JPH06332017A - Semiconductor optical switch - Google Patents

Abstract

PURPOSE:To improve switching characteristics by arranging a gate in the upper part of a region where plural optical waveguides consisting of semiinsulating crystals intersect and arranging a source and drain on the outer side thereof to constitute an MESFET structure. CONSTITUTION:A semiinsulating AlGaAs buffer layer 103, an InGaAs optical waveguide layer 112 and an AlGaAs cap layer 107 are successively epitaxially grown on a GaAs substrate 100 to form the X-type optical waveguides 200, 300,400, 500. Ohmic electrodes 115, 114 which are the source and the drain are then deposited by evaporation on the periphery of the switching region 121 and are alloyed; thereafter, a Schottky electrode which is the gate is formed in the upper part thereof. Further, protoions are implanted into the X-type optical waveguides exclusive of the switching region 121 to semiinsulate the optical waveguides. The carriers of the switching region are rapidly and effectively switched by impressing the electric field by the drain and gate of the metal-semiconductor field effect type transistor (MESFET) structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch required for optical communication, optical switching, optical information processing or an optical computer, and more particularly to a semiconductor optical switch suitable for high speed operation.

[0002]

2. Description of the Related Art Up to now, many materials and methods for optical switches have been proposed. Among them, an optical switch using a compound semiconductor is small and can be integrated with other optical elements. It has the feature. The method of the compound semiconductor optical switch includes a forward direction type and a reverse direction type depending on the direction of the applied electric field. The forward operation type semiconductor optical switch that has been announced so far has a problem that the switching time is limited by the life of the carrier, so that it is difficult to operate at high speed or the power required for the switching operation becomes large. Although the reverse direction semiconductor optical switch has few problems as described above, it has problems such as high driving voltage and insufficient switching characteristics.

The operation principle and problems of the conventionally proposed compound semiconductor optical switch will be described in detail below.

(1) Carrier injection type optical switch This type of optical switch is disclosed by K. Ishida et al. In "Applied Physics Letter".
s ") Vol. 30, pages 141-142 (19
As described in 87), when carriers are injected into the switching region, the incident light is switched by total reflection utilizing a phenomenon that the refractive index is lowered due to a band-filling effect or the like. The outline is shown in FIG. This method has the advantage that the element size can be reduced and the switching state does not depend on the polarization state of the incident light, but it is difficult to achieve high speed because the switching time is limited by the life of injected carriers. is there.

(2) Multiple quantum well (MQW) type optical switch This system is based on, for example, Electronics Letters ("E
lectronics Letters ”) Vol. 24, pp. 415, page 416 (1988). Since multiple quantum wells are used in the switching region as shown in FIG. Although there is an advantage that the change in the refractive index can be used, there are problems that it is difficult to obtain a high extinction ratio and the operating voltage becomes high.

(3) Carrier-depleted optical switch, for example, IEEE Photonics Technology Letters, Vol. 11, pp. 168 to 170, or Japanese Journal of Applied Physics, No. 31. As described in Volumes 2748 to 2752, switching is performed by externally applying an electric field to extract carriers previously doped in a predetermined region. The outline of this method is shown in FIG. This method has an advantage that total reflection is efficiently performed because the switching region is clearly defined, but it has problems such as difficulty in obtaining a high extinction ratio and high driving voltage. In addition, the switch structure of this method has problems that the waveguide loss becomes large and the scattering loss at the boundary of the depletion region becomes large due to the absorption loss due to the relatively high concentration of carriers doped in the waveguide. It was

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to overcome the problems of the compound semiconductor optical switches that have been heretofore announced as described above and to provide a carrier injection type optical switch, in other words, a forward voltage application type optical switch. An object of the present invention is to provide an optical switch having the advantages of the switch, that is, having sufficient switching characteristics and also having advantages such as high-speed switching which is a characteristic of the reverse voltage application type optical switch.

