JPH045174B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to optical switches. In particular, the present invention relates to an optical switch applied to an optical integrated circuit that turns on and off optical output by branching guided light.

Conventional Structure and Problems There is a total internal reflection switch as a conventional optical switch using this type of branching waveguide. The configuration of an optical branching waveguide used in a total reflection type switch and the like and its problems will be explained below with reference to the drawings. FIG. 1 shows a total internal reflection type optical switch 10 constructed on a substrate having an electro-optic effect. In the same figure, 11 and 13
and 12 and 14 indicate optical waveguides that intersect with each other. Reference numerals 15 and 16 indicate electrodes provided on the optical waveguide, and 17 indicates a light propagation control section, which is provided on the intersection of the optical waveguides. In the optical switch having such a configuration, by applying a voltage to the electrodes 15 and 16, the control unit 1 is controlled by the electro-optic effect.
The refractive index of the optical waveguide portion below 7 becomes small. Therefore, when a voltage is applied to the electrodes 15 and 16, the guided light incident from 11 satisfies the total reflection condition at the control section 17 and propagates to 14.
Note that when no voltage is applied, the guided light incident from 11 travels straight through the control section 17 and is propagated to the waveguide 13. The guided light incident from the waveguide 12 is also switched to the waveguides 13 and 14 in the same way. When integrating optical switches, the intensity ratio of the optical outputs of the waveguides 13 and 14 on the optical output side when the voltage is off, that is, the branching ratio, and the voltage on/off of a specific waveguide 13 or 14 on the optical output side are determined. The characteristic of the intensity ratio of light output, that is, the extinction ratio, is important.

Such conventional optical switches have the following drawbacks or problems. That is, since the change in refractive index due to the electro-optic effect is small, the intersection angle between waveguides 11 and 12 is small, and the guided light that enters from waveguide 11 and propagates to waveguide 13 passes through waveguide 1.
4, and it was extremely difficult to obtain a branching ratio and extinction ratio of 10 dB or more. For this reason, it was difficult to obtain sufficient switching characteristics, posing a practical problem.

Further, in order to improve this point, the configuration shown in FIG. 2 is used. This structure is shown in the figure as parabolic waveguides 111 and 12 in which the line width of the waveguides is increased parabolically near the intersection and connected.
1,141,151 are provided. In this configuration, the amount of mode exchange is theoretically small, e.g.
In TEoo mode, the light propagated from 11 is
It is said that the light travels straight in the TEoo mode and propagates from 151 to 13 without leaking to the waveguide 141.

However, in this structure, there is a shape condition in the line width of the parabolic waveguide that does not change the propagation mode. That is, W ² =(2αλ _p /nb)Z+W _p ² .

Here, λo: wavelength of light, nb: bulk refractive index of the optical waveguide, Z: distance from the constant-width waveguide (see Figure 2), W: width of the parabolic waveguide, W _p : constant-width waveguide. Wave width.

From the above equation, it can be seen that as α becomes larger, the waveguide width increases rapidly toward the intersection. Therefore, in order to widen the waveguide width sufficiently to obtain a sufficient leakage suppression effect and to keep the parabolic portion as short as possible for miniaturization, α should be increased and the waveguide width should be made as steep as possible. It would be good if it spread to.

However, as α becomes larger, the connection between the parabolic waveguide and the constant width waveguide becomes a point of sudden change. Therefore, the accuracy of processing the waveguide shape has a large influence on the accuracy of the waveguide width. If the accuracy is low, the shape condition expressed by the above equation will not be satisfied, resulting in conversion of the propagation mode. For example, in the case of TE ₀₀ mode light, a part of it is mainly converted to TE ₀₁ mode. Since the TE ₀₁ mode is attenuated at a higher rate in the waveguide 14 than the TE ₀₀ mode, a problem arises in that the branching ratio deteriorates.

On the other hand, if α is set small, the change in the waveguide width toward the intersection will be gradual, and the influence of processing accuracy on the waveguide width will be small. You need to make the pieces longer. For example, if α is set to 0.5 in order to provide a practical margin for processing accuracy, the element size will be 10 mm or more, which is not suitable for integration.

As described above, unless extremely high-precision processing is performed, it is not possible to ensure the characteristics of a small size and a branching ratio and extinction ratio of 10 dB or more, and it is difficult to manufacture an element with a high yield.

The present inventors have discovered that by devising an optical branching waveguide, a structure that can significantly improve the branching characteristics and can be formed at a high yield has been realized, and an optical switch with excellent switching characteristics can be realized.

OBJECTS OF THE INVENTION An object of the present invention is to provide an optical switch with good branching characteristics that eliminates the drawbacks and problems of the above-mentioned conventional examples.

