JPH01198706A - Embedded type optical waveguide - Google Patents

Abstract

PURPOSE:To suppress or eliminate an increase of the loss of waveguide light caused by the roughness of a core corner part by forming the border surface part between a lower clad and a core above the top surface of the lower clad or forming a buffer layer between the core and upper clad. CONSTITUTION:This embedded type optical waveguide has the waveguide light propagated in its core 13. At this time, the border surface part 15 between the lower clad 12 and core 13 is formed above the top surface of the lower clad 12, so neither of both lower corner parts 13c and 13d of the core 13 have scatter loss and the transmission characteristics of the optical waveguide is improved by as much as the scatter loss is suppressed. Further, the scatter loss of not only both lower corner parts 13c and 13d of the core 13, but also both upper corner parts 13a and 13b of the core is also suppressed. Consequently, the transmission characteristics of the optical waveguide are improved more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a buried optical waveguide, which is a type of three-dimensional waveguide.

rPrior art 1 Generally, in waveguide devices with optical modulation and switching functions, three-dimensional optical waveguides of the type that confine light waves in the thickness and width directions of the waveguide layer are widely used. As one type of three-dimensional optical waveguide, a buried optical waveguide shown in FIG. 5 is provided.

In the buried optical waveguide shown in FIG. 5, a core 3 having an isosceles trapezoidal cross section is formed on a lower cladding 2-L formed on the upper surface of a substrate l, and the upper surface and both side surfaces of the core 3 are covered with an upper cladding 4.
It is covered by

In this case, the refractive index of the core 3 is n1, the refractive index of the lower cladding 2 is 12. The refractive index of the upper C-4 is n3, and the relationship between these is n+>n2. n4>n:+.

The buried optical waveguide shown in Fig. 5 includes a process of planting a lower cladding 2 on a substrate l, a process of forming a two-dimensional waveguide on the lower cladding 2 by epitaxial growth, and a process of photorinsing unnecessary parts of the two-dimensional waveguide. The core 3 is manufactured through a step of removing an etch lag using lithography to form the core 3, a step of covering the core 3 with an upper cladding 4, and the like.

It is said that such a buried waveguide can easily have a low-loss crotch portion, and that an optical modulator and an optical switch can be easily constructed by loading a control electrode on the waveguide surface.

rProblems to be Solved by the InventionJ However, when making the core 3 having an isosceles trapezoid cross section in the embedded waveguide shown in FIG. ) is core 3
The roughness of the corners 3a, 3b, 3C13d causes scattering of the guided light, resulting in increased loss.

In view of the above-mentioned problems, the present invention aims to provide a buried optical waveguide that can suppress or eliminate the increase in loss of guided light caused by the roughness of the core corners.

Means for Solving Problems J In order to achieve the intended purpose, the first invention (specific invention) according to the present invention includes a lower clad and a rectangular cross section formed in a raised manner on the upper surface of the lower clad. In a buried optical waveguide, the core has a higher refractive index than the lower cladding and the upper cladding, and the interface between the lower cladding and the core is It is characterized by being formed higher than the upper surface of the lower cladding.

The second invention according to the present invention, in order to achieve the intended purpose,
The core has a lower cladding, a core with a rectangular cross section that is raised on the upper surface of the lower cladding, and an upper cladding that covers the upper surface and both sides of the core, and the core has a higher refractive index than the lower cladding and the upper cladding. A certain buried optical waveguide is characterized in that the interface between the lower cladding and the core is formed higher than the upper surface of the lower cladding, and a buffer layer is formed between the core and the upper cladding.

r Effect J In the buried optical waveguide of the present invention, guided light propagates through its core.

In this case, in the first invention, since the interface between the lower cladding and the core is formed higher than the upper surface of the lower cladding, scattering loss does not occur at both lower corners of the core, as will be described later. The transmission characteristics of the leading wavepath are improved by the amount that loss is suppressed.

