JPH0593892A - Two-layered type optical modulator - Google Patents

Abstract

PURPOSE:To suppress the higher mode of the optical modulator and to widen a band by sticking a low dielectric constant plate near to at least the electrode on the rear surface of the substrate of the optical modulator and loading the optical modulator in contact with a grounded metallic housing. CONSTITUTION:The low dielectric constant plate 15 is stuck near to at least the electrode on the rear surface of the substrate of the optical modulator and is directly loaded to the grounded metallic housing 16. The optical modulator of the thinly formed lithium niobate substrate 11 is reinforce in strength by the low dielectric plate 15 stuck thereto, by which the handling is facilitated according to this constitution. Since the thickness of the optical modulator element itself can be increased by the low dielectric plate 15, the degree of freedom in design in packaging elements, such as optical fibers and connectors, is increased and the production is facilitated. In addition, the higher mode of the optical modulator is suppressed and the band is widened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator, and more particularly to a waveguide type optical modulator formed on a lithium niobate substrate.

[0002]

2. Description of the Related Art A modulator using lithium niobate as a substrate has a smaller chirping during modulation than a semiconductor modulator.
Features such as low insertion loss. Research has been conducted to improve the modulation band, and examples of conventional techniques include the following.

FIG. 3 shows the 16th European International Conference on Optical Communication (Eu).
ropeconference on Opti
cal Communication, pp999-1
002, 1990). The planar configuration of this optical modulator is shown in FIG. A sectional view taken along the section line I of FIG. 2 is shown in FIG. It is composed of a Maha-Zehnder type optical waveguide 22 that branches into two near the center of the optical modulator and merges again, and a traveling wave type electrode 24 loaded in the vicinity thereof.

A traveling wave type electrode 34 is loaded on a Maha-Zehnder type titanium diffusion optical waveguide 32 formed on the surface of a Z-cut lithium niobate substrate 31 via a buffer layer 33 made of silicon dioxide (SiO ₂ ). By applying a microwave signal to the electrode 34, a phase change is given to the two guided lights via the electro-optic effect of the lithium niobate crystal.
The signals are combined and interfered in the vicinity of the output end and output as light intensity modulation.

The light modulation characteristics depend on the electrical transmission characteristics of microwaves traveling through the electrodes. In order to prevent the deterioration of electrical transmission characteristics, the optical modulator element that uses lithium niobate as a substrate acts as a dielectric resonator, causing dips in microwave transmission characteristics and exciting higher-order modes of microwaves. Need to be suppressed. In the example of FIG. 3, the width and thickness of the optical modulator element are reduced, and an air gap is provided below the element to mount the optical modulator element, whereby the resonance frequency is shifted to the high frequency side of the target frequency band and the effect of resonance To avoid the occurrence of higher-order microwave modes.

[0006]

In the conventional optical modulator described above, in order to improve the microwave transmission characteristics, the thickness of the substrate forming the optical modulator is reduced, and the air gap is provided under the optical modulator. Is installed. Therefore, there is a problem that 1) it is easily damaged and it is difficult to handle the element. 2) The mounting means such as fiber and connector connection is limited.

[0007]

According to the optical modulator of the present invention, a low dielectric plate having a lower dielectric constant than that of the substrate is attached to at least an electrode on the back surface of the substrate of the optical modulator, and the low dielectric plate is grounded. The feature is that it was loaded in contact with the metal housing.

[0008]

In the past, the back surface of the optical modulator was the air layer having the lowest dielectric constant.

According to the present invention, a low dielectric constant plate is adhered to at least the electrodes on the back surface of the substrate of the optical modulator, and the low dielectric constant plate is directly loaded on the grounded metal housing without impairing the effect of improving the microwave transmission characteristics. It is possible to reinforce a thin optical modulator and diversify mounting means. In an experiment conducted by the inventors, a dielectric constant of lithium niobate of 35
In the glass plate of low value (dielectric constant: 4-8) compared to
It has been confirmed that it has the same effect of improving microwave transmission characteristics as an air layer.

[0010]

The present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining an embodiment of the present invention.
It is a cross-sectional view of a layered optical modulator. Thickness 0.2mm-0.8m
A Z-cut Y-axis propagating lithium niobate substrate 11 having a width of 6 to 12 μm and a pattern of a titanium thin film having a thickness of 40 to 120 nm is formed on a substrate 11, and heat diffusion is performed at 950 to 1100 ° C. to perform a Maha-Zehnder single mode. The titanium diffusion optical waveguide 12 is produced. The traveling-wave electrode 14 is formed by photolithography using a silicon dioxide (S) layer having a thickness of 0.3 to 2 μm.
It is formed on the buffer layer 13 of an iO ₂ ) thin film. The planar configuration of this optical modulator is the same as in FIG. A sectional view taken along the section line I of FIG. 2 shows FIG.

On the back surface of the optical modulator, a glass plate having a dielectric constant lower than that of lithium niobate (dielectric constant: 35) (dielectric constant: 4 to
8) The low dielectric plate 15 as shown in FIG. The optical modulator is loaded in contact with the grounded metal housing 16.

This structure has the same effect of improving the microwave transmission characteristics as the mounting method in which the back surface of the optical modulator is an air layer.

[0014]

As described above, according to the present invention, the low dielectric constant plate is attached to at least the electrodes on the back surface of the substrate of the optical modulator, and the low dielectric constant plate is loaded in contact with the grounded metal housing. The strength of the lithium niobate substrate optical modulator thinned by the dielectric plate can be reinforced, and the handling becomes easy. (2) Since the thickness of the optical modulator element itself can be increased by the attached low dielectric plate, the degree of freedom in designing the element mounting such as optical fiber and connector mounting becomes large, and the manufacturing becomes easy. (3) With the above structure, higher-order modes of the optical modulator can be suppressed, and the band can be widened. It can be said that the effect of supplying such an optical modulator is extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining an embodiment of a two-layer type optical modulator of the present invention.

FIG. 2 is a plan view for explaining the configuration of the optical modulator in detail, and a cross-sectional view taken along a cutting line I is FIG. 1 or FIG.

FIG. 3 is a diagram for explaining a conventional technique.

[Explanation of symbols]

 11, 21, 31 Lithium niobate substrate 12, 22, 32 Titanium diffused optical waveguide 13, 33 Buffer layer 14, 24, 34 Traveling wave type electrode 15 Low dielectric plate 16 Grounded metal housing

Claims (1)

[Claims] 1. An optical modulator comprising an optical waveguide formed on a substrate and a traveling wave type electrode loaded in the vicinity of the optical waveguide, wherein a low dielectric constant lower than that of the substrate is provided at least on the back surface of the substrate near the electrode. A two-layer type optical modulator characterized in that a dielectric plate is attached, and the low dielectric plate is loaded in contact with a grounded metal housing.