JPH0778591B2 - Optical half adder - Google Patents

Description

The present invention relates to an optical half adder used in an optical communication system, an optical information processing system, an optical switching system, an optical computer and the like.

[Conventional technology]

2. Description of the Related Art In recent years, with the development of optical fiber technology and optical semiconductor technology, a long-distance optical communication system for backbone transmission and an optical LAN system for highly efficiently connecting distributed processing devices have been put to practical use. In these systems, optical technology is mainly used as a connection means between functional devices, and the function is largely owed to electronic circuit technology centered on LSI.

Reflecting the arrival of the advanced information society in the near future, as the diversification of the information to be processed and the increase in the capacity have been increasing, it has been required to increase the processing speed and increase the complexity of the processing. To meet these demands, it has become necessary to use optical technology not only as a connection means but also as a logic processing means. That is, the transmitted optical digital signal is digitally processed as it is, and the processing result is output as light and can be transmitted to other devices. Optical processing devices (optical information processing systems, optical switching systems, etc.) that make full use of the above are essential.

To realize this type of device, an optical operation circuit similar to that used in a general electric logic circuit is required. In particular, the optical half adder is a basic circuit that constitutes an optical arithmetic circuit.

The conventional optical half adder is not composed of a pure optical circuit, but is composed of a hybrid of an optical circuit and an electric circuit. That is, light input data is received by a light receiving element, converted into light and electricity, processed by an electric circuit, and then a light emitting element is driven to obtain a calculation output.

[Problems to be solved by the invention]

In the above-mentioned conventional optical half adder, since the optical digital data is processed through the electric circuit, its characteristic depends on the characteristic of the electric circuit. In other words, stray inductance and stray capacitance when constructing an electric circuit deteriorate the band,
It impedes the high speed and wide bandwidth of optical signals.

An object of the present invention is to provide an all-optical type optical half adder that does not require an electric circuit, is small in size, and is suitable for integration.

[Means for solving problems]

The optical half adder of the present invention comprises an optical multiplexer for multiplexing the first optical logic input and the second optical logic input, and an optical bistable element cascaded in the optical multiplexer. The optical bistable element is configured as a Y-shaped branching device having a first output optical waveguide and a second output optical waveguide, and a light intensity-dependent refractive index is provided at a branch connection portion with the second optical output optical waveguide. It has a section. Then, the carry optical output generated from the logical product of the first optical logic input and the second optical logic input is output to the first output optical waveguide, and the first optical logic input and the second optical logic input are output. The exclusive OR of is output to the second output optical waveguide.

[Action]

In this configuration, a carry adder output from the first output optical waveguide and a logical sum output output from the second output optical waveguide can be used to configure a half adder using light. .

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an optical half adder according to an embodiment of the present invention. This optical half adder comprises an optical multiplexer 8 and an optical bistable element 9. The optical multiplexer 8 multiplexes the optical logic inputs P _A and P _B input to the first and second input optical waveguides 1 _A and 1 _B ,
The optical multiplexed signal P _AB is output to the optical waveguide 6. The optical bistable element 9 connects the optical waveguide 6 to each of the first and second output optical waveguides 2, 3
The Y-shaped branch optical waveguide 4 is divided into

The Y-shaped branched optical waveguide 4 is composed of a prism portion 5 whose refractive index N _P has a light intensity dependency, and an optical waveguide 6 whose refractive index N _CO does not depend on the light intensity. Where the optical waveguide
The refractive index of each core of 1 _A , 1 _B , 2 and 3 is the refractive index N of the optical waveguide 6.
It is selected to be the same as _CO . As a result, the prism portion 5 as the light intensity dependent refractive index portion is provided at the branch connection portion with the second output optical waveguide 3.

These optical waveguides are realized by semiconductor optical waveguides. That is, mixed crystal GaAs is used as a well layer on a GaAs substrate 10 and mixed crystal Al _x G
The prism portion 5 is formed by forming a multiple quantum well structure semiconductor 5A using a _1-x As as a barrier layer. Furthermore, GaAs substrate 10
A mixed crystal Al _y Ga _1-y As layer 11 is grown on the above and patterned by photolithography to form the optical waveguides 1 _A , 1 _B , 2, 3 and 6
To form.

Multiple quantum well structure semiconductor 5A forming the prism part 5
Refractive index N _{P of} is applied Physics Letters, 41 (8), October issue, 1982, p. 679 (Applied Physics L
etters, 41 (8), 15 October, 1982), it has a remarkable light intensity dependency near the exciton wavelength.

That is, the refractive index Np is represented by the following formula, difference _{Np = N 1 -N 2 · P} AB refractive index does not depend on the light input P _AB N ₁ and the refractive index depends on the optical input P _AB N ₂ · P _AB become.

Here, since the refractive index coefficient N ₂ of the multiple quantum well structure semiconductor is larger by, for example, two digits than that of the conventional bulk GaAs, it is possible to give a large change to the refractive index Np with a relatively low light intensity.

