JP2007171769A - Optical multiplexing waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical multiplexing waveguide that makes reduction of leaked light possible in a merging section and that needs no extension of a waveguide length. <P>SOLUTION: The optical multiplexing waveguide is provided with two optical waveguides 31, 32 on the input side and one optical waveguide 33 on the output side that is merged into the optical waveguides 31, 32. The optical waveguide 32 on the input side is coupled with the end of the optical waveguide 33 on the output side in a coupling section 35, while the optical waveguide 31 on the input side is coupled with an inner part from the end of the optical waveguide 33 on the output side in a coupling section 34. The two optical waveguides 31, 32 on the input side can each employ an S-shaped bend waveguide which is formed by coupling two circular arcuate shapes in point symmetry, wherein the radius of curvature of the optical waveguide 32 is made smaller than that of the optical waveguide 31. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical multiplexing waveguide, and more particularly to an optical multiplexing waveguide in which an optical multiplexing section is generally Y-shaped.

  The optical multiplexing waveguide is used as one of basic components constituting, for example, an optical wavelength division multiplex transmission device or an optical integrated circuit. 2. Description of the Related Art Conventionally, as one form of optical multiplexing waveguide, there has been a generally Y-shaped (hereinafter simply referred to as Y-shaped) combining waveguide that guides two waveguides formed by symmetrically joining waveguides having an arc shape to the waveguide after joining. is there. When the cause of the loss of this Y-shaped optical multiplexing waveguide is examined, the leakage light at the waveguide junction is mostly occupied. This will be described with reference to FIG.

FIG. 1 is a diagram illustrating an example of a merging portion in a Y-shaped optical multiplexing waveguide. As shown in the drawing, the Y-shaped optical multiplexing waveguide has two waveguides 11 and 12 and a post-merging waveguide 13. A tapered portion 14 is formed at the junction where the two waveguides 11 and 12 intersect. Here, for example, when the propagating light 15 enters the tapered waveguide wall from the waveguide 11 at an incident angle θ, when the propagating light 15 exceeds the reflection critical angle of the waveguide wall, leakage light due to the leakage mode occurs, This is a loss. Therefore, in the Y-type optical multiplexing waveguide, reducing the incident angle θ contributes to a reduction in loss. In addition to this, various measures have been taken to reduce the loss of the Y-shaped optical multiplexing waveguide. For example, as a method of reducing the leakage light in the waveguide junction, there is a method in which the slope of the waveguide near the junction (branch point) is asymptotic to zero. Is a shape based on a raised cosine function. Similarly, in order to reduce the angle formed by the two input side waveguides at the junction, an S-shaped bend in which arc-shaped waveguides are joined point-symmetrically or a sinusoidal shape has been used.
Japanese Patent No. 2589367

  However, the reduction of leakage light at the junction in the Y-type optical multiplexing waveguide is still not sufficient. As a method of reducing the angle formed by the two input side waveguides at the junction, it can be realized by forming the two input side waveguides by arc-shaped waveguides and increasing their curvature radii. However, in this method, it is possible to reduce the leakage light, but the waveguide needs to be extended, resulting in an increase in size, or a taper formed by two input-side waveguides at the junction. There is a problem that the shape of the tip of the part becomes more acute and difficult in the manufacturing method, and the roundness or the defect of the tip of the tapered part increases the loss of propagating light.

  Accordingly, an object of the present invention is to provide an optical multiplexing waveguide that can reduce the leakage light at the junction and does not require extension of the waveguide length.

  The object is a Y-shaped optical multiplexing waveguide having first and second optical waveguides and a third optical waveguide to which the first and second optical waveguides are coupled, wherein the first optical waveguide is the first optical waveguide. This is achieved by an optical multiplexing waveguide in which an optical waveguide is coupled to the end of the third optical waveguide and the second optical waveguide is coupled to an inner portion of the end of the third optical waveguide.

  Here, each of the first and second optical waveguides may have an arc shape. Each of the first and second optical waveguides may be an S-shaped bend waveguide formed by connecting two circular arc shapes symmetrically. In this case, it is preferable that the radius of curvature of the first optical waveguide is smaller than the radius of curvature of the second optical waveguide. Further, the tangential slopes of the first and third optical waveguides in the coupling portion of the first and third optical waveguides are equal to each other, and the second and third in the coupling portion of the second and third optical waveguides It is preferable that the tangent slopes of the third optical waveguide are equal to each other.

