Optical modulating device and apparatus including the same

An optical modulating device may include a plurality of quantum dot (QD)-containing layers having QDs and a plurality of refractive index change layers. The QD-containing layers may be disposed between the refractive index change layers, respectively. The optical modulating device may be configured to modulate light-emission characteristics of the plurality of QD-containing layers. At least two of the QD-containing layers may have different central emission wavelengths. At least two of the plurality of refractive index change layers may include different materials or have different carrier densities.

BACKGROUND

Example embodiments of the present disclosure relate to optical modulating devices and apparatuses including the same.

2. Description of the Related Art

Optical devices for changing the characteristics of light such as transmission/reflection, phase, amplitude, polarization, intensity, path, etc. of light are used in a variety of optical apparatuses. Optical modulators having various structures have been suggested to control the above characteristics of light in a desired method in an optical system. For example, liquid crystal having optical anisotropy or a microelectromechanical system (MEMS) structure using a fine mechanical movement of a light blocking/reflection element is used for general optical modulators. Such optical modulators have a slow operation response time of over several microseconds (μs) due to the characteristics of a driving method.

SUMMARY

One or more example embodiments provide optical modulating devices which may adjust and/or modulate optical characteristics at high speed by using quantum dots as an optical modulating element.

One or more example embodiments also provide optical modulating devices which may emit light of a multi-wavelength region and more easily control and/or modulate the light.

One or more example embodiments also provide optical modulating devices which may multiplex light of a multi-wavelength region.

One or more example embodiments also provide apparatuses including the optical modulating devices.

According to an aspect of an example embodiment, there is provided an optical modulating device including a plurality of refractive index change layers, and a plurality of quantum dot (QD)-containing layers disposed between the plurality of refractive index change layers, respectively, wherein the optical modulating device is configured to modulate light-emission characteristics of the plurality of QD-containing layers.

The at least two of the plurality of QD-containing layers may have central emission wavelengths that are different from each other.

The plurality of QD-containing layers may include a first QD-containing layer and a second QD-containing layer, the first QD-containing layer may include first quantum dots and the second QD-containing layer may include second quantum dots, and the first quantum dots and the second quantum dots may include materials that are different from each other and/or have different sizes that are different from each other.

The at least two of the plurality of QD-containing layers may include thicknesses that are different from each other.

The each of the plurality of QD-containing layers may include an insulating layer and a plurality of quantum dots embedded in the insulating layer.

The at least two of the plurality of refractive index change layers may include materials that are different from each other.

The at least two of the plurality of refractive index change layers may have carrier densities that are different from each other.

The at least two of the plurality of refractive index change layers may have thicknesses that are different from each other.

The plurality of refractive index change layers may include at least one of a transparent conductive oxide and a transition metal nitride.

The optical modulating device may further include a signal application device configured to apply an electrical signal to the plurality of refractive index change layers, the optical modulating device being configured to change refractive indexes of the plurality of refractive index change layers based on the electrical signal applied by the signal application device.

The plurality of refractive index change layers and the plurality of QD-containing layers may form a stack structure, and the optical modulating device may further include a reflector disposed on a first surface of the stack structure, and a band-stop mirror disposed on a second surface, opposite to the first surface, of the stack structure.

The optical modulating device may further include a light source provided between the stack structure and the reflector and configured to emit light to optically excite quantum dots included in the plurality of QD-containing layers, respectively, or an optical waveguide disposed between the stack structure and the reflector and configured to guide light to optically excite the quantum dots included in the plurality of QD-containing layers.

The plurality of refractive index change layers and the plurality of QD-containing layers may form a stack structure, the optical modulating device may further include a light source provided on a surface of the stack structure and configured to emit light to optically excite quantum dots included in the plurality of QD-containing layers, or an optical waveguide provided on the surface of the stack structure and configured to guide light to optically excite the quantum dots included in the plurality of QD-containing layers.

The plurality of refractive index change layers and the plurality of QD-containing layers may form a stack structure, the optical modulating device further including a nano-antenna structure disposed on a first surface of the stack structure.

The nano-antenna structure may include one of a metallic antenna, a dielectric antenna, and a slit-containing structure.

The nano-antenna structure may include one of a multi-patch antenna structure and a fishbone shaped antenna structure.

The nano-antenna structure may include an output coupler.

The optical modulating device may further include a light source provided at a second surface, opposite to the first surface, of the stack structure and configured to emit light to optically excite quantum dots included in the plurality of QD-containing layers, or an optical waveguide provided at the second surface of the stack structure and configured to guide light to optically excite the quantum dots included in the plurality of QD-containing layers, wherein the stack structure is disposed between the nano-antenna structure and the light source or the optical waveguide.

The optical modulating device may further include a reflector disposed on the light source or the optical waveguide, and a band-stop mirror disposed between the stack structure and the nano-antenna structure.

An optical apparatus may include the optical modulating device.

