JPH0670693B2 - Waveguide type optical control device - Google Patents

Description

The present invention relates to a structure of a waveguide type optical control device.

[Conventional technology]

In a waveguide type optical device in which a ferroelectric material having an electro-optic effect is used for the optical waveguide layer and an electrode is provided on the optical waveguide layer, guided light can be controlled by applying a voltage to the electrode, and a switch, a grating can be used. -It is possible to obtain elements having many functions such as couplers, demultiplexers, and reflectors.

FIG. 5 shows an example of a grating coupler made of titanium-diffused lithium niobate, which has been widely used as an optical waveguide material having an electro-optical effect. Z-cut LiNb
An optical waveguide layer 52 in which Ti is diffused is formed on an O ₃ substrate 51, and grating electrodes 53 and 54 are formed on the optical waveguide layer 52. By applying a voltage between the electrodes 53 and 54, an electric field 55 is generated in the optical waveguide layer 52, and the refractive index of the optical waveguide layer is periodically changed to form a refractive index modulation type grating and guide the guided light to the outside. be able to. It is known that the degree of change in the refractive index changes and the coupling efficiency of the grating coupler changes by changing the applied voltage.

[INVENTION AND SUMMARY Problems] However, in the waveguide type optical control device using the conventional LiNbO _3, the refractive index change of the LiNbO ₃ is due to the primary electro-optic effect, large refractive index change Has the drawback that a high voltage must be applied to obtain
Further, since the electrodes are on the same plane, there is a horizontal electric field component that does not contribute to the change in the refractive index, so that there is a drawback that the applied voltage must be increased to obtain high diffraction efficiency.

An object of the present invention is to provide a waveguide type optical control device that can obtain a large change in refractive index even when an applied voltage is low.

[Means for solving problems]

According to the present invention, a spinel layer is formed on a silicon substrate, first and second PLZT thin film layers having different refractive indices are formed thereon, and an electrode is formed on the second PLZT thin film layer. And a means for applying a voltage between the electrode of the element and the silicon substrate, wherein the second PLZT thin film layer has a larger refractive index than the first PLZT thin film layer,
A waveguide type optical control device for controlling guided light by using a PLZT thin film layer as an optical waveguide can be obtained.

[Action]

In the present invention, a PL having a secondary electro-optical effect is used as the optical waveguide layer.
Since the ZT thin film layer is used, a much larger change in the refractive index can be obtained as compared with the first-order electro-optical effect. Furthermore, by applying a voltage between the electrode on the optical waveguide layer and the silicon substrate,
Only a vertical electric field is generated with respect to the optical waveguide layer, and most of the generated electric field can be used for changing the refractive index. In addition, the buffer layer that reduces the leakage of light from the optical waveguide layer has a two-layer structure of a PLZT thin film and a spinel layer, and the spinel layer, which has a lower dielectric constant than the PLZT thin film layer and is easy to concentrate the electric field, is thinned. , The electric field can be concentrated on the optical waveguide layer and the applied voltage can be effectively applied to the PLZT thin film layer. Therefore, by forming the buffer layer into two layers and thinning the spinel layer, a high diffraction efficiency can be obtained at a low voltage.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a grating according to a first embodiment of the present invention.
It is a perspective view which shows the structure of a coupler. Spinel (MgAl ₂ O ₄ ) layer 12 and PLZT as a buffer layer on the silicon substrate 11.
(PbLaZiTi) buffer layer 13, PLZT optical waveguide layer 14 on top of it
And a grating electrode 15 is formed on the PLZT optical waveguide layer 14. The spinel layer 12 is a buffer layer for preventing leak of guided light to the silicon substrate 11, and also functions as an intermediate layer for epitaxially growing single crystal of PLZT. Further, the PLZT buffer layer 13 satisfies the conditions required for the buffer layer: (a) smaller and closer than the refractive index of the PLZT optical waveguide layer 14, (b) good adhesion with the PLZT optical waveguide layer 14, etc. ing.

By applying a voltage between the grating electrode 15 and the low-resistance silicon substrate 11, an electric field 19 is generated in the direction perpendicular to the PLZT optical waveguide layer 14, and a periodic change in refractive index occurs. As a result, the PLZT optical waveguide layer 14 becomes a refraction index modulation type grating, the incident light 16 can be taken out, and the outgoing light 17
Is obtained. When no voltage is applied, it becomes a normal optical waveguide, and the incident light 16 is guided as it is. Since the electric field 19 is applied vertically, the change in the refractive index in the depth direction is uniform, and the diffraction efficiency of the grating is much higher than that when an electric field is applied in the lateral direction. Further, since the buffer layer is composed of two layers, the PLZT buffer layer 13 and the spinel layer 12, the spinel layer 12 having a low dielectric constant is thinned, and the generated electric field is concentrated within the PLZT layer thickness, so that the grating electrode 15 The applied voltage between the silicon substrate 11 and the silicon substrate 11 can be reduced. Further, it is possible to increase the diffraction angle by setting the grating pitch to 1 μm or less. The voltage applied to the grating electrode can be significantly reduced by the secondary electro-optical effect of the device structure and the PLZT optical waveguide layer.