  The optical multiplexing waveguide according to the present invention is a Y-shaped optical multiplexing waveguide having first and second optical waveguides and a third optical waveguide to which the first and second optical waveguides are coupled. The end portion of the first optical waveguide is coupled to the end portion of the third optical waveguide, and the second optical waveguide forms a tapered portion at an inner portion from the end portion of the third optical waveguide. Then, it is gradually coupled to the third optical waveguide. Here, each of the first and second optical waveguides can be an S-shaped bend waveguide formed by connecting two circular arcs symmetrically with respect to a point, and the third optical waveguide is a linear waveguide. It can be.

  According to the present invention, it is possible to obtain an optical multiplexing waveguide that can reduce leakage light at the junction and does not require extension of the waveguide length. In the present invention, in the Y-shaped optical multiplexing waveguide, the tapered portion formed by the waveguide merging portion by making the merging portion (coupling portion) of the two input side waveguides and one output side waveguide different. Can be reduced, thereby reducing the loss at the junction. Furthermore, the curvature radii of the two input-side waveguides having an arc shape are made different, and the arc shape of the waveguide having a small curvature radius is finished, and a waveguide having a large curvature radius is merged at a straight line. It becomes possible not to extend the waveguide length. In addition, when the loss reduction is kept small and the joining position and the radius of curvature are optimized, the optical multiplexing waveguide can be reduced in size.

  The present invention relates to a generally Y-shaped optical multiplexing waveguide in which two waveguides are coupled to one waveguide. In order to show the best mode, two S-shaped bend waveguides formed by connecting two circular arcs with point symmetry are used as general Y-shaped optical multiplexing waveguides, and they are further joined line-symmetrically. An optical multiplexing waveguide formed by guiding to a straight waveguide will be described.

  In the improved form, the points where two waveguides having an arc shape merge with one linear waveguide are different from each other. Accordingly, the angle of the tapered portion of the joining portion is made smaller than that when joining at the same place, and the leakage light caused by the angle of the tapered portion is reduced to reduce the loss. Further, by reducing the radius of curvature of the S-shaped bend waveguide closer to the input side (the negative side with respect to the propagation direction) of the two S-shaped bend waveguides, the straight waveguide and the straight line at the arc-shaped end point are reduced. In this junction, since there is no junction with other waveguides, it can be approximated to a single S-shaped bend and leakage light can be suppressed. The other S-shaped bend waveguide joins linearly from the end of the straight waveguide to the inner part, and even if the radius of curvature is increased, the increase in loss can be suppressed, and as a result, extension of the waveguide length can be avoided. It becomes possible. Hereinafter, as a preliminary step for explaining the present invention, a loss relationship related to the coupling between the S-shaped bend waveguide and the straight waveguide will be explained.

FIG. 2 is a diagram illustrating a coupling example of an S-shaped bend waveguide and a straight waveguide. In the figure,
(1) a conventional optical multiplexing waveguide in which S-shaped bend waveguides 21 and 22 are symmetrically combined with a straight waveguide 23;
(2) an optical multiplexing waveguide in which the S-shaped bend waveguide 24 is joined to the straight waveguide 25;
(3) a waveguide in which a straight waveguide 27 is followed by an S-shaped bend waveguide 26;
Indicates. The curvature radii of the respective S-shaped bend waveguides are the same. Here, when light is incident on one of the S-shaped bend waveguides 21 and 22 of (1) and light is incident on the S-shaped bend waveguides 24 and 26 of (2) and (3), respectively. The relationship of the loss in the waveguide coupling portion is (1)>(2)> (3). This is because the smaller the taper angle formed at the coupling portion of the two waveguides, the smaller the loss because the generation of leakage light can be suppressed, and the smaller the loss when there is no tapered portion. The present invention utilizes the loss relationship in the coupling between these waveguides.

