KR102040881B1 - Optical modulation element with wideband nonlinear optical response - Google Patents

Abstract

Disclosed is an optical modulation device for inducing a wideband nonlinear optical response in a free space by using a plasmonic resonance structure. The optical modulation device according to the present invention comprises: a multi-quantum-well (MQW) layer providing a nonlinear response related to subband transition in a nonlinear optical process; and at least one nanoantenna array disposed on the upper part of the MQW layer, and coupled to the subband transition to perform electromagnetic resonance. The MQW layer has a structure in which well layers and barrier layers are alternately stacked, wherein at least three well layers are prepared. Nanoantennas of the at least one nanoantenna array are symmetrical with respect to a long axis crossing the nanoantennas in the longitudinal direction, and have a symmetrical geometric shape with respect to a short axis perpendicular to the long axis in the same plane.

Description

OPTICAL MODULATION ELEMENT WITH WIDEBAND NONLINEAR OPTICAL RESPONSE

Embodiments in accordance with the inventive concept of the present invention relate to optical modulation devices, in particular meta having a broadband nonlinear optical response based on plasmonic resonators coupled to intersubband transitions in optical metamaterials. It is about the surface.

The field of optical metamaterials has evolved in recent years, including super resolution imaging and optical cloaking, with many applications demonstrated based on linear interactions with light.

Recently, optical metamaterials with nanoscale optical switching and memory, as well as custom nonlinear responses capable of efficient frequency conversion and optical control of highly relaxed phase-matching conditions, have been actively studied. Increasing degrees of freedom and new applications based on metamaterials are being explored.

, 총 27개 성분)을 갖도록 설계될 수 있음이 알려져 있다.Until now, nonlinearity of metamaterials has been exploited by using the natural nonlinear response of plasmonic metal or by combining plasmonic nanoantennas with natural nonlinear photonic crystals. Another approach to realizing a huge nonlinear optical response has been presented by quantum engineering electronic subband transitions in n-doped multi-quantum-well (MQW) heterojunction semiconductor heterostructures. By utilizing electron conduction band subband transitions occurring in n-doped MQW structures, 2nd order nonlinear susceptibility, which is 3-4 orders higher (thousands to tens of thousands) higher than conventional nonlinear materials in nature,

It is known that it can be designed to have a total of 27 components).

FIG. 1A is a one-cycle conduction band diagram of an MQW structure using an InGaAs / AlInAs heterojunction structure. Referring to (a) of FIG. 1, the light of frequency w is used for the electronic subband transition (1-> 2 or 2-> 3) and the second harmonic is generated by the electronic subband transition (3-> 1). w + w = 2w).

만 매우 큰 값을 가진다. 여기서 방향 z-축 방향은 MQW 구조에서 반도체 층에 수직인 것으로 정의된다. 따라서, 다중양자우물구조의 거대 비선형성은 광도파로 기반의 구조에 적용되고 있으나, 구조층에 수직으로 입사된 빛에 대한 비선형 반응을 이용하는 자유공간에서의 응용은 제한적이었다.FIG. 1B shows the second order nonlinear electrical susceptibility induced between the electronic subbands of FIG. 1. Referring to FIG. 1 (b), the large nonlinear reaction occurring in the multi-quantum well structure is a z-axis component due to its characteristic of acting only for polarization with TM polarization, i.e., z-axis electric field component.

Only has a very large value. The direction z-axis direction here is defined as perpendicular to the semiconductor layer in the MQW structure. Therefore, the large nonlinearity of the multi-quantum well structure is applied to the optical waveguide-based structure, but its application in the free space using the nonlinear response to light incident perpendicularly to the structural layer is limited.

U.S. Patent No. 9,733,545 discloses a free space by combining an MQW structure layer and a plasmonic nano resonance structure as shown in FIG. A nonlinear metasurface that operates at is presented.

Thus, the nonlinear metasurface structure produces a very large nonlinear response to any polarization and angle of incidence of the incoming and outgoing wave by the nonlinear optical process determined by the plasmonic nanoresonance structure as shown in FIG. And a very large nonlinear response that occurs in a sub-wavelength structure that is much thinner than the operating wavelength, resulting in very relaxed phase junction conditions and efficient frequency conversion.

However, the above prior art document indicates that the large second order nonlinear electrical susceptibility of the MQW structure is generated based on the resonance characteristics due to the subband transition, and thus has a high nonlinearity only near the resonant wavelength. The second harmonic generation (SHG) operating wavelength is also limited to near the subband transition resonance wavelength.