According to another aspect of an example embodiment, there is provided an optical modulating device including a plurality of refractive index change layers, and a plurality of quantum dot (QD)-containing layers disposed between the plurality of refractive index change layers, the plurality of QD-containing layers including quantum dots (QDs), and at least two of the plurality of QD-containing layers having central emission wavelengths that are different from each other, wherein the optical modulating device is configured to modulate, based on a refractive index change of the plurality of refractive index change layers, light-emission characteristics of the plurality of QD-containing layers to have characteristics of emitting light of a plurality of wavelength regions.

The at least two of the plurality of refractive index change layers may include materials that are different from each other or include different carrier densities that are different from each other.

The plurality of refractive index change layers and the plurality of QD-containing layers may form a stack structure, the optical modulating device may further include a light source provided on a surface of the stack structure and configured to emit light to optically excite quantum dots included in the plurality of QD-containing layers, or an optical waveguide provided on the surface of the stack structure and configured to guide light to optically excite the quantum dots included in the plurality of QD-containing layers.

The plurality of refractive index change layers and the plurality of QD-containing layers may form a stack structure, wherein the optical modulating device further includes a reflector disposed on a first surface of the stack structure, and a band-stop mirror disposed on a second surface, opposite from the first surface, of the stack structure.

An optical apparatus may include the optical modulating device.

The nano-antenna structure may further include an input coupler.

According to another aspect of an example embodiment, there is provided an optical modulating device including a plurality of refractive index change layers, a plurality of quantum dot (QD)-containing layers disposed between the plurality of refractive index change layers, respectively, and a signal application device configured to apply an electrical signal to the plurality of refractive index change layers, respectively, wherein the optical modulating device is configured to change refractive indexes of the plurality of refractive index change layers based on the electrical signal applied by the signal application device to the plurality of refractive index change layers, and modulate light-emission characteristics of each of the plurality of QD-containing layers based on the changed refractive indexes of the plurality of refractive index change layers.

The plurality of QD-containing layers may include a plurality of quantum dots embedded in an insulating layer.

The plurality of refractive index change layers and the plurality of QD-containing layers may form a stack structure, the optical modulating device further including a nano-antenna structure disposed on a surface of the stack structure.

DETAILED DESCRIPTION

Various example embodiments will now be described more fully with reference to the accompanying drawings in which example embodiments are shown.

Reference will now be made in detail to example embodiments of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. Also, the size of each layer illustrated in the drawings may be exaggerated for convenience of explanation and clarity. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein.

FIG. 1is a cross-sectional view of an optical modulating device according to an example embodiment.

Referring toFIG. 1, a plurality of layers, each including a plurality of quantum dots (QDs), which is referred to as QD-containing layers, may be arranged apart from each other. For example, first to third QD-containing layers A10, A20, and A30may be provided. However, example embodiments are not limited thereto, and the number of QD-containing layers is exemplary and may be changed. The first to third QD-containing layers A10, A20, and A30may respectively include first to third insulating layers N10, N20, and N30and a plurality of quantum dots QD1, QD2, and QD3respectively embedded in the first to third insulating layers N10, N20, and N30. The quantum dots QD1included in the first QD-containing layer A10may be referred to as first QDs, the quantum dots QD2included in the second QD-containing layer A20may be referred to as second QDs, and the quantum dots QD3included in the third QD-containing layer A30may be referred to as third QDs. At least two of the first to third QD-containing layers A10, A20, and A30may have different central emission wavelengths. In this regard, at least two of the first to third quantum dots QD1, QD2, and QD3may include different materials and/or have different sizes. The central emission wavelengths of the first to third QD-containing layers A10, A20, and A30may vary according to the material or size of the QDs. All of the first to third quantum dots QD1, QD2, and QD3may have different central emission wavelengths. However, example embodiments are not limited thereto, and in some cases, at least two of the first to third quantum dots QD1, QD2, and QD3may have the same central emission wavelength, where the at least two of the first to third quantum dots QD1, QD2, and QD3may be substantially the same.

A plurality of refractive index change layers may be provided spaced apart from each other. For example, first to fourth refractive index change layers R10, R20, R30, and R40may be provided, and the first to third QD-containing layers A10, A20, and A30may be arranged between the first to fourth refractive index change layers R10, R20, R30, and R40. The first to fourth refractive index change layers R10, R20, R30, and R40each may be a layer having a refractive index that is changed according to an electrical signal applied thereto or other conditional changes. The first to fourth refractive index change layers R10, R20, R30, and R40may be layers in which permittivity is changed according to an electrical condition. A charge concentration (charge density) of an area(s) in the first to fourth refractive index change layers R10, R20, R30, and R40may be changed according to an electric field applied to the first to fourth refractive index change layers R10, R20, R30, and R40. Accordingly, the permittivity of the first to fourth refractive index change layers R10, R20, R30, and R40may be changed. For example, each of the first to fourth refractive index change layers R10, R20, R30, and R40may include a transparent conductive oxide (TCO) such as indium tin oxide (ITO), indium zinc oxide (IZO), aluminium zinc oxide (AZO), gallium zinc oxide (GZO), aluminium gallium zinc oxide (AGZO), or gallium indium zinc oxide (GIZO), or a transition metal nitride such as titanium nitride (TiN), zirconium nitride (ZrN), hafnium nitride (HfN), or tantalum nitride (TaN). In addition, the first to fourth refractive index change layers R10, R20, R30, and R40may include an electro-optic (EO) material whose effective permittivity is changed when an electrical signal is applied thereto. The EO material may include, for example, a crystal material such as lithium niobate (LiNbO3), lithium tantalate (LiTaO3), potassium tantalate niobate (KTN), or lead zirconate titanate (PZT), or various polymers having EO characteristics. The first to fourth refractive index change layers R10, R20, R30, and R40may be a semiconductor, a conductor, or a dielectric. The first to fourth refractive index change layers R10, R20, R30, and R40may be transparent or substantially transparent.

