JPS6083005A - Optical waveguide and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an optical waveguide having a structure enabling monolithic coupling to laser of a III-V compound semiconductor or an optical waveguide of a III-V compound semiconductor by converting an islandlike thin film of garnet contg. no iron into a single crystal by a zone melting method and by growing a thin iron-garnet film in a solid phase using the single crystal as a substrate. CONSTITUTION:An amorphous film 10 of SiO2, Si3N4 or the like is formed on a GaAs substrate 9, and part of the surface of the film 10 is filled with slender islandlike Gd3Ga5O12. Laser beams 13 are irradiated along the Gd3Ga5O12 island to form a slender single crystal region 11 by zone melting. An islandlike Y3Fe5O12 film 18 is formed on the formed islandlike Gd3Ga5O12 single crystal region 16 (11), and it is heated to grow Y3Fe5O12 in a solid phase. The Y3Fe5O12 18 can be grown into an islandlike single crystal using the Gd3Ga5O12 as a single crystal substrate. An upper layer having a slightly lower refractive index is then formed on the grown single crystal by vapor-depositing a Gd3Ga5O12 film. Thus, an embedded optical waveguide is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical waveguide used in optical communication and a method for manufacturing the same.

[Backing force of invention t]

In recent years, the practical application of optical communications has progressed rapidly, and research and development into making optical components smaller and more reliable has been actively promoted. Optical isolators made of magneto-optic materials are used as components of optical communication systems to stabilize laser light sources.

As a conventional optical isolator, one having a basic configuration as shown in FIG. 1 is known. [For example, Taki, Miyazaki,
Akao, IEICE Technical Report MW 8O-95 (1981)] consists of a Bi:YIG thin film 2 and a ZnO upper layer 3 formed by RF sputtering on a GGG single crystal substrate 1, and further includes an At cladding layer. mode selection circuit 4,
It has a structure in which a non-reciprocal circuit 5 made of a magnetized film, a reciprocal circuit 6, and a rutile prism 7 are added. In this optical isolator, the plane of polarization of the laser beam incident from the rutile prism 7 is rotated under the influence of the Faraday effect and the Kotton-Mouton effect, and the laser beam is emitted toward the rutile prism 8 at the other end. The incident light cannot pass through the front rutile prism 7 because the plane of polarization is further rotated due to the Faraday effect and the Kotton-Mouton effect.

The above are typical examples of conventional optical isolators. However, optical isolators with this type of structure are generally constructed by collecting single parts made of oxides, and when applied to optical integrated circuits, a ■-■ compound semiconductor laser or ■-V compound semiconductor laser, which is generally used as a light source, is used. It has been impossible to couple compound semiconductor optical paths and wave paths nonlithically.

[Purpose of the invention]

Therefore, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an optical waveguide having a structure that can be monolithically coupled with a ■-■ compound semiconductor laser or a ■-■ compound semiconductor optical waveguide. Another object of the invention is to provide a compact planar optical waveguide.A further object of the invention is to provide an embedded optical waveguide.A still further object of the invention is to provide a small-sized planar optical waveguide. Still another object of the present invention is to provide an optical isolator comprising the optical waveguide of the present invention.A still further object of the present invention is to provide an optical isolator comprising the optical waveguide of the present invention. In addition to providing a circuit, another object of the present invention is to provide a method for manufacturing the four-wavelength optical waveguide of the present invention.

[Summary of the invention]

The present invention includes an island-like thin film of iron formed on a substrate of different materials;
An iron garnet optical waveguide is formed by solid-phase growth of an iron garnet thin film using this single crystal portion as a plum crystal.

As a technique for forming a single-crystalline thin film on an amorphous material, for example, there is a method published by J-F, Gibbong et al. in which polycrystalline SI formed in an island shape on amorphous 513N4 is made into a single crystal by laser annealing. [J,
F. Gibbons et at, Appl.
pHys.