In this embodiment, the PLZT optical waveguide layer 14 and the PLZT buffer layer 13
The spinel layer 12 and the spinel layer 12 were formed by a magnetron sputtering method, and the film thickness was 9 μm, 1.4 μm, and 0.01 μm, respectively.
The grating electrode 15 is made of transparent ITO so as not to prevent the emitted light 17, and is patterned by ion milling.

Next, an application example of the first embodiment of the present invention will be shown. FIG. 2 is a perspective view showing an example in which the present invention is applied to an optical path changing element. In FIG. 2, the pitch Λ of the grating electrodes 25
The optical deflection can also be performed by keeping the value constant and periodically changing the refractive index. In particular, in FIG. 2, when the incident light 26 is incident in the horizontal direction of the grating electrode 25 at an angle θ and a voltage is applied to the grating electrode 25, a vertical electric field is generated between the grating electrode 25 and the silicon substrate 11, and the PLZT optical waveguide is generated. Wave layer 14
The outgoing light 27 can be extracted at a low voltage due to the change in the refractive index of.
If no voltage is applied, the guided light goes straight on and goes out.
Becomes For example, in the case of incident light with a wavelength λ = 1.3 μm, if the grating pitch Λ = 0.5 μm, the deflection angle 2θ
Is estimated to be about 55 °. Therefore, if the grating pitch is set appropriately, any deflection can be obtained.

FIG. 2 shows a reflection type of the grating, but FIG. 3 shows an example in which the incident light 36 is made incident on the grating electrode 26 at an angle θ to change the optical path.

FIG. 4 shows a second embodiment of the present invention in which a channel waveguide 44 having a patterned optical waveguide and a plane electrode 45 on the upper portion of the intersection are provided.
By providing, a total reflection type optical switch capable of operating at a low voltage is shown. When the incident light 46 is made incident and a voltage is applied to the electrode 45, a vertical electric field is generated between the electrode 45 and the silicon substrate 11, and the change in the refractive index of the PLZT channel optical waveguide 44 allows the emitted light 47 to be extracted at a low voltage. If no voltage is applied,
Incident light 46 goes straight through the incident channel.

〔The invention's effect〕

A comparison will be made between the case where two buffer layers (PLZT buffer layer and spinel layer) as in the present invention and the case where all the buffer layers are composed of spinel layers are compared by their capacities. In FIG. 1, the PLZT optical waveguide layer 14 is 9 μm, and the PLZT buffer layer is
13 and the spinel layer 12 are 1.4 μm and 0.01 μm respectively,
The capacitance between electrodes when there are two buffer layers is 155 × 10 ⁶ / s
[F] (where s is the electrode area). When the buffer layer is composed of only the spinel layer (thus, the thickness of the buffer layer is 1.41 μm), the interelectrode capacitance is 5.53 × 10 ⁶ / s.
[F]. When there are multiple dielectric layers between electrodes, the electric field generated in each layer is inversely proportional to the capacitance ratio of each layer. Therefore, by using two buffer layers, a PLZT buffer layer and a spinel layer, only the spinel layer provides a buffer. It is sufficient to apply a voltage of 1/30 in order to obtain the same diffraction efficiency as when the layers are formed. Therefore, the present invention can reduce the applied voltage to 1/30.

As described above, according to the present invention, guided light can be controlled at a low voltage in the guided light control device.

[Brief description of drawings]

FIG. 1 is a perspective view showing a grating coupler which is a first embodiment of the present invention, and FIG. 2 is a perspective view showing an example in which the first embodiment of the present invention is applied to a reflection type optical path conversion element, Third
FIG. 4 is a perspective view showing an example in which the first embodiment of the present invention is applied to a transmission type optical path conversion element, and FIG. 4 is a perspective view showing an internal total reflection type switch which is a second embodiment of the present invention. Figure 5 shows Li
FIG. 7 is a perspective view showing a conventional example using NbO ₃ . 11 ... Silicon substrate, 12 ... Spinel layer, 13 ... PLZT buffer layer, 14 ... PLZT optical waveguide layer, 15, 25, 53, 54 ... Grating electrode, 16, 26, 36, 46 ... Incident light, 17, 27, 37 , 47 ... Emitted light (diffracted light), 28, 38 ... Emitted light (non-diffracted light), 19, 55 ... Electric field, 44
… PLZT channel optical waveguide, 45… Planar electrode, 51… LiNbO ₃
Substrate, 52 ... Ti diffuse optical waveguide layer.

Claims (1)

[Claims] 1. A device in which a spinel layer is formed on a silicon substrate, first and second PLZT thin film layers having different refractive indexes are further formed thereon, and an electrode is formed on the second PLZT thin film layer. And a means for applying a voltage between the electrode and the silicon substrate, wherein the second PLZT thin film layer has a refractive index larger than that of the first PLZT thin film layer, and the second PLZT thin film layer is optically guided. A waveguide-type optical control device characterized by controlling guided light as a waveguide.