Structure of the Invention In the present invention, the line width of the waveguide in the vicinity of the waveguide is increased toward the center of the intersection, and the lines are connected smoothly, and the outer circumferential line in the vicinity of the intersection is made hyperbolic.

Description of examples The present invention will be explained below using the drawings.

FIG. 3 shows the structure of an optical switch according to the present invention. In the figure, the optical switch according to the present invention includes optical waveguides 321 and 322 and 331 and 332 that are formed on the surface 31 of the substrate and intersect with each other.
It is composed of control electrodes 351 and 352 provided on the surface of the intersection 34 to select the propagation path of light, and further includes waveguides 3211, 3221, 3311 in the vicinity of the intersection 34 of the waveguides,
The line width of 3321 is increased toward the center of the intersection 34 and connected smoothly, and the outer circumferential line 36 of the waveguide near the intersection is made hyperbolic.

Conventionally, it has been thought that such a configuration does not limit the natural spread of guided light, and therefore it is not possible to obtain a sufficient branching ratio. Further, as shown in the conventional example, the guided light l ₁ of the waveguide 321 is mainly propagated to the waveguide 322, for example. However, due to the natural spread of light, some of the light leaks into the waveguide, making it impossible to obtain a sufficient branching ratio on the light output side.

However, the present inventors have discovered that even in the structure according to the present invention, the guided light l ₁ does not leak into the waveguide 332 even when passing through an intersection, and continues straight as it is and is guided to the waveguide 322. Headline: Invented a new light switch.

As a result of a detailed study of the structure according to the present invention, it was found that there is an optimum range for the waveguide width. That is, a waveguide width of 5 to 30 μm is optimal. 5μm
In the following, the guided light had a large natural spread within the cross-path, and it was not possible to obtain a good branching ratio.
Moreover, if it is 30 μm or more, the cross-path size becomes large, making it difficult to downsize and not suitable for integration. Furthermore, the optimum crossing angle of the waveguides was within a range of 1 to 5 degrees.
At less than 1°, leakage is thought to have occurred due to the natural expansion of the guided light. If it is 5° or more, the branching ratio is good and 20 dB or more can be easily obtained without any modification to the crossroad shape, and the present invention has no meaning. Furthermore, in this case, when an optical switch was created with the above configuration with the cross-path dimension L ₁ of 3 mm or less, a branching ratio of 15 dB or more could be obtained simply by processing the waveguide width into a hyperbolic shape. Therefore, in an optical switch having this type of structure, it is possible to form an element that is smaller in size with more dimensional tolerance than conventional ones, has excellent branching ratio characteristics, and therefore has a good extinction ratio.

The details of the operating principle of the invention are not clear. Estimating from the above results, when the guided light is propagated through the intersection, the guided light spreads and propagates quasi-statically in accordance with the width of the waveguide because the outer periphery of the intersection is configured in a hyperbolic shape. Therefore, it is assumed that the propagation mode is preserved. Furthermore, the guided light propagated to the intersection has a narrow waveguide width of 10 to 40 μm at the center of the intersection, so the natural spread of the light is small, and therefore it is considered that the waveguide is guided with little leakage. Next, on the optical output side, the waveguide width changes quasi-statically to become narrower, similar to the propagation on the input side, so it is thought that the propagation mode is preserved. Therefore, it is presumed that a good branching ratio was obtained, and therefore a good extinction ratio was obtained in both of the waveguides on the optical output side.

Note that the distance required to sufficiently widen the waveguide width toward the intersection and to smoothly connect the outer circumferential lines of the input side and the output side is the conventional example shown in Fig. 2, depending on the nature of the hyperbola. Since it can be shorter than the case of a parabola, it is possible to miniaturize the element.

Hereinafter, specific examples will be explained so that the content of the present invention can be better understood.

Example 1 An example of the present invention will be explained in detail with reference to FIG. For example, the surface 31 of the substrate is α-Al ₂ O ₃ ,
PLZT is known as a material with large electro-optic effect.
(28/0/100) When a thin film is deposited using, for example, sputtering, magnetron sputtering, or ion beam sputtering at a substrate temperature of 550 to 650°C, a (111) plane epitaxial single crystal film is formed and light propagation loss is reduced. 3dB/
You can get one in cm. For example, the thickness of the formed film
The structure shown in FIG. 3 is formed on a 0.3 μm PLZT thin film using photolithography technology used in normal semiconductor processes. For example, an AZ with a negative pattern formed using the lift method of photolithography technology.
A load device type optical waveguide can be formed by depositing a Ta ₂ O ₅ film with a thickness of 0.2 μm on the resist using, for example, magnetron sputtering and removing the AZ resist with acetone. In this structure, the light is Ta ₂ O ₅
It is trapped under the membrane and propagates. The structure near the intersection is, for example, as shown in Figure 3, when the line width W ₁ of the optical waveguide is 4 μm and the intersection angle θ ₁ = 2°, the width W ₂ at the center of the intersection is 40 μm. Length near the part L ₁
The line width is gradually widened within the length of 2 mm, and the line width is gradually narrowed from the center of the intersection, and the connection is made smoothly.

