A slow light device based on composite micro-nano structure dynamic adjustable and a design method thereof

Abstract

The application discloses a kind of based on composite micro-nano structure dynamic adjustable slow light device and its design method, including substrate, and gold nanorod array and hBN nanobelt being arranged above substrate;hBN nanobelt is located at the gap between gold nanorod two two, gold nanorod array and hBN nanobelt are perpendicular to each other on xy plane;Substrate material selects non-infrared active CaF2.The application utilizes the strong coupling and weak coupling between the gap plasmon mode supported by gold nanorod and the hyperbolic phonon polariton mode supported by hBN nanobelt to realize electromagnetic induction transparent phenomenon, and the group delay generated thereby can be used as slow light device;By adjusting the angle of incident light, dynamic regulation of group delay can also be realized, i.e., a dynamically adjustable slow light device is realized;And, due to the existence of high-order hyperbolic phonon polariton, the device can also realize the conversion function of fast and slow light.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optoelectronic functional device design, and particularly relates to a slow light device based on a composite micro-nano structure and a design method thereof. BACKGROUND

[0002] In the field of modern optoelectronics, slow light devices have attracted much attention due to their great potential applications in optical information processing, optical communication, and optical sensing. Implementing slow light effects on optoelectronic chips can greatly improve the performance of optoelectronic chip devices and find wide applications in optical sensing, optical communication, optical computing, and optical buffering. For example, slow light devices can provide adjustable optical signal delay, data buffering and switching, which are very useful for implementing anti-interference signal processing.

[0003] Slow light devices can also enhance the interaction between optical signals and nonlinear media, which is very helpful for implementing optical switches and other nonlinear optical devices. These devices can be used to build anti-interference optical communication links, as they can quickly switch communication paths when interference is detected.

[0004] The design of slow light devices relies on the realization of slow light effect, which is the phenomenon of a significant reduction in the group velocity of light in a medium. The main methods to realize slow light effect are based on electromagnetically induced transparency, which utilizes the quantum coherence effect between atomic system transition channels to eliminate the influence of the medium on the propagation of electromagnetic waves. Alternatively, periodic structures such as photonic crystals, gratings, and micro-ring resonant cavities can be designed to achieve slow light effect. 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 periodic waveguide structures, large dispersion can be obtained by the relationship between waveguide structure parameters and wavelength, thus achieving slow light effect; the introduction of resonant cavity structure can strengthen the interaction between light and modulation region, thereby achieving slow light effect.

[0005] Although these methods have made some progress in theory and experiment, there are still some limitations. The generation of electromagnetically induced transparency requires specific complex conditions such as cryogenic temperature and high-intensity laser, which limits its application scenarios; the preparation process of photonic crystals is complex and requires very high processing precision, which limits its application in large-scale production; in the micro-ring resonant cavity structure, the waveguide refractive index difference is small, resulting in a large device and the need for improvement in integrability. SUMMARY

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

[0007] To achieve the above object, the application provides a slow light device based on a composite micro-nano structure with dynamic adjustment, which comprises a substrate, a gold nanorod array and an hBN nanobelt arranged above the substrate, the hBN nanobelt being arranged at a gap between two gold nanorods, and the gold nanorod array and the hBN nanobelt being perpendicular to each other in an xy plane.

[0008] Further, the width W of the hBN nanobelt is 240 nm. h The width W of the gold nanorod is 240 nm. A The direction parallel to the gold nanorod is an x direction, and the direction parallel to the hBN nanobelt is a y direction. The period Px and Py of the x and y directions are 2.6 μm and 2.5 μm, respectively. The thickness of the gold nanorod and the hBN nanobelt is 40 nm. The substrate material is CaF2 which is non-infrared active.

[0009] Further, the refractive index of the substrate is 1.37.

