JPH04226435A - Fully optical optical nonlinear type element - Google Patents

Abstract

PURPOSE:To obtain the element with which the characteristic for switching output light intensity is obtd. purely by light by adopting the constitution having the characteristic that the intensity of the output light is steeply changed with the intensity or wavelength of input light by a change in the internal electric field of a quantum well layer by photoexciting carriers. CONSTITUTION:The quantum well 3 consisting of the periodic laminated structure held by two clad layers 2, 4 is formed on an (n) type substrate 5. The exciting carriers are generated by absorption in the quantum well 3 when the input light is made incident on this element. The exciting carriers act to negate the built-in electric field by a p-n junction when the numbers of the electrons and holes which are the exciting carriers are both designated as (n). The energy band structure in the quantum well region inclines less steep with an increase in the (n). The wavelength of the optical transition is shortened by a Stark effect and, therefore, the response relation of the (n) and the absorption coefft. is obtd. if the input wavelength is selected.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention does not require an external electric circuit, and it is possible to obtain optical switching characteristics of the output light intensity using pure light, as well as optical bistable characteristics or optical multistable characteristics. This invention relates to an all-optical optical nonlinear element.

0002

BACKGROUND ART FIG. 12 shows, for example, Applied Physics Letters, Vol. 45, No. 1, p. 13, (1984) (Appl. Phys. Lett. Vol. 4).
5, No. 1, p. 13, (1984)) is a diagram showing a bistable device using the conventional self-electro-optic effect, in which 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 explained. In the quantum well structure, sharp absorption by excitons is stably obtained, and the peak wavelength shifts with respect to the electric field, so 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,
The response is shown by the solid line in FIG.

Here, when the value of the resistor 6 is R, the reverse bias voltage 7 is Vex, the input optical power is Pin, and the photocurrent is I, the load characteristics are as follows.

[0005]

[Math 1]

Therefore, it is a straight line that intersects the horizontal axis at Vex and has a slope of -1/RPin.

By selecting R and Vex from FIG.
In a certain input light intensity range, the load line is the response curve and 3
They intersect at a point and have two stable points. That is, the input light intensity P
Figure 14 shows the photocurrent I and output light intensity Pout for in.
It exhibits bistable characteristics as shown in Figure 15.

[0008]

[Problems to be Solved by the Invention] Conventional bistable elements are configured as described above, and it is necessary to connect an electric circuit to the outside in order to apply electrical feedback. There was a problem.

Furthermore, since only one current peak is used, there is a problem in that only bi-stable characteristics can be obtained.

The present invention was made to solve the above-mentioned problems, and it is possible to measure the switching characteristics of the optical output with respect to the input optical intensity or the input optical wavelength by using only light without connecting an external electric circuit. The purpose of this study is to obtain an optical nonlinear device that exhibits optical bistable characteristics.

[0011] Another object of the present invention is to obtain an optical nonlinear element that can obtain optical multiplex stability characteristics with respect to input light intensity or input light wavelength purely using light without connecting an external electric circuit. do.

0012

[Means for Solving the Problems] An all-optical optical nonlinear element according to the present invention includes an electrically floating first conductivity type semiconductor having a surface into which light enters, and an electrically floating semiconductor having a surface through which light is emitted. a second conductivity type semiconductor floating in the semiconductor layer; and an undoped semiconductor layer sandwiched between the first conductivity type semiconductor and the second conductivity type semiconductor and including a quantum well layer that absorbs input light; It has a characteristic that the intensity of the output light changes sharply with respect to the intensity or wavelength of the input light due to changes in the internal electric field of the quantum well layer due to photoexcited carriers generated by absorption in the well layer. .

Further, the all-optical optical nonlinear device according to the present invention has the structure described above, in which the quantum well layers are laminated with a barrier layer thin enough to couple the energy levels of each well layer with each other. The device has two or more well layers and has an asymmetrical coupling structure or a symmetrical coupling structure in which the energy levels of the well layers intersect due to changes in the internal electric field.

[0014]

[Operation] In the present invention, 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 an undoped semiconductor layer sandwiched between a conductive type semiconductor and a second conductivity type semiconductor and including a quantum well layer that absorbs input light; Because the structure has a characteristic that the intensity of the input light or the intensity of the output light changes sharply with respect to the wavelength due to changes in the internal electric field of the layer, it is possible to obtain optical switching characteristics purely using light. , it is possible to obtain optical bistability characteristics of output light intensity with respect to input light intensity and input light wavelength.

