JPH02187705A - Light guide structure - Google Patents

Abstract

PURPOSE:To decrease the adverse influence of slab guided light at the time of signal introduction by forming recesses from which light guide layer parts are removed on both sides of a strip-shaped clad layer of an input port part. CONSTITUTION:A lower clad layer 13 and the light guide layer 15 are formed on a GaAs substrate 11 and the strip-shaped upper clad layer 17a is formed thereon. The layers from the light guide layer 15 to the substrate 11 are partly removed to form the recesses 31 in the prescribed regions on both sides of the clad layer 17a. Signal light enters not only the part of the clad layer 17a but also the part of the slab structure of the region II at the time of inputting the signal light from the optical fiber to the input port part of such waveguide layer and, therefore, the loss of the slab guided light increases and the slab guided light hardly propagates in the optical element 21. The adverse influence thereof is thus decreased.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to an optical waveguide structure of an input port portion of an optical device, such as an optical switch or an optical integrated circuit, which receives an optical signal from the outside. .

(Prior art) Functional elements such as light-emitting/light-receiving elements, optical switches, optical modulators, and optical amplifiers, as well as optical integrated circuits that are monolithic of these elements (hereinafter sometimes referred to collectively as optical elements), are: The added value of optical communication can be further increased. Among such optical devices, for those in which signal light transmitted from the outside of the optical device via an optical fiber etc. is input and processed inside the optical device through the input port section, the signal light is transmitted inside the optical device at this input port section as well. Similarly, an optical waveguide structure is required to guide the optical signal.

An example of such an optical waveguide structure is, for example, the literature (49th Japan Society of Applied Physics Academic Lecture Proceedings, Volume 3, Volume T).
, 350 Lecture No. 5p-S-5). FIG. 3(A) is a diagram for explaining this, and is a cross-sectional view of the optical waveguide structure taken in a direction perpendicular to the waveguide.

The strip-loaded optical waveguide structure disclosed in this document includes a GaAs substrate 11 and /l! 2GaAs lower cladding layer 13
and GaAs optical waveguide layer 15, and this GaAs optical waveguide layer 1
#jGaAs is provided on the optical waveguide layer 15 and is formed into a strip shape on the portion of the optical waveguide layer 15 that is desired to be used as an optical waveguide, and the other portion is thinner than the strip-shaped portion 17a +7b.
The upper crack is similar to the strip-loading type disclosed in Reference No. 78, but
A strip-loaded optical waveguide structure as shown in cross-section in FIG. 3(B), in which the upper cladding layer has only a strip-shaped portion 17a, has also been known.

Further, as another optical waveguide structure, a rib type structure as shown in cross section in FIG. 3(C) is known. This includes a compound semiconductor substrate 11, a lower cladding layer 13 provided on this substrate 11, an optical waveguide layer 15 provided on the lower cladding layer 13, and an optical waveguide of this optical waveguide layer 15. 1 and a strip-shaped layer 15a made of the same material as the optical waveguide layer 15.

In both the strip-loaded type and the rib type, a strip-shaped upper cladding layer portion 17a or a strip-shaped layer made of the same material as the optical waveguide layer 15 is placed on the dimensional slab waveguide (optical waveguide layer 15). 15a such as protrusion 17a. I5a is provided, and the optical waveguide layer 15
The equivalent refractive index distribution in the lateral direction is high immediately below the protrusions 17a, 15a and low on both sides thereof. By adjusting the width W of the protrusions 17a, 15a and the thickness T of the optical waveguide layer 15, the protrusions 15a. I
In the region corresponding to 7a (the region shown in FIGS. 3(A) to 3(C)), an optical waveguide (intrinsic) moat with a three-dimensional distribution was generated.

In addition, when using an optical device having such an optical waveguide structure in the input boat section by linking it with an external device, for example, the perspective view and side view are shown in FIGS. 4(A) and (B). As shown in FIG.
The signal light is input to the portion 15b directly below 5a (see 9 in FIG. 4(A)).

(Problem to be Solved by the Invention) However, in both the strip-loaded type and rib type optical waveguide structures as described above, a dimensional slab waveguide (optical waveguide layer 15) is provided on the upper side of the substrate. It has a structure in which protrusions 15a and 17a are provided on specific areas of the substrate.