[0010] Further, as an anisotropic crystal, the dielectric constant tensor of the hBN is diagonal in a Cartesian coordinate system, has two independent components, and the in-plane dielectric constant component is represented as ε ⊥ , and the out-of-plane dielectric constant component is represented as ε || . The 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 Γ ⊥ of the in-plane mode is 5 cm -1 . The wave number of the in-plane optical phonon is ω TO，⊥ = 1370 cm -1 . The wave number of the longitudinal optical phonon is ω LO，⊥ = 1610 cm -1 . The dielectric function parameter of the out-of-plane phonon mode is ε ∞，|| = 2.95. The line width Γ || of the out-of-plane mode is 4 cm -1 . The wave number of the out-of-plane optical phonon is ω TO，|| = 780 cm -1 . The wave number of the longitudinal optical phonon is ω TO,|| = 830 cm -1 .

[0013] A design method of a slow light device based on a composite micro-nano structure with dynamic adjustment, comprising the following steps:

[0014] Step 1, selecting CaF2 which is non-infrared active as a substrate material.

[0015] Step 2: Design a composite micro / nano structure including a substrate, an array of gold nanorods disposed on the substrate, and hBN nanoribbons; optimize the optical properties of the composite structure by adjusting the size, period, and thickness of the gold nanorods and hBN nanoribbons; the optimized parameters are as follows: the width W of the hBN nanoribbons... h The width W of the gold nanorods A Both are 240 nm in diameter. The direction parallel to the gold nanorod is the x-direction, and the direction parallel to the hBN nanoribbon is the y-direction. The period P in the x and y directions is... x and P y The thicknesses are 2.6 μm and 2.5 μm, respectively, and the thicknesses of the gold nanorods and hBN nanoribbons are both 40 nm.

[0016] Step 3: Input the material parameters of the substrate, gold nanorods, and hBN into the simulation software Comsol; the relative permittivity 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 incident light is polarized along the x-direction, and a periodic boundary condition is applied, so that the two-dimensional hBN nanoribbon extends infinitely in the y-direction;

[0018] Step 5: By adjusting the angle of the incident light, test the group delay at different angles to verify the dynamic tunability of the composite structure and its fast-slow light conversion function.

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

[0020] (1) The excellent light field confinement 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 higher than the 70% 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; the slow light can be actively controlled by changing the incident angle. The highest group delay that can be achieved is 7.319 ps, which corresponds to a distance delay of 2.196 mm.

[0022] (3) The hyperbolic phonon polaritons and their higher-order modes provided by hBN nanobelts enable the group delay to continuously reverse under strong phase dispersion, thus realizing the fast and slow light conversion function. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a composite structure consisting of periodic gold nanorods coupled with hBN nanoribbons.

[0024] Figure 2 In (a) and (b), the resonant wavelength of the gold nanorods varies with the width W.A and period P x , (c), (d) are the variation diagrams of the resonance wavelength of two-dimensional hBN nanobelt with width W h and period P x .

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

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

[0027] By constantly exploring new methods and materials, it is expected to realize more efficient and more controllable slow light devices. Since the nanogap composed of two or more adjacent metal nanostructures is the best in the light field binding ability among many surface plasmon structures, the two-dimensional hBN strip is placed in the metal gap to enhance the action of light and the modulation region as much as possible. At the same time, the structure designed by the application is simple, which is conducive to improving the precision and efficiency in the processing process, so as to carry out large-scale production.

[0028] Therefore, the application provides a dynamic adjustable slow light device based on a composite micro-nano structure, which can realize active regulation of group delay by changing the incident angle. Since the two-dimensional material hBN is introduced in the structure, as a natural hyperbolic material, it has high thermal conductivity and extremely low loss, which is very important for the thermal management, signal transmission quality, device speed and power consumption reduction of optoelectronic devices.

