Optical bistable device based on optical Tamm state and application thereof

Abstract

The invention provides an optical bistable device based on an optical Tamm state and application of the optical bistable device. The optical bistable device comprises a metal substrate layer, a transparent conductive oxide film and a photonic crystal layer, wherein the transparent conductive oxide film and the photonic crystal layer are sequentially arranged on the metal substrate layer; the photonic crystal layer comprises x unit cell structures stacked on the transparent conductive oxide film from bottom to top, and x is greater than or equal to 2; each unit cell structure comprises A Si layers and B SiO2 layers; in each unit cell structure, n (Si) d (Si) = n (SiO2) d (SiO2), so that the band gap of the photonic crystal layer covers the ENZ wavelength of the transparent conductive oxide film; and the surface equivalent impedance of the metal substrate layer and the transparent conductive oxide film is matched with the relative surface impedance of the photonic crystal layer, so that a Tamm state is formed between the interfaces of the transparent conductive oxide film and the photonic crystal layer. According to the invention, the bistable effect is realized under multiple incident angles, two polarizations and different wavelengths, the bistable working wavelength can be moved to an area smaller than the ENZ wavelength of the material, and the optical bistable state is realized.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and in particular relates to an optical bistable device based on an optical Tamm state. Background Art

[0002] As an important technology for next-generation information processing, all-optical technology has shown broad application prospects in optical communications, information processing, and information storage. Compared with traditional electronic technology, all-optical technology can break through the limitations of bandwidth and speed and is regarded as a key support for promoting future technological development. Among such technologies, optical bistability is a key mechanism for achieving high-speed optical control and processing, and has important applications in all-optical memory, optical switches, optical logic gates, and other fields. For example, in optical memory, the bistability effect allows data to be stored and read between the two stable states of "0" and "1"; in optical switches, it can be used for selective transmission or blocking of signals; and in optical logic gates, the bistability effect can realize specific logical operations, providing basic support for all-optical computing.

[0003] The realization of optical bistability relies on the nonlinear effects of the system. In recent years, transparent conducting oxides (TCOs) have emerged as promising materials for Kerr-like nonlinearities due to their strong nonlinear effects, sub-picosecond response speeds, enhanced light-matter interaction in the near-zero (Epsilon-Near-Zero) region of dielectric constant, and excellent complementary metal oxide semiconductor (CMOS) compatibility. This nonlinearity arises from the nonparabolic conduction band of TCOs, which increases the effective electron mass and leads to a redshift in the plasma frequency with increasing absorbed energy.

[0004] Optical bistability based on TCOs is primarily achieved by exciting Berreman or ENZ modes. However, these methods have the following limitations: bistability is typically limited to obliquely incident TM polarized light and occurs primarily at wavelengths greater than the ENZ wavelength of the TCO material, limiting their applications. Furthermore, current research ignores the effect of optical loss on light intensity, a factor that poses a challenge to achieving bistability. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies in the prior art and provide an optical bistable device based on the optical Tamm state, which realizes a bistable effect at different wavelengths under multiple incident angles, moves the bistable operating wavelength to a region smaller than the ENZ wavelength, and maintains the nonlinear response of the transparent conductive oxide film to achieve high-contrast optical bistability.

[0006] The present invention is achieved through the following technical solutions:

[0007] An optical bistable device based on an optical Tamm state comprises a metal base layer and a transparent conductive oxide film and a photonic crystal layer sequentially arranged on the metal base layer; the photonic crystal layer comprises x unit cell structures stacked from bottom to top on the transparent conductive oxide film, where x ≥ 2;

[0008] Each of the unit cell structures includes A Si layers and B SiO2 layers;

[0009] In each of the unit cell structures, n (Si) d (Si) =n (SiO2) d (SiO2) , so that the band gap of the photonic crystal layer covers the ENZ wavelength of the transparent conductive oxide film, where n (Si) is the refractive index of Si, d (Si) is the total thickness of the Si layer in each of the unit cell structures, n (SiO2) is the refractive index of SiO2, d (SiO2) is the total thickness of the SiO2 layer in each of the unit cell structures;

[0010] The surface equivalent impedance of the metal base layer and the transparent conductive oxide film matches the relative surface impedance of the photonic crystal layer, so that a Tamm state is formed at the interface between the transparent conductive oxide film and the photonic crystal layer.

[0011] In the optical bistable device based on the optical Tamm state provided by the present invention, the transparent conductive oxide film has high electron mobility, a narrow full width at half maximum, and low loss of incident light intensity, which is conducive to achieving bistability. However, the absorption peak of the transparent conductive oxide film is reduced under high light intensity, and the bandwidth of the absorption peak is broadened, resulting in increased loss of incident light intensity. The photonic crystal layer can form a band gap covering the ENZ region of the transparent conductive oxide in the near-infrared band. At the same time, the surface equivalent impedance of the transparent conductive oxide film matches the relative surface impedance of the photonic crystal layer, so that a Tamm state is formed at the interface between the transparent conductive oxide film and the photonic crystal layer. The bistability effect is achieved at multiple incident angles, two polarizations, and different wavelengths, so that the transparent conductive oxide film achieves perfect absorption under high light intensity and effectively reduces bandwidth broadening. Without changing the carrier concentration of indium-doped cadmium oxide, the bistable operating wavelength is moved to a region smaller than the ENZ wavelength while maintaining the nonlinear response of the transparent conductive oxide film, thereby achieving high-contrast optical bistability.

[0012] Furthermore, in the unit cell structure, A Si layers and B SiO2 layers are stacked alternately from bottom to top on a side of the transparent conductive oxide film facing away from the substrate layer, where A = 2 and B = 1. The A Si layers and B SiO2 layers are stacked alternately from bottom to top, forming a Tamm state between the Si layers and the transparent conductive oxide film.