Therefore, even in the region tf2 (region ■ in FIGS. 3(A)-(C)) other than directly under the protrusions 15a and 17a of the optical waveguide layer 15, the waveguide mode has a two-dimensional distribution different from that in the region (■). exists.

In addition, the dimensions of each part of both strip-loaded and rib-type optical waveguide structures depend on the size of the optical switch to be made into a monolithic structure, but for example, an example of integrating a directional coupler type optical switch Considering that, the optical waveguide layer 15
The thickness T is 0.5 um, and the strip-like protrusion 15a, 1
The width W of 7a is about 3 um. On the other hand, the core diameter φ (see FIG. 4) of the single-mode optical fiber 23 (hereinafter abbreviated as optical fiber 23) for sending signal light to the optical element 21 having such an optical waveguide structure is: Currently IO
It is about um. That is, the core diameter φ is extremely large, such as 3 to 20 times the cross section +5b of the waveguide of the optical element 21.

Therefore, in such a situation, the optical fiber 23 and the optical element 21
When trying to perform optical coupling with the optical fiber 21, the signal light emitted from the optical fiber 21 having a three-dimensional light distribution will also irradiate the region II, which is also the region II, as shown in FIG. will be done. As a result, within the optical element 21,
Normal mode light S guided in area I%. Then, two-dimensional mode light (indicated by S in FIG. 5, hereinafter also referred to as slab waveguide light) guided through region I+ begins to propagate. This slab waveguide light enters other elements 21b and 2+c other than the desired element 21a among the many elements provided in the optical element 21 through the optical waveguide layer 15 and disturbs the operation of these elements 21b and 21c. ,
Originally it should have been removed.

The present invention has been made in view of the above points, and therefore, an object of the present invention is to provide an optical waveguide structure provided at the input port portion of an optical element, which is capable of reducing the influence of slab guided light. Our goal is to provide the following.

(Means for Solving the Problems) In order to achieve this object, the present invention provides an optical waveguide structure provided at an input port portion of an optical element, which includes at least a substrate and an optical waveguide structure provided on the upper side of the substrate. an optical waveguide layer;
In an optical waveguide structure with a refractive index distribution formed by a strip-shaped layer provided on the optical waveguide layer and defining an optical waveguide, the input-side end region of the input port section on both sides of the strip-shaped layer It is characterized in that each of the optical waveguides has a recess formed by removing at least a portion of the optical waveguide layer in a predetermined region of the optical waveguide.

Note that the above-mentioned strip-shaped layer can be constructed using a strip-shaped upper cladding layer or a strip-shaped layer using the same material as the material of the optical waveguide layer.

Further, a structure may be adopted in which a lower cladding layer is provided between the above-mentioned substrate and the above-mentioned optical waveguide layer.

(Function) According to such a structure, at least the optical waveguide layer is absent in the recesses provided on both sides of the strip-like layer. Therefore, since the diameter of the optical fiber is larger than the cross-sectional area of the part directly under the strip-like layer of the optical waveguide layer, when the signal light is introduced into the part directly under the strip-like layer of the optical waveguide layer, the surrounding area Even if the signal light enters one part of the slab waveguide structure, the recess increases the loss of the slab waveguide light, making it difficult for the slab waveguide light to propagate within the optical element.

(Embodiments) Hereinafter, embodiments of the optical waveguide structure of the present invention will be described with reference to the drawings. However, the figures used in the following explanation are merely shown schematically to the extent that this invention can be understood, and therefore, the dimensions, shapes, distribution and closing of each component, and dimensional ratios between each component, etc. It should be understood that this is only schematic and the invention is not limited to the illustrated example. Further, the following embodiments will be described based on an example in which the present invention is applied to the strip-loaded optical waveguide structure described using FIG. 3(B).

-80 Figures 1 (A) and (B) are diagrams for explaining the optical waveguide structure of the first embodiment, and Figure 1 (A) is an optical FIG. 1(B) is a perspective view focusing on the vicinity of the input port of the element 21 (for example, an optical switch or an optical integrated circuit), as viewed from the direction indicated by P in FIG. 1(A). FIG.