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

[0030] As shown in Figure 1 , the geometric configuration diagram of the composite micro-nano structure is composed of a gold nanorod array and an hBN nanobelt. The width W h of the hBN nanobelt and the width W A of the gold nanorod are both 240 nm, the periods Px and Py in the x and y directions are 2.6 μm and 2.5 μm respectively, and the thicknesses of the gold nanorod and the hBN nanobelt are both 40 nm. In order to reduce the interference of substrate phonons, CaF2 which is not infrared active is selected as the substrate material, and the refractive index is 1.37. As an anisotropic crystal, the dielectric constant tensor of hBN has a diagonal relationship in the Cartesian coordinate system, and has two independent components ε xx = ε yy = ε ⊥(in-plane) and ε zz =ε || (Outside the plane). Its associated dielectric constant is as follows:

[0031]

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

[0033] The resonant wavelength of gold nanorods varies with 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 increases with increasing width. A The change in the period P has a relatively small effect on its resonant wavelength. With increasing width, the resonant wavelength exhibits a slight blue shift. x The resonant wavelength continuously redshifts as the wavelength increases. Figure 2 The thumbnail in (a) shows a typical localized surface plasmon mode supported by gold nanorods. In contrast, the resonant wavelength of two-dimensional hBN nanoribbons varies with width W. h and period P x Changes such as Figure 2 As shown in (c) and 2(d). With the width W h As the period P increases, the resonance wavelength continuously redshifts, and the transmittance of the spectrum decreases. x As the resonant wavelength increases, the resonant wavelength remains almost unchanged, while the transmittance continuously increases. Figure 2 (c) shows the surface phonon polariton mode supported by hBN nanoribbons, which also exhibits hyperbolic behavior within the hBN material, and can also be called hyperbolic phonon polariton.

[0034] Figure 2 (a) shows the transmission spectrum of gold nanorods as a function of W. A The change in P at this time x(a) is the transmission spectrum of the gold nanorod as a function of W x , where P A is 2.6 μm, and the thumbnail is the electric field pattern supported by the gold nanorod; (b) is the transmission spectrum of the gold nanorod as a function of P h , where W x is 240 nm; (c) is the transmission spectrum of the hBN nanoribbon as a function of W x , where P h is 2.6 μm, and the thumbnail is the electric field pattern supported by the gold nanorod; (d) is the transmission spectrum of the hBN nanoribbon as a function of P x , where W A is 240 nm.

[0035] To achieve strong mode interaction in the composite structure, we design the period P h to be 2.6 μm, the gold nanorod width W x to be 240 nm, and the two-dimensional hBN nanoribbon width W h to be 240 nm, so that the localized surface plasmon mode resonance wavelength and the surface phonon polariton mode resonance wavelength are zero detuned, both at 6.80 μm. The transmission spectra before and after coupling are shown in Figure 3 . Obvious transmission enhancement is produced at 6.49 μm, 6.79 μm, and 7.05 μm [corresponding to III, II, I in Figure 3 ], and obvious transmission reduction is produced at 6.42 μm, 6.53 μm, and 8.25 μm [corresponding to 1, 2, 3 in Figure 3 ], and the overall electromagnetic induced transparency phenomenon is exhibited.

[0036] To further analyze the physical source of the electromagnetic induced transparency phenomenon, we tune the localized surface plasmon mode by changing the period P x , and the transmission spectrum of the composite structure exhibits splitting. The surface phonon polariton mode resonance on the hBN nanoribbon and the localized surface plasmon mode resonance of the gold nanorod are excited at the same time at the peak wavelength of 6.8 μm, and a transparent window with a transmission rate of up to 91.2% is produced at 7.05 μm, which is higher than the 70% transparent window of the same type of hBN nanoribbon composite structure.