The first to fourth refractive index change layers R10, R20, R30, and R40may be formed of the same material, and may have the same carrier density. By varying an electrical signal applied to the first to fourth refractive index change layers R10, R20, R30, and R40, or other conditions, the characteristics of the first to fourth refractive index change layers R10, R20, R30, and R40may be independently controlled. According to example embodiments, at least two of the first to fourth refractive index change layers R10, R20, R30, and R40may include different materials and/or may have different carrier densities. In this case, controlling the characteristics of the first to third QD-containing layers A10, A20, and A30to be different from one another may be easier by using the first to fourth refractive index change layers R10, R20, R30, and R40.

The optical modulating device according to the example embodiment may be configured to modulate the light-emission characteristics of the first to third QD-containing layers A10, A20, and A30based on a change in the refractive indexes of the first to fourth refractive index change layers R10, R20, R30, and R40. When the first to third QD-containing layers A10, A20, and A30have different central emission wavelengths, the optical modulating device may emit light beams of a multi-wavelength region and the light beams of a multi-wavelength region may be independently controlled. Accordingly, an optical modulating device according to an example embodiment may emit light beams of a multi-wavelength region and more easily control the light beams. According to an example embodiment, an optical modulating device may multiplex the light beams of multiple wavelength regions. According to an example embodiment, a multiplexing optical modulating device may actively tune a light beam for each wavelength region.

The first to fourth refractive index change layers R10, R20, R30, and R40and the first to third QD-containing layers A10, A20, and A30may form a stack structure, as illustrated inFIG. 1. The optical modulating device may further include a reflector RT10provided at a surface of the stack structure and a band-stop mirror MR10provided at an opposite surface of the stack structure. Furthermore, the optical modulating device may further include, between the stack structure and the reflector RT10, a light source element LS10to emit light to optically excite the first to third quantum dots QD1, QD2, and QD3of the first to third QD-containing layers A10, A20, and A30.

The band-stop mirror MR10may have reflection characteristics with respect to light of a specific wavelength region and transmission characteristics with respect to the wavelength regions other than the specific wavelength region. The band-stop mirror MR10may have, for example, a distributed Bragg reflector (DBR) structure. Two dielectric layers having different refractive indexes may be repeatedly stacked under a λ/4 thickness condition, where λ is the wavelength of light, thereby increasing reflectivity or transmissivity of a desired wavelength region. However, example embodiments are not limited thereto, and the band-stop mirror MR10may have a structure other than the DBR structure. The reflector RT10may be formed of a conductor such as metal or may have a DBR structure. The reflector RT10may be a back reflector electrode. The light source element LS10may include an inorganic-based light-emitting device (iLED), an organic light-emitting device (OLED), or a laser diode (LD). Light to excite the first to third quantum dots QD1, QD2, and QD3, that is, excitation light, may be radiated from the light source element LS10toward the first to third QD-containing layers A10, A20, and A30. The reflector RT10and the band-stop mirror MR10may be configured in a cavity structure such that the excitation light emitted from the light source element LS10is internally reflected in the optical modulating device. Accordingly, the light source element LS10, the reflector RT10, and the band-stop mirror MR10may increase luminous efficacy and modulation efficiency of the optical modulating device. The light emitted and modulated in the first to third QD-containing layers A10, A20, and A30may be output (emitted) above the band-stop mirror MR10by passing through the same.

