JPH0254930B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a waveguide type optical switch that switches light by electrically controlling the traveling direction of light traveling through a waveguide.

[Conventional technology]

As a conventional optical switch of this kind, there is a waveguide type optical switch patent application No. 1986-11 which uses a balanced bridge type waveguide with an asymmetric branching structure. It has advantages such as being relatively gentle, making it easy to lower the driving voltage, and having a simple control method.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional waveguide type optical switch requires two parts: an asymmetrical branching section that separates optical modes, and an interfering section that creates a phase difference.In addition, the optical switch generally has a long element length. This reduces the voltage required for switching, but in the above-mentioned waveguide optical switch, only the length of the interferometer section is related to the voltage required for switching, so the ratio of the voltage required for switching to the element length decreases. It still has the problem of being large.

The present invention has been made to solve these problems, and has developed a waveguide-type optical switch that uses a waveguide with an asymmetric branch structure and is capable of switching light at low voltage while having a relatively short element length. The purpose is to achieve this goal.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention forms an asymmetrical branch with different widths between the input and output parts of a pair of waveguides, and arranges an electrode in the asymmetrical branch. It also has the function of an interference device.

[Effect]

According to the above-mentioned means, in addition to the original effect of the asymmetric branching part in the waveguide which separates the even mode and odd mode of the guided light, it also performs an interference effect by controlling the asymmetry with a voltage, so it is relatively effective. Switching can be performed by giving a phase difference to the guided light with a short element length and low voltage.

〔Example〕

Examples will be described below with reference to the drawings.

Although not shown in this embodiment, LiNb ₃ -Z is used as the substrate on which the waveguide is provided.

FIG. 1 is a plan view showing a first embodiment of a waveguide type optical switch according to the present invention. In the figure, 1 and 2 are a pair of waveguides formed in an asymmetric branch structure.

The waveguides 1 and 2 have input sections 1a and 2, respectively.
a, input-side asymmetric branch parts 1b, 2b connected to the input parts 1a, 2a and having mutually different widths, and output-side asymmetric branch parts 1c, 2c connected to the input-side asymmetric branch parts 1b, 2b and having mutually different widths. and an output section 1 connected to the output side asymmetric branch sections 1c and 2c.
d, 2d, where the input side asymmetric branch part 1b and the output side asymmetric branch part 1c of the waveguide 1 are formed to have the same width, and the input side asymmetric branch part 2b and the output side asymmetric branch part of the waveguide 2 are formed to have the same width. 2c is also formed to have the same width, and furthermore, 1b and 1c are formed to be wider than 2b and 2c.

3 is the input section 1a, 2a and the input side asymmetric branch section 1
b, contact part with 2b, 4 is output side asymmetric branch part 1
contact points between c and 2c and output parts 1d and 2d; 5 is an asymmetrical branching part 1b on the input side and an asymmetrical branching part 1 on the output side;
an electrode for asymmetry control provided on c, 6 an input side asymmetric branch part 2b and an output side asymmetric branch part 2;
This is an electrode for asymmetry control provided on c.

2A to 2D are explanatory diagrams showing the operation of the optical switch with the above-described configuration, in which 7a to 7d are electric field intensity distributions of input light, and 8a to 8d are electric field intensity distributions of even mode light at the contact portion 3 on the input side. , 9a to 9d are the electric field intensity distributions of odd mode light in the contact portion 3 as well.

10a to 10d are the electric field intensity distributions of light at the midpoint between the input-side asymmetric branch 1b and the output-side asymmetric branch 1c of the waveguide 1, and 11a to 11d
is the electric field intensity distribution of light at the midpoint between the input-side asymmetric branch section 2b and the output-side asymmetric branch section 2c of the waveguide 2.

12a to 12d are the electric field intensity distributions of even mode light at the contact portion 4 on the output side, 13a to 13d are the electric field intensity distributions of odd mode light at the contact portion 4, and 14a to 14d are the electric field intensity distributions of the output light. be.

Next, the operation will be explained with reference to FIGS. 2A to 2D.

() First, consider the state in which light travels in a straight line, the so-called Bar state.

