JPH049928A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To allow an edge to a high electric field part and to increase superposition between the formed part and input light by arranging 2nd clad part on a prescribed position adjacent to 1st clad part and having electric resistance different from that of the 1st clad part. CONSTITUTION:The optical switch is obtained by adjacently forming the 1st clad part 51 having low electric resistance and the 2nd clad part 52 having electric resistance higher than that of the 1st clad part 51 on the surface of a base 50 forming an electrode 50a on its bottom. An optical wave guide layer 53 is formed on the whole surface of both the clad parts 51, 52 and clad layers 54a, 54b, clad layers 55a, 55b and electrodes 56a, 56b are successively formed on the layer 53 with a prescribed interval. When voltage is impressed to the electrode 56a an electric field E is concentrated into the edge part 51a of the clad layer 51 and a high electric field part is generated. Consequently, superposition between the high electric field part and input light is increased and operation voltage necessary for switching can be reduced.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a waveguide type optical switch used in optical integrated circuits and the like, which performs switching control on light propagating in a waveguide, particularly an electric field edge switch. This invention relates to a waveguide type optical switch that enables reduction of operating voltage due to its effects.

(Prior Art) Conventionally, as a technology in this type of field, there is a technique called Guid-Wav Optoelectronics (Guid-Wav Optoelectronics).
e 0ptoelectronics>(1988-1
>Springer Perleg Co., Ltd., P, 376-377.

FIG. 2 is a cross-sectional perspective view showing an example of the configuration of a conventional waveguide type optical switch described in the above-mentioned document.

This optical switch has an electrode 10a formed on the bottom surface and an n+G
It has a substrate 10 made of aAs, and on the substrate 10,
A lower cladding layer 11 made of n+ AlGaAs and an optical waveguide layer 12 made of n-GaAs are sequentially formed. Furthermore, rib-shaped upper cladding layers 13a, 13b and cap layers 14a, 14b are formed in sequence on the optical waveguide layer 12 so as to oppose each other.

Electrodes 15a and 15b having the same width as the upper cladding layers 13a and 13b and the cap layers 14a and 14b are formed on the cap layers 14a and 14b, respectively.

Here, the upper cladding layers 13a and 13b are made of p+AlGa
As, and the cap layers 14a and 14b are p+ GaAs.
Each is composed of In addition, the upper cladding layer 13
The optical waveguide layers 12 directly below a and 13b form optical waveguide sections 12a and 12b that propagate input light, and these optical waveguide sections 12a,
12b, upper cladding layers 13a and 13b, and cap layer 14a14b constitute a waveguide.

In the optical switch configured as described above, for example,
It is assumed that light is input from the input port of the optical waveguide section 12a. At this time, electrode 15a, electrode 10a, and electrode 15
If no voltage is applied between the electrode 10a and the electrode 10a, the incident light is transferred to the adjacent optical waveguide 12b, and output light is output from the output port of the optical waveguide 12b.

On the other hand, when a predetermined voltage is applied between the electrode 15a and the electrode 10a, for example, the refractive index of the optical waveguide 12a changes. As a result, the similarity between the optical waveguide section 12a and the optical waveguide section 12b is lost, the light travels straight through the optical waveguide section 12a, and output light is obtained from the output port of the optical waveguide section 12a.

In this way, switching for light can be performed.

(Problem to be Solved by the Invention) However, in the waveguide optical switch having the above configuration, the intensity of the generated electric field is almost uniform with respect to the optical waveguides 12a and 12b, and there are few high electric field portions. , the overlap between the input light and the high electric field region was small. For this reason, the operating voltage required for switching could not be lowered satisfactorily.

Further, the generated electric field has only a component perpendicular to the surface of the substrate 10, and the direction of this electric field cannot be changed to a direction other than the perpendicular direction. As a result, it has been reported that the input polarized light is limited in order to perform normal switching operations.

The present invention provides a waveguide type optical switch that solves the problems of the prior art in that the operating voltage cannot be lowered and that the input polarized light is limited.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a waveguide in which a cladding layer is formed on a substrate, and an optical waveguide layer for input light propagation is further formed on the cladding layer. In the waveguide optical switch that controls input light propagating through the waveguide by an electric field, the cladding layer includes a first cladding portion having a predetermined electrical resistance; The second cladding portion is formed adjacent to the waveguide at a position corresponding to the waveguide, and has a second cladding portion having an electrical resistance different from the aforementioned electrical resistance.

