JP3145138B2 - All-optical optical nonlinear element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention does not require an external electric circuit, and can obtain an optical switching characteristic of an output light intensity purely by light alone, and an optical bistable characteristic or an optical multi-stable characteristic. The present invention relates to an all-optical non-linear element.

[0002]

2. Description of the Related Art FIG. 12 shows, for example, Applied Physics Letters, Vol. 45, No. 1, page 13, (1984) (Appl.
s. Lett. Vol. 45, No. 1, p. 13, (1984)) is a diagram showing a conventional bistable element using the self-electro-optical effect, in the figure, 1 is an electrode, 2 is a p-type AlGaAs cladding layer, 3 is a GaAs / AlGaAs quantum well layer, 4 is an n-type AlGaAs cladding layer, 5 is an n-type GaAs substrate,
6 is an electric resistance, and 7 is a bias voltage.

Next, the operation will be described. In the quantum well structure, sharp absorption by excitons is stably obtained, and the peak wavelength shifts with respect to the electric field. Therefore, the photocurrent per unit power at a certain wavelength λ corresponding to one exciton absorption is: When the voltage applied to the element is V,
Responds as shown by the solid line in FIG.

[0004] Here, the value of the resistor 6 R, a reverse bias voltage 7 V _ex, the input optical power P _in, when the photocurrent is I, load characteristics,

[0005]

(Equation 1)

[0006] a since, intersect at the horizontal axis and the V _ex, inclination becomes a straight line of -1 / RP _in.

By selecting R and V _ex from FIG. 13, in a certain input light intensity range, the load straight line intersects the response curve at three points and has two stable points. That is, the input light intensity P _in
On the other hand, the photocurrent I and the output light intensity P _out are shown in FIGS.
Bistability characteristics such as

[0008]

The conventional bistable element is constructed as described above, and it is necessary to connect an external electric circuit in order to electrically feed back. For example, in terms of integration, etc. There was a problem.

In addition, since only one current peak is used, there is a problem that only bistable (double) stability characteristics can be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and does not connect an electric circuit to the outside, and uses only pure light to switch the optical output switching characteristics with respect to the input light intensity or the input light wavelength. It is an object of the present invention to obtain an optical non-linear element having optical bistable characteristics.

It is another object of the present invention to provide an optical non-linear element which can obtain an optical multiplexing stability characteristic with respect to an input light intensity or an input light wavelength by purely light without connecting an external electric circuit. I do.

[0012]

SUMMARY OF THE INVENTION An all-optical optical nonlinear element according to the present invention comprises an electrically floating first conductive type semiconductor having a light incident surface, and an electrically floating first conductive semiconductor having a light emitting surface. A second conductivity type semiconductor floating on the substrate, and an undoped semiconductor layer including a quantum well layer absorbing the input light, sandwiched between the first conductivity type semiconductor and the second conductivity type semiconductor. The intensity of the output light changes sharply with respect to the input light intensity or wavelength due to a change in the internal electric field of the quantum well layer due to photoexcited carriers generated by absorption in the well layer. .

Further, in the all-optical optical nonlinear device according to the present invention, the quantum well layers in the above-described structure are stacked via a barrier layer sufficiently thin enough that the energy levels of the respective well layers are mutually coupled. It has two or more well layers, and has an asymmetric coupling structure or a symmetric coupling structure in which the energy level of each well layer crosses due to a change in the internal electric field.

[0014]

According to the present invention, an electrically floating first conductive type semiconductor having a light incident surface, an electrically floating second conductive type semiconductor having a light emitting surface, and the first conductive type semiconductor are provided. An undoped semiconductor layer including a quantum well layer that absorbs input light, sandwiched between the type semiconductor and the second conductivity type semiconductor, wherein the quantum well is formed by photoexcited carriers generated by absorption of the input light in the quantum well layer. The structure is such that the intensity of the input light or the intensity of the output light changes steeply with respect to the wavelength due to the change in the internal electric field of the layer, so that the optical switching characteristics can be obtained purely with light alone. The optical bistability of the output light intensity with respect to the input light intensity and the input light wavelength can be obtained.

Further, in the present invention, the quantum well layer is provided with two or more well layers stacked via a barrier layer that is sufficiently thin so that the energy levels of the respective well layers are coupled to each other, and the quantum well layer has an internal electric field. Since the structure has an asymmetric coupling structure or a symmetric coupling structure in which the energy levels of the well layers cross each other due to the change, it is possible to obtain the optical switching characteristics and to obtain the input light intensity and the light having the output light intensity with respect to the input light wavelength. Multi-stable characteristics can be obtained.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a structural view of an all-optical optical nonlinear device according to a first embodiment of the present invention. In FIG. 1, reference numeral 2 denotes beryllium, which is transparent to an input light wavelength λ, doped with 5 × 10 ¹⁸ cm ^−3. 1 μm p-type AlGaAs cladding layer, 3
Is a quantum well layer having a periodic lamination structure of GaAs and 100 AlGaAs, and 1 μm n-type Al doped with 1 × 10 ¹⁸ cm ^{−3 of} silicon transparent to an input light wavelength λ.
It is a GaAs cladding layer. No external electric circuit is connected to this element.

