JPH02214828A - Integrated optical waveguide 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] [Summary] Regarding an integrated optical waveguide device including a plurality of light control elements, adjacent light waves caused by elastic waves excited in a substrate by a control voltage applied to a light control electrode A planar substrate having an electro-optic effect, an optical waveguide having a plurality of optical control waveguide sections formed on the substrate, and an optical waveguide for the purpose of eliminating electrical crosstalk between control electrodes; A plurality of light control electrodes provided on a plurality of light control waveguide sections, and an elastic wave propagation provided on the substrate between adjacent light control electrodes among the plurality of light control electrodes. The integrated optical waveguide device is configured to include at least blocking means.

[Industrial application field]

The present invention relates to the configuration of an integrated optical waveguide device having a plurality of optical control elements on one substrate.

In recent years, with the progress and development of optical fibers and laser light sources, various systems and devices that apply light wave technology, including optical communication, have been put into practical use and widely used. The demand has become stronger.

In particular, due to the recent demand for higher speed optical communication systems, optical transceivers that transmit and receive optical signals require optical modulators to modulate light at high speed and sequential switching of multiple time-division multiplexed optical input signals. Integrated optical control devices such as high-speed optical switch arrays to connect multiple outputs have become necessary.

These optical control devices integrate a large number of high-speed optical control elements by forming a planar waveguide on a single substrate with an electro-optic effect and combining traveling wave electrodes on the waveguide. This is a so-called optical integrated circuit, and is expected to be a promising technology for miniaturizing and increasing the speed of optical signal processing devices.

However, much of this technology is still in the development stage, and there are many issues that need to be resolved.As the demand for large-capacity and long-distance communications becomes stronger in the future, faster, more stable, and more reliable There is a need for the development of highly integrated optical waveguide devices.

[Conventional technology]

As high-speed optical control devices, external modulators that externally modulate semiconductor laser light and optical waveguide type optical switches are known.

In either case, the most promising method is to provide an optical waveguide on a substrate with an electro-optic effect and drive it using a traveling wave type optical control electrode. The number of light control electrodes formed has also increased, and the spacing between them has become narrower.

Figure 5 is a diagram explaining a conventional directional coupler type optical switch, in which (a) is a plan view and (b) is a cross-sectional view.
b) x-y cross section].

In the figure, 1 is a substrate having an electro-optic effect, for example, Li
The NbO3 Z plate 2 is an optical waveguide, and three directional coupler type parallel optical waveguides 2A and 2B are formed in the middle, and the optical control waveguide section 2 is constituted by these two parallel optical waveguides. This optical waveguide is usually made by selectively diffusing a metal such as Ti on the surface of a LiNbO3 substrate only to the optical waveguide portion, so that the refractive index of that portion is slightly larger than that of the surrounding portions.

Note that the distance and length of the parallel optical waveguides 2a and 2m are, for example, 6 μm each in an optical switch of several GHz band.
It is designed to have a value of about 15 mm, which allows mode coupling of propagating light.

Reference numeral 4 denotes a light control electrode, which is composed of a traveling wave type control electrode (4A) and a ground electrode (4B). is formed by vapor deposition or plating.

The buffer layer 3 is provided to reduce the absorption of light into the metal electrode layer on the optical waveguide, and is usually made of a thin film of SiO2 or the like.

SWI, SW2, and SW3 each indicate a directional coupler type optical switch, and are driven and controlled by the optical control electrode 4.

■ is the light input end, ■, ■, ■ and ■ are the light output ends,
Therefore, this example shows the case of a so-called x4 optical switch array. Connection with optical fibers is performed using ruby beads or a fiber array with a convex structure.

Now, for example, when time-division multiplexed signal light enters the optical waveguide 2 from the left input end 2 and reaches the parallel optical waveguide 2A of the SWI, parallel optical waveguides 28 are arranged parallel to it at a required interval and a required length. Due to the mode coupling between the , p1051.
(see 1988 publication).