United States Patent Publication No. 9,733,545

The present invention has been made to solve the above problems, the optical modulation device of the present invention three quantum well structure and the second non-linear electrical susceptibility modulation phenomenon according to the voltage and voltage applied to the quantum well structure plasma The objective is to induce a wideband nonlinear optical response in free space using a monaural resonant structure.

The optical modulation device of the present invention for achieving the above object is a multi-quantum-well (MQW) layer that provides a nonlinear response associated with the subband transition in a nonlinear optical process, and the top of the MQW layer At least one nanoantenna array coupled to the subband transitions for electromagnetic resonance, wherein the MQW layer has a structure in which a well layer and a barrier layer are alternately repeatedly stacked, the at least three well layers, The nanoantennas of the at least one nanoantenna array have an asymmetrical geometry with respect to the major axis traversing the longitudinal direction of the nanoantenna and a symmetrical geometric form with respect to the minor axis orthogonal to the major axis in the same plane.

The light modulation device further includes a ground layer disposed below the MQW layer.

Each of the nanoantenna and ground layer of the at least one nanoantenna array is used as an electrode and a voltage is applied across the MQW layer to control and shift the resonant frequency of the MQW layer.

The electron subband energy level of the MQW layer is adjusted according to the applied voltage.

The nanoantenna array is patterned into a complementary split-ring-resonator (CSRR) shape and includes a nanogap between the CSRR shapes in a first axis direction.

The nano-antenna may include a first region having a longitudinal direction in the first axial direction, a second region protruded convexly in a second axial direction orthogonal to the first axial direction at the center of the first region, and Both ends of the first region include a third region and a fourth region which protrude convexly in the second axial direction.

The length in the first axis direction of the first region is determined according to the frequency of incident light, and the length in the second axis direction of the first region and the first axis direction of the second region is determined according to the frequency of light emitted. The length and the length in the second axial direction are determined.

The length in the first axial direction of the first region is longer than the sum of the length in the second axial direction of the first region and the length in the second axial direction of the second region.

The nanoantenna may include a fifth region facing the third region based on the first axial direction of the first region, and facing the fourth region based on the first axial direction of the first region. And a sixth region.

Since the optical modulation device of the present invention as described above can induce a wideband nonlinear optical response in free space, it can provide an effect of developing a wideband nonlinear light source.

In addition, the broadband non-linear light source of the present invention does not require a phase bonding condition and can be manufactured in a small size, thereby providing a mid-infrared laser light source at low cost.

The detailed description of each drawing is provided in order to provide a thorough understanding of the drawings cited in the detailed description of the invention.
Figure 1 (a) is a one-cycle conduction band diagram of the MQW structure using a conventional InGaAs / AlInAs heterojunction structure.
FIG. 1B shows the second order nonlinear electrical susceptibility induced between the electron subbands of FIG. 1A.
2 (a) shows a conventional nonlinear metasurface unit cell.
FIG. 2B is a conceptual diagram illustrating the nonlinear response of FIG. 2A.
3 illustrates a metasurface structure according to an embodiment of the present invention.
4 illustrates a metasurface unit cell according to an embodiment of the present invention.
5 is a conceptual diagram illustrating a structure of a nanoantenna according to an exemplary embodiment of the present invention.
6 is a plan view of a normalized Ez electric field distribution induced inside a multi-quantum well structure by a nanoantenna according to an exemplary embodiment of the present invention.
7 illustrates an electron conduction band of a multi quantum well structure according to voltage according to an embodiment of the present invention.
8 shows the second nonlinear electrical susceptibility according to the voltage.
9 is a view for explaining a method of manufacturing a meta surface according to an embodiment of the present invention.

Hereinafter, the present invention will be further described with reference to embodiments and drawings according to the present invention.

3 illustrates a metasurface structure according to an embodiment of the present invention. Referring to FIG. 3, a light modulation device (meta surface structure or light modulation device or meta surface; 10, hereinafter referred to as a meta surface) includes a substrate 100, a ground layer 200 disposed on the substrate 100, and a ground layer. Multi-quantum-well (MQW) layer 300 disposed above 200, and one or more nanoantenna array 400 disposed over MQW layer 300.

Metasurfaces according to embodiments of the invention are designed for nonlinear response to nonlinear optical processes. The substrate 100 may be made of a semiconductor (eg, InP) or a dielectric material, and the ground layer 200 may be made of a metal or a doped semiconductor, but is not limited thereto.

MQW layer 300 is sandwiched between a ground layer and a patterned array of metal nanoantennas. For example, nano antenna array 400 is disposed on top of MQW layer 300.