[0013] Furthermore, the optical bistable device based on the optical Tamm state also includes a dielectric layer; in the photonic crystal layer, B SiO2 layers and A Si layers are alternately stacked from bottom to top on the side of the transparent conductive oxide film facing away from the metal substrate, where A=1 and B=2; the dielectric layer is disposed between the photonic crystal layer and the transparent conductive oxide film, and the surface equivalent impedance of the metal substrate layer, the transparent conductive oxide film, and the dielectric layer matches the relative surface impedance of the photonic crystal layer, forming a Tamm state at the interface between the dielectric layer and the photonic crystal layer. By adjusting the material composition and structural parameters, the operating wavelength and contrast can be controlled. Under vertical incidence, the surface equivalent impedance of the transparent conductive oxide film on the metal substrate is a negative imaginary number. When A SiO2 layers and B Si layers are alternately stacked from bottom to top on the side of the transparent conductive oxide film facing away from the substrate layer in the unit cell structure, the surface impedance of the photonic crystal layer is a negative imaginary number. By adding a dielectric layer on the transparent conductive oxide film, the surface equivalent impedance value of the dielectric-transparent conductive oxide film-metal substrate layer structure is changed to a positive imaginary number to achieve impedance matching.

[0014] Furthermore, the dielectric layer includes magnesium oxide.

[0015] Furthermore, the transparent conductive oxide film includes indium-doped cadmium oxide.

[0016] Furthermore, the metal base layer includes Au.

[0017] The present invention also provides an application of the above-mentioned optical bistable device based on the optical Tamm state in an all-optical memory, an optical switch, and an optical logic gate.

[0018] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of the ENZ wavelength of indium-doped cadmium oxide, where Figure 1 (a) is the electron temperature T e =300K (dark line) and T e =4000K (bright line) of the real part (blue line) and imaginary part (red line) of the dielectric constant of indium-doped cadmium oxide In: CdO. Figure 1 (b) and Figure 1 (c) is related to T e The plasma frequency ω p (Te), ENZ wavelength λ ENZ (T e ) and damping rate γ(T e ).

[0020] Figure 2 This is a schematic diagram of the structure of an optical bistable device based on the Tamm state, where: Figure 2 (a) is a schematic diagram of the structure of an optical bistability device based on Tamm state. Figure 2 (b) is a schematic diagram of the structure of another optical bistability device based on Tamm state. Figure 2 (c) is the band structure of the photonic crystal layer.

[0021] Figure 3 Schematic diagram of the surface equivalent impedance matching between the photonic crystal layer and the transparent conductive oxide film-metal substrate layer structure, where: Figure 3 (a) Figure 1 (a) The surface impedance of the photonic crystal layer and the surface equivalent impedance of the transparent conductive oxide film-metal substrate structure under vertical incidence conditions. Figure 3 (b) Figure 1 (b) The surface impedance of the photonic crystal layer and the surface equivalent impedance of the dielectric layer-transparent conductive oxide film-metal substrate structure under vertical incidence conditions. Figure 3 (c) Figure 1 (a) The corresponding results of the structure shown under TM polarized light with an incident angle of 60°.

[0022] Figure 4 is the reflectance spectrum, where Figure 4 (a) Yes Figure 1 The structure shown in (a) is different from the electron temperature T e Reflectance spectrum under ; Figure 4 (b) is the indium-doped cadmium oxide-metal substrate structure at different electron temperatures T e Reflectance spectrum under ; Figure 4 (c) is the different electron temperatures T e In the complex frequency plane, Figure 4 (a) and Figure 4 (b) The associated reflection zero point.

[0023] Figure 5 This is a graph showing the relationship between the light absorption rate and the electron temperature of a bistable device based on the Tamm state.

[0024] Figure 6 is a schematic diagram of the reflectivity of a bistable device based on the Tamm state, where Figure 6(a) Yes Figure 1 (a) Reflectivity curve of the structure shown at normal incidence when the electron temperature Te = 300K; Figure 6 (b) is at vertical incidence Figure 1 (a) Reflectivity contrast ΔR of the two stable states of the structure shown; Figure 6 (c) shows Figure 1 (a) shows a structure with vertical incidence and an incident wavelength of 2107 nm (at Figure 6 (marked by the blue dotted line in (b)) shows the relationship between the reflectivity and the incident light intensity.

[0025] Figure 7 is the reflectivity spectrum of the bistable device based on the Tamm state, where Figure 7 (a) Yes Figure 1 Reflectance spectrum of the structure in (a); Figure 7 (b) is TE polarization, when the incident angle is 60°, Figure 1 (a) The reflectivity contrast ΔR between the two stable states of the structure shown varies with wavelength. Figure 7 (c) is the change of reflectivity with incident light intensity at a wavelength of 1935 nm; Figure 7 (d)-(f) are Figure 1 (a) The corresponding results for TM polarization of the structure shown.

[0026] Figure 8 The bistable response characteristic curve of the bistable device based on the Tamm state at an incident angle of 30° to 80° is shown in FIG. Figure 8 (a) is the bistability response characteristic curve under TM polarization, Figure 8 (b) is the bistability response characteristic curve under TE polarization.

[0027] Figure 9 yes Figure 2 (b) Schematic diagram of the bistability characteristics of the structure under vertical incidence, where Figure 9 (a) is the change of reflectivity contrast ΔR with wavelength, Figure 9 (b) is the relationship between the reflectivity at a wavelength of 2335nm and the incident light intensity.

[0028] Figure 10 yes Figure 2 (b) Schematic diagram of the bistable characteristics of the structure under oblique incidence, where Figure 10 (a) Variation of reflectivity with incident angle and wavelength under TE polarization. Figure 10 (b) shows the change of the reflectivity contrast ΔR between the two stable states of the same structure with wavelength when the incident angle is 60° under TE polarization. Figure 10 (c) shows the change of reflectivity with incident light intensity at a wavelength of 1934 nm; Figure 10 (d)-(f) Corresponding results for TM polarization.

