JPH0666510B2 - Optical memory writing method - Google Patents

Description

The present invention relates to a writing system for an optical memory using a bistable semiconductor laser exhibiting a hysteresis characteristic between an injection current and an emitted light quantity.

(Prior Art) Conventionally, as a device for performing a logical operation of an electric signal at a high speed, a current mode logic has been known with a current switch as a basic block, and in recent years, an ultra-high speed using a GaAs FET or a Josephson coupling element. Research on logical operation devices is in progress.

However, there is a limit in terms of calculation speed, power consumption, and the like for performing high-speed digital information processing of a large amount of two-dimensional data such as image information using electric signals. For this reason, it is desired to realize an optical logic operation device capable of digital information processing of optical signals as they are, which is compatible with high-speed two-dimensional parallel information processing. An optical memory capable of reading and writing information is essential.

As such an optical memory, for example, a bistable semiconductor laser described in Document Electronics Letter, Vol. 17, page 741 is known.

FIG. 5 is a sectional view showing a specific example of a bistable semiconductor laser. The structure is almost the same as that of a commonly used current injection type semiconductor laser. For example, GaAlAs / GaAs or InGaAsP / I
This is a laser with a double heterojunction structure made of nP.
However, this is different from a normal semiconductor laser in that the electrode 501 is not uniform and a part 502 where current is not injected exists in part. Since the current non-injection region 502 functions as a saturable absorber, the injection current i vs. optical output P _o characteristic can have a hysteresis characteristic in the bistable semiconductor laser of FIG. Instead of making the electrodes 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 part in part. In these bistable semiconductor lasers, by appropriately selecting the injection current i, bistable characteristics can be obtained in the characteristics of the outgoing light P _o with respect to the injection light P _i from the outside.

FIGS. 6 (a) and 6 (b) are views for explaining the operation of the bistable semiconductor laser of FIG. Figure 6 (a) shows the incident light intensity P _i
It is a figure which shows the relationship between the injection electric current i and the emitted light quantity P _o when = 0. That is, the injection current i rapidly emission light intensity P _o increases with i = i _u in when increasing from i _c, the amount of emitted light P _o if the injected current i in the opposite reduced from i _u or more values i
Shows a hysteresis characteristic that decreases sharply at = i _d ,
When i = i _b , the two stable points A with zero output and P _oh
And B. Reference numeral 600 shown in FIG. 6 (b) denotes the incident light quantity P _i and the outgoing light quantity P _o when the injection current i = i _{w in} FIG.
Shows the relationship with. That is, when the incident light amount P _i is increased from 0 at the first stable point A where the emitted light amount P _o = 0, the emitted light amount P _o sharply increases at P _i = P _iu and thereafter the incident amount P _i = When it is decreased from P _{ih, the} amount of emitted light P _o hardly decreases and the amount of emitted light P _o = P _oh moves to the second stable point B. Points A and B in FIG. 6 (a) are points A and B in FIG. 6 (b), respectively.
Represents the same point as.

(Problems to be Solved by the Invention) In FIG. 6 (a), when the value of the injection current i is decreased from i _w to i _b , as shown by 601 in FIG. increases from the incident light intensity P _i is P _iu is the amount of emitted light P _o rises to P _iu ', thereby bistable semiconductor laser, the amount of incident light P _i
Even if is increased from 0 to P _ih , the oscillation state is not reached, and the emitted light amount P _o remains 0.

FIG. 7 is a diagram showing a conventional optical memory writing method.

In FIG. 7, the same reference numerals as those in FIG.
The same components as in the figure are shown.

FIG. 8 shows a time chart for explaining the operation of the optical memory shown in FIG.

According to FIG. 8, the bistable semiconductor laser 50 shown in FIG.
The injection current i indicated by 800 is supplied to the electrode 501 of 0 by the variable constant current source 700.
The optical signal P _i indicated by 801 incident from
The optical signal P _o indicated by 802 is emitted from one end 702 and the other end 703.

Sixth bistable semiconductor laser 500 shown in FIG. 7 also the optical signal P _i is the incident injection current i value i _b a is as long as if the light amount P _ih as shown in Figure (b) the previous in accordance with the written value holds one of the outgoing light P _o of the light quantity 0 or P _oh.

Here, the value of the injection current i is set to the sixth value as shown in FIG.
Once i _b shown in FIG. 6A is decreased to i _c , the bistable semiconductor laser 500 is reset at any stable point A or B shown in FIG. _6A , and the amount of emitted light P _o is It becomes 0. After this, the value of the injection current i is changed as shown in FIG.
When it increases to i _w shown in (a), the bistable semiconductor laser 500 can be set by the incident light P _{i having the} light quantity P _ih as shown in FIG. 6 (b). That is, the bistable semiconductor laser 500 shown in FIG. 7 stores a value corresponding to the optical signal P _i incident on the one end 702 of the active layer 701 during the period 804 in which the value of the injection current i becomes i _w. As long as the value of the injection current i is i _b , that value is held.

