JPS6130089A - Optical logic circuit - Google Patents

Abstract

PURPOSE:To enable integration of an optical ligic circuit, by forming a plurality of phototransistors on a semiconductor laser in an integrated manner, and electrically isolating the phototransistors from each other. CONSTITUTION:Two phototransistors Tr 2 are formed on a semiconductor laser 1 in series in the direction of the resonator axis. Thereafter, a groove 116 is provided in such a manner as to cut the resonator axis for the purpose of increasing the electrical resistance between the two phototransistors Tr 2. Thus, the phototransistors Tr 2 can be substantially isolated electrically from each other. When signal beam 200 are simultaneously injected into the phototransistors Tr 2, the laser 1 is allowed to oscillate. When either one of the beam 200 is absent, no oscillation occurs. In this way, it is possible to form an optical integrated AND circuit which operates at low power consumption. An OR circuit can also be formed by changing the size of the beam 200 in this optical logic circuit. When the width of the groove 116 is enlarged, the optical output-electric current characteristics or the like of the laser 1 have hysteresis. Therefore, the optical logic circuit can operate as a memory circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical logic circuit that performs arithmetic functions for optical information processing.

(Prior art and its problems) In recent years, the development of computers that process vast amounts of information has been progressing, and the technology used for this can be said to be centered around semiconductor electronics, in which the information carrier is electronic. However, since information in the natural world, including that of humans, is mainly recognized through visual perception, it would be desirable to be able to process the recognition and analysis of many phenomena using optical images as they are. In addition, light has environmental resistance that electrons do not have, such as not being affected by surrounding electromagnetic noise, and is considered to be effective in combining with optical communication, which is increasingly being put into practical use. To achieve this, it is necessary to replace wiring with optical fibers and optical waveguides, and to develop optical logic circuits that can perform calculation functions using light. Since the concept of optical logic circuits was invented in the late 1960s, when semiconductor lasers were invented, circuits with various structures have been proposed. Typical of these are those that combine a photodetector and a semiconductor laser, such as Bazov (N,
G.

Mr. BASOV) et al.
and electronic fixtures (RADIOE)
NGINEERING AND ELECTRONIC
PHY-8IC8) Magazine, 1969, Volume 14, No. 14
There is an article written on pages 09-1417. This method uses a method in which signal light is detected by a photodetection element, photoelectrically converted, and then current amplified and injected into a semiconductor laser as a forward or reverse current. By selecting the direction of this current, you can use ``and'' and ``or.''

Logical functions such as "memory" can be realized. In order to further develop this and increase the number of bits, one set of a semiconductor laser and a photodetector element may be treated as one bit, and these may be integrated. However, since an electric circuit for current amplification is inserted between each pixel element for each bit, there is a problem that integration using this method cannot be realized. Therefore, it has been desired to realize an optical logic circuit with a structure that can be integrated with only a semiconductor laser and a photodetector element.

(Objective of the Invention) An object of the present invention is to eliminate such conventional drawbacks and provide an optical logic circuit that can be integrated. .

(Structure of the Invention) The present invention is an integrated light emitting/receiving circuit consisting of a semiconductor laser and a phototransistor, in which a plurality of phototransistors are stacked side by side along a resonator axis direction on a common semiconductor layer of the semiconductor laser. , and is characterized in that the phototransistors are electrically isolated from each other.

(Operation/Principle of the Invention) The present invention solves the problems of the prior art by adopting the above-described configuration. First, a plurality of optical transistors are arranged on a semiconductor laser along the cavity axis direction. The optical transmitter is a photodiode, which is a normal photodetection element, P
Unlike the -IN photodiode, it has a current amplification effect, and as long as it is not used as an individual element, the existence of a dark current of several tens of microamperes can be ignored. Furthermore, even if it has a current amplification function, it does not require an applied voltage of several tens of volts unlike an aberration photodiode, so it becomes possible to stack a phototransistor on a semiconductor laser. A groove or a high resistance layer is formed between the individual phototransistors so that they are electrically isolated from each other. The photocurrent generated by the optical injection of signal light into the phototransistor acts only to increase the gain in the active layer directly below the phototransistor because of the grooves or high resistance layers that separate the individual phototransistors.