[0029] Figure 11 is a reflectivity diagram based on a three-periodic unit cell structure, where Figure 11 (a) is the reflectivity contour map based on the three-periodic unit cell structure. Figure 11 (b) Relationship between the reflectivity and incident light intensity of the three-periodic unit cell structure at 1655 nm (dark blue), 1435 nm (light blue), and 2120 nm (orange), with an incident angle of 60°. DETAILED DESCRIPTION

[0030] The following is a further detailed description of the embodiments of the present invention in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the embodiments of the present invention and are not intended to limit the embodiments of the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions of the embodiments of the present invention, rather than all structures.

[0031] Furthermore, the terms "first," "second," "third," etc., in the specification and claims are used solely for descriptive purposes to distinguish between identical technical features. They are not to be construed as indicating or implying relative importance, or as implicitly specifying the number of technical features, nor do they necessarily describe a sequential or chronological order. The terms are interchangeable where appropriate. Thus, a feature specified as "first" or "second" may explicitly or implicitly include at least one of those features.

[0032] Similarly, the terms "fixed" and "connected" used in the specification and claims should not be construed as limited to direct connections. Thus, the expression "device A is connected to device B" should not be limited to devices or systems in which device A is directly connected to device B. Rather, it means that a path exists between device A and device B, which may include other devices or tools.

[0033] Example 1

[0034] This embodiment provides an optical bistable device based on an optical Tamm state, comprising a metal substrate layer, and a transparent conductive oxide film and a photonic crystal layer sequentially disposed on the metal substrate layer;

[0035] The photonic crystal layer includes x unit cell structures stacked from bottom to top on a transparent conductive oxide film, where x≥2;

[0036] Each unit cell structure consists of A Si layers and B SiO2 layers;

[0037] In each unit cell structure, n (Si) d (Si) =n (SiO2)d (SiO2) , so that the band gap of the photonic crystal layer covers the ENZ wavelength of the transparent conductive oxide film, where n (Si) is the refractive index of Si, d (Si) is the total thickness of the Si layer in each unit cell structure, n (SiO2) is the refractive index of SiO2, d (SiO2) is the total thickness of the SiO2 layer in each unit cell structure;

[0038] The surface equivalent impedance of the metal substrate layer and the transparent conductive oxide film matches the relative surface impedance of the photonic crystal layer, so that a Tamm state is formed at the interface between the transparent conductive oxide film and the photonic crystal layer.

[0039] In the optical bistable device based on the optical Tamm state provided by the present invention, the transparent conductive oxide film has a high electron mobility, a narrow full width at half maximum, and a small loss of incident light intensity, which is conducive to achieving bistability. However, the absorption peak of the indium-doped cadmium oxide of the transparent conductive oxide film is reduced under high light intensity, and the bandwidth of the absorption peak is widened, resulting in an increase in the loss of incident light intensity; the photonic crystal layer can form a band gap covering the ENZ region of the transparent conductive oxide in the near-infrared band. At the same time, the surface equivalent impedance of the transparent conductive oxide film matches the relative surface impedance of the photonic crystal layer, so that a Tamm state is formed between the interface of the transparent conductive oxide film and the photonic crystal layer. The bistability effect is achieved under multiple incident angles, two polarizations and different wavelengths, so that the transparent conductive oxide achieves perfect absorption under high light intensity and effectively reduces bandwidth broadening. Without changing the carrier concentration, the bistable operating wavelength is moved to a region smaller than the ENZ wavelength and the nonlinear response is maintained, thereby achieving high-contrast optical bistability.

[0040] Under normal incidence, the photonic crystal layer-transparent conductive oxide film-metal substrate structure exhibits significant bistability hysteresis loop characteristics, with an initial on-off contrast ratio exceeding 0.5. Adjusting the oblique incidence angle improves the maximum contrast ratio by 0.2 compared to normal incidence. Under oblique incidence, the TM polarization bistability operating wavelength window is 154nm wider than that of TE polarization. In other words, bistability is achieved under both TE and TM polarizations, but the TM polarization bistability has a larger operating wavelength window.

[0041] In this embodiment, in the unit cell structure, A Si layers and B SiO2 layers are stacked alternately from bottom to top on the side of the transparent conductive oxide film facing away from the substrate layer, where A=2 and B=1. Specifically, two Si layers and one SiO2 layer are stacked alternately from bottom to top on the side of the transparent conductive oxide film facing away from the substrate layer to form a Si-SiO2-Si photonic crystal (PhC) unit cell structure, and n (Si) d (Si) =n (SiO2) d(SiO2) , the total thickness of the two Si layers is related to d (Si) The total thickness of one SiO2 layer is the same as d (SiO2) The values ​​are the same.

[0042] In order to meet the surface equivalent impedance (Z ENZ-metal ) and the relative surface impedance of the photonic crystal layer (Z PhC ) matches, Z PhC +Z ENZ-metal =0.