  FIG. 3 is a conceptual diagram showing an example of an optical multiplexing waveguide according to the present invention. The optical multiplexing waveguide of this example is Y-shaped as shown in the figure, and two optical waveguides 31 and 32 on the input side, and one optical waveguide 33 on the output side joined to these optical waveguides 31 and 32. And have. The optical waveguide 32 on the input side is linearly coupled to the end of the optical waveguide 33 on the output side at the coupling portion 35, and the optical waveguide 31 on the input side is a portion inside the end of the optical waveguide 33 on the output side at the coupling portion 34. Are linearly coupled to each other. That is, the coupling portion 35 is a point where the end portion of the optical waveguide 32 on the input side and the end portion of the optical waveguide 33 on the output side are coupled, and the coupling portion 34 is from the end portion of the optical waveguide 33 on the output side. This is a point where the end of the optical waveguide 31 on the input side joined to the inner part is located. In other words, the end portion of the optical waveguide 32 is coupled to the end portion 33 of the coupling portion 35, but the optical waveguide 31 is tapered between the end portion of the optical waveguide 33 and the inner portion of the coupling portion 34. A portion 36 is formed and gradually coupled to the optical waveguide 33, and finally coupling is completed at the coupling portion 34. Further, the slopes of the tangent lines of the optical waveguides 32 and 33 in the coupling portion 35 are equal to each other, and the slopes of the tangent lines of the optical waveguides 31 and 33 in the coupling portion 34 are equal to each other. When the optical waveguide 33 is a linear waveguide, the tangents of the optical waveguides 31 and 32 in each coupling portion and the inclination of the optical waveguide 33 are equal to each other. Here, the two optical waveguides 31 and 32 on the input side are S-shaped bend waveguides formed by connecting two circular arc shapes in a point-symmetric manner, and the curvature radius of the optical waveguide 32 is the curvature radius of the optical waveguide 31. Has been smaller than.

  The two optical waveguides 31 and 32 of the S-shaped bend waveguide are independent waveguides, and linear portions may be extended on the input side, or a light emitting element may be provided. When these two optical waveguides 31 and 32 are merged with the output-side optical waveguide 33, the arc portion of the optical waveguide 32 having a small curvature radius is finished, and light is emitted from the coupling portion 35 coupled to the linear optical waveguide 33. The optical waveguide 31 having a large curvature radius is coupled to the linear optical waveguide 33 at the coupling portion 34 inside the waveguide 33. In this example, S-shaped bend waveguides are used as the optical waveguides 31 and 32, but the present invention is not limited to this. That is, it is sufficient that the loss due to the leakage mode can be suppressed by equalizing the slope of the tangent at each coupling portion of the optical waveguide, and the configuration of the optical waveguides 31 and 32 may be, for example, a sine function or a raised cosine function. .

  In this example, the curvature radii of the two optical waveguides 31 and 32 are different, but the curvature radii of both may be the same. If the positions of the coupling portions 34 and 35 of the two optical waveguides 31 and 32 and the one optical waveguide 33 are different, the taper of the tapered portion 36 is compared with the conventional case of the joining portion at the same point. This is because the angle is reduced and the effects of the present invention can be exhibited. However, when the radius of curvature of both is the same and the coupling portion to the optical waveguide 33 is different, the optical multiplexing waveguide length of the entire system is extended as compared with the case where the coupling portion is the same. The curvature radius of 31 is preferably smaller than that of the optical waveguide 32 from the viewpoint of avoiding the extension of the waveguide length. Even if the radius of curvature of the optical waveguide 31 is reduced, both the optical waveguides are regarded as a single bent waveguide due to the coupling with the linear optical waveguide 33 in the coupling portion 34, and therefore other than the arc-shaped portion of the optical waveguide 31. There is little loss. In this way, the taper angle of the tapered portion 36 can be reduced by shifting the coupling portion 34 and the coupling portion 35 of the optical waveguide, thereby reducing the loss of the optical multiplexing waveguide.

  4A is a diagram for explaining a conventional symmetric optical multiplexing waveguide, and FIG. 4B is a diagram for explaining an embodiment of the optical multiplexing waveguide according to the present invention. As shown in FIG. 4A, the conventional symmetric optical multiplexing waveguide is formed by linearly connecting optical waveguides 41 and 42 composed of two S-shaped bend waveguides having the same curvature radius of 10 mm at the same coupling portion 44. The optical waveguide 43 is coupled.

