JPH06313905A - Optical switch - Google Patents

Abstract

PURPOSE:To respectively provide the 1X2 optical switch capable of making crosstalk characteristics better than heretofore by using Y branch waveguide structures and the 2X2 optical switch capable of making crosstalk characteristics better than heretofore by using X branch waveguide structures. CONSTITUTION:The 1X2 optical switch is produced by connecting the one branch waveguide 33a of the second Y branch waveguide structure 33 to the one branch waveguide 31a of the first Y branch waveguide structure 31 and connecting the one branch waveguide 35a of the third Y branch waveguide structure 35 to the other branch waveguide 31b of the first Y branch waveguide structure 31. The 2X2 optical switch is produced by connecting the respective one branch waveguides of the first to fourth branch waveguides structure to constitute the X branch waveguide and connecting the respective other branch waveguides of the first and second Y branch waveguide structures and connecting the respective other branch waveguides of the third and fourth Y branch waveguide structures.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch for electrically controlling the traveling direction of light.

[0002]

2. Description of the Related Art As the most basic optical switch, 1
There are 2 × 2 type optical switches and 2 × 2 type optical switches.
As a conventional example of a 1 × 2 type optical switch, for example, reference I (Applied Physics Letters (Applie
d Physics Letters), Vol. 29, p. 790 (1
976) there was an optical switch using a Y-branch waveguide structure. This is as shown in FIG.
The waveguide 11 is formed on the substrate (not shown) exhibiting the electro-optic effect.
And two branch waveguides 13 and 15 separated from it.
And the electrodes 17a and 17b for controlling the refractive index. This 1 × 2 optical switch is turned on and off such that the light entering the waveguide 11 reaches either the one branch waveguide 13 or the other branch waveguide 15 depending on how the voltage is applied to the electrodes. Type behaves,
It is widely used because it is an easy-to-use optical switch. In this optical switch, when the input light is operated so as to reach one of the branch waveguides, the leakage characteristic of the input light to the other waveguide, that is, the so-called crosstalk (extinction ratio) characteristic is shown in FIG.
It was as shown in (B). In FIG. 6 (B), K ₀ L means that the coupling coefficient at the branch root of the two branch waveguides 13 and 15 is K _0, and each branch waveguide 13 and
This is a parameter given when the length of 15 is L.

On the other hand, as a conventional example of a 2 × 2 type optical switch, for example, reference II (Applied Physics Letters, Vol. 51, p.
1230 (1987) as disclosed in X-Branch (Asymmetric X
There was an optical switch using a (branch) waveguide structure. As shown in FIG. 7A, this is because two input waveguides 21a and 21b are provided on a substrate (not shown) that exhibits an electro-optical effect.
And two output waveguides 23a and 23b so that an X-shaped waveguide is constituted by them, and the refractive index control electrodes 25a and 25a on the output waveguides 23a and 23b, respectively.
25b, respectively. This 2x2
In the optical switch of No. 2, the light input from the input waveguide 23a or 23b is applied to the output waveguide 2 depending on how the voltage is applied to the electrodes.
2 inputs 2 such as reaching either 3a or 23b.
It was possible to perform selective switching depending on the combination of outputs. The crosstalk characteristics of this optical switch were as shown in FIG. 7 (B).

[0004]

However, the crosstalk characteristic of each of the above-mentioned conventional optical switches is about -35 dB at best for the 1 × 2 type, and 2 ×
In the case of the 2 type, it was about -27 dB, which was not sufficient.

The present invention has been made in view of the above points, and therefore an object of the present invention is a 1 × 2 optical switch using a Y-branch waveguide structure, which can improve the crosstalk characteristic as compared with the conventional case. The purpose of the present invention is to provide a 2 × 2 optical switch and a 2 × 2 optical switch that uses an X-branch waveguide structure and that can improve crosstalk characteristics compared to the conventional one.

[0006]

In order to achieve this object, a 1 × 2 optical switch according to the present invention comprises first, second and third Y-branch waveguide structures, and has the above-mentioned first structure. Y of 1
The one branch waveguide of the second Y-branch waveguide structure is connected to the one branch waveguide of the branch waveguide structure, and
The other branch waveguide of the Y-branch waveguide structure is connected to one branch waveguide of the above-mentioned third Y-branch waveguide structure.

The 2 × 2 optical switch of the present invention is
A first, a second, a third, and a fourth Y-branch waveguide structure, and an X-branch waveguide structure formed by connecting one of the branch waveguides of each of the first to fourth Y-branch waveguide structures And connecting the other branch waveguides of the first and second Y-branch waveguide structures to each other, and the other branch waveguides of the third and fourth Y-branch waveguide structures, respectively. It is characterized in that they are configured by connecting each other.

