavelength changes. However, the refractive index difference Δn between the core and the clad is designed so as to hardly change. For this reason, this method using refraction has less wavelength dependency than the conventional loss reduction method, that is, a method using phenomena such as interference, mode coupling, and diffraction.

  As the shapes of the structures 52, 53, and 54, as shown in FIGS. 2A to 2C, a triangle, a quadrangle, a circle, or the like can be used, and a polygon or an ellipse between these can also be used. . Furthermore, the effect is more easily exhibited when a plurality of these structures are arranged. These may be arranged in islands separated from each other, but may be arranged structure bodies 55 connected to each other as shown in FIG. It is desirable to select an optimal arrangement according to each shape.

  Table 1 shows the calculated values of loss when the rectangular (diamond) structure 56 shown in FIG. 3B is arranged separately from the Y-branch optical waveguide shown in FIG. Yes. In the calculation, as shown in FIG. 5A, the blunting of the branching clad tip 26 is assumed to be a case where there is a flat portion having a width W, but by providing a structure, an ideal case where there is no blunting ( It can be seen that the loss can be further reduced (when W = 0). Even when the apex of the structure is dull or when a triangular or circular structure is used, the same level of loss can be reduced by optimizing the number and interval of the structures.

  By connecting Y branch optical waveguides in multiple stages, a 1 × 4, 1 × 8, 1 × 16, 1 × 32, etc. multi-branch optical splitter can be configured. FIG. 4 shows an example in which an 8-branch optical splitter is configured by connecting seven Y-branch optical waveguides of the present invention. In such a case, the small loss of each Y branch optical waveguide is extremely important in order to suppress an increase in loss due to the cascade connection of a plurality of branch optical waveguides. Also, the small variation in the branching ratio of each Y branching optical waveguide is extremely important for obtaining a desired branching ratio when multi-branching. Therefore, it can be said that the Y-branch optical waveguide of the present invention is suitable for multistage.

It is a figure explaining the principle of a light splitting structure. It is a schematic diagram which shows the Example of the branch optical waveguide of this invention. It is a schematic diagram which shows the example of the branch optical waveguide used as a calculation model. It is a figure which shows an example of a structure of the multi-branch optical splitter of this invention. It is a figure which shows the structural example of the conventional optical splitter. It is a figure which shows the problem of the conventional Y branch optical waveguide.

Explanation of symbols

10, 20 Optical waveguide 30 Tapered optical waveguide 50, 52, 53, 54, 55, 56 Light splitting structure 100 Light beam

Claims (3)

  In a branched optical waveguide in which one optical waveguide and two optical waveguides are connected in a Y shape by a tapered optical waveguide, an optical splitting structure having a refractive index different from that of the core in the core of the tapered optical waveguide A branched optical waveguide characterized by comprising:   2. The branched optical waveguide according to claim 1, wherein the light splitting structure has a triangular shape, a quadrangular shape, a polygonal shape, a circular shape, or an elliptical shape, which are islands separated from each other or connected to each other. A branched optical waveguide, wherein the branched optical waveguide according to claim 1 is connected in multiple stages.

Images