On the other hand, the mixed crystal Al _y Ga forming the optical waveguides 1 _A , 1 _B , 2, 3 and 6
The refractive index Nco of the _1-y As layer 11 can be determined with a relatively large degree of freedom by appropriately selecting the mixed crystal ratio y.

Therefore, it is easy to establish the relationship shown in FIG. 2 between the refractive index Np of the prism portion 5 and the refractive index Nco of the optical waveguide 6.

That is, the refractive index Nco smaller than the refractive index N ₁ when the optical input P _AB is not, also the threshold value P _th2 or more light input P _AB, can be set larger than the refractive index Np of the prism. Therefore, the refractive index distribution of the cross section AA ′ of the Y-shaped branched optical waveguide 4 is as shown in FIG. 3 (a) when the optical input P _AB is equal to or less than the threshold P _th2 .
FIG. 3B shows that _AB is _{equal to} or greater than the threshold P _th2 .

The optical input P _{AB is} input to the Y-shaped branch waveguide 4 having such characteristics.
Is applied. While the optical input P _AB is increasing from zero to the threshold P _th2 , the refractive index of the prism part 5 is increased as shown in FIG.
Since Np is larger than the refractive index Nco of the optical waveguide 6, the light is guided toward the prism portion 5, and the second output optical waveguide 3 has an optical output P _S proportional to the optical input P _AB in FIG. ) Is obtained (point 21 to point 22). On the other hand, almost no light is guided to the first output optical waveguide 2, and the optical output as shown in FIG.
P _C keeps low value P _L (point 31 to point 32). Optical input
If P _AB further increases and the optical input P _AB exceeds the threshold P _th2 , the third
On the contrary, as shown in FIG. 6B, the refractive index Nco of the optical waveguide 6 becomes larger than the refractive index Np of the prism portion 5, so that the light is guided to the optical waveguide 6 and almost to the prism portion 5. It will not be guided.

Therefore, the optical output P _S of the output optical waveguide 3 sharply decreases (point 23) as shown in FIG.
The optical output P _C of the abruptly increases as shown in FIG. 4 (b) (point 33). When the optical input P _AB further increases, the prism part 5
The refractive index Np of the optical waveguide 6 becomes smaller than that of the optical waveguide 6, and the light is completely guided to the optical waveguide 6, resulting in the optical output.
P _S asymptotically approaches zero (point 24), while the optical output P _C maintains a high value P _H (point 34).

From this state, the optical input P _AB decreases conversely, and while the refractive index Nco of the optical waveguide 6 maintains a value larger than the refractive index Np of the prism portion 5, the optical output P _C has a high value P _H. Keep (point 35
Optical output P _S keeps a low value P _L (up to point 25).

When the light input P _AB is further reduced to be equal to or smaller than the threshold P _th1 (different from the threshold P _th2 ) and conversely the refractive index Nco is smaller than the refractive index Np, the light is rapidly guided to the prism portion 5. . Therefore, the optical output P _C has a low value P _L (point 36) and the optical output P _S has a high value.
Take P _H (point 26) sharply.

At this time, as shown in FIGS. 4 (a) and 4 (b), the optical input
P _AB History when increasing (History 30 for optical output P _C , History 20 for optical output P _S ) and History when decreasing (History 37 for optical output P _C , Optical output P _S
Then, history 27) takes a different history, which is explained as follows.

In FIG. 1, the boundary 7 between the prism portion 5 and the optical waveguide 6 can be defined as a non-linear interface. Non-linear interfaces can be found in the Soviet Physics JE 56 (2), August, 1982, p. 299 (Soviet Phusics JE
TP, 56 (2), August, 1982),
It is a boundary between a medium having a light-intensity-dependent refractive index (prism portion 5 in FIG. 1) and a medium having a light-intensity-independent refractive index (optical waveguide 6 in FIG. 1). In the nonlinear interface 7, as theoretically proved in the above-mentioned literature, the refractive index change state is different when the optical input increases and when the optical input decreases, and the threshold P _th1 becomes a value lower than the threshold P _th2 . Therefore, as shown in FIGS. 4 (a) and 4 (b), the optical input
It shows different histories when P _AB increases and decreases.

Further, as the optical input P _AB approaches zero from the threshold P _th1 , the optical output P _S decreases proportionally from the high value P _H , and the optical output P _C maintains the low value P _L while maintaining the origins 21 and 31 respectively. Return to.

After all, the optical outputs P _C and P _S are complementary to each other, and
A positive output is obtained at P _C and a negative output is obtained at optical output P _S.

Therefore, in the bistable element having this configuration, the negative optical bistable characteristic and the positive optical bistable characteristic can be obtained at the same time.

As shown in FIG. 1, the optical logic inputs P _A and P _B are connected to the Y-shaped optical branching waveguide having such optical bistable identification via the optical multiplexer 8.
The logical operation when inputting is input will be described with reference to FIG.

