JPH11109172A - Optical coupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical coupler having satisfactory characteristics without depending on the kind of waveguides. SOLUTION: This optical coupler is provided with a base 1, an input waveguide 2 consisting of a first input waveguide 2a and a second input waveguide 2b and an output waveguide 4 consisting of a first output waveguide 4a and a second output waveguide 4b, the input waveguide 2 and the output waveguide 4 being formed on the base 1, and a multimode waveguide 5 having a slit part 21 having a prescribed space and a small refractive index formed between the input waveguide 2 and the output waveguide 4. The optical beam from the input waveguide is equally divided to the first output waveguide 4a and the second output waveguide 4b while suppressing the propagation to between the two output waveguides by the slit part 21, and the propagation efficiency or distribution efficiency is improved without causing a loss by the generation of the optical beam never propagated to the output waveguide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupler, and more particularly, to an optical coupler included in micro optical components used for optical communication and the like.

[0002]

2. Description of the Related Art Conventionally, an optical coupler has been used to obtain an optical action such as coupling or splitting of light beams. Some of these optical couplers use multimode waveguides.Optical couplers using multimode waveguides do not require curved waveguides for connection because the input and output waveguides are separated. It has the advantage of miniaturization due to the above.

As shown in FIG. 1, an example of the structure of an optical coupler using a multi-mode waveguide is such that an input waveguide 2 comprising a first input waveguide 2a and a second input waveguide 2b is provided on a substrate 1. A mode waveguide 3 and an output waveguide 4 including a first output waveguide 4a and a second output waveguide 4b are formed and configured. In this optical coupler, the light beam propagated through the first input waveguide 2a or the second input waveguide 2b is substantially equally divided and output from each of the first output waveguide 4a and the second output waveguide 4b (Ultracompact Multimode Interference Waveg
uide Devices. pp. 193-194, 1993-11, LEOS'93). Note that the width of the multimode waveguide 3 is 3
The width is more than double.

[0004]

However, a conventional optical coupler using a multimode waveguide shows good characteristics when used in a step-type refractive index distribution waveguide with the above configuration, but has a diffusion type. When used for a waveguide, there is a problem that the loss increases. That is, when the light beam is distributed and output from the first output waveguide 4a and the second output waveguide 4b, the first input waveguide 2a in the multimode waveguide 3 is used.
Of the side light beam (near the peak of the light beam power)
Is gradually transferred from the first output waveguide 4a to the second output waveguide 4b, and is also propagated between the first output waveguide 4a and the second output waveguide 4b. For this reason, a light beam that does not propagate to the first output waveguide 4a and the second output waveguide 4b is generated, and the loss increases.

[0005] The present invention has been made to solve the above problems, and has as its object to provide an optical coupler capable of obtaining good characteristics without depending on the type of waveguide used.

[0006]

In order to achieve the above object, an optical coupler according to the present invention comprises one or more input waveguides for propagating an input light beam and a predetermined direction for outputting the light beam. A plurality of output waveguides for propagating a light beam; and a plurality of output waveguides provided between the input waveguide and the output waveguide, for suppressing propagation of the light beam in at least a direction along the predetermined direction, and A multi-mode waveguide for distributing the input light beam, having a light propagation suppression region formed in a direction along the predetermined direction toward at least a pair of output waveguides adjacent to each other in the waveguide; , Is provided.

According to a second aspect of the present invention, in the optical coupler according to the first aspect, the multi-mode waveguide has a width exceeding approximately three times a width of each of the input waveguide and the output waveguide. It is characterized by being formed.

According to a third aspect of the present invention, in the optical coupler according to the first or second aspect, the light propagation suppressing region has a refractive index smaller than the refractive index of the multimode waveguide other than the light propagation suppressing region. It is characterized by being formed by.

According to a fourth aspect of the present invention, in the optical coupler according to any one of the first to third aspects, the light propagation suppressing region is formed in a slit shape having a substantially constant width. Features.

In the present invention, a light beam input through an input waveguide is propagated. There are one or more input waveguides, and one or more input light beams are distributed to a plurality of output waveguides. For this distribution, a multi-mode waveguide provided between the input waveguide and the output waveguide is used.
The multimode waveguide has a light propagation suppression region formed in a direction along a predetermined direction toward at least a pair of output waveguides adjacent to each other among the plurality of output waveguides. In the light propagation suppression region, the propagation of the light beam is suppressed, so that the light is efficiently distributed to each of the output waveguides without loss due to the generation of the light beam that is not propagated to the output waveguide.