[0043] In this embodiment, an optical bistable device based on an optical Tamm state further includes a dielectric layer. In a unit cell structure, B SiO2 layers and A Si layers are alternately stacked from bottom to top on a side of the transparent conductive oxide film facing away from the substrate layer, where A=1 and B=2. The dielectric layer is disposed between the photonic crystal layer and the transparent conductive oxide film. The surface equivalent impedances of the metal substrate, the transparent conductive oxide film, and the dielectric layer match the relative surface impedance of the photonic crystal layer, forming a Tamm state at the interface between the dielectric layer and the photonic crystal layer. Under normal incidence, the surface equivalent impedance of the transparent conductive oxide film on the metal substrate is a negative imaginary number. When B SiO2 layers and A Si layers are alternately stacked from bottom to top on a side of the transparent conductive oxide film facing away from the substrate layer, the surface impedance of the photonic crystal layer is a negative imaginary number. By adding the dielectric layer above the transparent conductive oxide film, the surface equivalent impedance of the dielectric layer-transparent conductive oxide film-metal substrate layer structure is changed to a positive imaginary number, thereby achieving impedance matching. Specifically, two SiO2 layers and one Si layer are alternately stacked from bottom to top on the side of the transparent conductive oxide film facing away from the substrate layer to form a SiO2-Si-SiO2 coupling structure, and n (Si) d (Si) =n (SiO2) d (SiO2) , the total thickness of the two SiO2 layers is related to d (SiO2) The value of d is the same, the thickness of one Si layer is (Si) The values ​​are the same.

[0044] In order to meet the surface equivalent impedance (Z dielectric-ENZ-metal ) and the relative surface impedance of the photonic crystal layer (Z PhC ) matches, Z PhC +Z dielectric-ENZ-metal =0.

[0045] In this embodiment, the dielectric layer includes magnesium oxide. By adding magnesium oxide as the dielectric layer, the maximum switching contrast ratio of the photonic crystal layer-transparent conductive oxide film-metal substrate layer structure is improved by approximately 0.2 under normal incidence conditions compared to the aforementioned unit cell structure without a dielectric layer. This successfully establishes multi-dimensional control freedom, enabling the control of operating wavelength and contrast by adjusting material composition and structural parameters. In another embodiment, the dielectric layer includes at least one of zinc oxide or aluminum oxide.

[0046] In one embodiment, the magnesium oxide has a thickness of 400 nm and a refractive index n=1.706.

[0047] In this embodiment, the transparent conductive oxide film comprises indium-doped cadmium oxide. Indium-doped cadmium oxide has high electron mobility and low loss of incident light intensity, which is conducive to achieving bistability. In another embodiment, the transparent conductive oxide film comprises ITO.

[0048] The sensitivity of the shift of the Tamm resonance frequency to the change of the dielectric constant in In:CdO increases with the widening of the band gap. (Si) d (Si) =n (SiO2) d (SiO2) , and Si and SiO2 have a large nA / nB contrast, which is conducive to optimizing the band gap width and bistability performance.

[0049] In this embodiment, the metal base layer comprises Au. In another embodiment, the metal base layer comprises Ag.

[0050] Electron temperature T e The increase will lead to an increase in the damping rate of indium-doped cadmium oxide. If indium-doped cadmium oxide is used alone as a transparent conductive oxide with ENZ characteristics, perfect absorption occurs at a lower electron temperature, Te≈1200K, and the bistability reflectivity contrast is only 0.5.

[0051] The optical bistable device based on the optical Tamm state of this embodiment introduces a photonic crystal layer to form a Tamm state at the junction of the photonic crystal layer and the transparent conductive oxide film. The perfect absorption of the Tamm state (located at 2150nm) and the ENZ mode of the transparent conductive oxide film (located at 1750nm) occur at Te≈4000K and Te≈7000K, respectively, significantly improving the switching contrast of the bistable state to 0.7–0.8, effectively suppressing the performance degradation caused by absorption broadening of indium-doped cadmium oxide under high light intensity.

[0052] The optical bistability device based on the optical Tamm state of this embodiment successfully achieves multi-angle optical bistability suitable for TM / TE polarization. Compared with the TCOs system in the prior art, the optical bistability device based on the optical Tamm state of this embodiment breaks through the polarization and angle limitations of the existing TCOs system and moves the operating wavelength of the bistability to a region smaller than the ENZ wavelength of the transparent conductive oxide without increasing the carrier concentration.

[0053] In this embodiment, indium-doped cadmium oxide is used as the transparent conductive oxide, and the thickness of the unit cell structure is optimized. (Si) d (Si) =n (SiO2) d (SiO2) , d (Si) =150nm,d (SiO2) =365nm. Without increasing the carrier concentration, the bistability operating wavelength is shifted to a region below the ENZ wavelength: the operating wavelength of the optical bistability induced by the Tamm state in the coupled structure is 1655nm at normal incidence and 1435nm at an angle of incidence of 60°, both shorter than the ENZ wavelength of In:CdO (1840nm). When the operating wavelength is greater than the ENZ wavelength, the increased electron density leads to an increase in the heat capacity of the electronic subsystem, reducing the electron temperature response to light excitation and weakening the optical nonlinearity. However, when the operating wavelength is less than the ENZ wavelength, the system's strong nonlinear response is maintained.

[0054] Indium-doped cadmium oxide (In:CdO) as a transparent conductive oxide has ENZ characteristics and high electron mobility. The change in relative dielectric constant and Kerr-like nonlinearity in the Drude model are analyzed:

[0055]

[0056] where ε′ and ε″ are the real and imaginary parts of the dielectric constant of In:CdO, respectively, and ε ∞ =5.5 is the dielectric constant at infinite frequency, ω p (T e) is the plasma frequency, γ(T e ) is the electron damping coefficient. T is calculated using the free electron model in a non-parabolic conduction band. e Related parameters ω p (T e ) and γ(T e ), where the non-parabolic coefficient is E g =2.92eV, and the effective mass of the electron at the bottom of the conduction band is m=0.12me.

