JPH1090738A - Non-linear optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-linear optical device with wide band gain width and a high response speed and capable of manufacturing with a simple process by forming an active layer so that a size of an energy wall of each self quantum well is equal or reduced along the direction of an electric field applied to a multiplex quantum well structure. SOLUTION: A laser active layer 7 is constituted of at least partial each quantum well of the multiplex quantum well structure consisting of plural quantum wells formed on a part of an optical waveguide 2, and light inductive emission by transition between sub-bands occurs. Then, in this active layer 7, the size of the self energy wall is equal or reduced along the direction of the electric field applied to the multiplex quantum well structure. Thus, the wide band gain width and the high response speed are realized. Further, respective layers are formed by a nitride system compound semiconductor layer, and a wall layer with high energy is formed easily, and further, even an integrated structure between a laser amplifier and an intersub-band absorption layer is manufactured with the simple process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a nonlinear optical device such as an optical switch, an optical modulator, and a wavelength conversion element.

[0002]

2. Description of the Related Art In recent years, with the development of optoelectronics-related technologies such as semiconductor lasers, low-loss optical fibers, optical fiber amplifiers, and high-speed integrated circuits, it has become possible to transmit large amounts of information at a rate of 10 gigabits per second over long distances.
However, in the coming multimedia era, in order for ordinary end users to be able to use large amounts of information, such as high-definition video information, in real time, it is necessary to build an infrastructure that can transmit and process even larger amounts of information. Have been.

Here, in order to transmit and process a large amount of information by making use of the broadband characteristics of an optical fiber, it is appropriate to use an optical frequency multiplexing (optical FDM) technique or an optical time division multiplexing (optical TDM) technique. Conceivable. Therefore, large-scale and efficient light F
To realize a DM network or an optical TDM network, it is urgently necessary to develop an optical element having a new function, such as a compact and highly efficient wavelength conversion element, an optically controlled ultra-high-speed nonlinear optical switch, and the like.

As an optical element of this type, for example, an ultra-high-speed optical nonlinear effect based on an intra-band electron relaxation effect is used.
Non-linear optical devices that generate four-wave mixing outputs are known. Such a nonlinear optical device may have a structure in which a traveling-wave semiconductor laser amplifier and an intersubband absorption layer having a multiple quantum well structure are superposed. In other words, the nonlinear optical device aims to improve the response speed and the nonlinearity by combining a well-known structure using a traveling-wave semiconductor laser amplifier and an intersubband absorption layer.

Incidentally, these traveling wave type semiconductor laser amplifiers and intersubband absorption layers need to be operated at a wavelength around 1.55 μm used in optical communication. Regarding the absorption between sub-bands, the InG formed on the InP substrate
Absorption at this wavelength has been reported using an aAs / AlAs quantum well layer (JHSmetal., Appl. Phys. Lett., V0
1.64, pp986.987 (1994)). However, in the case of this material system, the height of the energy barrier is relatively small, and when combined with a traveling-wave type semiconductor laser amplifier, electrons cross over the barrier, and the effect of the intersubband absorption layer is not sufficient. It is feared that it will not be demonstrated. Therefore, it is desirable to form the intersubband absorption layer from a nitride semiconductor having a larger band gap, such as GaN or AlN.

On the other hand, current traveling wave type semiconductor laser amplifiers utilize an inter-band transition between a conduction band and a valence band, such as a device having an InGaAsP quantum well layer formed on an InP substrate as an active layer. Have been. That is, since the nitride semiconductor has a wide band gap, a laser amplifier having a wavelength of 1.55 μm based on an interband transition cannot be realized.

It is also conceivable to join a traveling-wave laser amplifier formed on an InP substrate and an intersubband absorption layer formed of a nitride semiconductor to each other by a direct bonding technique. And there is a problem of increasing the number of manufacturing steps.

As described above, it is impossible to realize a laser amplifier in the 1.55 μm wavelength band using the transition between bands of a nitride semiconductor. By the way, as a related technique that does not use the inter-band transition, a laser using the inter-sub-band transition in the quantum well, that is, a so-called cascade laser can be considered.

If a nitride semiconductor is used, a quantum well having a sufficiently large energy barrier can be easily formed. That is, a cascade laser having a wavelength of 1.55 μm can be formed.

If the cascade laser can be made of the same nitride-based material as the intersubband absorption resonance region, the laser amplifier and the intersubband absorption layer can be continuously epitaxially grown on the same substrate. Therefore, the above-described problem of joining can be avoided.