Next, the operation will be described. Now, when the input light enters the device, excited carriers are generated by absorption in the quantum well 3. Here, the number of electrons and holes as excited carriers is both n. Since the excited carriers work to cancel the built-in electric field due to the pn junction, the absorption increases and as the number of n increases, the energy band structure of the quantum well region changes from FIG. 2A to FIG. 2B as shown in FIG.
The slope becomes gentle as shown in FIG. At this time, it is well known that the wavelength of the optical (absorption) transition indicated by the arrow becomes shorter due to the Stark effect. Therefore, if the input wavelength λ is selected, a response relationship between n and the absorption coefficient α can be obtained as shown in FIGS. 3 (a) and 3 (b).

Meanwhile, the A proportional constant, when the input light intensity P _in, approximately

[0019]

(Equation 2)

The following holds. Here, the straight line slope becomes moderate as the input light intensity P _in is increased.

The intersection between this straight line and the response curves shown in FIGS. 3A and 3B is a stable response point indicated by an actual element.

FIGS. 4 (a) and 4 (b) show the input light intensity P _in
Shows the relationship between the absorption coefficient α and the output light intensity P _out .

In FIG. 4 (a), the input light intensity P _in corresponding to a
, An abrupt change in the absorption coefficient α, that is, the output light intensity P _out is obtained. Also in FIG. 4 (b), it can be seen that the bistable characteristic of the output light intensity P _out between the input light intensity P _in corresponding to b and c are obtained.

[0024] In the above description has dealt with how to obtain the total optical light non-linear characteristics of the output light intensity P _out to the input light intensity P _in, absorption characteristics as shown in FIG. 5 for the long-wavelength input light Since the maximum value is obtained at a smaller value of n, it can be seen that a bistable characteristic of the output light intensity P _{out with} respect to the input light wavelength can be obtained as shown in FIG.

Next, a second embodiment of the present invention will be described. FIG. 7 is a diagram of an all-optical nonlinear element according to a second embodiment of the present invention.

In the figure, reference numeral 21 denotes 1 μm doped with 5 × 10 ¹⁸ cm ^{−3 of} beryllium transparent to an input light wavelength λ.
The p-type AlGaAs cladding layer 22 is 1 μm doped with 1 × 10 ¹⁸ cm ^{−3 of} silicon transparent to the input light wavelength λ.
m n-type AlGaAs cladding layer, 23 is undoped A
1 GaAs layer, 24 is 100 Å GaAs
A quantum well, 25 is an 80 Å GaAs quantum well, 26 is an 8 Å AlGaAs barrier layer, and 27 is an n-type GaAs substrate. The input light intensity and wavelength P _in and λ, the output light intensity and P _out.

The barrier layer 26 provided between the quantum wells 24 and 25 is set to be sufficiently thin as described above so that the energy levels of the quantum wells 24 and 25 are mutually coupled.

No external electric circuit is connected to this element.

Next, the operation will be described. As in the first embodiment, the excited carriers function to cancel the built-in electric field due to the pn junction, so that the slope of the energy band structure in the quantum well region becomes gentle. FIG. 8 is an energy band diagram showing this state. In the figure, A indicates the energy level of the quantum well 25, and B indicates the energy level of the quantum well 24. The internal electric field changes from the state shown in FIG. 8A to the state shown in FIG. 8B due to photoexcited carriers generated by absorption of input light. At this time, since the quantum well 24 is wider than the quantum well 25, the energy level The vertical relationship between A and B is reversed. For this reason, the absorption peak wavelength is determined by the Journal of Applied Physics, Vol. 65, 2168.
P., (1989) (J. Appl. Phys., 65 (5)-March 1989, pp.2
As shown in FIG. 168), n changes as shown in FIG. 11 (a). Therefore, the change of the absorption coefficient α for a certain wavelength λ is as shown in FIG. Here, the relationship of Equation 2 is approximately established between n and α. This line slope becomes moderate as the input light intensity P _in is increased. The intersection of this straight line and the response curve of FIG. 11 (b) is the actual response point indicated by the element. That is, as shown in FIG. 11B, the output light intensity P _out has triple stability characteristics with respect to the input light intensity P _in sandwiched between two broken lines.

[0030] While in the second embodiment showing a triple stability properties with respect to the input light intensity P _in, as can be seen from FIG. 11, as shown in FIG. 13 because the response shown in FIG. 11 (b) replacing the wavelength The triple stability characteristic of the output light intensity P _out can be obtained for the wavelength.

