Dynamic adjustable slow light device based on composite micro-nano structure and design method thereof

Abstract

The invention discloses a dynamic adjustable slow light device based on a composite micro-nano structure and a design method thereof. The dynamic adjustable slow light device comprises a substrate, a gold nanorod array and an hBN nanobelt, wherein the gold nanorod array and the hBN nanobelt are arranged above the substrate; the hBN nanobelts are located in gaps between every two gold nanorods, and the gold nanorod array and the hBN nanobelts are perpendicular to each other on an xy plane; caF2 with non-infrared activity is selected as a substrate material. According to the invention, the electromagnetic induction transparency phenomenon is realized by utilizing the combined action of strong coupling and weak coupling between a gap plasmon mode supported by the gold nanorods and a hyperbolic phonon polariton mode supported by the hBN nanoribbons, and group delay which can be generated can be used as a slow light device; the group delay can be dynamically regulated and controlled by adjusting the angle of the incident light, namely, a dynamic adjustable slow light device is realized; moreover, due to the existence of the high-order hyperbolic phonon polaritons, the device can also realize the conversion function of fast light and slow light.

Description

Technical Field

[0001] The present invention belongs to the field of photoelectric functional device design, and specifically relates to a slow light device based on a composite micro-nano structure and a design method thereof. Background Art

[0002] In the field of modern optoelectronics, slow light devices have attracted much attention due to their great application potential in optical information processing, optical communication, and optical sensing. Realizing the slow light effect on optoelectronic chips can greatly improve the performance of optoelectronic chip devices and have been widely used in the fields of optical sensing, optical communication, optical computing, and optical caching. For example, slow light devices can provide adjustable optical signal delay, data caching and switching, which is very useful for realizing anti-interference signal processing.

[0003] Slow-light devices can also enhance the interaction of optical signals with nonlinear media, which is helpful for realizing optical switches and other nonlinear optical devices. These devices can be used to build interference-resistant optical communication links because they can quickly switch communication paths when interference is detected.

[0004] The design of slow-light devices depends on the realization of the slow-light effect, which is the phenomenon that the group velocity of light in a medium is significantly reduced. The method to achieve the slow-light effect is mainly based on the electromagnetic induced transparency phenomenon, which uses the quantum coherence effect between the transition channels of the atomic system to eliminate the influence of the medium during the propagation of electromagnetic waves. Or it can be achieved by designing periodic structures such as photonic crystals, gratings, and micro-ring resonators. The band structure of photonic crystals has a very small slope at the band edge, which can achieve a significant reduction in group velocity; in the periodic waveguide structure, a large dispersion can be obtained through the relationship between the waveguide structure parameters and the wavelength, thereby achieving the slow-light effect; and the introduction of the resonant cavity structure can strengthen the interaction between light and the modulation zone, thereby achieving the slow-light effect.

[0005] Although these methods have made some progress in theory and experiment, they also have some limitations. The electromagnetically induced transparency effect requires specific complex conditions, such as refrigeration temperature, high-intensity laser, etc., which limits its application scenarios; the preparation process of photonic crystals is complex and requires extremely high processing accuracy, which limits its application in large-scale production; in the micro-ring resonator structure, the waveguide refractive index difference is small, resulting in a larger device, and the integration needs to be improved. Summary of the invention

[0006] The purpose of the present invention is to provide a dynamically adjustable slow light device based on a composite micro-nano structure and a design method thereof.

[0007] To achieve the above-mentioned purpose of the invention, the present invention proposes the following technical solution: a dynamically adjustable slow light device based on a composite micro-nano structure, comprising a substrate, and a gold nanorod array and hBN nanoribbons arranged above the substrate, the hBN nanoribbons being located in the gaps between the gold nanorods, and the gold nanorod array and the hBN nanoribbons being perpendicular to each other in the xy plane.

[0008] Furthermore, the width W of the hBN nanoribbon is h and the width W of the gold nanorod A Both are 240nm, the direction parallel to the gold nanorods is the x direction, and the direction parallel to the hBN nanobelts is the y direction. The periods Px and Py in the x and y directions are 2.6μm and 2.5μm respectively. The thickness of the gold nanorods and hBN nanobelts are both 40nm; the substrate material is non-infrared active CaF2.

[0009] Furthermore, the substrate refractive index is 1.37.