However, the cascade laser has a very narrow band gain width due to its characteristics. Therefore, when the wavelength range of the incident light is wide, only a part of the cascade laser can obtain a gain. Is unsuitable for

[0012]

As described above, as a nonlinear optical device, there is no semiconductor laser amplifier having a wide band gain using a nitride semiconductor, and a laser amplifier is formed of another material. Then, there is a problem that the manufacturing process becomes complicated.

Although the cascade laser can be used, it is difficult to apply it to a nonlinear optical device due to its characteristics. The present invention has been made in consideration of the above circumstances, and has as its object to provide a nonlinear optical device having a wide bandwidth gain and a high response speed, which can be realized by a simple manufacturing process.

[0014]

According to a first aspect of the present invention, there is provided an optical waveguide, a multiple quantum well structure including a plurality of quantum wells formed in a part of the optical waveguide, and a multiple quantum well structure. An active layer constituted by at least a part of each quantum well and generating light-induced emission by an intersubband transition, wherein the active layer has a size of an energy barrier of its own quantum well. Saga,
A nonlinear optical device formed to be equal or decreasing along a direction of an electric field applied to the multiple quantum well structure.

According to a second aspect of the present invention, there is provided an optical waveguide, a multiple quantum well structure including a plurality of quantum wells formed in a part of the optical waveguide, and at least a part of the multiple quantum well structure. A non-linear optical device comprising an active layer formed by each quantum well and generating light-induced emission by intersubband transition, wherein the size of the energy barrier of each quantum well of the active layer is The thickness of the barrier layer formed to be equal or decreasing along the direction of the electric field applied to the multiple quantum well structure and forming each of the quantum wells is applied to the multiple quantum well structure. This is a non-linear optical device that is a nitride-based compound semiconductor layer formed so as to be equal or increase along the direction of the electric field. (Operation) Therefore, the invention corresponding to claim 1 takes the above-described means, so that the size of the energy barrier of each quantum well of the active layer in the optical waveguide is limited to the multiple quantum well structure. Since the energy is equal or decreased along the direction of the electric field applied to the well layer, the energy between sub-bands in each well layer decreases along this direction, and the ground level and the excitation level when no electric field is applied. However, at this time, when a predetermined electric field is applied, the energy values of the excitation levels become substantially equal, and electrons are distributed and confined in the excitation levels of each well layer by the resonance tunnel. Since electrons in each well layer emit light and transition to the ground level, and escape from the ground level to the ground level of the next well layer by resonance tunneling, distribution inversion is realized, and laser operation becomes possible. , Subband Since energy is different for each well layer, the gain bandwidth becomes wider, with it, it can realize a broad band gain width and a high response speed.

According to a second aspect of the present invention, the active layer in the optical waveguide is formed of a nitride-based compound semiconductor layer, and the size of the energy barrier of each quantum well is reduced to a multiple quantum well structure. The thickness of the barrier layer forming each quantum well is equal or decreases along the direction of the applied electric field, and is equal or increases along the direction of the electric field applied to the multiple quantum well structure. Therefore, in addition to the function corresponding to the first aspect, since it is formed by the nitride-based compound semiconductor layer, it can be realized by a simple manufacturing process.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a perspective view showing the entire configuration of a nonlinear optical device according to a first embodiment of the present invention.
FIG. 2 is a sectional view showing a layer structure of the nonlinear optical device. In this nonlinear optical device, an optical waveguide 2 is laminated on a sapphire substrate 1. This optical waveguide 2 has an n-type A
1GaN cladding layer 3, n-type InGaN / undoped AlGaN multiple quantum well layer 4 for intersubband absorption,
The structure is such that an undoped GaN layer 5 having a thickness of 0.1 μm, an n-type GaN layer 6 serving as a laser contact layer, a laser active layer 7, and an n-type GaN layer 8 serving as an upper contact layer are stacked.

An electrode 9 is formed on the n-type GaN upper contact layer 8. n-type GaN contact layer 6
An electrode 10 is formed thereon. An electrode 11 is formed on the n-type AlGaN cladding layer 3 to form a multilayer structure.

