JPH05323388A - Semiconductor optical switch element - Google Patents

Abstract

PURPOSE:To provide a waveguide type optical switch element which has low loss, a high extinction ratio, low polarization.wavelength dependency, and can, adjust and outputs input power at an optional ratio. CONSTITUTION:This semiconductor optical switch element consists of two parallel optical waveguides 1 and 2 for output which are loaded with electrodes 7 and 8 for guiding in an electric signal and one optical waveguide 9 for input composed of a tapered optical waveguide part 9b which is positioned at the center position between the optical waveguides 1 and 2 for output, decreased in width in the propagation direction of light from an input terminal 9a, and loaded with electrodes for guiding in an electric signal. The waveguide mode of one optical waveguide for output can be cut off by putting the electrode in operation, so light inputted to the center optical waveguide for input is coupled with the other optical waveguide for output to develop 0 1 switching characteristics. The dependency on polarized wave.wavelength is small and the low loss and high extinction ratio are obtained. Further, the output power from the optical waveguide for output can optionally be adjusted by putting the electrode loaded on the tapered optical waveguide part in operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch element made of a semiconductor material, and more particularly to a novel structure having little polarization dependence or wavelength dependence, low loss and high extinction ratio, and easy to manufacture. Semiconductor optical switch.

[0002]

2. Description of the Related Art Recently, various waveguide type optical switch elements made of semiconductor materials have been proposed. This is because all the optical switching elements of this type are made of a semiconductor material, which enables monolithic integration with other active elements.

As such an optical switching element, for example, Photonic Switching (p35 to p37, 1990) is used.
Published by K. Komatsu et al. Directional coupler type with an applied voltage of ± 29 V and an extinction ratio of about 14 dB; ECOC '8
9 (p531 to p534) published by H. Yanagawa et al., Y-branch type that exhibits an extinction ratio of about 20 dB at an injection current of 250 mA; Electronics Letters (Vol26. No.7, p476 to 477,
1989), C. Wuethrich et al.
Mach-Zehnder type that exhibits an extinction ratio of about a dozen dB at 19 to -26V; further, IEEE J. of Quantum Elect
F. Ito et al., published in ronics (Vol. 25, No. 7, July. 1989), is known to have an X-branch type that exhibits an extinction ratio of about several ten dB at an injection current of 100 mA.

[0004]

The above-mentioned four kinds of optical switch elements have no problem in terms of monolithic integration, but have the following drawbacks. First, the directional coupler type has a low loss and a high extinction ratio, but it has polarization dependence and wavelength dependence, which poses a problem when incorporated into an actual optical fiber communication system. Occurs.

Since the Y-branch type operates by cutting off the guided mode in the output side optical waveguide, it becomes polarization independent and wavelength independent, and has a fairly good extinction ratio characteristic. ing. However, on the other hand, the radiation loss at the Y branch point is large, and the branch angle is a small angle of about 2 °, and the distance between the optical waveguides in the vicinity of the Y branch point is extremely narrow, so that the two output side There is a problem that the manufacturing precision becomes difficult when the electrodes are loaded so that the optical waveguides are not short-circuited with each other.

Further, the Mach-Zehnder type is problematic in that it is polarization-dependent and wavelength-dependent, and further has a low extinction ratio. Finally, the X-branch type is
Since it operates by utilizing the plasma effect of current injection,
It is polarization-independent and wavelength-independent, but there is a problem that a high extinction ratio cannot be obtained because the initial crosstalk is large and the absorption loss increases due to current injection.

As described above, the above-mentioned 4
The type of optical switch element has a problem that it is polarization-dependent and wavelength-dependent, or has a large loss.
And it is common that it has a low extinction ratio. In the present optical communication system, an extinction ratio of at least 20 dB or more is required, but in order to achieve this target value, in the case of the above-mentioned optical switch element, its manufacturing precision must be set more severely. Disappear.