In FIG. 2A, when light with an electric field intensity distribution 7a is incident on the input part 2a of the waveguide 2, this light propagates through the input part 2a and then becomes an even mode light with an electric field intensity distribution 8a at the contact part 3. Electric field strength distribution 9a
It is divided into odd mode light. After that, the even mode light becomes 1 due to the operation of the input side asymmetric branching parts 1b and 2b.
b, and the first-order mode light moves to 2b, becoming guided lights with electric field intensity distributions 10a and 11a, respectively. When these guided lights further propagate through the output-side asymmetric branches 1c and 2c, the By the operation of the output-side asymmetric branching parts 1c and 2c, the guided light 10a is converted back into even mode light with an electric field intensity distribution 12a, and the guided light 11a is converted back into odd mode light with an electric field intensity distribution 13a at the contact part 4. , as described later, the input side asymmetric branch part 1
b, the even mode light generated while propagating through the output side asymmetric branch 1c, and the input side asymmetric branch 2b.
The phase difference at the contact portion 4 between the odd mode light and the odd mode light generated while propagating through the output side asymmetric branch portion 2c can be adjusted by the voltage applied to the electrodes 5 and 6. Therefore, the voltage Va applied to the electrodes 5 and 6
If the phase difference between the even mode light of the electric field intensity distribution 12a and the odd mode light of the electric field intensity distribution 13a is adjusted to 2mπ (m: an integer), the guided light will be transmitted from the output section 2a to the electric field intensity distribution 14a. It is emitted as light.

On the other hand, as shown in FIG. 2B, when light with an electric field intensity distribution 7b is incident on the input part 1a of the waveguide 1, this light propagates through the input part 1a and then reaches the contact part 3 with an electric field intensity distribution 8b. The light is divided into even mode light with an electric field intensity distribution 9b and odd mode light with an electric field intensity distribution 9b. The phase difference between this even mode light and odd mode light is
Compared to the case in Figure 2A, it has changed by π,
By the operation of the input side asymmetric branching parts 1b and 2b, even mode light is transferred to the input side asymmetrical branching part 1b, and odd mode light is transferred to the input asymmetrical branching part 2b, and guided light with electric field intensity distributions 10b and 11b, respectively. Become. This guided light further propagates through the output side asymmetric branch parts 1c, 2c, and due to the characteristics of the output side asymmetric branch parts 1c, 2c, the guided light with the electric field intensity distribution 10b at the contact part 4 changes to the electric field intensity distribution 12
The guided light with the electric field intensity distribution 11b is converted back into the even mode of b and into the odd mode light with the electric field intensity distribution 13b. Here, when the same voltage Va as in the case of FIG. 2A is applied to the electrodes 5 and 6, the even mode light generated while propagating through the input side asymmetric branch part 1b and the output side asymmetric branch part 1c, Input side asymmetric branch part 2b and output side asymmetric branch part 2
The phase difference between the odd mode light and the odd mode light generated while propagating through the contact point 4 is the phase difference between the even mode light and the odd mode light at the contact point 3, that is, the phase difference before undergoing a phase change due to voltage. If the phase difference between both mode lights is the same as in Figure 2 A, then 2mπ
becomes. However, in the case of FIG. 2B, the phase difference between the even mode light of the electric field intensity distribution 8b and the first mode of the electric field intensity distribution 9b at the contact portion 3 is Δφ compared to the case of FIG. 2A. = π, the phase difference between the even mode light of the electric field intensity distribution 12b and the odd mode light of the electric field intensity distribution 13b at the contact portion 4 is 2mπ+Δφ=(2m
+1)π, and therefore the guided light is emitted from the output section 1d as light with an electric field intensity distribution 14b.

() Next, let us consider the cross state of light, the so-called cross state.