[0008]

In order to achieve the above object, in the present invention, a semi-insulating crystal is used for the waveguide, and only the switching region is previously doped with a carrier having a higher concentration than that of the surrounding waveguide. Then, switching is performed by applying a reverse electric field to this region.

At this time, by using only the electric field generated by both the drain and the gate of the metal-semiconductor field effect transistor (MESFET) structure, carriers doped in the switching region can be switched quickly and efficiently. It is what

[0010]

The details of the present invention will be described in detail with reference to the drawings.
FIG. 4A shows an outline of the semiconductor optical switch of the present invention.
Further, in FIG. 4B, the MESFET structure portion (switching area A
-A ') shows a sectional view. When the drain and gate voltages are 0, that is, when the switch is in the OFF state, the light incident from the optical waveguide 200 is caused by the high concentration carriers doped in the switching region, and the refractive index of this region is the waveguide around it. Since it is lower than that, it is totally reflected at the interface and guided to the emission end 500. On the other hand, when an electric field is applied to the drain and gate, when the switch is in the ON state, the carriers doped by these electric fields are extracted, so that the refractive index of the switching region becomes uniform with that of the waveguide, and the incident light Goes straight and exit end 4
00.

In this way, it becomes possible to switch the incident light to either of the emission ends 400 and 500 by the electric field from the outside. Here, since the gate voltage is applied in the vertical direction of the waveguide and the drain voltage is applied in the in-plane direction, carriers are more effectively extracted as compared with the conventional reverse application type optical switch.

[0012]

EXAMPLE One example of the present invention will be described with reference to FIG.
0.5 μm thick semi-insulating AlGaAs on GaAs substrate 100
(Al: 0.3, Ga: 0.7) buffer layer 103, 0.5 μm thick carrier concentration 2 × 10 ¹⁷ / cm ³ InGaAs (I
n: 0.35, Ga: 0.65) Optical waveguide layer 112, thickness 0.1 μ
1 × 10 ¹⁶ / cm ³ AlGaAs (Al: 0.3, Ga: 0.
7) The cap layer 107 was sequentially epitaxially grown.
Then, an X-shaped optical waveguide 2 having a crossing angle of 4 ° and a width of 3 μm is formed by a normal photolithography technique and a chemical etching method.
00, 300, 400, 500 were formed. SnNi /
The source and drain ohmic electrodes 115 and 114 made of Ni / AuGe / Au are deposited around the switching region 121 as shown in the figure, alloyed at 380 ° C., and then Pt /
A Schottky electrode serving as a gate was formed using Au. Proton ions were injected into the X-type optical waveguide other than the switching region 121, and the region other than the switching region was semi-insulated. As a result, the absorption loss due to the carriers in the optical waveguide portion becomes small, and at the interface with the switching region, the refractive index is different between the two as described above.
Total internal reflection occurs.

When a voltage is applied to the gate of the optical switch prototyped in this manner, the depletion layer reaches the interface between the optical waveguide layer and the buffer layer at a voltage of -1V, and the active region is completely covered by a voltage as low as -2V. . Further, the lateral electric field applied by the drain voltage also has a large effect on depletion of the active region. According to the numerical simulation, it is possible to deplete the carrier of 1.9 × 10 ¹⁷ / cm ³ by applying the gate voltage of −2V.

FIG. 5 shows the result of measuring the gate voltage dependence of the optical output at both exit ends of the waveguide by injecting light of a semiconductor laser having a wavelength of 0.98 μm into the prototype optical switch. The extinction ratio reached 15 dB, which was experimentally confirmed to be sufficient for practical use. The change in refractive index calculated from this result reached 0.32%.

