JPH0743482B2 - Optical matrix switch - Google Patents

Description

The present invention relates to an optical matrix switch in an optical switch.

(Prior Art) An optical matrix switch is an important basic element of an optical switch, and therefore, researches on it have been vigorously carried out.

Fig. 4 shows the Japanese Patent Application No. 62-25526 filed by the applicant of this application.
FIG. 3 is a plan view schematically showing the optical matrix switch proposed in No. 1.

This optical matrix switch has m input waveguides 17 configured by connecting first directional couplers 15 having a first waveguide 11 and a second waveguide 13 in n stages (3 stages in this example). (Three in this example), and an output waveguide configured by connecting a second directional coupler 25 having a third waveguide 21 and a fourth waveguide 23 in m stages (3 stages in this example). 27 n (3 in this example)
In addition, the first waveguide 11 and the fourth waveguide 23
Are connected via a total reflection corner 31 and the second waveguide 13 and the third waveguide 21 are crossed so that the input / output waveguides 1
It was a matrix of 7,27. According to this optical matrix switch, the optical signal passes through the total reflection corners when any of the multiple propagation paths of light formed between the input ports 17a, 17b, 17c and the output ports 27a, 27b, 27c is used. Since the structure is such that it only needs to pass once, even if each component is configured by a known component, the loss in propagating an optical signal can be reduced as compared with the conventional one.

Also, various studies have been made on directional couplers, for example, one proposed in Japanese Patent Application No. 62-293360 of the present applicant. This directional coupler has a layer (also referred to as a coupling layer) that is formed of a compound semiconductor material and that enhances electric field coupling between the two waveguides provided in the directional coupler. The length Lc can be shortened and therefore the size can be further reduced, and the optical circuit element incorporating this can be downsized.

Therefore, the inventor of the present application proposes the directional couplers 15 and 25 of the optical matrix switch shown in FIG.
An attempt was made to construct the directional coupler proposed in 60. The optical matrix switch was configured to have a strip-loaded waveguide using an AlGaAs / GaAs-based compound semiconductor material.

FIG. 5, FIG. 6, FIG. 7 and FIG. 8 are diagrams for explaining the optical matrix switch having such a configuration,
FIG. 5 is a plan view shown in correspondence with FIG. 4 (however, some of the numbers of the similar constituents are omitted), and FIG. 6 shows this optical matrix switch at I- of FIG. A cross-sectional view taken along line I (however, hatching showing the cross-section is omitted), FIG. 7 is an enlarged perspective view of a region indicated by P in FIG. 5, and FIG. The figure is an enlarged perspective view of the portion of the total reflection corner 31. It should be understood that both figures are schematic.

In this optical matrix switch, as shown in the plan view of FIG. 5, the coupling layer 40 is provided with two waveguides of each directional coupler (in the case of the first directional coupler 15, the first waveguide 11 and The second waveguide 13) is provided while facing each other (including the region where the total reflection corner exists). Further, as shown in FIG. 6, a GaAs substrate of the first conductivity type (n type in this example) is used, and on the n type GaAs substrate 41, the n type AlGaAs lower clad layer 43 and the i type GaAs are used. The light guide layer 45 is provided in this order, and further, the first waveguide 11 and the second waveguide 13 of the light guide layer 45 are provided.
P-type AlGaAs upper cladding layer 47 and p-type
The GaAs cap layer 49 is provided in this order. In addition, p-type Ga
P is provided on the region of the As cap layer 49 corresponding to the directional coupler.
A side electrode 51 is provided, and an n-side electrode 53 is provided on the lower surface of the n-type GaAs substrate 41. The coupling layer 40 described with reference to FIG. 5 is made of the same material as the upper clad layer,
A portion 45a of the directional coupler 45 between the two waveguides of each directional coupler (including a region where the total reflection corner 31 is present) is provided to be thinner than the upper cladding layer. This tie layer 40
The first and second waveguides 11 and 13 (third and fourth waveguides 2
It is possible to increase the electric field coupling between 1,23) and thus to shorten the coupling length Lc. As the total reflection corner 31, as shown in FIG. 8, the p-type cap layer 51 and the p-type AlGaAs cladding layer 4 in the portion where the first waveguide 11 and the fourth waveguide 23 are connected to each other.
9. The i-type GaAs optical guide layer 45 and the n-type AlGaAs lower clad layer 43 were removed perpendicularly to the main surface of the substrate 41.