The QDs applied to example embodiments, that is, the first to third quantum dots QD1, QD2, and QD3, may include semiconductor particles having a ball shape of a nanometer size or a shape similar thereto, and may have a size (diameter) of about several nanometers (nm) to about several tens of nanometers. A QD may have a monolithic structure or a core-shell structure. The core-shell structure may be a single shell structure or a multi-shell structure. For instance, the core-shell structure may include a core part, which is a central body of a QD, formed of a certain first semiconductor and a shell part formed of a second semiconductor. The QD may include at least one of II-VI group based semiconductor, III-V group based semiconductor, IV-VI group based semiconductor, and IV group based semiconductor. Since the QD has a significantly small size, a quantum confinement effect may be obtained. When particles are very small, electrons in the particle have a discontinuous energy state near an outer wall of the particle. In this case, as the size of a space in the particle decreases, the energy state of the electrons relatively increases and an energy band gap increases, which is referred to as the quantum confinement effect. According to the quantum confinement effect, when light such as an infrared ray or a visible ray is incident on QDs, light having a wavelength of various ranges may be generated. The wavelength of light generated from a QD may be determined based on the size, material, or structure of a QD particle. For example, when light of a wavelength having energy greater than the energy band gap is incident on a QD, the QD may absorb energy of the light and be excited, and may return to the ground state by emitting light of a specific wavelength. In this case, as the size of a QD or the core part of the QD decreases, light of a relatively short wavelength, for example, a blue-based light or a green-based light, may be generated. As the size of a QD or the core part of the QD increases, light of a relatively long wavelength, for example, a red-based light, may be generated. Accordingly, light of various colors may be embodied depending on the size of a QD or the core part of the QD. The emission wavelength may be adjusted not only by the size/diameter of a QD, but also by the constituent material and structure thereof. The first to third insulating layers N10, N20, and N30, in which the quantum dots QD1, QD2, and QD3are embedded, may be dielectric layers made of, for example, a silicon oxide (SiO) or a silicon nitride (SiN). Each of the first to third QD-containing layers A10, A20, and A30may have a thickness of, for example, about several tens of nanometers or less. Each of the first to fourth refractive index change layers R10, R20, R30, and R40may have a thickness of, for example, about several tens of nanometers or less. However, the thicknesses of the first to third QD-containing layers A10, A20, and A30and the first to fourth refractive index change layers R10, R20, R30, and R40are not limited thereto and may vary.

According to an example embodiment, based on a change in the characteristics of the first to fourth refractive index change layers R10, R20, R30, and R40, the light-emission characteristics of the first to third QD-containing layers A10, A20, and A30may be more quickly and easily modulated. In particular, the characteristics of the first to fourth refractive index change layers R10, R20, R30, and R40may be more easily modulated based on a changed electrical signal, and consequently faster optical modulation may be possible. Furthermore, by using the first to third QD-containing layers A10, A20, and A30having different central emission wavelengths, light of multiple wavelength regions, that is, multi-color, may be multiplexed, and may be more quickly modulated. Light beams of different wavelength regions may be independently controlled and modulated. When the first to third QD-containing layers A10, A20, and A30all include the same quantum dots, as an optical modulating device is formed by inserting the first to third QD-containing layers A10, A20, and A30between the first to fourth refractive index change layers R10, R20, R30, and R40, luminous efficiency and modulation efficiency may be improved.

According to an example embodiment, the reflector RT10and the band-stop mirror MR10as illustrated inFIG. 1may not be included, and an example thereof as illustrated inFIG. 2.

Referring toFIG. 2, an optical modulating device may include the first to third QD-containing layers A10, A20, and A30and the first to fourth refractive index change layers R10, R20, R30, and R40on the light source element LS10.

According to example embodiments, an optical waveguide WF10may be provided at a position of the light source element LS10inFIGS. 1 and 2, as illustrated inFIGS. 3 and 4.

FIGS. 3 and 4respectively illustrate that an optical waveguide WG10is provided at a position of the light source element LS10ofFIGS. 1 and 2. The optical waveguide WG10may guide light to optically excite the first to third quantum dots QD1, QD2, and QD3. In this case, a separate light source element optically connected to the optical waveguide WG10may be further provided.

According to an example embodiment, the band-stop mirror MR10as illustrated inFIGS. 1 and 3may not be included, as illustrated inFIG. 5.

According to an example embodiment, inFIG. 5, the light source element L510may not be included as illustrated inFIG. 6. In this case, the light to excite the first to third quantum dots QD1, QD2, and QD3may be radiated from an external light source toward the first to third QD-containing layers A10, A20, and A30.

According to an example embodiment, inFIG. 6, the reflector RT10may not be used, and an example thereof is illustrated inFIG. 7. In this case, the excitation light may be externally radiated toward the first to third QD-containing layers A10, A20, and A30.

FIG. 8is a cross-sectional view of an optical modulating device according to an example embodiment.

Referring toFIG. 8, at least two of a plurality of QD-containing layers, for example, first to third QD-containing layers A11, A21, and A31, may include QDs having different sizes. For example, first quantum dots QD11of the first QD-containing layer A11, second quantum dots QD21of the second QD-containing layer A21, and third quantum dots QD31of the third QD-containing layer A31may have different sizes.

FIG. 9is a cross-sectional view of an optical modulating device according to an example embodiment.

Referring toFIG. 9, at least two of a plurality of QD-containing layers, for example, first to third QD-containing layers A12, A22, and A32, may have different thicknesses. For example, a first insulating layer N12of the first QD-containing layer A12, a second insulating layer N22of the second QD-containing layer A22, and a third insulating layer N32of the third QD-containing layer A32may have different thicknesses. In this case, the amounts of first to third quantum dots QD1, QD2, and QD3respectively included in the first to third QD-containing layers A12, A22, and A32may be different from one another.

FIG. 10is a cross-sectional view of an optical modulating device according to an example embodiment.

Referring toFIG. 10, at least two of a plurality of refractive index change layers, for example, first to fourth refractive index change layers R11, R21, R31, and R41, may have different thicknesses. For example, the first to fourth refractive index change layers R11, R21, R31, and R41may have different thicknesses. However, the changes in the sizes of the QDs and the thicknesses of the layers described with reference toFIGS. 8 to 10are exemplary, and may be variously changed.

