JP2007293097A - Y-branched optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Y-branched optical waveguide that facilitates manufacturing while practical branching efficiency is secured. <P>SOLUTION: The Y-branched optical waveguide 10 branches light propagating in one input waveguide 11 into two directions by two branching waveguides 12a, 12b. The branched tip end part 13 held between the two branching waveguides 12a, 12b is provided with a stepped structure comprising a tip end face 13a vertical to the longitudinal direction of the input waveguide 11, a side face 13b orthogonal to the tip end face 13a, and a bottom face 13c orthogonal to the side face 13b, wherein the width d<SB>1</SB>of the tip end face 13a is made wider than the width D of the input waveguide 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a Y-branch optical waveguide used for optical communication and the like.

  Conventionally, as shown in FIG. 4A, a Y-branching optical waveguide that branches light propagating through one input waveguide 91 provided in parallel with the X direction in two directions by two branching waveguides 92a and 92b ( A splitter 90 is known in which the shape of a branch tip 93 sandwiched between two branch waveguides 92a and 92b is a wedge shape. The smaller the branch angle θ is, the better the branching efficiency is. However, the manufacture of a Y-branch optical waveguide having a small branch angle θ and a sharply branched branch tip 93 is accompanied by technical difficulties. In addition, there is a large variation in product characteristics when manufactured.

  In order to solve such a problem, as shown in FIG. 4B, a Y-branch optical waveguide 90A having a branching tip 94 having a flat surface perpendicular to the incident direction, or an input waveguide 91 as shown in FIG. 4C. There is known a Y-branch optical waveguide 90B having a branching tip portion 95 provided with a substantially rectangular projection 95a projecting toward (see, for example, Patent Literature 1 and Non-Patent Literature 1).

  However, the Y-branch optical waveguide 90A having the structure shown in FIG. 4B has a problem that the branching efficiency is lowered. Moreover, it becomes easy to become a radiation mode by the reflected light by the flat surface orthogonal to an incident direction.

On the other hand, in the Y-branch optical waveguide 90B having the structure shown in FIG. 4C, the width of the protrusion 95a must be narrowed. For this purpose, a Y-branch optical waveguide having a sharp branching tip 93 having a small branching angle θ is included. As with manufacturing, there are technical difficulties in manufacturing.
JP2003-185867A (FIG. 6 etc.) Shinnosuke Sawa, Tetsuro Tsuji, Hirohito Mase, Masatsugu Shimodai, “Reducing Loss of New Structure Low Loss Y-Branch Optical Waveguide by Optimization Method”, IEICE Technical Report, (1997), LQE-97 ~ 100

  The present invention has been made in view of such circumstances, and an object thereof is to provide a Y-branch optical waveguide that is easy to manufacture while ensuring practical branching efficiency.

  According to the present invention, when a three-dimensional optical waveguide is viewed as a two-dimensional slab waveguide, Y-branched light that branches light propagating through one input waveguide in two directions by two branch waveguides. A branch tip portion sandwiched between the two branch waveguides includes a tip surface perpendicular to the longitudinal direction of the input waveguide, a side surface orthogonal to the tip surface, and a bottom surface orthogonal to the side surface. And a Y-branch optical waveguide characterized in that the width of the tip end face is wider than the width of the input waveguide.

  In practice, the definition of an optical waveguide having a three-dimensional structure as a two-dimensional slab waveguide is a technique used by those skilled in the art for convenience of calculation, and even when viewed as two-dimensional, The characteristics of the optical waveguide can be sufficiently grasped (for example, see “Tetsuro Tsuji, Shinnosuke Sawa,“ Analysis Method of Optical Waveguide ”, Optics (1998), Vol. 27, No. 11, pp 632-639)).

  In this Y branch optical waveguide, the width of the input waveguide is 4 μm to 6 μm, the width of the branch tip is 8 μm to 12 μm, the length of the branch tip is 10 μm to 350 μm, and the branch angle of the two branch waveguides is 1. It is preferable to set it at 8 degrees to 5.0 degrees.

  Further, according to the present invention, when a three-dimensional optical waveguide is viewed as a two-dimensional slab waveguide, the Y-branch branches light propagating through one input waveguide in two directions by two branch waveguides. An optical waveguide having a branching tip portion sandwiched between the two branching waveguides, a tip surface perpendicular to the longitudinal direction of the input waveguide, a side surface orthogonal to the tip surface, and a right angle to the side surface The input waveguide has a width of 4 μm to 6 μm, the tip surface has a width of 2 μm to 4 μm, the side surface has a length of 10 μm to 200 μm, and the two branch waveguides have a bottom surface. A Y-branch optical waveguide having a branching angle of 1.6 degrees to 2.0 degrees is provided.

