JPS6083904A - Optical waveguide and its manufacture - Google Patents

Abstract

PURPOSE:To enable monolithic coupling to laser of a III-V group compound semiconductor or the like by forming a layer of an iron-garnet single crystal between a layer of a garnet single crystal contg. no iron and an amorphous or polycrystalline layer contg. no iron to manufacture an optical waveguide. CONSTITUTION:An amorphous Si3N4 film 10 is formed on a III-V group compound substrate 9 such as an InP single crystal substrate, and an amorphous or polycrystalline film 11 of Gd3Ga5O12 or the like contg. no iron is formed on the film 10. Laser beams 13 split into two parts are irradiated on the film 11 to form a Gd3Ga5O12 single crystal region 12 by zone melting, and a Y3Fe5O12 film 17 is formed on the single crystal region 16 (12) by a solid phase epitaxial method. An amorphous or polycrystalline layer 18 of Gd3Ga5O12 is then formed to complete an embedded optical waveguide. Since the optical waveguide film 17 of garnet contg. iron has high efficiency, small-sized optical isolator or an optical integrated circuit can be formed with high reliability.

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.

[Background of the invention]

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. An optical isolator made of a magneto-optic material is used as a component of an optical communication system in order to stabilize a laser light source.

As a conventional optical isolator, one having a basic configuration as shown in Fig. 1 is known.

Miyazaki, Akao, Ichigaku Technical Report MW80-95 (1981)
).

That is, a Bi:YIG thin film 2 and a ZnO upper layer 3 are formed on a GGG single crystal substrate 1 by RF sputtering.
Furthermore, a mode selection circuit 4 of A4 cladding layer, a non-reciprocal circuit 5 consisting of a magnetized film, and a reciprocal circuit 6
, has a structure in which a rutile prism 7 is added. In this optical isolator, the plane of polarization of the laser beam incident on the rutile prism 7 is rotated under the influence of the Faraday effect and the Kotton-Mouton effect, and the laser beam is emitted from the rutile prism 3 at the other end. The light incident from the prism 8 cannot pass through the rutile prism 7 because the plane of polarization is further rotated due to the effects of the Faraday effect and the Kotton-Mouton effect.

The above are typical examples of conventional optical isolators. However, optical isolators with such a configuration are generally constructed by collecting single parts made of oxides, and when applied to optical integrated circuits, they are generally used as a light source. It was not possible to monolithically couple it with a compound semiconductor optical waveguide.

[Purpose of the invention]

Therefore, the present invention has been made to overcome the above-mentioned problems, and the first object is to provide a 4-channel semiconductor laser that can be monolithically combined with a III-V compound semiconductor laser or a III-V compound semiconductor optical waveguide. The second object is to provide an optical waveguide having an IJ structure, the second object is to provide a small planar optical waveguide, the third object is to provide an embedded optical waveguide, and the fourth object is made of iron garnet. The fifth object is to provide an optical waveguide, the fifth object is to provide an optical isolator comprising the optical waveguide of the invention, and the sixth object is to provide an optical integrated circuit using the optical waveguide of the invention.
A seventh object is to provide a method for manufacturing an optical waveguide of the present invention.

[Summary of the invention]

The present invention produces iron garnet by monocrystallizing at least a part of the surface of a non-iron garnet thin film formed on a substrate made of a different material, and solid-phase growth of an iron garnet thin film using this single crystal part as a seed crystal. This was achieved by developing the e1M technology for forming optical waveguides.

As a technique for forming a single crystal thin film on an amorphous material, for example, SO using the split beam method announced by Kashiwazaki
I formation is mentioned [Proceedings of the 30th Spring Conference on Applied Physics, 1983, 6 a-T-10, p.
-6601゜The present invention involves a zone melt experiment using laser annealing of a garnet film that does not contain iron, and a solid-phase epitaxial growth experiment of an iron garnet single crystal film on a garnet single crystal that does not contain iron! i! This is based on the fact that, as a result of conducting this process, a technique was established that allows a desired single crystal film to 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 garnet film is formed on a garnet sample that does not contain iron is as follows.