[0008]

According to the configuration of the 1 × 2 optical switch and the 2 × 2 optical switch of the present invention, in the middle of the path along which light propagates,
In addition to the original Y-branching portion, another Y-branching portion (hereinafter referred to as “Y-branching portion”) arranged so that the branching waveguides provided in the Y-branching portion merge in the direction along the light propagation direction. For convenience of explanation, it is referred to as a "reverse Y branch".)
An optical switch having a structure having is obtained. Therefore, in these optical switches, the leakage light generated in the branch waveguide which is not desired to be selected out of the two branch waveguides when switching is performed in the original Y branch portion has the opposite direction to the above in the middle of the propagation path. Since most of the Y-branch is eliminated and sunk in the substrate, the crosstalk characteristic is improved accordingly.

[0009]

Embodiments of the optical switch of the present invention will be described below with reference to the drawings. However, the drawings used in the description merely schematically show the dimensions, shapes, and arrangement relationships of the respective constituents to the extent that the present invention can be understood. Further, in each drawing used for the description, the same constituent components are designated by the same reference numerals, and the duplicate description thereof will be omitted.

Description of Embodiment of 1.1 × 2 Optical Switch FIG. 1 is a plan view for explaining an embodiment of a 1 × 2 optical switch of the present invention. In particular, an example using a Z-cut LiNbO ₃ substrate (not shown) is shown.

The 1 × 2 optical switch of this embodiment comprises a first Y-branch waveguide structure 31, a second Y-branch waveguide structure 33 and a third Y-branch waveguide structure 35 on a substrate. And one branch waveguide 3 of the first Y branch waveguide structure 31.
One branch waveguide 33a of the second Y branch waveguide structure 33 is connected to 1a, and one branch of the third Y branch waveguide structure 35 is connected to the other branch waveguide 31b of the first Y branch waveguide structure 31. The branch waveguide 35a is connected. further,
On each branch waveguide of the first to third Y-branch waveguide structures 31 to 35, on the substrate portion beside the other branch waveguide 33b of the second Y-branch waveguide structure 33, and on the third Y-branch. Electrodes 37a, 37b, 37c, 37 for controlling the refractive index are formed on the substrate portion beside the other branching waveguide 35b of the branching waveguide structure 35.
d, 37e or 37f. In this 1 × 2 optical switch, the waveguide portions of the first to third Y-branch waveguide structures that are not branch waveguides are respectively input / output ports 39a.
~ 39c.

In this embodiment, in order to reduce the crosstalk at the part where the branch waveguides are connected to each other, the branch waveguides are constructed to have an appropriate curvature. Further, in order to improve the easiness of the electro-optical effect occurring in the other branching waveguides 33b and 35b of the second and third Y branching waveguide structures 33 and 35, these branching waveguides 33b and 3b are formed.
The length of 5b is made somewhat longer (as indicated by P in FIG. 1) than that of one of the branch waveguides 33a and 35a.

The 1 × 2 optical switch of this embodiment can be operated as follows. When a positive voltage is applied to the electrodes 37b, 37d, and 37f with the electrodes 37a, 37c, and 37e grounded, a light exchange can be performed between the input / output port 39a and the input / output port 39c. Further, when a negative voltage is applied to the electrodes 37b, 37d, and 37f with respect to the ground while the electrodes 37a, 37c, and 37e are grounded, optical exchange can be performed between the input / output port 39a and the input / output port 39b.

The crosstalk characteristic of the 1 × 2 optical switch of this embodiment is analyzed using a coupling equation. However, in this analysis, the coupling coefficient K ₀ at the root of each branching waveguide 31a, 31b of the first Y branching waveguide structure 31 and the portion where the distance between these branching waveguides is the largest (the first branch in FIG. 1). Two
And the ratio r between the coupling coefficient at the base around) the third Y-branch waveguide structure is 0.001, and 30 K ₀ L shown out with the K ₀ and the element length L (see FIG. 1) . The results of this analysis are shown in FIG. 2 (A) with ΔβL / π on the horizontal axis and crosstalk on the vertical axis. As is clear from FIG. 2A, in the 1 × 2 optical switch of this embodiment, Δ
When βL / π> 1.5, a crosstalk characteristic of −20 dB or less is obtained, and in the best case, the crosstalk is −4.
It can be seen that it can be set to 0 dB or less.

Description of Embodiment of 2.2 × 2 Optical Switch FIG. 3 is a plan view for explaining an embodiment of a 2 × 2 optical switch of the present invention. Also in this case, an example using a Z-cut LiNbO ₃ substrate (not shown) is shown as in the case of the above 1 × 2 substrate.

