JPH0667244A - Semiconductor optical differentiator - Google Patents

Abstract

PURPOSE:To provide the optical differentiator which has a simpler constitution than a conventional example and a smaller power consumption and makes a fast time response. CONSTITUTION:Two heterojunction pin type diodes D1 and D2 which have intrinsic semiconductor (i) layers 13 and 23 in multi-quantum well structure or superlattice structure and vary in light absorptivity in a wavelength range nearby a light absorption end by varying a reverse bias voltage are connected in series, and a variable voltage source 10 for reverse bias voltage application is connected across both the series-connected end; while a specific quantity of bias light Pin 1 is applied to one pin type diode D1, signal light pin 2 to optically be differentiated is made incident on the other pin diode D2 and then the differentiated light Pout 2 generated by optically differentiating the signal light Pin 2 is obtained from the pin type diode D2 on which the signal light Pin 2 is made incident.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical differentiator using a semiconductor optical bistable element.

[0002]

2. Description of the Related Art FIG. 3 shows the configuration of a conventional electro-optical differentiator. As shown in FIG. 3, conventionally, an incident optical pulse is once converted into an electric signal by a photoelectric conversion element 30 such as a photodiode and then electrically differentiated by an electric differentiator 31. Next, an electric signal output from the electric differentiator 31 is driven through an amplifier 32 to another light emitting element 33 (or an optical modulator) such as a laser diode, whereby an optical differentiated output can be obtained.

[0003]

The above-mentioned conventional example has the following drawbacks and problems. (A) The number of electric circuit components is increased, and the device scale is relatively large. (B) Power consumption is relatively high. (C) The light emitting element 33 after being processed by the electric circuits 31 and 32
Alternatively, since the optical modulator is driven, the delay time until obtaining the optical differential output is large and the time response is slow.

An object of the present invention is to solve the above problems and to provide an optical differentiator having a simpler structure, lower power consumption, and faster time response than the conventional example.

[0005]

A semiconductor optical differentiator according to a first aspect of the present invention has an intrinsic semiconductor i-layer having a multi-quantum well structure or a superlattice structure, respectively. Two heterojunction pin type diodes whose light absorptance changes in the wavelength region near the absorption end are connected in series, and a variable voltage source for applying a reverse bias voltage is connected to both ends of the series connection, and one pin is connected. A predetermined amount of bias light is applied to the diode, while the signal light to be optically differentiated is incident on the other pin diode to differentiate the signal light from the pin diode on which the signal light is incident. It is characterized by getting light.

A semiconductor optical differentiator according to a second aspect of the present invention has an intrinsic semiconductor i layer having a multiple quantum well structure or a superlattice structure, and a wavelength near the light absorption edge by changing the reverse bias voltage. A constant constant current source supplies a predetermined constant current to a heterojunction pin type diode whose light absorption rate changes in a region, and the signal light to be optically differentiated is made incident on the pin type diode, so that the pin that made the signal light incident is detected.
The differential light obtained by optically differentiating the signal light from the type diode is obtained.

[0007]

In the semiconductor optical differentiator according to claim 1, an intrinsic semiconductor i having a multiple quantum well structure or a superlattice structure, respectively.
In each diode, which has a layer and whose light absorption rate changes in the wavelength region near the light absorption edge by changing the reverse bias voltage, a relatively high transmissive state and a relatively low transmissive state that can be alternately switched are used. Two static optical bistable behaviors are obtained. In the present invention, first, the other diode, which was in a relatively high light transmission state, self-switches by an optical carrier dynamically generated inside itself by an optical pulse incident on the diode itself, and a relatively high light is emitted. The optical differential operation is carried out by utilizing a new dynamic process in which an optical pulse passes through the other diode only during the transition time from the transmission state to the lower light transmission state.

That is, when the bias light always enters one of the diodes, the variable voltage source and the one diode act as a pseudo constant current source, and a constant current is supplied to the other diode. Become. The other diode receives the signal light that is its optical input (Pi
n2 = 0), the applied voltage is always maintained at a relatively high transmission state near point D in FIG. When the signal light is incident in the form of a light incident pulse with this relatively high transmission state as the initial state, the load curve of FIG. 2 sequentially transits to the characteristics 102, 103, 104 due to the rise of the light intensity of the light incident pulse, When the voltage exceeds 104, the voltage applied to the other diode transits to point B. As a result, the other diode switches to a relatively low transmission state, and holds this state until the optical pulse of the signal light falls thereafter. Therefore, while the light incident pulse of the signal light is rising, the other diode, which has a relatively high transmission state, passes through the rising portion of the light incident pulse and exits, so that the differential light is output as the output light of the other diode. Will be obtained.

Further, as in the semiconductor optical differentiator according to claim 2, by replacing the one pin type diode according to claim 1 with the variable voltage source, a constant current source is connected. Get the action.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an embodiment of the present invention, in which two pis each having an intrinsic semiconductor i-layer having a multiple quantum well structure are provided.
It is sectional drawing and the circuit diagram which show the structure of the semiconductor optical differentiator using n-type diode D1, D2.

As shown in FIG. 1, the optical differentiator of this embodiment has intrinsic semiconductor i-layers each having a multiple quantum well structure and changes the reverse bias voltage to absorb light in the wavelength region near the light absorption edge. Two heterojunction pin type diodes D1 and D2 whose rate changes and photocurrent changes accordingly are connected in series, and a variable voltage source 10 for applying a reverse bias voltage is connected to both ends of the series connection. The pin
A predetermined amount of bias light is applied to the diode D1, while the signal light to be optically differentiated is incident on the other pin diode D2 to generate differentiated light obtained by optically differentiating the signal light from the pin diode D2. It is characterized by getting.

The pin type diode D1 used in this embodiment has a p-type diode D1 between electrodes 11 and 15 as shown in FIG.
Type semiconductor clad layer 12, an intrinsic semiconductor i layer 13 having a multiple quantum well layer structure, and an n-type semiconductor substrate 14 are sandwiched, and the light absorptance is changed by changing the reverse bias voltage. This has the characteristic that the photocurrent changes. The other pin type diode D
Similarly to the diode D1, 2 is also formed by sandwiching a p-type semiconductor clad layer 22, an intrinsic semiconductor i layer 23 having a multiple quantum well layer structure, and an n-type semiconductor substrate 24 between electrodes 21 and 25. It has light absorption and photocurrent characteristics with respect to a reverse bias voltage similar to the diode D1.

The electrodes 15 and 21 are connected, the electrode 11 is connected to the negative electrode of the variable voltage source 10, and the electrode 25 is connected to the positive electrode of the variable voltage source 10.

Each of the diodes D1 and D2 has a light absorption characteristic as shown in FIG. 2 due to the absorption rate modulation effect by the electric field in the intrinsic semiconductor i layers 13 and 23. Here, FIG.
FIG. 4 is a graph showing characteristics of a photocurrent Ip (or a light absorption rate) with respect to a reverse bias voltage, for explaining the operation of the semiconductor optical differentiator of FIG. 1. In addition, each diode D1, D2
The light absorptivity of is almost inversely proportional to the light transmittance.

As is apparent from FIG. 2, each diode D
By increasing the reverse bias voltage applied to 1 and D2, the photocurrent Ip or the light absorption rate once increases in the wavelength region near the light absorption edge, and then decreases. Here, the maximum value of the photocurrent Ip or the light absorptance shows a characteristic of increasing by increasing the optical power Pin2 of the signal light in the order of P1 to P5, for example.

The diodes D1 and D2 having such a configuration have the optical power Pin1 of the bias light incident on the p-type semiconductor cladding layer 12 of the diode D1 as shown in FIG.
The optical bistable operation described below is performed due to the difference in power between the signal light and the optical power Pin2 of the signal light incident on the p-type semiconductor cladding layer 22 of the diode D2.

In the wavelength region where the light absorption decreases due to the increase of the reverse bias voltage, when bias light having a constant wavelength and a constant intensity is incident on the diode D1, the diode D1 is low because the charge carriers generated by the light absorption exist. The diode D2 enters the impedance state, and the reverse bias voltage is applied to the diode D2 almost as it is, while the diode D2 enters the high impedance state. At this time, due to the so-called known quantum Stark effect, the diode D1 is in a state where the light absorption is relatively larger than that of the diode D2, and the diode D2 is in a state where the light absorption is relatively smaller than that of the diode D1.

Next, when signal light is incident on the diode D2 and its intensity is increased, the photocurrent flowing through the diode D2 increases as shown by the solid line in FIG. 2, and the current flowing through the circuit is the load curve of the diode D1. The current value is determined by the intersection with (dotted line in FIG. 2). When the optical power Pin2 of the signal light with which the diode D2 is irradiated is smaller than the optical power Pin1 of the bias light with which the diode D1 is irradiated, the application state of the reverse bias voltage in the diodes D1 and D2 is the same as that described above. Become. That is, the diode D1 is in a low impedance state, while the diode D2 is in a high impedance state.

Further, when Pin2> Pin1 and the optical power Pin2 of the signal light exceeds a predetermined threshold Pth, there is an intersection A of the load curve where the diode D2 can exist in a high impedance state. Since it disappears, the diode D2 is in a low impedance state, and as a result of switching the applied bias voltage value, the diode D1 switches from the low impedance state to the high impedance state B. At this time, the diode D1
Has a small light absorption and therefore a large light transmission, that is, a large light absorption rate. Therefore, due to the increase in the optical power Pin2 of the signal light, the optical switching operation of the transmitted light of the bias light (its optical power Pout1) emitted from the diode D1 from ON to OFF can be obtained.

On the other hand, when the optical power Pin2 of the signal light is reduced below the predetermined threshold value Pth, the low impedance state of the diode D2 is maintained until the intersection C with the load curve, so that the diode D1 is in the ON state, That is, the high impedance state is maintained. However, when the optical power Pin2 of the signal light decreases and exceeds the intersection C with the load curve, there is no intersection with the load curve shown by the dotted line in FIG. 2 below C, so the optical switching operation to the initial state,
That is, the transition operation from C to D occurs.

As described above, optical bistable operation can be obtained in the circuit device. The above-described bistable operation is a static operation, in which the magnitude of the optical power Pin1 and the magnitude of the optical power Pin2 are alternately entered to transition between the two states, thereby switching the light.

In this embodiment of the present invention, first,
The diode D2, which has been in a relatively high light transmission state, self-switches by an optical carrier that is dynamically generated inside itself by the light pulse incident on the diode D2 itself, so that the relatively high light transmission state becomes a lower light transmission state. The optical differential operation is performed by utilizing a new dynamic process in which the optical pulse passes through the diode D2 only during the transition time to.

That is, when the bias light is always incident on the diode D1, the variable voltage source 10 and the diode D1 operate as a pseudo constant current source, and a constant current is supplied to the diode D2. When there is no signal light which is the optical input of the diode D2 (Pin2 =
0), the applied voltage is always maintained in a relatively high transmission state near point D in FIG. When the signal light is incident in the form of a light incident pulse with this relatively high transmission state as the initial state, the load curve of FIG. 2 sequentially changes to the characteristics 102, 103, 104 due to the rise of the light intensity of the light incident pulse.
When the characteristic 104 is exceeded, the applied voltage of the diode D2 is B
Transition to a point. As a result, the diode D2 switches to a relatively low transmission state, and holds this state until the optical pulse of the signal light falls thereafter. Therefore, while the light incident pulse of the signal light is rising, the diode D2 having a relatively high transmission state is emitted with the rising portion of the light incident pulse passing through, and thus the light of the optical power Pout2 is output as the output light of the diode D2. Differentiated light will be obtained.

As described above, according to the semiconductor optical differentiator of this embodiment, optical differentiation is possible with a simple structure, and the load power curve is easily changed by changing the optical power Pin1 of the bias light. Since it can be adjusted, it has a unique advantage that it can be differentiated for a wide range of incident light. Further, it has the following advantages as compared with the conventional example. (A) The structure is simple as compared with the conventional example. (B) Since only the reverse bias voltage applied to one pin type diode D1 is applied, the power consumption is smaller than that of the conventional example. (C) Since the signal light only passes through one pin-type diode D2 and does not pass through a plurality of circuits as in the conventional example, the time response is faster than in the conventional example.

In the above embodiments, each diode D
The intrinsic semiconductor i layers 13 and 23 in 1 and D2 have a multiple quantum well structure, but the present invention is not limited to this, and a similar effect can be obtained even if they have a superlattice structure.

Although the variable voltage source 10 and the diode D1 are used in the above embodiments, a constant current source that constantly supplies a predetermined current to the diode D2 may be used instead of them.

[0028]

As described in detail above, according to the present invention, an intrinsic semiconductor i having a multi-quantum well structure or a superlattice structure, respectively.
Two hetero-junction pin type diodes, each having a layer and having a light absorption coefficient in the wavelength region near the light absorption edge that is changed by changing the reverse bias voltage, are connected in series, and the reverse bias voltage is applied to both ends of the series connection. A variable voltage source for application is connected, and a predetermined amount of bias light is applied to one pin-type diode, while the signal light to be optically differentiated is made incident on the other pin-type diode. A wavelength near the light absorption edge is obtained by obtaining differentiated light obtained by optically differentiating the signal light from the incident pin type diode or by changing the reverse bias voltage by having an intrinsic semiconductor i layer having a multiple quantum well structure or a superlattice structure. A signal to be optically differentiated to the pin diode by supplying a predetermined constant current to the heterojunction pin diode whose light absorption rate changes in a region by a constant current source. By entering to obtain a light obtained by differentiating the differential optical signal light from the pin-type diode which is incident the signal light.

Therefore, the semiconductor optical differentiator according to the present invention is
It has the following unique advantages. (A) The structure is simple as compared with the conventional example. (B) Since only the reverse bias voltage or the constant current applied to one of the pin type diodes is supplied, the power consumption is smaller than that of the conventional example. (C) Since the signal light only passes through one pin-type diode and does not pass through a plurality of circuits as in the conventional example, the time response is faster than in the conventional example.

[Brief description of drawings]

FIG. 1 is a cross-sectional view and a circuit diagram showing a configuration of a semiconductor optical differentiator using two pin type diodes D1 and D2 each having an intrinsic semiconductor i layer having a multiple quantum well structure, which is an embodiment of the present invention. Is.

FIG. 2 is a graph showing a photocurrent Ip with respect to a reverse bias voltage, for explaining the operation of the semiconductor optical differentiator of FIG.

FIG. 3 is a block diagram showing a configuration of a conventional electrical differentiator.

[Explanation of symbols]

 D1, D2 ... Pin type diode, 10 ... Variable voltage source, 11, 15, 21, 25 ... Electrode, 12, 22 ... P type semiconductor clad layer, 13, 23 ... Intrinsic semiconductor i layer of multiple quantum well structure, 14, 24 ... N-type semiconductor substrate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Kawashima, No. 5 Sanhiraya, Inui, Osamu, Seika-cho, Soraku-gun, Kyoto Pref., ATR Optical & Radio Communications Laboratory, Inc. (72) Kenzo Fujiwara Kitakyushu, Fukuoka 1-1, Sensui-cho, Tobata-ku, Department of Electrical Engineering, Faculty of Engineering, Kyushu Institute of Technology

Claims (2)

[Claims] 1. Two heterojunction pins, each of which has an intrinsic semiconductor i-layer having a multiple quantum well structure or a superlattice structure and whose light absorption rate changes in the wavelength region near the light absorption edge by changing the reverse bias voltage. Type diodes are connected in series, a variable voltage source for applying a reverse bias voltage is connected to both ends of the series type diode, and one pin type diode is applied with a predetermined amount of bias light, while the other pin is connected.
A semiconductor optical differentiator, characterized in that, by injecting a signal light to be optically differentiated into a type diode, a differential light obtained by optically differentiating the signal light is obtained from a pin type diode into which the signal light is incident. 2. A heterojunction pin-type diode having an intrinsic semiconductor i-layer having a multi-quantum well structure or a superlattice structure, in which the light absorption rate changes in the wavelength region near the light absorption edge by changing the reverse bias voltage. A predetermined constant current is supplied from a current source, and the signal light to be optically differentiated is made incident on the pin type diode, so that the signal light is incident on the pi.
A semiconductor optical differentiator which obtains a differentiated light by optically differentiating a signal light from an n-type diode.