JPH04296726A - Semiconductor optical switch element - Google Patents

Abstract

PURPOSE:To offer the waveguide type optical switch element which has low loss, a high extinction rate and small polarization and wavelength dependency. CONSTITUTION:The semiconductor optical switch element consists of two parallel optical waveguides 1 and 2 which are mounted with electrodes 7 and 8 for electric signal input and one optical waveguide part 9 consisting of a tapered optical waveguide part 9b which is arranged at the center position between the optical waveguides 1 and 2 for output and decreases gradually in path width from an input terminal 9a in the propagation direction of light and a straight optical waveguide part 9c which is connected optically to the tapered optical waveguide part 9b. Consequently, the waveguide mode of one optical waveguide for output can be cut off by operating the electrodes, so light which is inputted to the center optical waveguide for input is coupled with the other optical waveguide for output to obtain a 0 1 switching characteristic. The dependency on polarization and wavelength is small and the low loss and high extinction rate are obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical switching element made of a semiconductor material, and more specifically, it has a novel structure that has little polarization dependence and wavelength dependence, low loss and high extinction ratio, and is easy to manufacture. This invention relates to a semiconductor optical switch.

0002

2. Description of the Related Art Recently, a variety of waveguide type optical switching devices made of semiconductor materials have been proposed. This is because all optical switching elements of this type are manufactured entirely from semiconductor materials, allowing monolithic integration with other active elements.

[0003] As such an optical switching element, for example, Photonic Switching (p. 35
~p37, 1990) by K. Komatsu et al. announced a directional coupler type that exhibits an extinction ratio of approximately 14 dB at an applied voltage of ±29 V;
~p534) H. Published by Yanagawa et al.
Y exhibits an extinction ratio of approximately 20 dB at an injection current of 250 mA.
Branch type; Electronics Letter
s (Vol26. No.7, p476-477
, 1989) in C. The Mach-Zehnder type that was announced by Wuethrich et al. and exhibits an extinction ratio of about 10-odd dB at an applied voltage of -19 to -26 V;
J. of Quantum Electronic
s (Vol25. No.7, July.1989
) to F. An X-branch type is known, which was published by Ito et al. and exhibits an extinction ratio of about 10-odd dB at an injection current of 100 mA.

0004

SUMMARY OF THE INVENTION None of the four types of optical switching elements described above have problems in terms of integration, but they do have the following drawbacks. First, the directional coupler type has low loss and high extinction ratio, but it has polarization dependence and wavelength dependence, which causes problems when incorporating it into an actual optical fiber communication system. arise.

The Y-branch type operates by cutting off the waveguide mode in the output optical waveguide, so it is polarization-independent and wavelength-independent, and has fairly good extinction ratio characteristics. 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 spacing between the optical waveguides near the Y-branch point is extremely narrow. There is a problem in that manufacturing precision becomes strict when loading electrodes on the optical waveguide to prevent short-circuiting between them.

Furthermore, the Mach-Zehnder type has problems in that it is polarization dependent and wavelength dependent, and furthermore, it has a low extinction ratio. Finally, the X-branched type is
It operates by utilizing the plasma effect caused by current injection, so
Although it is polarization-independent and wavelength-independent, it is difficult to obtain a high extinction ratio due to large initial crosstalk, and there are problems such as increased absorption loss due to current injection.

[0007] As described above, the above-mentioned 4 conventionally known
These types of optical switching devices have the problem of either being polarization-dependent and wavelength-dependent, or having a large loss. The common feature is that they have a low extinction ratio. Current optical communication systems require an extinction ratio of at least 20 dB, but in order to achieve this target value, the manufacturing precision of the above-mentioned optical switch elements must be set even more strictly. It disappears.

The present invention solves all of the above-mentioned problems, and provides an optical switch element with a new structure that is polarization-independent, wavelength-independent, has low loss and relatively high extinction ratio, and is easy to manufacture. For the purpose of providing.