  These Y branch optical waveguides are preferably used for branching and propagating light having a wavelength of 1.50 μm to 1.60 μm.

  The Y-branch optical waveguide of the present invention is easy to manufacture while ensuring practical branching efficiency. In particular, when compared with a conventional shape having a flat branch tip, a high branching efficiency can be obtained when the position of the branch tip is the same.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic structure of a Y branch optical waveguide. This Y-branch optical waveguide 10 includes one single-mode input waveguide 11 having a width D and two branch waveguides 12a that branch light propagating through the input waveguide 11 in two directions at a branch angle θ. , 12b. These input waveguide 11 and branching waveguides 12a and 12b are core portions, and the other portions are clad portions.

  1 is shown in a plan view, the actual Y-branch optical waveguide 10 has a thickness in a direction perpendicular to the paper surface. As shown in FIG. 1, the light propagation direction of the input waveguide 11 is assumed to be the X direction. Further, in FIG. 1, the branch waveguides 12a and 12b branched into Y-shapes are respectively parallel to the X direction thereafter, which reflects the structure of the Y-branch optical waveguide used for the BPM calculation described later. It is a thing.

  A step-shaped branch tip 13 is formed at the tip of the triangular portion 15 sandwiched between the two branch waveguides 12a and 12b.

The branch tip 13 includes a plane including sides P ₁ -P ₂ orthogonal to the X direction, which is the light propagation direction of the input waveguide 11 (hereinafter referred to as “tip plane”, and indicated by reference numeral “13a” in FIG. 1). And a plane orthogonal to the side P ₁ -P ₂ (hereinafter referred to as “side surface”, indicated by reference numeral “13b” in FIG. 1), and an inner wall 14a of each of the branched waveguides 12a and 12b orthogonal to the side surface. , 14b (hereinafter referred to as “bottom surface” and indicated by reference numeral “13c” in FIG. 1). Points P ₁ and P ₂ are on extensions of the inner walls 14a and 14b, respectively.

Width _{d 1} of the distal end surface 13a is defined by the length of the side _P 1 -P _2. The length L ₁ of the side surface 13b is defined by its X-direction length.

In the Y branch optical waveguide 10, the width d ₁ of the tip surface 13 a is made wider than the width D of the input waveguide 11. That is, the D _{<d 1.} As a result, manufacturing can be facilitated and desired branching efficiency can be obtained without any practical problems. In particular, the X-direction position of the tip surface 13a with reference to the end point position (X-direction end point) of the input waveguide 11 is based on the end point position of the input waveguide 91 in the Y-branch optical waveguide 90A shown in FIG. 4B. When the position is the same as the position in the X direction of the front end surface of the branch front end portion 94, the branching efficiency can be increased.

Specifically, in the Y branch optical waveguide 10, when the branch angle θ is 1.8 degrees to 5.0 degrees (°) and the width D of the input waveguide 11 is 4 μm to 6 μm, the width of the distal end surface 13a. It is preferable that d ₁ is 8 μm to 12 μm, and the length L ₁ of the side surface 13 b is ₁₀ μm to 350 μm. In the case of such a shape, the wavelength of light incident on the single mode input waveguide 11 is preferably 1.50 μm to 1.60 μm, and high branching efficiency can be obtained.

FIG. 2 shows a schematic structure of another Y-branch optical waveguide 10A. That the Y branch optical waveguide 10A is different from the Y branch optical waveguide 10 shown in FIG. 1 is narrower than the width D of the width d ₂ is the input waveguide 11 of the front end surface 13a of the branch tip 13, i.e. , D> d _2, and due to such a shape, there is a limitation on the shape in order to obtain a desired branching efficiency.

  In the Y branch optical waveguide 10A, the position in the X direction of the distal end surface 13a of the branch distal end portion 13 when the end point position of the input waveguide 11 is used as a reference is the same as that of the input waveguide 91 in the Y branch optical waveguide 90A shown in FIG. 4B. From the Y-branch optical waveguide 90A, when the end point position is the same as the position in the X direction of the distal end surface of the branch distal end portion 94 and the branch angle θ is as small as 1.6 ° to 2.0 °. Can also increase the branching efficiency. However, for example, when the branch angle θ is as large as 5 °, the branching efficiency is lower than that of the Y-branch optical waveguide 90A. Although this cause is not certain, it is presumed that the radiation efficiency is likely to be caused by the bottom surface 13c of the branch tip portion 13 of the Y-branch optical waveguide 10A, thereby reducing the branching efficiency.

