JPH01260416A - Optical modulator - Google Patents

Abstract

PURPOSE:To improve the modulation efficiency by providing a first electrode through a buffer layer on a three-dimensional optical waveguide which is formed on the upper face of a substrate, and also, providing a second electrode which is formed directly on the surface of the substrate in parallel to an optical waveguide. CONSTITUTION:On a three-dimensional optical waveguide 11 which is formed on the upper face of a substrate 10 consisting of an electro-optical crystal, the first electrode 13 is formed through a buffer layer 12, and also, the second electrode 14 which is formed directly on the surface of the substrate 10 in parallel to the optical wavguide 11 is provided. Accordingly, a capacitance is not constituted between the second electrode 14 and the substrate 10, therefore, in modulation voltages applied between the electrodes 13, 14, the voltage applied to the substrate 10 part contributed to the modulation can be increased. In such a way, the modulation efficiency can be improved.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to optical modulators used in optical communication devices, etc., and is aimed at improving the modulation efficiency of lumped constant optical phase modulators using optical waveguides. a three-dimensional optical waveguide formed on the upper surface of the substrate; a first electrode formed on the optical waveguide via a buffer layer; and a first electrode formed directly on the surface of the substrate parallel to the optical waveguide. This configuration has a second electrode and a second electrode.

[Industrial application field]

The present invention relates to an optical waveguide device in an optical communication device,
In particular, it relates to a phase modulator with improved modulation efficiency.

In optical modulators, lithium niobate (LiN
An electric field is applied to an optical W wave path formed on the surface of a crystal substrate such as b03) to change the refractive index and perform phase modulation on the optical signal traveling through the waveguide.

If a strong electric field can be applied to the optical waveguide with less modulation power, the modulation efficiency will improve, and an electrode structure for this purpose is desired.

[Conventional technology]

A conventional lumped constant type optical modulator, as shown in FIG. 3(A), includes a substrate 1 made of an electro-optic crystal such as LiNbO3, which is cut so that the Z-axis of the crystal axis is perpendicular to the surface;
An optical waveguide 2 is formed by thermally diffusing a band-shaped titanium (Ti) vapor deposited film deposited on the upper surface of the substrate 1, and the optical waveguide 2 has a higher refractive index than the substrate I, and the entire upper surface of the substrate 1 covers the optical waveguide 2. Buffer N3 made of silicon oxide (SiO2) formed in
, a first electrode 4 formed on the upper surface of the buffer layer 3 at a position corresponding to the optical waveguide 2, and a second electrode 4 formed outside the optical waveguide 2 on the buffer N3 parallel to the second electrode. It consists of an electrode 5. This buffer layer 3 is provided to prevent light loss due to the first electrode 4 on the optical waveguide 2.

Then, when a modulation voltage V is applied between both electrodes, an electric field shown in the figure E is generated perpendicularly to the optical waveguide 2, and through the electro-optic effect,
Phase modulation was performed by changing the refractive index of the wave path portion and changing the propagation speed of the optical signal propagating inside the wave path in the X-axis direction.

[Problem to be solved by the invention]

Figure 3 (
(b) Shown in (b). In the figure, C1 is the capacitance based on the buffer layer under the first electrode 4, C2 is the capacitance based on the buffer layer under the second electrode 5, and Cp is the capacitance due to the substrate 1; The capacitance between them is represented by a series connection of three capacitors.

In order for the phase modulator to modulate efficiently, it is necessary to increase the electric field applied to the optical waveguide, that is, the electric field applied to the substrate. Since the voltage is also distributed to the capacitances C+ and C2, the voltage applied to the substrate is reduced, which causes the problem of poor modulation efficiency.

The present invention was created in view of the above problems, and an object of the present invention is to improve the modulation efficiency of a lumped constant optical modulator using an optical waveguide.