In the second embodiment, an all-optical nonlinear element using an asymmetric coupling quantum well structure has been described as an example. However, as shown in FIGS. 9, 10 (a) and 10 (b). A symmetrical coupling quantum well structure may be used. For example, if the second and third level crossings are used, the same effect as in the second embodiment can be obtained.

FIG. 7 shows a structure in which a pair of coupled quantum well structures is inserted. However, in order to further enhance the absorption efficiency, it is better to insert a plurality of coupled quantum well structures.

[0033]

As described above, according to the all-optical optical non-linear element of the present invention, an electrically floating first conductivity type P-type semiconductor having a light incident surface and light incident thereon. An electrically floating second conductivity type n-type semiconductor having a surface, and an undoped semiconductor layer including a quantum well layer for absorbing input light, sandwiched between the first conductivity type semiconductor and the second conductivity type semiconductor. A characteristic in which the intensity of the input light or the intensity of the output light changes sharply with respect to the wavelength by the change of the internal electric field of the quantum well layer due to the photoexcited carriers generated by the absorption of the input light in the quantum well layer. With this configuration, the optical switching characteristics can be obtained purely by using only light, and the optical bistable characteristics of the output light intensity with respect to the input light intensity and the input light wavelength can be obtained.

Further, according to the present invention, the quantum well layer is formed as a quantum well having an asymmetric coupling structure or a symmetric coupling structure in which the energy levels of the respective well layers intersect due to changes in the internal electric field. Accordingly, the optical switching characteristics can be obtained, and the optical multiplexing stability characteristics of the output light intensity with respect to the input light intensity and the input light wavelength can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of an all-optical nonlinear element according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an energy band structure of a quantum well section for different input light intensities in the first embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the number n of excited carriers and the absorption coefficient α of the device of FIG. 1 according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between an absorption coefficient and an output light intensity with respect to an input light intensity corresponding to FIG.

5 is a diagram showing the relationship between the number n of excited carriers and the absorption coefficient α for three different input wavelengths in the device of FIG.

FIG. 6 is a diagram showing a relationship between an output intensity and an input wavelength of the device of FIG. 1;

FIG. 7 is a diagram showing a structure of an all-optical optical nonlinear element using an asymmetric coupling quantum structure according to a second embodiment of the present invention.

FIG. 8 is a diagram showing an energy band structure of an asymmetric coupling quantum well portion for different input light intensities in the second embodiment of the present invention.

FIG. 9 is a diagram showing the structure of an all-optical optical nonlinear element using a symmetric coupling quantum structure according to a third embodiment of the present invention.

FIG. 10 is a diagram showing an energy band structure of a symmetrical coupling quantum well portion for different input light intensities in the third embodiment of the present invention.

11 shows the number n of excited carriers and the absorption coefficient α of the device shown in FIG.
FIG.

FIG. 12 is a diagram showing an output light intensity with respect to an input light intensity of the device of FIG. 7;

FIG. 13 is a diagram showing the output light intensity with respect to the input light wavelength of the device of FIG. 7;

FIG. 14 is a structural diagram of a conventional optical bistable element using electro-optical feedback.

FIG. 15 is a diagram showing a photocurrent characteristic with respect to a voltage of the device of FIG.

16 is a diagram showing a relationship between a photocurrent and a light output with respect to an input light intensity of the device of FIG.

17 is a diagram showing a relationship between a photocurrent and a light output with respect to an input light intensity of the device of FIG.

[Explanation of symbols]

 Reference Signs List 1 electrode 2 P-type AlGaAs cladding layer 3 GaAs / AlGaAs quantum well layer 4 n-type AlGaAs cladding layer 5 n-type GaAs substrate 6 electric resistance 7 bias voltage 21 P-type AlGaAs cladding layer 22 n-type AlGaAs cladding layer 23 undoped AlGaAs 24 100 angstroms GaAs quantum well 25 80 angstroms GaAs quantum well 26 8 angstroms AlGaAs barrier 27 n-type GaAs

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/35 G02F 3/02 JICST file (JOIS)

Claims (3)

(57) [Claims] An electrically floating first conductivity type semiconductor having a light incident surface, an electrically floating second conductivity type semiconductor having a light emitting surface, and the first conductivity type semiconductor. In an all-optical optical nonlinear device including an undoped semiconductor layer including a quantum well layer that absorbs input light and sandwiched between semiconductors of the second conductivity type , the quantum well layer has an energy level of each well layer. Are mutually
Two or more layers stacked through a barrier layer that is thin enough to
Upper well layer, and each well
It has a structure in which the energy levels of the door layer intersect, and changes in the internal electric field of the quantum well layer due to photoexcited carriers generated by absorption of the input light in the quantum well layer.
An all-optical optical non-linear element having a characteristic that the intensity of output light changes sharply with the intensity or wavelength of input light. 2. The all-optical optical non-linear element according to claim 1, wherein the quantum well layer has an asymmetric coupling structure. Wherein the quantum well layer, the total optical light non-linear element according to claim 1, wherein the one having a symmetrical coupling structure.