[0057] Figure 1 is a schematic diagram of the ENZ wavelength of indium-doped cadmium oxide, where Figure 1(a) is the electron temperature T e =300K (dark line) and T e =4000K (bright line) of the real part (blue line) and imaginary part (red line) of the dielectric constant of indium-doped cadmium oxide In: CdO. Figure 1 (b) and Figure 1 (c) is related to T e The relevant plasma frequency ωp(Te), ENZ wavelength λENZ(Te) and damping rate γ(Te). Figure 1 ,Depend on Figure 1 (b) It can be seen that the plasma frequency ω p (T e ) decreases with increasing electron temperature, while ε′ increases, indicating that the resonance frequency of In:CdO will redshift with increasing incident light intensity. Figure 1 (c), damping rate γ(T e ) with the electron temperature T e As a result, ε″ increases at high light intensities. As a result, the absorption peak of In:CdO decreases and the bandwidth of the absorption peak broadens at high light intensities. This phenomenon poses a challenge to the formation of optical bistability. To suppress this effect, a photonic crystal layer structure is introduced, which can still achieve perfect absorption at high light intensities and effectively reduce bandwidth broadening, providing important support for high-contrast optical bistability.

[0058] Figure 2 This is a schematic diagram of the structure of an optical bistable device based on the Tamm state, where: Figure 2 (a) is a schematic diagram of the structure of an optical bistability device based on Tamm state. Figure 2 (b) is a schematic diagram of the structure of another optical bistability device based on Tamm state. Figure 2 (c) Band structure of the photonic crystal layer, where the first band gap (gray area) is designed to overlap with the ENZ region of In:CdO, where the ENZ region of In:CdO is defined as |ε| < 1 and is highlighted in light blue.

[0059] exist Figure 2 (a) and Figure 2 In the structure shown in (b), x=2, which makes the photonic crystal layer have a double-periodic unit cell structure. The parameters of the photonic crystal layer need to be precisely selected to ensure that a Tamm state can be formed in the band gap at the junction of the photonic crystal layer and the ENZ-metal substrate structure.

[0060] In order to make the band gap of the photonic crystal layer cover the ENZ wavelength of In:CdO, the following conditions must be met: (n A d A +n B d B )≈mλ ENZ / 2, where n A and d A (B) represent the refractive index and thickness of layer A, n B and d B Represent the refractive index and thickness of layer B respectively, and m is a positive integer representing the band gap. In this embodiment, m=4, n (Si) d (Si) =n (SiO2) d (SiO2) .

[0061] See also Figure 2 (a) and Figure 2 (b) In this embodiment, Si layers and SiO2 layers are alternately stacked to form a photonic crystal layer. The thickness of the Si layer is set to 150nm, with a refractive index n = 3.43, and the thickness of the SiO2 layer is 365nm, with n = 1.4. Figure 2 (c) The photonic crystal layer can form a wide bandgap covering the ENZ region of In:CdO in the near-infrared band of 1650–2200 nm.

[0062] The formation of Tamm states at the interface between the photonic crystal layer and the ENZ-metal substrate structure requires the surface impedance to meet the following conditions:

[0063] Z PhC +Z (dielectric)-ENZ-metal =0

[0064] Z PhC Z represents the surface impedance of the photonic crystal layer PhC, and the specific value can be obtained by calculating the transmission matrix of the PhC unit cell. (dielectric)-ENZ-metal It represents the surface equivalent impedance of the (dielectric)-ENZ-metal structure. The dielectric layer and the metal substrate layer are the key to satisfying the impedance matching conditions and realizing the Tamm state.

[0065] Because Z PhC The value of is highly sensitive to the surface termination position, so the surface termination position is coincident with the inversion center of the unit cell, that is, it is terminated at the center of layer A or layer B. In this configuration, Z PhC is a pure imaginary number, and its imaginary part Im(Z PhC ) remains constant within the band gap region and increases from 0 to ±∞ as the frequency within the band gap changes. It can be found that the sensitivity of the shift in the Tamm resonance frequency to the change in the dielectric constant of In:CdO increases as the band gap widens. Therefore, when selecting materials, it is necessary to meet the requirements of n A d A =n B d B , and Si and SiO2 have larger n A / n B contrast, which is beneficial to optimize the bandgap width and bistability performance.

[0066] See also Figure 2 (a) Under normal incidence, the surface impedance of PhC is a positive imaginary number (i.e., Im(Z PhC )>0), Au is used as the metal substrate, and the surface equivalent impedance of the In:CdO film on Au is a negative imaginary number (i.e., Im(Z (dielectric)-ENZ-metal) <0), satisfying the impedance matching formula, and thus the Tamm state can be realized at the interface of PhC and In:CdO film.

[0067] Figure 3 Schematic diagram of the surface equivalent impedance matching between the photonic crystal layer and the transparent conductive oxide film-metal substrate layer structure, where: Figure 3 (a) Figure 1 (a) The surface impedance of the photonic crystal layer (blue) and the surface equivalent impedance of the transparent conductive oxide film-metal substrate layer structure (orange) under normal incidence conditions. Figure 3 (b) Figure 1 (b) The surface impedance of the photonic crystal layer (blue) and the surface equivalent impedance of the dielectric layer-transparent conductive oxide film-metal substrate structure (orange) under vertical incidence conditions. Figure 3 (c) Figure 1 (a) The corresponding results of the structure shown under TM polarized light with an incident angle of 60°, where the dark and bright lines represent the real and imaginary parts of the impedance, respectively.

[0068] See also Figure 3 (a), the dark line indicates that the real part of the surface impedance is zero, and the incident wavelength value of the excited Tamm state can be obtained at the intersection of the two bright lines.

[0069] Please also see Figure 2 (b) and Figure 3 (a) By exchanging the stacking order of Si layer and SiO2 layer, the surface impedance of PhC becomes a negative imaginary number, i.e. Im(Z PhC )<0, by adding a dielectric layer MgO between PhC and In:CdO film, the surface equivalent impedance value is changed to a positive imaginary number to achieve impedance matching, which increases the freedom of structural design. Figure 3 As shown in (b), at the intersection of the two bright lines, we can obtain Figure 2 (b) The incident wavelength value of the structure excited Tamm state. Figure 3 (c) indicates Figure 1 The structure shown in (a) has two intersections under TM polarized light with an incident angle of 60°, indicating the existence of two resonances in the linear state.