Lett, 34, (12), 831 (19
79) l. The present invention was developed as a result of a zone melt experiment using laser annealing of a garnet film that does not contain iron, and a solid phase epitaxy growth experiment of an iron garnet single crystal film on a garnet single crystal that does not contain iron. This is based on the determination of the technology that can be obtained. Furthermore, the present invention was made based on the discovery that the island-shaped single crystal film formed by this method functions as an optical waveguide, particularly as a buried optical waveguide.

In the present invention, the reason why an iron carnet film is formed on a garnet film not enriched with iron is as follows. That is, in order to form elongated single crystal regions such as optical waveguides on different types of substrates, liquid phase growth is more advantageous than solid phase growth, and zone melting is preferred. However, iron garnet cannot be melted because it is a decomposition-melting compound. For this reason, it is necessary to once form a garnet single crystal film that does not contain iron by the zone melting method, and then to grow an iron garnet film thereon in a solid phase. Furthermore, by covering the periphery of the iron garnet optical waveguide with iron-free garnet, which has a slightly lower refractive index,
Optical waveguide characteristics with high efficiency can be obtained.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 FIG. 2 shows an example of the process for forming an optical waveguide according to the present invention. S j 02 or S on the GaAS substrate 9
An amorphous film 10 made of i3N4 or the like was formed, and part of its surface was filled with elongated island-shaped Gd3Ga5012.

G d s (ia s 012) is preferably formed by sputter deposition.

The laser beam 13 was scanned along the Gd3Ga5O12 islands to perform zone melting of Qd3Ga5012. At this time, since the molten G (13Ga5012) is surrounded by amorphous materials 10 such as 5i02 or 5isNa, which have low thermal conductivity, crystallization occurs from the low temperature surface, resulting in a long and narrow shape as shown in Figure 2. Single crystal region 11
Fully formed. In this example, polycrystalline formation was observed in the portion 12 in contact with the amorphous material 10.

On the thus formed island-like Gd3 Gas 012 single crystal region, Y3Fe5O12
After the film 18 was formed in the shape of an island along the Gd 3 Gas 012 single crystal region 16, solid phase growth of Ys Fe 5012 was performed by heating to 600 to 800 c. As a result, YaFes01218 could be grown into an island-like single crystal using Gd3Ga5O12 as a single crystal substrate. Furthermore, an upper layer having a slightly lower refractive index was formed by depositing two films of Gd3Ga5Q on top of this, thereby creating a buried optical waveguide of the present invention.

Example 2 As shown in FIG. 4, a Gd3Ga5012 single crystal region 23 was formed by the method shown in Example 1 on the optical axis extension of the 11-body laser 210 on the InGaAsP half formed on the lnp single crystal plate 2o. In addition, S I 3N 4 thin film 2
4 was deposited by plasma C'VD method as shown in the figure.

Next, the Y3Fe6012 thin film 25 is coated with Gds Gas.
After forming on the 012 single crystal region 23 and the 5jsN4 film 24, single crystallization was attempted by in-phase epitaxy growth.

As a result, Y3Fes012 thin film 25 is
The growth continued until it reached the N4 i layer, and it was possible to form a single crystal up to the interface with the laser part 21. Furthermore, Gd3Ga
By covering with the Y'3 Fe5012 thin film 26, an optical waveguide made of Y'3 Fe5012 could be formed on the extension of the optical axis of a part of the laser.

Example 3 Actual 1ilx Example 2 K>Ite, Y3Frs-Ot2(1)
Instead, an optical waveguide made of (YBi>3Fe5012 single crystal thin film) was formed. Then, as shown in FIG.
Mode selection circuits 34 and 35 made of A7 thin films were formed on the Gd5Gas 0121 film 32, and reciprocal and non-reciprocal circuits 36 made of magnetized films were further formed.