Furthermore, in the second aspect of the invention, scattering loss is suppressed not only at both lower corners of the core but also at both upper corners of the core due to the interposition of the buffer layer, so that the transmission characteristics of the leading waveguide are further improved.

rEmbodiment 1 First, an embodiment of the buried optical waveguide according to the first invention will be described with reference to FIG.

In the buried optical waveguide shown in FIG. 1, a lower cladding 12 is formed on a substrate 11, a core 13 is formed on the lower cladding 12, and the upper surface and both side surfaces of the core 13 are covered with an upper cladding 14. and the interface part 15 between the lower Clara White 2 and the core 13 is
It is formed higher than the upper surface of the lower clad 12.

The refractive index n1 of the core 13 and the lower cladding 12 in the above
The refractive index n2 of the upper cladding 14 and the refractive index n3 of the upper cladding 14 have a relationship of II+>112. Il+>113.

As for the composition of the core and cladding that satisfy such a relative refractive index difference, for example, the core 13 is made of GaAs,
The lower cladding 12 and the upper cladding 14 are made of AlGa.
Consisting of As.

In addition, the composition of the substrate 11 is also made of GaAs, for example.

In the buried optical waveguide shown in Figure 1, the core 1 has a square cross section.
3 is the four corner parts 13a, 13b, 13c,
13d, the lower cladding 12 and the core 13
Since the interface portion 15 with the lower cladding 12 is one step higher than the upper surface of the lower cladding 12, the lower cladding 12 has two corner portions 12a and 12b.

Therefore, a relative distance S1 occurs between each lower corner 13c, 13d of the core 13 and each corner 12a, 12b of the lower cladding 12, and each corner 13c, 13d has a distance 111st from each corner. Separate from 12a and 12b.

In the buried optical waveguide shown in FIG. 1, guided light propagates through a core 13 covered with a lower cladding 12 and an upper cladding 4, as in the general example.

In this case, the corners 12a and 12b of the lower cladding 12
, Scattering loss occurs at the corners 13a and 13b of the core 13 due to minute irregularities in these parts, but as described above, the core corners 13c and 13d are located at the lower cladding corner 12a.
, 12b, these corners 12a
, 12b do not affect the core 13, and the transmission characteristics of the waveguide are improved accordingly.

Next, an example of manufacturing the buried optical waveguide shown in FIG. 1 will be briefly described with reference to FIGS. 2(a), 2(b), and 2(c).

In the process shown in FIG. 2(a), after the substrate 11 made of a GaAs wafer is surface-treated, Alo, O3Gao, and Alo, O3Gao, and Alo, O3Gao, and O3Gao with a film thickness of 5 mm and 9 mm are deposited on the substrate 11 as the lower cladding 12, respectively.
rAs is epitaxially grown, and then Ga with a film thickness of 21L is grown as a core 13 on the lower Clara Shiro 2.
As is grown epitaxially.

For such continuous epitaxial growth, MOCVD method is employed, for example.

In the step shown in FIG. 2(B), a generally known photolithography method is carried out, and the unnecessary portion of the core 13 and the upper layer portion of the lower cladding 12 (excluding the interface portion 15) are removed by etching. By removing it, a core 13 having an isosceles trapezoidal cross section and a lower cladding 12 whose upper surface except for the interface portion 15 is one step lower are formed.

Core 13 in the above photophosphorography method. The etching depth of Lower Clara White 2 is 3.5 pots in total.

As the etching liquid, for example, a tartaric acid-based etching liquid is used.

In the step shown in FIG. 2(c), the upper cladding 14 is epitaxially grown over the upper surface of the lower cladding 12 and each exposed surface (upper surface, both side surfaces) of the core 13 using the same method as described above. , covering both sides.

In this way, the buried optical waveguide shown in FIG. 1 is obtained.

Next, an embodiment of the buried optical waveguide according to the second invention will be described with reference to FIG. 3.

