JPH01134434A - Optical bistable element - Google Patents

Abstract

PURPOSE:To put a superlattice p-i-n photodiode (SEED) in faster operation by using a circuit or element which is constituted by using a DC current source as its power source, connecting the SEED and a superconductor thereto, and connecting a resistance in series with the superconductor. CONSTITUTION:This element consists of the SEED1 as the superlattice p-i-n photodiode with GaAs/GaAlAs superlattice structure in an (i) layer, Y-Ba-Cu-O superconductor 2, DC stabilized current source 3, and resistance 4. Therefore, the resistance and serial resistance in the normal conduction state of the superconductor are reduced. Consequently, the SEED1 is put in fast operation even with a low light input and the arithmetic speed and switching speed are increased even with low light input.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to the fields of optical communications and optical computers.

In particular, the present invention relates to optical bistable elements suitable for optical switches and optical logic operations.

[Conventional technology]

For information on optical bistable operation of photodiodes using conventional superlattices, see Applied Physics.

Letter 45. (1984) pp. 13-15 (A
ppl, Phys, Lett, 45t PP,
13 15).

[Problem that the invention seeks to solve]

The above conventional technology is self-electro-op.
tic-effect-device (hereinafter 5EE
Abbreviated as D. ) is named. The operating speed of the 5EED is determined by the RC time constant, and in order to operate with weak incident light, it is necessary to increase R, which poses a problem that the operating speed becomes slow.

An object of the present invention is to operate the 5EED at higher speed.

[Means for solving problems]

The above purpose uses a DC current source as a power source, connects a superlattice type pin photodiode (SEED) and a superconductor in parallel, and then connects a resistor in series with the superconductor. This can be achieved by using circuits or elements that

The feature of the present invention is that the i-layer has a superlattice structure.
-N photodiode and superconductor are connected in parallel, and a DC constant current power source is connected in series.

This is an optical bistable device in which a photodiode is reverse biased. It is preferable to connect a resistor in series to the superconductor, it is preferable to provide a temperature controller to the superconductor, and it is preferable to separately connect a circuit including a constant current power supply with a variable current value to the superconductor. preferable.

In order to spread the depletion layer in the iW of 5EED, it is necessary to apply a reverse bias of a certain voltage Vreach, for example, 2V or more. If the voltage is lower than this, the operating speed will be very slow. ■In order to satisfy r≧V reach, it is recommended to insert a resistor r in series with the superconductor. The resistance value is preferably as small as possible within the range of IBr≧V reach.

When designing a device, a desired value of vn can be obtained by selecting the superconducting material and its volume. IC depends on the critical current density Jc and cross-sectional area of the superconductor, so you can adjust either of them. °J0 changes depending on the temperature, so if you control the temperature of the superconductor with a temperature controller, you can choose Jc well. Can be done. Temperature control is also effective for stable operation. Furthermore, in order to select the bistable operating point, it is sufficient to flow a direct current through the superconductor in a subcircuit.By applying a current bias, the Ig that causes the phase transition can be varied; By adjusting the current value, the bistable operating point can be selected.

[Effect]

■ Constant current source output. , If the photocurrent of 5EED is IP, then the current I8 flowing through the superconductor is I, =IO-IP.When the intensity of light incident on 5EED is weak and Tp is small, ■8 becomes large, and Is>Ic( Ic is the critical current of the superconductor), and in this state the superconductor is in a normal conduction state and generates a voltage vn at both ends. If a resistor r is connected in series with the superconductor, the reverse bias voltage of the 5EED becomes v r = v n + I B r. When the intensity of the incident light is increased, (2) increases and I decreases. I8≦I
At C, the superconductor transitions to a superconducting state, the voltage drop disappears, and the reverse bias voltage of the 5EED becomes vr=Igr and rapidly decreases. As vr decreases, photoelectric conversion efficiency increases, so IP increases and I8 decreases. Furthermore vl
The lower the 5EED, the lower the transmittance of the 5EED. Because of this positive feedback, the transmitted light intensity exhibits bistable property with respect to the incident light intensity.