As is clear from FIG. 7, the optical matrix switch configured in this manner passes from the region sandwiched by the first and second waveguides 11 and 13 to the third and fourth regions through the region where the total reflection corner 31 is present. The coupling layer 40 extends to the region sandwiched by the waveguides 21 and 23.
(Shown with diagonal lines). The main dimensions of this optical matrix switch are that the width W (also called rib width) of the upper clad layer 47 of each directional coupler is 2 to 5 μm, and the upper clad on the first and second waveguides is large. The gap S (rib spacing) between the layers 47 is 2 to 5 μm,
The height H (rib height) of the upper clad layer 47 is about 1 μm,
The thickness of the light guide layer 45 was about 0.1 to 1 μm.

(Problems to be Solved by the Invention) However, in the optical matrix switch described with reference to FIGS. 5 to 7, as is clear from FIG.
Second waveguide 13 of the waveguides connecting the directional couplers
Also, there is a problem that the third waveguide 21 is arranged in the immediate vicinity of the total reflection corner 31.

Generally, when the waveguide is a strip-loaded waveguide, the electric field strength in the direction near the waveguide and parallel to the substrate surface in the vicinity of the waveguide is as follows.
7) It is maximum in the area directly below, but shows a certain value even in the area without ribs 47. However, in the case of a waveguide that passes in the immediate vicinity of the total reflection corner 31 like the second waveguide 13 and the third waveguide 21 described above, the optical guide thick portion near the waveguide near the total reflection corner 31 causes total reflection. Since the waveguide structure is partly removed to form the corner 31, the waveguide structure becomes asymmetric, and the electric field strength distribution changes significantly. Specifically, the electric field strength distribution near the portion near the total reflection corner of the second waveguide 13 is as shown by adding I in FIG. 7, and the center of the strength is in the width direction of the waveguide. It shifts from the center in the direction opposite to the total reflection corner 31. On the other hand, the electric field intensity distribution in the first and second waveguides in the portion where the coupling layer 40 for enhancing the electric field coupling between the first and second waveguides is present is shown by II in FIG. Therefore, the centers of the intensity distributions of both waveguides are close to each other. Therefore, in the structure shown in FIG. 5 to FIG. 7, the electric field intensity distribution of the second waveguide 13 suddenly changes (II → I) at the total reflection corner 31, so that the inside of the directional coupler is changed. The light guided and transferred to the second waveguide 13 will not be guided in the vicinity of the total reflection corner 31 of the second waveguide 13 due to the inconsistent electric field intensity distribution, resulting in loss.

The present invention has been made in view of the above circumstances, and therefore an object of the present invention is to provide an optical matrix switch with less optical loss in a waveguide.

(Means for Solving the Problems) In order to achieve this object, according to the present invention, a first directional coupler having a first waveguide and a second waveguide is connected in n stages. M input waveguides, and n output waveguides configured by connecting a second directional coupler having a third waveguide and a fourth waveguide in m stages. An optical matrix switch in which one waveguide and the above-mentioned fourth waveguide are connected through a total reflection corner, and the above-mentioned second waveguide and the above-mentioned third waveguide are crossed to form each of the above-mentioned input / output waveguides in a matrix. And a lower clad layer and an optical guide layer in which the above-mentioned first to fourth waveguides are sequentially provided on a substrate, and the first to fourth waveguides of the optical guide layer. A strip-loaded waveguide having an upper clad layer provided on the region, In an optical matrix switch made of a physical semiconductor, in a region of the optical guide layer portion between the first waveguide and the second waveguide of each of the above-mentioned first directional couplers, which is separated from the above-mentioned total reflection corner. A first coupling layer, which is made of the same material as the upper clad layer and is thinner than the upper clad layer, is provided, and the third waveguide and the fourth waveguide of each of the second directional couplers are opposed to each other. A second coupling layer made of the same material as the upper clad layer and thinner than the upper clad layer is provided on a region of the optical guide layer portion away from the total reflection corner. .

(Operation) With such a configuration, there is no coupling layer around the total internal reflection corner that enhances the electric field coupling between the two waveguides of the directional coupler. Therefore, even though the center of the electric field intensity distribution of each waveguide is deviated to the opposite waveguide side in the portion in contact with the coupling layer, each waveguide is eliminated in the portion where the coupling layer on the way to the direction of the total reflection corner disappears. Return to the center side in the width direction.

Further, in the vicinity of the total reflection corner of the waveguide, since there is no coupling layer, that is, the cladding layer on both sides of the waveguide, the influence of the total reflection corner on the waveguide, which has been a problem in the related art, can be alleviated. Therefore, the center of the electric field intensity distribution in this vicinity comes to approach the center side of the waveguide from the state shown by I in FIG. Therefore, the electric field intensity distribution of the portion in contact with the coupling portion of the same waveguide and the electric field intensity distribution of the portion near the total reflection corner become similar.

