JPH0785152B2 - Waveguide optical switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention is an inverting Δβ type directional coupler type waveguide optical switch, in which a propagation constant difference is given in advance between two adjacent optical waveguides. The operating voltage for switching the switch operation is reduced, and the bias voltage is unnecessary.

[Industrial application field]

The present invention relates to an optical switch, and more particularly to an inverting Δβ type directional coupler type waveguide optical switch.

The waveguide optical switch can be miniaturized and integrated, has a low operating voltage, has a possibility of high-speed operation, and is suitable for mass production. Therefore, its practical application is expected. The waveguide optical switch includes a directional coupler type, a crossed waveguide type, a total reflection type, and the like. Among them, the directional coupler type switch has a feature that the operating voltage is relatively low. But,
This switch has a problem that it is not easy to manufacture because it requires high precision, such as having to strictly control the coupling length.

In order to solve this problem, there is an inverting Δβ type switch in which electrodes are divided so that the operating point can be electrically adjusted.

[Conventional technology and its problems]

The inverted Δβ type directional coupler type waveguide optical switch is described, for example, in “Optical Integrated Circuits”, pages 306 to 309, published by Ohmisha in 1985. 2 and 3 show such an inversion Δ.
A conventional example of a β type directional coupler type waveguide optical switch is shown.
The switch shown in FIG. 2 is obtained by dividing the electrode 3 into two parts, and
The switch in the figure is obtained by dividing the electrode 3 into three parts. In addition,
In each of these figures, (A) shows the configuration of the switch, and (B) shows its operation mode. In these figures, reference numerals 1 and 2 indicate optical waveguides having the same characteristics formed by diffusing Ti on a LiNbO ₃ substrate, and reference numeral 3 indicates an electrode. Also,
The element length is L, the complete coupling length is 1, the propagation constant difference between both waveguides is Δβ, and the operating modes are shown by using the vertical axis and the horizontal axis as L / l and ΔβL / π, respectively. , The line connecting the symbols = indicates the non-coupling state of the optical waveguides 1 and 2 (light path straight traveling state), and the line connecting the symbol x indicates the coupling state of the optical waveguides 1 and 2 (optical path crossing state).

These switches apply a voltage of opposite polarity to each electrode as shown in the figure, and the positive and negative opposite propagation constant difference + Δ in each divided area.
By causing β, −Δβ, and changing the voltage to change the propagation constant difference Δβ, the uncoupled state (=) and the coupled state (×) are switched.

However, these switches have drawbacks in that the operating voltage is large in both absolute value and change range, and therefore it is difficult to speed up the operation and DC bias is required.

[Means for solving problems]

In order to solve the above problems, the present invention divides two adjacent optical waveguides into a plurality of regions in the light traveling direction in an inverted Δβ type directional coupling type optical switch, and the adjacent regions have different signs. A propagation constant difference having the same absolute value is given in advance between the optical waveguides in each region, and the smallest amount of the propagation constant difference necessary for switching the operation of the switch is generated using the electrodes in each region. It is configured as follows.

[Work]

According to the above configuration, the operating voltage required for switching the operating state of the switch is reduced by the voltage corresponding to the propagation constant difference given in advance.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which FIG. 1A shows the configuration, FIG. 1B shows the operation mode 1, and FIG. 1C shows the operation mode 2. In the figure, symbols 11 and 12 are T on the substrate of LiNbO _3.
An optical waveguide formed by diffusing i is shown, and reference numeral 13 is an electrode.

This switch divides a coupling portion (length L) of two optical waveguides 11 and 12 which are close to each other into two regions I and II, and divides them into electrodes 13
Are divided and formed for each region. And regions I and II
The width of the optical waveguide 11 at W ₁ and W ₂ (W ₁ > W ₂ ) respectively
In addition, by setting the widths of the optical waveguides 12 to W ₂ and W ₁ , respectively, the propagation constant difference + Δβ in the region I and the propagation constant −Δβ in the region II are previously set between the optical waveguides 11 and 12. I have given each.

To give the propagation constant difference in advance, in addition to changing the width of the optical waveguide as described above, the thickness of the non-waveguide may be made different, or the diffusion amount of T _i may be changed to make the refractive index different. It is possible.

The value of the propagation constant difference Δβ given in advance may be various, but the following examples are practically advantageous.

The propagation constant difference [Delta] [beta] for example 1 previously assigned to the propagation constant difference [Delta] [beta] ₁ which corresponds to the operating voltage V ₁ of the bound state as shown in FIG. 1 (B) (×). In this case, when the operating voltage V is not applied to the electrode 13 (V = 0), the switch is in the coupled state (x).
Has become. Therefore, in order to switch to the uncoupled state (=) in which the propagation constant difference is Δβ ₃ , the difference between the operating voltage V _{3 in} the uncoupled state (=) and the operating voltage V _{1 in} the coupled state (×), that is, V _3- V ₁ = V _s may be applied to the electrode 13.

That is, the operating voltage of the above switch is not the operating voltage V ₃ in the uncoupled state (=) but a small V _s lower by V ₁ than that.

Moreover, in the coupled state (x), the application of the operating voltage V ₁ is unnecessary, and the DC bias voltage is unnecessary.

Example 2 The propagation constant difference Δβ given in advance is 1/2 of the sum of the operating voltage V ₁ in the coupled state (×) and the operating voltage V _{3 in} the uncoupled state (=) as shown in FIG. 1 (C). , That is, the propagation constant difference Δβ ₂ corresponding to (V ₁ + V ₃ ) / 2 = V ₂ . In this case, the operating voltages for switching to the coupled state (×) and the uncoupled state (=) can be set to −V _s / 2 and + V _s / 2, respectively. The value is halved.

Although the above embodiment is a case of the two-division type switch,
It is also applicable to a three-division type switch as shown in FIG.

〔The invention's effect〕

As described above, the waveguide optical switch according to the present invention provides the following effects by providing the optical waveguide with a predetermined propagation constant difference.

The operating voltage (absolute value) is reduced, and therefore VL
The product becomes smaller and the speed can be increased.

 DC bias is unnecessary.

The large tolerance for the manufacturing error of the coupling length, which is the basic feature of the inverting Δβ type optical switch, is maintained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing a conventional example. [Explanation of symbols] 11, 12 …… Optical waveguide 13 …… Electrode

Claims (3)

[Claims] 1. An inversion Δβ type directional coupler type waveguide optical switch, in which two adjacent optical waveguides are divided into a plurality of regions in the light traveling direction, and adjacent regions have different signs and absolute values. Are given in advance between the optical waveguides in each region, and in each region, the smallest amount of the propagation constant difference necessary for switching the operation of the switch is generated by using the electrodes. A waveguide optical switch characterized by being configured. 2. The waveguide optical switch according to claim 1, wherein the widths of the two waveguides are made different from each other to give a difference in propagation constant in advance. 3. The refractive indexes of both waveguides are made different from each other,
The waveguide optical switch according to claim 1, wherein a propagation constant difference is given in advance.