The 2 × 2 optical switch of this embodiment has a first Y-branch waveguide structure 41, a second Y-branch waveguide structure 43, a third Y-branch waveguide structure 45 and a third Y-branch waveguide structure 45 and a third Y-branch waveguide structure 45 on a substrate. 4 Y
Branch waveguide structure 47 and one branch waveguide 41 of each of the first to fourth Y branch waveguide structures 41 to 47
a, 43a, 45a and 47a are connected to form an X-branch (asymmetric X-branch in this example) waveguide structure 49,
Further, the other branch waveguides 41b and 43b of the first and second Y-branch waveguide structures are connected to each other, and the other branch waveguide 45 of each of the third and fourth Y-branch waveguide structures is connected.
b and 47b are connected to each other. Furthermore, the first
Further, the refractive index control electrode 51a or 51b is provided on the other branching waveguides 41b and 43b of the second Y branching waveguide structure and on the substrate portion beside it. Further, a refractive index control electrode 51c is provided on the one branch waveguide 41a to 47a of each of the first to fourth Y branch waveguide structures and on the substrate portion sandwiched by the one branch waveguide. Further, a refractive index control electrode 51d or 51c is provided on the other branching waveguide 45b, 47b of each of the third and fourth Y branching waveguide structures and on the substrate portion beside it. In this 2 × 2 optical switch, the waveguide portions of the first to fourth Y-branch waveguide structures that are not the branch waveguides become the input / output ports 53a to 53d, respectively.

In this embodiment, the Y-branch waveguide structures have the same branch angle. Further, in each Y-branch waveguide structure, the widths of the one and the other branch waveguides are the same. In addition, the first and fourth Y branch waveguide structures 41,
47 has the same size and shape, and the second and third
The Y-branch waveguide structures 43 and 45 are of the same size and shape. However, the width W ₁ of the branch waveguide of the first (fourth) Y-branch waveguide is different from the width W ₂ of the branch waveguide of the second (third) Y-branch waveguide. In this case, the widths of the two branched waveguides are different so that the relationship of W ₁ : W ₂ = 1.05: 0.95 is established.

The 2 × 2 optical switch of this embodiment can be operated as follows. When a positive voltage is applied to the electrodes 51b and 51d with respect to the ground while the electrodes 51a, 51c and 51e are grounded, a diagonal line between the input / output ports (53a in FIG. 3) of this optical switch is applied.
And 53d and between 53c and 53b). This state is schematically shown in FIG.
In FIG. 4A, + dn means that the refractive index of the corresponding portion of the substrate becomes larger than that before the voltage is applied due to the electro-optical effect due to the voltage application, and it is the same as -dn. It is shown (same in FIG. 4B below). Further, when a negative voltage is applied to the electrodes 51b and 51d with respect to the ground while the electrodes 51a, 51c and 51e are grounded, the input / output ports 53a and 53a.
Optical exchange can be performed between b and 53c and 53d. This state is schematically shown in FIG.

In the 2 × 2 optical switch of this embodiment, when the light is input to the input / output port 53a and the light is output from the input / output port 53c, the crosstalk characteristic at the input / output port 53b is calculated using a coupling equation. To analyze. However, the following conditions are set for this analysis.

(1). The propagation constant difference due to the difference between the width of the branch waveguide 43a and the width of the branch waveguide 47a in the X branch waveguide structure 49 is Δβ _0, and the angle formed by both branch waveguides 43a and 47a. Δβ given when θ (corresponding to the branching angle) and γ _{3 as} a parameter for the exudation of guided light
₀ / γ ₃ θ is set to 3.14.

(2). The coupling coefficient K ₀ at the root of the two branches constituted by the branch waveguide 43a and the branch waveguide 47a in the X branch waveguide structure 49 and the distance between these branch waveguides are widest. The ratio r with the coupling coefficient in the portion (around the root of the second and fourth Y-branch waveguide structures in FIG. 3) is 0.000.
3 and then, the 90 K ₀ L shown out with the K ₀ and the element length L (see FIG. 3).

The result of this analysis is shown in FIG.
βL / π was taken and the vertical axis represents crosstalk.
As is apparent from FIG. 2B, 2 × of this embodiment is used.
In the optical switch of No. 2, -2 at ΔβL / π> 3.6
It can be seen that the crosstalk characteristic of 0 dB or less is obtained, and in the best case, the crosstalk can be reduced to -40 dB or less.

Although the embodiments of the 1 × 2 optical switch and the 2 × 2 optical switch of the present invention have been described above, the present invention is not limited to the above embodiments.