It is preferable that the multi-mode waveguide is formed to have a width exceeding approximately three times the width of each of the input waveguide and the output waveguide. With this configuration, the efficiency of light beam propagation suppressed in the light propagation suppression region is improved, and the light is efficiently distributed to each of the output waveguides.

The optical coupler is easily manufactured by forming the light propagation suppressing region with a smaller refractive index than the refractive index of the multi-mode waveguide other than the light propagation suppressing region. be able to.

Further, as described in claim 4, by forming the light propagation suppressing region in a slit shape having a substantially constant width, an optical coupler can be easily manufactured.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the present embodiment, the present invention is applied to an optical coupler that divides an input light beam into two equal parts and outputs two output light beams.

As shown in FIG. 2, the optical coupler according to the embodiment of the present invention includes a substrate 1 on which an input waveguide 2, a multi-mode waveguide 5, and an output waveguide 4 are provided. Is formed. The input waveguide 2 includes a first input waveguide 2a
And the second input waveguide 2b, and the output waveguide 4 includes a first output waveguide 4a and a second output waveguide 4b. The multi-mode waveguide 5 is provided with a light beam propagating direction (FIG. 2).
Are provided at predetermined intervals along the vicinity of the center in the direction intersecting with the direction indicated by arrow A in FIG. The refractive index of the slit 21 is smaller than that of the portions 5a and 5b of the multimode waveguide 5 other than the slit 21.

As an example of a method for manufacturing the multimode waveguide 5 having the slit portion 21, a LiNbO ₃
In the case where a waveguide is manufactured by Ti diffusion using the method described above, the Ti pattern may be diffused so that the shape shown in FIG. 2, that is, only the portions 5a and 5b are formed as a multimode waveguide.

As is well known, many modes are excited in a multimode waveguide. The field distribution of the fundamental mode in this multimode waveguide is the same as that of the conventional multimode waveguide 3.
In FIG. 1, the multimode waveguide 3 has a large peak at the central axis. Therefore, at the output end of the multimode waveguide 3, that is, near the boundary of the multimode waveguide 3 to which the output waveguides 4 a and 4 b are connected, the light beam is output from the output waveguide 4.
a and the output waveguide 4b. For this reason, a light beam that does not propagate to the first output waveguide 4a and the second output waveguide 4b is generated, and the loss increases.

On the other hand, in the multimode waveguide 5 (FIG. 2) of the present embodiment, since the propagation of the light beam is suppressed in the slit portion 21, the field distribution form of the fundamental mode is It has a concave shape. Therefore, the output side termination of the multimode waveguide 5, that is, the output waveguides 4a and 4b
The output (power) of the light beam is suppressed in a region between the output waveguides 4a and 4b near the boundary of the multi-mode waveguide 3 to which is connected.

The present inventor conducted a comparative experiment on the mode field distribution shape of the conventional multimode waveguide 3 and the multimode waveguide 5 of the present embodiment. In this experiment, the field distribution shape of the mode was obtained by simulation using the beam propagation method (BPM). FIGS. 3 and 4 show the experimental results of this comparative experiment. FIG. 3 shows a mode field distribution shape in the conventional multimode waveguide 3, and FIG. 4 shows a mode field distribution shape in the multimode waveguide 5 of the present embodiment. Note that the experiment was performed with a lateral diffusion width of 2 μm.

The horizontal axis in FIGS. 3 and 4 indicates the position in the direction intersecting with the propagation direction of the light beam with respect to the center of the multimode waveguide (in the example of FIG. 2, the direction intersecting with the direction of arrow A). ing. The vertical axis in FIGS. 3 and 4 indicates the position in the propagation direction of the light beam (the direction of arrow A in the example of FIG. 2) with reference to the incident end of the multimode waveguide. 3 and 4, the shape of the optical coupler is also shown for easy understanding. The field distribution shape of the mode was drawn on the coordinate plane having the horizontal axis and the vertical axis. 3 and 4, the horizontal direction (the direction intersecting with the light beam propagation direction, that is, the direction in which the light beam propagates along the propagation direction of the light beam in each multi-mode waveguide). In the example of FIG. 2, the power distribution of the light beam in the direction intersecting with the arrow A) is obtained, the distribution is normalized by setting the maximum value of the input light beam to “1”, and the arbitrary position (the value on the vertical axis) is distributed. Are the field distribution shapes 7a to 7h, 8a to
8h was drawn. The field distribution shapes 7a and 8a are the same as the field distribution shapes of the modes of the input light beam.