MQW layer 300 may provide a nonlinear response associated with subband transitions in a nonlinear optical process. For example, the MQW layer 300 may have a structure in which a well layer and a barrier layer are alternately stacked alternately, and the wells may be at least three. The material of the MQW layer 300 is GaN, AlN, InN, InGaN, AlGaN, InAlN, InAlGaN, AlAs, GaAs, GaP, InP, AlP, AlGaAs, AlInAs, InGaAs, AlGaP, AlInP, InGaP, AlInGap, AlInGaAs or AlInGaAsP. It may include at least one.

For example, the MQW layer 300 may be based on a heterojunction of a material having a small band gap (eg, InGaAs) and a material having a large band gap (eg, AlInAs).

One or more nanoantenna arrays 400 may be plasmonic resonators. Each of the nanoantennas of one or more nanoantenna arrays 400 may have an asymmetrical geometry and the MQW region outside the nanoantenna may be etched. The invention includes the construction of a nanoantenna such that the resonant electromagnetic mode of the metallic nanoantenna can be connected to the subband transition of the MQW layer.

For example, the nanoantenna array 400 is patterned into a complementary split-ring-resonator (CSRR) shape, and has an array form including nanogaps between CSRR shapes in the x-axis direction. The reason why the array 400 includes nanogaps in the x-axis direction will be described in detail with reference to FIG. 6.

4 illustrates a meta surface unit cell according to an exemplary embodiment of the present invention, and FIG. 5 is a conceptual diagram illustrating a structure of a nanoantenna according to an exemplary embodiment of the present invention. Referring to FIG. 4, the metasurface unit cell 20 includes a substrate 100, a ground layer 200 disposed on the substrate 100, an MQW layer 300 disposed on the ground layer 200, and an MQW layer ( Nanoantenna 410 coupled to the subband transition of 300).

Referring to FIG. 5, the nanoantenna 410 may have an asymmetric geometric shape. According to an embodiment, the nanoantenna 410 may be a complementary split-ring-resonator (CSRR) type, according to an exemplary embodiment, based on a long axis that extends in the longitudinal direction of the nanoantenna 410. It is asymmetric, and may have a geometric shape symmetrical with respect to a short axis orthogonal to the long axis in the same plane, but is not limited thereto.

값이 쉬프트하게 된다. 따라서, 광대역의 거대 제2차 비선형 전기감수율을 얻을 수 있는 효과가 있다.3 and 5, metal electrode lines A3 to A6 are attached to both ends of the T-shaped structure or the gamma structures A1 and A2 that generate the second harmonic, thereby connecting both the T-shaped structure or the gamma structure. have. When a voltage is supplied between the nanoantenna array 400 and the substrate 100, the voltage is applied in the vertical direction to each resonance structure. A voltage is then applied across the MQW layer 300, depending on the applied voltage

The value is shifted. Therefore, there is an effect that can obtain a large second order nonlinear electrical susceptibility of broadband.

에 의해 주파수 2w의 z-축 방향 제2차 분극으로 변환된다. 각 나노 안테나(410)는 주파수 2w의 z-축 방향 제2차 분극을 y-축 방향으로 편광된 주파수 2w 빛으로 방출하는 역할을 한다.3 and 4, when light of frequency w is incident in the z-axis direction to the nanoantenna array 400, the light of frequency w generates an electric field polarized in the x-axis direction perpendicular to the z-axis. Have Each nanoantenna 410 absorbs light of frequency w having an electric field polarized in the x-axis direction, and induces an electric field in a vertical direction (z-axis direction) inside the MQW layer 300. The induced vertical electric field is the second nonlinear electrical susceptibility of the MQW layer 300.

Is converted into the second-order polarization in the z-axis direction at the frequency 2w. Each nanoantenna 410 serves to emit a second polarization in the z-axis direction at a frequency of 2w as light polarized at a frequency of 2w in the y-axis direction.

The structure of each nanoantenna 410 well absorbs (or emits) light of frequency w with an electric field polarized on the x-axis, and well absorbs (or emits light of frequency 2w with an electric field polarized on the y-axis. It is formed to

Specifically, the larger the frequency, the smaller the wavelength, but since the resonance structure is determined according to the wavelength, the horizontal portion (x1 in FIG. 5) and the vertical portion (y1 + y2 in FIG. 5) of the nanoantenna 410 are dependent on the frequency w and the frequency 2w. ) Length is determined. Therefore, the horizontal portion x1 determined by w is longer than the vertical portion y1 + y2 determined by 2w.