For example, each of the above-described embodiments has been described by using the Z-cut LiNbO ₃ substrate as the substrate, but the type of substrate cutting and the type of substrate are not limited to this, and can be changed to any suitable one. The electrode shape and electrode arrangement in that case can be determined according to a known optical switch manufacturing method.

Further, in the above embodiment of the 1 × 2 optical switch, the branch waveguides are given a curvature, and some of the branch waveguides are made longer than others. Of course, this is just one example.

Further, in the embodiment of the 2 × 2 optical switch described above, all the branch waveguides of the portion forming the X branch are straight waveguides. The X-branch waveguide structure 149 may be configured by using a waveguide having a curvature as shown and combining these waveguides 141a to 147a having a curvature. First to fourth Y in this case
One of the branch waveguide structures 141, 143, 145, and 147, respectively, of the branch waveguides 141a, 143a, 145a
And 147a, and the degree of coupling of the branch waveguides 141a to 147a when forming the X-branch waveguide structure 149 is preferably optimized according to the design. In the case of the 2 × 2 optical switch using the branch waveguide having the curvature as described above, compared with the 2 × 2 optical switch described with reference to FIG.
The element length L can be shortened.

[0027]

As is apparent from the above description, according to each of the 1 × 2 optical switch and the 2 × 2 optical switch of the present invention, the original Y-branch waveguide structure is provided in the light propagation path. Separately, a reverse Y-branch portion is additionally provided, so that leakage light can be eliminated, so that the crosstalk characteristic is improved as compared with the conventional 1 × 2 optical switch having a Y-branch waveguide structure and 2 × 2 optical switch having an X-branch waveguide structure. Can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a 1 × 2 optical switch of the present invention.

FIG. 2 is a diagram showing crosstalk characteristics of the optical switch of each example, (A) of the 1 × 2 optical switch,
(B) is for a 2 × 2 optical switch.

FIG. 3 is a diagram showing an embodiment of a 2 × 2 optical switch of the present invention.

4A and 4B are diagrams for explaining the operation of the 2 × 2 optical switch of the embodiment.

FIG. 5 is a diagram for explaining another example of the 2 × 2 optical switch of the present invention.

6A and 6B are diagrams for explaining a conventional 1 × 2 optical switch.

7A and 7B are diagrams for explaining a conventional 2 × 2 optical switch.

[Explanation of symbols]

31: First Y-branch waveguide structure 31a: One branch waveguide of the first Y-branch waveguide structure 31b: The other branch waveguide of the first Y-branch waveguide structure 33: Second Y-branch guide Waveguide structure 33a: One branch waveguide of the second Y-branch waveguide structure 33b: The other branch waveguide of the second Y-branch waveguide structure 35: Third Y-branch waveguide structure 35a: Third Y-branch structure One branch waveguide 35b of the branch waveguide structure: The other branch waveguide of the third Y branch waveguide structure 37a to 37f: Refractive index control electrodes 39a to 39c: Input / output port 41: First Y branch conductor Waveguide structure 41a: One branch waveguide of the first Y-branch waveguide structure 41b: The other branch waveguide of the first Y-branch waveguide structure 43: Second Y-branch waveguide structure 43a: The second Y One branch waveguide 43b of the branch waveguide structure 43b: second Y branch waveguide 45: Third Y-branch waveguide structure 45a: Third Y-branch waveguide structure one branch waveguide 45b: Third Y-branch waveguide structure other branch waveguide 47: Fourth Y-branch waveguide structure 47a: One branch waveguide of the fourth Y-branch waveguide structure 47b: The other branch waveguide of the fourth Y-branch waveguide structure 49: X-branch (asymmetric X-branch) ) Waveguide structure 51a to 51e: Refractive index control electrodes 53a to 53d: Input / output ports 141 to 147: Y-branch waveguide structure of another example 149: X-branch waveguide structure composed of a branched waveguide having a curvature

Claims (2)

[Claims] 1. A first, a second and a third Y-branch waveguide structure, wherein one branch waveguide of the first Y-branch waveguide structure is provided with the second Y-branch waveguide structure. One branch waveguide is connected, and one branch waveguide of the third Y branch waveguide structure is connected to the other branch waveguide of the first Y branch waveguide structure. Characteristic 1x2 optical switch. 2. An X formed by connecting first, second, third and fourth Y-branch waveguide structures to one branch waveguide of each of the first to fourth Y-branch waveguide structures. A branch waveguide structure, and connects the other branch waveguides of the first and second Y branch waveguide structures to each other, and connects the other branch waveguides of the third and fourth Y branch waveguide structures to each other. A 2 × 2 optical switch, characterized in that branch waveguides are connected to each other.