In the case of the buried optical waveguide shown in FIG. 3, a lower cladding 12 is formed on the substrate 11, a core 13 is formed on the lower cladding 12, and a buffer layer 1B is formed on the upper surface of the core 13. At the same time, both sides of the core 13 and the top surface of the papua layer 18 are covered with the upper Clara White 4, and the interface part 1 between the lower Clara White 2 and the core 13 is covered.
5 is formed higher than the upper surface of the lower cladding 12.

The refractive index Ill of the core 13 in the above, the lower cladding 1
The refractive index n2 of the upper Clara white 4, the refractive index n3 of the buffer layer 16, and the refractive index n4 of the buffer layer 16 have the following relationship: nl>n2,
n+>n3, nl>nn, and the composition of each part that satisfies such relative refractive index difference is, for example, core 13.
is made of GaAs, the lower cladding 12, the upper cladding 4 and the buffer layer 1B are made of AlGaAs, and the substrate 11 is also made of Gaks, for example.

The embedded optical waveguide shown in FIG. 3 also has a core 13 with a square cross section.
are the four corners 13a, 13b, 13c, 1
3d, and the lower cladding 12 has two corner parts 12a,
12b, but in addition to this, the buffer layer 1B has two corners lea and 1I3b.

Therefore, both lower corners 13c and 13d of the core 13
A relative distance S+ is generated between the upper corners 13a, 13b of the core 13 and both corners lea, 18b of the bar/77 layer 16. Relative distance +11s2
occurs, therefore, both lower corners 13c, 1 of the core 13
3d is separated from both corners 12a and 12b by the distance *S+, and both upper corners 13a and 13b of the core 13 are separated by a distance of +11
Both corners tea and Hlb are separated by s2.

In the buried optical waveguide shown in FIG. 3, guided light propagates through a core 13 covered with a lower cladding 12 and an upper cladding 14, as in the general example.

In this case, the corners 12a and 12b of the lower cladding 12
, at the corners 113a and 1flb of the buffer layer 16,
Scattering loss occurs due to minute irregularities in each of these parts, but as described above, the core corners 13a, 13b, 13c,
13d are these corners 12a, 12b, lea
, 18b, each color portion 12a,
The influence of the minute irregularities of 12b, 18a, and 18b does not spread to the core 13, and the transmission characteristics of the waveguide are improved overall.

Next, an example of manufacturing the buried optical waveguide shown in FIG. 3 will be briefly described with reference to FIGS. 4(a), 4(b), and 4(c).

In the process shown in FIG. 4(A), after surface-treating the substrate 11 made of a GaAs wafer, a lower cladding 12 of Alo, o3Gao, and uA with a film thickness of 5ILs+ is formed on the substrate ll.
a with a film thickness of 2 as the core 13 on the lower cladding 12.
A buffer layer IB is placed on the core 13 of the IL layer GaA+.
As a result, Alo, o3Gao, and uAs having a thickness of 2 μm are each successively grown epitaxially.

For such continuous epitaxial growth, the same MOCVD method as in the previous example is employed.

In the step of FIG. 4(b), the photolithography method described above is carried out, and etching is carried out at that time.

removing unnecessary parts of the core 13 and buffer layer 16 and the upper layer part of the lower cladding 12 (excluding the interface part 15),
This forms a core 13 whose upper surface is covered with the buffer layer 1B and whose cross section is an isosceles trapezoid, and a lower cladding 12 whose upper surface except for the interface portion 15 is lowered.

The total etching depth of the buffer layer 1B, core 13, and lower cladding 12 in the photolithography method is 5.51 Lys.

As the etching liquid, for example, the tartaric acid type mentioned above is used.

In the step shown in FIG. 4(c), the upper cladding 14 is epitaxially grown over the upper surface of the lower cladding 12 and each exposed surface (upper surface, both side surfaces) of the core 13 using the same method as described above. , covering both sides.

In this way, the buried optical waveguide shown in FIG. 3 is obtained.