As shown in FIG. 2C, when light with an electric field intensity distribution 7c is incident on the input section 2a, this light propagates through the input section 2a and then transforms into even mode light with an electric field intensity distribution 8c at the contact section 3. Electric field strength distribution 9
It is divided into odd mode light of c. The phase difference between this even mode light and odd mode light is the same as in the case of FIG. 2A. Here, due to the operation of the input side asymmetric branching parts 1b and 2b, the even mode light moves to the input side asymmetrical branching part 1b, and the odd mode light moves to the input side asymmetrical branching part 2b, and the electric field intensity distribution 1
This becomes guided light of 0c and 11c. When this guided light further propagates through the output side asymmetric branch parts 1c, 2c, the electric field intensity distribution 10c occurs at the contact part 4 due to the characteristics of the output side asymmetric branch parts 1c, 2c.
The guided light is in the even mode of the electric field intensity distribution 12c,
Furthermore, since the guided light with the electric field intensity distribution 11c is converted back into odd mode light with the electric field intensity distribution 12c,
The odd mode light generated while propagating through the input side asymmetric branch 1b and the output side asymmetric branch 1c, and the odd mode light generated while propagating through the input side asymmetric branch 2b and the output side asymmetric branch 2c. The phase difference between the even mode light and the odd mode light at the contact part 4 is adjusted by adjusting the phase difference between them with the voltage Vc applied to the electrodes 5 and 6, and the phase difference between the even mode light and the odd mode light at the contact part 4 is (2m'+1)π (m: integer)
If this is done, the guided light is emitted from the output section 1d as light having an electric field intensity distribution 14c.

On the other hand, as shown in FIG. 2D, when light with an electric field intensity distribution 7d is incident on the input section 1a,
After propagating through the input section 1a, this light passes through the contact section 3.
The light is divided into even mode light and odd mode light. The phase difference between this even mode light and odd mode light is
The difference is π compared to the case shown in FIG. 2C.
Here, due to the operation of the input side asymmetric branching parts 1b and 2b, the even mode light goes to the input side asymmetrical branching part 4b,
In addition, the odd mode light moves to the input side asymmetric branch 1b, and the electric field intensity distributions 10d and 1
It becomes a 1d waveguide light. When this guided light further propagates through the output side asymmetric branching parts 1c and 2c, the guided light with the electric field intensity distribution 10d changes to the electric field intensity distribution 12d at the contact part 4 due to the operation of the output side asymmetrical branching parts 1c and 2c. Even mode light and guided light with electric field intensity distribution 11d have electric field intensity distribution 13.
d odd mode light. Here, when the same voltage Vc as in the case of FIG. 2C is applied to the electrodes 5 and 6, the input side asymmetric branch part 1b
The phase difference between the even mode light and the first mode light generated while propagating through the output side asymmetric branching section 1c is (2m'+1)π, which is the same as in the case of FIG. 2C. However, in the case of FIG. 2D, the phase difference between the even mode light and the odd mode light at the contact portion 3 is shifted by Δφ=π compared to the case of FIG. Even mode light with electric field intensity distribution 12d and electric field intensity distribution 13d in
The phase difference between the odd mode light and the odd mode light is (2m′+1)π
+Δφ=2m″π (m″: integer), and the guided light is output from the output section 2d as light with an electric field intensity distribution 14d.

Light switching is performed in the manner described above.

Next, even mode light propagates through the input asymmetric branch 1b and output asymmetric branch 1c of the waveguide 1, and odd mode light propagates through the input asymmetric branch 2b and output asymmetric branch 2c of the waveguide 2. The reason why a phase difference occurs between light and the mechanism for adjusting the phase difference will be explained with reference to FIG.

When the asymmetry of the asymmetric branch is small, for example, as shown by the solid line in Figure 3, when the waveguide spacing is small, the difference in propagation constant between even and odd modes is large; As the distance increases, the propagation constant becomes almost the same size.

However, when the asymmetry of the bifurcation is large,
As shown by the dotted line in Figure 3, as the waveguide spacing increases, the difference from the case with small asymmetry increases, and the difference in propagation constant between even and odd modes increases even when the waveguides are separated. It becomes like it occurs.

In this way, the fact that there is a difference in the propagation constant between the two modes of light means that when light propagates over a certain distance,
This means that a phase difference occurs that is proportional to the product of the propagation distance and the difference in the propagation constant.

By the way, a difference in waveguide width has the same effect as a difference in equivalent refractive index, and the effective refractive index can also be changed by the refractive index of the waveguide.