[0070] Figure 4 is the reflectance spectrum, where Figure 4 (a) Yes Figure 1 The structure shown in (a) is different from the electron temperature T e Reflection spectrum under the conditions where the incident angle is 60° and the incident light is TM polarized light; Figure 4 (b) is the indium-doped cadmium oxide-metal substrate structure at different electron temperatures T e The reflectance spectrum below, the inset shows the relationship between reflectance and incident light intensity; Figure 4 (c) is the different electron temperatures T e In the complex frequency plane, Figure 4 (a) and Figure 4 (b) The associated reflection zeros. The solid and hollow points represent the results of (a) and (b), respectively. The reflection zeros are calculated using the Cauchy integral and transfer matrix method.

[0071] Damping rate γ(T e ) with the electron temperature T e Under high illumination intensity, ε″ increases. As a result, the absorption peak of In:CdO decreases and the bandwidth of the absorption peak broadens under high light intensity. Figure 4 (b) Without PhC regulation, the perfect absorption of In:CdO film can only be achieved at T e This is achieved at a low temperature of ≈1200 K, with a reflection contrast as low as 0.5. For TCOs materials with lower carrier mobility, such as ITO, this contradictory effect will be more significant, making it difficult to achieve bistability.

[0072] To compensate for this effect, at higher electron temperatures T e Strong absorption under high T is crucial to achieve high reflection contrast. This embodiment introduces the PhC structure and optimizes the design to achieve high reflection contrast under high T e Perfect absorption occurs when the reflection zeros associated with the structural resonances in the complex frequency plane are tracked. Perfect absorption is achieved when the reflection zeros reach the real frequency axis.

[0073] Please also see Figure 2 (a) and Figure 4 (c), Figure 4 (c) The solid points in the figure represent the reflection zero point trajectory of the PhC structure. e When the temperature rises to 4000K and 7000K, the zero point indicates that the Tamm state and ENZ mode touch the real axis, and the imaginary part of the complex frequency is zero, indicating that Figure 2 The structure shown in (a) produces perfect absorption at high temperature. Figure 4As shown in (b), in contrast, the zero point (hollow point) of the structure without PhC is always far away from the real axis, and perfect absorption cannot be achieved in the high-intensity region. This difference is directly reflected in the reflectivity contrast: the contrast of the device containing PhC reaches 0.7–0.8, while that of the structure without PhC is only 0.5, indicating that PhC can promote the transfer of perfect absorption conditions to higher T e , enhancing the bistability performance.

[0074] Figure 5 is the relationship between light absorption rate and electron temperature, where A=F(Te), I up (blue straight line) and I down The brown straight line is the bistability threshold light intensity for switching between two stable states. The relationship between light absorption rate and electron temperature calculated using the transfer matrix method is A=F(Te).

[0075] The mechanism to achieve bistability is as follows Figure 5 As shown in the figure, the relationship between light absorption rate and electron temperature A = F(Te) calculated using the transfer matrix method is shown in the figure. The relationship between the required light intensity I and the absorption rate A is:

[0076]

[0077] where g ep is the electron-phonon coupling coefficient, d CdO is the In:CdO thickness. The two curves may have two tangent states, indicating the existence of a bistable solution; there may be three intersection points, one of which represents an unstable state, and a small perturbation can drive this state to one of the stable states.

[0078] Figure 6 is a schematic diagram of the reflectivity of a bistable device based on the Tamm state, where Figure 6 (a) Yes Figure 1 The structure shown in (a) is at the electron temperature T e =Reflectivity curve under vertical incidence conditions at 300K; Figure 6 (b) is at vertical incidence Figure 1 (a) Reflectivity contrast of the two stable states of the structure shown Δ R, where gray indicates the monostable region; Figure 6 (c) shows Figure 1 (a) shows a structure with vertical incidence and an incident wavelength of 2107 nm (at Figure 6 The relationship between the reflectivity and the incident light intensity is shown in Figure 2 (marked by the blue dotted line in (b), where the dotted line represents the unstable solution of the reflectivity.

[0079] See also Figure 6(a) When the electron temperature Te = 300K, a significant decrease in reflectivity is observed at wavelength λ = 2070nm, which helps to achieve bistability under normal incidence. Figure 6 (b) The hysteresis width of the bistability (threshold intensity difference ΔIth) and the reflectivity contrast (ΔR) gradually increase with the increase of the wavelength of the incident light. In this process, the wavelength range in which the bistability can be achieved is between 2103nm and 2110nm (width is 7nm). Figure 6 As shown in (c), a significant bistability hysteresis loop is observed at 2107 nm at normal incidence, and the reflectivity contrast ΔR between the two states exceeds 0.5 at 2107 nm.

[0080] Figure 7 is the reflectivity spectrum of the bistable device based on the Tamm state, where Figure 7 (a) Yes Figure 1 Reflectivity spectrum of the structure in (a) (reflectivity changes with incident angle and wavelength under TE polarization). Figure 7 (b) is TE polarization, when the incident angle is 60°, Figure 1 (a) The reflectivity contrast ΔR between the two stable states of the structure shown varies with wavelength. Figure 7 (c) is the change of reflectivity with incident light intensity when the wavelength is 1935nm. Figure 7 (d)-(f) are Figure 1 (a) The corresponding results of TM polarization of the structure shown, where Figure 7 (f) shows the variation of reflectivity with incident light intensity at wavelengths of 1750 nm (orange) and 2150 nm (blue).

