JPS63141021A - Mach-zehnder type optical waveguide modulator - Google Patents

Abstract

PURPOSE:To reduce an applied voltage required for modulation and to maintain the performance of a modulator by forming a groove between two optical waveguides and arranging an electrode at the bottom part of the groove. CONSTITUTION:The electrostatic capacity between electrodes 5 is equivalent to a series circuit of two electrostatic capacities because an intermediate electrode 4 is present in the middle and the distance of a part except metal between the electrodes becomes extremely small, so the electric field on the light guide becomes intense. Further, the groove 3 is provided between two branched optical waveguides 2 to prevent two branched light beam from being mixed. Further, the direction of the electric field approximates to the direction perpendicular to the substrate surface by the groove 3 and intermediate electrode 4 and when, for example, a Z-cut LiNbO3 substrate is used and TM light is used, the electric field is utilized more effectively.

Description

[Detailed Description of the Invention] [Summary] In a Matsuhatsu Enda type optical waveguide modulator, a groove is provided between two optical waveguides, an electrode is placed at the bottom of the groove,
This reduces the applied voltage required for modulation and maintains the performance of the modulator.

[Industrial application field]

The present invention relates to an optical modulator using an optical waveguide, and particularly to a Matsuhatsu Enda type optical waveguide modulator.

[Conventional technology]

The Matsuhatsu Enda type optical waveguide modulator is, for example, LiNb
Ti is deposited on an O3 substrate to form two branched waveguides, a buffer layer is created on top of that, and electrodes are placed above it at positions corresponding to the branched waveguides. . When a voltage is applied between these two electrodes, an electric field is generated that provides lines of electric force as shown by the arrows in FIG. 3, which is a cross-sectional view of a conventional Matsuhatsu Enda type optical waveguide modulator.

This electric field causes the refractive index of light in the optical waveguide 2 to change due to the electro-optic effect, thereby changing the phase of the light transmitted through the waveguide 2. This change occurs on the positive electrode side (right side) and on the negative electrode side (
On the left side), the effect is doubled, and when the two branched waveguides are combined again, the two lights interfere with each other, resulting in modulation of the light.

Since a high voltage is required to be applied to the electrodes for this modulation, there is a strong need to reduce this voltage, and attempts are being made to achieve this. That is, by reducing the distance between the optical waveguides 2 and at the same time reducing the distance between the electrodes 5, a stronger electric field is obtained for the same applied voltage, but if the two branched optical waveguides 2 are brought too close together, A problem arises in that the two branched lights combine, resulting in a deterioration of the extinction ratio.

[Problem that the invention seeks to solve]

In view of the problems in the prior art described above, an object of the present invention is to improve the performance of the modulator, that is, the extinction ratio, without deteriorating the extinction ratio.
The aim is to reduce the driving voltage applied to the electrodes for modulation.

[Means for solving problems]

As shown in FIG. 1, a groove 3 is provided between two branched optical waveguides 2 provided on an optical waveguide substrate 1, and an intermediate electrode 4 made of a metal film is placed at the bottom of the groove 3.

[For production]

If the above-mentioned method is used, the capacitance between the electrodes 50 is equivalent to a series circuit of two capacitances because the intermediate electrode 4 is present in the middle, and the distance between the electrodes and the non-metal part is very small. Therefore, the electric field in the optical waveguide becomes stronger. Further, a groove 3 is provided between the two branched optical waveguides 2 to prevent coupling of the two branched lights. In addition, the direction of the electric field approaches the direction perpendicular to the substrate surface due to the groove 3 and the intermediate electrode 4 (see Figure 2). For example, when using a Z-caft LiNb0z substrate and applying TM light, the electric field can be used more effectively. Ru.

〔Example〕

A perspective view of a Mannha-Zehnder optical waveguide modulator as an embodiment of the present invention is shown in FIG.
A cross-sectional view of II is shown in FIG.

For the optical waveguide substrate 1, an optical waveguide 2 is fabricated by thermally diffusing Ti onto a Z-cut LiNb0z substrate. The optical waveguide 2 is branched into two near the center. A groove 3 is formed in the substrate 1 between the two optical waveguides 2 using a method such as etching. In order to prevent absorption of light by the metal electrode (using Au or A1, etc.), a buffer layer 6 is provided on the substrate 1 processed as described above.

Next, electrodes are formed on the optical waveguide and at the bottom of the groove 3 by vapor deposition or the like. /I! The electrode provided at the bottom of the optical waveguide 2 serves as an intermediate electrode 4, and the electrode 5 provided on the optical waveguide 2 serves to apply a driving voltage. One of the electrodes 5 is grounded, and the voltage V is applied to the other. No voltage is applied to the intermediate electrode 4.

Light is transmitted in the direction of the thick arrow. The Z-cut substrate is processed so that the C-axis is in the direction shown by the arrow in FIG. 1 (thickness direction).

Referring to FIG. 2, by providing the intermediate electrode 4,
The positive electrode 5 and the intermediate electrode 4 constitute one capacitance, and the negative electrode 5 and the intermediate electrode 4 constitute another capacitance,
The distance between the electrodes 5 and the non-metal parts becomes smaller. This means that the electric field strength increases at the two-branched portion of the optical waveguide 2. Therefore, even if a low driving voltage is applied to the electrode 5, it is possible to obtain optical modulation equivalent to that of the conventional type.

In the conventional optical modulator shown in FIG. 3, the electric field lines indicated by arrows have a long distance to pass through the substrate l, so the electric field obtained with the same applied voltage is weak.

Comparing the directions of the electric lines of force indicated by the arrows in FIGS. 2 and 3, the lines of electric force in FIG. 2 tend to increase in the direction perpendicular to the substrate surface, that is, the C-axis direction component, due to the intermediate electrode 4. When using TM light, which has a large electro-optic effect,
The electric field acts more effectively on the optical waveguide. Furthermore, since the groove 3 is provided between the two branched four-wave paths, there is less possibility of coupling of the two branched lights.

〔Effect of the invention〕

According to the present invention, the driving voltage applied to the electrodes for modulation can be reduced without deteriorating the performance of the modulator, that is, the extinction ratio.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a Matsuha-Zehnder type optical waveguide modulator as an embodiment of the present invention, FIG. 2 is a cross-sectional view of the modulator along line ■-■ in FIG. 1,
3 is a sectional view similar to FIG. 2 of a conventional Matsuhatsu Enda type optical waveguide modulator. In the figure, 1... optical waveguide substrate, 2... optical waveguide, 3...
groove, 4... intermediate electrode, 5... electrode,
6...Buffer layer.

Claims (1)

[Claims] A groove (3) is provided between the two branched optical waveguides (2),
A Mach-Zehnder optical waveguide modulator in which an intermediate electrode (4) made of a metal film is arranged at the bottom of the groove (3).