In the Y branch optical waveguide 10A, when the branch angle θ is 1.6 ° to 2.0 ° and the width of the input waveguide is 4 μm to 6 μm, the width d ₂ of the tip surface 13a is ₂ μm to 4 μm and the side surface 13b the length _{L 2} to 10 m to 200 m. Also in the Y branch optical waveguide 10A, the wavelength of light incident on the input waveguide 11 is preferably 1.50 μm to 1.60 μm.

  For the Y-branch optical waveguides 10 and 10A having the above-described structure, calculation was performed by a two-dimensional beam propagation method (BPM) when the relative refractive index difference (Δ) was 0.476%. This calculation is a two-dimensional slab waveguide calculation, but reproduces the optical branching characteristics of a three-dimensional optical waveguide well.

The relative refractive index difference (Δ) of 0.476% is a numerical value of the level of the relative refractive index difference of a normal rectangular waveguide. For the BPM calculation, OptiBPM manufactured by Optiwave, which is BPM calculation software, was used. In setting the calculation parameters, the width D of the input waveguide 11 is 5 μm, the refractive index n ₁ of the core portion is 1.467, and the refractive index of the cladding portion is n ₂ = 1.460. Set. Further, the branch angle θ was set to 1.8 ° and 5.0 °. The incident light was TE-polarized light (that is, the direction of the electric vector was perpendicular to the paper surface), and its wavelength was 1.55 μm.

  If the input waveguide 11 and the branch waveguides 12a and 12b are set as shown in FIG. 1, the width of the branch waveguides 12a and 12b is narrower than the width of the input waveguide 11 before branching. Since θ is small, it is approximately the same as the width D of the input waveguide 11.

Under such conditions, in the BPM calculation, calculation models were set in which the widths d ₁ and d ₂ of the tip surface 13a of the branch tip 13 and the lengths L ₁ and L ₂ of the side surface 13b were variously changed. For comparison, a Y-branch optical waveguide 90 having the structure shown in FIG. 4A (Reference Examples 1 and 2; width d ₁ = 0 μm, length L ₁ = 0 μm), and a Y-branch optical waveguide having the structure shown in FIG. 4B The same calculation was performed for 90A (Comparative Examples ₁ to 3, 5; length L ₁ = 0 μm). This calculation result is a value in a portion parallel to the X direction of each of the branched waveguides 12a and 12b branched in a Y shape as shown in FIGS. 1 and 2 in all calculation models.

  The results are shown in Table 1. The “branching efficiency” in Table 1 indicates the ratio of the power of the light that is branched into the branching waveguides 12 a and 12 b and propagates in the single mode with respect to the power of the propagation light in the single mode incident on the input waveguide 11. If the structures of the branch waveguides 12a and 12b are the same, the branch efficiencies of the branch waveguides 12a and 12b are also the same, and ideally 0.5 (50%) when there is no loss. In this setting, the branching waveguides 12a and 12b have the same structure.

The “efficiency improvement ratio” is represented by the ratio of the branch efficiency of each calculation model to the branch efficiency of each of Comparative Examples 1 to 3 and 5 when the input / branch waveguide width, the tip width, and the branch angle are the same.

  As shown in Table 1, the Y-branch optical waveguide 90 having the structure shown in FIG. 4A has branch angles θ of 1.8 ° and 5.0 ° as shown in the results of Reference Examples 1 and 2. In any case, it can be seen that the branching efficiency is larger than that of other calculation models having the same branching angle θ. However, as described above, the manufacture of the Y-branch optical waveguide 90 is not easy.

As is clear from the comparison between Comparative Example 1 and Example 1, when the branch angle θ is 1.8 ° and the width of the branch tip 13 is 3 μm (= d ₂ ), Example 1 (Y-branch optical waveguide) The branching efficiency of 10A) is slightly improved as compared with Comparative Example 1 (Y-branch optical waveguide 90A).

Comparing Comparative Example 2 and Example 2, when the branch angle θ is 1.8 ° and the width of the branch tip 13 is 10 μm (= d ₁ ), Example 2 (Y-branch optical waveguide 10) Is improved to 1.54 times that of Comparative Example 2 (Y-branch optical waveguide 90A).

  Comparative Example 3 (Y-branch optical waveguide 90A) has a structure in which the branching angle θ is 5 ° with respect to Comparative Example 1, while Comparative Example 4 has a branching angle θ of 5 with respect to Example 1. However, the branching efficiency is lower than that of Comparative Example 3. This is presumably because the radiation mode increases because the area of the bottom surface of the stepped branch tip increases as the branch angle θ increases.

