JPH04254819A - Light waveguide for device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an optical waveguide device formed with an optical waveguide, an electrode, and a buffer layer, and more particularly to an optical waveguide device characterized by the basic arrangement structure thereof. .

0002

2. Description of the Related Art Conventionally, the basic structure of this type of optical waveguide device is disclosed in, for example, Japanese Unexamined Patent Publication No. 1-155323. This publication discloses an optical waveguide device of X cut and Y propagation. In this device, a buffer layer (
A buffer layer) is coated on the optical waveguide, and an electrode for applying an electric field to the optical waveguide is formed on the buffer layer.

[0003] Furthermore, as an active type optical waveguide type device, a device having a structure shown in FIG. 6 has conventionally existed. In this device, an optical waveguide 2 is formed on a Z-cut LiNbO3 (lithium niobate; hereinafter referred to as LNO) substrate 1, and a buffer layer 3 is further formed on the entire surface of the substrate 1. The propagation direction of this waveguide 2 is
Further, a positive electrode 4 is loaded on the buffer layer 3 above the waveguide 2, and a negative electrode 5 is loaded on the buffer layer 3 a little distance away.

0004

[Problems to be Solved by the Invention] Each of the above conventional devices has a structure in which a buffer layer is provided on the entire surface of the substrate, and an electric field is applied from the electrode to the optical waveguide via this buffer layer. . The reason why such a buffer layer is provided is as follows. In other words, if an electrode made of metal or the like is directly loaded onto the waveguide, the guided light propagating through the waveguide will be absorbed by the electrode made of a conductive material, resulting in increased transmission loss.

[0005] Furthermore, in order to effectively operate the device, it is necessary to apply a sufficient electric field to the optical waveguide, and it is known that for this purpose, an electric field must be applied to the optical waveguide from the Z direction. . Therefore, in the device shown in FIG. 6, a positive electrode 4 is loaded on the buffer layer 3 located directly above the waveguide 2, and an electric field is applied to the waveguide 2 from the Z direction as indicated by the arrow in the figure. The structure is such that the voltage is applied.

However, in any of the above conventional devices, an electric field is ultimately applied to the waveguide via the buffer layer. Therefore, the electric field component effectively applied to the waveguide is weakened by the presence of the buffer layer, that is, by the thickness of the buffer layer. As a result, conventional optical waveguide devices have not been able to fully demonstrate their functions.

[0007]

[Means for Solving the Problems] The present invention has been made to solve the above problems, and provides an LNO substrate with X-cut Y propagation or Y-cut X propagation, and an LNO substrate formed in the Y direction or an optical waveguide, electrodes directly loaded on a substrate sandwiching the optical waveguide, and a buffer layer partially formed only on the optical waveguide where the wiring to the electrode and the optical waveguide intersect. An optical waveguide type device is formed.

[0008]

[Operation] LNO of X cut Y propagation or Y cut X propagation
In the substrate, the Z direction, in which an electric field is effectively applied to the optical waveguide formed in the Y direction or the The electrode positions sandwiching the two are suitable positions.

[0009] Furthermore, by forming the buffer layer only in the necessary portions of the electrical wiring where the wiring to the electrode and the optical waveguide intersect, contact between the optical waveguide and the electrode wiring can be avoided, and transmission loss can be prevented. is prevented.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view showing the basic structure of an optical waveguide device according to an embodiment of the present invention.

[0011] On the X-cut Y-propagation LNO substrate 11,
An optical waveguide 12 is formed along the Y direction of the substrate 11. As shown in the figure, the X direction, Y direction, and Z direction of the LNO substrate 11 are such that the direction perpendicular to the drawing is the X direction, the horizontal direction of the drawing is the Y direction, and the vertical direction of the drawing is the Z direction. Further, a pair of electrodes 13 and 14 are connected to this optical waveguide 12.
It is directly loaded onto the substrate 11 sandwiching the. This situation is shown in FIG. This figure is a sectional view taken along line II-II in FIG. 1, and the same parts as in FIG. 1 are denoted by the same reference numerals. Electrodes 13 and 14 on both sides of the optical waveguide 12 are LNO
It is understood that it is formed in close contact with the substrate 11.