6 is a plan view of a normalized Ez electric field distribution induced inside a multi-quantum well structure by a CSRR type nanoantenna according to an exemplary embodiment of the present invention. Referring to FIG. 6, since the nanoantenna array 400 includes a nanogap between CSRR shapes in the x-axis direction, free electrons of the metal are trapped, and resonance occurs in the x-axis direction at the frequency w.

 Although one nanoantenna array 400 is shown in FIG. 3, one or more nanoantenna arrays that exist above and / or below the MQW layer 300 with electromagnetic resonance coupled to the subband transitions of the MQW layer 300. It may include a multi-nano antenna array comprising a.

The nanoantennas of one or more nanoantenna arrays may be made of metal or doped semiconductors, but are not limited thereto.

The nanoantennas of the nanoantenna array are designed to have a resonance approximately equal to the input and / or output frequency of the nonlinear optical process. In addition, each of the nanoantennas may have the same design, or one or more nanoantennas may have a different design.

The MQW layer 300 may be composed of a multilayer structure in which individual MQW structures are placed on top of each other. Individual MQW structures can be designed to provide a nonlinear response in a nonlinear optical process. These individual MQW structures may have the same design with each other, or one or more MQW structures may have different designs.

Each of the nanoantenna and ground layer is used as an electrode and a voltage is applied across the MQW layer 300 to control and shift the resonant frequency of the MQW layer 300.

Arrow 500 represents the incident pump beam at the fundamental frequency w and arrow 600 represents the second harmonic beam reflected at 2w as will be described later.

Referring to FIG. 5, the structure of the nanoantenna 410 will be described in detail. The nanoantenna 410 may include a first area A1 and a second area A2. The length x1 in the first axial direction of the first region of the nanoantenna 410 is determined according to the frequency w, and the length Y1 in the second axial direction of the first region A1 and the second according to the frequency 2w. The length X2 in the first axial direction of the region A2 and the length Y2 in the second axial direction of the second region A2 are determined. According to an embodiment, the length X1 of the horizontal portion x1, that is, the first axial direction X of the first region A1, is the second portion of the vertical portion y1 + y2, that is, the first region A1. The length Y1 of the axial direction Y and the length Y2 of the second axial direction Y of the second region A2 are longer than the length y1 + y2.

The first axis direction X may be a longitudinal direction and the second axis direction Y may be a direction perpendicular to the first axis direction X in the same plane, and the second area A2 may be the first area A1. It may protrude convexly in the second axial direction (Y) in the center of.

The nanoantenna 410 may further include a third region A3 and a fourth region A4 protruded convexly in the second axial direction Y at both ends of the first region A1. The lengths Y3 and Y4 of the second axial direction Y of each of the third area A3 and the fourth area A4 are larger than the length Y2 of the second axial direction Y of the second area A2. It may be longer, but is not limited to such.

The length X2 of the first axis direction X of the second area A2 is greater than the lengths X3 and X4 of the first axis direction X1 of each of the third area A3 and the fourth area A4. It may be long, but is not limited thereto.

The nanoantenna 410 refers to the fifth region A5 facing the third region A3 based on the first axial direction X of the first region, and the first axial direction X of the first region. As a result, the display device may further include a sixth region A6 facing the fourth region A4. Each of the fifth region A5 and the sixth region A6 protrudes convexly in a direction opposite to the second axial direction Y. FIG. The length Y3 of the second axial direction Y of the third region is longer than the length Y5 of the second axial direction Y of the fifth region, and the length of the second axial direction Y of the fourth region. Y4 may be longer than the length Y6 of the second axis direction Y of the sixth region, but is not limited thereto.

The lengths X5 and X6 of the first axial direction X of each of the fifth region A5 and the sixth region A6 are respectively defined in the first axial direction (the third region A3 and the fourth region A4). It may be the same as the length (X3, X4) of X), but is not limited thereto.

Referring again to FIG. 4, examples of the dimensions of each layer constituting the metasurface 20 are shown in Table 1 below.

Nano antenna MQW Ground layer Board thickness 50 nm 400 nm 50 nm 200 nm

7 illustrates an electron conduction band of a multi quantum well structure according to voltage according to an embodiment of the present invention. (A), (b), and (c) of FIG. 7 each show electron conduction bands when voltages of 0 V, +2 V, and -2 V are applied to the quantum well structure.

It is possible to induce a large second order nonlinear electrical susceptibility in two quantum well structures based on conventional InGaAs / AlInAs heterojunction structures, but in this structure, 1-> 3 subband transition energy cannot be modulated by voltage or electric field. Large nonlinearities could not be induced in broadband.