The present invention solves all of the above-mentioned problems, is polarization independent, wavelength independent, has a low loss and a relatively high extinction ratio, is easy to manufacture, and further has an output ratio of An object of the present invention is to provide a semiconductor optical switch device having a novel structure that can be adjusted arbitrarily.

[0009]

In order to achieve the above-mentioned object, in the present invention, two output optical waveguides, which are arranged in parallel with each other and are loaded with electric signal introducing electrodes, And a tapered optical waveguide portion disposed at a central position between the output optical waveguides and having a path width gradually decreasing from the input end in the light propagation direction, and a linear optical waveguide portion optically connected to the tapered optical waveguide portion. Further, there is provided a semiconductor optical switch element, characterized in that at least the tapered optical waveguide portion is provided with one input optical waveguide in which an electric signal introducing electrode is loaded.

The basic structure of the optical switch element of the present invention is shown in FIG. 1 as a plane pattern diagram. Further, FIG. 2 shows a schematic perspective view of the vicinity of an electrode loading portion described later. In the optical switch element of the present invention, first, two output optical waveguides 1 and 2 of equal width, each of which has a path width W, have heights g relative to each other with a distance 2S between the path width centers. Are arranged in parallel in a ridge shape. Then, in each of the output optical waveguides 1 and 2, the linear optical waveguides 5 and 6 having the path width W are separated from each other by the curved optical waveguides 3 and 4 having the same path width W, respectively. It is optically connected by G ₀ to form an output terminal.

Electrodes 7 and 8 to be described later are loaded on the output optical waveguides 1 and 2, and the output optical waveguides 1 and 2 are attached from there.
It is possible to introduce an electric signal to each independently. Between the output optical waveguides 1 and 2, the above-mentioned space 2 is provided.
An input optical waveguide 9 is arranged in a ridge shape at the center position of S.

This input optical waveguide 9 is a tapered optical waveguide whose path width gradually decreases from the input end 9a located in the same plane as one end 1a, 2a of the output optical waveguides 1, 2 in the light propagation direction. The waveguide section 9b and the linear optical waveguide section 9c optically connected to the tapered optical waveguide section 9b are provided. That is, when the path width of the input end 9a is a, the desired length from here to the light propagation direction is L, and the path width at the point of the length L is b, the tapered optical waveguide portion 9b is Is (a-b)
It gradually decreases at an inclination of / 2L, and further, from the point of L, a straight optical waveguide portion 9c having a path width b is optically connected and extends.

At least the tapered optical waveguide portion 9b
An electrode 10 is loaded on the upper part of the electrode so that a predetermined electric signal can be introduced into the tapered optical waveguide portion 9b from here. Here, the above-mentioned parameters are such that the taper optical waveguide portion 9 has a length L (tapered optical waveguide portion 9b).
b is set to a value such that coupling of guided modes may occur between the optical waveguides 1 and 2 for output, and at the same time, between the linear optical waveguide section 9c and the optical waveguides 1 and 2 for output, It is set to a value that will prevent binding.

That is, when light is input from the input end 9a of the input optical waveguide 9 when forming each of the above-mentioned optical waveguides, all of the input light is coupled to the output optical waveguide 1 or 2 and output. The distance S between the center of the path width between the output optical waveguide 1 or 2 and the input optical waveguide 9 so as to output from the end 5 or 6, the path widths a and b of the tapered optical waveguide portion 9b, and the length L.
Is set.

[0015]

First, in the optical switch element of the present invention, since the tapered input optical waveguide is arranged at the center position of the two output optical waveguides arranged in parallel, light is input from the input optical waveguide. When I typed, Y. Cai et al.
As announced in p17 to p23, almost the same optical coupling efficiency can be obtained for the TE mode and the TM mode, and at the same time, the wavelength dependence of this coupling efficiency is small.
That is, the polarization dependence and the wavelength dependence are reduced.

When light is input from the input end 9a of the input optical waveguide 9 without operating all the electrodes, the light propagating through the output optical waveguide 1, the output optical waveguide 2 and the input optical waveguide 9 is input. The power output ratio is x ₁ : x ₁ : 1-2x ₁
(Where x ₁ is the optical power propagating through the output optical waveguide). That is, the optical power of the same intensity is output from the output ends 5 and 6 of the output optical waveguides 1 and 2.