That is, in order to form an elongated single crystal region such as an optical waveguide on a different type of substrate, liquid phase growth is more advantageous than solid phase growth, and zone melting is preferable. However, since iron garnet is a decomposition-melting compound, it cannot be melted in a bath. For this reason, it is necessary to first form a non-iron-rich garnet single crystal film by the zone melting method and then grow an iron garnet film thereon in a solid phase. Furthermore, by covering the periphery of the iron garnet optical waveguide with garnet that does not contain iron and has a slightly lower refractive index, more efficient optical waveguide characteristics can be obtained.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail by way of examples.

Example 1 FIG. 2 shows an example of the process for forming an optical waveguide according to the present invention. An Si3N4 amorphous film 10 was formed on an InP single crystal substrate 9, and a Gd5Ga50I2 film was further formed by sputter deposition. Next, Qd3 Qd5012
The surface was irradiated with two laser beams 13 and scanned. As a result, the surface of the Gd3Ga5O12 film continued to be melted and crystallized as the laser beam 13 was scanned, and single crystal regions 12 could be formed in the shape of elongated islands with a width equal to the interval between the split beams. Further, it was observed that the area around the single crystal region 12 was a polycrystalline or amorphous negative region 11. In addition, in this experiment,
When scanning with a single laser beam without splitting the beam, it was often difficult to form elongated single crystal regions.

Next, on the island-like Gd5GasO+z single crystal region, as shown in FIG. 3, an island-like Y3 Fes O+ 2 film 17 is formed along the Gd3Ga5O12 single crystal region 16, and Y3F65012 film is heated to 600-L800C. A sample of solid-phase growth was performed. As a result, Y, l penalty 5 (JI2
could be grown into island-like single crystals. Further, a G d3 Ga50+ 2 film 18 was sputter-deposited thereon to create a buried optical waveguide of the present invention.

Embodiment 2 FIG. 4 shows another example of the optical waveguide forming process of the present invention. K on GaAS substrate 19 (JdsfJasO+z
A GdxGasO+z single crystal region 21 was formed using the same method as in Example 1. In the figure, 20 was an amorphous or polycrystalline region. Then the third
As shown in the figure, Y311' e5 (J+ 2 film is
It is formed on the d3Ga5O12 single crystal region and grown in a solid phase in the same manner as in the example. As a result, the island-like Y3F
The e5O12 film was epitaxially grown on a Gd, Ga, 0.2 single crystal to become a single crystal. Furthermore, on top of this, Gd3G
By sputter-depositing an a5O12 film, a buried optical waveguide similar to that shown in FIG. 3 could be formed.

Example 3 In Example 1, instead of replacing Gd3Ga5O12J, an iron-free garnet film shown in Table 1 was formed, and this was zone-melted by scanning with a split laser beam to form a single crystal region. . 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 solid-phase eclipse growth.

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

Example 4 After forming a Gd3Ga5O12 single crystal region in Example 2VC, as shown in FIG.
A 5i02 amorphous film 26 is formed on the Gd3Ga layer.
An opening was formed just above the 5O12 single crystal region 25 as shown in FIG. Furthermore, on top of this, Y3 F e50+
2 MB k Sputter deposition method is used to form one film area wider than the opening, and Y3 is formed by in-phase epitaxy growth.
A Fe50+ 2 single crystal film 27 was formed. At this time Y
It was revealed that the sF e5012 film was grown by in-phase epitaxy and continued to grow on the amorphous film 26 through the opening of the amorphous film 26, so that the entire surface of the Y3Fe5O12 film was made into a single crystal. Furthermore, on top of this ()daGasOt2B!
By performing X28'c sputter deposition, a buried large-area optical waveguide could be formed.

Example 5 As shown in FIG. 6, a Gd3Ga5O12 single crystal region 32 was formed by the method shown in Example 1 on the optical axis extension of an InGaAsP semiconductor laser 3o formed on an engineered np single crystal substrate 29, and an S 1a A N4 thin film 33 was deposited by plasma CVD as shown in the figure. Then Ys
1;' es OH2/J9 film f< Gd3Ga5O1
After forming the 2 single crystal regions 32 and the 5 jaN film 33, the entire structure was made into a single crystal by solid phase epitaxy.

As a result, Ya Fe50+ 2 KM 34 is 5i
The growth continued until the sN< film was reached, and single crystallization was achieved up to the interface with the laser part 30. Furthermore, Gd5Ga50
By covering with the H thin film 35, an optical waveguide made of Y3Fe5O12 could be formed on the extension of the optical axis of a part of the laser.