As understood from FIG. 3, in the conventional multi-mode waveguide 3, the light beam is diffused between the output waveguides to the substrate. That is, the peak of the mode field distribution shape gradually shifts from the shape 7a to the shape 7h. Further, a light beam is propagated between the first output waveguide 4a and the second output waveguide 4b.

On the other hand, in the multimode waveguide 5 having the slit λ configuration according to the present embodiment, as can be understood from FIG. 4, the mode field distribution gradually shifts from the shape 8a to the shape 8h. However, the first output waveguide 4a and the second output waveguide 4a
The propagation of the light beam toward the output waveguide 4b is suppressed, and the light beam is propagated toward each of the first output waveguide 4a and the second output waveguide 4b.

When the optical coupler of the present embodiment is formed as a 3 dB coupler for equal distribution, when a light beam enters the input waveguide 2a, the light beam from the input waveguide 2a is converted to the first output waveguide 4a. And the second output waveguide 4b
Is suppressed, and is equally divided into the first output waveguide 4a and the second output waveguide 4b.

As described above, the optical coupler of the present embodiment equally divides the light beam from the input waveguide into each of a plurality of (two in the present embodiment) output waveguides in the multi-mode waveguide. In addition, since the propagation of the light beam toward the space between the two output waveguides is suppressed by providing the slit portion, the light beam is transmitted to the first output waveguide 4a and the second output waveguide 4b. Propagation or distribution efficiency is improved without loss due to the generation of a light beam that is not split and not propagated to the output waveguide.

In the above embodiment, a case has been described in which the present invention is applied to an optical coupler that divides an input light beam into approximately two equal parts and outputs two output light beams.
The present invention is not limited to this, and may be distributed to three or more. Further, the ratio of the output light beams may be set to a predetermined ratio (for example, 1: 2 for two distributions).

In this embodiment, an optical coupler capable of inputting two input light beams has been described. However, one input light beam is divided into approximately two equal parts (or predetermined equal parts) or at a predetermined ratio. The present invention may be applied to an optical coupler that outputs two or more output light beams.

[0027]

As described above, according to the present invention, a multimode waveguide for distributing a light beam is provided in a predetermined direction toward at least a pair of adjacent output waveguides of a plurality of output waveguides. Since the light propagation suppression region is formed along the direction, the propagation of the light beam is suppressed in the light propagation suppression region, and the light is efficiently output without any loss due to the generation of the light beam that is not propagated to the output waveguide. There is an effect that the light can be distributed to each of the waveguides.

[Brief description of the drawings]

FIG. 1 is a plan view showing a schematic structure of an optical coupler using a conventional multimode waveguide.

FIG. 2 is a plan view showing a schematic structure of an optical coupler using a multimode waveguide according to an embodiment of the present invention.

FIG. 3 is a diagram showing an experimental result of obtaining a mode field distribution shape of a conventional multimode waveguide.

FIG. 4 is a diagram showing an experimental result of obtaining a mode field distribution shape of the multimode waveguide of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Input waveguide 2a 1st input waveguide 2b 2nd input waveguide 3 Multimode waveguide 4 Output waveguide 4a 1st output waveguide 4b 2nd output waveguide 21 Slit part (light propagation suppression area)

Claims (4)

[Claims] An input waveguide for propagating an input light beam; a plurality of output waveguides for propagating a light beam in a predetermined direction for outputting a light beam; A plurality of output waveguides that are provided between the plurality of output waveguides and at least between the pair of adjacent output waveguides of the plurality of output waveguides. An optical coupler, comprising: a multimode waveguide having a light propagation suppression region formed in a direction along a direction, and distributing the input light beam. 2. The optical coupler according to claim 1, wherein the multi-mode waveguide is formed to have a width exceeding approximately three times a width of each of the input waveguide and the output waveguide. 3. The optical coupler according to claim 1, wherein the light propagation suppressing region is formed with a refractive index smaller than a refractive index of the multimode waveguide other than the light propagation suppressing region. 4. The optical coupler according to claim 1, wherein the light propagation suppressing region is formed in a slit shape having a substantially constant width.