Here, for example, a predetermined electric signal is introduced only from the electrode 7. The electric signal is a current or voltage having a predetermined value. When such an electric signal is introduced, a plasma effect and a band-filling effect are exhibited in the semiconductor material forming the output optical waveguide located immediately below the electrode, and the refractive index thereof is lowered. The degree of decrease in the refractive index at that time is defined by the magnitude of the introduced electric signal. For example, the electric signal is a current, and when the injected current value exceeds a certain value, the output optical waveguide that has received the current injection cuts off all of the guided modes propagating therethrough. That is, the output optical waveguide that has received the current injection can be in a state in which it does not electromagnetically exist as an optical waveguide even though it exists as a physical shape.

Therefore, all of the light input to the input optical waveguide 9 is combined with the other output optical waveguide 2 into which no electric signal is introduced and is output from the output end 6. Then, when the introduction of the electric signal to the electrode 7 is stopped and the electric signal is introduced only from the electrode 8, the waveguide mode cutoff is performed in the output optical waveguide 2 located immediately below the electrode 8.
The light input to the input optical waveguide 9 is combined with the output optical waveguide 1 in which the cutoff state of the waveguide mode is released, and is output from the output end 5.

That is, by operating the electrodes 7 and 8, a switching operation of 0 ← → 1 can be realized between the output optical waveguides 1 and 2. Further, in the case of this optical switching element, by injecting a current of a predetermined value from the electrode 10, the refractive index of the tapered optical waveguide portion 9b located immediately below the electrode 10 is reduced, and the optical waveguide for output 1 or 2 is propagated. By preventing the recombination of the light that is generated, the light output from the tapered optical waveguide portion 9b is always zero, and the light input to the input optical waveguide 9 is distributed to the output optical waveguide 1 and the output optical waveguide 2. It can also function as a coupler element.

In this case, if the values of the electric signals introduced from the electrodes 7 and 8 are independently selected, the amount of decrease in the refractive index in the output optical waveguide located immediately below each electrode can be appropriately changed. Therefore, the output ratio from the output optical waveguide 1 and the output optical waveguide 2 is x ₂ : 1-x
₂ (x ₂ is the output power from one output optical waveguide).

[0021]

EXAMPLE An optical switch element as shown in the plan pattern view of FIG. 1 and the schematic perspective view of FIG. 2 was manufactured. In the figure, a: 4.0 μm, b: 2.0 μm, L: 14.285 mm,
W: 3.6 μm, S: 5.8 μm, height of each optical waveguide g: 1.
It is 0 μm. Therefore, the inclination of the path width of the tapered optical waveguide section 9b is 0.00014.

The tapered optical waveguide portion 9 of this optical switch element
b and the linear optical waveguide part 9c are respectively III-II of FIG.
The structure is as shown in FIG. 3, which is a sectional view taken along line I, and FIG. 4, which is a sectional view taken along line IV-IV in FIG. That is, on the lower electrode 11 made of AuGeNi / Au,
Substrate 1 made of n ⁺ GaAs by MOCVD method 1
Buffer layer 1 made of 2, n ⁺ GaAs and having a thickness of 0.5 μm 1
3, a lower cladding layer 14 made of n ⁺ Ga _0.9 Al _0.1 As and having a thickness of 3.0 μm, and a thickness of 1.0 μ made of n ⁻ GaAs
m core layers 15 are laminated in this order. Furthermore, on the core layer 15, a ridge-shaped upper cladding layer 1 composed of a cladding 16a made of n ^-- Ga _0.9 Al _0.1 As and a cladding 16b made of p ^-- Ga _0.9 Al _0.1 As.
5, the cap 17 made of p ⁺ GaAs is sequentially MOCV
The layers are stacked by the D method, and the upper surface thereof is covered with an insulating film 18 such as a SiO ₂ film.

