An indium tin oxide-based tunable electromagnetically induced transparency resonator

Abstract

The present invention relates to the technical field of electromagnetic metamaterials, and specifically relates to an adjustable electromagnetic induced transparency resonator based on indium tin oxide, which includes a base layer, a dielectric layer, a dark mode resonator, and a bright mode resonator. The dielectric layer includes doped silicon, hafnium dioxide, and an indium tin oxide layer. The doped silicon, hafnium dioxide, and indium tin oxide layer are sequentially stacked between the base layer and the dark mode resonator from bottom to top. Different from the method of separately designing parameters for each structural unit to achieve and adjust electromagnetic induced transparency (EIT) with other structures, dynamic modulation can be achieved in the same device, that is, by applying an external voltage to control the dielectric constant of indium tin oxide, thereby controlling the transmission spectrum of the entire structure, which is more conducive to practical applications. The present invention helps to improve the diversity and functionality of the adjustable electromagnetic induced transparency effect.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic metamaterials, and particularly to an adjustable electromagnetically induced transparency resonator based on indium tin oxide. Background Art

[0002] The phenomenon of electromagnetically induced transparency (EIT) refers to a quantum interference effect between an electromagnetic field and an atomic energy level system during the interaction between a material medium and an electromagnetic field, and was first discovered in a quantum system. Electromagnetically induced transparency can change the transmission coefficient of a material to an electromagnetic wave and has potential applications in slow light, optical switches, filters, and sensors. In a traditional atomic system, extremely harsh conditions, such as extremely low temperature and a strong resonant pump field, are required to achieve the electromagnetically induced transparency phenomenon, which limits the application of the EIT phenomenon. Due to the unique properties of metamaterials and the interaction between electromagnetic waves and metamaterials, the EIT phenomenon can be achieved with metamaterials in the visible light band, terahertz band, and microwave band. Using metamaterials to achieve the EIT phenomenon makes the experimental conditions relatively simple, without the need for extremely low temperature, can be achieved at room temperature, and the phenomenon is stable, improving its applicability. Generally, the EIT effect in metamaterials can be achieved through the near-field coupling between bright-mode and dark-mode resonators.

[0003] The dynamic regulation of the EIT phenomenon is of great significance, especially for achieving the slow light effect. There are various ways to achieve the regulation of the EIT phenomenon, such as changing the geometric parameters of the structure to change its operating frequency, changing the incident light angle, adding substances with changeable properties, etc.

[0004] In this method of adding substances, indium tin oxide (ITO) is an ideal external material and is widely used in the transparent electrodes of flat panel displays. Indium tin oxide has a large refractive index change and tuning range, has an epsilon-near-zero (ENZ) frequency region where its dielectric constant changes sign from positive to negative, and has a short response time in the near-infrared band. The spatial area of ITO dielectric constant modulation under an external bias voltage is very small. For a tunable ITO metasurface, resonance excitation of a high confinement field needs to be carried out in the active layer. This poses strict requirements on the properties of the constituent materials and the geometry of the units to achieve the desired tunable function. Indium tin oxide is a transparent conductive oxide with dielectric constant electrical properties. The transparent conductive oxide material layer can quickly form a carrier accumulation region or depletion region at the interface with the dielectric layer, and the accumulation region can be adjusted by applying an external bias voltage or changing the carrier concentration in the depletion region, which can change the dielectric constant of the transparent conductive oxide. Changing the bias voltage of indium tin oxide under near-infrared conditions can change its free carrier concentration, thereby changing its dielectric constant, and it has good applications in electro-optic modulators and photovoltaics. And the adjustment of its dielectric constant is continuously controllable. Adjusting the dielectric constant of indium tin oxide by voltage is more practical than changing the doping concentration method. The dielectric constant of indium tin oxide and the applied voltage satisfy ε(ω) = ε ∞ -ω 2 p / (ω 2 +iωГ).

[0005] When adjusting the transparent window for existing electromagnetic induced transparency structures, the device size needs to be changed passively, and the size cannot be changed after the device is processed. Summary of the Invention

[0006] The purpose of the present invention is to provide a tunable electromagnetic induced transparency resonator based on indium tin oxide, aiming to solve the technical problem in the prior art that when adjusting the transparent window for an electromagnetic induced transparency structure, the device size needs to be changed passively and the device needs to be reprocessed.

[0007] To achieve the above purpose, the present invention provides a tunable electromagnetic induced transparency resonator based on indium tin oxide, including a base layer, a dielectric layer, a dark mode resonator, and a bright mode resonator. The dielectric layer and the bright mode resonator are both arranged at the top of the base layer. The bright mode resonator is located on one side of the dielectric layer, and the dark mode resonator is arranged on the top of the dielectric layer;

[0008] The dielectric layer includes doped silicon, hafnium dioxide, and an indium tin oxide layer. The doped silicon, the hafnium dioxide, and the indium tin oxide layer are stacked in sequence from bottom to top between the base layer and the dark mode resonator. The base layer uses a quartz substrate, and the dark mode resonator uses a silicon ring.