In this multilayer structure, an anti-reflection film 12 is formed on an input / output surface (resonator surface) orthogonal to the longitudinal direction of each layer. Here, the InGaN / AlGaN multiple quantum well layer 4 has, for example, a structure in which five types of well layers having different In ratios in the range of 0 to 0.32 and different by about 0.08 are stacked for 20 periods. Since the lattice constant of InN is larger than that of GaN, the thickness of the well layer increases with an increase in the In composition. For example, the thickness of the layer with the smallest In is about 1.8 nm, and the thickness of the layer with the largest In is About 1.95n
m thickness.

As shown in FIG. 3, the laser active layer 7 has an n-type GaN layer 71 having a thickness of 100 nm on the contact layer 6,
1 in which the ratio of Al was continuously changed from 0 to 0.46
An n-type AlGaN grading layer 72 having a thickness of 70 nm and an undoped AlGaN / undoped GaN quantum well layer 73 are stacked.

Specifically, the quantum well layer 73 is made of Al _0.67
Ga _0.33 N barrier layer 73a, GaN well layer 73b, Al
_0.67 Ga _0.33 N barrier layer 73 c, GaN well layer 73 d, A
l _0.78 Ga _0.22 N barrier layer 73e, GaN well layer 73f,
Al _O.78 Ga _0.22 N barrier layer 73 g, GaN well layer 73
h, Al _O.89 Ga _0.11 N barrier layer 73i, GaN well layer 7
3j, Al _O.89 Ga _0.11 N barrier layer 73k, GaN well layer 73l, AlN barrier layer 73m, GaN well layer 73n, A
The 1N barrier layers 73o are sequentially stacked.

Each of the layers 73a to 73o has a thickness of 7 monolayers. In the barrier layer, the lattice constant changes according to the change in the Al composition, and the thickness becomes the same or slightly smaller in the stacking order. The energy barrier of each well layer is
They are equal or larger in the stacking order.

On the quantum well layer 73, the ratio of Al is set to 0.1.
An n-type AlGaN grading layer 74 having a thickness of 125 nm continuously changed from 12 to 0.46 is formed. These AlGaN / GaN quantum well layers 73 and n-type A
A total of 25 combinations with the 1GaN grading layer 74
Pairs are sequentially stacked. 25th set of AlGaN / Ga
On the N quantum well layer 73, 100 nm thick n-type GaN
A layer 75, an n-type AlAs cladding layer 76 and an n-type GaN contact layer 8 are formed.

The laser active layer 7 includes the layers 71 to 71 between the contact layer 6 and the n-type GaN contact layer 8.
76. Next, a description will be given of a manufacturing method and operation of the nonlinear optical device configured as described above. (Manufacturing method) After forming a GaN buffer layer grown at a low temperature on the sapphire substrate 1, a nitride epitaxial multilayer film is laminated by epitaxial growth. This laminated structure is dry-etched, and the n-type G
The aN layer 6 is exposed. Further, an etching mask is formed, and dry etching is performed again to expose the n-type AlGaN cladding layer 3. Thereafter, through the steps of forming the electrodes 9 to 11, polishing the back surface of the sapphire substrate 1, cutting out the chip, and forming the antireflection film 12, the nonlinear optical device having the structure shown in FIGS. 1 to 3 is formed. (Operation of Laser Amplifier) First, as shown in FIG. 4, the multiple quantum well layer 73 is formed so that the height of the energy barrier decreases along the direction of the electric field Ei to be applied. As a result, the inter-subband energy ΔEs of each well layer decreases along this direction, and the heights of the ground level E0 and the excitation level E1 when no electric field is applied also decrease. The thickness of the barrier layer of the multiple quantum well layer 73 is set so that when an electric field is applied, the energy value of the excitation level E1 becomes substantially equal at a certain electric field intensity. Inevitably, the energy of the ground level E0 decreases along the direction opposite to the electric field Ei.

The multiple quantum well layer 73 is a low potential side n-type AlGaN grading layer 7 for injecting electrons.
2 (74) and n-type A on the high potential side for extracting electrons
It is sandwiched between the GaN grading layer 74 and the GaN grading layer 74. As shown in FIG. 5, electrons are injected into the excitation level E1 of the n-type GaN well layer 73b having the minimum inter-subband energy ΔEs by a resonance tunnel under a predetermined electric field strength. Are set so that electrons escape from the ground level E0 of the n-type GaN well layer 73n having the largest inter-subband energy by resonance tunneling.

Next, the electrode 10 is set to a low potential and a voltage is applied between the electrodes 9 and 10 so that an electric field of 60 kV / cm is applied to the active layer 7. That is, the application is performed so that the energy barrier value of the well is small and the potential of the side where the thickness of the barrier layer is thick is low.