[0009]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides two output optical waveguides arranged parallel to each other and loaded with electrodes for introducing electrical signals. , and a tapered optical waveguide portion disposed at a central position between the output optical waveguides and whose path width gradually decreases from the input end to the light propagation direction, and a straight optical waveguide optically connected to the tapered optical waveguide portion. Provided is a semiconductor optical switch element characterized in that it includes one input optical waveguide consisting of:

FIG. 1 shows the basic configuration of the optical switch element of the present invention as a plan pattern diagram. Further, FIG. 2 shows a schematic perspective view of the vicinity of the electrode loading section, which will be described later. In the optical switch element of the present invention, first, two equal-width output optical waveguides 1 and 2, both of which have a path width of W, are arranged at a distance of 2S between the centers of the path widths.
They are arranged parallel to each other in a ridge shape with an interval of . The output optical waveguides 1 and 2 are connected to curved optical waveguides 3 and 4 having the same path width W, respectively.
Straight optical waveguides 5 and 6 having a path width W are optically connected at a distance G0 between the centers of their path widths to form an output end.

Electrodes 7 and 8, which will be described later, are loaded on the output optical waveguides 1 and 2, from which the output optical waveguides 1 and 2 are connected.
It is now possible to introduce electrical signals to each independently. Between the output optical waveguides 1 and 2, the above-mentioned interval 2 is provided.
An input optical waveguide 9 is arranged in a ridge shape at the center position of S.

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

[0013] Here, each of the above parameters has a length L
The portion (tapered optical waveguide section 9b) is set to a value such that coupling of the waveguide mode can occur between the tapered optical waveguide section 9b and the output optical waveguides 1 and 2, and at the same time, the straight optical waveguide section 9c The value is set to such a value that coupling of waveguide modes does not occur between the output optical waveguides 1 and 2. That is, when forming each of the above-mentioned optical waveguides, when light is input from the input end 9a of the input optical waveguide 9, all of the input light is coupled to the output optical waveguide 1 or 2 and output to the output end 5 or 2. The distance S between the center widths of the output optical waveguide 1 or 2 and the input optical waveguide 9, and the path widths a, b and length L of the tapered optical waveguide section 9b are set so that the output optical waveguide 1 or 2 and the input optical waveguide 9 are outputted from the optical waveguide 6.

[0014]

[Operation] First, the optical switch element of the present invention has a tapered input optical waveguide placed at the center of two output optical waveguides arranged in parallel, so that light is not transmitted from this input optical waveguide. When you enter Y. Cai et al. OQE88-1
40. As announced on pages 17 to 23, substantially the same optical coupling efficiency can be obtained for both the TE mode and the TM mode, and at the same time, the wavelength dependence of this coupling efficiency is small. That is, polarization dependence and wavelength dependence are reduced.

Now, when light is input from the input end 9a of the input optical waveguide 9 without operating the electrodes 7 and 8, it propagates through the output optical waveguide 1, the output optical waveguide 2, and the input optical waveguide 9. The optical power output ratio is x1:x1:1-2
x1 (here, x1 is the optical power propagating through the output optical waveguide). That is, the output optical waveguide 1,
Optical power of the same intensity is output from the output ends 5 and 6 of 2.

Here, a predetermined electrical signal is introduced only from the electrode 7, for example. The electrical signal is a current or voltage of a predetermined value. When such an electric signal is introduced, the refractive index of the semiconductor material constituting the output optical waveguide located directly below the electrode is lowered due to the occurrence of a plasma effect or a band filling effect. The degree of refractive index reduction at that time is determined by the magnitude of the introduced electrical signal. For example, when the electrical signal is a current and the value of the injected current exceeds a certain value, the output optical waveguide that receives the current injection cuts off all waveguide modes propagating there. That is, even if the output optical waveguide that receives the current injection exists in physical form, it can be brought into a state where it does not exist electromagnetically as an optical waveguide.