  As is apparent from the efficiency improvement ratios of Examples 3 to 5 (Y branch optical waveguide 10) with respect to Comparative Example 5 (Y branch optical waveguide 90A), the branch efficiency is about a maximum by making the branch tip portion stepped. It was confirmed that it improved by 1.9 times. It can be seen that Examples 3 to 5 have excellent characteristics that a branching efficiency greater than that of Comparative Example 2 in which the branching angle θ is 1.8 ° can be obtained while the branching angle θ is 5 °. In particular, Example 4 shows a high branching efficiency close to that of Reference Example 2.

  As described above, the step of the branch tip is not only when the branch angle θ is as small as 1.8 ° but also when the branch angle θ is as large as 5 ° as compared with the structure having a branch structure with a flat tip. Is also effective.

  The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the invention described in the claims.

  For example, the input waveguide and the branch waveguide constituting the Y branch optical waveguide are not limited to linear ones as shown in FIGS. Specifically, even in a structure having a structure in which the end portion of the input waveguide 11 is widened like the Y-branch optical waveguide 10B shown in the plan view of FIG. 3A, it is formed by the branching waveguides 12a and 12b. The branch tip 13 can be stepped. Further, even if the branch waveguides 12a and 12b are curved like the Y-branch optical waveguide 10C shown in the plan view of FIG. 3B, the branch tip portion 13 can be stepped.

  Further, the branch tip portion 13 may have a plurality of steps. For example, when the branching tip 13 of the Y-branch optical waveguide 10 shown in FIG. 1 is deformed into a plurality of steps, separate side surfaces parallel to the X direction from the inner side walls 14a, 14b side end of the bottom surface 13c, respectively. And another bottom surface orthogonal to the side surface may be formed, and the number of steps may be further increased in the same manner.

The top view which shows the structure of a Y branch optical waveguide. The top view which shows the structure of another Y branch optical waveguide. The top view which shows the structure of another Y branch optical waveguide. The top view which shows the structure of another Y branch optical waveguide. The top view which shows the structure of the conventional Y branch optical waveguide. The top view which shows the structure of another conventional Y branch optical waveguide. Plan view showing the structure of yet another conventional Y-branch optical waveguide

Explanation of symbols

  10, 10A, 10B, 10C ... Y branch optical waveguide, 11 ... input waveguide, 12a, 12b ... branch waveguide, 13 ... branch tip, 13a ... tip surface, 13b ... side surface, 13c ... bottom surface, 14a, 14b ... Inner side wall, 15 ... triangular part, 90, 90A, 90B ... Y branch optical waveguide, 91 ... input waveguide, 92a, 92b ... branch waveguide, 93,94,95 ... branch tip, 95a ... projection.

Claims (4)

A Y-branch optical waveguide that splits light propagating through one input waveguide in two directions by two branch waveguides when the three-dimensional optical waveguide is viewed as a two-dimensional slab waveguide,
A branch tip portion sandwiched between the two branch waveguides has a staircase having a tip surface perpendicular to the longitudinal direction of the input waveguide, a side surface orthogonal to the tip surface, and a bottom surface orthogonal to the side surface. Formed into a shape,
A Y-branch optical waveguide characterized in that a width of the front end face is wider than a width of the input waveguide.   The width of the input waveguide is 4 μm to 6 μm, the width of the branch tip is 8 μm to 12 μm, the length of the branch tip is 10 μm to 350 μm, and the branch angle of the two branch waveguides is 1.8 degrees to The Y-branch optical waveguide according to claim 1, wherein the angle is 5.0 degrees. A Y-branch optical waveguide that splits light propagating through one input waveguide in two directions by two branch waveguides when the three-dimensional optical waveguide is viewed as a two-dimensional slab waveguide,
A branch tip portion sandwiched between the two branch waveguides has a staircase having a tip surface perpendicular to the longitudinal direction of the input waveguide, a side surface orthogonal to the tip surface, and a bottom surface orthogonal to the side surface. Formed into a shape,
The input waveguide has a width of 4 μm to 6 μm, the tip surface has a width of 2 μm to 4 μm, the side surface has a length of 10 μm to 200 μm, and the branch angle of the two branch waveguides is 1.6 ° to 2.0 °. A Y-branch optical waveguide characterized in that   The Y-branch optical waveguide according to any one of claims 1 to 3, wherein a wavelength of light introduced into the input waveguide is 1.50 µm to 1.60 µm.

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