JPH0425524B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveguide type optical control device that modulates light waves and controls light such as switches using an optical waveguide installed on a substrate.

The development of optical application systems such as optical communication systems, optical sensors, and optical information processing systems is progressing.
In these systems, efforts are being made to expand the amount of information, transmission speed, and system functionality. Therefore, there is an increasing need for optical control devices such as optical modulators that modulate optical signals and optical switches that arbitrarily switch the optical path of optical signals. For the above devices, high efficiency, high speed, small size, and coupling with single mode fiber are necessary conditions, but in addition to these, for the purpose of expanding functionality, it is necessary to be able to integrate multifunctional devices. This is an important condition. Waveguide type optical control devices are being developed to satisfy all of the above requirements, and are constructed using an optical waveguide furnace installed on a substrate. Attempts have also been made to integrate a large number of waveguide optical control devices on a single substrate to obtain the above-mentioned multifunctional integrated device.

To obtain high efficiency and high speed in waveguide optical control devices, ferroelectric materials such as lithium niobate (LiNbO ₃ ) crystals and lithium tantalate (LiTaO ₃ ) crystals are often used as substrates. This is because the above-mentioned crystal has a large electro-optic effect, and an optical waveguide can be manufactured relatively easily by metal diffusion. A directional coupling type configuration or a total internal reflection type configuration is commonly used as a light control device. In the directional coupling type configuration, two optical waveguides each having a width of several μm to several + μm are brought close to each other at an interval of several μm, and a voltage is applied to a control electrode provided near the optical waveguides.
This controls the degree of coupling between the optical waveguides.
On the other hand, in the total reflection type configuration, two optical waveguides are crossed at an angle of several degrees, and a control electrode is installed at the intersection to control the reflectance of light waves at the intersection.

By integrating a plurality of the above-mentioned directional coupling type or total reflection type light control devices as one light control element on a single substrate,
It is possible to obtain an optical control device having multiple functions such as a matrix of optical switches, an optical switch array, an optical modulator array, and the like. However, in this case, if the elements are placed close to each other, a problem arises in that the electric field applied to one control electrode leaks to the adjacent element. On the other hand, since it becomes necessary to increase the distance between each element and integrate the light control elements, and to bend the optical waveguide at a large angle or a small curvature, the optical propagation loss becomes large. The above-mentioned leakage electric field disturbs the state of adjacent elements, causing adverse effects such as increased crosstalk in optical switches, for example. Therefore, in the past, the number of elements that could be integrated was limited in order to reduce propagation loss and prevent leakage electric fields.

An object of the present invention is to provide a waveguide optical control device in which a large number of elements can be integrated by reducing the influence of electric field leakage as described above when the elements are placed close to each other.

In the waveguide type light control device of the present invention, a plurality of light control elements each consisting of an optical waveguide and a control electrode provided close to the optical waveguide are arranged on a dielectric substrate having an electro-optic effect, such as a lithium niobate crystal substrate. However, it is constructed by installing a groove between the light control elements.

In the light control device of the present invention, even if the light control elements are arranged close to each other, the influence of electric field leakage can be minimized, so that a large number of elements can be integrated.

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

FIG. 1 is a diagram showing an example of a conventional waveguide type optical control device, and is a plan view of a 2×4 waveguide type optical switch using three directionally coupled type optical control elements. In FIG. 1, optical waveguides 2, 3, 4, 5, 6, and 7 are formed on a Z-plate LiNbO ₃ crystal substrate 1 by the usual titanium diffusion method. The titanium diffusion method is a method in which the patterns of optical waveguides 2, 3, 4, 5, 6, and 7 are created using a titanium thin film with a thickness of several hundred Å, and the optical waveguides are obtained by performing thermal diffusion at approximately 1000°C for several hours. be. Here, optical waveguides 2, 3, 4, 5, 6, 7
The widths of all of them are from several μm to more than ten μm. Optical waveguide 2
and 3, 4 and 5, and 6 and 7 are each several μm apart from each other.
Directional couplers 11, 12, 13 in close proximity to
is formed. Optical waveguides 2 and 5, and 3 and 6 are connected, respectively. Directional couplers 11, 12,
Since the amount of coupling of 13 varies greatly depending on the phase velocity difference between the two optical waveguides that make up the waveguide, normally, in an optical switch, a voltage is applied to a control electrode installed near the optical waveguide. Switching control is performed by changing the phase velocity of the optical waveguide using the electric field generated in the optical waveguide and the electro-optic effect. Since this optical switch uses a Z plate substrate, the control electrodes 14 and 15, 16 and 17, 18 and 19 for each of the directional couplers 11, 12, and 13 are SiO ₂ on the optical waveguide to prevent light absorption. They are installed with a membrane 20 in between. In addition, in this optical switch, the directional couplers 11, 12, and 13 are manufactured so that they are 100% coupled to each other when no voltage is applied to the control electrode, and the coupling becomes 0 when a voltage V is applied to the control electrode. ing. That is, when all voltages applied to the control electrodes are 0, the incident light 21 to the optical waveguide 2
is coupled to the optical waveguide 3 by the directional coupler 11, coupled to the optical waveguide 7 by the directional coupler 13, and output light 23
becomes. Similarly, incident light 22 to the optical waveguide 3 is coupled to the optical waveguide 4 and becomes output light 24. If the voltage V is applied only to the control electrode 18 here, the coupling of the directional coupler 13 becomes 0, so the incident light 21 becomes the output light 25 from the optical waveguide 6. Normally, when connecting a plurality of directional coupler type optical control elements like this optical switch, the optical waveguides are bent at a small angle θ to connect them. However, a very small value for θ is used so that the optical loss at the bend is small. For example, in order to reduce the optical loss to 1 dB or less, θ needs to be several mrad or less. At this time, if the length of the bent portion is several mm, the distance S between the directional couplers 12 and 13 will become extremely narrow. For example, if θ = 4mrad, = 2.5mm, S
= approximately 20 μm. According to calculations, control electrode 18
By applying a voltage V to the control electrodes 16, 17, 19
When the voltage is 0, an electric field is generated in the optical waveguides 4 and 5, and there is a phase velocity difference between the optical waveguides 4 and 5 that is equivalent to 8% of the phase velocity difference that occurs between the optical waveguides 6 and 7. of the output light 24 from the optical waveguide 4.
The light corresponding to about 1.6% (-18dB) reaches the optical waveguide 5.
It leaks.