When the optical logic input P _A has the amplitude A and the optical logic input P _B has the amplitude B (both the amplitudes A and B are equal to the intermediate value P _M between the thresholds P _th1 and P _th2 of the optical bistable characteristic, the amplitude A and the amplitude suppose the sum of B is greater than P _th2), the optical multiplexer output P _AB, the amplitude a and amplitude B
The sum amplitude of is obtained as shown in FIG. This sum amplitude, high value P _H is the optical output P _C is a low value in the optical output P _S
P _L is output respectively.

When only the optical logic input P _A (or only P _B ) has the amplitude A (or the amplitude B), the optical multiplexing output P _AB has the amplitude A (or the amplitude B) in FIG. 5 (b) (or (c )) Is obtained. Due to such amplitude, the optical output P _C has a low value P
_A high value P _H is output to the optical output P _S , respectively.

When the optical logic inputs P _A and P _B have zero amplitude, as shown in FIG. 5D, the optical outputs P _C and P _S also have zero amplitude.

The above logical operation is explained in FIG.

FIG. 6 (a) is the equivalent circuit of FIG. 1, and FIG. 6 (b) is its logic truth table. In the equivalent circuit, optical logic input P _A
And P _B are multiplexed by the optical multiplexer 8, and the outputs thereof further swing the positive optical bistable characteristic 102 and the negative optical bistable circuit 101 having the positive optical bistable circuit 100 and the negative optical bistable characteristic 103. Entered in. As a result, optical outputs P _C and P _S are obtained.

The truth values “0” and “1” in the logic value table correspond to zero amplitude and amplitude value A or B in the case of the optical logic inputs P _A and P _{B in} FIG. 5, respectively, and the optical output. In the case of P _C and P _S , they correspond to a low value P _L and a high value P _H , respectively.

As is clear from this logic truth table, the optical output P _S and the optical output P _C are respectively exclusive-ORed and ANDed with the optical logic inputs P _A and P _B to obtain the sum output and carry. Output is output.
Therefore, it can be seen that it operates as a half adder.
It becomes clear that the configuration of the figure operates as an optical half adder.

It should be noted that although the above embodiments have been described by using the GaAs-based semiconductor material, the optical bistable element is not limited to the above-mentioned materials and can be made of other materials having a large effect of dependence of the refractive index on the light intensity. It is obvious that can be realized. For example, recently published literature Applied Physics Letters 46 (7), 1,4
Month, 1985, p. 619 (Applied Physics Letters, 46
(7), 1 April 1985) announced GaInAs / AlInAs
A similar optical bistable device can be realized also in a multi-quantum well structure semiconductor of the system.

Further, the above-mentioned optical bistable device can be realized by using a semiconductor material such as InSb or ZnSe. Further, instead of the semiconductor material, an organic material (for example, liquid crystal
An optical bistable device can be realized even with MBBA).

Therefore, it goes without saying that an optical half adder is configured using these.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY As described above, the present invention is compact and suitable for integration because it is configured by the optical multiplexer and the Y-type branching device having the positive and negative optical bistable characteristics connected in cascade. There is an effect that an all-optical type optical half adder can be realized.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the optical half adder of the present invention, and FIG.
The figure shows the Y of the optical bistable element used in the optical half adder of the present invention.
FIG. 3 (a) and FIG. 3 (b) are the optical input dependence diagrams of the refractive index of the bifurcated waveguide, and are shown in FIG. 1A'A line of the Y bifurcated waveguide of the optical bistable device under different threshold values. FIG. 4 (a) and FIG. 4 (b) are optical input-optical output characteristic diagrams of the optical bistable element of the present invention, and FIG. 5 is an optical logic input P to the conventional optical bistable element. _a and P _B, shows the relationship between the optical output P _S and P _C, FIG. 6 (a) is an equivalent circuit of the light semi-adder diagram according to the invention, FIG. 6 (b) is the logical truth It is a table. P _A , P _B ...... optical logic input, P _C ...... carrying light output, P _S ...... wako output, 1 _A ...... first input optical waveguide, 1 _B ...... second input optical waveguide, 2 ...... First output optical waveguide, 3 ... Second output optical waveguide, 4 ... Y-shaped branch waveguide, 5 ... Non-linear refractive index prism portion (light intensity dependent refraction portion), 6 ... Optical waveguide, 7 ...
Non-linear interface, 8 ... Optical multiplexer, 9 ... Optical bistable element, 10 ... GaAs substrate, 11 ... Al _y Ga _1-y As layer, 100 ...
… Positive type optical bistable circuit, 101 …… Negative type bistable circuit, 102
…… Positive optical bistability characteristic, 103 …… Negative optical bistability characteristic.

Claims (1)

[Claims] 1. An optical multiplexer for multiplexing a first optical logic input and a second optical logic input, and an optical bistable element cascaded in the optical multiplexer, the optical bistable element comprising: It is configured as a Y-shaped branching device having a first output optical waveguide and a second output optical waveguide, and a light intensity dependent refractive index portion is provided at a branch connection portion with the second optical output optical waveguide. , A carry optical output generated from a logical product of the first optical logic input and the second optical logic input is output to the first output optical waveguide, and the carry optical output of the first optical logic input and the second optical logic input is output. An optical half adder which outputs an exclusive OR to a second output optical waveguide.