[0037] The transmission spectrum of the composite structure is further studied by changing the incident angle of the plane wave, and the Bloch boundary condition is used in the ±x direction to ensure the correction of the incident angle of the plane wave source. It is found that the spectral position of the transparent window almost does not change in the incident angle range of 0° to 70°. At the same time, the transmission spectrum of the plane wave is studied under the polarization angle of 0° to 80°, and the incident angle is 0°, and the periodic boundary condition remains unchanged. It is found that the spectral position and intensity of the transparent window are not sensitive in the polarization angle range of 0° to 50°, and the transparent window gradually disappears as the polarization angle increases. This means that the proposed composite structure has angle independence within a certain range of incident angle change, and has polarization independence within a certain range of polarization angle change, which can enhance the compatibility of the structure in the application of actual slow light devices.

[0038] The electromagnetic induced transparency phenomenon is often accompanied by extreme changes in the dispersion characteristics, resulting in slow light effects. The measurement of slow light effects is represented by the group delay t g of the incident wave through the structure, compared with the group refractive index n g . The calculation of t g does not require the effective thickness of the composite structure. Therefore, the group delay t g is introduced here to describe the slow light capability of the coupled system. It is represented 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 the steepest at the maximum of the transparent window as in previous studies, but at the wavelength position where the high-order surface plasmon polariton is generated. At the same time, the maximum of the group delay does not correspond to the maximum of the transparent window, but to the wavelength region where the high-order surface plasmon polariton mode and the surface plasmon mode are coupled. The positive and negative of the group delay represent the slow light and fast light phenomena of the light passing through the device, Figure 4 The maximum group delay shown in (b) is 0.86 ps, which corresponds to a distance delay of 0.258 mm when the light propagates in free space. In the wavelength range of 6-7 μm, the positive and negative of the group delay are constantly reversed, Figure 4 The inset of (b) can more clearly see this trend. This means that the composite structure can also realize the function of fast-slow light conversion.

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

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

[0043]

[0044] The above results prove that the slow light effect of the designed composite micro-nano structure has an active tunable ability, and the light speed control function of the composite structure is expected to be integrated into an optoelectronic chip and a quantum photon circuit to realize higher performance of optoelectronic devices and quantum information processing technology.

[0045] The application also provides a design method of a slow light device based on a dynamically adjustable composite micro-nano structure, comprising the following steps:

[0046] Step 1, selecting CaF2 which is not infrared active as a substrate material because it has lower phonon loss and suitable refractive index (1.37);

[0047] Step 2, designing a composite micro-nano structure including a substrate and a gold nanorod array and an hBN nanobelt arranged above the substrate. By adjusting the size, period and thickness of the gold nanorod and the hBN nanobelt, the optical properties of the composite structure are optimized to achieve the best slow light effect and dynamic regulation ability. The optimized parameters are as follows: the width W of the hBN nanobelt h and the width W of the gold nanorod A are both 240 nm, the periods P x and P y in the x and y directions are 2.6 μm and 2.5 μm respectively, and the thicknesses of the gold nanorod and the hBN nanobelt are both 40 nm;

[0048] Step 3, inputting the material parameters of the substrate, the gold nanorod and the 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 which is approximately a polar dielectric crystal;

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

[0050] Step 5, by adjusting the angle of the incident light, the group delay at different angles is tested to verify the dynamic tunable ability and the fast-slow light conversion function of the composite structure.

[0051] The above only describes the preferred embodiments of the application. Since the design idea of the application is clear and has wide application prospects, any simple equivalent changes and modifications made according to the content of the claims and the description of the application shall still belong to the scope covered by the patent of the application.

Claims

1. A slow light device based on composite micro-nano structure dynamic adjustable, characterized in that, The device includes a substrate, and an array of gold nanorods and hBN nanoribbons disposed on the substrate. The hBN nanoribbons are located in the gaps between pairs of gold nanorods, and the gold nanorod array and hBN nanoribbons are perpendicular to each other in the xy plane; the width W of the hBN nanoribbons is... h The width W of the gold nanorods A Both are 240 nm thick. The x-direction is parallel to the gold nanorods, and the y-direction is parallel to the hBN nanoribbons. The periods Px and Py in the x and y directions are 2.6 μm and 2.5 μm, respectively. The thickness of both the gold nanorods and hBN nanoribbons is 40 nm. The substrate material is non-infrared active CaF2.