[0015]

According to the present invention, since the optical switch of the present invention is of the voltage application type, it can be expected that the power consumption can be greatly reduced as compared with the carrier injection type, and the switching speed is not limited to the carrier life. There is. Furthermore, since the method uses a semi-insulating crystal with small propagation loss and doping is performed only in the switching region, the insertion loss can be significantly reduced compared to the conventional voltage application type optical switch.
Further, the scattering loss caused by the refractive index discontinuity at the switching region / optical waveguide interface can be reduced. In addition, the MESFET structure including the semi-insulating region is a system that effectively applies vertical and horizontal electric fields to the switching region.
A low driving voltage and good switching characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of a conventional carrier injection type optical switch.

FIG. 2 is a perspective view of a conventional multiple quantum well optical switch.

FIG. 3 is a perspective view of a conventional depletion type optical switch.

FIG. 4 is an explanatory diagram of an optical switch according to the present invention.

FIG. 5 is a switching characteristic diagram of the optical switch according to the present invention.

[Explanation of symbols]

100 ... Substrate, 101 ... Bottom of ridge type optical waveguide, 10
2 ... Side wall of ridge type optical waveguide, 103 ... Buffer layer, 1
04 ... Optical waveguide layer, 107 ... Switching region cladding layer, 108 ... Waveguide cladding layer, 109 ... Second optical waveguide, 110 ... First optical waveguide, 112 ... Waveguide layer inside switching region, 113 ... Shot Key electrode (gate), 114 ... Ohmic electrode (drain), 115 ...
Ohmic electrode (source), 116 ... Channel between drain and switching region, 121 ... Switching region, 2
00 ... 1st optical waveguide entrance, 300 ... 2nd optical waveguide entrance, 400 ... 1st optical waveguide exit, 500 ... 2nd optical waveguide exit.

Claims (12)

[Claims] 1. A first optical waveguide comprising a semi-insulating crystal and a second optical waveguide.
2. The semiconductor optical switch having the MESFET structure in which the optical waveguides of 1. intersect with each other, the gate is disposed above the intersecting region, and the source and the drain are disposed outside thereof. 2. The semiconductor optical switch according to claim 1, wherein the switching region has a carrier concentration higher than those of the first and second optical waveguides made of a semi-insulating crystal and is arranged on the drain side. 3. The semiconductor optical switch according to claim 1, which has a Schottky electrode. 4. The semiconductor optical switch according to claim 1, wherein an optical signal propagating through the optical waveguide changes its propagation direction by a change in a refractive index caused by a change in carrier concentration in a switching region. 5. The optical signal according to claim 1, 2, 3 or 4, wherein when no voltage is applied from the outside, an optical signal incident on the first optical waveguide is transmitted to the switching region by a carrier doped in the region. A semiconductor optical switch that changes its optical path to the second optical waveguide in order to have a low refractive index. 6. The method according to claim 1, 2, 3, 4 or 5.
A semiconductor optical switch in which an incident optical signal propagates without changing its optical path by extracting carriers from the switching region by a voltage applied to a drain and a gate. 7. The effective refractive index according to claim 1, 2, 3, 4, 5 or 6, wherein the effective refractive index is a carrier extraction effect, a band shift effect,
A semiconductor optical waveguide that is changed by the plasma effect, electric field effect, Pockels effect, and Franz-Keldysh effect. 8. The semiconductor optical waveguide according to claim 7, wherein the extraction of carriers is performed by a vertical electric field between the source and the drain and a horizontal electric field between the source and the drain. 9. The semiconductor optical switch according to claim 1, wherein the MESFET structure is composed of source and drain ohmic electrodes and a Schottky electrode. 10. The semiconductor optical switch according to claim 9, wherein the switching region comprises a clad layer having a low carrier concentration and a guide layer having a high carrier concentration. 11. Claims 1, 2, 3, 4, 5, 6, 7,
A semiconductor optical switch according to 8, 9, or 10, wherein the switching region and the drain are coupled by a channel. 12. Claims 1, 2, 3, 4, 5, 6, 7,
8. A semiconductor optical switch according to 8, 9, 10 or 11 wherein source and drain electrodes are formed outside the waveguide region.