However, if a high-frequency pulse voltage is applied to the optical control electrode 4 of Ski at this time, the refractive index changes due to the electro-optic effect in the parallel optical waveguide 2A211 provided on the substrate 1 having an electro-optic effect, resulting in a symmetrical・The phase difference between the two asymmetric modes also shifts in π. In the case of this conventional example, by selecting the applied voltage to be 4 to 5 V, it is possible to completely prevent light from moving from the parallel waveguide 2A to 2B. That is, the configuration is such that light can be switched at high speed depending on whether or not a high frequency pulse voltage is applied to the light control electrode 4.

In SW2 and SW3, all (function in the same way,
As a whole, it constitutes an IX4 high-speed optical switch array.

Furthermore, attempts have been made to increase the degree of integration and increase the number of switch elements to construct a high-speed optical matrix switch and use it in a high-speed, multiplex optical communication system.

[Problem to be solved by the invention]

However, in an optical switch array with such a configuration,
As the degree of integration increases, for example, the distance between SW2 and SW3 becomes narrower, as shown in FIG. On the other hand, since the substrate 1 having an electro-optic effect always exhibits piezoelectricity, some kind of surface acoustic wave or pseudo surface acoustic wave is often excited between the SW 2 and the needle 3.

Figure 4 is a crosstalk/transmission loss characteristic diagram of a conventional directional coupler type optical switch.
This figure shows the transmission loss characteristics of SW2 and electrical crosstalk from SW2 to needle 3 when the distance between SW2 and SW3 is 300 μm.

Measurement of transmission loss is performed using control electrode 4A and ground electrode 4 of SW2.
．． A high-frequency swept sinusoidal voltage output from a network analyzer was applied to the input end of the network analyzer, and the other end was connected to the detector side of the network analyzer. Crosstalk was similarly measured by connecting a network and an analyzer to the output terminals of the control electrode 4A and ground electrode 4B of SW3.

As you can see from the figure, 1.2.2.8. and 4.6
At GHz, dips can be seen in the transmission characteristics of SW2, and at the corresponding frequencies, SW2 to SW3
A large amount of loss talk is occurring.

When the losstalk increases like this, the signal light S/
There is a problem in that N is decreased and the signal error rate is increased, and a solution to this problem is required.

[Means to solve the problem]

The above-mentioned problems include a substrate 1 having an electro-optic effect processed into a flat surface, an optical waveguide 2 having a plurality of optically controlled waveguide sections 2 formed on the substrate 1, and a plurality of optically controlled waveguides formed on the substrate 1. A plurality of light control electrodes 4 provided on the part 2' and an elastic wave propagation layer provided on the substrate 1 between adjacent light control electrodes 4 among the plurality of light control electrodes 4. Prevention means 5
This can be solved by an integrated optical waveguide device comprising at least the following.

[Effect]

According to the configuration of the present invention, adjacent optical switches, for example,
Since the elastic wave propagation blocking means 5 is provided on the substrate 1 between the sides 2 and 3, electrical crosstalk from SW2 to SW3, which occurs mainly through elastic waves propagating near the substrate surface, can be prevented. It can be removed.

〔Example〕

FIG. 1 is a plan view of a directional coupler type optical switch according to the present invention. The difference from the conventional structure is that an elastic wave propagation blocking means 5 is attached to a substrate 1 between adjacent optical switches, for example, SW2 and SW3. This is a point that is established.

The substrate 1 is made of Li with a size of 60 mm x 8 mm and a thickness of 1 mm.
The surface of the NbO3 Z plate was mirror polished and used.

On this substrate, Ti was vacuum-deposited to a thickness of about 70 nm.
After processing with a normal photoetching method so that Ti remains in the three optical control waveguide sections 2'', that is, the portions corresponding to the optical waveguide 2 including the three pairs of parallel optical waveguides 2A and 2Il, it is heated at approximately 1035°C. Heated in oxygen for 8 hours to convert Ti to Li.
An all-optical waveguide 2 was formed by thermal diffusion into NbO3.