FIG. 11is a perspective view illustrating the principle of optical modulation which is applicable to an optical modulating device according to an example embodiment.

Referring toFIG. 11, a QD-containing layer20may be disposed between a conductive layer10and a refractive index change layer30. The QD-containing layer20may include a plurality of QDs20bprovided in an insulating layer20a. For example, the conductive layer10may include silver (Ag), and the refractive index change layer30may include TiN. The insulating layer20amay include silicon dioxide (SiO2), and the QDs20bmay include indium phosphide (InP). A signal application device VGmay be connected between the conductive layer10and the refractive index change layer30to apply an electrical signal therebetween. A carrier density in a partial area, a carrier density change area30a, of the refractive index change layer30may be changed according to the electric signal (voltage) applied by the signal application device VGbetween the conductive layer10and the refractive index change layer30. The carrier density change area30amay be located on a boundary surface between the refractive index change layer30and the QD-containing layer20. A local density of states (LDOS) of the refractive index change layer30may be changed according to a change in the carrier density. Light ωPLis generated from the QDs20bthat are excited by external light ωextby a photoluminescence (PL) effect. The light-emission characteristics of QDs may be controlled and tuned by LDOS modulation.

FIG. 12is a graph showing a change in the intensity of PL according to a change in a voltage VGapplied to the optical modulating device ofFIG. 11according to an example embodiment. The graph ofFIG. 12illustrates that the intensity of PL changes according to the change in the voltage VG.

FIG. 13is a graph showing a change in the physical properties of the refractive index change layer30according to a change in the voltage VGapplied to the optical modulating device ofFIG. 11according to an example embodiment.

Referring toFIG. 13, it may be seen how carrier density N and permittivity Re of the refractive index change layer30are changed according to a change in the voltage VG. In particular, the physical properties of a portion of the refractive index change layer30adjacent to the QD-containing layer20may change more rapidly according to a change in the voltage VG. In the graph, ENZ denotes an epsilon near zero point.

FIG. 14is a graph showing a change of a LDOS enhancement spectrum at the position of QD according to a change in the voltage VGaccording to an example embodiment. In the graph ofFIG. 14, a dashed curve denotes that VGis less than 0 V, in which a refractive index change layer made of TiN is in an ENZ area. A solid curve denotes that VGis greater than 0 V, in which the refractive index change layer made of TiN includes an optically plasmonic TiN area. It may be seen from the graph that an LDOS enhancement effect occurs according to a change in the voltage VG.

FIG. 15is a graph showing a result of the measurement of the amount of changes in the intensity of PL of QDs according to a change in the voltage VGaccording to an example embodiment. The result is obtained from the optical modulating device ofFIG. 11. In the graph ofFIG. 15, I0PLdenotes the intensity of PL at 0 V, and ΔIPLdenotes a difference between the intensity of PL at a certain voltage other than 0 V and the intensity of PL at 0 V. It may be seen from the result ofFIG. 15that the amount of changes in the intensity of PL, that is, ΔIPL/I0PL(%), is changed according to a change in the voltage VG.

FIG. 16is a graph showing an example of a central emission wavelength of a plurality of QDs and an emission wavelength of a light source element that is applicable to an optical modulating device according to an example embodiment.

Referring toFIG. 16, first QDs may have a first central emission wavelength λ1, second QDs may have a second central emission wavelength λ2, and third QDs may have a third central emission wavelength λ3. The first to third central emission wavelengths λ1, λ2, and λ3may be different from each other. The first to third QDs may respectively correspond to, for example, the first to third quantum dots QD1, QD2, and QD3of example embodiments such as an example illustrated inFIG. 1. An emission wavelength λ0of a light source element may be less than the first to third central emission wavelengths λ1, λ2, and λ3. As the emission wavelength λ0of a light source element is relatively short, the light-emission energy of a light source element may be relatively high.

FIG. 17is a graph showing an example of the reflection characteristics of a band-stop mirror that is applicable to an optical modulating device according to an example embodiment.

Referring toFIG. 17, a band-stop mirror may have high reflectivity to the emission wavelength λ0of a light source element and a wavelength less than or equal to the emission wavelength λ0, and may have lower reflectivity, that is, higher transmissivity, to the emission wavelengths λ1, λ2, and λ3of the QDs. The band-stop mirror may correspond to, for example, the band-stop mirror MR10ofFIG. 1.

FIG. 18is a cross-sectional view illustrating an example in which a signal application device is connected to an optical modulating device according to an example embodiment.

Referring toFIG. 18, a signal application device for applying an electrical signal to the first to fourth refractive index change layers R10, R20, R30, and R40may be connected to the optical modulating device. For example, the signal application device may include a first voltage application device V10for applying a voltage to the first refractive index change layer R10, the second voltage application device V20for applying a voltage to the second refractive index change layer R20, the third voltage application device V30for applying a voltage to the third refractive index change layer R30, and the fourth voltage application device V40for applying a voltage to the fourth refractive index change layer R40. An electrical signal (voltage) may be independently applied to each of the first to fourth refractive index change layers R10, R20, R30, and R40. The refractive indexes of the first to fourth refractive index change layers R10, R20, R30, and R40may be changed based on the voltages applied by the signal application device.