[0081] Figure 7 (a) shows Figure 1 (a) The reflectivity spectrum of the structure at 60°, please also refer to Figure 7 (b) When the incident angle is 60°, under TE polarization, a clear bistability region appears near 1935nm (marked by the blue dashed line), covering a wavelength range of 1927nm to 1943nm (width of 16nm), which is 9nm wider than the case of vertical incidence (from 7nm to 16nm). The maximum contrast ΔR reaches 0.9, which is an improvement over the 0.7 at vertical incidence. Figure 7 (c) shows the bistability curve of the incident light with a wavelength of 1935 nm under TE polarization of 60°.

[0082] For TM polarization, the reflection spectrum of the PhC coupling structure changes significantly: the precise control of the thickness of the PhC layer can induce the Tamm state and the ENZ mode to avoid the crossover phenomenon. Figure 7As shown in (d), two decoupled resonance branches are formed at 1750nm and 2150nm: the former shows the characteristics of ENZ-dominated localized surface plasmons, while the latter shows typical Tamm state characteristics. Figure 7 (e) This mode separation extends the bistable operating wavelength range to 170nm (1710nm-1790nm, 2110nm-2200nm), which is 154nm wider than TE polarization (16nm). The two branches produce dual-wavelength bistability, achieving reflection contrast ratios of 0.8 and 0.7 at 1750nm and 2150nm, respectively ( Figure 7 This characteristic indicates that the structure can achieve a bistable response at different wavelengths. By adjusting the thickness of the unit cell structure in the PhC layer, the strength of the coupling can be controlled, providing a reference for the future design of multi-wavelength optical devices.

[0083] Figure 8 The bistable response characteristic curve of the bistable device based on the Tamm state at an incident angle of 30° to 80° is shown in FIG. Figure 8 (a) is the bistability response characteristic curve under TM polarization, and the incident angle θ is marked by the color sequence: θ = 80° (blue), 70° (orange), 50° (green), 40° (deep red), 30° (gold). Figure 8 (b) is the bistability response characteristic curve under TE polarization, and the incident angle θ is marked by the color sequence: θ = 80° (blue), 70° (orange), 50° (green), 40° (deep red), 30° (gold).

[0084] Figure 8 (a) and Figure 8 (b) The corresponding operating wavelengths of the two figures are as follows:

[0085] TM polarization ( Figure 8 (a)): λ(θ=80°)=1773nm, λ(70°)=2193nm, λ(50°)=1843nm, λ(40°)=1899nm, λ(30°)=1965nm.

[0086] TE polarization ( Figure 8 (b)) λ(θ=80°)=1875nm,λ(70°)=1896nm,λ(50°)=1960nm,λ(40°)=1998nm,λ(30°)=2023nm. The light intensity I corresponding to the black dotted line is the bistable threshold light intensity I th .

[0087] See also Figure 8 (a)-(b) are system verification Figure 2(a) The bistability characteristics of the structure shown in Figure 1 at multiple incident angles. The incident light fields in TM and TE polarization modes are selected, and the bistability response analysis is performed at 10° intervals within the incident angle range of 30° to 80°. The experimental results show that for TM polarization, the bistability threshold light intensity (I th ) (the light intensity I corresponding to the black dotted line in the figure) shows a decreasing trend with the increase of the incident angle θ, and the 5 angles tested can achieve a bistable response. TE polarization exhibits characteristics opposite to TM polarization: when θ decreases, I th The bistable contrast ΔR is significantly reduced, and a better bistable contrast ΔR is obtained when θ≤50°. Figure 8 As shown in (a) and (b), for TM polarization, changes in the incident angle will lead to the reconstruction of the dynamic coupling between the ENZ mode and the Tamm state, but the coupling effect still exists. Since the optical bistability curve of the ENZ mode under TM polarization is selected, its local field enhancement effect increases significantly with the increase of θ, thereby reducing the bistability threshold. Under TE polarization, only the Tamm state exists, which is sensitive to changes in interface impedance and is more conducive to achieving low-threshold bistability at a smaller θ (θ<50°). Under multiple incident angles, the actual bistability threshold of TM polarization decreases, while only the Tamm state exists under TE polarization, and low-threshold bistability can also be achieved.

[0088] Figure 9 yes Figure 2 (b) Schematic diagram of the bistability characteristics of the structure under vertical incidence, where Figure 9 (a) is the change of reflectivity contrast ΔR with wavelength, Figure 9 (b) is the relationship between the reflectivity at a wavelength of 2335nm and the incident light intensity.

[0089] See also Figure 9 , Figure 2 (b) The structure shown can still achieve a reflectivity contrast of 0.7 at 2335 nm. The bistable response window of the structure is red-shifted, and the wavelength increases by about 227 nm (from Figure 6 (b) The 2103 nm red shift to Figure 9 The maximum reflectivity contrast is increased to ΔR=0.9, which is about 0.2 higher than the initial structure without the introduction of the MgO dielectric layer (ΔR≤0.7). This can provide multi-dimensional control freedom for the interface impedance matching design of bistable devices and adapt to photonic integrated systems with different wavelengths and contrast requirements.

[0090] Figure 10 yes Figure 2 (b) Schematic diagram of the bistable characteristics of the structure under oblique incidence, where Figure 10 (a) Variation of reflectivity with incident angle and wavelength under TE polarization. Figure 10(b) shows the change of the reflectivity contrast ΔR between the two stable states of the same structure with wavelength when the incident angle is 60° under TE polarization. Figure 10 (c) shows the change of reflectivity with incident light intensity at a wavelength of 1934 nm; Figure 10 (d)-(f) The corresponding results of TM polarization, where (f) shows the variation of reflectivity with incident light intensity at wavelengths of 1750 nm (orange) and 2150 nm (blue).

[0091] See also Figure 10 (b) and Figure 10 (c), contrast Figure 2 (a) with Figure 2 (b) Two structures found that in the TE polarization state, the reflectivity contrast ΔR required by the PhC-MgO-CdO-Au structure at 60° oblique incidence is equivalent to that of the PhC-CdO-Au structure without MgO addition, see Figure 10 (e) and Figure 10 (f) In the TM polarization state, the contrast of the PhC-MgO-CdO-Au structure is limited to the range of 0.6-0.7.

