JPS6165223A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To make variation in the refractive index of a waveguide area formed on electrooptic crystal opposite in sign between the center part and both peripheral parts and to perform low-voltage operation by providing electrodes in an area which covers the center part and both peripheral parts. CONSTITUTION:The rectangular waveguide area 2 which is made larger in refractive index than the substrate crystal by diffusing Ti, incident light waveguides 3 and 4, and projection light waveguides 5 and 6 are provided on the substrate 1 of Z-plate LiNbO3 crystal; and a thin electrode 7 is arranged at the center part on the waveguide 2 and electrodes 18 and 19 are also arranged covering the peripheral parts. When a voltage is applied between the electrode 7 and electrodes 18 and 19, lines 20 of electric force are generated and the waveguide area 2 varies in refractive index. The direction of the electric field under the electrode 7 at the center part is opposite to the direction of electric fields under the electrodes 18 and 19 at the peripheral parts, and the sign of refractive index variation under the electrodes at the peripheral parts is different, thereby improving switching effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical circuit element, and in particular to an optical switch that can be driven at a low voltage.

A waveguide pattern made of a titanium (Ti) Ftt film is formed on an electro-optic crystal such as lithium niobate (LiNbOi), and then a heat treatment is performed on this to diffuse Ti into the crystal and adjust the refractive index to the substrate crystal. Those with a larger area are used as optical waveguides.

Since the refractive index changes when an electric field is applied to this electro-optic crystal, optical switches using optical waveguides formed on such crystal substrates have been put into practical use. The inventors of the present invention previously discovered that compact, low-voltage driving is possible with an optical switch formed in an electro-optic crystal;
431 Optical Switch] Further reduction in voltage is required for miniaturization and integration of optical circuit elements.

[Conventional technology]

FIG. 3 is a plan view showing the structure of a conventional waveguide type optical switch, in which a rectangular waveguide region 2 is formed on a substrate 1 made of a ZiLiNbOi crystal and has a refractive index larger than that of the substrate crystal by diffusing Ti into the crystal. and two input optical waveguides 3.4 and two output optical waveguides 5, 6 connected to both ends thereof,
Furthermore, a thin electrode 7 is arranged in the central part of the rectangular waveguide area 2 in the length direction of the waveguide area 2, and an electrode 8.9 is arranged on the outside of the waveguide area 2 in parallel with the thin electrode 7 in the center part. ing.

FIG. 4 is a cross-sectional view taken along line xx' in FIG. 3,
When a voltage is applied between the electrode 7 provided on the rectangular waveguide region 2 and the two electrodes 8 and 9 provided outside the waveguide region 2, electric lines of force 10 as shown by broken lines are generated. This vertical component changes the refractive index of the rectangular waveguide region 2. Therefore, by adjusting the direction and magnitude of the electric field, the incident light from the input optical waveguide 4 can be selectively switched to either of the output optical waveguides 5 and 6. The principle of the switch operation is detailed in JP-A-59-093431 Optical Switch, and will therefore be omitted here.

[Problem that the invention seeks to solve]

In the above-mentioned conventional optical switch, the vertical component of the electric field in the waveguide region that exhibits the electro-optic effect occurs only in the center of the waveguide region, and therefore the necessary switching is performed. However, there was a problem in that the element had to be made longer or the applied voltage had to be increased in order to increase the change in the refractive index in the central portion.

[Means for Solving the Problems] The present invention provides an optical switch that solves the above-mentioned problems. A narrow electrode is provided along the central part of the waveguide region, and an electrode is provided in a region covering both peripheral parts of the waveguide region, and a voltage is applied between the central electrode and the electrodes of both peripheral parts, and the electro-optic effect is applied. This is solved by changing the refractive index of the waveguide region.

[Effect]

In the above optical switch, an electric field is generated in a very narrow space by applying an electric field to a narrow electrode provided along the center of the waveguide region and an electrode provided in a region covering both peripheries of the waveguide region. In addition to being concentrated, the electric field is applied perpendicularly to the waveguide at both the center and the periphery, and in opposite directions, so the sign of the change in the refractive index of the waveguide is reversed between the center and both peripheries.
As a result, the signs of the changes in the propagation constants of even and odd modes are reversed, and the operating voltage is reduced.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a plan view showing the structure of a waveguide type optical switch which is an embodiment of the present invention, in which Ti is diffused into the crystal on a substrate 1 of Z@LiNb0+ crystal to make the refractive index larger than that of the substrate crystal. A rectangular waveguide area 2 with two input optical waveguides 3.4 and two output optical waveguides 5 connected to both ends of the waveguide area 2.
, 6 are provided at the center of the rectangular waveguide region 2, and electrodes 18 and 19 are arranged in parallel with the thin electrode 7 and the central electrode 7 so as to cover the periphery of the waveguide region 2. ing.

FIG. 2 is a cross-sectional view taken along line xx' in FIG. 1,
An electrode 7 provided on the rectangular waveguide region 2.

When a voltage is applied between the electrodes 18 and 19 provided outside the waveguide region 2, electric lines of force 20 as shown by broken lines are generated, and this vertical component changes the refractive index of the rectangular waveguide region 2. Change.

However, the electrodes 18°19
Therefore, the direction of the electric field under the central electrode is opposite to the direction of the electric field under the peripheral electrode.

Therefore, in the conventional case, only the portion under the central electrode contributed to the refractive index change, but in the structure of the present invention, the refractive index change under the peripheral electrode also contributed. The sign of this refractive index change is opposite because the direction of the electric field is opposite, and acts in a direction that enhances the switching effect.

As a result, when selectively switching the incident light from the input optical waveguide 4 to either the output optical waveguide 5 or 6, it is possible to drive with a lower voltage than in the past.

〔Effect of the invention〕

As explained above, according to the present invention, the sign of the change in the refractive index of the waveguide region between the center and the periphery is reversed between the center and both peripheries, making it possible to operate at a lower voltage than in the past. effective.

[Brief Description of the Drawings] Figures 1 and 2 are a plan view and a sectional view showing the structure of a waveguide type optical switch which is an embodiment of the present invention, and Figures 3 and 4 are views of a conventional waveguide type optical switch. FIG. 2 is a plan view and a cross-sectional view showing the structure of a type optical switch. In the figure, 1 is the substrate, 2 is the waveguide region, 3.4 is the input optical waveguide, 5.6 is the output optical waveguide, ? ,8.9,18,1
9 represents an electrode, 10 and 20 represent lines of electric force, respectively. lI 1 Figure 1I 2

Claims (1)

[Claims] An electro-optic crystal waveguide type optical switch in which a rod-shaped electrode is arranged in the center of a rectangular waveguide region having two waveguides at each end, and a pair of control electrodes are arranged on both sides of the waveguide region. A waveguide type optical switch, wherein the pair of electrodes on both sides overlap at least a part of the rectangular waveguide region.