FIG. 19is a cross-sectional view illustrating an example in which a signal application device is connected to an optical modulating device according to an example embodiment.

Referring toFIG. 19, the signal application device may include a first voltage application device V11for applying a voltage between the first refractive index change layer R10and the second refractive index change layer R20, a second voltage application device V21for applying a voltage between the second refractive index change layer R20and the third refractive index change layer R30, and a third voltage application device V31for applying a voltage between the third refractive index change layer R30and the fourth refractive index change layer R40. In this case, one of the first to fourth refractive index change layers R10, R20, R30, and R40may be grounded.FIG. 19illustrates that the second refractive index change layer R20is illustrated to be grounded, however this is exemplary and none of the first to fourth refractive index change layers R10, R20, R30, and R40may be grounded or a different refractive index change layer may be grounded.

AlthoughFIGS. 18 and 19illustrate examples in which the signal application device for applying an electrical signal to the first to fourth refractive index change layers R10, R20, R30, and R40is connected thereto, example embodiments are not limited thereto and the connection method of the signal application device may vary.

The optical modulating device according to an example embodiment may further include a non-antenna structure that is configured to control the output characteristics of light emitted from the QD-containing layers and provided on one surface of a stack structure including a plurality of QD-containing layers and a plurality of refractive index change layers. The nano-antenna structure may include an output coupler, and may further include an input coupler. The nano-antenna structure is described in detail with reference toFIGS. 20 to 31.

FIG. 20is a cross-sectional view of an optical modulating device according to an example embodiment.

Referring toFIG. 20, a stack structure of the first to fourth refractive index change layers R10, R20, R30, and R40and the first to third QD-containing layers A10, A20, and A30may be provided on the light source element LS10, and a nano-antenna structure NA10may be provided on the stack structure opposite to the light source element LS10. The nano-antenna structure NA10may be an output coupler that improves the output characteristics of light emitted from the first to third QD-containing layers A10, A20, and A30. The nano-antenna structure NA10may have a configuration coupled to an emission wavelength of at least one of the first to third QD-containing layers A10, A20, and A30. For example, a resonance wavelength region of the nano-antenna structure NA10may be at least partially overlapped with an emission wavelength region of the first to third QD-containing layers A10, A20, and A30. The light-emission/output characteristics in the first to third QD-containing layers A10, A20, and A30may be improved by the nano-antenna structure NA10, and the directivity and directionality of output light may be improved. Accordingly, far-field emission characteristics may be embodied by using the nano-antenna structure NA10.

The nano-antenna structure NA10may include any one of various structures such as a metallic antenna, a dielectric antenna, or a slit-containing structure, for example, a structure in which a slit is formed in a metal layer. The output characteristics of light may vary according to the size, shape, or material of the nano-antenna structure NA10. Furthermore, the nano-antenna structure NA10may include a refractive index change material or a phase change material. In this case, the output characteristics of light may be controlled by using the nano-antenna structure NA10, that is, a refractive index change or phase change of the output coupler.

FIG. 21is a cross-sectional view of an optical modulating device according to an example embodiment. The example embodiment shows an example in which the nano-antenna structure NA10is applied to the optical modulating device ofFIG. 1. The nano-antenna structure NA10may be applied to a variety of the optical modulating devices described with reference toFIGS. 1 to 10andFIGS. 18 and 19.

FIG. 22is a graph showing a relationship between the central emission wavelength of a plurality of QDs and a resonance wavelength region of an output coupler which is applicable to an optical modulating device according to example embodiments.

Referring toFIG. 22, the resonance wavelength region of an output coupler may cover regions of the central emission wavelengths λ1, λ2, and λ3of a plurality of QDs. Accordingly, the light-emission coupling characteristics in a plurality of QDs may be improved by the output coupler.

FIG. 23is a plan view illustrating a nano-antenna structure which is applicable to an optical modulating device according to an example embodiment.

Referring toFIG. 23, a stack structure SS10of a plurality of refractive index change layers and a plurality of QD-containing layers may include a plurality of nano-antennas. The nano-antennas may include, for example, a first nano-antenna NA11, a second nano-antenna NA21, and a third nano-antenna NA31. At least two of the first, second, and third nano-antennas NA11, NA21, and NA31may have different sizes, may include different materials, or may have different shapes. In the an example embodiment, the first, second, and third nano-antennas NA11, NA21, and NA31are illustrated having different sizes. The first nano-antenna NA11may have a first resonance wavelength region corresponding to the emission wavelength of the first quantum dots QD1, the second nano-antenna NA21may have a second resonance wavelength region corresponding to the emission wavelength of the second quantum dots QD2, and the third nano-antenna NA31may have a third resonance wavelength region corresponding to the emission wavelength of the third quantum dots QD3. In this case, light of different wavelengths may be output from the first, second, and third nano-antennas NA11, NA21, and NA31. However, example embodiments are not limited thereto.