(Embodiment) An embodiment of the optical matrix switch of the present invention will be described below with reference to the drawings. However, the drawings used in the following description are only schematically illustrated to the extent that the present invention can be understood. It should be understood that the present invention is not limited to the illustrated examples. In addition, the number of input waveguides m is set to 3 in the following embodiment.
An example in which the present invention is applied to a 3 × 3 optical matrix switch in which the number of output waveguides n is 3 will be described. As a material for manufacturing the optical matrix switch, an AlGaAs / GaAs-based compound semiconductor was used as in the conventional case.

FIG. 1 and FIG. 2 are diagrams for explaining the optical matrix switch of the embodiment. FIG. 1 is a plan view schematically showing the overall configuration, and FIG. 2 is shown by Q in FIG. It is the perspective view which expanded and showed the part. In each drawing, the same components as those of the conventional components are designated by the same reference numerals. Further, in FIG. 1, in order to avoid making the drawing complicated, some of the numbering of similar constituent components is omitted.

As shown in the plan view of FIG. 1, the optical matrix switch of this embodiment is configured by connecting three first directional couplers 15 each having a first waveguide 11 and a second waveguide 13 in three stages. In addition to providing three input waveguides 17 and three output component paths configured by connecting three stages of the second directional coupler 25 having the third waveguide 21 and the fourth waveguide 23, The first waveguide 11 and the fourth waveguide 23 are connected via a total reflection corner 31, and the second waveguide 13 and the third waveguide 23 are crossed to each input / output waveguide 17, 27.
Are matrixed. Then, as described above with reference to FIG. 6, each of the first to fourth waveguides is an n-type waveguide.
N-type AlGaAs lower clad layer sequentially provided on the GaAs substrate 41
43 and an i-type GaAs optical guide layer 45, and an upper clad layer 47 and a p-type GaAs cap layer 49, which are sequentially provided on the regions of the optical guide layer 45 to be the first to fourth waveguides, and are strip-loaded. It is composed of a waveguide. Further, a p-side electrode 51 is provided on a region of the p-type GaAs cap layer 49 corresponding to the directional coupler, and an n-side electrode 53 is provided on a lower side surface of the n-type GaAs substrate 41 (see FIG. 1 and FIG. In FIG. 2, the cap layer 49, the p-side electrode 51, and the n-side electrode 53 are not shown).

Furthermore, in this optical matrix switch, as shown in FIGS. 1 and 2, the first waveguide 11 of each first directional coupler is used.
And a region of the optical guide layer portion, which is separated from the total reflection corner 31 by l ₁ while the second waveguide 13 is opposed, is made of the same material as the upper clad layer 47 and thinner than the upper clad layer 47. Respective coupling layers 61 (shown with diagonal lines) are provided, and the total reflection corners 31 of the optical guide layer portion while the third waveguide 21 and the fourth waveguide 23 of each second directional coupler 25 face each other.
A second coupling layer 63 (shown by hatching) made of the same material as the upper clad layer 47 and thinner than the upper clad layer 47 is provided on each of the regions separated from each other by 1 ₂ .
The thickness of each of the first bonding layer 61 and the second bonding layer 63 is changed according to the design, but in the case of this example, it is set to a value within the range of 0.01 to 0.1 μm. . The length of the first coupling layer 61 L _1, the length of the second binding layer 63 L ₂ (see FIG. 2) is determined in accordance with the design. Also, the distance l ₂ from the distance l ₁ and total reflection corner 31 of the second binding layer 63 from the total reflection corner 31 of the first binding layer 61 is intended to be changed in accordance with each design However, in this example, l ₁ > 2W, l ₂ > with respect to the width w of the waveguide (see FIG. 2).
The preferred value is 2W.

Next, the electric field intensity distribution in the waveguide of the optical matrix switch of the embodiment will be described in comparison with the conventional electric field intensity distribution shown in FIG.

First, the electric field intensity distribution in the first and second waveguides at the portion where the first coupling layer 61 exists between the first and second waveguides 11 and 13 is shown by II in FIG. This is the same as the conventional one shown by II in FIG.

Next, the electric field intensity distribution in the first and second waveguides in the portion where the first coupling layer 61 between the first and second waveguides 11 and 13 does not exist and which does not reach the total reflection corner 31 is , Fig. 2 III
As compared with the electric field intensity distribution II in the portion where the first coupling layer 61 is present, the center comes closer to the center side in the width direction of each waveguide.

Further, the electric field strength distribution near the portion of the second waveguide 13 on the side of the total reflection corner is less affected by the total reflection corner 31 because there is no coupling layer, and therefore is shown with IV in FIG. As shown in FIG. 7, the center of the intensity is closer to the center side in the width direction of the waveguide as compared with the one indicated by I in FIG.