Further, in the present invention, the quantum well layer is provided with two or more well layers laminated via a sufficiently thin barrier layer such that the energy levels of each well layer are coupled to each other, and the internal electric field is Since the structure has an asymmetrical coupling structure or a symmetrical coupling structure in which the energy levels of each well layer intersect with each other due to the change, it is possible to obtain optical switching characteristics and to change the output light intensity with respect to the input light intensity and the input light wavelength. Multiple stability properties can be obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a structural diagram of an all-optical optical nonlinear device according to a first embodiment of the present invention.
1 μm doped p-type AlGaAs cladding layer, 3 a quantum well layer consisting of a periodic stacked structure of 100 μm GaAs and 100 μm AlGaAs, 4 a 1 μm doped silicon transparent to the input light wavelength λ at 1×10 18 cm −3 This is an n-type AlGaAs cladding layer. Note that this element is not connected to any external electrical circuit.

Next, the operation will be explained. Now, when input light enters the device, excited carriers are generated by absorption in the quantum well 3. Here, the numbers of electrons and holes, which are excited carriers, are both n. Excited carriers act to cancel the built-in electric field due to the pn junction, so absorption increases and as n increases, the energy band structure of the quantum well region changes from (a) to (b) as shown in Figure 2. As shown in , the slope becomes gentler. At this time, it is well known that the wavelength of the optical (absorption) transition shown by the arrow becomes shorter due to the Stark effect. Therefore, by selecting the input wavelength λ, it is possible to obtain the response relationship between n and the absorption coefficient α as shown in FIGS. 3(a) and 3(b).

On the other hand, when A is a proportionality constant and Pin is the input light intensity, approximately

[0019]

[Math 2]

##EQU1## holds true. Here, the slope of this straight line becomes gentler as the input light intensity Pin increases.

The intersection of this straight line and the response curves shown in FIGS. 3(a) and 3(b) is the stable response point exhibited by the actual device.

FIGS. 4(a) and 4(b) show the absorption coefficient α and the output light intensity Pout with respect to the input light intensity Pin, respectively.
Indicates the relationship between

In FIG. 4(a), a sudden change in the absorption coefficient α, ie, the output light intensity Pout, is obtained at the input light intensity Pin corresponding to a. Also, in Figure 4(b), b and c
The output light intensity Pout is between the input light intensity Pin corresponding to
It can be seen that the bistable property of is obtained.

In the above explanation, the method of obtaining the all-optical optical nonlinear characteristic of the output light intensity Pout with respect to the input light intensity Pin was described, but as shown in FIG. 5, the absorption characteristic is smaller for long wavelength input light. Since the maximum value is taken at n, Figure 6
It can be seen that a bistable characteristic of the output light intensity Pout with respect to the input light wavelength is also 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 optical nonlinear element according to a second embodiment of the invention.

In the figure, 21 is 1 doped with 5×10 18 cm −3 of beryllium, which is transparent to the input light wavelength λ.
μm p-type AlGaAs cladding layer, 22 is a 1×1018 cm-3 silicon layer transparent to the input light wavelength λ.
Doped 1 μm n-type AlGaAs cladding layer, 23
is an undoped AlGaAs layer, 24 is a 100 angstrom GaAs quantum well, 25 is an 80 angstrom GaAs quantum well, and 26 is an 8 angstrom AlG layer.
The aAs barrier layer 27 is an n-type GaAs substrate. Let Pin and λ be the input light intensity and wavelength, and Pout be the output light intensity.

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 coupled to each other.

Note that this element is not connected to any external electric circuit.

Next, the operation will be explained. As in the first embodiment, the excited carriers act to cancel the built-in electric field due to the pn junction, so the slope of the energy band structure in the quantum well region becomes gentle. FIG. 8 is an energy band diagram showing this situation. In the figure, A indicates the energy level of the quantum well 25, and B indicates the energy level of the quantum well 24. Due to photoexcited carriers generated by absorption of input light, the state shown in Fig. 8(a) changes to Fig. 8(b).
The internal electric field changes to the state shown in , but at this time, the quantum well 24 is wider than the quantum well 25, so the energy level A
The hierarchical relationship between and B is reversed. Therefore, the absorption peak wavelength is determined by the following: Journal of Applied Physics, Volume 65, Page 2168, (1989) (J. App.
l. Phys. , 65 (5) -March 1989
, pp. 2168), it changes with respect to n as shown in FIG. 11(a). Therefore, the change in the absorption coefficient α with respect to a certain wavelength λ is as shown in FIG. 11(b). Here, the relationship of equation 2 approximately holds true between n and α. The slope of this straight line becomes gentler as the input light intensity Pin increases. The intersection of this straight line and the response curve of FIG. 11(b) becomes the actual response point of the element. That is, Figure 11
As shown in (b), the output light intensity Pout takes a triple stability characteristic with respect to the input light intensity Pin sandwiched between two broken lines.