FIG. 24is a graph showing a relationship between the central emission wavelength of a plurality of quantum dots and the resonance wavelength region of a plurality of output couplers (nano-antennas) which are applicable to an optical modulating device according to an example embodiment.

Referring toFIG. 24, a resonance wavelength region of the first output coupler NA11may correspond to the central emission wavelength λ1of the first quantum dots QD1, a resonance wavelength region of the second output coupler NA21may correspond to the central emission wavelength λ2of the second quantum dots QD2, and a resonance wavelength region of the third output coupler NA31may correspond to the central emission wavelength λ3of the third quantum dots QD3. Accordingly, the light-emission coupling characteristics in each of the QDs may be improved by each output coupler.

FIG. 25is a plan view illustrating a nano-antenna structure which is applicable to an optical modulating device according to an example embodiment. In the example embodiment, a nano-antenna structure includes a slit.

Referring toFIG. 25, a certain slit may be formed in a material layer M10. For example, a plurality of slits S10may be arranged forming an array. The characteristics and direction of output light may be controlled according to the size and arrangement manner of the slits S10. However, the arrangement manner of the slit S10proposed herein is merely exemplary and may be changed in various ways. The material layer M10may be a metal layer.

A nano-antenna structure according to an example embodiment may further include an output coupler and an input coupler apart from the output coupler. For example, a nano-antenna structure may include a multi-patch antenna structure or a fishbone antenna structure, which is described with reference toFIGS. 26 to 31.

FIG. 26is a cross-sectional view of an optical modulating device according to an example embodiment.FIG. 27is a perspective view ofFIG. 26.

Referring toFIGS. 26 and 27, a nano-antenna structure NA50having a dual patch structure may be provided on the stack structure of the first to fourth refractive index change layers R10, R20, R30, and R40and the first to third QD-containing layers A10, A20, and A30. The nano-antenna structure NA50may include an input coupler NA51corresponding to a first patch and an output coupler NA52corresponding to a second patch. A resonance wavelength region of the input coupler NA51may be at least partially overlapped with excitation wavelength regions of the quantum dots QD1, QD2, and QD3. When the light source element LS10is used, excitation light generated from the light source element LS10may be used, and excitation light coming from the outside may be further used altogether. The input coupler NA51may improve input efficiency (input coupling efficiency) with respect to the excitation light (incident light) coming from the outside. The resonance wavelength region of the output coupler NA52may be at least partially overlapped with the emission wavelength regions of the quantum dots QD1, QD2, and QD3. Accordingly, the light output characteristics (output coupling characteristics) in the first to third QD-containing layers A10, A20, and A30may be improved by the output coupler NA52. The width of the output coupler NA52may be greater than the width of the input coupler NA51. A central resonance wavelength may vary according to the width of the coupler NA51or NA52.

FIG. 28is a cross-sectional view of an optical modulating device according to an example embodiment. The example embodiment shows an example in which the nano-antenna structure NA50is applied to the optical modulating device ofFIG. 1. The nano-antenna structure NA50may be applied to various optical modulating devices described with reference toFIGS. 1 to 10andFIGS. 18 and 19.

AlthoughFIGS. 26 to 28illustrate a case of using the nano-antenna having a dual patch structure, a nano-antenna having a multi-patch structure having three or more patches may be used. An example thereof is illustrated inFIG. 29.

FIG. 29is a cross-sectional view of an optical modulating device according to an example embodiment.

Referring toFIG. 29, a nano-antenna structure NA60having a multi-patch structure may be provided on a stack structure of a plurality of refractive index change layers R15, R25, R35, and R45and a plurality of QD-containing layers A15, A25, and A35. For example, the nano-antenna structure NA60may include at least one input coupler NA61and a plurality of output couplers, such as, first to third output couplers NA62, NA63, and NA64. The first to third output couplers NA62, NA63, and NA64may be designed to be optically coupled to different emission wavelength regions. In this regard, the first to third output couplers NA62, NA63, and NA64may have different sizes, include different materials, and have different shapes. The first output coupler NA62may correspond to an emission wavelength region of first quantum dots QD15, the second output coupler NA63may correspond to an emission wavelength region of second quantum dots QD25, and the third output coupler NA64may correspond to an emission wavelength region of third quantum dots QD35. Accordingly, the nano-antenna structure NA60may be designed such that light beams emitted from the QD-containing layers A15, A25, and A35are output through different output couplers from the first to third output couplers NA62, NA63, and NA64. The shape, size, or arrangement order of the input coupler NA61and the first, second, and third output couplers NA62, NA63, and NA64illustrated inFIG. 29are merely exemplary and may vary.

FIGS. 30 and 31are plan views illustrating a nano-antenna having a fishbone structure which is applicable to an optical modulating device according to an example embodiment.

FIG. 30illustrates a nano-antenna having a fishbone structure which is applicable to an optical modulating device according to an example embodiment.