Therefore, even if the refractive index of each asymmetric branch of the waveguide is changed, the same characteristics as shown in FIG.
When the waveguides are separated from each other, it is possible to adjust the propagation constant difference by controlling the refractive index of the waveguides. Therefore, if the electro-optic effect is used, it is possible to electrically further reduce the propagation constant difference. can control the phase difference.

In FIG. 3, the magnitude of change in the propagation constant when the electrode spacing is 10 μm and the applied voltage is 5 V is shown by the vertical arrow A. The propagation constant is changed by this amount with respect to the structurally set propagation constant, that is, the line shown in FIG.

The characteristics of the asymmetric branch are as follows: Δβ/γθ>const (1) Δβ: Difference in propagation constant between 1b and 1c of waveguide 1 and 2b and 2c of waveguide 2 θ: 1b and 1c of waveguide 1 1c and waveguide 2
Angle formed by b and 2c γ: A parameter representing the seepage of light from 1b, 1c and 2b, 2c of the waveguides 1 and 2 const: Usually selected to be 1 or more.

However, taking into account changes due to voltage, the above
A sufficiently large asymmetry and a sufficiently small angle are required so that equation (1) holds true.

FIG. 4 is a plan view showing a second embodiment of the present invention, in which electrodes 5a and 5b divided into two are provided on the input side asymmetric branch part 1b and the output side asymmetric branch part 1c of the waveguide 1. Further, electrodes 6a and 6b, which are similarly divided into two parts, are arranged on the input side asymmetric branch part 2b and the output side asymmetric branch part 2c of the waveguide 2, respectively, and these two sets of electrodes 5a, 5b and 6a, 6b By applying slightly different voltages and finely adjusting the asymmetry, a higher extinction ratio can be obtained.

FIG. 5 is a plan view of a third embodiment of the invention. When designed as a device for long wavelengths, the device becomes larger as a whole and the waveguide spacing increases;
At that time, in order to prevent the electrode spacing from widening and the operating voltage from increasing, this embodiment consists of the input-side asymmetric branch section 1b and output-side asymmetric branch section 1c of the waveguide 1, and the input-side asymmetric branch section 2b of the waveguide 2. Electrodes 7 and 8 are arranged on both sides of the output-side asymmetric branch portion 2c, and an electrode 9 is also arranged in the middle.

〔Effect of the invention〕

As explained above, the present invention provides an asymmetric branch in a waveguide by forming an asymmetric branch part with different widths between the input part and output part of a pair of waveguides, and arranging an electrode in the asymmetric branch part. In addition to its original function of separating the even mode and odd mode of the guided light, it also functions as an interferometer that gives a phase difference to the guided light by controlling the asymmetry with voltage. Therefore, it has the effect of being able to perform light switching with a shorter element length than the conventional one when compared with the same voltage, or with a lower voltage when compared with the same element length.

For example, in the case of an element designed to operate at 5V, the element length of the present invention can be reduced by 2/2 compared to a conventional waveguide type optical switch using a balanced bridge type waveguide with an asymmetric branch structure. 3 (approximately 7mmHe−
Ne light source), and the value of the operating voltage x element length of the element according to the present invention is 35V゜mm.
This value is comparable to that of a conventional directional coupler type switch.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the first embodiment of the waveguide type optical switch according to the present invention, FIG. 2 is a plan view showing the operation of the first embodiment, and FIG. 3 is a plan view showing the even mode light in the asymmetric branch. FIG. 4 is a plan view showing the second embodiment, and FIG. 5 is a plan view showing the third embodiment. 1, 2: waveguide, 1a, 2a: input section, 1b,
2b: Input side asymmetric branch part, 1c, 2c: Output side asymmetric branch part, 1d, 2d: Output part, 5, 6, 5
a, 5b, 6a, 6b, 7, 8, 9: electrode.

Claims (1)

[Claims] 1. An asymmetrical branch with different widths is formed between the input and output parts of a pair of waveguides, and an electrode for asymmetry control is disposed in the asymmetrical branch. Features of waveguide type optical switch. 2. The waveguide type optical switch according to claim 1, characterized in that the electrodes disposed in the asymmetric branch portion are divided into an input side and an output side.