[Means to solve the problem]

The above problem consists of a substrate made of electro-optic crystal, a three-dimensional optical waveguide formed on the upper surface of the substrate, a buffer layer formed to cover the waveguide, and an optical waveguide formed on the optical waveguide via the buffer layer. The present invention provides an optical modulator comprising: a first electrode formed directly on the surface of the substrate in parallel with the optical waveguide; and a second electrode formed directly on the surface of the substrate in parallel with the optical waveguide.

[Effect]

Since the second electrode is formed directly on the substrate, no capacitance is formed between the second electrode and the substrate, so that C2 caused by the buffer layer in the equivalent circuit can be eliminated.

Therefore, the applied modulation voltage is applied to the series connection between C1 by the buffer layer directly under the first electrode and Cp by the substrate, so that the voltage can be concentrated on the substrate part more efficiently by eliminating C2. can.

〔Example〕

FIG. 1 is a diagram showing the configuration of an optical modulator according to the present invention, and FIG.
The figure is a schematic diagram showing an electric field applied to an optical waveguide.

In FIG. 1, 10 is a substrate cut as a Z plate made of LiNbO3. In this case, if the crystal is cut so that the Z-axis of the crystal is in the thickness direction and the X-axis of the crystal is in the depth direction as shown in the figure, and an electric field is applied perpendicular to the surface of the substrate, the maximum electro-optic coefficient is obtained. The refractive index is changed.

Then, a titanium film is formed in a strip shape perpendicular to the crystal axis Z direction on the optical waveguide forming portion of the surface of the substrate 10 to perform thermal diffusion, thereby creating a three-dimensional optical waveguide 1 with a refractive index larger than that of the substrate 10.
1 is formed.

Reference numeral 12 denotes a buffer layer made of silicon oxide (Si02) with a thickness of several thousand layers, which is provided only on the upper surface of the optical waveguide 11, and is deposited on the upper surface of the substrate 10 by vapor phase epitaxy (CVD) or the like. , the portion other than the upper surface portion of the waveguide 11 is removed from the surface of the substrate 10 by a predetermined etching process.

A first electrode 13 is made of a thin gold film or the like, and is formed on the upper surface of the buffer layer 12 so as to cover at least the upper part of the optical waveguide 1. It is designed to apply an electric field in the same direction.

This buffer layer 12 is provided to prevent an increase in optical transmission loss that would occur if the electrode 13 was directly formed on the optical waveguide 11.

A second electrode 14 is made of a gold thin film provided in parallel with the first electrode 13 at a predetermined distance from the substrate 10.
It is formed directly on the surface of the substrate without intervening a buffer layer.

When a modulation voltage is applied between both electrodes of the optical modulator of the present invention in which the picture electrode is formed in this way, an electric force &'l is generated from the bottom surface of the first electrode 13 as shown in FIG. The substrate 10 passes through the optical waveguide 11 approximately perpendicularly through the buffer N12.
is generated so as to reach the second electrode 14 on the surface of the substrate 10.

In this case, since there is no buffer layer under the second electrode 14, the electric field loss is reduced compared to the conventional example, and the electric field is strengthened because it is distributed to the part of the substrate including the optical waveguide, which improves the modulation efficiency. is improved.

〔Effect of the invention〕

According to the present invention, in a lumped constant optical modulator using an optical waveguide, it is possible to increase the voltage applied to the substrate portion contributing to modulation among the modulation voltages applied between the electrodes, and the modulation efficiency can be increased. It has the effect of being improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an optical modulator according to the present invention, FIG. 2 is a diagram showing an electric field applied to an optical waveguide, and FIG. 3 is a diagram showing a conventional optical modulator. In the figure, 1 - substrate, 11 - 4 optical wave paths, 12 -
buffer layer, I3-first electrode, 14-second electrode. Δ57H is used for the construction of the λi Suzaku ear-divining device.

Claims (1)

[Claims] A substrate (10) made of electro-optic crystal, and a three-dimensional optical waveguide (10) formed on the upper surface of the substrate (10).
1), a first electrode (13) formed on the optical waveguide (11) via a buffer layer (12), and a first electrode (13) formed on the surface of the substrate (10) parallel to the optical waveguide (11). a directly formed second electrode (14).