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

37.

3. The slow light device based on composite micro-nano structure dynamic adjustable according to claim 1, characterized in that, As an anisotropic crystal, the dielectric constant tensor of hBN is diagonal in the Cartesian coordinate system, with two independent components, the in-plane dielectric constant component denoted as ε ⊥ , and the out-of-plane dielectric constant component denoted as ε || ; the relevant dielectric constants are as follows: wherein the dielectric function parameter of the in-plane phonon mode is ε ∞,⊥ = 4.87, the line width Γ corresponding to the in-plane mode ⊥ = 5 cm -1 , the wave number ω corresponding to the transverse optical phonon of the in-plane mode is ω TO，⊥ = 1370 cm -1 , the wave number ω corresponding to the longitudinal optical phonon is ω LO，⊥ = 1610 cm -1 , the dielectric function parameter of the out-of-plane phonon mode is ε ∞，|| = 2.95, the line width Γ corresponding to the out-of-plane mode is Γ || = 4 cm -1 , the wave number ω corresponding to the transverse optical phonon of the out-of-plane mode is ω TO，|| = 780 cm -1 , the wave number ω corresponding to the longitudinal optical phonon is ω TO，|| = 830 cm -1 .

4. The design method of claim 1, wherein the method comprises the steps of: a) designing a slow light device based on a composite micro-nano structure; b) designing a dynamic tunable slow light device based on the composite micro-nano structure; and c) designing a dynamic tunable slow light device based on the composite micro-nano structure. It comprises the following steps: Step 1, select non-infrared active CaF2 as the substrate material; Step 2, design a composite micro-nano structure including a substrate and gold nanorod array and hBN nanobelt arranged above the substrate; by adjusting the size, period and thickness of the gold nanorod and the hBN nanobelt, the optical properties of the composite structure are optimized; the optimization result parameters are as follows, the width W of the hBN nanobelt h and the width W of the gold nanorod A are both 240 nm, the direction parallel to the gold nanorod is the x direction, the direction parallel to the hBN nanobelt is the y direction, the periods P x and P y of the x and y directions are 2.6 μm and 2.5 μm respectively, and the thicknesses of the gold nanorod and the hBN nanobelt 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 approximating a polar dielectric crystal; Step 4, the polarization of incident light is along the x direction, and the periodic boundary condition is adopted, and the two-dimensional hBN nanobelt is infinitely extended in the y direction; Step 5, by adjusting the angle of incident light, the group delay under different angles is tested, the dynamic tunable ability of the composite structure is verified, and the fast and slow light conversion function is verified.

5. The method of claim 4, wherein, The substrate refractive index is 1.

37.

6. The method of claim 4, wherein, As an anisotropic crystal, the dielectric constant tensor of hBN is diagonal in the Cartesian coordinate system, with two independent components, the in-plane dielectric constant component denoted as ε ⊥ , and the out-of-plane dielectric constant component denoted as ε || ; the relevant dielectric constants are as follows: wherein the dielectric function parameter of the in-plane phonon mode is ε ∞，⊥ = 4.87, the line width Γ corresponding to the in-plane mode ⊥ = 5 cm -1 , the wave number ω corresponding to the transverse optical phonon of the in-plane mode is ω TO，⊥ = 1370 cm -1 , the wave number ω corresponding to the longitudinal optical phonon is ω LO，⊥ = 1610 cm -1 , the dielectric function parameter of the out-of-plane phonon mode is ε ∞，|| = 2.95, the line width Γ corresponding to the out-of-plane mode is Γ || = 4 cm -1 , the wave number ω corresponding to the transverse optical phonon of the out-of-plane mode is ω TO，|| = 780 cm -1 , the wave number ω corresponding to the longitudinal optical phonon is ω TO，|| = 830 cm -1 .

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