JPH02272505A - Optical waveguide device - Google Patents

Abstract

PURPOSE:To obtain the inexpensive device which is not limited in the design of the optical waveguide by growing an electrooptical crystal in the form of a thin film on a substrate crystal having the lattice constant nearly equal to the lattice constant of the electrooptical crystal and forming a waveguide on the thin film. CONSTITUTION:The thin film 2 of the electrooptical crystal KTP(KTiOPO4) is grown by a liquid phase epitaxy method on the substrate crystal 1 which has the crystal structure analogous with the crystal structure of the KTP and has the lattice constant nearly equal to the lattice constant thereof. The optical waveguide 3 is formed by an ion exchange or thermal diffusion on this thin film 2. An electrode 5 for applying an electric field to the optical waveguide is formed via a buffer layer 4 on the optical waveguide 3. The buffer layer 4 is needed in order to prevent the absorption of light (TM mode) by the electrode 5 and is formed by using silicon dioxide SiO2 and magnesium fluoride MgF2 or the like. An increase in the degree of freedom in designing the optical waveguide which is heretofore restricted by the infeasibility of growing a large crystal is resulted by widening the area of the substrate crystal surface to be grown with the thin film 2. The high-performance optical waveguide device is thus inexpensively obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical waveguide device used for performing optical branching/coupling, optical demultiplexing/combining, optical modulation, optical switching, and the like.

[Conventional technology]

Conventionally, this type of optical waveguide device.

An optical waveguide is formed on a ferroelectric substrate such as LiNbOs.

While the light is confined in the optical waveguide, it is possible to perform 2-branching/combining 1-branching/combining, modulation, switching, etc. by utilizing the shape of the optical waveguide itself, interference between optical waveguides, electro-optic effect, acousto-optic effect, etc. Those that obtain the function are known.

In addition to LiNb0, °L r
KTP (KT
As shown in FIG. 2, an optical waveguide 3 is formed on a KTP substrate 6, and an electrode 5 for applying an electric field to the optical waveguide is placed on the optical waveguide 3 via a buffer layer 4. and an optical waveguide device is constructed.

[Problem that the invention seeks to solve]

By the way, in conventional optical waveguide devices, the optical waveguide is formed on a ferroelectric substrate by a method such as thermal diffusion or ion exchange, so the substrate is required to have mechanical strength.

Furthermore, a ferroelectric substrate generally has a smaller electro-optic effect than a semiconductor substrate such as InGaAsP.

A homogeneous crystal substrate with a wide area and a thickness of 0.5 xx or more is required. However, in the case of a single ferroelectric substrate, there are problems such as it is difficult to obtain large crystals of good quality and the material is very expensive.

On the other hand, KTP (KT 10
In the case of PO4), it is grown by hydrothermal method or flux method, but it is difficult to grow high-quality, large crystals, which limits the design of optical waveguides and makes devices expensive. There is a problem with storing it away.

Furthermore, although a thickness of several tens of μm is sufficient for forming an optical waveguide, a crystal substrate with a thickness of 0.5 mm or more is used from the viewpoint of mechanical strength, making the optical waveguide device expensive. The problem is that it becomes.

[Means for solving problems]

In the optical waveguide device of the present invention, electro-optic crystal KTiO
PO is grown into a thin film by liquid phase epitaxial growth on a substrate crystal having approximately the same lattice constant as KT 1OPO4, and an optical waveguide is formed on the electro-optic crystal thin film.

〔Example〕

Next, the present invention will be explained with reference to examples.

Referring to FIG. 1, electro-optic crystal KTP (KT i
The OPo 4 ) thin film 2 has a similar crystal structure to KTP and is grown by liquid phase epitaxial growth on a substrate crystal 1 with approximately the same lattice constant, and an optical waveguide 3 is formed on this thin film 2 by ion exchange or thermal diffusion. has been done.

An electrode 5 for applying an electric field to the optical waveguide is formed on the optical waveguide 3 with a buffer layer 4 interposed therebetween. The buffer layer 4 is required for light from the electrode 5 (TM mode)
This is to prevent the absorption of

Silicon dioxide S s O2, Magnenium oxide MgF
'2 mag is used.

Note that it depends on the direction of the electric field and the propagation mode of light.

The buffer layer 4 may not be necessary in some cases. Electrode 5 is.

kl, Cr-Au, Ti-Au, etc. are used.

〔Effect of the invention〕

As explained above, in the present invention, by growing an electro-optic crystal KTP (KT i OPO4) thin film that forms an optical waveguide on a crystal plate by liquid phase epitaxial growth, an optical waveguide can be formed with a thickness of only several tens of μm. Not only can waveguides be formed, but by increasing the area of the substrate crystal plane on which thin films are grown, the design of optical waveguides, which had been limited by the inability to grow large crystals, now has more flexibility and is cheaper. This has the effect that high-performance optical waveguide devices can be manufactured.

Figure 1

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of an optical waveguide device according to the present invention, and FIG. 2 is a sectional view showing an example of a conventional optical waveguide device. 1...Substrate crystal, 2...・KTP (KT 10P0
4) Thin film; 3.・Optical waveguide, 4...buffer layer, 5.
... Electrode, 6...KTP (KTiOPO4). Figure 2

Claims (1)

[Claims] 1. An optical waveguide device characterized in that an electro-optic crystal is grown in the form of a thin film on a substrate crystal having substantially the same lattice constant as the electro-optic crystal, and an optical waveguide is formed on the electro-optic crystal thin film.