[0010] Furthermore, as an anisotropic crystal, the dielectric constant tensor of hBN is diagonally related in the Cartesian coordinate system and has two independent components. The in-plane dielectric constant component is represented by ε ⊥ , the out-of-plane dielectric constant component is expressed as ε || ; Its related dielectric constant is as follows:

[0011]

[0012] The dielectric function parameter of the in-plane phonon mode is ε ∞，⊥ =4.87, the line width of the in-plane mode Γ ⊥ =5cm -1 , the corresponding wave number of the in-plane mode transverse optical phonon is ω TO，⊥ =1370cm -1 , the corresponding wave number of the longitudinal optical phonon is ω LO，⊥ =1610cm -1 , the dielectric function parameter of the out-of-plane phonon mode is ε ∞，|| =2.95, the line width of the out-of-plane mode is Γ || =4cm -1 , the wave number corresponding to the out-of-plane mode transverse optical phonon is ω TO，|| =780cm -1 , the longitudinal optical phonon corresponds to wave number ω TO,|| =830cm -1 .

[0013] A design method for a dynamically adjustable slow light device based on a composite micro-nano structure comprises the following steps:

[0014] Step 1, selecting non-infrared active CaF2 as substrate material;

[0015] Step 2, designing a composite micro-nanostructure including a substrate, a gold nanorod array disposed on the substrate, and a hBN nanobelt; optimizing the optical properties of the composite structure by adjusting the size, period, and thickness of the gold nanorods and the hBN nanobelt; the optimization result parameters are as follows: the width W of the hBN nanobelt h and the width W of the gold nanorod A The length of the nanorods is 240 nm, the direction parallel to the gold nanorods is the x direction, the direction parallel to the hBN nanoribbons is the y direction, and the period P in the x and y directions is x and P y They are 2.6 μm and 2.5 μm respectively, and the thickness of gold nanorods and hBN nanoribbons are both 40 nm;

[0016] Step 3, input the material parameters of the substrate, gold nanorods and hBN in the simulation software Comsol; the relative dielectric constant of gold is determined by experimental results; the two-dimensional hBN is represented by a Lorentz oscillator model that is approximately a polar dielectric crystal;

[0017] Step 4, the polarization of the incident light is along the x-direction, and periodic boundary conditions are used, and the two-dimensional hBN nanoribbon is infinitely extended in the y-direction;

[0018] Step 5, by adjusting the angle of the incident light, testing the group delay at different angles, verifying the dynamic tunability of the composite structure and the fast-slow light conversion function.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The excellent light field binding ability of gap plasmons and the combined effect of strong and weak coupling are utilized to increase the transmittance of the transparent window. The transmittance is as high as 91.2%, which is 70% higher than the transparent window of the same type of hBN nanoribbon composite structure.

[0021] (2) There is no need to passively adjust the slow light effect by changing the structural parameters. Active regulation of slow light can be achieved by changing the incident angle. The highest group delay that can be achieved is 7.319ps, corresponding to a distance delay of 2.196mm.

[0022] (3) The excitation of the hyperbolic phonon polaritons and their higher-order modes provided by the hBN nanoribbons causes the positive and negative groups of the group delay to be reversed continuously under strong phase dispersion, thus realizing the fast-slow light conversion function. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the composite structure of periodic gold nanorods coupled with hBN nanoribbons.

[0024] Figure 2 (a) and (b) show the resonance wavelength of the gold nanorod as a function of its width W.A and period P x (c) and (d) are the changes of the resonance wavelength of the two-dimensional hBN nanoribbon with the width W. h and period P x 's change graph.

[0025] Figure 3 It is a schematic diagram of the transmission spectrum before and after coupling.

[0026] Figure 4 It is a schematic diagram of the transmission phase shift and group delay of the composite structure at an incident angle of 0°. DETAILED DESCRIPTION

[0027] By continuously exploring new methods and materials, it is expected that more efficient and controllable slow light devices can be realized. Since the nanogap composed of two or more adjacent metal nanostructures has the best light field binding ability among many surface plasmon structures, the present invention places the two-dimensional hBN strip in the metal gap to enhance the interaction between light and the modulation area as much as possible. At the same time, the structure designed by the present invention is simple, which is conducive to improving the accuracy and efficiency in the processing process, so as to carry out large-scale production.

[0028] In view of this, the present invention proposes a slow light device based on a composite micro-nano structure that is dynamically adjustable, and the device can achieve active regulation of group delay by changing the incident angle. Since the two-dimensional material hBN is introduced into the structure, as a natural hyperbolic material, it has high thermal conductivity and extremely low loss, which is very important for thermal management, signal transmission quality, device speed and power consumption reduction of optoelectronic devices.

