JPS58153378A - Optical bistable device - Google Patents

Abstract

PURPOSE:To obtain the optical bistabilizing device with which input-output characteristics can be electrically changed optionally and continuously by a method wherein a photo waveguide path, consisting of a light modulating element having electrically variable light transmittance, is provided between a light-receiving element and a light-emitting element. CONSTITUTION:A p type GaAs layer 12, an n type GaAS layer 13, an n type GaAlAs layer 15 are formed by lamination in an n<+> type GaAs substrate 1, these layers are insulation-isolated in an island form using SiO2 films 10 and 11 which are penetrating to the layer 12, and the above is used as a light modulating element PM. Also, an n<+> type GaAs layer 4, a p<+> type GaAlAs layer 5, and a p type GaAS layer are formed by lamination in the substrate 1 between the films 10 and 11 and used as a photo diode PD and a laser diode LD, and terminals 8 and 9 are attached to the avove diodes respectively. Then, the surface of the element PM is covered by an SiO2 film 18, an aperture is provided, and electrodes 16 and 17 are formed on the exposed surface of the layer 13 which is extending to the center part and the surface of the substrate 1. Through these procedures, the DC voltage to be applied to the electrodes 16 and 17 can be changed and the output is brought to a variable state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical bistable device, which is a type of optical integrated circuit, and particularly relates to an optical bistable device whose input/output characteristics can be changed electrically and continuously.

Figure 1A shows a typical structure of a conventional optical bistable device,
FIG. 1B shows the equivalent circuit.

This optical bistable device has a normal double heterostructure photodiode PD and laser diode LD on one semiconductor substrate 1. They are integrally formed so as to face each other via II2. For example, the compositions of the semiconductor constituent layers of the photodiode PD and the laser diode LD are as follows.

1 ・N horizontal Qa As substrate 3 - N 10-type Ga A, eAs layer 4 - P 10-type Ga AS II 5-= P 10-type Ga AJAs II 6 ・r' 10-type Ga AS II And on the back side of the substrate 1 A common cathode electrode 7 is formed, and anode electrodes 8 and 9 are formed on the top layer of each of the photodiode PD and laser diode LD. The laser diode LD generates output light PO from both end faces of its resonator, but the output light PO emitted from one face passes through the groove 2 to the photodiode PD.
The light will begin to be received.

In the above configuration, the positive electrode of an appropriate DC power supply is connected to the anode electrode 9 of the laser diode LD, the negative electrode is connected to the anode electrode 8 of the photodiode PD, and an appropriate bias circuit is connected to the common cathode electrode 7 side.

In this state, input light P from the outside enters the photodiode PD.
1, a reverse photocurrent flows through the photodiode PD, this current becomes a forward driving current of the laser diode LD, and the output light P from the laser diode LD is
o occurs. As described above, a part of this output light po is given to the photodiode PD and acts to further increase the photocurrent of the photodiode PD. This increase in current acts to further strengthen the output light po. In other words, the output light P.

When a portion of the light is received by the photodiode PD, positive feedback is applied to the above-mentioned circuit. Due to this positive feedback effect,
The level of the output light po is stabilized at a substantially constant value.

FIG. 2 shows the input/output characteristics of the above-mentioned optical bistable device. As is clear from the figure, due to the positive feedback effect of the light, when the level of the input light Pi becomes greater than a certain value a, the level of the output light po rapidly increases and becomes approximately stable at a certain value C.

Furthermore, when the level of the input light Pi becomes smaller than a certain value b (b<a), the level of the output light PO rapidly decreases to almost 0.
It becomes close to. In this way, the input/output characteristics are similar to that of a comparator with hysteresis. This characteristic can be used to binarize the input light Pi whose level changes in an analog manner at a certain threshold, or to use it for waveform shaping of optical signals, or even to store optical signals by utilizing the hysteresis mentioned above. Applications are being made to

By the way, in the conventional optical bistable device described above, in order to arbitrarily change the values a and b of the changing points in the input/output characteristics shown in FIG. 2, a bias circuit connected to the common cathode terminal 7 side, That is, the resistance value of the resistor connected between terminals 7 and 8 or between terminals 7 and 9 must be changed. For this reason, once the characteristics have been determined and incorporated into a circuit, it is extremely troublesome to change the characteristics or change the characteristics. In addition, it was not possible to use the device in such a way that the input/output characteristics were varied in various ways.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to provide an optical bistable device integrated into a single semiconductor chip, in which the above-mentioned input/output characteristics are continuously controlled by an external voltage signal. An object of the present invention is to provide an optical bistable device that can be changed.

In order to achieve the above object, the optical bistable device of the present invention forms a leading wavepath made of a semiconductor between a light emitting element and a light receiving element to guide a part of light generated from the light emitting element to the light receiving element, Further, the optical waveguide is characterized in that a light modulation element whose light transmittance can be electrically varied is integrally formed.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 3A shows the structure of an optical bistable device according to an embodiment of the present invention, and FIG. 38 shows its equivalent circuit.

This optical bistable device has a light modulation element PM formed in the groove 2 of the conventional optical bistable device shown in FIG. 1A. The configurations of the photodiode PD and laser diode LD are the same as those in FIG. 1A, and each configuration!
13.4°5.6 is as explained above.

