JPS60156012A - Flush type optical waveguide - Google Patents

Abstract

PURPOSE:To enable addition of functions such as demultiplexing, multiplexing, switching and modulation of light by forming a groove for an optical waveguide on the surface of a substrate and porviding a c-axis oriented ZnO crystal body. CONSTITUTION:A flush type optical waveguide device has a Y-shaped optical waveguide 2 consisting of the c-axis oriented film of ZnO formed in an Si single crystal substrate 1. The Si substrate 1 is cut out at the face perpendicular to the (1, 1, 1) face, for example, (1, 1, -2) face. The waveguide 2 is formed at 45mum in both width and depth (thickness) in this embodiment. Such waveguide in adequate for connection to an optical fiber having 50mum core diameter. The top flank of the waveguide 2 and the surface of the substrate are flush with each other. The other three flanks of the waveguide 2 are enclosed by an SiO2 film 3. The SiO2 film 3 protects optically the ZnO film 2 and increases numerical aperture.

Description

[Detailed description of the invention] Background of the invention The present invention relates to an embedded optical waveguide device.

In recent years, along with the development of optical communication technology, the miniaturization and monolithicization of optical transmission components have been promoted, and instead of the conventional combination of lenses, half mirrors, prisms, etc., all optical functions are integrated on one substrate. There is an increasing demand for a guiding waveguide device that can realize this. Therefore, materials that can achieve active functions such as optical branching, multiplexing, switching, and modulation are required as guide waveguide materials.

There are two types of guiding waveguide devices: one for extremely thin single mode light with a cross-section of the optical waveguide (thickness, width) of about 2 to 5 μm, and one for multi-mode light with a large diameter of 50 to 200 μm. There is something.

L i N b for single mode guiding waveguide device
There are materials using materials such as O 3 , LiTaO 3 , PLZT, and GaAa1-nP as substrates, and optical waveguides can be relatively easily fabricated by techniques such as thermal diffusion of impurities into these substrates. Since these optical materials have an electro-optic effect or an acousto-optic effect, they can achieve the above-mentioned active functions for light by applying an electric field and propagating surface acoustic waves. however,
Since the optical waveguide to be manufactured has a depth of 1 to 2 μm, or at most 2 to 5 μm, it is extremely difficult to input single mode light into the optical waveguide. Especially if the core diameter is 5~
When connecting to a 10 μm single mode optical fiber, there are many problems in practical use, such as the difficulty in aligning the optical axis and the optical axis shifting due to changes in the environment such as temperature.

On the other hand, the optical waveguide device for multi-mode light has the advantage of being easy to connect because it can be used in connection with a large-diameter optical fiber having a diameter of 50 to 200 .mu.m. However, it has the drawback of not being able to achieve the active functions described above. For example, a technique using a polymer material has been devised as a technique for manufacturing an optical waveguide with a large cross section for multi-mode light. This involves mixing polycarbonate with a monomer and forming it into a film by casting. The monomer used is one that undergoes photopolymerization upon irradiation with light and changes its refractive index as it becomes a polymer. By selectively irradiating light onto such film-like materials using masking technology,
A three-dimensional optical waveguide is created by partially changing the refractive index. According to this technique, it is possible to manufacture an optical waveguide with a thickness of about 50 to 200 μm, and it is possible to easily connect it to a multi-mode optical fiber. However, since polymeric materials such as polycarbonate do not have electro-optic or acousto-optic effects, they cannot achieve the above-mentioned active function for light using an external signal. Multi-
Another example of an optical waveguide device for mode light is one in which a leading waveguide with a high refractive index is formed by implanting metal ions such as Ag 10 into a glass substrate. However, even with this device it is not possible to achieve the above-mentioned active functions.

Summary of the Invention The present invention makes it possible to fabricate an optical waveguide with a large cross-sectional area so that it can be connected not only to single-mode optical fibers but also to multi-mode optical fibers.
The present invention provides an embedded optical waveguide device to which active functions such as multiplexing, switching, and modulation can be added.

