JP2004101995A - Optical combining/branching device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical combining/branching device which easily obtains a low loss and, especially, a low branching ratio in a small element size. <P>SOLUTION: In the optical combining/branching device where input optical waveguides 11, a multimode interference optical waveguide 12 connected to the input optical waveguides 11, and a plurality of output waveguides 13 connected to the multimode interference optical waveguide 12 are arranged on a substrate 10, at least one of the input optical waveguides 11 is arranged in a position shifted from the center of the multimode interference optical waveguide 12 by an amount of offset 14 which is a half of the width of the input optical waveguide 11 or smaller. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical coupling / branching element, for example, used as a basic circuit element of an optical circuit used for optical communication or optical signal processing.
[0002]
[Prior art]
With the advancement of optical communication systems and optical signal processing techniques, optical circuits that perform complicated functions are required.
Planar optical circuits using silica-based optical waveguides have many degrees of freedom in design, and because optical circuits can be manufactured on substrates in a manner similar to electronic components, manufacturing is simple. It has the characteristic that a stable same road can be realized.
For this reason, the method of manufacturing an optical component that is indispensable in the current wavelength division multiplexing optical communication system is represented by an array waveguide diffraction grating, which is a wavelength multiplexer / demultiplexer, as a representative.
[0003]
It is considered that these optical circuits will become more and more important in the future increase in capacity and speed of optical communication and in optical signal processing systems. As a circuit element constituting these optical circuits, a light coupling / branching function is one of the most important ones.
The present invention provides a new configuration method.
Note that the optical branching element functions as an optical multiplexing circuit by reversing the propagation direction of light, and thus may be collectively referred to as an optical multiplexing / branching element.
[0004]
First, FIG. 9 shows an example of a conventional optical branching element.
Various methods are used for forming the optical branching element.
First, a Y branch circuit shown in FIG. 9A is one example.
This method is problematic in that the distribution of light propagating through the waveguide changes abruptly due to the Y-branch portion, so that excess loss is likely to occur, and the element size increases due to the small branch angle of the Y-branch. It has become.
Further, although comparison with the present invention will be made later, there is a problem that it is difficult to obtain a small amount of branches with low loss.
[0005]
FIG. 9B shows an optical branching element using a directional coupler.
In this method, light is branched by coupling between adjacent optical waveguides, so that it is difficult to obtain a stable coupling rate, and there is a problem that characteristics are greatly changed due to a slight manufacturing error.
FIG. 9C shows a splitter circuit using a slab waveguide.
Although this is a very excellent method for distributing light to a large number of optical waveguides, it has a problem in that light loss increases when distributing light to a small number of optical waveguides.
[0006]
FIG. 9D shows a method of splitting a part of light by using a partial reflection mirror in the waveguide.
Although this method can achieve relatively stable branching, it is necessary to manufacture the partially reflecting mirror and the optical circuit separately, so that in order to realize a complicated optical circuit, there are problems in manufacturing yield and cost. Had.
FIG. 9E shows an optical branching element using a multi-mode interference waveguide (MMI) (this technology is described in detail in Non-Patent Document 1).
This configuration has a feature that a relatively small optical path can be easily realized as compared with other methods.
Further, it is known that the device is a useful device that can stably obtain a light branching ratio of a specific ratio.
[0007]
However, it is difficult to obtain a free branching ratio, although it has a feature that a stable branching ratio can be obtained.
In particular, achieving a small branching ratio has been a difficult task.
Here, in order to utilize the complex interference phenomenon of light in the multi-mode interference waveguide, the multi-mode interference waveguide exhibits completely different device characteristics by selecting parameters, so that appropriate parameters must be selected. Is very important.
The parameters referred to here are the refractive index of the waveguide, the refractive index difference of the waveguide, the width of the incident waveguide, the connection position of the incident waveguide, the width and length of the multi-mode waveguide, the width of the output waveguide, There are a connection position of an output waveguide, a connection angle of a waveguide, and the like, and a very large number of parameter combinations are conceivable.
[0008]
As described above, in the conventional optical branching device, an optical branching device that satisfies all requirements such as a small device size, a low-loss device configuration, and a free branching ratio (especially a small branching ratio) is realized. Realization was difficult, and improvement was needed as a basic element of the optical circuit.
In addition, some of the conventional devices require a special process in manufacturing, which has been a problem in realizing an optical circuit having many functions.
[0009]
[Non-patent document 1]
L. B. Soldano, and E.S. C. M. Pennings, "Optical multi-mode interference devices based on self-imaging: principals and applications" of Lightwave Technology. , Vol. 13 pp. 615-627, 1995,
[0010]
[Problems to be solved by the invention]
As described above, in the conventional optical branching device, all the requirements such as a small device size, a low-loss configuration, a free branching ratio (particularly a small branching ratio), and no special process in manufacturing are required. It is difficult to realize a satisfying optical branching element, and improvement has been required as a basic element of an optical circuit.