[0092] In this embodiment, a multi-period PhC is formed and the thickness of the PhC layer is controlled through structural design to excite the Tamm state, thereby achieving a bistable operating wavelength shifted to a region shorter than the ENZ wavelength.

[0093] The photonic crystal layer includes x unit cell structures stacked from bottom to top on the transparent conductive oxide film, x≥2, and x=3, that is, the photonic crystal layer includes two unit cell structures to form a three-period unit cell structure. Figure 11 is the reflectivity diagram based on the three-period PhC coupling structure, where Figure 11 (a) Reflectivity contour map based on a three-periodic unit cell coupling structure, where the PhC thickness is reduced (d Si =105nm and d SiO2 =258nm). Figure 11 (b) Relationship between the reflectivity and incident light intensity of the three-periodic unit cell structure at 1655 nm (dark blue), 1435 nm (light blue), and 2120 nm (orange), with an incident angle of 60°.

[0094] exist Figure 2 In the structure shown in (a), x = 2, which makes the photonic crystal layer have a double-periodic unit cell structure. Figure 2 Based on the structure shown in (a), a periodic unit cell structure is added, that is, x = 3, so that the photonic crystal layer has a three-periodic unit cell structure. By calculating n (Si) d (Si) =n (SiO2) d (SiO2), get d Si =105nm and d SiO2 =258nm, and Figure 2 Compared with the structure shown in (a), when x=3, the Si layer and SiO2 layer in each unit cell structure are thinner. Figure 11 (a) shows a thinner PhC layer (d Si =105nm and d SiO2 =258 nm) corresponds to two strong absorption features of the Tamm state and the ENZ mode, respectively. Both states support optical bistability with relatively high reflectivity contrast, such as Figure 11 (b). In addition, the operating wavelength of the optical bistability induced by the Tamm state is 1655 nm at normal incidence and 1435 nm at an incident angle of 60°, both of which are shorter than the ENZ wavelength of In:CdO. This shows that the Tamm state-based approach provides an alternative strategy to shift the operating wavelength to the short wavelength region without increasing the carrier concentration in the In:CdO film. This is particularly beneficial because when the electron density increases, the heat capacity of the electron subsystem also increases, thereby reducing the response of the electron temperature to light excitation, reducing the plasma frequency offset, and resulting in a reduction in optical nonlinearity. Therefore, this embodiment effectively alleviates the problems associated with the reduction of optical nonlinearity by adding a photonic crystal layer to excite the Tamm state, maintaining strong bistability.

[0095] It can be understood that, depending on the ENZ wavelength of different transparent conductive oxides, n (Si) d (Si) =n (SiO2) d (SiO2) As well as impedance matching, the number of periods of the unit cell structure, the thickness of the Si layer and the SiO2 layer, and the thickness of the dielectric layer are adjusted.

[0096] Example 2

[0097] This embodiment 2 provides the application of the optical bistable device based on the optical Tamm state of embodiment 1 in all-optical memory, optical switch, and optical logic gate.

[0098] The present invention is not limited to the above-mentioned embodiments. If various changes or modifications of the present invention do not depart from the spirit and scope of the present invention, and if these changes and modifications fall within the scope of the claims of the present invention and equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. An optical bistable device based on an optical Tamm state, characterized in that: It comprises a metal base layer and a transparent conductive oxide film and a photonic crystal layer sequentially arranged on the metal base layer; The photonic crystal layer includes x unit cell structures stacked from bottom to top on the transparent conductive oxide film, where x≥2; Each of the unit cell structures includes A Si layers and B SiO2 layers; In each of the unit cell structures, n (Si) d (Si) =n (SiO2) d (SiO2) , so that the band gap of the photonic crystal layer covers the ENZ wavelength of the transparent conductive oxide film, where n (Si) is the refractive index of Si, d (Si) is the total thickness of the Si layer in each of the unit cell structures, n (SiO2) is the refractive index of SiO2, d (SiO2) is the total thickness of the SiO2 layer in each of the unit cell structures; The surface equivalent impedance of the metal base layer and the transparent conductive oxide film matches the relative surface impedance of the photonic crystal layer, so that a Tamm state is formed at the interface between the transparent conductive oxide film and the photonic crystal layer.

2. The optical bistability device based on the optical Tamm state according to claim 1, characterized in that: In the unit cell structure, A Si layers and B SiO 2 layers are alternately stacked from bottom to top on a side of the transparent conductive oxide film facing away from the base layer, where A=2 and B=1.

3. The optical bistable device based on the optical Tamm state according to claim 1, characterized in that: Also comprising a dielectric layer; In the unit cell structure, B SiO2 layers and A Si layers are alternately stacked from bottom to top on a side of the transparent conductive oxide film facing away from the base layer, where A=1 and B=2; The dielectric layer is arranged between the photonic crystal layer and the transparent conductive oxide film. The surface equivalent impedance of the metal base layer, the transparent conductive oxide film and the dielectric layer matches the relative surface impedance of the photonic crystal layer. A Tamm state is formed at the interface between the dielectric layer and the photonic crystal layer.

4. The optical bistable device based on the optical Tamm state according to claim 3, characterized in that: The dielectric layer includes magnesium oxide.

5. The optical bistable device based on the optical Tamm state according to claim 1, characterized in that: The transparent conductive oxide film includes indium-doped cadmium oxide.

6. The optical bistable device based on the optical Tamm state according to claim 1, characterized in that: The metal base layer includes Au.

7. Application of the optical bistable device based on the optical Tamm state according to any one of claims 1 to 6 in all-optical memory, optical switch, and optical logic gate.

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