Parallel optical waveguide 2. The distance between and 2B is 6.4 μm, and the length is 1
The width of each optical waveguide was 7 μm. The waveguide spacing at the output end was 180 μm.

Next, a buffer layer 3 of 5 in 2 was formed to a thickness of 350 nm by CVD.

The light control electrode 4 is formed on the buffer layer 3 by T i -A u
After the alloy film was deposited, a pattern was etched onto the optical waveguide 2 to form an electrode having a width of 10 μm, and a 3 μm thick ^U was further deposited thereon by plating. The distance between the control electrode 4A and the ground electrode 4B on the three pairs of parallel optical waveguides 2A and 2B is 5 μm.

The distance between optical switches SW2 and SW3 is 360 μm,
The distance between SWI and SW3 is 20 mm.

As the elastic wave propagation blocking means 5, a groove having a width of 100 μm, a depth of 200 μm, and a length of 20 mm was formed between SW2 and SW3 using a cutting blade.

FIG. 2 is a sectional view of a directional coupler type optical switch according to the present invention, and (A) shows a groove 51 as an elastic wave propagation blocking means.
showed that.

FIG. 3 is a crosstalk/transmission loss characteristic diagram of the directional coupler type optical switch according to the present invention, and the measurement method is the same as that of the conventional example.

As can be seen from the figure, there is almost no dip in the transmission loss characteristics of SW2, and the crosstalk from SW2 to SW3 is also significantly improved compared to that of the conventional example shown in FIG.

In addition, in the above embodiment, the groove 51 is used as the elastic wave propagation blocking means.
However, as shown in FIG. 2 (b), an elastic wave absorbing material 52. For example, a silicone resin mixed with heavy metal powder may be applied or screen printed, or an elastic wave absorbing material 52 may be filled in the groove 51 as shown in FIG. It can also be increased.

In this embodiment, SWI and SW2, or SWI and S
Since there was a wide distance from W3 of about 20 mm and crosstalk was hardly a problem, no elastic wave propagation blocking means was particularly provided, but it is of course possible to provide one if necessary.

Also, in this example, the number of optical switches was three, but
Not only in the case of four or more optical control elements, but also in the case where the optical control element is not a directional coupler type optical switch (or a branching interference type optical modulation element or an optical phase modulation element, or a mixture of them), this book does not apply. It goes without saying that the invented method can be applied.

〔Effect of the invention〕

As explained above, according to the present invention, even if a plurality of light control electrodes are integrated adjacently on the same substrate, electrical crosstalk between adjacent light control electrodes can be eliminated, so that integrated light guide This greatly contributes to improving the performance of waveguide devices.

[Brief explanation of the drawing]

Fig. 1 is a plan view of a directional coupler type optical switch according to the present invention, Fig. 2 is a cross-sectional view (x-y section) of a directional coupler type optical switch according to the present invention, and Fig. 3 is a direction view according to the present invention. Figure 4 is a crosstalk/transmission loss characteristic diagram of a conventional directional coupler type optical switch. Figure 5 is a diagram of a conventional directional coupler type optical switch. FIG. In the figure, 1 is a substrate, is an optical waveguide, is an optical control waveguide section, is a buffer layer, is an optical control electrode, is an elastic wave propagation blocking means, 1 is a groove, and 2 is an elastic wave absorbing material.

Claims (1)

[Claims] An optical waveguide (2) comprising: a substrate (1) having an electro-optic effect processed into a plane; and a plurality of optically controlled waveguide sections (2') formed on the substrate (1). and a plurality of light control electrodes (2') provided on the light control waveguide sections (2').
4), and an elastic wave propagation blocking means (5) provided on the substrate (1) between adjacent light control electrodes (4) among the plurality of light control electrodes (4). An integrated optical waveguide device comprising at least: