JPH0560277B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an optical memory using a bistable semiconductor laser that exhibits hysteresis characteristics between the injection current and the amount of emitted light, and in particular to an optical memory that can electrically monitor the optical memory output. Regarding.

(Prior art and its problems) Optical communication that uses optical fibers as transmission paths has the advantages of being able to transmit large amounts of information because the optical fibers have a wide band, and that the optical fibers are not subject to induced noise. Therefore, it is expected that it will be widely used in the future. In this optical communication, the information to be sent is converted from an electrical signal to an optical signal by a transmitting device, transmitted through an optical fiber, and then converted back into an electrical signal by a receiving device. In this case, the optical signal is nothing more than a transmission means that transmits the signal from one side to the other by taking advantage of the fact that the transmission loss of the optical fiber of the transmission line is extremely small, and it is used for signal processing such as logical operations and optical information storage. Optical signals have yet to play an active role. If optical information could be stored and the storage results could be obtained as optical signals, it would be extremely effective for diversifying the functions of optical communication systems.

As described in Japanese Patent Application No. 57-216708 ``Time Division Optical Exchanger'', this optical memory can be achieved by providing a saturable absorbing portion, for example, a portion into which no current is injected, in a part of the resonator of the semiconductor laser. By giving a hysteresis characteristic to the injection current vs. output characteristic and setting the injection current within the hysteresis (hereinafter, the value of this injection current is referred to as a bias current), one of the two values of light intensity is memorized. Also known are devices that can be set by injecting an optical signal and reset by reducing the injected current.

In such optical memories, it is often necessary to monitor the contents of stored optical information.

Generally, in a semiconductor laser, two optical outputs are obtained from two semi-transparent mirror surfaces of a Fabry-Perot resonator. Therefore, in a transmitter of an optical fiber transmission device, an optical signal obtained from one semi-transparent mirror surface of a semiconductor laser is sent out to an optical fiber transmission line.
By optical-to-electrical conversion of the optical signal obtained from the other semi-transparent mirror surface, the optical signal sent to the optical fiber transmission line can be monitored.

However, in an optical memory using a bistable semiconductor laser, optical information is written by inputting an optical signal into one semi-transparent mirror surface of a Fabry-Perot resonator, and the output light obtained from the other semi-transparent mirror is used to write the optical information into the optical memory. Use as memory information. Therefore, in order to obtain the optical information stored in the optical memory as an electrical signal, for example, a semi-transparent mirror is provided in the optical path of the emitted light obtained from the other semi-transparent mirror surface of the Fabry-Perot resonator, and a part of this emitted light is converted into an optical signal.・There was a need for electrical conversion.

In this way, in order to monitor optical information stored in an optical memory using a bistable semiconductor laser using conventional technology, new optical and electronic components such as a semi-transparent mirror and an optical-to-electrical conversion circuit are required. In addition, since a semi-transparent mirror is inserted into the optical path of the emitted light, optical loss increases.

This point will be explained in more detail below with reference to FIG. 4.

FIG. 4 is a diagram showing an example of an optical memory monitor circuit according to the prior art.

An injection current ib is supplied to the positive electrodes 100, 101 and 102 of the bistable semiconductor laser 400 shown in FIG. Binary optical information is stored in accordance with the optical signal Pin, and the optical information thus stored is read out as light Pout from the other end of the active layer 103. In this way, in the optical memory using the bistable semiconductor laser 400 shown in FIG. 4, a writing optical signal is incident on one end 106 of the active layer 103, and the light emitted from the other end 107 of the active layer 103 is used for storage in the optical memory. Use as information. Therefore, to monitor the optical information stored in the bistable semiconductor laser 400, as shown in FIG.
2, the output light Pout is branched into a reading optical signal _P1 and a monitoring optical signal _P2 , and this monitoring optical signal _P2 is converted into an electrical signal by an optical to electrical conversion circuit 403. It is done by

However, the optical memory monitor circuit shown in FIG.
Since the semi-transparent mirror 402 is inserted into the optical path of the Pin, the optical loss increases.

(Objective of the Invention) An object of the present invention is to provide an optical memory monitor circuit that does not cause loss to emitted light, does not require optical components such as a semi-transparent mirror, an optical-electrical conversion circuit, or electronic components, and has a simple circuit configuration. There is a particular thing.

(Structure of the Invention) According to the present invention, a bistable semiconductor laser having a saturable absorption region in an active layer, and a constant electrode having one end connected to a positive electrode and the other end connected to a negative electrode of the bistable semiconductor laser, respectively, have a saturable absorption region in an active layer. and a current source, further comprising means for comparing the voltage between the positive electrode and the negative electrode of the bistable semiconductor laser with a predetermined voltage. An optical memory monitor circuit is obtained.

(Detailed Description of Configuration) Next, the present invention will be described with reference to the drawings.

FIG. 2 is a sectional view showing a specific example of a bistable semiconductor laser used in the present invention. The structure is almost the same as a commonly used current injection type semiconductor laser,
For example, it is a laser with a double heterojunction structure made of GaAlAs/GaAs or InGaAsP/InP.
However, the electrodes are not uniform, and the positive electrode is divided into three parts, the first positive electrode 100, the second positive electrode 101, and the third positive electrode 102, so that a current flows inside the active layer 103. uninjected portion 104 of
This is different from normal semiconductor lasers in that there is a Since the current non-injection region 104 functions as a saturable absorber, the bistable semiconductor laser shown in FIG. 2 can have a hysteresis characteristic in the injection current vs. optical output characteristic. Note that instead of making the electrode non-uniform, similar bistable characteristics can be provided by providing non-uniformity in the part of the active layer that is the light-emitting region and providing a saturable absorption region in a portion. In these bistable semiconductor lasers, by appropriately selecting the injection current i, bistable characteristics can also be obtained in the characteristics of the output light Pout with respect to the externally injected light Pin. Details of such bistable semiconductor lasers can be found in the literature Electronics Letter Vol. 17, page 741 and in 1982.
This is stated in the Proceedings of the National Conference of the Optical and Radio Division of the Institute of Electronics and Communication Engineers (Volume 2), No. 272.

Furthermore, in the bistable semiconductor laser shown in FIG. 2, the negative electrode 105 is connected to the ground.
Optical information is written by inputting an optical signal Pin into one end 106 of the active layer 103, and the emitted light obtained from the other end 107 is used as information stored in the optical memory.

3a, b, and c are diagrams for explaining the operation of the bistable semiconductor laser shown in FIG. 2. FIG. FIG. 3a is a diagram showing the relationship between the injection current i and the output light amount Pout when the incident light amount Pin=0. In other words, when the injection current i is increased from a value of i ₁ or less, i
The output light amount Pout suddenly increases when = i ₃ , and conversely, when the injection current i is decreased from a value of i ₄ or more, the output light amount Pout shows a hysteresis characteristic such that it suddenly decreases when i = i ₂ . At i=i _b , the output light amount P ₀ and
P ₁ has two stable points A and B. FIG. 3b is a diagram showing the relationship between the amount of incident light Pin and the amount of output light Pout when the injection current i=i _b in FIG. 3a. In other words, if the input light amount Pin is increased from 0 when the output light amount Pout=P ₀ is at the first stable point A, the output light amount Pout increases rapidly at Pin=P ₁ ', and thereafter the incident light amount Pin=P ₂ ' When the output light amount Pout is decreased from
=P Move to the second stable point B of ₁ . Points A and B in Figure 3b are points A and B in Figure 3a, respectively.
represents the same point.

When the injected current i is i _b and the incident light Pin is 0, the bistable semiconductor laser moves to one of the two stable points A and B in Figure 3 a and b according to the previously written data. position and maintain the output light amount P ₀ or P ₁ . In Fig. 3a, when the bistable semiconductor laser maintains one stable point B (output light amount P ₁ ) and the injection current i is once set to a value below i ₁ and returned to i _b again, the output light amount Pout becomes B→ It changes in the order of D→A, and thereafter holds the other stable point A (output light amount P ₀ ). That is, the bistable semiconductor laser is reset. Further, in Fig. 3b, when the bistable semiconductor laser maintains the stable point A (output light amount P ₀ ) and the incident light amount is once set to a value of P ₂ ' or more and then returned to 0, the output light amount Pout changes from A→E→ B, and thereafter maintains a stable point B (output light amount P ₁ ). That is, the bistable semiconductor laser is set.