Therefore, as can be understood from FIG. 2, according to the structure of this embodiment, in the same waveguide in this illustrated example, the electric field intensity distribution of the portion in contact with the first coupling portion 61 of the second waveguide 13 and the total reflection corner. The electric field strength distribution of the distribution near 31 becomes similar, but the change of the electric field strength distribution becomes gentler than before, so that the loss of guided light becomes small. The same applies to the third waveguide 21 passing through the side of the total reflection corner 31.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be added.

For example, the connection relationship of the first to fourth waveguides of the optical matrix switch is not limited to that shown in FIG. 1, but, for example, the connection relationship shown in the plan view of FIG. It may have a structure in which a basic unit having is repeated.

Further, although the above-described embodiment describes the example of the 3 × 3 optical matrix switch, this is merely an example, and even when the numbers m and n of the input / output waveguides are different from each other, It is apparent that the present invention can be applied even when the number of input / output waveguides is changed to another number with the same number.

Further, in the above-mentioned embodiments, the n-type GaAs substrate is used as an example, but the substrate may be of p-type and each semiconductor layer may be of the conductivity type opposite to that of the embodiment. In addition, the light guide layer is not limited to the i-type in both the embodiment and the modification, and may be p-type or n-type. Furthermore, the constituent material of the optical matrix switch may be another material such as InGaAsP / InP system.

(Effect of the Invention) As is apparent from the above description, according to the optical matrix switch of the present invention, the coupling layer for enhancing the electric field coupling between the two waveguides included in the directional coupler is provided around the total reflection corner. There is no structure. Therefore, even though the center of the electric field intensity distribution of each waveguide is deviated to the opposite waveguide side in the portion in contact with the coupling layer, each waveguide is eliminated in the portion where the coupling layer on the way to the direction of the total reflection corner disappears. Return to the center side in the width direction. Further, in the vicinity of the total reflection corner of the waveguide, there is no coupling layer, that is, the cladding layer on both sides of the waveguide, so that the influence of the total reflection corner on the waveguide, which has been a problem in the related art, can be alleviated. For this reason, Japanese Patent Application Sho 62-293360
Even when using the directional coupler proposed in, the electric field strength distribution of the portion in contact with the coupling portion of the same waveguide becomes similar to the electric field strength distribution of the portion near the total reflection corner. The optical loss in the waveguide in the vicinity of each total reflection corner is smaller than that in the case of FIG.

[Brief description of drawings]

FIG. 1 is a plan view for explaining the optical matrix switch of the embodiment, FIG. 2 is a partial perspective view for explaining the optical matrix switch of the embodiment, and FIG. 3 is a modification of the present invention. FIG. 4 is a plan view showing a configuration example of a conventional optical matrix switch, FIG. 5 is a plan view showing another configuration example of a conventional optical matrix switch, and FIG. FIG. 7 is a partial sectional view of the optical matrix switch shown in FIG. 7, FIG. 7 is an enlarged perspective view of a portion of the optical matrix switch shown in FIG. 5, and FIG. It is a perspective view to offer. 11 …… First waveguide, 13 …… Second waveguide 15 …… First directional coupler 17 …… Input waveguide 17a, 17b, 17c …… Input port 21 …… Third waveguide, 23… … Fourth waveguide 25 …… Second directional coupler 27 …… Output waveguide 27a, 27b, 27c …… Output port 31 …… Total reflection corner 41 …… Substrate (n-type GaAs substrate) 43 …… Bottom Side cladding layer (n-type AlGaAs layer) 45 ... Optical guide layer (i-type GaAs layer) 47 ... Upper cladding layer (p-type AlGaAs layer) 61 ... First coupling layer, 63 ... Second coupling layer .

Claims (1)

[Claims] 1. An input waveguide formed by connecting n stages of first directional couplers having a first waveguide and a second waveguide.
And n output waveguides formed by connecting m second stages of second directional couplers having a third waveguide and a fourth waveguide, the first waveguide and the fourth waveguide. An optical matrix switch in which the waveguides are connected via a total reflection corner and the input / output waveguides are formed into a matrix by intersecting the second waveguide and the third waveguide, the first waveguides to A strip having a lower clad layer and an optical guide layer sequentially provided with a fourth waveguide on a substrate, and an upper clad layer provided on a region of the optical guide layer to be the first to fourth waveguides. In an optical matrix switch made of a compound semiconductor, which is composed of a loaded waveguide, the total reflection of the optical guide layer portion while the first waveguide and the second waveguide of each of the first directional couplers face each other. The upper corner is placed on the area that is separated from the corner. A first coupling layer made of the same material as the rud layer and thinner than the upper cladding layer is provided, and an optical guide layer is provided between the third waveguide and the fourth waveguide of each of the second directional couplers. 2. An optical matrix switch, characterized in that second coupling layers made of the same material as the upper clad layer and thinner than the upper clad layer are provided on regions separated from the total reflection corners.