However, as shown in FIG. 7, when inducing at least three electron subbands into different quantum wells using at least three quantum well structures and applying a voltage to the quantum well structure, a stark effect is obtained. Since the electronic subband energy level can be adjusted according to the voltage applied by, it is possible to induce broadband giant nonlinearity.

Accordingly, by combining the multi-quantum well structure layer with the plasmonic resonant structure and simultaneously utilizing the plasmonic resonant structure as an electrode, it is possible to develop a meta-surface that can induce the generation of the second harmonic with high efficiency.

8 shows the second nonlinear electrical susceptibility according to the voltage. Referring to FIG. 8, as the graph moves to the right, the voltage applied to the multi-quantum well structure layer increases, and the second nonlinear electrical susceptibility varies according to the voltage. As described in FIG. 7, since the subband transition energy can be adjusted according to the voltage applied to the multi quantum well structure layer, the second nonlinear electrical susceptibility can be induced over a wide wavelength range according to the voltage applied to the multi quantum well structure layer. .

In addition, the broadband large nonlinearity combined with the plasmonic resonant structure can produce the second harmonic with high efficiency when fabricated as an active metasurface.

9 is a view for explaining a method of manufacturing a meta surface according to an embodiment of the present invention. Referring to FIG. 9, a metal or a doped semiconductor is formed on a first substrate, and an MQW layer and a metal or doped semiconductor are sequentially stacked on a second substrate (FIG. 9A). The metal or doped semiconductor of the first substrate and the metal or doped semiconductor of the second substrate are bonded by thermo-compression wafer bonding (FIG. 9B).

Thereafter, the second substrate on which the MQW layer is formed is removed (FIG. 9C). The second substrate is removed to form a metal or doped semiconductor corresponding to the antenna on the removed MQW layer. After that, the antenna is etched to a desired shape using a mask, and the mask is removed (Fig. 9 (d)).

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

10; Meta surface
20; Meta surface unit cell
100; Board
200; Ground layer
300; MQW floor
400; Nano antenna array
410; Nano antenna

Claims (9)

A multi-quantum-well (MQW) layer providing a nonlinear response associated with subband transitions in a nonlinear optical process; And
One or more nanoantenna arrays disposed on top of the MQW layer and coupled to the subband transitions for electromagnetic resonance;
The MQW layer has a structure in which a well layer and a barrier layer are alternately stacked alternately, and the well layers are at least three,
The nanoantennas of the at least one nanoantenna array have a geometrical shape which is asymmetrical with respect to the long axis crossing the longitudinal direction of the nanoantenna and symmetrical with respect to the short axis perpendicular to the long axis in the same plane.
The nanoantenna array is patterned in a complementary split ring resonator (CSRR) shape, and includes a nanogap between the CSRR shapes in a first axis direction, so that free electrons of metal are trapped and in the x-axis direction at frequency w. Resonance occurs,
The nano antenna,
A first region A1 having a longitudinal direction in the first axial direction;
A second area A2 protruded convexly from a center of the first area in a second axis direction perpendicular to the first axis direction;
Third and fourth regions A3 and A4 protrudingly convex in the second axial direction at both ends of the first region A1;
A fifth region A5 facing the third region A3 based on the first axial direction of the first region A1; And
And a sixth region (A6) facing the fourth region (A4) based on the first axial direction of the first region (A1). The method of claim 1,
And a ground layer disposed below the MQW layer. The method of claim 2,
Each of the nanoantenna and the ground layer of the at least one nanoantenna array is used as an electrode,
And a voltage is applied across the MQW layer to control and shift the resonant frequency of the MQW layer. A multi-quantum well (MQW) layer having a structure in which a well layer and a barrier layer are alternately repeatedly stacked, the well layer being at least three;
A nanoantenna array disposed on top of the MQW layer and arranged with at least one nanoantenna coupled to a subband transition for electromagnetic resonance; And
And a ground layer disposed below the MQW layer.
Each of the nanoantennas and the ground layer is used as an electrode, and the electron subband energy levels of the MQW layer are induced to three quantum well structures, respectively, by a voltage applied across the MQW layer.
And modulating a wavelength at which the maximum value of the second order nonlinear electrical susceptibility occurs according to the voltage applied to the MQW layer, and inducing a large second order nonlinear electrical susceptibility to a predetermined wavelength range. delete delete The method of claim 1,
The length in the first axis direction of the first region is determined according to the frequency of incident light, and the length in the second axis direction of the first region and the first axis direction of the second region is determined according to the frequency of light emitted. A length and a length in a second axis direction are determined. The method of claim 7, wherein
And the length in the first axial direction of the first region is longer than the sum of the length in the second axial direction of the first region and the length in the second axial direction of the second region. delete

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