The Guhi optical waveguide produced in this way is a semiconductor laser 3
It is clear that the laser light emitted from 33 is emitted from the other end without being completely attenuated, but the light incident from the other end passes through the laser part 33 before being delayed, so it functions as an optical isolator. became. Furthermore, the optical isolator of the present invention is characterized in that it is integrated with the laser light source using the same substrate, and the iron-free garnet film shown in Table 1 is used to achieve miniaturization and high reliability. form,
This was zone-melted by laser irradiation to form a single crystal. Furthermore, an island-shaped iron garnet film shown in Table 1 was formed on this single crystal region, and an iron garnet single crystal film was formed by in-phase epitaxy growth.

Table 1 It was confirmed that the elongated iron garnet single crystal obtained as a result functions as an optical waveguide. In addition, by depositing a garnet film that does not contain iron again on this iron garnet single crystal, we were able to form an optical waveguide with even higher light trapping efficiency.

[Effects of the Invention] As shown in the above embodiments, the optical waveguide of the present invention has ■-
Since it has a structure that can be monolithically coupled with a compound semiconductor laser or a chemical semiconductor optical waveguide, it is possible to form a compact and highly reliable optical isolator or optical circuit.

Further, according to the method of the present invention, it becomes possible to easily form a planar optical waveguide and a buried optical waveguide.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional optical isolator, and FIG. 2 is an example of the present invention in which island-shaped Gd3 is formed by laser irradiation.
Figure 3 showing the process of single crystallizing Ga5O12 film.
4 is a cross-sectional view showing an optical waveguide monolithically coupled to a laser light source section as another embodiment of the present invention, and FIG. 5 is a diagram showing an optical waveguide according to another embodiment of the present invention. FIG. 3 illustrates an example laser light source assembly and optical isolator coupled to a monolift. DESCRIPTION OF SYMBOLS 1... GGG single crystal substrate, 2... Bi:YIG thin film, 3... ZnO upper layer part, 4... Mode selection circuit, 5
... Non-reciprocal circuit, 6... Reciprocal circuit, 7, 8... Rutile prism, 9... GaA3 single crystal substrate, 10...
・Amorphous film such as 5i02 or 5i3N4, 11-=
Gd3Ga5012 single crystal region, 12...Gd5(J
a5012 polycrystalline region, 13... laser beam, 1
4...GaAs single crystal substrate, 15...S i 02
6 or amorphous film such as Si3N4, 16-Gd3
Qa 5012 single crystal region, 17-Gci3Gas01
2 polycrystalline region, 1 B -Ya Fe5O12 single crystal film, 19... ocl, oa, 01m thin film, 20 ・I
nP single crystal substrate, 21-InGaAsP semiconductor V-
Zer, 22-8iO2 film, 23...-Gd3Qa5Q1
2 single crystal region, 24-8r3N4 film, 25-YsFe5
0sz single crystal film, 26”4ds Ga5O12 thin film,
27...InP single crystal substrate, 28...5in2 film,
29...oa, oa 5012 single crystal region, 30-
GdsGasOt2 polycrystalline region, 31 ・= (YB
i) sF”esO12 single crystal thin film, 32,',,Qd
3Qa5012 thin film, 33-InGaAsP semiconductor laser, 34.35...Mote selection circuit, 36th l
l Figure 2 Figure 3 Figure 3 4th port

Claims (1)

[Claims] 1. An optical waveguide characterized in that an iron-free garnet single crystal region is present between a material having a lower thermal conductivity than the garnet and an iron carnet single crystal layer. 2. In claim 1, the optical waveguide is
[An optical waveguide characterized by being formed on an IV compound substrate. 3. The optical waveguide according to claim 1, wherein the optical waveguide is covered with a garnet thin film that does not contain iron. 4. A step of single-crystallizing an iron-free garnet thin film by a zone melt method, and a step of single-crystallizing the above-mentioned iron ganinet thin film by a solid-phase epitaxy method using the single-crystallized iron-free garnet as a seed crystal. A method for manufacturing a leading waveguide characterized by the following.