[0009] Among them, the thickness of the base layer is 200 nm, the length is 750 nm, and the width is 750 nm.

[0010] Among them, the thickness of the doped silicon is 10 nm, the thickness of hafnium dioxide is 5 nm, and the thickness of indium tin oxide is 10 nm. The lengths of the doped silicon, hafnium dioxide, and indium tin oxide are all 535 nm, and the widths are all 750 nm.

[0011] Among them, the thickness of the dark mode resonator is 110 nm, the outer diameter is 225 nm, and the inner diameter is 110 nm.

[0012] Among them, one electrode is led out from the surface of the indium tin oxide and the surface of the doped silicon, and a bias voltage is applied to change the properties of the indium tin oxide.

[0013] An adjustable electromagnetic induced transparency resonator based on indium tin oxide according to the present invention is different from the method of separately designing parameters for each structural unit to realize and adjust EIT in other structures. It can achieve dynamic modulation in the same device, that is, by applying an external voltage to control the dielectric constant of the indium tin oxide, thereby controlling the transmission spectrum of the entire structure, which is more conducive to practical applications. The present invention helps to improve the diversity and functionality of the adjustable electromagnetic induced transparency effect. Brief Description of the Drawings

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0015] Figure 1 It is a top view of an adjustable electromagnetic induced transparency resonator based on indium tin oxide provided by the present invention.

[0016] Figure 2 It is a front view of an adjustable electromagnetic induced transparency resonator based on indium tin oxide provided by the present invention.

[0017] Figure 3 It is a relationship diagram of the real part, imaginary part of the dielectric constant of indium tin oxide and voltage provided by the present invention.

[0018] Figure 4 It is a transmission spectrum diagram of the EIT transparent window of the overall structure provided by the present invention.

[0019] Figure 5 It is a transmission spectrum diagram of the EIT transparent window during the modulation of indium tin oxide provided by the present invention.

[0020] 1 - Substrate layer, 2 - Doped silicon, 3 - Hafnium dioxide, 4 - Indium tin oxide layer, 5 - Dark mode resonator, 6 - Bright mode resonator. Detailed implementation mode

[0021] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0022] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. In addition, in the description of the present invention, the meaning of "a plurality" is two or more unless otherwise specifically defined.

[0023] Please refer to Figures 1 to 5 , the present invention provides an adjustable electromagnetic induced transparency resonator based on indium tin oxide, including a substrate layer 1, a dielectric layer, a dark mode resonator 5 and a bright mode resonator 6. The dielectric layer and the bright mode resonator 6 are both disposed at the top of the substrate layer 1. The bright mode resonator 6 is located on one side of the dielectric layer, and the dark mode resonator 5 is disposed on the top of the dielectric layer; the dielectric layer includes doped silicon 2, hafnium dioxide 3 and an indium tin oxide layer 4. The doped silicon 2, the hafnium dioxide 3 and the indium tin oxide layer 4 are stacked in sequence from bottom to top between the substrate layer 1 and the dark mode resonator 5. The substrate layer 1 uses a quartz substrate, and the dark mode resonator 5 uses a silicon ring; the materials of the dark mode resonator 5 and the bright mode resonator 6 are silicon, and their dielectric constant is 11.9; the material of the substrate layer 1 is quartz, and its dielectric constant is 3.75, and its side length P x is 750 nm, and the side length P y is 750 nm, and the thickness is 200 nm; the dark mode resonator 5 is a ring structure, and the difference r between the outer diameter and the inner diameter of the ring is 115 nm. The bright mode resonator 6 is strip-shaped, the length of the silicon strip is 720 nm, the width is 145 nm, and the thickness is 135 nm. The distance between the bright mode resonator 6 and the dark mode resonator 5 is 70 nm, the thickness of the dark mode resonator is 110 nm, the outer diameter is 225 nm, and the inner diameter is 110 nm.

[0024] In this embodiment, an electrode is led out from the surface of the indium tin oxide and the surface of the doped silicon 2, and a bias voltage is applied to change the properties of the indium tin oxide. When the applied voltage of the indium tin oxide layer 4 is changed, the obtained electromagnetically induced transparency window will change, that is, the applied voltage can tune the electromagnetically induced transparency phenomenon. The control principle is as follows:

[0025] The dielectric constant of the indium tin oxide is consistent with the Drude model, and the calculation formula is as follows:

[0026]

[0027] Among them, N ITO is the electron concentration of the indium tin oxide, ω is the angular frequency, γ is the carrier scattering rate, m * is the effective mass of the carrier, q is the electron charge, and ε0 is the dielectric constant of free space.

[0028] To calculate the change in the carrier concentration of indium tin oxide caused by voltage control, the following simple model is used:

[0029]

[0030] N O is the intrinsic carrier concentration of the indium tin oxide, H Hf02 is the thickness of the hafnium dioxide 3, and H acc is the thickness of the free carriers accumulated by the hafnium dioxide under the indium tin oxide surface.