Example 6 In Example 5, (YB
i) An optical waveguide made of a 3Fe5012 single crystal thin film was formed. Then, as shown in FIG. 7, GdsGagOt
* On the film 40, At thin film outer 0 top) selection circuits 42 and 43 were formed, and reciprocal and non-reciprocal circuits 44 made of a magnetized film were further formed.

The optical waveguide fabricated in this way has a semiconductor laser 41
It has been revealed that the laser beam emitted from the laser beam is emitted from the other end without being attenuated, but the light incident from the other end is attenuated by the time it reaches the laser part 41, so that it functions as an optical isolator. Furthermore, the optical isolator of the present invention is characterized in that it is integrated with the laser light source using the same substrate, making it possible to achieve miniaturization and high reliability.

In addition, in the optical waveguide and the manufacturing method thereof of the present invention, conventional knowledge in the technical field may be used for the points not mentioned above.

[Results of invention]

As shown in the above embodiments, the optical waveguide of the present invention has ■-
(1) Since it has a structure that can be monolithically coupled with a compound semiconductor laser or (2)-v compound semiconductor optical waveguide, it is possible to form a small and reliable optical isolator or optical integrated 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. It should be noted that the zone melt method in the present invention can be achieved by using a donut-shaped laser beam, an acid ion beam, etc. in addition to the split laser beam shown in the embodiments.

Table 1

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a conventional optical isolator, FIG. 2 is a diagram showing the process of single crystallizing a Gd3Ga5O12 film by laser irradiation, FIG. 3 is a diagram showing an example of the optical waveguide of the present invention, and FIG. Gd3Ga5O by laser irradiation
Figure 5 showing another example of the process of single crystallizing 12 films.
The figure shows a wide optical waveguide, Figure 6 is a cross-sectional view of an optical waveguide monolithically coupled to a laser light source, and Figure 7 is a diagram showing an optical isolator monolithically coupled to a laser light source. . 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... LnP single crystal substrate, lO...
S; SN4 amorphous film, 11...Gd3Ga5O12 amorphous or polycrystalline region, 12...Gd5GasO+
2 single crystal film, 13-L/- sir beam, 14-I n
P substrate, 15- Gd3 Gas 012 amorphous or polycrystalline region, 16... Gd3Ga5O12 single crystal region, 17... YB F' es O+ 2 single crystal film,
18...Gd3Ga5O12 film, 19...GaAs
Single crystal substrate, 20...Gd1lGa5012 amorphous or polycrystalline chain acid, 21...Gd5GatO+z single crystal region, 22...laser beam, 23. InP
Single crystal substrate, 24-Gd5(Ja5012 amorphous or polycrystalline region, 25...()d8(Jal+012
Single crystal region, 26...5j02 amorphous film, 27...
Y3Fe5O12 single crystal film, 28 =-Gd5GasO
tz film, 29 ・InP single crystal substrate, 30-In
OaksP semiconductor laser, 31...Gd3Ga5O
12 amorphous or polycrystalline region, 32...Qd3Ga
50tz single crystal region, 33...Si3N4 thin film, 3.
4- Y3Fe5O12 single crystal film, 35-, Gd5Ga
sOtz 117 film, 36 InP single crystal substrate, 37
...Gd3Ga5O12 amorphous or polycrystalline region,
38...GdaGasOt2 single crystal region, 39-...
・(YB i )sFesO++ single crystal region, 40-
Gd3Ga5O12+14x... Part of semiconductor laser, 42.43... Mo No. 1 Port No. 2 VJ No. 3 Port No. 4 Fig. 5 No. 6 Fig. 7 Country 9

Claims (1)

[Claims] 1. An optical waveguide characterized in that an iron-free garnet single-crystal layer is present between an iron-garnet single-crystal layer and an iron-free garnet amorphous or polycrystalline layer. . 2. The optical waveguide according to claim 1, wherein the optical waveguide is formed on a 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 using the all-zone melt method, and a step of single-crystallizing an iron-garnet thin film using a solid-phase epitaxy method using the single-crystallized iron-free garnet as a seed crystal. ,. Oh special grain, optical waveguide manufacturing method.