In the conventional optical memory writing method shown in FIG. 7, the value of the optical signal P _i incident from one end 702 of the active layer 701 is latched by controlling the injection current i.

It is an object of the present invention to provide an optical memory writing method capable of selecting and storing either one of two optical signals incident on one end and the other end of an active layer.

(Means for Solving the Problems) In the present invention, the electrode is composed of two first and second electrodes in the resonance axis direction.
In an optical memory including a bistable semiconductor laser divided into two and first and second variable current sources that supply first and second injection currents to the first and second electrodes, respectively, By controlling the first and second injected current values independently of each other, two optical signals respectively incident from the first electrode side end surface and the second electrode side end surface of the active layer of the bistable semiconductor laser are The optical memory writing method is characterized by storing either one of the values.

(Operation) With the above-described configuration, the present invention makes it possible to select and store either one of the optical signals applied to both ends of the active layer of the bistable semiconductor laser.

That is, as a bistable semiconductor laser, a bistable semiconductor laser having a tandem electrode structure in which an electrode is divided into two in a direction of a resonance axis across a groove is used, and two injection currents respectively supplied to the two electrodes are used. By individually controlling, either one of the optical signals incident on both ends of the active layer can be selected and stored.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a sectional view showing a specific example of a bistable semiconductor laser used in the present invention. The basic structure is almost the same as that of the bistable semiconductor laser 500 shown in FIG. 5, but in the present invention, the electrode is divided into two electrodes 301 and 302 in the resonance axis direction with a groove in between. This is different from the bistable semiconductor laser 500 shown in FIG.

As a bistable semiconductor laser of this kind, Proceedings of the 57th National Congress of the Institute of Electronics and Communications, Division of Light and Radio, 1987 (Volume 2) 27
The one mentioned in number 2 is known. This document only describes the operation when two electrodes of a bistable semiconductor laser usable in the present invention are connected to each other and driven by one current source circuit. Also, the number of optical signals input is one.

The electrode 301 of the bistable semiconductor laser 300 shown in FIG.
The injection currents i ₁ and i ₂ are supplied to 302, respectively, whereby the values of one of the _two optical signals P ₁ and P ₂ incident on one end 304 and the other end 305 of the active layer 303, respectively. And the optical signal P _o from both ends of the active layer 303.
Is emitted.

FIG. 4 is a diagram showing characteristics of the bistable semiconductor laser 300 shown in FIG. As shown in FIG. 4 (a), the bistable semiconductor laser 300 shown in FIG. 3 has an incident light amount P ₁ = 0 and an injection current i.
_{When 2} = i _2b , there is 400 between the injection current i ₁ and the emitted light quantity P _o.
Has a hysteresis characteristic indicated by the value of the injected current i ₁ to i _1b
Two stable points A and B are shown by setting to. Furthermore, the bistable semiconductor laser 300 shown in FIG.
_Has a hysteresis characteristic similar to the hysteresis characteristic 400 even when i ₂ = i _2w . Figure 4 (b) shows the injection current i.
₂ = a i _2b incident light amount P ₁ when a is a diagram showing a relationship between light emission amount P _o, third bistable semiconductor laser 300 shown in figure injection current i values a fourth view of ₁ (a The characteristic indicated by 401 is obtained by setting the value of i _1b shown in (). Where injection current i ₁
When the value of is set to i _1w shown in FIG. 4 (b), the bistable semiconductor laser 300 exhibits the characteristic indicated by 402.

Furthermore, the bistable semiconductor laser 300 shown in FIG.
_{Even when 2} = i _2w , it has the same characteristics as 401 and 402.

On the other hand, as shown in FIG. 4 (c), the bistable semiconductor laser 300 shown in FIG. 3 also has an injection current i ₂ and an emission light amount P _o when the incident light amount P ₂ = 0 and the injection current i ₂ = i _2b. Two stable points A and B are shown by setting the value of the injection current i ₂ to i _2b which has a hysteresis characteristic indicated by 403 between and. Furthermore, the bistable semiconductor laser 300 shown in FIG. 3 has i ₁ = i _1w
In this case also, it has the same hysteresis characteristic as 403. Figure 4 (d) shows the incident light intensity P ₂ when the injection current i ₁ = i _1b.
FIG. 4 is a diagram showing the relationship between the emitted light amount P _o and the bistable semiconductor laser 300 shown in FIG. 3, in which the injection current i ₂ is set to the value of i _2b shown in FIG. 4 (c). Has the characteristic indicated by 404. Here, when the value of the injection current i ₂ is set to i _2w shown in FIG. 4 (c), the bistable semiconductor laser 300 exhibits the characteristic indicated by 403. Furthermore, the bistable semiconductor laser 300 shown in FIG.
Has the same characteristics as 403 and 404 even when i ₁ = i _1w . Points A and B in Fig. 4 (a) are shown in Fig. 4, respectively.
The same points as points A and B in (b) to (d) are shown.