In the optical bistable 1iii of this invention, the photodiode P
S ioJ 1 'O is formed on the inner side surface of D, and 5iOzW! is formed on the inner side surface of laser diode LD. A1
1 is formed, and a P-type Ga AS layer is further formed on the bottom surface of the groove 2, and these layers 10 and 1 are formed.
The optical modulation element PM is insulated and separated by 1 and 112. Senyasu lll element PM is made of N0 type GaAs1113 and N
Type Ga Ai! , As [114 and P+ type Ga A,
It consists of an eAs layer 15, P lateral GaA, gAs 1i
An electrode 16 is formed at the center of i15, and both end portions of the N horizontal Qa As layer 13 are exposed upward, and electrodes 16 and 17 are formed there. Note that 3 i 0z @ 1 B is present in areas other than the area where the electrodes 16 and 17 are formed.
is insulated by.

FIG. 4 shows the basic structure of only the light modulation element PM, and each structure 1113, 14.15 and electrode 16.17 in FIG. 3A are shown in correspondence with each other in both figures. When this light modulation element PM transmits light from one end surface to the other end surface in the seven directions shown in FIG.
It can be controlled by a DC voltage applied between 6.17 and 17.

This light modulation element is a P-type Ga /'/! AS layer 15 and N
+ type GaAs1113 and N type GaAlAs 11
The light incident in the Z-axis direction is confined in NlGa A, eAs Ill 4 due to the refractive index difference due to the carrier concentration difference in the Y direction, but the refractive index is higher in the X direction. It diverges in the direction of the high N lateral GaAs layer 13. However, when a reverse bias voltage is applied between the N lateral GaASI 113 and the P 10 type GaA, gAs layer 15, the electric field is concentrated in the depletion layer and Nl! Ga A4As
1111F) A non-uniform electric field EX is generated between the upper and lower parts.

It is well known that the refractive index change Δn due to the nonuniform electric field Ex is expressed as Δ−(R−n3·EX)/2. Here, R is Ga
A, the electro-optical constant of eAs, and n, Ga A, the refractive index of eAs. This refractive index change changes depending on the magnitude of the reverse bias voltage applied to the electrodes 16° and 17@, and as a result, the optical confinement effect in the X direction exhibited by the N-type Ga AfAs layer 14 increases as the reverse bias voltage increases. Become.

In other words, in FIG. 3A, the light emitted from the left side of the laser diode LD (part of the output light PO) is transmitted to the light modulation element PM.
At this time, depending on the magnitude of the reverse bias voltage applied between the electrodes 16 and 17 of the light modulation element PM, the light passes through the laser diode LD side and reaches the right side of the photodiode PD. The diffusivity of the light reaching the side changes, and the amount of light received by the photodiode PD changes. That is, the larger the reverse bias voltage is, the stronger the light confinement effect of the N-type Ga AffiAs 14 becomes, and in that case, the light is received by the photodiode PD without being diffused.

As is clear from the above explanation, in an optical bistable device that acts to guide a part of the output light PO generated from the laser diode LD to the photodiode PD and apply positive feedback, the light that becomes the waveguide for the positive feedback light is *The light transmittance of the optical element PM can be controlled by the voltage applied to the electrodes 16, 171111, and as a result, the loop gain of the positive feedback loop can be arbitrarily and continuously controlled by the voltage signal, Change points a and b in the input/output characteristics between the input light Pi and the output light 80 shown in Fig. 2 can be changed by changing the applied voltage without changing the external connection elements (you can adjust and set them arbitrarily with t). However, it can also be used while changing this, further expanding the range of applications of this polar light bistable device.

Note that in the above embodiments, the photodiode is used as a light receiving element and the laser diode is used as a light emitting element, but the present invention is not limited to this, and other light receiving elements such as a phototransistor may be used, or Other light emitting elements such as light emitting diodes can also be used.

Further, in the above embodiment, the P-type GaAs layer 12 is used to separate the substrate 1 and the N0-type GaAs layer 13 of the light modulation element PM.
, but an insulator such as 3i02 may also be used. In addition, in order to separate the optical modulation element PM from the laser diode LD and photodiode PDh\, Si 021
110.11 is formed, but this may be simply separated by etching etc. A highly integrated optical bistable device can be provided.

[Brief explanation of drawings]

FIG. 1A is a perspective view showing the structure of a conventional optical bistable device;
FIG. 1B is an equivalent circuit of FIG. 1A, FIG. 2 is an input/output characteristic diagram of the optical bistable device, FIG. 3A is a sectional view of the optical bistable device according to an embodiment of the present invention, and FIG. The equivalent circuit diagram in the figure and FIG. 4 are basic structural diagrams of the light modulation element. 1...Substrate PD...Photodiode LD...Laser diode PM...Luminous intensity m element Patent applicant Tateishi Electric Co., Ltd. Figure 1A Figure 1A Figure 2 Figure 4

Claims (1)

[Claims] (1) A light-receiving element that receives input light, a light-emitting element that generates output light, and a leading waveguide made of a semiconductor that guides a part of the light generated from the light-emitting element to the light-receiving element, and An optical bistable device in which an optical adjustment element whose light transmittance is electrically variable is integrally formed on one semiconductor chip.