  On the other hand, as shown in FIG. 4B, the optical multiplexing waveguide according to the present embodiment includes an optical waveguide 51 on the input side composed of an S-shaped bend waveguide with a curvature radius of 10 mm, and an S-shaped bend waveguide with a curvature radius of 5 mm. And an output-side linear optical waveguide 53 to which they are coupled. The optical waveguide 52 is linearly coupled to the end portion of the optical waveguide 53 at the coupling portion 55, and the optical waveguide 51 is linearly coupled to the inner portion from the end portion of the optical waveguide 53 at the coupling portion 54. In this case, the tangent of the optical waveguide 52 and the inclination of the linear optical waveguide 53 in the coupling portion 55 are equal to each other, and the tangent of the optical waveguide 51 and the inclination of the linear optical waveguide 53 in the coupling portion 54 are equal to each other.

  The optical multiplexing waveguide is made of, for example, an ultraviolet curable polymer material and cut out as a 5 mm × 15 mm film type. The core diameter was 50 × 50 μm □, and the interval between the straight portions before joining of the two S-shaped bend waveguides was 500 μm. These optical waveguides were produced using a silicon rubber mold. A Fabry-Perot laser diode with a wavelength of 850 nm is used as the light source, the light source to the input side optical waveguide is guided by a single mode fiber, and the exit end of the output side linear optical waveguide is routed through a φ62.5 multimode GI fiber. Connected to a light intensity meter. Matching oil was used between each fiber and the optical waveguide.

  Table 1 shows the parameters (S-shaped bend curvature radius) and the loss measurement results of the conventional optical multiplexing waveguide and the optical multiplexing waveguide according to this example.

  As can be seen from Table 1, in the conventional type, the loss of light transmitted to the optical waveguide 53 through the optical waveguide 41 or 42 is 3.08 dB, respectively, whereas in this embodiment, the optical waveguide 53 is transmitted through the optical waveguide 51. The loss of light transmitted to the optical waveguide is 2.38 dB, and the loss of light transmitted to the optical waveguide 53 through the optical waveguide 52 is 1.79 dB. That is, the optical multiplexing waveguide according to the present example has a lower loss than the conventional optical multiplexing waveguide. Further, by making the radius of curvature of the optical waveguide 52 smaller than that of the optical waveguide 51, it becomes unnecessary to extend the waveguide length as compared with the conventional optical multiplexing waveguide.

  The present invention relates to an optical multiplexing waveguide, and more particularly to an optical multiplexing waveguide in which the optical multiplexing section is generally Y-shaped, and has industrial applicability.

It is a figure which shows an example of the confluence | merging part in a Y-shaped optical multiplexing waveguide. It is a figure which shows the example of a coupling | bonding of an S-shaped bend waveguide and a linear waveguide. It is a conceptual diagram which shows an example of the optical multiplexing waveguide which concerns on this invention. (A) is a figure for demonstrating the conventional symmetrical optical multiplexing waveguide, (b) is a figure for demonstrating one Example of the optical multiplexing waveguide based on this invention.

Explanation of symbols

31, 32 Optical waveguide on input side 33 Optical waveguide on output side 34, 35 Coupling portion 36 Tapered portion

Claims (6)

  A Y-shaped optical multiplexing waveguide having first and second optical waveguides and a third optical waveguide to which the first and second optical waveguides are coupled, wherein the first optical waveguide is An optical multiplexing waveguide coupled to an end portion of a third optical waveguide, wherein the second optical waveguide is coupled to an inner portion of the end portion of the third optical waveguide.   2. The optical multiplexing waveguide according to claim 1, wherein each of the first and second optical waveguides has an arc shape.   2. The optical multiplexing waveguide according to claim 1, wherein each of the first and second optical waveguides is an S-shaped bend waveguide formed by connecting two arc shapes in a point-symmetric manner.   4. The optical multiplexing waveguide according to claim 3, wherein a radius of curvature of the first optical waveguide is smaller than a radius of curvature of the second optical waveguide.   The inclinations of the tangent lines of the first and third optical waveguides in the coupling portion of the first and third optical waveguides are equal to each other, and the second and third in the coupling portion of the second and third optical waveguides The optical multiplexing waveguide according to any one of claims 1 to 4, wherein inclinations of tangents of the optical waveguides are equal to each other.   Each of the first and second optical waveguides is an S-shaped bend waveguide formed by connecting two arcuate shapes in a point-symmetric manner, and the third optical waveguide is a linear waveguide. The optical multiplexing waveguide according to claim 1.

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