[0029] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. However, it should be understood that the present invention can be implemented in various forms, and some exemplary and non-limiting embodiments shown in the accompanying drawings and described below are not intended to limit the present invention to the specific embodiments described.

[0030] like Figure 1 As shown in Figure 2, the geometric configuration of the composite micro-nanostructure is composed of gold nanorod arrays and hBN nanobelts. The width of the hBN nanobelt is W. h and the width W of the gold nanorod A The period Px and Py in the x and y directions are 2.6 μm and 2.5 μm respectively. The thickness of gold nanorods and hBN nanobelts is 40 nm. In order to reduce the interference of substrate phonons, non-infrared active CaF2 is selected as the substrate material with a refractive index of 1.37. As an anisotropic crystal, the dielectric constant tensor of hBN is diagonally related in the Cartesian coordinate system, with two independent components ε xx =ε yy =ε ⊥(in-plane) and ε zz =ε || (out-of-plane). The dielectric constant associated with it is as follows:

[0031]

[0032] The dielectric function ε of the in-plane mode is ∞,⊥ =4.87, line width Γ ⊥ =5cm -1 ,ω TO,⊥ =1370cm -1 ,ω LO,⊥ =1610cm -1 , the dielectric function of the out-of-plane mode ε ∞,|| =2.95, line width Γ || =4cm -1 ,ω TO,|| =780cm -1 ,ω TO,|| =830cm -1 .

[0033] The resonance wavelength of the gold nanorod varies with its width W A and period P x Changes such as Figure 2 As shown in (a) and 2(b), the bandwidth of the transmission spectrum increases with W A and P x The width of the gold nanorod W A The change in the resonant wavelength has a relatively small effect. As the width increases, the resonant wavelength slightly blueshifts. x As the resonance wavelength increases, it continues to redshift. Figure 2 The thumbnail image in (a) shows a typical localized surface plasmon mode supported by a gold nanorod. In contrast, the resonant wavelength of a 2D hBN nanoribbon varies with its width W. h and period P x Changes such as Figure 2 (c) and 2(d). As the width W h As the period P increases, the resonance wavelength continues to redshift, and the transmittance of the spectrum decreases. x With the increase of , the resonance wavelength remains almost unchanged, while the transmittance increases continuously. Figure 2 The thumbnail image of (c) shows the surface phonon polaritons supported by hBN nanoribbons, which also exhibit hyperbolicity inside the hBN material and can also be called hyperbolic phonon polaritons.

[0034] Figure 2 (a) Transmission spectrum of gold nanorods as W A The change of P xis 2.6μm, and the thumbnail is the electric field mode supported by the gold nanorods; (b) is the transmission spectrum of the gold nanorods with P x The change of W A is 240nm; (c) is the transmission spectrum of hBN nanobelts with W h The change of P x The thumbnail is the electric field mode supported by gold nanorods; (d) the transmission spectrum of hBN nanobelts changes with P x The change of W h It is 240nm.

[0035] In order to achieve strong mode interaction in the composite structure, we design the period P x The width of the gold nanorod is 2.6 μm. A The width of the two-dimensional hBN nanoribbon is 240 nm. h The transmission spectra before and after coupling are shown in Figure 2. Figure 3 As shown. Obvious transmission enhancement is produced at 6.49μm, 6.79μm and 7.05μm respectively [corresponding to Figure 3 III, II, I], and a significant decrease in transmission occurs at 6.42 μm, 6.53 μm, and 8.25 μm [corresponding to Figure 3 1, 2, 3], and the whole exhibits electromagnetically induced transparency.

[0036] In order to further analyze the physical source of the electromagnetically induced transparency phenomenon, we change the period P x The transmission spectrum of the composite structure shows splitting by tuning the localized surface plasmon mode. The surface phonon exciton mode resonance on the hBN nanoribbon and the localized surface plasmon mode resonance of the gold nanorods are simultaneously excited at a peak wavelength of 6.8μm, and a transparent window with a transmittance of up to 91.2% is generated at 7.05μm, which is higher than the 70% transparent window of the same type of hBN nanoribbon composite structure.

