JPH019933Y2 - - Google Patents

Description

[Detailed description of the invention] (Technical field) The present invention relates to a light modulation device, and includes:
Specifically, the present invention relates to an improvement of an optical modulation device configured to intensity-modulate light passing through an optical waveguide.

(Conventional example) By thermally diffusing metal impurities such as titanium (Ti) into a substrate made of electro-optic material such as lithium niobate (LiNbO ₀ ), an optical waveguide with a higher refractive index than the substrate is formed, and electro-optic An optical waveguide body with extremely high efficiency can be obtained. When an electric field is applied to such an optical waveguide, the intensity of light passing through the optical waveguide is modulated by the electro-optic effect.

One type of such an optical waveguide body is a branching interference type optical waveguide body as shown in FIG.

In FIG. 1, 10 is a substrate, 20 is an optical waveguide, 30 is an electrode, and 40 is a signal source.

The substrate 10 is made of an electro-optic material, such as lithium niobate (LiNbO ₀ ), which has an electro-optic effect. The optical waveguide 20 is formed into a linear shape by thermally diffusing metal impurities such as titanium (Ti) into the substrate 10, and has a higher refractive index than the substrate 10. The phase shift section 22 and the Y-shaped coupling section 23 are continuously integrated. The electrode 30 is the optical waveguide 2
Optical waveguide 2 to intensity modulate the light passing through
0, and the phase shift section 22
A first electrode 31 and a second electrode 32 are provided on the substrate 10 such that they are sandwiched therebetween. signal source 40
supplies an electric field and is connected between the first electrode 31 and the second electrode 32. In addition,
An optical fiber for transmitting light from a light source such as a laser diode is connected to the end of the Y-shaped branch part 21 of the optical waveguide 20, and the Y-shaped coupling part 2
An optical fiber for transmitting intensity-modulated light to a light-receiving element such as a phototransistor is connected to the end of 3, but is not shown.

In such a configuration, when light from a light source is applied to the end of the Y-shaped branch 21 of the optical waveguide 20, the light is split into two by the branch 21 and sent to the phase shifter 2.
2. In the phase shifting unit 22, a signal source 4 is applied between the two divided lights via an electrode 30.
A phase difference is given according to the magnitude of the zero output.
Then, these lights having a phase difference are combined again at the coupling part 23. As a result, intensity-modulated light is sent out from the end of the coupling section 23.
Here, by applying a phase difference of λ/4 to the phase shifting unit 22 and applying intensity-modulated light from the coupling unit 23 to the light receiving element, the output of the signal source 40 applied via the electrode 30 is adjusted. It is possible to obtain electrical signals.

By the way, in such a device, the X and Z axes of the substrate 10 are horizontal planes, as shown in FIG.
High sensitivity characteristics can be obtained by using one cut so that the axis is perpendicular.

However, although high sensitivity characteristics can be obtained, there is a drawback that the refractive index ne in the Z-axis direction and the electro-optic coefficient r ₀₀ in the Z-axis direction vary greatly depending on temperature changes.

(Purpose of the invention) The present invention solves these conventional drawbacks, and its purpose is to obtain high sensitivity characteristics and improve the refractive index ne in the Z-axis direction and the electro-optical property in the Z-axis direction due to temperature changes. The purpose of varying the coefficient r ₀₀ is to provide a small light modulation device.

(Structure of the invention) The present invention achieves the above object by using a substrate made of an electro-optic material cut so that the X and Z axes are horizontal planes and the Y axis is a vertical plane, and a light guide formed on the substrate. A waveguide, an electrode formed on a substrate to apply an electric field to the light passing through the optical waveguide to modulate its intensity, and a temperature coefficient formed on the substrate to cover the optical waveguide and electrode and have a polarity different from that of the substrate. and an insulating protective layer.

(Example) Hereinafter, it will be explained in detail using the drawings.

FIG. 3 is a sectional view showing the main parts of an embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. In FIG. 3, 50 is an optical waveguide 20
and an insulating protective layer made of silicon dioxide (SiO ₂ ) formed on the substrate 10 so as to cover the electrode 30. Such an insulating protective layer 50 can be formed, for example, by sputtering, and has a thickness of about 1 μm.

In such a configuration, in a room temperature atmosphere, the substrate 10 made of lithium niobate has a positive temperature coefficient, and the insulating protective layer 50 made of silicon dioxide has a positive temperature coefficient.
has a negative temperature coefficient. Here, the temperature coefficient includes a coefficient of thermal expansion and a modulus of rigidity, but the coefficient of thermal expansion is dominant.

With this configuration, the boundary surface of displacement due to the opposite temperature coefficient is several μm from the surface of the substrate 10.
5 μm deep from the surface of the substrate 10 in the same direction as the insulating protective layer 50. Therefore, the substrate 10
Mechanical distortion due to temperature change does not occur at the interface between the insulating protective layer 50 and the insulating protective layer 50.

As a result, the temperature coefficient of the surface layer of the substrate 10 in a region of several μm can be made almost zero, and the temperature characteristics of the refractive index ne in the Z-axis direction and the electro-optic coefficient r ₀₀ in the Z-axis direction can be significantly improved. Can be done.

Further, by providing such an insulating protective layer 50, it is possible to insulate the electrodes 30 from each other and to isolate the device surface from the external atmosphere, thereby achieving long-term stability.

According to such a configuration, for example, it is possible to realize an optical voltmeter that can measure the magnitude of the output signal of a signal source in a completely electrically isolated state, and it can also be used in various optical signal processing devices in optical communication systems. be able to.

In the above embodiments, an example of a branch interference type optical waveguide body has been described, but similar effects can be obtained with a gate-coupled type, cut-off type, cobra type, etc.

Furthermore, the substrate may be made of lithium tantalate (LiTaO ₀ ).

(Effects of the invention) As is clear from the above, according to the invention,
It is possible to realize an optical modulation device that has high sensitivity characteristics and has small changes in the refractive index ne in the Z-axis direction and the electro-optic coefficient r ₀₀ in the Z-axis direction due to temperature changes, which has great practical effects.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the configuration of an example of a branching interference type optical waveguide body, Fig. 2 is an explanatory diagram of the crystal orientation of the substrate used in the present invention, and Fig. 3 shows the main part of an embodiment of the present invention. FIG. DESCRIPTION OF SYMBOLS 10... Substrate, 20... Optical waveguide, 30... Electrode, 40... Signal source, 50... Insulating protective layer.

Claims (1)

[Scope of utility model registration request] A substrate made of an electro-optical material cut so that the X and Z axes are horizontal planes and the Y axis is a vertical plane;
An optical waveguide formed on a substrate, an electrode formed on the substrate to apply an electric field to the light passing through the optical waveguide to modulate its intensity, and an electrode formed on the substrate to cover the optical waveguide and the electrode. An optical modulator comprising a substrate and an insulating protective layer having temperature coefficients of different polarities.