A part of the insulating film 18 covering the upper surfaces of the output optical waveguides 1 and 2 is removed in a slit shape to form a window 19a, from which a window, for example, Ti / Pt / is formed on the cap 17.
The electrodes 7 and 8 are loaded by depositing Au. Also in the tapered optical waveguide portion 9b, as shown in FIG. 3, a part of the insulating film 18 is removed in a slit shape to form a window 19b, and from this, for example, Ti / Pt / Au is formed on the cap 17. And the electrode 10 is loaded.

The electrodes 7, 8 and 10 may be loaded so as to cover the entire surfaces of the output optical waveguides 1 and 2 and the tapered optical waveguide portion 9b. It may be loaded in a state of covering the part. The ridge-shaped upper clad layer is formed as a plane pattern as shown in FIG. 1 by stacking each of the above-mentioned semiconductor materials and then performing an etching process thereon.
Is etched so as to be deeper than the pn junction surface 16c formed by the claddings 16a and 16b.

In this device, TE mode guided light having wavelengths of 1.3 μm and 1.55 μm was inputted from the input end 9a of the input optical waveguide 9, respectively. While inputting light, a current was injected only from the electrode 7. The relationship between the output from the output optical waveguide 1, the output optical waveguide 2, and the input optical waveguide 9 and the injected current value is shown in FIG. In the figure, ○ indicates the output optical waveguide 1, Δ indicates the output optical waveguide, and □ indicates the input optical waveguide. The solid line shows a wavelength of 1.3 μm and the broken line shows a wavelength of 1.55 μm.
Represents the case.

When the injection current was set to 0 mA and 150 mA and the TM mode guided light was input instead of the TE mode, the same test was conducted, and the same result as in FIG. 5 was obtained. As is clear from FIG. 5, when the injection current from the electrode 7 is 0 mA, the output optical waveguide 1, the output optical waveguide 2, and the guided light (TE mode) of 1.3 μm and 1.55 μm are provided.
The output ratio in the input optical waveguide 9 is 0.42:
It is 0.42: 0.16, 0.43: 0.43: 0.14. here,
Focusing on the output optical waveguide 1 and the output optical waveguide 2, when the injection current is 0 mA, the output is equally divided, but when the injection current is 250 mA or more, the output of the output optical waveguide 1 is 0, the output of the output optical waveguide 2 becomes 1,
A switching characteristic of 0 ← → 1 appears. in this way,
When the injection current is 250 mA or more, this device functions as an optical switch. And this switching characteristic is
The dependence on polarization and wavelength is suppressed.

Next, the current is not injected into the output optical waveguides 1 and 2, and the tapered optical waveguide portion 9b of the input optical waveguide 9 is used.
Current injection was carried out only in. The change in the output power ratio from the output optical waveguides 1 and 2 at this time is shown in FIG. Figure 6
As is clear from the figure, the injection current from the electrode 10 is 50 mA.
The output optical waveguide 1, the output optical waveguide 2,
The output ratio of the optical power from the input optical waveguide 9 is 0.5: 0.
It will be 5: 0.

FIG. 7 is a plan pattern view showing another embodiment. In the case of this element, electrodes 7a and 8a are loaded on the linear optical waveguide portion 9c of the input optical waveguide 9, and these electrodes 7a and 8a are loaded on the output optical waveguides 1 and 2, respectively. It is in continuity with 8. In this element, even when a slight amount of light is input to the input optical waveguide 9 for other wavelength bands, a current of a predetermined value is injected into the electrode 7a or the electrode 8a to cause the linear optical waveguide portion 9c to receive the current. Since stray light can be absorbed, some loss occurs, but if attention is paid to the output optical waveguides 1 and 2, they can also function as an optical switch with a high extinction ratio.

Although the above description has been made for the element in which the optical waveguides are all formed in a ridge shape, the optical switch element of the present invention is not limited to this mode.
All the optical waveguides may be embedded.