[0037] The transmission spectral characteristics of the composite structure are further studied by changing the plane wave incident angle α. At this time, the Bloch boundary conditions are used in the ±x direction to ensure the correction of the incident angle of the plane wave light source. The study found that the spectral position of the transparent window hardly changes in the incident angle range from 0° to 70°. The transmission spectrum changes of the plane wave under the polarization angle of rotation from 0° to 80° are also studied here. At this time, the incident angle is 0° and the periodic boundary conditions remain unchanged. The study found that the spectral position and intensity of the transparent window are also insensitive to the polarization angle range of 0° to 50°. As the polarization angle continues to increase, the transparent window will gradually disappear. This means that the proposed composite structure has angle independence within a certain range of incident angle changes and polarization independence within a certain range of polarization angle changes, which can enhance the compatibility of the structure in actual slow light device applications.

[0038] Electromagnetically induced transparency is often accompanied by extreme changes in dispersion properties, leading to the slow light effect. The slow light effect is measured by the group delay t of the incident wave passing through the structure. g To represent, with the group refractive index n g In comparison, t g The calculation of does not require the effective thickness of the composite structure. Therefore, the group delay t is introduced here g To describe the slow light capability of the coupled system. It is expressed as:

[0039]

[0040] Where ψ is the transmission phase shift and ω is the corresponding frequency. Figure 4 The transmission phase shift and group delay of the composite structure at an incident angle of 0° are shown. Interestingly, the slope of the phase shift is not steepest at the maximum transparent window as in previous studies, but is steepest at the wavelength where high-order surface phonon polaritons are generated. At the same time, the maximum value of the group delay does not correspond to the maximum transparent window, but is in the wavelength region where high-order surface phonon polaritons and surface plasmon modes are coupled to each other. The positive and negative values ​​of the group delay represent the slow light and fast light phenomena of light passing through the device, respectively. Figure 4 The maximum group delay shown in (b) is 0.86ps, which corresponds to a distance delay of 0.258mm when light propagates in free space. In the wavelength range of 6 to 7μm, the positive and negative of the group delay are constantly reversed. Figure 4 The inset of (b) shows this trend more clearly, which means that the composite structure can also realize the conversion function of fast and slow light at the same time.

[0041] With the change of the incident angle, the active control of the slow light effect of the composite structure can be achieved, and the detailed data are shown in Table 1. Between the incident angle of 50°-70°, the composite structure has a strong phase dispersion mutation, and the group delay can reach up to 7.319ps, corresponding to a distance delay of 2.196mm.

[0042] Table 1 Group delay and corresponding distance delay of the composite structure at different incident angles

[0043]

[0044] The above results confirm that the slow light effect of the designed composite micro-nanostructure has the ability of active tunability. The light speed control function of the composite structure is expected to be integrated into optoelectronic chips and quantum photonic circuits to achieve higher performance optoelectronic devices and quantum information processing technology.

[0045] The present invention also provides a design method for a slow light device based on a composite micro-nano structure that is dynamically adjustable, comprising the following steps:

[0046] Step 1, select non-infrared active CaF2 as the substrate material because it has low phonon loss and a suitable refractive index (1.37);

[0047] Step 2, design a composite micro-nanostructure including a substrate, a gold nanorod array disposed on the substrate, and a hBN nanobelt. By adjusting the size, period, and thickness of the gold nanorods and hBN nanobelts, the optical properties of the composite structure are optimized to achieve the best slow light effect and dynamic regulation capability. The optimization result parameters are as follows: the width W of the hBN nanobelt h and the width W of the gold nanorod A Both are 240nm, and the period P in the x and y directions is x and P y They are 2.6 μm and 2.5 μm respectively, and the thickness of gold nanorods and hBN nanoribbons are both 40 nm;

[0048] Step 3, input the material parameters of the substrate, gold nanorods and hBN in the simulation software Comsol. The relative dielectric constant of gold is determined by experimental results. The two-dimensional hBN is represented by the Lorentz oscillator model which is approximately a polar dielectric crystal;

[0049] Step 4: The polarization of the incident light is along the x-direction, and periodic boundary conditions are adopted, and the two-dimensional hBN nanoribbon is infinitely extended in the y-direction.

[0050] Step 5, by adjusting the angle of the incident light, testing the group delay at different angles, verifying the dynamic tunability of the composite structure and the fast-slow light conversion function.

[0051] The above is only a preferred embodiment of the present invention. Since the present invention has a clear design concept and a wide range of application prospects, all simple equivalent changes and modifications made according to the claims and the invention description should still fall within the scope of the present invention.

Claims

1. A dynamically adjustable slow light device based on a composite micro-nano structure, characterized in that: The invention comprises a substrate, and a gold nanorod array and a hBN nanobelt arranged on the substrate. The hBN nanobelt is located in the gaps between two gold nanorods. The gold nanorod array and the hBN nanobelt are perpendicular to each other in the xy plane.