The crosstalk caused by the above-mentioned electric field leakage becomes larger than the normally allowable crosstalk of -20 to -24 dB. On the other hand, if the distance S is increased to prevent electric field leakage, the length of the bent portion becomes extremely long, making it impossible to integrate many light control elements on a small substrate.

In the present invention, the above-mentioned drawbacks can be eliminated by providing grooves between the control electrodes of the light control element.

FIG. 2 is a sectional view showing an embodiment of the waveguide type optical control device according to the present invention. In this embodiment, the shapes of the optical waveguide and control electrode are all the same as those of the conventional waveguide type optical control device shown in FIG. Groove 30
The difference is that the . FIG. 2 shows a cross section including the groove 30 and the directional couplers 12 and 13. In this embodiment, even when the voltage V is applied to the control electrode 18 and the voltage of the control electrodes 16, 17, and 19 is set to 0, the leakage of the electric field to the optical waveguides 4 and 5 can be reduced. The crosstalk that occurs between them is less than -20dB. Here, the effect of the present invention can be obtained if the depth of the groove 30 is approximately the same as the depth of the electric field distribution (usually 3 to 10 μm). Further, in this embodiment, the distance between the directional couplers 12 and 13 can be made closer, and the length of the bent portion can be further shortened, so that many optical control elements can be integrated on a small substrate.

FIG. 3 is a sectional view showing another embodiment of the waveguide type optical control device according to the present invention. This example is also the second
The shapes of the optical waveguide and control electrode are all the same as in the embodiment shown in the figure, but the positions and shapes of the grooves are different. In this embodiment, grooves 31 and 32 are provided adjacent to control electrodes 16 and 18, respectively, and grooves 33 and 34 are provided adjacent to control electrodes 17 and 19, respectively. However, the grooves 31, 32, 33, and 34 are separated from the optical waveguides 5, 6, 4, and 7 by several μm or more, and since the SiO ₂ film 20 is coated after forming the grooves, the optical propagation characteristics may be affected. The grooves are formed so that the influence of the grooves is reduced. In this embodiment, the effect of confining the applied electric field is stronger than in the embodiment shown in FIG. 2, so there is very little electric field leakage to adjacent optical control elements, and the electric field is effectively applied within the optical waveguide. Therefore, it has the advantage of being highly efficient.

As described above, according to the present invention, when light control elements are placed close to each other, the influence of electric field leakage is reduced, and a waveguide light control device in which a large number of elements can be integrated can be obtained.

It goes without saying that the present invention is not limited to the above embodiments. For example, the substrate is usually an X plate or a Y plate on which electrodes are installed across the optical waveguide.
LiNbO ₃ or LiTaO ₃ crystal can be used.
Furthermore, the present invention can also be used when integrating a light modulator, a polarization converter, a variable wavelength filter, etc. as a light control element, or when integrating a total reflection type light control element.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a conventional waveguide type light control device, and FIGS. 2 and 3 are sectional views showing an embodiment of the waveguide type light control device according to the present invention. In the figure, 1 is a dielectric substrate, 2, 3, 4,
5, 6, 7 are optical waveguides, 14, 15, 16, 1
7, 18, 19 are control electrodes, 30, 31, 32,
33 and 34 indicate grooves.

Claims (1)

[Claims] 1. In a waveguide type light control device configured by arranging a plurality of light control elements each consisting of an optical waveguide and a control electrode provided close to the optical waveguide on a dielectric substrate having an electro-optic effect, A waveguide light control device characterized in that a groove is provided between adjacent light control elements.