In this manner, the bistable semiconductor laser shown in FIG. 2 can function as an optical memory that can be set by injecting light and reset by reducing the injected current.

FIG. 3c is a diagram showing the relationship between the injection current i and the voltage V of the positive electrodes 100, 101, and 102 when the incident light amount Pin=0. In the bistable semiconductor laser shown in Fig. 2, when the injection current i is increased from a value of i ₁ or less, the voltage V increases along the path H→F→I, and conversely, the injection current i is increased to a value of i ₄ or more. When the voltage V is decreased from 0 to 1, the voltage V exhibits hysteresis such that it decreases along the path I→G→H. Therefore, if the injection current i = i _b , the bistable semiconductor laser shown in Fig. 2 will have a positive electrode voltage SO when it is at the stable point A in Figs. Each shows a positive electrode voltage V ₁ when at point B. Therefore, by comparing the positive electrode voltage with Vth, which is an intermediate voltage between the voltages V ₀ and V ₁ , the optical memory output can be monitored.

(Example) FIG. 1 is a diagram showing an example of the present invention. 1st
In the figures, the same numbers as in Figure 4 are shown in Figure 4.
The same components as in the figure are shown.

The embodiment of the invention shown in FIG. 1 utilizes the characteristics of bistable semiconductor laser 400 shown in FIG. 3c. That is, according to FIG. 3c, the positive electrodes 100, 10 of the bistable semiconductor laser 400 shown in FIG.
1 and 102 are applied to the bistable semiconductor laser 40.
When 0 is at stable point A in Figure 3 a, b, V ₀ ,
When at stable point B, each shows V ₁ . The comparator 110 shown in FIG.
and the voltage of 102 is the electromotive force of the reference voltage source 111.
By comparing with Vth, it is determined whether the bistable semiconductor laser 400 is at the stable point A or B shown in FIG. 3a or b.
The electromotive force Vth has the voltages V ₀ and V ₁ shown in Figure 3c.
A value between is chosen.

In this way, in the embodiment of the present invention shown in Figure 1, it is possible to monitor the optical memory using only the comparator, without requiring any optical components such as a semi-transparent mirror, a photo-electrical conversion circuit, or electronic components, and to monitor the output light Pout. Since there is no need to branch and use it, an amount of output light with little optical loss can be obtained.

In the embodiment described above, the parameters of each part are, for example, as shown in FIGS. 3a to 3c.
When a bistable semiconductor laser is operated under the following conditions: ib = 35mA, P ₀ OmW, P ₁ = 2.5mW, V ₀ ≒
1.22V, V ₁ ≒ 1.28V, so it is sufficient to set Vth = 1.25V.

(Effects of the Invention) As described above, according to the present invention, there is no loss in the emitted light, there is no need for optical components such as a semi-transparent mirror, an optical/electrical conversion circuit, or electronic components, and the circuit structure is simple. An optical memory monitor circuit is obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a cross-sectional view of a bistable semiconductor laser used in the present invention, and FIG.
The figure is a diagram for explaining the operation of the bistable semiconductor laser shown in Figure 2, and Figure 3a shows the incident light amount Pin.
Figure 3b is a diagram showing the relationship between the injected current i and the output light amount Pout when the injection voltage is 1 = 0; FIG. c shows the relationship between the injection current i and the voltage V of the positive electrode when the amount of incident light Pin=0. FIG. 4 shows an example of an optical memory monitor circuit according to the prior art. In the figure, 110... Comparator, 111... Reference voltage source, 400... Bistable semiconductor laser, 40
1...constant current source, 402...semi-transparent mirror, 403...
Optical and electrical conversion circuits are shown respectively.

Claims (1)

[Claims] 1 Consisting of a bistable semiconductor laser having a saturable absorption region in its active layer, and a constant current source connected at one end to the positive electrode and the other end to the negative electrode of the bistable semiconductor laser, respectively. An optical memory further comprising means for comparing the voltage between the positive electrode and the negative electrode of the bistable semiconductor laser with a predetermined voltage.