Referring toFIG. 30, a nano-antenna structure NA70may include a first nano-antenna element NA71extending in a first direction and a second nano-antenna element NA72extending in a second direction perpendicular to the first direction. In the example embodiment, the first nano-antenna element NA71may include a plurality of first nano-antenna elements NA71intersecting the second nano-antenna element NA72. Accordingly, the nano-antenna structure NA70may have a fishbone structure.

The first nano-antenna element NA71may be an input coupler, and the second nano-antenna element NA72may be an output coupler. In this case, incident light may have a first polarized direction by the first nano-antenna element NA71, and output light may have a second polarized direction perpendicular to the first polarized direction by the second nano-antenna element NA72. Accordingly, when the nano-antenna NA70having a fishbone structure is used, the polarized directions of the incident light and the output light may be controlled.

FIG. 31illustrates a nano-antenna having a fishbone structure which is applicable to an optical modulating device according to an example embodiment.

Referring toFIG. 31, the nano-antenna structure NA70may include a plurality of nano-antenna structures NA70which are arranged according to a certain rule. In the example embodiment, only two nano-antenna structures NA70are illustrated as an example. While the two nano-antenna structures NA70may be substantially the same, in some cases, the size, pattern size, or pattern interval thereof may vary. Furthermore, the nano-antenna structures NA70may be arranged apart from one another, or the first nano-antenna elements NA71of the nano-antenna structures NA70may be connected to each other. The nano-antennas having a fishbone structure described with reference toFIGS. 30 and 31are exemplary and may be variously changed.

The nano-antenna may be an antenna having a nano structure with respect to light, which may convert incident light including all visible and invisible electromagnetic waves of a specific wavelength or frequency to a shape of a localized surface plasmon resonance, and capture energy thereof. The nano-antenna may include a conductive layer pattern, for example, a metal layer pattern, and the conductive layer pattern may be in contact with a non-conductive layer, for example, a dielectric layer. Plasmon resonance may be generated at an interface between the conductive layer pattern and the non-conductive layer, for example, a dielectric layer. An interface where surface plasmon resonance is generated, such as, the interface between the conductive layer pattern and the non-conductive layer, for example, a dielectric layer, may collectively form a meta surface or a meta structure. The nano-antenna may be formed of a conductive material and may have a dimension of a sub-wavelength which is a dimension less than the operation wavelength of the nano-antenna. At least any one of dimensions forming a shape of the nano-antenna, for example, a thickness, a horizontal length, a vertical length, or an interval between nano-antennas, may have the dimension of a sub-wavelength.

The nano-antenna may have a variety of structures/shapes such as a rectangular pattern, a line pattern, a circular disc, an oval disc, a cross, or an asterisk. A cross type may have a shape in which two nanorods intersect perpendicular to each other. An asterisk type may have a star shape in which three nanorods intersect with one another. In addition, the nano-antenna may have a variety of modified structures such as a cone, a triangular pyramid, a sphere, a hemisphere, a rice grain, or a rod. Furthermore, the nano-antenna may have a multilayer structure in which a plurality of layers are stacked, or a core-shell structure including a core part and at least one shell part. Additionally, two or more nano-antennas having different structures/shapes forming one unit may be periodically arranged.

A resonance wavelength, a resonant wavelength width, resonant polarization characteristics, a resonance angle, reflection/absorption/transmission characteristics may be changed depending on the structure/shape and arrangement method of the nano-antenna. Accordingly, by controlling the structure/shape and arrangement method of the nano-antenna, an optical modulating device having characteristics suitable for a certain purpose may be manufactured.

The optical modulating devices according to example embodiments may be applied to a variety of optical apparatuses such as a thin display, an ultrathin display, an on-chip emitter for an integrated optical circuit, a light fidelity (Li-Fi) field corresponding to a next generation wireless fidelity (Wi-Fi), or a light detection and ranging (LiDAR) apparatus. Furthermore, the optical modulating device according to example embodiments may be applied to a holographic display apparatus and a structured light generation apparatus. Furthermore, the optical modulating device may be applied to a variety of optical element/apparatus such as a hologram generation apparatus or an optical coupling device. Furthermore, the optical modulating device may be applied to a variety of fields in which a meta surface or a meta structure is used. In addition, the optical modulating device according to example embodiments and the optical apparatus including the same may be applied to a variety of optical and electronic apparatus fields for various purposes.

Additionally, although, in example embodiments, application of an electrical signal, a voltage, is described for modulating a refractive index of the refractive index change layer. However, example embodiments are not limited thereto, and there may be a variety of methods of modulating the refractive index of the refractive index change layer. For example, a modulating method of the refractive index of the refractive index change layer may include electric field application, magnetic field application, heating and cooling, optical pumping, or microscale or nanoscale electro-mechanical deformation and modulation. Furthermore, a material and a configuration/structure of the refractive index change layer may be changed in various ways.

It should be understood that example embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. For example, one of ordinary skill in the art to which the present disclosure pertains would understand that the structure of the optical modulating device described with reference toFIGS. 1 to 10andFIGS. 18 to 31may be changed in various ways.

While one or more example embodiments have been described with reference to the drawings, it will be understood by those of ordinary skill in the art that various changes may be made therein without departing from the spirit and scope of the present disclosure as defined by the following claims.