In the buried optical waveguide device according to the present invention, an optical waveguide groove is formed on the surface of a predetermined substrate, and a ZnOc axis-oriented crystal is grown on the substrate surface including the optical waveguide groove until it fills the leading waveguide groove. It is characterized in that the ZnOo-axis oriented crystal on the substrate surface is removed and the Zn0c-axis oriented crystal remains in the optical waveguide groove as a leading waveguide.

As the substrate, it is preferable to use a Si substrate, particularly a Si single crystal). The thermal expansion coefficients of ZnO and Si are each 4.
OXl 0 /deg, 3.6X10 /deg
are approximately the same, and both materials have good compatibility with changes in ambient humidity. Formation of optical waveguide grooves on the substrate surface is performed using techniques such as anisotropic etching and laser processing depending on the properties of the substrate. This groove may be determined depending on the number of leading waveguides to be fabricated;
It may have an appropriate bend, a three-branched shape, or any other arbitrary pattern. The Zn0 (zinc oxide) C-axis oriented crystal includes a C-axis oriented film in which the C-axis of ZnO is oriented in one direction, and a ZnO single crystal.

The Zn0c axis alignment film is produced, for example, on an amorphous substrate such as glass by magnetron sputtering. A ZnO single crystal is produced, for example, on a single crystal of Si or sapphire by a CvD (chemical vapor deposition) method.

Of course, in addition to the above-mentioned materials, it is also possible to use polymeric materials such as polyimide as the substrate, and methods for producing the crystal body include other sputtering methods, plasma CVD methods,
Various methods such as ion brating method and reactive cluster ion beam method can be employed. The Zn0C axis-oriented crystal on the substrate surface can be removed by optical (mirror) polishing.

The use of ZnOC axially oriented crystals as optical waveguide materials is new. It was found that this crystal has high transparency and low optical transmission loss. Therefore, it can be used as an optical waveguide. This crystal can be grown on the substrate and in the groove to a thickness of about 1 to 5 μm (corresponding to the core diameter of a single mode optical fiber), or to a larger thickness, for example 20 to 5 μm.
It is also possible to grow it to a thickness of about 200 μm (corresponding to the core diameter of a multi-mode optical fiber). Therefore, it is possible to easily connect optical fibers with various core diameters.

ZnOC axially oriented crystals can also achieve various active functions for light, such as electro-optic effects and acoustic modulation. In this way, it is possible to manufacture a guiding waveguide which can be easily connected to various optical fibers including multi-mode optical fibers and which can also have various active functions.

Since the ZnO optical waveguide is embedded in the substrate, the optical waveguide is sufficiently protected by the surrounding substrate.

Furthermore, since the substrate surface and one side of the optical waveguide can be flush with each other, it is easier to form the above-mentioned light control electrodes than in the case of an optical waveguide formed protruding from the substrate surface.

Description of Examples Fig. 1 shows a Si single crystal substrate (simply referred to as Si substrate) (1
) shows a buried optical waveguide device having a Y-shaped optical waveguide 1 (2) made of a ZnOC axis alignment film (referred to as a ZnO film). Si substrate (11 is (1, 1, 1
-) plane perpendicular to the (1°1.2) plane, for example. In addition, in this embodiment, the optical waveguide (2)
is formed to have a width, depth, and thickness of 45 μm.

This is suitable for connecting to an optical fiber with a core diameter of 50 μm.

The upper side of the optical waveguide (2) and the surface of the substrate (1) are flush with each other. The other upper side of the optical waveguide (2) is S i02
Surrounded by a membrane (3). 5i02 film (3) is Z
This is to optically protect the nO film (2) and increase the numerical aperture.

An example of the manufacturing process of such an embedded optical waveguide device will be described in detail below.

A plane perpendicular to the (1,1,1) plane, for example (1,1,2)
Clean the Si substrate (1) with the surface as the surface, and set this Si substrate (1) and a 5i02 target in a magnetron sputtering device. Room temperature, Ar gas pressure 6X10-3
By sputtering for 15 minutes under sputtering conditions of Torr and high frequency input power of 400 W, a film thickness of 0.
3fim 5i02 film (41+5+ Si substrate+1) is grown on the front and back surfaces (see FIG. 2).