As a result, the conduction band of the grading layer 72 (74) on the low potential side and the excitation level E1 of the quantum well layer 73 are reduced.
And the electrons are injected into the quantum well layer 73 by resonance tunneling, and are distributed to the excitation level E1 of each well layer by resonance. However, n on the high potential side
The excitation level E
Since there is no level that resonates with 1 (the energy difference from the conduction band of the n-type AlGaN grading layer 74 on the high potential side is sufficiently large), the electrons in the next-stage quantum well layer 73 on the high potential side depend on the resonance tunnel. Does not leak to the type GaN layer 73b, and does not leak even thermally due to the high energy barrier of the AlN layer 73o, and thus the electrons at the excitation level E1 are confined.

On the other hand, the electrons injected into the excitation level E1 emit photons and transition to the ground level E0. On the other hand, under this electric field Ei, the ground level E0 of each well layer gradually decreases toward the higher potential side.
AlGaN grading layer 74 on the high potential side
Is slightly lower than the ground level of the n-type GaN well layer 73n. Therefore, electrons at the ground level E0 can escape to the AlGaN grading layer 74 at high speed by tunneling. The escaped electrons are transmitted to the next quantum well layer 73.
And emits photons again.

As described above, the electrons at the excitation level E1 are confined, and the electrons at the ground level E0 escape to the high potential side, so that the distribution inversion between the two levels is realized, and the cascade laser operation becomes possible.

At this time, since the energy barrier of each quantum well is slightly different, the inter-subband transition energy ΔEs (oscillation wavelength) from the excitation level E1 to the ground level E0 is different for each well layer. In addition, the stimulated emission gain band can be widened. In the case of the present embodiment, about 1.4
There is a gain band from 5 μm to about 1.65 μm. (Function of Intersubband Absorption Layer) InGaN / AlGaN
In the multiple quantum well layer 4, since the inter-subband energy of each quantum well is made slightly different by the structure in which the composition of In is changed stepwise, the spectrum width of the intersubband absorption can be widened. .

Further, by applying a voltage between the electrodes 10 and 11, the InGaN /
An electric field can be applied to the AlGaN multiple quantum well layer 4. At this time, the absorption wavelength and the absorption coefficient of the absorption layer can be adjusted by changing the magnitude of the electric field. For example, since the electrons in each well are loosely coupled across a thin barrier layer, the application of an electric field changes the electron distribution in the multiple quantum well and absorbs light that resonates in the well where many electrons are distributed. The coefficient increases, and conversely, the absorption coefficient decreases for light that resonates with a well having few electrons. (Operation of Entire Nonlinear Optical Device) In the nonlinear optical device according to the present embodiment, when light is incident on one antireflection film, a stimulated emission gain is generated in the active layer 7. Out of the antireflection film. It functions as a so-called traveling wave type laser amplifier.

At this time, part of the incident light is n-type InGa
Since the N / undoped AlGaN multiple quantum well layer 4 oozes out, it is absorbed in accordance with the electron distribution in the multiple quantum well and excites subband electrons in the multiple quantum well. Therefore, the carrier distribution between the subbands changes, and the absorption coefficient and the refractive index of the optical waveguide change.

Here, in the case of incident light having a certain frequency, electronic transition between subbands occurs when light disappears. Normally, the relaxation time of the transition between subbands is several tens fs or more.
Because of the ultra-high speed of several hundred fs, the nonlinear optical device according to the present embodiment can exhibit an ultra-high-speed optical nonlinear effect. This kind of ultra-high-speed nonlinear optical effect can generate, for example, four-wave mixing (FWM), and is expected to be applied to various optical devices.

As described above, according to the first embodiment, as the active layer 7 in the optical waveguide 2, the size of the energy barrier of each quantum well is determined by the electric field applied to the multiple quantum well structure. , The inter-subband energy ΔEs for each well layer decreases along this direction, and the ground level E when no electric field is applied.
However, when a predetermined electric field Ei is applied, the energy level of the excitation level E1 becomes substantially equal, and electrons are excited by the resonance tunnel to the excitation level of each well layer. It is distributed and confined in E1, and electrons in each well layer emit light to transition to the ground level E0 and escape from the ground level E0 to the ground level E0 of the next well layer by a resonance tunnel. Inversion is realized and laser operation becomes possible, and the energy Δ
Since Es is different for each well layer, the gain bandwidth is widened,
Thus, a wide bandwidth gain and a high response speed can be realized.