Therefore, for example, if we consider the case of two phototransistors,
It is considered as if the active layer was divided into two in the resonator axis direction. Therefore, if we consider that one phototransistor is used for the reset signal and the other phototransistor is used for the set signal, the combination of signal light to the scarce phototransistors can be achieved.
It can have any arithmetic function. When the photocurrents generated by injecting signal light into each phototransistor are IA and IB, with respect to the oscillation current threshold Ith+ of the semiconductor laser, (1) Ia, IB<Ith+
If it satisfies <IA+In, it becomes an "AND" circuit, and if it satisfies [2]I66, <IA, IB, it becomes an "OR" circuit. Regarding the "memory" circuit,
To simplify the explanation, FIG. 1 shows its operating method and characteristics. When a saturable absorber is provided in a part of the active layer,
Semiconductor lasers generally exhibit hysteresis in their optical input/output characteristics and optical output-current characteristics (FIG. 1(a)).

At this time, the oscillation starting current threshold is set to 19 oscillation starting current threshold I-t-h. First Ia-IA<I+hx
<Is I↓) Under conditions that satisfy Is < IA+IB, IB is made to be a periodic signal that returns to zero at regular intervals (FIG. 1(b)). Next, as shown in FIG.
When an inmate acts as a trigger, the on state can be maintained for a certain period of time (FIG. 1(d)).

As described above, the signal light gives a command to the semiconductor laser simply by passing through the optical transistor, and a light-to-light calculation function is configured. Structurally, it is sufficient to simply arrange optical transistors on a semiconductor laser, and there is no need for an electric circuit for current amplification, so that the integration of optical logic circuits can be easily realized.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a perspective view of an embodiment of the invention.

This embodiment is configured such that two optical transistors 2 are arranged above a semiconductor laser 1 along the resonator axis direction.

The manufacturing order is as follows: n-InP buffer layer 101 . Non-doped InGaAsP active layer 10
2. A photoresist is applied onto a DH substrate on which a p-InP cladding layer 103 is successively crystal-grown, and a mesa 104 narrowed by two grooves is fabricated by ordinary photolithography and etching. Next, this wafer was coated with a p-InP first current blocking layer (105°n) using a liquid phase growth method.
- InP second current propagation layer 106. Buried layer 107 of p-InP. Electrical coupling layer 108 with phototransistor 2. n-InP emitter layer 111.

p-InGaAmP space layer 112 e n I n
The crystal growth is completed by sequentially growing the P collector layer 113. Regarding the crystal growth of semiconductor lasers, details can be found in Japanese Patent Application No. 166,666/1983 by Mr. Kitamura et al. Here, the electrical coupling layer 10
8 is a layer using a tunnel junction. Next, in order to reduce the junction capacitance of the phototransistor 2 and further divide it into two, for example, the shape is made cylindrical and the surrounding area is made of n-InP.
Light receiving surface 1 for injecting signal light 200 into the plane of the n-InP collector layer 113 by removing up to the emitter layer 111
14 and a positive electrode 115 around it are formed. After that, in order to increase the electrical resistance between the two phototransistors 20, a groove 116 is provided to separate the resonator axis. The groove 116 was formed by removing the p-InP buried layer 107 by etching. As a result, the optical transistors 2 were almost electrically isolated.

Next, the desired thickness 9 is usually about 100 to 150 μm.
The nP substrate 100 is polished to form a negative electrode 117. The wavelength of the signal light 2000 was set to 1.3 μm, and the composition of the paste layer 112 was set to a wavelength of 1.5 μm. Therefore, the signal light 200 from the optical fiber 118 is injected into the phototransistor 2 after being adjusted to a spot diameter that matches the light receiving surface 114 of the phototransistor 2 using the coupling circuit 119 . If the optical gain of each phototransistor 2 is 1000 and the photoelectric conversion efficiency is 0.7, then
For an optical input of 30 pW of each signal light 200, a current of 21 mA is injected into each of the two semiconductor lasers 1.