Therefore, all of the light input to the input optical waveguide 9 is coupled to the other output optical waveguide 2 into which no electrical signal is introduced, and outputted from its output end 6. Then, when the introduction of the electrical signal to the electrode 7 is stopped and the electrical signal is introduced only from the electrode 8, the waveguide mode is cut off in the output optical waveguide 2 located directly below the electrode 8,
The light input to the input optical waveguide 9 is coupled to the output optical waveguide 1 in which the cutoff state of the waveguide mode has been released, and is output from the output end 5 thereof.

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.

[0019]

EXAMPLE An optical switch element as shown in the plan pattern diagram 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: 14.28
5 mm, W: 3.6 μm, S: 5.8 μm, and the path height g of each optical waveguide: 1.0 μm. Therefore, the slope of the path width of the tapered optical waveguide portion 9b is 0.00014.

Tapered optical waveguide section 9 of this optical switch element
b and straight optical waveguide section 9c are shown in FIG. 1, respectively.
3, which is a cross-sectional view along the line IV-I of FIG.
The configuration is as shown in FIG. 4, which is a cross-sectional view taken along the V line. That is, on a lower electrode 10 made of AuGeNi/Au, a substrate 11 made of n+ GaAs and a substrate 11 made of n+ GaAs with a thickness of 0.5 μm is formed by MOCVD.
m buffer layer 12, n+ Ga0.9 Al0.1
A lower cladding layer 13,n made of As and having a thickness of 3.0 μm
- A core layer 14 made of GaAs and having a thickness of 1.0 μm is laminated in this order. Further, on this core layer 14, there is a ridge-shaped upper cladding layer 1 consisting of a cladding 15a made of n-Ga0.9Al0.1As and a cladding 15b made of p-Ga0.9Al0.1As.
5, the cap 16 made of p+ GaAs is sequentially MOC
The layers are laminated by the VD method, and the upper surface thereof is covered with an insulating film 17 such as a SiO2 film.

A window 18 is formed by removing a part of the insulating film 17 covering the upper surfaces of the output optical waveguides 1 and 2 in the form of a slit.
The electrodes 7, 8 are loaded by evaporating u. Note that these electrodes 7 and 8 may be loaded so as to cover the entire surface of the output optical waveguides 1 and 2 over the entire length thereof, or may be loaded so as to partially cover the output optical waveguides 1 and 2. .

The ridge-shaped upper cladding layer is formed by laminating the above-mentioned semiconductor materials and then etching it to form a planar pattern as shown in FIG.
The depth g at that time is the cladding 15a and the cladding 15b.
The etching process is performed so as to be deeper than the pn junction surface 15c formed by the pn junction surface 15c. In this element, guided light in the TE mode with wavelengths of 1.3 μm and 1.55 μm was input from the input end 9a of the input optical waveguide 9, respectively. A current was injected from electrode 7 while inputting light. FIG. 5 shows the relationship between the outputs from the output optical waveguide 1, the output optical waveguide 2, and the input optical waveguide 9 and the injection current value. In the figure, the ○ mark represents the output optical waveguide 1, the △ mark represents the output optical waveguide 2, the □ mark represents the input optical waveguide, the solid line represents the wavelength of 1.3 μm, and the broken line represents the case of the wavelength of 1.55 μm. .

When a similar test was conducted with the injection currents set to 0 mA and 150 mA, and TM mode guided light was input instead of the TE mode, results similar to those shown in FIG. 5 were obtained. As is clear from FIG. 5, when the current injected from the electrode 7 is 0 mA, for guided light of 1.3 μm and 1.55 μm (TE mode), the output optical waveguide 1, the output optical waveguide 2, the input optical waveguide The output ratios in the optical waveguide 9 are 0.42:0.42:0.16 and 0.43:0.4, respectively.
3:0.14. Here, output optical waveguide 1
Focusing on the output optical waveguide 2, when the injected current is 0 mA, the output is divided into equal parts, but when the injected current is 250 mA or more, the output of the output optical waveguide 1 becomes 0.
, the output of the output optical waveguide 2 becomes 1, and a switching characteristic of 0←→1 is expressed. That is, the injection current is 25
At 0 mA or more, this element functions as an optical switch. This switching characteristic has suppressed dependence on polarization and wavelength.