Note that in the second embodiment, the input light intensity Pin
However, as can be seen from Fig. 11, the response in Fig. 11(b) changes depending on the wavelength, so as shown in Fig. 13, the output light intensity Pout is
Obtains heavy stability properties.

Furthermore, in the second embodiment, an all-optical nonlinear element using an asymmetric coupled quantum well structure was explained as an example, but as shown in FIGS. 9, 10(a), and (b), A symmetrical coupled quantum well structure may be used for this purpose. For example, if a crossing between the second and third levels is used, the same effect as in the second embodiment can be obtained.

Although FIG. 7 shows a structure in which one set of coupled quantum well structures is inserted, it is better to insert a plurality of coupled quantum well structures in order to further increase the absorption efficiency.

[0033]

As described above, according to the all-optical optical nonlinear element of the present invention, the electrically floating P-type semiconductor of the first conductivity type having the surface on which light enters and the P-type semiconductor of the first conductivity type on which light enters. an electrically floating second conductivity type n-type semiconductor having a surface, and an undoped semiconductor layer including a quantum well layer that absorbs input light and sandwiched between the first conductivity type semiconductor and the second conductivity type semiconductor. The characteristic is that the intensity of the output light changes sharply with respect to the intensity or wavelength of the input light due to 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. Because of this structure, it is possible to obtain optical switching characteristics purely using light, and it is also possible to obtain optical bistable characteristics of the output light intensity with respect to the input light intensity and the input light wavelength.

Further, according to the present invention, since the quantum well layer is a quantum well having an asymmetrical coupling structure or a symmetrical coupling structure in which the energy levels of each well layer intersect with each other due to changes in the internal electric field, only light can be used. This has the effect that not only optical switching characteristics can be obtained, but also optical multiplexing stability characteristics of output optical intensity with respect to input optical intensity and input optical wavelength can be obtained.

[Brief explanation of the drawing]

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

FIG. 2 is a diagram showing the 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 shown in FIG. 1 in the first embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the absorption coefficient and the output light intensity with respect to the input light intensity, corresponding to FIG. 3 above.

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. 1. FIG.

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

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

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

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

FIG. 10 is a diagram showing the energy band structure of a symmetric coupled quantum well section for different input light intensities in a third embodiment of the present invention.

[Figure 11] Number of excited carriers n and absorption coefficient α of the device in Figure 7
FIG.

12 is a diagram showing the output light intensity relative to the input light intensity of the element in FIG. 7. FIG.

13 is a diagram showing output light intensity versus input light wavelength of the element in FIG. 7; FIG.

FIG. 14 is a structural diagram of an optical bistable device using conventional electro-optic feedback.

FIG. 15 is a diagram showing photocurrent characteristics with respect to voltage of the device in FIG. 14;

16 is a diagram showing the relationship between photocurrent and optical output with respect to input light intensity of the element in FIG. 14. FIG.

17 is a diagram showing the relationship between photocurrent and optical output with respect to input light intensity of the device in FIG. 14. FIG.

[Explanation of symbols]

1 Electrode 2 P-type AlGaAs cladding layer 3 Ga
As/AlGaAs quantum well layer 4 n-type AlGa
As cladding layer 5 N-type GaAs substrate 6 Electrical resistance 7 Bias voltage 21 P-type AlGaAs cladding layer 22 N-type AlGaAs cladding layer 23 Undoped AlGaAs 24 100 angstrom GaAs quantum well 25
80 angstrom GaAs quantum well 26 8
Angstrom AlGaAs barrier 27 n-type Ga
As

Claims (4)

[Claims] 1. An electrically floating first conductivity type semiconductor having a surface into which light enters, an electrically floating second conductivity type semiconductor having a surface through which light is emitted, and the first conductivity type semiconductor; an undoped semiconductor layer sandwiched between a second conductivity type semiconductor and including a quantum well layer that absorbs input light; An all-optical optical nonlinear element characterized by having the characteristic that the intensity of input light or the intensity of output light changes sharply with respect to wavelength due to changes in electric field. 2. The quantum well layer comprises two or more well layers laminated via a barrier layer that is thin enough to couple the energy levels of each well layer with each other, and the quantum well layer has two or more well layers laminated through a barrier layer that is thin enough to couple the energy levels of each well layer with each other. 2. The all-optical optical nonlinear device according to claim 1, wherein the well layers have a structure in which the energy levels intersect. 3. The all-optical optical nonlinear device according to claim 2, wherein the quantum well layer has an asymmetric coupling structure. 4. The all-optical optical nonlinear device according to claim 2, wherein the quantum well layer has a symmetrical coupling structure.