Further, the position where the first and second cladding parts are adjacent to each other may be a position corresponding to approximately the center of the waveguide.

(Function) The present invention has a waveguide optical switch configured as described above, so that when the first or second crat part has a low resistance, the electric field is concentrated on the edge part due to the edge effect of the electric field. to generate a high electric field area.

Thereby, the direction of the electric field can be changed to an oblique direction, etc., and the input light propagates close to the high electric field portion, so the superposition of the high electric field portion and the input light increases, and the operating voltage is reduced.

Therefore, the above problem can be solved.

(Example) FIG. 1 is a cross-sectional perspective view of a waveguide type optical switch showing an example of the present invention.

This optical switch has a substrate 50 made of a compound semiconductor InP (n+ GaAs) with an electrode 50a formed on the bottom surface. On the surface of this substrate 50, there is a first cladding part 51 made of InP (n+ AIGaAs) having a low electrical resistance, and a first cladding part 51 made of InP (n+ AIGaAs) having a higher electrical resistance than the first cladding part 51. A second cladding portion 52 is formed. Further, a waveguide layer 53 made of InGaAsP (n-GaAs) is formed on the surfaces of the first cladding part 51 and the second cladding part 52, and a waveguide layer 53 made of InGaAsP (n-GaAs) is formed on the optical waveguide layer 53 at regular intervals. InP (GaA) is separated and opposed to each other.
The electrode 5 includes rib-shaped cladding layers 54a, 55b made of IAs>, rib-shaped cladding layers 55a, 55b made of InP (p+ GaAIAs), and a cap layer.
6a and 56b are formed in sequence.

Here, the optical waveguide layer 53 directly under the cladding layers 54a and 54b
Optical waveguide sections 53a, 53 that propagate polarized light whose input light is
b, and these optical waveguide parts 53a.

53b, cladding layers 54a, 54b and cladding layer 54
a and 55b constitute waveguides 60a and 60b, respectively.

3 is an explanatory diagram of the operation of FIG. 1, and FIG. 4 is a diagram showing the edge effect of an electric field.The operation of FIG. 1 will be explained with reference to these FIGS. 3 and 4.

As shown in FIG. 3, when a voltage is applied to the electrode 56a, the electric field E is concentrated at the upper right edge portion 51a of the first cladding portion 51 due to the edge effect of the electric field, and a high electric field portion is created at the edge portion 51a. generate. In numerical calculation using Laplace's equation, the electric field strength at this edge portion 51a is more than twice that at other portions. An example of calculating this electric field strength is shown in FIG.

In FIG. 4, the width of the first cladding part 51 is 2 μm,
The distance between the cladding layers 55a, 55b and the first cladding portion 51 is 2 μm, and the numerical value representing the electric field strength indicates the relative strength.

As is clear from this figure, the electric field strength at a location 1 μm away from the first cladding portion 51 is 0.25, but the closer it gets to the edge portion 51a, the more the electric field strength increases by 0.5.0.7.
It becomes stronger as 5.1.0.1.5. Furthermore, it is understood that the edge effect is large even when the width of the first cladding part 51 is as narrow as 2 μm. In this manner, due to the edge effect of the electric field, an electric field E is generated which has a diagonal component in addition to a component perpendicular to the substrate 50.

When no voltage is applied to the electrode 56a and no electric field E is generated, polarized light P having an optical axis perpendicular to the substrate 50 is generated.
Alternatively, when polarized light Q having a horizontal optical axis is input from the input port of the optical waveguide 53a, the polarized light P'i or polarized light Q is transferred to the adjacent optical waveguide 53b and output from the output port. .

With a voltage applied to the substrate 50a and an electric field E having an oblique component as described above generated, polarized light P having an optical axis perpendicular to the substrate 50 is input to the optical waveguide 53a. When the polarized light P passes through, an electro-optic effect is generated on the polarized light P, and the polarized light P propagates through the same optical waveguide 53a and is output from the output port of the optical waveguide 53a.

Furthermore, even when polarized light Q having a horizontal optical axis is input to the optical waveguide 53a while the electric field E is generated,
Similarly, it is output from the output port of the optical waveguide section 53a.

This embodiment has the following advantages.