Further, since each layer is formed of a nitride-based compound semiconductor layer, a barrier layer having high energy can be easily formed, and even if the laser amplifier and the inter-subband absorption layer have an integrated structure. It can be realized by a simple manufacturing process of one-time epitaxial growth without using a complicated process of direct bonding between different kinds of semiconductors.

Further, the nonlinear optical device according to the present embodiment can exhibit a large optical nonlinear effect at a very high speed, and can be expected to be applied to various optical devices. (Second Embodiment) Next, a nonlinear optical device according to a second embodiment of the present invention will be described with reference to FIGS.

That is, the nonlinear optical device according to the present embodiment is a modification of the first embodiment, in which the composition of both the barrier layer and the well layer in the multiple quantum well layer 73 is changed. Specifically, as shown in FIG.
Instead of the active layer 7, a laser active layer 270 having an AlGaN barrier layer having a different Al composition and an InGaN well layer having a different In composition is provided.

Here, as shown in FIG. 6, the laser active layer 270 has an n-type GaN layer 271 having a thickness of 100 nm, and a 460 n layer in which the ratio of Al is continuously changed from 0 to 0.45.
An m-type n-type AlGaN grading layer 272 and an undoped AlGaN / undoped InGaN quantum well layer 273 are stacked.

The quantum well layer 273 is specifically made of Al
_0.67 Ga _0.33 N barrier layer 273 a, GaN well layer 273
b, Al _0.67 Ga _0.33 N barrier layer 273c, n-type In _0.02
Ga _0.98 N well layer 273d, Al _0.76 Ga _0.24 N barrier layer 273e, n-type In _0.03 Ga _0.97 N well layer 273f, A
l _0.76 Ga _0.24 N barrier layer 273 g, n-type In _0.04 Ga
_0.96 N well layer 273 h, Al _O.86 Ga _0.14 N barrier layer 27
3i, n-type In _0.06 Ga _0.94 N well layer 273j, Al
_O.86 Ga _0.14 N barrier layer 273k, n-type In _0.07 Ga _0.93
N well layer 273l, Al _O.97 Ga _0.03 N barrier layer 273
m, n-type In _0.08 Ga _0.92 N well layer 273n, Al _O.97
Ga _0.03 N barrier layers 273o are sequentially stacked.

The energy barrier value of each well layer is sequentially equal or increases in the order of stacking. In addition, each layer 273a
The thickness of ２７273o is 7 monolayers, and the well layer is gradually thickened and the barrier layer is gradually thinned in correspondence with the difference in lattice constant due to the different materials.

On the quantum well layer 273, 374n in which the ratio of Al is continuously changed from 0.08 to 0.45
An m-type n-type AlGaN grading layer 274 is stacked.

AlGaN / InGaN quantum well layer 273
And the n-type AlGaN grading layer 274 are sequentially laminated in a total of 25 sets. 25th set of AlGaN / G
On the aN quantum well layer 273, an n-type G
An aN layer 275 and an n-type AlAs cladding layer 276 are formed.

Next, the operation of the nonlinear optical device configured as described above will be described. The electrode 10 is set to a low potential and a voltage is applied between the electrodes 9 and 10 so that an electric field of 22 kV / cm is applied to the active layer 7. That is, the application is performed such that the energy barrier of the well is small and the potential of the side where the thickness of the barrier layer is thick is low.

As a result, the conduction band Ec of the n-type AlGaN grading layers 272 and 274 matches the energy value of the excitation level E1 of the quantum well layer 273, and electrons are injected into the quantum well layer 273 by a resonance tunnel.

Hereinafter, a cascade laser operation with a wide gain band can be realized as described above. Note that the nonlinear optical device according to the present embodiment has a gain band from about 1.43 μm to about 1.65 μm.