Further, a positive voltage is applied to the electrode 13 in FIG. 1 through an electrode lead portion 13a, and a negative voltage is applied to the electrode 14 through an electrode lead portion 14a. Electrode 1
The lead portion 13a to the optical waveguide 3 partially intersects with the optical waveguide 12 due to the necessity of electrical wiring. This crossing condition is shown in FIG. FIG. 3 is a sectional view taken along the line III--III in FIG. 1, and the same parts as in FIG. 1 are denoted by the same reference numerals. That is, the buffer layer 15 is formed on the optical waveguide 12 where the electrode lead portion 13a and the optical waveguide 12 intersect. This buffer layer 15 is formed only at this intersection. Optical waveguide 12 and electrode lead part 13a
The buffer layer 15 prevents mutual contact, and the optical signal propagating through the optical waveguide 12 is directed to the electrode lead portion 13a.
This prevents transmission loss from occurring.

In such a structure, an electric field is applied to the optical waveguide 12 from the Z direction shown in FIG. Note that this figure is a cross-sectional view of the LNO substrate similar to that in FIG. 2, and the same parts are denoted by the same reference numerals as in FIG. 2, and the explanation thereof will be omitted. Next, the effectiveness of applying an electric field to the optical waveguide 12 from the Z direction in this manner will be explained below.

This type of active LNO optical waveguide device utilizes the Pockels effect of the LNO. Taking this LNO device as an example, the Pockels effect is a phenomenon in which the refractive index changes with respect to the electric field vector E (Ex, Ey, Ez) applied in the direction of the crystal axis of the LNO substrate 11. Here, the refractive index for the ordinary ray of LNO is n
0 and the refractive index for extraordinary light is ne, the refractive index ellipsoid can be expressed by the following equation.

(x2 /n0 2 )+(y2 /n0 2 )
+(z2 /ne 2 )=1 Z on this LNO board 11
When an electric field is applied from the direction (Ex=Ey=0, E=Ez
), the refractive index ellipsoid shown in the above equation changes as shown in the following equation.

(1/n0 2 +γ13・Ez)x2 + (1/
n0 2 +γ13・Ez)y2
+(
1/ne 2 + γ33・Ez) z2 = 1 where γ
13 and γ33 are components of the Pockels constant tensor of LNO, and γ33 is the largest among the components. Further, this γ33 contributes only when an electric field is applied in the Z direction as shown in the above equation. Therefore, it is understood that in order to effectively operate an active optical waveguide device, it is essential to apply an electric field from the Z direction of the LNO substrate 11.

In this embodiment, since the electric field is applied from the Z direction as described above, the electric field is effectively applied to the optical waveguide 12. Furthermore, applying an electric field in the Z direction on the LNO substrate 11 with X cut and Y propagation means that the LNO substrate 11
applying an electric field laterally along the surface of the Therefore, as for the arrangement position of each electrode 13, 14, as mentioned above, the electrode position sandwiching the optical waveguide 12 away from directly above the optical waveguide 12 is a suitable position, so that the electric field is distributed more horizontally. Become. Therefore, there is no need to provide an electrode directly above the optical waveguide 12, so unlike the conventional
There is no need to form a buffer layer on top. However, as described above, the buffer layer 15 is provided only in a portion due to the necessity of electrical wiring. For this reason, each electrode 13,
14 can be directly loaded onto the LNO substrate 11 without using a buffer layer, and the effective electrical distance between each electrode 13 and 14 is shortened by the thickness of the buffer layer. As a result, the electric field from the positive electrode 13 toward the negative electrode 14 becomes stronger, and a sufficient electric field is applied to the optical waveguide 12.

Note that in the description of the above embodiment, X cut Y
Although a device for forming an optical waveguide 12 in the Y direction on a propagation LNO substrate 11 has been described, this is a device for forming an optical waveguide in the X direction on a Y-cut, X-propagation LNO substrate in which the Also good. Even in such a device, an electric field is effectively applied to the optical waveguide from the Z direction, and the same effects as in the above embodiments are achieved.

Next, a case where the basic structure of the X-cut Y-propagation LNO substrate shown in the above embodiment is applied to a directional coupler type optical switch will be described below with reference to FIG. This figure is a process cross-sectional view showing the method of manufacturing this optical switch, and each direction of the substrate is the same as that shown in FIG. 1, so the explanation thereof will be omitted.

