JPS6022120A - Optical switch - Google Patents

Abstract

PURPOSE:To reduce the leak of light to be transmitted and to improve the branching ratio by gently changing the structure of the crossing section of an optical switch made of a material having a significant electro-optical effect. CONSTITUTION:An epitaxial single crystal film grown on the <111> face is formed on the alpha-Al2O3 surface 31 of a substrate as a thin PLZT film having a significant electro-optical effect to regulate the optical transmission loss to 3dB/cm. A negative pattern of an AZ resist is formed on the PLZT film by a lift process, a Ta2O5 film is vapor-deposited on the resist, and the resist is removed with acetone to manufacture load device type optical waveguides. Light is kept under the Ta2O5 film and transmitted. In case of 4mum width W1 of the optical waveguide 32 and theta1 angle of crossing, the width W2 at the center of the crossing section is regulated to 40mum, it is gradually increased within the range of 2mm. length L1, and a smoothly connected structure is provided. Light is transmitted through the waveguide 321 in 16dB branching ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 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 branch waveguide. Hereinafter, the configuration of an optical branching waveguide used in a total reflection type switch and the like and its problems will be explained with reference to the drawings. FIG. 1 shows a total internal reflection type optical switch 1o constructed on a substrate having an electro-optic effect. In the 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 1i15.16, the refractive index of the optical waveguide portion below the control section 17 is reduced due to the electro-optic effect. Therefore, the guided light incident from electrode 11 is transmitted to electrode 15.
When a voltage is applied to 16, the total reflection condition is satisfied at the control section 17, and the signal propagates to 14. In addition,
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 similarly switched to the waveguides 13 and 14.

Such conventional optical switches have the following drawbacks or problems. That is, since the refractive index change due to the electro-optic effect is small, the intersection angle between the waveguides 11 and 12 is small, and the guided light that enters the waveguide 11 and propagates to the waveguide 13 can also propagate to the waveguide 14. Yes, 10
(It was very difficult to obtain an extinction ratio of iB or higher.

For this reason, it is difficult to obtain sufficient switching characteristics, which poses a practical problem.

Further, in order to improve this point, the configuration shown in FIG. 2 is used. In this structure, parabolic waveguides 111 and 121°141.1151 are provided in which the line width of the waveguide is increased in a parabolic manner near the intersection and connected. In this configuration, the amount of mode conversion is theoretically small; for example, in the TEoo mode, the light propagated from 11 travels straight in the TEoo mode, and propagates from 161 to 13 without leaking into the waveguide 141. ing.

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, W2=(2αλ./nb)Z+W0' It is.

Here, λ0: wavelength of light, nb□: bulk refractive index of optical waveguide, z: distance from constant width waveguide (see Figure 2), W
: Width of parabolic waveguide, Wo: Width of constant width waveguide, α: 1
A small positive real number.

Therefore, in order to shorten the length of the parabolic waveguide, α
:1, the length of the parabolic waveguide will be 2 mm or more, and the entire device will be about 5 mm.

Therefore, in order to provide a margin for the dimensional tolerance of the element,
When α=0.6, the element size becomes 10Ill#1 or more, which is not suitable for integration. Therefore, in order to set α:1,
It is necessary to configure the waveguide width with high precision.

If α>1, the connection between the parabolic waveguide and the constant-width waveguide is not coupled smoothly, so propagation mode conversion occurs, and for example, part of the TKoo mode light becomes TE0
When 1-mode light propagates from the waveguide 11, the rate of leakage to the waveguide 14 is higher than that of TEoo, which reduces the proportionality of this optical switch. It was difficult to increase the value to 10 dB or more.

The inventors of the present invention did not limit themselves to devising optical branching waveguides, but discovered a structure that could significantly improve the branching characteristics and that could be easily formed from one position to another, thereby realizing an optical switch with excellent switching characteristics. I found it.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an optical switch with good branching characteristics that eliminates the drawbacks or 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 into a polygonal shape.

Description of examples The present invention will be explained below with reference to 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 is shown.

Optical waveguides 32 that intersect each other are formed on the surface 31 of the substrate.
1 and 322, 331 and 332, and a control electrode 3 provided on the surface of the intersection 34 for selecting a light propagation path.
61 and 362, and the waveguides 3211, 3221, .
The line width of 3311 and 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 has a hyperbolic shape.

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.

Furthermore, as shown in the conventional example, the guided light 11 of the waveguide 321 is not connected like a parabolic outer circumferential line determined from the relationship between the film thickness and the waveguide width, so the propagation mode is It was believed that many higher-order modes occur that are not preserved and degrade the branching ratio.

However, the inventors of the present invention have discovered that even in the structure according to the present invention, the guided light 11 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. , 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.

When the diameter is less than 5 μm, the guided light naturally spreads significantly within the cross-path, making it impossible 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. Moreover, the optimum crossing angle of the waveguides was within a range of 1 to 5 degrees.

If the angle is less than 1°, it is thought that leakage occurs due to the natural expansion of the guided light. If it is 5 degrees or more, the branching ratio is good and 2 odB or more can be easily obtained without any modification to the crossroad shape, and the present invention has no meaning. Furthermore, in this case, the intersection dimension L1
If the optical switch is made with the above configuration and the waveguide width is 311D11 or less, the width of the waveguide can be reduced to 15 d by simply machining it into a hyperbolic shape.
It was possible to obtain a branching ratio of B or higher. Therefore, in the optical switch having this type of structure, it is possible to form an element that is smaller in size with more margin in dimensional tolerance than the conventional one, has excellent branching ratio characteristics, and therefore has a good extinction ratio.