As described above, according to the second embodiment, the same effect as in the first embodiment can be obtained by changing the composition of both the barrier layer and the well layer in the active layer. Can be obtained. (Other Embodiments) In the first embodiment, the case where a voltage is applied between the electrodes 10 and 11 has been described. However, the present invention is not limited to this. Alternatively, the electrode 11 may be omitted. In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[0047]

As described above, according to the first aspect of the present invention, as the active layer in the optical waveguide, the size of the energy barrier of each of the quantum wells is determined by the electric field applied to the multiple quantum well structure. , The inter-subband energy for each well layer decreases along this direction, and the heights of the ground level and the excitation level when no electric field is applied also decrease. However, at this time, when a predetermined electric field is applied, the energy values of the excited levels become substantially equal, the electrons are distributed and confined in the excited levels of each well layer by the resonance tunnel, and the electrons of each well layer are confined. Emits light and transitions to the ground level, and escapes from the ground level to the ground level of the next well layer by resonance tunneling, thereby realizing laser inversion by realizing distribution inversion and energy between subbands. Is a well layer Different since the gain bandwidth becomes wider, with it, can provide a nonlinear optical device capable of realizing a broad band gain width and a high response speed.

According to the second aspect of the present invention, the active layer in the optical waveguide is formed of a nitride-based compound semiconductor layer, and the size of the energy barrier of each quantum well is reduced to a multiple quantum well structure. The thickness of the barrier layer forming each quantum well is equal or decreases along the direction of the applied electric field, and is equal or increases along the direction of the electric field applied to the multiple quantum well structure. Therefore, in addition to the effect of the first aspect, the nonlinear optical device which can be realized by a simple manufacturing process can be provided because the device is formed by the nitride-based compound semiconductor layer.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an entire configuration of a nonlinear optical device according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a layer configuration of the nonlinear optical device in the embodiment.

FIG. 3 is a sectional view showing a configuration of a laser active layer in the embodiment.

FIG. 4 is an energy band diagram when an electric field is not applied for explaining the operation in the embodiment.

FIG. 5 is an energy band diagram at the time of applying an electric field for explaining the operation in the embodiment.

FIG. 6 is a sectional view showing a configuration of a laser active layer according to a second embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 sapphire substrate 2 optical waveguide 3 n-type AlGaN cladding layer 4 n-type InGaN / undoped AlGaN multiple quantum well layer 5 undoped GaN layer 6 n-type GaN layer 7, 270 laser active layer 8 n-type GaN Layers 9 to 11 Electrode 12 Antireflection film 71, 271 n-type GaN 72, 74, 272, 274 n-type AlGaN grading layer 73, 273 undoped AlGaN / undoped Ga
N quantum well layers 73a, 73c, 273a, 273c... Al _0.67 Ga
_0.33 N barrier layers 73b, 73d, 73f, 73h, 73j, 73l, 7
3n, 273b: GaN well layer 73e, 73g, 73i, 73k: Al _0.78 Ga _0.22 N
Barrier layers 73i, 73k ... Al _O.89 Ga _0.11 N barrier layers 73m, 73o ... AlN barrier layers 75, 275 ... n-type GaN 76, 276 ... n-type AlAs cladding layers 273d ... n-type In _0.02 Ga _0.98 N well layers 273e , 273g ... Al _0.76 Ga _0.24 n barrier layer 273 f ... n-type In _0.03 Ga _0.97 n well layer 273h ... n-type In _0.04 Ga _0.96 n well layer _{273i, 273k ... Al O.86 Ga 0.14} n barrier layer 273j ... n-type In _0.06 Ga _0.94 N well layer 273l ... n-type In _0.07 Ga _0.93 N well layer 273m, 273o ... Al _O.97 Ga _0.03 N barrier layer 273n ... n-type In _0.08 Ga _0.92 N well layer ΔEs: inter-subband energy E0 Level E1: Excited level Ei: Electric field

Claims (2)

[Claims] An optical waveguide, a multiple quantum well structure including a plurality of quantum wells formed in a part of the optical waveguide, and at least a part of each quantum well of the multiple quantum well structure; An active layer that generates light-induced emission by transition between the active layer, the active layer, the size of the energy barrier of each quantum well of its own, the electric field applied to the multiple quantum well structure A nonlinear optical device characterized by being formed to be equal or decreasing along a direction. 2. A sub-band comprising an optical waveguide, a multiple quantum well structure comprising a plurality of quantum wells formed in a part of the optical waveguide, and each quantum well of at least a part of the multiple quantum well structure. An active layer that generates light-induced emission by transition between the active layer, the active layer, the size of the energy barrier of each quantum well of its own, the electric field applied to the multiple quantum well structure Formed to be equal or decreasing along the direction, and
The thickness of the barrier layer forming each of the quantum wells is a nitride-based compound semiconductor layer formed so as to be equal or increase along the direction of the electric field applied to the multiple quantum well structure. Characteristic nonlinear optical device.