First, directional coupler optical waveguides 22 and 23 are formed on the X-cut LNO substrate 21 by Ti diffusion along the Y direction of the substrate 21 (see FIG. 5(a)).
. Next, a buffer layer 24 made of, for example, SiO2 is placed at a location where the electrode lead portion is expected to intersect with the optical waveguide 23.
It is formed to a thickness of 000 angstroms (see figure (b)).
reference). Next, the positive electrode 25 and the negative electrode 26 are directly formed on the substrates 21 on both sides of the optical waveguide 23 . at the same time,
Electrode lead part 25 that electrically connects each electrode 25, 26
a, 26a are formed. At this time, the electrode lead part 25a connected to the positive electrode 25 is formed on the buffer layer 24 at a location where it intersects with the optical waveguide 23, and contact between the optical waveguide 23 and the electrode lead part 25a is prevented (see FIG. c)
reference).

In such a structure, the electric field in the waveguide 23 is controlled by the voltage applied between each electrode 25 and 26, and the refractive index for the optical signal in the waveguide is changed. This refractive index change controls the guided light propagating through each waveguide 22, 23, and functions as an optical switch.

In this optical switch, since the electric field is applied to the waveguide 23 without passing through the buffer layer, the electric field acts effectively, improving the sensitivity of the optical switch and fully utilizing its functions. Become. Further, the present optical switch can also be constructed using a Y-cut, X-propagation LNO substrate as described above, and the same effect can be obtained.

[0023]

[Effects of the Invention] As explained above, according to the present invention,
In an LNO substrate with cut Y propagation or Y cut X propagation, the Z direction in which an electric field is effectively applied to the optical waveguide formed in the Y direction or the A suitable position is an electrode position that is located on both sides of the optical waveguide and is not directly above the optical waveguide. In addition, by forming a buffer layer only in the necessary parts of the electrical wiring where the wiring to the electrode and the optical waveguide intersect, contact between the optical waveguide and the electrode wiring can be avoided, and transmission loss can be prevented. Ru.

[0024] Therefore, it is no longer necessary to form electrodes on the buffer layer, and it becomes possible to directly load the electrodes on the LNO substrate. As a result, the effective electrical distance between the electrodes becomes shorter due to the absence of the buffer layer, and the intensity of the electric field applied to the optical waveguide increases. This allows the device to perform its functions satisfactorily.

In particular, the present invention is effective when applied to lower driving voltages for active optical waveguide devices.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the basic structure of an optical waveguide device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the optical waveguide device according to the embodiment shown in FIG. 1, taken along line II-II.

FIG. 3 is a cross-sectional view of the optical waveguide device according to the embodiment shown in FIG. 1, taken along line III-III.

FIG. 4 is a cross-sectional view showing the state of electric field application in the optical waveguide device according to the present example.

5 is a process cross-sectional view showing a method of manufacturing a directional coupler type optical switch when the basic structure of the optical waveguide device according to the present embodiment shown in FIG. 1 is applied to the optical switch; FIG.

FIG. 6 is a cross-sectional view showing a state of electric field application in a conventional optical waveguide device.

[Explanation of symbols]

11...LNO board 12...Optical waveguide 13...Positive electrode 13a... Electrode lead part to positive electrode 13 14...Negative electrode 14a... Electrode lead part to negative electrode 14 15...Buffer layer

Claims (2)

[Claims] 1. An X-cut Y-propagation LiNbO3 substrate, an optical waveguide formed in the Y direction of this substrate, electrodes directly loaded on the substrate sandwiching this optical waveguide, wiring to this electrode, and an optical waveguide formed in the Y direction of this substrate. An optical waveguide type device formed with a buffer layer partially formed only on the optical waveguide where the optical waveguide intersects with the optical waveguide. 2. A Y-cut, X-propagation LiNbO3 substrate, an optical waveguide formed in the X direction of this substrate, electrodes directly loaded on the substrate sandwiching this optical waveguide, wiring to this electrode, and a An optical waveguide type device formed with a buffer layer partially formed only on the optical waveguide where the optical waveguide intersects with the optical waveguide.