2. The dynamically adjustable slow light device based on a composite micro-nano structure according to claim 1, characterized in that: The width W of the hBN nanoribbon h and the width W of the gold nanorod A Both are 240nm, the direction parallel to the gold nanorods is the x direction, and the direction parallel to the hBN nanobelts is the y direction. The periods Px and Py in the x and y directions are 2.6μm and 2.5μm respectively. The thickness of the gold nanorods and hBN nanobelts are both 40nm; the substrate material is non-infrared active CaF2.

3. The dynamically adjustable slow light device based on composite micro-nano structure according to claim 2, characterized in that: The substrate refractive index is 1.

37.

4. A dynamically adjustable slow light device based on a composite micro-nano structure according to claim 1 or 2, characterized in that: As an anisotropic crystal, the dielectric constant tensor of hBN is diagonally related in the Cartesian coordinate system and has two independent components. The in-plane dielectric constant component is represented by ε ⊥ , the out-of-plane dielectric constant component is expressed as ε || ; Its related dielectric constant is as follows: The dielectric function parameter of the in-plane phonon mode is ε ∞，⊥ =4.87, the line width of the in-plane mode Γ ⊥ =5cm -1 , the corresponding wave number of the in-plane mode transverse optical phonon is ω TO，⊥ =1370cm -1 , the corresponding wave number of the longitudinal optical phonon is ω LO，⊥ =1610cm -1 , the dielectric function parameter of the out-of-plane phonon mode is ε ∞，|| =2.95, the line width of the out-of-plane mode is Γ || =4cm -1 , the wave number corresponding to the out-of-plane mode transverse optical phonon is ω TO，|| =780cm -1 , the longitudinal optical phonon corresponds to wave number ω TO，|| =830cm -1 .

5. A design method for a dynamically adjustable slow light device based on a composite micro-nano structure as claimed in claim 1, characterized in that: The steps include: Step 1, selecting non-infrared active CaF2 as substrate material; Step 2, designing a composite micro-nanostructure including a substrate, a gold nanorod array disposed on the substrate, and a hBN nanobelt; optimizing the optical properties of the composite structure by adjusting the size, period, and thickness of the gold nanorods and the hBN nanobelt; the optimization result parameters are as follows: the width W of the hBN nanobelt h and the width W of the gold nanorod A The length of the nanorods is 240 nm, the direction parallel to the gold nanorods is the x direction, the direction parallel to the hBN nanoribbons is the y direction, and the period P in the x and y directions is x and P y They are 2.6 μm and 2.5 μm respectively, and the thickness of gold nanorods and hBN nanoribbons are both 40 nm; Step 3, input the material parameters of the substrate, gold nanorods and hBN in the simulation software Comsol; the relative dielectric constant of gold is determined by experimental results; the two-dimensional hBN is represented by a Lorentz oscillator model that is approximately a polar dielectric crystal; Step 4, the polarization of the incident light is along the x-direction, and periodic boundary conditions are used, and the two-dimensional hBN nanoribbon is infinitely extended in the y-direction; Step 5, by adjusting the angle of the incident light, testing the group delay at different angles, verifying the dynamic tunability of the composite structure and the fast-slow light conversion function.

6. The method according to claim 5, characterized in that The substrate refractive index is 1.

37.

7. The method according to claim 5, characterized in that As an anisotropic crystal, the dielectric constant tensor of hBN is diagonally related in the Cartesian coordinate system and has two independent components. The in-plane dielectric constant component is represented by ε ⊥ , the out-of-plane dielectric constant component is expressed as ε || ; Its related dielectric constant is as follows: The dielectric function parameter of the in-plane phonon mode is ε ∞，⊥ =4.87, the line width of the in-plane mode Γ ⊥ =5cm -1 , the corresponding wave number of the in-plane mode transverse optical phonon is ω TO，⊥ =1370cm -1 , the corresponding wave number of the longitudinal optical phonon is ω LO，⊥ =1610cm -1 , the dielectric function parameter of the out-of-plane phonon mode is ε ∞，|| =2.95, the line width of the out-of-plane mode is Γ || =4cm -1 , the wave number corresponding to the out-of-plane mode transverse optical phonon is ω TO，|| =780cm -1 , the longitudinal optical phonon corresponds to wave number ω TO，|| =830cm -1 .

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