With the above configuration, it has been confirmed that, for example, the light propagating through the optical waveguide 321 can have a branching ratio of 16 dB.

Especially in such a structure, Ti-diffused Li-NbO ₃
Since the difference in refractive index between the optical waveguide and the peripheral portion is larger than that of the optical waveguide, the configuration shown in FIG. 2 requires considerable accuracy. However, the present inventors have confirmed that in the configuration of the present invention, such a need is small and can be formed with high reliability.

In this structure, if the surface of the substrate is at least one of MgO, spinel, and _SiTiO3 ,
If BaTiO ₃ , PbTiO ₃ , or PLZT-based compounds are formed by, for example, a sputtering method to form this configuration, a crossed waveguide with a good branching ratio can be formed.

A thickness of 0.1 μm and a gap of 2 to 6 μm are formed on this crossed waveguide.
If the control electrodes 351 and 352 are made of evaporated Al, for example, an optical switch can be formed, and the extinction ratio is 20 dB.
The optical switching operation was confirmed.

Example 2 In the optical switch of this structure, the surface 31 of the substrate
is LiTaO ₃ and 0.5 μm LiNbO ₃ is deposited using, for example, magnetron sputtering, the LiNbO ₃ layer is exposed to light 2.
It can be used as a waveguide, and when the _three LiNbO layers are etched using ion silling to create a difference in film thickness, light waves are confined in the thicker region, forming a so-called ridge-type waveguide. In this case, if the intersection of two intersecting ridge-type waveguides is configured according to the present invention, the branching ratio is 15 dB, and the extinction ratio of switching due to turning on and off of the electrodes is 15 dB.
I was able to get 18dB.

Furthermore, the structure of the present invention is such that the surface of the substrate is covered with BGO.
(Bi ₁₂ GeO ₂₀ ), and the optical waveguide is made of BTO
(Bi ₁₂ TiO ₂₀ ) or BSO (Bi ₁₂ SiO ₂₀ ) can also provide the same effect. Furthermore, the surface of the substrate is
Composed of Al ₂ O ₃ , the optical waveguide is made of ZnO, ZnS, CdS,
It may also be composed of ZnSe or ZnTe. Alternatively, the surface of the substrate may be made of semiconductor GaP and an optical waveguide may be formed.
The present inventors have confirmed that the same effect can be obtained when the structure is made of a compound such as GaAs.

In addition, the effect of the present invention is achieved by the structure of the present invention,
The optical waveguide may be made of any material that has a large electro-optic effect, and is not limited to the above-mentioned materials.

Effects of the Invention As described above, the present invention has a configuration in which the structural change at the intersection of an optical switch made of a material with a large electro-optic effect is made gentle, and propagating light is less likely to leak into other waveguides. Since it propagates, it has the effect of improving the branching ratio. Therefore, the optical switch with this configuration has a good extinction ratio during on-off.
Therefore, by using the optical switch of the present invention, it is possible to realize an optical switch that is small in size, has little leakage of propagating light, and has excellent switching characteristics. Therefore, it is possible to integrate optical
There is great potential for IC development, and the contribution it will make to optoelectronics will be significant.

[Brief explanation of drawings]

Fig. 1 is a plan view of the main part of a conventional total reflection type optical switch, Fig. 2 is a plan view of the main part of another conventional total reflection type optical switch, and Fig. 3 is an embodiment of the optical switch of the present invention. FIG. 31... Substrate surface, 32, 33... Optical waveguide,
321, 322, 331, 332... optical waveguide,
34... Intersection, 351, 352... Control electrode,
3211, 3221, 3311, 3321... optical waveguide.

Claims (1)

[Claims] 1. Providing waveguides that cross each other on the surface of the substrate,
A control electrode for selecting a light propagation path is provided on the surface of the intersection, and the line width of the waveguide in the vicinity of the intersection increases toward the center of the intersection, and the connection is made smoothly. The line width in the constant width part other than 5 to 30 μm,
An optical switch characterized in that the outer periphery of the waveguide near the intersection has a hyperbolic shape, and the intersection angle is 1 to 5 degrees.