JPS6128925A - Optical modulating device - Google Patents

Abstract

PURPOSE:To obtain the optical modulating device which has small variation in characteristics with temperature by providing a branch interference type light guide through which light is transmitted in the Z-axial direction on the surface of a substrate of lithium niobate which is cut having horizontal planes in the X-and Z-axial directions and a vertical plane in the Y-axial direction. CONSTITUTION:The substrate 10 uses lithium niobate cut so as to have the horizontal surfaces in the X-axial and Z-axial directions and the vertical surface in the Y-axial direction, and the branch type interference light guide 20 is formed on the surface of the substrate 10 in one body so that light is passed in the Z-axial direction different from the conventional direction. Paying attention to the characteristics of this substrate 10, the refractive index (no) in the X-axial direction is 2.25 and the electrooptic coefficient r00 in the X-axial direction is 6-8X10<-12>m/V, so the sensitivity decreases slightly, but the temperature coefficient of the refractive index (no) in the X-axial direction is -1.4X10<-6>/ deg.C and the temperature coefficient of the electrooptic coefficient r22 in the X-axial direction is nearly 0, thereby reducing variation in sensitivity with temperature. Further, the branch type light guide 20 is formed on the surface of the substrate 10, so variation in characteristics due to angular deviation in the directivity of crystal is suppressed by performing differential output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an optical modulation device, and more particularly, a lithium niobate (LiNbOl) substrate configured to intensity-modulate light passing through a guiding waveguide. This paper relates to improvements to the optical modulation device used.

[Prior art]

By thermally diffusing metal impurities such as titanium (Ti) into a substrate made of an electro-optic material such as lithium niobate (LjNbO0), an optical waveguide with a higher refractive index than the substrate is formed, making the electro-optic effect extremely efficient. A high 6 optical waveguide body can be obtained. When an electric field is applied to such a leading wavepath,
The light passing through the optical waveguide is intensity-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. 2, 10 is a substrate, 20 is a branched interference type optical waveguide, 30 is an electrode, and 40 is a signal source.

The substrate 10 is made of lithium niobate (L), which has an electro-optic effect.
As shown in FIG. 3, it is cut so that the X and Z axes are horizontal planes and the Y axis is a vertical plane. The branch interference type optical waveguide 20 is connected to the substrate 10
It is formed into a linear shape by thermally diffusing a metal impurity such as titanium (T1) into the substrate 10, and has a higher refractive index than the substrate 10, and has a Y-shaped branch portion 21. The mutually parallel phase shift Y$22 and the Y-shaped coupling portion 23 are continuously integrated so as to transmit light in the X-axis direction.

The electrodes 30 apply an electric field to the branching interference type optical waveguide 20 in order to intensity-modulate the light passing through the branching interference type optical waveguide 20.
An electrode 31 and a second electrode 32 are provided on the substrate 10. The signal source 40 supplies an electric field and is connected between the first electrode 31 and the second electrode 32. Note that the figure 7-shaped branch portion 21 of the branch interference type optical waveguide 20
An optical fiber for transmitting light from a light source such as a laser diode is connected to the end of the figure-7 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, 7 of the branching interference type optical waveguide 20
When light from a light source is applied to the end of the branch part 21 of the letter,
The light is split into two by the branching section 21 and transmitted to the phase shifting section 22 . In the phase shift section 22, an electrode 3 is placed between the two divided lights.
A phase difference is given according to the magnitude of the output of the signal [40] applied through the signal [40]. 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 shift section 22 and applying intensity-modulated light to the light receiving element, the electrode 3
It is possible to obtain an electrical signal depending on the magnitude of the output of the signal source 40 applied via the signal source 40.

In such a configuration, focusing on the characteristics of the substrate 10, the refractive index Tlc in the Z-axis direction is 2.17, and the electro-optic coefficient r, in the two-axis directions is 30X10-'5III/V, so it is high. Although sensitivity characteristics are obtained, the temperature coefficient of the refractive index TIc in the biaxial direction is -6.0X10-'/'0, and the temperature coefficient of the electro-optic coefficient res in the biaxial direction is 4.0.
9 x 10-'/''O, which has the disadvantage that the sensitivity changes greatly in response to temperature changes.

[Purpose of the invention]

The present invention solves these conventional drawbacks, and an object of the present invention is to provide an optical modulation device whose characteristics change little due to temperature changes.

[Summary of the invention]

The present invention, which achieves these objectives, irradiates light in the Z-axis direction onto the surface of a substrate made of lithium niobium (LiNbO,) cut so that the X and Z axes are horizontal planes and the Y axis is a vertical plane. It is characterized in that a branching interference type optical waveguide is provided so as to pass through the optical waveguide.

〔Example〕

Hereinafter, a detailed explanation will be given using the drawings.

FIG. 1 is a configuration explanatory diagram showing one embodiment of the present invention, and parts equivalent to those in FIG. 2 are given the same reference numerals. In FIG. 1, the substrate 10 is made of niobium-dipped lithium (LiNbO), which is cut so that the x and z axes are horizontal planes and the Y axis is a vertical plane, as shown in FIG.
However, on the surface of the substrate 10 there is a branched interference type optical waveguide 2.
0 is continuously integrated in such a way that light passes in two axial directions different from that of the device shown in FIG.

In such a configuration, focusing on the characteristics of the substrate 10, the refractive index no in the X-axis direction is 2.25, and the electro-optic index l#r@@ in the X-axis direction is 6 to 8 XIO-''m/V. Therefore, although the sensitivity is somewhat lower than that of the device in Figure 3, the temperature coefficient of the refractive index no in the X-axis direction is -1.4X1
0-" PC, and the temperature coefficient of the electro-optic coefficient r in the Since the wave path 20 is provided, it is possible to compensate for variations in characteristics caused by angular deviations in crystal orientation by providing differential outputs.

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.

[Effects of the Invention] As is clear from the above, according to the present invention, an optical modulation device whose characteristics change little due to temperature changes can be realized.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the configuration of an example of a conventional device, and FIG. 3 is an explanatory diagram of the crystal orientation of a substrate used in the present invention. DESCRIPTION OF SYMBOLS 10... Substrate, 20... Leading wave path, 30... Electrode, 40... Signal source. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] Branching interference is applied to the surface of a substrate made of lithium niobate [LiNbO_■], which is cut so that the X and Z axes are horizontal planes and the Y axis is a vertical plane, so that light passes in the Z-axis direction. An optical modulation device characterized by being provided with a shaped optical waveguide.