[0011]
[Means for Solving the Problems]
In the present invention, it has been found that the above problem can be solved by setting appropriate conditions in an optical circuit using a multimode interference waveguide.
Specifically, on the substrate as set forth in claim 1, an input optical waveguide, a multimode interference optical waveguide connected to the input optical waveguide, and a plurality of optical waveguides connected to the multimode interference optical waveguide. Wherein the input waveguide is disposed at a position having an offset amount from the center of the multi-mode interference waveguide, and the offset amount is the input optical waveguide. By using an optical coupling / branching element having a width equal to or less than half the width, the light branching ratio can be changed.
[0012]
Further, as set forth in claim 2, on the substrate, an input optical waveguide, a multi-mode interference optical waveguide connected to the input optical waveguide, and a plurality of outputs connected to the multi-mode interference optical waveguide. In the optical multiplexing / branching device composed of the optical waveguides, the input waveguide is arranged obliquely with respect to the multi-mode interference waveguide. Can be changed.
[0013]
Further, in the optical coupling / branching device having three output waveguides, the input optical waveguide is offset from the center of the multi-mode interference waveguide by a very small amount as in the first aspect. By arranging the output waveguide at a specific position and arranging the output waveguide at a specific position, it is possible to easily realize a minute amount of branching ratio which is difficult with the conventional configuration method.
[0014]
In the fourth and fifth aspects, the optical branching ratio is finely adjusted by changing the waveguide offset amount or the waveguide width discontinuously in the three optical waveguides, thereby realizing a desired optical branching ratio. be able to.
[0015]
In a sixth aspect, the optical waveguide is a quartz optical waveguide formed on a silicon substrate or a quartz substrate.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
However, to avoid repetition of description, the same numbers are given to optical circuits having the same functions in the drawings.
In the following description, the optical waveguide is a quartz optical waveguide formed on a silicon substrate.
This is because a waveguide type optical filter which is stable and excellent in reliability can be realized.
However, the present invention is not limited to this configuration. Of course, other optical waveguides such as a semiconductor waveguide, a polymer waveguide, and a LiNbO ₃ waveguide may be used.
[0017]
[Embodiment 1]
FIG. 1 shows a configuration example of the optical branching device according to the first embodiment of the present invention.
As shown in FIG. 1, an input optical waveguide 11, a multi-mode interference waveguide 12, and two output waveguides 13 are arranged on a substrate 10, and the multi-mode interference waveguide 12 is , And the two output waveguides 13 are connected to the multi-mode interference waveguide 12.
Further, as a main requirement of the present invention, the center of the input optical waveguide 11 and the center of the multi-mode interference waveguide 12 have an offset amount 14, and the offset amount 14 is half the width of the input optical waveguide 11. It is characterized by the following.
[0018]
FIG. 1 shows an example in which one input waveguide 11 and two output waveguides 13 are shown in order to make the configuration easy to understand. The number of input waveguides 11 and output waveguides 13 is not limited as long as at least one is provided.
The effect of the present embodiment will be described with reference to FIG.
In the optical branching circuit as shown in FIG. 1, it is easy to obtain a branching ratio of 50%: 50% when the offset amount = 0, but it is not possible to change the branching ratio. It was difficult.
[0019]
On the other hand, in the present embodiment, by changing the offset amount 14, the light branching ratio can be changed.
FIG. 2 shows the output characteristics from each port and the total insertion loss when the offset amount 14 of the input waveguide 11 is changed in the optical branch circuit as shown in FIG.
As is clear from FIG. 2, the adjustment of the light intensity, which was difficult with the conventional method, can be realized with low loss.
[0020]
As described above, the adjustment of the light branching ratio, which was difficult in the conventional configuration, can be realized by using the configuration of the present embodiment.
If the offset amount 14 becomes too large, the excess loss increases as shown in FIG. 2B. Therefore, in order to realize a low-loss optical branch circuit, the offset amount 14 must be equal to the input waveguide width 11. Is preferably less than half.
[0021]
[Embodiment 2]
FIG. 3 shows a configuration example of an optical branching element according to the second embodiment of the present invention.
As shown in FIG. 3, on the substrate 10, an input optical waveguide 11, a multi-mode interference waveguide 12, and an output waveguide 13 are arranged.
As a main requirement of the present invention, the input optical waveguide 11 is obliquely connected to the multi-mode interference waveguide 12.
In the present embodiment, the position of the input optical waveguide 11 is desirably at or near the center of the multi-mode interference waveguide 12, but is not limited to only that location.