FIG. 1 is a diagram showing an embodiment of the present invention.

In FIG. 1, the ones given the same numbers as in FIG. 3 are the third
The same components as in the figure are shown.

FIG. 2 is a time chart for explaining the operation of the optical memory shown in FIG. According to FIG. 2, the injection currents 200 and 201 are supplied to the electrodes 301 and 302 of the bistable semiconductor laser 300 shown in FIG. 1 by the variable constant current sources 100 and 101, respectively. 30
3 is incident from one end 304 and the other end 305 of the second
The values of one of the optical signals P ₁ and P ₂ shown in FIGS. 202 and 203 are stored, and one end 304 and the other end 305 of the active layer 303 are stored.
To 204, the optical signal P _o indicated by 204 is emitted.

As shown in FIGS. 4 (b) and (d), as long as the injection currents i ₁ and i ₂ are i _1b and i _2b , respectively, the light signals P ₁ and P ₂ of the light _amounts P _1h and P _2h are respectively generated. One end 304 and the other end 305 of the active layer 303
Bistable semiconductor laser 300 shown in FIG.
Holds the emitted light P _o of either light intensity 0 or P _oh depending on the value written last time.

Here, as shown in 205 and 206 in FIG. ₂ , _one of the injection currents i ₁ and i ₂ is represented by i _1c and i 2 in FIGS. 4 (a) and 4 (b), respectively.
_When it is reduced to _2c , the bistable semiconductor laser 300 is shown in FIG.
It is reset at both stable points A and B shown in (c), and the amount of emitted light P _o becomes zero. After this, for example, Fig. 2
As shown in 206, the value of the injection current i ₂ is i _2w shown in Fig. 4 (a).
As shown in FIG. 4 (b), the bistable semiconductor laser 300 can be set by the incident light P _{1 having the} light quantity P _1h , and the active layer can be set as long as the injection current i ₁ remains i _1b. The optical signal P ₁ incident on the one end 304 of 303 does not have any influence on the setting operation. That is, the semiconductor laser 300 shown in FIG. ₁ keeps the injection currents i ₁ and i _1b and changes the optical signal P ₂ incident on the other end 305 of the active layer 303 during the period 206 during which the value of the injection current i ₂ is i _2w. Store the value according to the injection current
The values of i ₁ and i ₂ are held as long as they are i _1b and i _2b , respectively.

Similarly, in the semiconductor laser 300 of FIG. 1, the injection current i ₂ is i _2b
During the period 207 in which the value of the injection current i ₁ is i _1w .
A value corresponding to the optical signal P ₁ incident on one end 304 of the is stored and held thereafter as long as the values of the injection currents i ₁ and i ₂ are i _1b and i _2b , respectively.

(Effect of the Invention) As described above, the bistable semiconductor laser shown in FIG.
According to 300, which of the optical signals P ₁ and P ₂ is applied to the one end 304 and the other end 305 of the active layer 303 by controlling the injection electrodes i ₁ and i ₂ supplied to the two electrodes 301 and 302, respectively. One of them can be selected and stored, and the optical signal P _o can be emitted from the one end 304 and the other end 305 of the active layer 303.

That is, the optical memory writing method according to the present invention has an effect that a bidirectional optical memory operation can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a timing chart for explaining the operation of the optical memory shown in FIG. 1, and FIG. 3 is a bistable semiconductor laser used in the present invention. Is a sectional view showing a specific example of the above, FIG. 4 is a diagram showing characteristics of the bistable semiconductor laser shown in FIG. 3, and FIG. 5 is a specific example of the bistable semiconductor laser used in the optical memory according to the prior art. FIG. 6 is a sectional view, FIG. 6 is a diagram showing characteristics of the bistable semiconductor laser shown in FIG. 5, FIG. 7 is a diagram showing a conventional optical memory writing method, and FIG. 8 is an operation of the optical memory shown in FIG. FIG. 6 is a diagram showing a timing chart for explaining the above. In the figure, 100, 101 and 700 are variable constant current sources, and 300 and 500 are bistable semiconductor lasers, respectively.

Claims (1)

[Claims] 1. A bistable semiconductor laser in which an electrode is divided into two electrodes, a first electrode and a second electrode, in the direction of a resonance axis, and first and second injection currents to the first and second electrodes, respectively. In the optical memory constituted by the first and second variable current sources for supplying the first and second variable current sources, the first and second injected current values are controlled independently of each other, whereby the first of the active layers of the bistable semiconductor laser is controlled. An optical memory writing method, characterized in that a value of either one of two optical signals respectively incident from the end face on the electrode side and the end face on the second electrode side is stored.