A superconductor's resistance value changes greatly due to a small change in current,
Large voltage changes can be obtained. Therefore, the resistance and r of the superconductor in the normal conduction state can be reduced. Therefore, the RC time constant becomes smaller and the operating speed becomes faster.

〔Example〕

Embodiment 1 Hereinafter, one embodiment of the present invention will be explained with reference to FIG. p-1- with GaAs/GaAQAs superlattice structure in i-layer
5EED1, which is an n photodiode, and Y-
It consists of a Ba-Cu-0 based superconductor 2, a DC constant current source 3, and a resistor 4.

5EED l is a known method (Applied Physics Letters, 44 (1984) pp, 16-pp, 18
It was produced using the method disclosed in ).

Superconductors have a critical temperature of 87°C. The superconductor was placed in a taliostat using liquid nitrogen, and the temperature was set to 80°C using a temperature controller. The resistance 4 was 15Ω, and the constant current source output was 150mA.

The resistance value when a superconductor transitions to a normal conduction state is approximately 35
It was 0. Figure 2 shows the characteristics of the incident light power Pin and the transmitted light power Pout, where the incident light power Pin=4
Good optical bistability can be obtained by selecting 0 μW as the operating point. The switching characteristics are approximately 1n as shown in Figure 3.
get s. In the conventional method, it takes about 20 μs under this optical input condition.
In short, a semiconductor laser is used as a light source, and a p-1-n photodiode is used as a light receiver.

Example 2 In a system similar to Example 1, but with the temperature set at 85K, the result is as shown in FIG. 4. In this way, it is possible to change the operating point depending on the temperature.

Example 3゜ Another embodiment of the present invention will be described with reference to FIG.

Except that a DC constant current source 5 was added to the superconductor.

Same as Figure 1. The current value of DC constant current source 5 is 5 μA.
Figure 6 shows the characteristics when
It can be seen that the optical bistable operating point has shifted to the low input side.

By appropriately selecting the current value in this manner, the bistable operating point can be set at a desired position. Furthermore, when the operating point drifts, such as when temperature control is not performed, controlling this current value has the effect of stabilizing the operating point.

The superconducting materials used in the above examples include an oxygen-deficient perovskite structure whose general formula is (REx-x2Mxa)Cu03-)', and K 2 NiF 4
Type structures are available. Here, RE is La, Y,
Sr, Wb, Lu, Tm, Dy.

Sc, Ce, Pr, Nd, Sm, Eu, Gd.

1M represents elements such as Tb, l-1o, Er1, etc. or any combination thereof; 1M represents elements such as Ba, Sr, Ca, etc., or any combination thereof;

〔Effect of the invention〕

According to the present invention, since SET':D can be operated at high speed even with a low optical input, there is an effect that the calculation speed and switching speed are increased even with a low optical input. Furthermore, since the operating point can be changed depending on temperature or bias current without changing the operating speed, the range of application to the system is expanded.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG.
A hysteresis characteristic curve diagram of the incident optical power and transmitted optical power of the element with the configuration shown in the figure at a temperature of 80 degrees, Figure 3 shows its operating characteristics, and Figure 4 shows the element with the configuration shown in Figure 1 at an incident temperature of 86 degrees. FIG. 5 is a circuit configuration diagram of an embodiment of the present invention, and FIG. 6 is a hysteresis characteristic curve of the optical power and transmitted light power. 1...5EED, 2...Superconductor, 3...DC constant current source, 4...Resistor, 5...DC constant current source. ′! J20 Input dimension 9 quantity FcrL (μW) Fig. 3 leaf 41 Input dimension 9] 1 and in (μW) No.

Claims (1)

[Claims] 1. A pin photodiode having a superlattice structure in the i-layer and a superconductor are connected in parallel, a DC constant current power source is connected in series, and the photodiode is reverse biased. An optical bistable element characterized by multiplication. 2. The optical bistable device according to claim 1, characterized in that a resistor is connected in series with the superconductor. 3. The optical bistable device according to claim 1 or 2, characterized in that the superconductor is provided with a temperature controller. 4. The optical bistable device according to any one of claims 1 to 3, characterized in that a circuit including a constant current power supply with a variable current value is separately connected to the superconductor.