[0022]
For example, a higher effect can be obtained by providing an offset amount as set forth in claim 1.
FIG. 3 shows an example in which one input waveguide 11 and two output waveguides 13 are shown for easy understanding of the configuration. The number of input waveguides 11 and output waveguides 13 is not limited as long as at least one is provided.
[0023]
The effect of this embodiment is almost the same as that of the first embodiment.
For the sake of simplicity, description will be made based on the case where the waveguide is arranged at the center of the multimode waveguide. However, when the difference between the angles of the input waveguide 11 and the multimode interference waveguide 12 is 0, Is equivalent to the conventional configuration. That is, the branch ratio is 50%: 50%.
On the other hand, by making the input waveguide 11 oblique, the light branching ratio can be changed.
As described above, the adjustment of the light branching ratio, which was difficult in the conventional configuration, can be realized by using the configuration of the present embodiment.
[0024]
[Embodiment 3]
FIG. 4 shows a configuration example of an optical branching element according to the third embodiment of the present invention. The present embodiment is described in claim 3.
As shown in FIG. 4, on a substrate 10, an input optical waveguide 11, a multi-mode interference waveguide 12, first, second, and third output waveguides 13 are arranged. Are connected to the input waveguide 11, and the three output waveguides 13 are connected to the multimode interference waveguide 12.
[0025]
Further, similarly to the first embodiment, the center of the input optical waveguide 11 and the center of the multi-mode interference waveguide 12 have an offset amount 14, and the offset amount 14 is equal to or less than half the width of the input optical waveguide 11. In the optical branching device, the width of the multi-mode interference waveguide 12 is W _S , the widths of the three output waveguides 13 are W ₁ , W ₂ , W ₃ , and the connection positions of the output waveguides 13. offset amount delta ₁ between the center of the multi-mode interference waveguide 12, delta _2, as _{Δ 3, Δ 1 = (W} S -W 1) / 2, Δ 2 = 0, Δ 3 = - (W S -W ₃ ) / 2 is set.
[0026]
As described above, in an optical circuit using the multi-mode interference waveguide 12, it is known that the characteristics change largely depending on the selection of these parameters. It becomes possible to realize a small amount of branching, which was difficult to realize, with low loss.
[0027]
The effect of the present embodiment will be described with reference to FIG.
FIG. 5 shows the output characteristics from each port and the total insertion loss when the offset amount 14 of the input waveguide 11 is changed in the optical branch circuit shown in FIG.
As shown in FIG. 5, it has become possible to realize a small amount of light branching with low loss, which was difficult with the conventional method.
In FIG. 4, the number of input waveguides 11 is not limited as long as at least one input waveguide 11 that satisfies the condition of claim 1 or 2 is provided.
[0028]
[Embodiment 4]
FIG. 6 shows a configuration example of an optical branching element according to the fourth embodiment of the present invention. The present embodiment is described in claim 4.
The optical coupling / branching element according to claim 3, wherein the connection position of the output waveguide (13) is changed by a small amount equal to or less than half of the width of the output waveguide, so that the first output waveguide (13) and the third output waveguide (13) are changed. The optical output intensity of the waveguide 13 is matched.
[0029]
In ordinary optical circuits, it is often required that the branching ratio of light is symmetrical, that is, the first output waveguide 13 and the third output waveguide 13 have the same intensity. Is desirable.
In the present embodiment, the adjustment can be performed by changing the connection position of the output waveguide 13 by a small amount.
[0030]
[Embodiment 5]
FIG. 7 shows a configuration example of an optical branching element according to the fifth embodiment of the present invention. The present embodiment is described in claim 5.
[0031]
4. The optical coupling / branching element according to claim 1, wherein the output waveguide is connected to another output waveguide having the same width as the output waveguide, and an offset is provided at a connection position between the waveguides. Alternatively, another output waveguide 16 having a smaller width than this is connected to the output waveguide 13. That is, the light intensity can be adjusted by changing the waveguide width discontinuously.
[0032]
As described above, the optical coupling / branching element of the present invention can realize a branching circuit having a low loss, a small size, and a high degree of freedom in designing a branching ratio. In particular, the effect is high in that a relatively small branching ratio can be realized.
FIG. 8 shows the relationship between the shape of a conventional branch circuit, the width and branch ratio of the branch portion, and the width and length of the branch portion.
FIG. 8A shows a conventional W-shaped branch circuit in which two Y-branch elements are combined.
In this device, the terminal width of the tapered waveguide and the taper spread angle (taper length) are important parameters for obtaining good characteristics.
If the spread angle of the taper is too steep, light cannot be stably expanded, which causes a loss.
If the angle is too small, the element length is unnecessarily long, which is not preferable.
[0033]
FIGS. 8B and 8C show the relationship between the branching ratio and the element length under almost optimized conditions.