The optical waveguide structure of the first embodiment uses, for example, GaA as a substrate.
s substrate 11, an ALI GaAs lower cladding layer 13 as a lower cladding layer provided on this GaAs substrate 11, a GaAs optical waveguide layer 15 as an optical waveguide layer, and an optical waveguide of this GaAs optical waveguide layer 15. a strip-shaped upper cladding layer 17a provided on a desired portion to define an optical waveguide, and both sides of the strip-shaped upper cladding layer 17a in the input side end region of the input port portion of the optical element 21. The structure includes recesses 31 formed by removing a portion of each of the optical waveguide layer 15, the lower cladding layer 13, and the substrate 11 from the surface of the optical waveguide layer 15 to the substrate 11 in a predetermined area 1. . Furthermore, the recessed portion 31 in this case is, as shown in FIG. 1(B),
It has a rectangular shape with an area of W2, and starts from the strip-shaped upper clamp layer 17a! , and is provided at a position spaced apart by β2 from the input side end surface 21a of the optical element 21. Note that the lower cladding layer 13, the optical waveguide layer 15, and the strip-shaped upper cladding layer a have a composition and layer thickness each having a predetermined refractive index so that an optical waveguide structure with a refractive index distribution can be constructed. Strip-shaped upper cladding layer 1? The width W of a (see FIG. 1(B)) is a predetermined width.

According to the optical waveguide structure of the first embodiment, as shown in FIG. 1CB), the signal light incident from the input side end face 21a of the optical element is transmitted to the upper cladding layer in the form of a strip. 1
7a.

On the other hand, the slab waveguide light that is about to propagate in region IIu of the signal light is guided through the recess 31, and therefore passes through a region without a waveguide structure, so that it passes through the optical element end face 2I.
When entering the recess 31 from the optical waveguide layer portion near a, it spreads in the vertical direction. Therefore, the slab waveguide light suffers a loss and only a part of it reenters the optical waveguide layer from the recess 30. And the loss becomes 20 dB or more. Therefore, the adverse effects of slab waveguide light on optical elements can be reduced.

Next, in order to deepen the understanding of the present invention, an example of the method for manufacturing the optical waveguide structure described using FIGS. 1(A) and 1(B) will be described.

First, on the GaAs substrate 11, AL1 with x=0.3
xGaXAs lower urat layer 13 has a thickness of 1 day m, and GaAs optical waveguide layer 15 has a thickness of 0.5 um, roughly X=0.3 A+jyGa+-x^S upper upper side 9
Make it 91.

Next, this AQGaAs upper cladding layer is processed as described below to form a strip-shaped upper cladding layer 17a.
%Form. First, a stripe-like resist pattern with a stripe width of, for example, 3 um is formed on the A9GaAs upper crat layer, and then /l! The portion of the jGaAs upper cladding layer exposed from this resist baton is
For example, reactive ion etching (RI) using gas
E) to form a linear protrusion, ie, a strip-shaped A+jGaAs upper cladding layer 17a, with a width of 3 um and a height of 1 um.

Next, as shown in FIG. 1(B), the two sides of the recess 31 are spaced apart by β1 from the strip-shaped upper crund layer 17a and spaced apart by ρ from the end face of the optical element. , W+XW2 is applied to the region from the optical waveguide layer 15 to the substrate.
The recessed portion 31 having an area of is formed by, for example, photolithography technology and RIE technology.

In this way, the optical waveguide structure of the first example was formed. In addition, the dimensions of each part of the optical waveguide structure of the first example are w=3u
m. w+ = W2 = 50um, u+ = 3gm. ρ2
=lOum. However, these dimensions are merely examples, and it is clear that the dimensions can be changed to suit the design.

Figure 2 is a diagram for explaining the optical waveguide structure of the second embodiment, and is a plan view showing this optical waveguide structure corresponding to Figure 1 (B). be.

The optical waveguide structure of this second embodiment is characterized in that the recess 31 is provided over the end surface 21a of the optical element. The rest of the configuration is the same as that of the first embodiment, so the explanation thereof will be omitted.