[0030]

As is apparent from the above description, the optical switch element of the present invention has two output optical waveguides, which are arranged in parallel with each other and are loaded with electric signal introducing electrodes, and , A taper optical waveguide portion disposed at a central position between the output optical waveguides, the path width of which gradually decreases from the input end in the light propagation direction, and a linear optical waveguide portion optically connected to the tapered optical waveguide portion, Further, at least the tapered optical waveguide portion is loaded with an electric signal introducing electrode 1
Since the input optical waveguide of the present invention is provided, the electric signal is alternately introduced from one of the electrodes to cut off the waveguide mode in the output optical waveguide located immediately below it, The switching operation of ← → 1 can be realized.

When the electric signal is a current, the absorption loss increases due to this injection current, but this phenomenon appears only in the current-injected output optical waveguide. However, since a high extinction ratio can be obtained in the output optical waveguide with current injection so that there is no light output, and the loss increase in the cutoff state of the guided mode is irrelevant to the entire device, As a result, the device of the present invention exhibits a high extinction ratio. This means that even if a small amount of stray light is present, this stray light is absorbed and does not output, so that the extinction ratio is high.

Further, since this element has a directional coupler structure, it does not cause a radiation loss unlike the Y-branch type and the X-branch type and has a low loss. Moreover, since the operation is performed by the cutoff of the guided mode, the dependence on the polarization and the wavelength can be suppressed. Further, by introducing a predetermined electric signal from the electrode loaded on the tapered optical waveguide portion in this element, the refractive index of the optical waveguide located immediately below can be arbitrarily changed, and as a result, the input light Power can be distributed to the output optical waveguide at any ratio.

[Brief description of drawings]

FIG. 1 is a plan pattern diagram showing an example of an optical switch element of the present invention.

FIG. 2 is a schematic perspective view showing a main part of the optical switch element of the present invention.

FIG. 3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a sectional view taken along line IV-IV in FIG.

FIG. 5 is a graph showing switching characteristics of the optical switch element of the present invention.

FIG. 6 is a graph showing an output ratio from an output optical waveguide when a current is injected into the tapered optical waveguide portion.

FIG. 7 is a plan pattern diagram showing another example of the optical switch element of the present invention.

[Explanation of symbols]

 1 Output Optical Waveguide 1a One End of Output Optical Waveguide 1 2 Output Optical Waveguide 2a One End of Output Optical Waveguide 2 3,4 Curved Optical Waveguide 5,6 Linear Optical Waveguide (Output End) 7, 8 Electric Signal Introducing Electrodes 7a, 8a Electrodes 9 Input Optical Waveguide 9a Input Optical Waveguide 9 Input End 9b Tapered Optical Waveguide 9c Straight Optical Waveguide 10 Electric Signal Introducing Electrode 11 Lower Electrode 12 Substrate 13 Buffer Layer 14 Lower Clad layer 15 Core layer 16 Upper clad layer 16a Clad 16b Clad 17 Cap 18 Insulating films 19a, 19b Window a Tapered optical waveguide part 9b input end path width b Tapered optical waveguide part 9b path width L Tapered optical waveguide Length of the portion 9b W Path width of the output optical waveguides 1 and S Distance between the center of the path width of the output optical waveguides 1 and 2 g Height of the optical waveguide

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Tetsuya Mizumoto 61-9 Ikebukuro, Naka-ku, Yokohama, Kanagawa 6-203 Honmoku Housing 6-203 (72) Inventor Yoshiyuki Naito 8-9-29, Tsukimino, Yamato-shi, Kanagawa (72) Inventor Hanmei 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor, Kuji Yanagawa 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (1)

[Claims] 1. Two output optical waveguides arranged in parallel with each other and loaded with an electric signal introducing electrode, and arranged at a central position between the output optical waveguides,
An electrode for introducing an electric signal, which comprises a tapered optical waveguide portion whose path width gradually decreases from the input end in the light propagation direction, and a linear optical waveguide portion optically connected to the tapered optical waveguide portion, and at least the tapered optical waveguide portion. 1. A semiconductor optical switch element, comprising one input optical waveguide loaded with.