FIG. 8B shows the branching ratio of light to the waveguides at both ends with respect to the terminal width of the waveguide expanded in a tapered shape.
As shown in the figure, the branching ratio can be reduced as the terminal waveguide width increases.
It can be seen that the waveguide width may be set to about 90 μm in order to realize a branching ratio of 1%.
On the other hand, as shown in FIG. 8C, the size is as large as 10000 μm or more, which is not suitable for use in integrated circuits.
[0034]
On the other hand, in the present invention, a small branching ratio can be realized with a size of 1000 μm or less, and an element can be realized with a size of 1/10 or less of the conventional type.
As is apparent from the above, the present invention is suitable for realizing a low-loss and small-sized element, and is a circuit suitable for an optical integrated circuit.
[0035]
As described above, the present invention relates to an optical multiplexing / branching device using a multimode interference waveguide, and is characterized by an arrangement relationship (offset, inclination, width, etc.) of an input / output waveguide with respect to the multimode interference waveguide. And a low loss and a high degree of freedom in branching ratio can be realized.
[0036]
【The invention's effect】
As described above in detail with reference to the drawings, by using the optical multiplexer / demultiplexer of the present invention, it is possible to freely design a small element size and low loss, particularly a small branching ratio, which were difficult with the conventional method. And the manufacturing is simplified.
Since the present element is a basic element for realizing an optical circuit, the manufacture of the optical circuit is simplified, which can contribute to the realization of an inexpensive element.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an optical branching element according to a first claim of the present invention.
FIG. 2 is a graph showing a relationship between a branch ratio (excess loss) and an offset amount according to the first embodiment of the present invention.
FIG. 3 is a configuration diagram of an optical branching element according to a second claim of the present invention.
FIG. 4 is a configuration diagram of an optical branching element according to a third claim of the present invention.
FIG. 5 is a graph showing a relationship between output intensity and Loss with respect to an offset amount according to the third embodiment of the present invention.
FIG. 6 is a configuration diagram of an optical branching element according to a fourth aspect of the present invention.
FIG. 7 is a configuration diagram of an optical branching element according to a fifth aspect of the present invention.
8A is a plan view showing the shape of a conventional branch circuit, FIG. 8B is a graph showing the relationship between the width of a branch portion and the branch ratio of the conventional branch circuit, and FIG. () Is a graph showing the relationship between the width and length of the branch portion of the conventional branch circuit.
FIG. 9 is a configuration diagram of a conventional optical branching element.
[Explanation of symbols]
REFERENCE SIGNS LIST 10 Substrate 11 Input waveguide 12 Multi-mode interference waveguide 13 Output waveguide 14 Offset amount between input waveguide and multi-mode interference waveguide 15 Other output waveguide 16 Other output waveguide

Claims (6)

On a substrate, an input optical waveguide, a multimode interference optical waveguide connected to the input optical waveguide, and an optical coupling / branching element in which a plurality of output waveguides connected to the multimode interference optical waveguide are arranged. Wherein at least one of the input waveguides is arranged at a position having an offset amount from the center of the multi-mode interference waveguide, and the offset amount is not more than half of the width of the input optical waveguide. Optical coupling and splitting element. On a substrate, an input optical waveguide, a multimode interference optical waveguide connected to the input optical waveguide, and an optical coupling / branching element in which a plurality of output waveguides connected to the multimode interference optical waveguide are arranged. An optical coupling / branching element, wherein at least one of the input waveguides is arranged obliquely with respect to the multimode interference waveguide. 3. The optical coupling / branching device according to claim 1, wherein the output waveguide includes at least three waveguides, each of the output waveguides has a width of W ₁ , W ₂ , and W _{3. 4.} the waveguide width is _{W S,} the connection position of the output waveguide, as the offset amount delta ₁ between the center of the multi-mode interference _{waveguide, Δ 2, Δ 3, Δ} 1 = (W S -W 1 _{) / 2, Δ 2 = 0} , Δ 3 = - (W S -W 3) / 2 and the wavelength division element characterized in that set. 4. The optical coupling / branching device according to claim 3, wherein the connection position of the output waveguide is changed by a small amount equal to or less than half of the width of the output optical waveguide so that the optical output intensity of the output waveguide located symmetrically is reduced. An optical coupling / branching element characterized by being matched. 5. The optical coupling / branching device according to claim 1, wherein the light intensity is adjusted by providing an offset amount in the output waveguide or changing the width of the output waveguide discontinuously. An optical coupling / branching element characterized by the above-mentioned. The optical coupling / branching device according to claim 1, 2, 3, 4, or 5, wherein the optical waveguide is a silica-based optical waveguide formed on a silicon substrate or a quartz substrate.

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