[0031] According to Equation (1) and Equation (2), it is proved that the conductivity of the indium tin oxide can be changed by applying an external voltage to the indium tin oxide. During the process of applying the voltage, a destructive interference phenomenon occurs between the silicon strip and the silicon ring, thereby generating an electromagnetically induced transparency phenomenon.

[0032] The resonance frequency of the destructive interference phenomenon between the silicon strip and the silicon ring is 202 THz. The theoretical fitting results show that the change in the transparency peak amplitude is due to the increase in the loss of the silicon resonator unit caused by the change in the dielectric constant of the indium tin oxide, resulting in a smaller transparency peak.

[0033] Furthermore, the dielectric constant of the doped silicon 2 is 11.9, the thickness is 10 nm, the dielectric constant of the hafnium dioxide 3 is 25, and the thickness is 5 nm. According to formula (1), the dielectric constant of the indium tin oxide layer 4 is related to the applied voltage, and the thickness is 10 nm. The side length X of the multi-layer material is 535 nm, and the side length Y is 750 nm. Figure 3 is the change in the real part and the imaginary part of the dielectric constant of the indium tin oxide at different voltages within the frequency range.

[0034] In this embodiment, a sharp transmission peak will appear in the EIT phenomenon of the metamaterial, as shown in Figure 4As shown, a narrow transmission peak appears between the two transmission valleys, i.e., the EIT phenomenon occurs. The frequencies of the two transmission valleys are 201.5 THz and 202.8 THz respectively, and the designed metamaterial transmission peak (resonance peak) is at 202 THz, with a transmission efficiency reaching 92%.

[0035] Figure 5 It is the curve of the relationship between the transmittance and frequency of the tunable electromagnetic induced transparency resonator based on indium tin oxide. As Figure 5 shown, when no voltage is applied, a transparent window appears in the transmission spectrum, which is the open state of the window. As the voltage increases, the amplitudes of the left and right transmission valleys decrease, producing a modulation effect. When the voltage is 8 V, the transparent window disappears in the transmission spectrum, which is the closed state of the window. This is because the voltage changes the carrier concentration in indium tin oxide, increasing its conductivity. At the same time, it also increases the damping rate of the dark mode resonator 5, changing the resonance between the bright mode resonator 6 and the dark mode resonator 5, resulting in the inability to maintain the original resonance and the disappearance of the transparent window.

[0036] Generally, the modulation depth and the quality factor Q value are used to evaluate the performance of the EIT metamaterial device. The formula for the modulation depth is:

[0037] T=(T max -T min ) / (T max +T min ) (3)

[0038] The formula for the quality factor Q value is:

[0039] Q = f0 / Δf (4)

[0040] Among them, T max 、T min are respectively the intensities of the transmission peaks at the resonance frequencies when the EIT transparent window appears and closes; f0 is the resonance frequency, and Δf is the full width at half maximum frequency bandwidth of the EIT peak with the center frequency of f0. During the modulation process, increasing the voltage can dynamically achieve the change of the modulation depth from high to low. As Figure 5 shown, when the control voltage increases from 0 V to 8 V, the dynamic modulation depth is 31%, and the Q value is as high as 116.

[0041] The above-disclosed is only a preferred embodiment of the present invention. Of course, it cannot be used to limit the scope of the rights of the present invention. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. An indium tin oxide-based tunable electromagnetically induced transparency resonator, characterized in that it includes a base layer, a dielectric layer, a dark mode resonator and a bright mode resonator. The dielectric layer and the bright mode resonator are both disposed at the top of the base layer. The bright mode resonator is located on one side of the dielectric layer, and the dark mode resonator is disposed on the top of the dielectric layer; the dielectric layer includes doped silicon, hafnium dioxide and an indium tin oxide layer. The doped silicon, the hafnium dioxide and the indium tin oxide layer are sequentially stacked between the base layer and the dark mode resonator from bottom to top. The base layer uses a quartz substrate, the dark mode resonator uses a silicon ring, and the bright mode resonator uses a silicon strip; one electrode is led out from the surface of the indium tin oxide and the surface of the doped silicon, and a bias voltage is applied to change the properties of the indium tin oxide.

2. The indium tin oxide-based tunable electromagnetically induced transparency resonator according to claim 1, characterized in that the thickness of the base layer is 200 nm, the thickness of the doped silicon is 10 nm, the thickness of hafnium dioxide is 5 nm, the thickness of indium tin oxide is 10 nm, the length of the dielectric layer is 535 nm, and the width is 750 nm; the length of the bright mode resonator is 145 nm, the width is 720 nm, and the thickness is 135 nm.

3. The indium tin oxide-based tunable electromagnetically induced transparency resonator according to claim 2, characterized in that the length of the base layer is 750 nm and the width is 750 nm.

4. The indium tin oxide-based tunable electromagnetically induced transparency resonator according to claim 3, characterized in that the thickness of the dark mode resonator is 110 nm, the outer diameter is 225 nm, and the inner diameter is 110 nm.

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