Next, on the surface of the Si substrate fi+, for example, AZ1400-
A resist (6) is formed by applying a resist solution No. 27 and prebaking at a constant temperature of 90° C. for about 30 minutes. Set such a Si substrate (1) in an ultraviolet light exposure device, and apply a mask plate (the optical waveguide pattern part is transparent and the other parts are opaque) having a 45 μm 7-shaped optical waveguide pattern in the optical waveguide with a resist ( 6) and expose for 5 seconds. Si substrate (1), for example, AZ DEVELOP
Add 40% to the phenomenon liquid, which is a mixture of ER liquid and pure water at a ratio of 1:1.
Immerse for ~50 seconds, then soak in a stop solution using pure water for 10~1
After soaking for 5 seconds, boil-bake at a constant temperature of 100°C for 1 hour. By the above process, the resist (6) in the part (7) of the mask plate corresponding to the optical waveguide pattern is removed (see Figure 3). Apply (8) to the entire surface and dry.

Such a Si substrate (1) is immersed in a mixed solution of hydrofluoric acid HF and ammonium fluoride NH4F, and the 5i02 film (4) in the portion (7) not masked by the resist (6) is removed by etching. After this, Regis) +61 (
81 is removed with a seven ton (see Figure 4).

Next, the process moves to a step of forming a guide waveguide groove by anisotropic etching. As an anisotropic etching solution for the (1,1,1) plane of a Si substrate, for example, 4 moI! % of pyrocatechol, 46m01! % ethylenediamine and pure water 5Qmot! % and heated to 118°C. When the Si substrate (1) is immersed in this etching solution for about 20 minutes, the areas not masked by the 5i02 film (4) will be removed.
7) Optical waveguide groove etched along the (1, 1, 1') plane, with a square cross section (the branch part of the figure 7 will have a rectangular cross section) with a width and depth of approximately 45μ. (9
) is formed (see Figure 5).

The Si substrate (1) with the grooves (9) formed thereon was again set in the magnetron sputtering device, and sputtered using a 5i02 target for 30 minutes under the same sputtering conditions as above to form a film with a thickness of 0.6 μm (DSi02 buffer layer [
01 is formed on the surface of the Si substrate (1) and the inner surface of the groove (9) (see FIG. 6).

The target of the magnetron sputtering equipment was changed to ZnO ceramics, the Si substrate temperature was 350°C, AX':
By continuous sputtering for about 6 hours under the sputtering conditions of 02=l:l, constant gas pressure lXl0 Torr, high frequency input power 400 W, and 49 mm distance between the Si substrates, the surface of the Si substrate (1) and the grooves ( 9) ZnO sputtered thick film with a thickness of about 60 μm (2
) (see Figure 7).

Finally, the Si3 plate (1) on which Z n OM (2) was formed was
) Place it in a polishing jig and mirror polish the surface to remove Si.
ZnO film (2) on the surface of substrate (1), 5i02 film +3
1 (41 is removed, leaving only the ZnO film (2) in the groove (9) (see Figure 8). In this way, the ZnO film (2) formed in the groove (9) is and the surrounding 5i
A buried optical waveguide is formed using the 02 film (3) as a cladding layer. If necessary, a Si substrate (1) and a ZnO film (
2) Form a new 5i02 film on the surface.

The refractive index of ZnO is 2.9% and the refractive index of 5i02 is 1.41.
If this is the case, the numerical aperture will be a very large value of 1.4.

The waveguide loss of this optical waveguide is 0 for He-Ne laser light.
, s ~1.6 dB/cm0

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of an embedded optical waveguide device, and FIGS. 2 to 8 are sectional views showing the manufacturing process thereof. That's all 1 person outside Tsui Ai Figure 2 Figure 3 Figure 4 Figure 5 "Fuko = 1° Figure 6 Figure i7? Figure 8

Claims (1)

[Claims] A guiding waveguide groove is formed on a predetermined substrate surface, and a ZnOC axis-oriented crystal is grown on the substrate surface including the optical waveguide groove until it fills the optical waveguide groove, and the ZnOc on the substrate surface is grown.
A buried optical waveguide device in which the axially oriented crystal is removed and the ZnOc axially oriented crystal remains as an optical waveguide in the optical waveguide groove.