In the buried optical waveguides of the first and second inventions, for example, when forming the lower cladding 12 made of AlGaAs by epitaxial growth on the substrate 11 made of a GaAs wafer, the crystal growth properties of the lower cladding 12 are made to be good. In order to achieve this, a film thickness of 0. I ILta level of Ga
A buffer layer made of As may be formed, and the lower cladding 12 may be formed on the buffer layer.

“Effect of the Invention 1 As explained above, in the buried optical waveguide of the first aspect of the present invention, since the interface between the lower cladding and the core is formed higher than the upper surface of the lower cladding, the core No scattering loss occurs at both lower corners, improving the transmission characteristics of the optical waveguide.

Furthermore, in the second aspect of the invention, the transmission characteristics of the optical waveguide are further improved because scattering loss does not occur not only at both lower corners of the core but also at both upper corners of the core due to the presence of the buffer layer.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view showing an embodiment of a buried optical waveguide according to the first invention of the present invention, and FIGS.
C) is an explanatory diagram schematically showing an example of manufacturing the buried optical waveguide according to the first invention in the order of the steps, and FIG.
Expanded cross-sectional views showing one embodiment of the buried optical waveguide according to the invention, (A), (B), and (C) in Figure 3 are schematic illustrations of manufacturing examples of the buried optical waveguide according to the second invention in the order of steps. The illustrated diagram, FIG. 5, is a sectional view showing a conventional buried optical waveguide. 11・・・・・・・・・・・・・・・・・・・・・Substrate 1
2・・・・・・・・・・・・・・・・・・Lower cladding 12a, 12b・・・・・・・・・・・・Corner part 13 of lower cladding・・・・・・・・・Conflict◆
・Bou・Core 13a, 13b, 13c, 13d -----
--Core FIAffl14・・・・・・・・・・・・
......Top cladding 15...
......Interface part 113- ・Conflict 1・ψ・
・11th Order ・1101111 Kenkai Buffer Layer 18a, 1
6b・・・・・・・・・・・・・・・・Corner of buffer layer Patent attorney Yoshio Saito Procedural amendment 2 Title of invention Buried optical waveguide 3 Relationship with the case of the person making the amendment Patent Applicant Furukawa Electric Co., Ltd. Nippon Telegraph and Telephone Company 4 Agent Address: 5 Kotani Building, 1-6-6 Yurakucho, Chiyoda-ku, Tokyo 100 Date of amendment order (voluntary) 6 Details of one invention in the specification to be amended Add the following sentence after line 20 on page 12 of the statement of contents for the correction in column 1. ``In addition, regarding the core shape which should be a square cross-section, in the above-mentioned embodiments, a core with an isosceles trapezoid cross-section was exemplified in view of the fact that the etching rate differs in the crystal direction.
An isosceles trapezoidal core formed using an etching solution, with the isosceles part slightly rounded, and a core formed using dry etching technology, with a roughly rectangular cross section. Furthermore, cores having these cross-sectional shapes, such as cores having a substantially rectangular cross-section with slightly rounded legs, are also included in cores having a rectangular cross-section. 1 or more

Claims (2)

[Claims] (1) A lower cladding, a core with a rectangular cross section that is raised on the upper surface of the lower cladding, and an upper cladding that covers the upper surface and both sides of the core, and the core is higher than the lower cladding and the upper cladding. In a buried optical waveguide with a refractive index, the interface between the lower cladding and the core is
A buried optical waveguide characterized by being formed higher than the upper surface of its lower cladding. (2) A lower cladding, a core with a rectangular cross section that is raised on the upper surface of the lower cladding, and an upper cladding that covers the upper surface and both sides of the core, and the core is higher than the lower cladding and the upper cladding. In a buried optical waveguide with a refractive index, the interface between the lower cladding and the core is
A buried optical waveguide, characterized in that the buffer layer is formed higher than the upper surface of the lower cladding, and a buffer layer is formed between the core and the upper cladding.