FIG. 6 is a plan pattern diagram showing another embodiment. In the case of this device, electrodes 7a and 8a are loaded on the straight optical waveguide section 9c of the input optical waveguide 9, and these electrodes 7a and 8a are the electrodes 7 and 8a loaded on the output optical waveguides 1 and 2, respectively. It is conducting with 8. Even when a small amount of light in other wavelength bands is input to the input optical waveguide 9, this element injects a predetermined amount of current into the electrode 7a or the electrode 8a, and this injects the current into the straight optical waveguide section 9c. Since stray light can be absorbed, although some loss occurs, 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.

[0025] Although the above explanation has been made regarding an element in which all optical waveguides are formed in a ridge shape, the optical switch element of the present invention is not limited to this form.
All optical waveguides may be of a buried type.

[0026]

As is clear from the above description, the optical switch element of the present invention includes two output optical waveguides arranged parallel to each other and loaded with electrodes for introducing electrical signals. and a tapered optical waveguide portion disposed at a central position between the output optical waveguides and whose path width gradually decreases from the input end to the propagation direction of light, and a straight optical waveguide optically connected to the tapered optical waveguide portion. Since it is characterized by having one input optical waveguide consisting of one electrode, an electric signal is alternately introduced from one electrode and the waveguide mode in the output optical waveguide located directly below it is cut off. Thus, a switching operation of 0←→1 can be realized.

When the electrical signal is a current, absorption loss increases due to the injected current, but this phenomenon occurs only in the output optical waveguide into which the current is injected. However, the extinction ratio is so high that there is no optical output in the output optical waveguide into which current is injected, and the increase in loss in the cut-off state of the waveguide mode is unrelated to the overall device. As a result, the device of the present invention exhibits a high extinction ratio. This means that even if there is a small amount of stray light, this stray light is absorbed and not output, resulting in a high extinction ratio.

Furthermore, since this element has a directional coupler structure, it does not cause radiation loss unlike Y-branch type or X-branch type, and has low loss. Moreover, since it is operated at the cutoff of the waveguide mode, dependence on polarization and wavelength is also suppressed.

[Brief explanation of the drawing]

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 the main parts of the optical switch element of the present invention.

FIG. 3 is a sectional view taken along line III-III in FIG. 1;

FIG. 4 is a sectional view taken along line IV-IV in FIG. 1;

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

FIG. 6 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 Straight optical waveguide (output end) 7, 8 Electric signal introduction electrodes 7a, 8a Electrode 9 Input optical waveguide 9a Input end 9b of input optical waveguide 9 Tapered optical waveguide section 9c Straight optical waveguide section 10 Lower electrode 11 Substrate 12 Buffer layer 13 Lower cladding layer 14 Core layer 15 Upper cladding layer 15a Cladding 15b Cladding 16 Cap 17 Insulating film 18 Window a Path width b at the input end of the tapered optical waveguide section 9b Path width L at point L of the tapered optical waveguide section 9b Length W of the tapered optical waveguide section 9b For output Path width S of optical waveguides 1 and 2 Distance g between path width centers of output optical waveguides 1 and 2
Optical waveguide height

Claims (1)

[Claims] 1. Two output optical waveguides arranged parallel to each other and loaded with electrodes for introducing electrical signals, and arranged at a central position between the output optical waveguides, and , comprising one input optical waveguide consisting of a tapered optical waveguide portion whose path width gradually decreases from the input end in the light propagation direction, and a straight optical waveguide optically connected to the tapered optical waveguide portion. Semiconductor optical switch device.