In the optical waveguide structure of the second embodiment, the distance from the optical fiber to the element end face 21a in region (2) and the distance from the optical fiber to the wall surface 31a of the recess 31 in region II are larger than the latter by W2. becomes longer. Therefore, the coupling efficiency between the optical fiber and the optical element becomes worse in region II, so the slab light guided in region 11% becomes smaller and its adverse effects can be reduced.

Note that this invention is not limited to the above-described embodiments, and can be modified in various ways as described below.

The above embodiment was an example in which the present invention was applied to the strip-loaded optical waveguide structure shown in FIG. 3(B). However, this invention is shown in Figure 3 (A)! Effects similar to those of the embodiment can be obtained even if the present invention is applied to the strip-loaded optical waveguide structure explained using the above embodiment and the rib-type optical waveguide structure explained using the embodiment shown in FIG. 3(C).

Further, in the embodiment, the recess 31 has been described as having a rectangular shape. However, the shape is not limited to this, and can be changed to a shape suitable for the design, such as a triangle or a circle.

Further, in the embodiment, the recess 31 has a depth extending from the surface of the optical waveguide layer 15 to the substrate 11, but the recess 31 may have a depth that at least substantially penetrates the optical waveguide layer 15.

Further, in the embodiment, the recesses 31 are arranged symmetrically with the strip-shaped upper cladding layer 17a interposed therebetween. However, depending on the design, the arrangement may be asymmetrical. Further, the shapes and sizes of the recesses 31 on both sides of the strip-shaped upper cladding layer do not necessarily have to be the same, and the number of recesses 31 on both sides of the strip-shaped upper cladding layer may be roughly two or more. The number of recesses may be different from each other.

Furthermore, in the above embodiment, /l9GaAs/GaAs
Although the explanation is given using an example using a type material, the materials that can be used are not limited to this, and similar effects can be expected even if other suitable materials are used.

(Effects of the Invention) As is clear from the above description, the optical waveguide structure of the present invention has a structure in which there is no optical waveguide layer at least in the recesses provided on both sides of the strip-like layer. Therefore, when the optical waveguide structure of the present invention is used in the input port of an optical integrated circuit, etc., when signal light is input into the strip-like layer surface of the optical waveguide layer, the signal is transmitted to the surrounding slab waveguide structure. Even if light enters, the recess increases the loss of the slab-guided light, making it difficult for the slab-guided light to propagate within the optical element.

This makes it possible to reduce the adverse effects of slab waveguide light.

[Brief explanation of the drawing]

FIG. 1(A) is a perspective view showing the optical waveguide structure of the first embodiment. FIG. 1(B) is a plan view showing the optical waveguide structure of the first embodiment, FIG. 2 is a plan view showing the optical waveguide structure of the second embodiment, and FIGS. 3(A) to (C) are FIG. 4 is a cross-sectional view for explaining the conventional optical waveguide structure; FIG. 4 is a diagram for explaining the conventional structure and the present invention; FIG. 5 is a perspective view for explaining the problems of the conventional technique. DESCRIPTION OF SYMBOLS 11... Substrate, 13... Lower cladding layer 15... Optical waveguide layer 17a... Strip-shaped upper cladding layer 21...
Optical element 21a... Input side end face of optical element 23... Optical fiber, 31... Recessed portion 31a.
...Part of the wall of the recess.

Claims (4)

[Claims] (1) An optical waveguide structure provided at an input port portion of an optical device, which includes at least a substrate, an optical waveguide layer provided on the upper side of the substrate, and a strip provided on the optical waveguide layer to define an optical waveguide. In an optical waveguide structure with a refractive index distribution composed of a strip-shaped layer, at least a portion of the optical waveguide layer is removed in a predetermined area on both sides of the strip-shaped layer in the input side end region of the input port section. An optical waveguide structure characterized by each having a concave portion. (2) The optical waveguide structure according to claim 1, wherein the strip-shaped layer includes an upper cladding layer. (3) The optical waveguide structure according to claim 1, wherein the strip-shaped layer is made of the same material as the optical waveguide layer. (4) The optical waveguide structure according to claim 1, further comprising a lower cladding layer between the substrate and the optical waveguide layer.