The oscillation current of the buried structure semiconductor laser 1 used this time [
Assuming that E is 30 mA, the semiconductor laser 1 was in an oscillating state when 30 μW of signal light 200 was simultaneously injected into the two optical transistors 2. Therefore, if one of the signal lights 200 is missing, oscillation will not occur. It can be seen that the "AND" circuit can be integrated with low power consumption in this way. Regarding this optical logic circuit, the signal light 200
An "OR" circuit that changes the magnitude of is also possible. Also, groove 116 is used for manufacturing this optical logic circuit.
By widening the zero width, it becomes difficult for the photocurrent from the two phototransistors 2 to be injected into the active layer 102 directly under the groove 116.
This allows the grooves 116 to function as saturable absorbers. Therefore, hysteresis is produced in the Kerr current characteristics and optical input/output characteristics of the semiconductor laser 1, so that it can also operate as a "memory" circuit. The semiconductor laser 1 of this embodiment has a mesa 1040 width of 1.5 μm, a cavity length of 150 μm, two cavities divided by grooves 116, each having an axial length of 70 μ′170 itm, and a groove 1040 having a width of 1.5 μm.
The width of the phototransistor 2 is 1011 m, and the wavelength of light oscillated by the photocurrent from the phototransistor 2 is 1.2 μm. Further, the diameter of the light receiving surface 114 of the phototransistor 2 was set to 20 μm. Based on this specification, we were able to realize an optical logic circuit that can be integrated.

It should be noted that since the manner of crystal growth varies greatly depending on the growth method, growth conditions, etc., it goes without saying that appropriate dimensions should be adopted in conjunction with these factors. Furthermore, the dimensions of the light-receiving surface 114 of the phototransistor 2, the dimensions of the positive electrode 115, and the material are not particularly limited. As described above, in the embodiment, I n
P/I nGaAsP-based semiconductor material was used, but Gm
Other semiconductor materials such as AlAm/GaAs may also be used. Further, the wavelength of the signal light 200, the composition of the base layer 112 of the optical transistor 20, and the oscillation wavelength of the semiconductor laser are not particularly limited. Therefore, phototransistor 2
It is also possible to extract the long wavelength signal light 200 as a signal shifted to the short wavelength side by passing the signal light 200 to the short wavelength side. Furthermore, on the premise that this optical logic circuit will be made into a 7-lay or matrix array, a waveguide layer will be formed above or below the active layer 102, and a diffraction grating will be made in that part to create a so-called DBR laser. D.F.B.
FB) It may also be configured like a laser. In this way, it becomes possible to integrate and configure optical switches and other functional elements on the extension of the waveguide layer of the optical logic circuit.

Furthermore, in the above embodiment, the npn type phototransistor 2
Although the electrical coupling between the semiconductor laser 1 and the n-substrate is realized by a tunnel junction, the coupling between the npn-type phototransistor 2 and the like can also be facilitated by changing the substrate itself from an n-type to a p-type. In this case, a normal method may be used in which the emitter layer 111 of the optical transistor 2 is provided on the negative electrode side and the signal light 200 is absorbed by the space layer 112 and collector layer 113. Therefore, the photocurrent generated by the optical injection is amplified and is injected into the semiconductor laser 1 from the collector layer 113 in large quantities. In the above embodiment, two optical transistors 2 are provided on the semiconductor laser 1.
However, the number is not particularly limited. If two or more phototransistors 2 are integrated on the semiconductor laser 1 and the phototransistors can function independently, the intensity of the signal light injected into each transistor 2 will depend on the magnitude of the signal light injected into each transistor 2. It is possible to change the optical output in various ways, and by changing the photocurrent from the phototransistor to either the forward direction or the reverse direction, it can be used to produce not only "and", "or", and "memory" but also "not" and "Nando'.

It becomes possible to expand the function to a "flip-flop" function.

[Brief explanation of the drawing]

FIG. 1 is a detailed operational characteristic diagram for explaining the present invention, and FIG. 2 is a perspective view showing an embodiment of the present invention. In the figure, 1: semiconductor laser, 2: optical transistor, 100-n-InP substrate, 101-n-InP
Buffer layer, 102-InGaA sP active layer, 1
03 ”・P-InP cladding layer, 104-・・Mesa,
105=p-InP first current blocking layer, 106...
・n-InP second current blocking layer, 107-n-In
P buried layer, 108--electrical coupling layer, 111=
n-InP emitter layer, 112-p-InGaA@P
Base layer, 113 = n-I nP: Lucta layer, 11
4... Light receiving surface, 115... Positive electrode, 116...
--Groove, 117--Negative electrode, 118--Optical fiber, 119--Coupling circuit, 200--Signal light, respectively.

Claims (1)

[Claims] A light-emitting/light-receiving integrated circuit comprising a semiconductor laser and a phototransistor, wherein a plurality of the phototransistors are stacked in line along a resonator axis direction on a common semiconductor layer of the semiconductor laser, and the phototransistors are mutually stacked. An optical logic circuit characterized in that the circuit is electrically interrupted.