The details of the operating principle of the present invention are not clear, but from the above results, the lower-order mode waveguide light is guided in the Maruna mode waveguide to the intersection, but since the outer circumferential line of the intersection is hyperbolic, the guided light transforms quasi-statically into the same low-order motive waveguide light corresponding to the expansion of the waveguide. In addition, in this case, since the waveguide width at the center of the intersection is about 10 to 40 μm, the natural width of the light wave is small, so it is thought that the waveguide can be guided with less leakage. Furthermore, it is considered that a good branching ratio was obtained because the guided light propagated to the waveguide while becoming narrower in a quasi-static manner, similar to the introduction of the light wave into the center of the intersection.

The content of the present invention will be explained below with reference to specific embodiments for better understanding.

(Example 1) An example of the present invention will be specifically described with reference to FIG. For example, the surface 31 of the substrate is made of α-mu1205, and PLZT (2810/1
00) Thin film, e.g. sputtering, magnetron sputtering, ion beam sputtering, substrate temperature 550-660°C
When vapor-deposited, a (111) plane epitaxial single crystal film is formed, and a light propagation loss of 36B/1M is obtained. For example, the structure shown in FIG. 3 is formed on the formed PLZT thin film with a thickness of 0.3 μm using a photolithography technique used in a normal semiconductor process. For example, a Ta205 film with a thickness of 0.2 μm is deposited by magnetron sputtering on a negative patterned M2 resist by using the atto method of the follitolithography technique, and the M205 film is removed by acetone using a loading device. type optical waveguide can be formed. In this structure, light is confined and propagated under the 'I'a20s film.

The structure near the intersection is, for example, as shown in FIG. 3, when the line width W1 of the optical waveguide is 4 μm and the intersection angle θ1, the convergence W2 at the center of the intersection is 40 μm, and the length Ll near the intersection is The line width is gradually widened between the length 211M, 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 1e aB.

In particular, in such a structure, the difference in refractive index between the optical waveguide and the peripheral portion is larger than that of the τi-diffusion type Li--NbO5 optical waveguide, so 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, the surface of the substrate is MgO and spinel.

If it is at least one type of SiTiO3, BaTi
Os.

If a PbTi0g, PLZT-based compound is formed by, for example, a sputtering method and this configuration is formed, a crossed waveguide with a good branching ratio can be formed.

An optical switch can be formed by forming control electrodes 361 and 352 with a thickness of 0.1 μm and a gap of 2 to 6 μm using, for example, vapor deposition on this crossed waveguide, and an optical switching operation with an extinction ratio of 20 dB was confirmed.

(Example 2) In the optical switch of this structure, the surface 31 of the substrate is LiT.
If LiNbO5 with a thickness of 0.574771 is deposited using magnetron sputtering, the LiNb0s layer can be used as an optical waveguide, and if the LiNbO5 layer is etched with ion spooling to create a difference in film thickness, the film can be formed. Light waves are confined in the thick region, forming a so-called ridge waveguide. In this case, if the intersection of the two intersecting ridge-type waveguides is configured according to the present invention, a branching ratio of 15 dB can provide an extinction ratio of 18 dB for switching by turning the electrodes on and off. .

Moreover, the structure of the present invention is such that the surface of the substrate is made of BGO (Bi+2G
e02o) Configure the optical waveguide as BTO (B1+2T
iO20) Alui is B SO (Bi12SiO2o)
The same effect can be obtained with Te. Furthermore, the surface of the substrate is α
1205, and the optical waveguide is made of ZnO, ZnS.
.

It may also be composed of CdS.Zn5e or ZnTe. Alternatively, the present inventors have confirmed that the same effect can be obtained when the surface of the substrate is made of semiconductor GaP and the optical waveguide is made of a compound such as GaAs.

In addition, the effect of the present invention is strong even if the optical waveguide in the structure of the present invention is limited to the above-mentioned materials as long as the optical waveguide has a large electro-optic effect.

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 slowed down, and propagating light leaks into other waveguides. This has the effect of improving the branching ratio because it propagates with less interference. 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 propagated light, and has excellent switching characteristics.

Therefore, it is possible to achieve integration, and there is great potential for optical ICs, making a large contribution to optical electronics.

[Brief explanation of drawings]

Figure 1 is a plan view of the main parts of a conventional total reflection type optical switch, Figure 2
The figure is a plan view of the main parts of another conventional total internal reflection type optical switch.
The figure is a schematic plan view of an embodiment of the optical switch of the present invention. 31... Substrate surface, 32.33... Optical waveguide, 321.322, 331.332...
...Optical waveguide, 34...Intersection, 351.35
2...Control electrode, 32.11°3221.33
11.3321--...Leading wavepath. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 16 Figure 2 Figure 3

Claims (1)

[Claims] Waveguides that intersect each other are provided on the surface of the substrate, a control electrode for selecting an optical propagation path is provided on the surface of the intersection, and the line width of the waveguide near the intersection of the waveguides is directed toward the center of the intersection. An optical switch characterized in that the outer circumferential line of the waveguide near the intersection has a hyperbolic shape.