(1) Since the edge portion 51a is located close to the optical waveguide portion 53a, the overlap between the high electric field portion and the input light due to the edge effect of the electric field is increased, and the operating voltage is halved compared to the conventional one. reduced to a certain extent.

(2) The electric field E has an oblique component in addition to a vertical component depending on the location. Since the refractive index changes due to the electro-optic effect for each polarized light in the vertical or horizontal direction, a switching operation that does not depend on the polarization direction is possible.

FIG. 5 is a cross-sectional perspective view of a waveguide type optical switch showing a second embodiment of the present invention, in which elements common to those in FIG. 1 are given the same reference numerals.

In this optical switch, the first cladding part 51 in FIG. 1 is changed to a second cladding part 52-1 which is a high resistance part, and the second cladding part 52 is connected to a first cladding part 51-1 which is a low resistance part. The configuration has been replaced with each other.

Even with such a configuration, as shown in FIG. 6, the electric field E is generated so as to be concentrated on the edge portions 51 to 1a due to the edge effect of the electric field, producing the same effect as in the first embodiment. .

FIG. 7 is a cross-sectional perspective view of a waveguide type optical switch showing a third embodiment of the present invention, and common elements with those in FIG. 1 are given the same reference numerals.

This optical switch corresponds to the cladding layers 54a and 5 in FIG.
As shown in FIG. 7, 1/2 of the forming portions of the cladding layers 55a and 55b formed on the cladding layers 55a and 55b formed on the cladding layers 54b and 4b are removed, and cladding layers 54a and 54a are formed on the removed portions of the cladding layers 55a and 55b.
54b, and the electric field E is generated so as to be concentrated at the edge portion 51a due to the edge effect of the electric field, producing the same effect as the first and second embodiments.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. For example, there are the following variations.

(B) In the above embodiment, the first cladding part 51 is a low-resistance rad layer, and the second cladding part 52 is a high-resistance rad layer. The second cladding portion 52 may be a low-resistance rad layer.

(b) In the above embodiment, the adjacent positions of the first cladding part 51 and the second cladding part 52 are
Although the position corresponds to approximately the center of 3b, the optical waveguide section 53
If the position corresponds to a, 53b, the optical waveguide 53
It is not necessary to limit it to approximately the center of a and 53b.

(Effects of the Invention) As described in detail above, according to the present invention, a cladding layer having a high electrical resistance portion and a low electrical resistance portion is provided on a substrate, and the high electrical resistance portion and the low electrical resistance portion are mutually connected to each other. Since the adjacent position corresponds to the waveguide formed on the cladding layer, it is possible to increase the overlap between the high electric field part and the input light, reducing the operating voltage required for switching. can do.

Furthermore, since electric fields can be generated in various directions depending on the design, switching operations that do not depend on polarization can be achieved by selecting the crystal axis.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional perspective view of a waveguide type optical switch according to an embodiment of the present invention, FIG. 2 is a cross-sectional perspective view of a conventional waveguide type optical switch, FIG. 3 is an explanatory diagram of the operation of FIG. 5 is a cross-sectional perspective view of a waveguide optical switch according to the second embodiment of the present invention, FIG. 6 is an explanatory diagram of the operation of FIG. 5, and FIG. 7 is a diagram showing the edge effect of an electric field. FIG. 7 is a cross-sectional perspective view of a waveguide optical switch according to a third embodiment of the invention. 50... Substrate, 51.51-1... First cladding part, 52.52-1... Second cladding part, 53... Optical waveguide layer, 53a, 53b
...... Optical waveguide section, 54a, 54b, 55a, 5
'5b-----On the cladding layer b... Waveguide, E... Electric field. 50, base bottle 0b 60° Fig. 1 Supporting example of fang 1 of the present invention +5b 15°

Claims (1)

[Claims] 1. A waveguide is provided in which a cladding layer is formed on a substrate, and an optical waveguide layer for propagating input light is formed on the cladding layer, and the input light propagating through the waveguide is converted into an electric field. In the waveguide optical switch, the cladding layer includes a first cladding portion having a predetermined electrical resistance;
A waveguide optical switch comprising: a second cladding portion formed adjacent to the cladding portion at a position corresponding to the waveguide and having an electrical resistance different from the electrical resistance. 2. The waveguide optical switch according to claim 1, wherein a position where the first and second cladding parts are adjacent to each other corresponds to approximately the center of the waveguide.