A phase modulator with a plasma metasurface etalon structure

Abstract

The invention relates to the technical field of optical phase modulation, and in particular to a phase modulator of a plasma metasurface etalon structure; the structure is a pentagonal prism-shaped nano-periodic array antenna composed of aluminum arranged on a flat plate of SiO2 material, the structure can excite Fabry-Perot resonance in a wavelength range of 600-1000nm, and the tuning of the LSPR and Fabry-Perot coupled resonances is achieved by adjusting LSP and Fabry-Perot parameters respectively, and the phase control in the full 2π range is achieved by changing the height and side length of the pentagonal prism, and the local surface plasmon resonance is tuned to achieve the control of reflectivity; the controller can realize the phase modulation in the range of 0-2π in the wavelength range of 600-1000nm, and complete the focusing effect at a focal length of 43μm, the invention has a simple structure, a compact device structure, is easy to be integrated into an existing system, is convenient to process, and has a low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of optical phase modulation, and in particular to a phase modulator with a plasma metasurface etalon structure. Background Art

[0002] Traditional refractive optical elements use the difference in material refractive index or surface shape to achieve a specific phase distribution, thereby constructing corresponding functional devices. However, the device size is large, difficult to integrate, has high loss, and is difficult to achieve conformal design in applications. With the development of technology, the research on metasurface devices has changed this situation. Metasurface devices based on surface plasmon use the modulation of SP local phase to make the device structure more compact, easy to integrate into existing systems, and simple in design. They are considered to be a promising technical means to replace traditional refractive devices. Compared with traditional optical devices, metasurface devices have many advantages such as arbitrary control of subwavelength scale phase, amplitude, and polarization, light weight, easy integration, low loss, and surface conformal design.

[0003] Traditional optical lenses are thick in the center and have defects such as spherical aberration, which limits the imaging and focusing capabilities of the optical system. Summary of the invention

[0004] The purpose of the present invention is to provide a phase modulator with a plasma metasurface etalon structure, aiming to solve the technical problems in the prior art that the center of traditional optical lenses is thick, spherical aberration of the lenses occurs, and the imaging and focusing capabilities of the optical system are limited.

[0005] To achieve the above-mentioned purpose, the present invention provides a phase modulator of a plasma metasurface etalon structure, wherein the phase modulator of the plasma metasurface etalon structure comprises a plasma nanoantenna array, an isolation layer and a reflection layer, wherein the isolation layer is fixedly connected to the plasma nanoantenna array and is located above the plasma nanoantenna array, and the reflection layer is fixedly connected to the isolation layer and is located above the isolation layer.

[0006] The plasma nanoantenna array is composed of a plurality of pentagonal metal columns, each of which is fixedly connected to the isolation layer and is periodically distributed above the isolation layer.

[0007] Wherein, the pentagonal side length w of each of the pentagonal metal pillars is 20 to 220 nm.

[0008] Wherein, the isolation layer is made of silicon dioxide, and the thickness h2 is 200 nm.

[0009] The reflective layer is made of aluminum, and has a thickness h3 of 200 nm.

[0010] The phase modulator of the plasma metasurface standard tool structure of the present invention can be periodically adjusted through the plasma nanoantenna array, and the transmission phase can be adjusted by utilizing the difference in equivalent refractive index corresponding to metal columns arranged with different duty cycles, so as to construct related planar optical devices, improve the defects of the traditional optical lens such as spherical aberration due to the thick center, which limits the imaging and focusing capabilities of the optical system. Since the metasurface structure is flat and works at the same thickness, the focusing lens realized based on the metasurface system will not have the problem of spherical aberration. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 It is a curve diagram showing the relationship between the side length and phase of the metal column provided by the present invention.

[0013] Figure 2 It is a graph showing the variation of the reflection intensity and phase of the metal column provided by the present invention with the side length and wavelength.

[0014] Figure 3 It is a curve diagram of the relationship between the target phase and the distribution position of the metal pillars provided by the present invention.

[0015] Figure 4 This is a diagram showing the effect of the lens provided by the present invention after focusing.

[0016] Figure 5 It is a structural schematic diagram of a phase modulator of a plasma metasurface etalon structure provided by the present invention.

[0017] 1-plasmonic nanoantenna array, 2-isolation layer, 3-reflection layer. DETAILED DESCRIPTION

[0018] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0019] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, in the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0020] See also Figures 1 to 5 The present invention provides a phase modulator of a plasma metasurface etalon structure, wherein the phase modulator of the plasma metasurface etalon structure comprises a plasma nanoantenna array 1, an isolation layer 2 and a reflection layer 3, wherein the isolation layer 2 is fixedly connected to the plasma nanoantenna array 1 and is located above the plasma nanoantenna array 1, and the reflection layer 3 is fixedly connected to the isolation layer 2 and is located above the isolation layer.

[0021] In this embodiment, the device is a simple periodic structure. By controlling the structural parameters of the metasurface structural unit (array period, metal film thickness, etc.), the band of the localized surface plasmon resonance and its accompanying phase delay (0-2π) can be effectively controlled. By utilizing this phase control characteristic of the metasurface, a reflective metasurface lens with a working band of 1000nm is designed and simulated. The designed focal length and the simulated focal length are highly consistent, and the focal spot size is close to the diffraction limit theoretical value.

[0022] The reflective surface plasmon metasurface structure based on a pentagonal array is composed of a metal-dielectric-metal (MIM) subwavelength resonant microcavity, with aluminum as the substrate material, the middle isolation layer is silicon dioxide, and the top layer is a periodic pentagonal aluminum metal column. Phase control is achieved through the optical path difference generated during the transmission of light.

[0023] Furthermore, the transmission phase type control is used to realize continuous phase control in the range of 0 to 2π, and the phase control is realized by the optical path difference generated during the transmission of light. The expression of the phase difference is:

[0024]

[0025] (where: is the phase difference; λ is the wavelength; n eff is the equivalent refractive index; d is the thickness)

[0026] In this embodiment, the phase can be controlled by adjusting the thickness or refractive index. Therefore, by using aluminum nanodisks of different side lengths and thicknesses and combining with localized surface plasmon resonance, the incident light can be fully phase-delayed (0-2π) modulated by changing the period. Using this reflective microstructure, a reflective metasurface flat microlens was designed and simulated at a wavelength of 1000 nm. The designed focal length and the simulated focal length are highly consistent, and the focal spot size is close to the diffraction limit theoretical value. Further simulation results show that the flexible phase control function of the metasurface can achieve perfect centrifugal focusing at any position of the flat lens.

[0027] Furthermore, the plasma nanoantenna array 1 is composed of a plurality of pentagonal metal columns, each of which is fixedly connected to the isolation layer 2 and is periodically distributed above the isolation layer 2, with a period P of 1000nm; the pentagonal side length w of each pentagonal metal column is 20 to 220nm, and continuous phase regulation is achieved by periodic variation of the side length; the isolation layer 2 is made of silicon dioxide, with a thickness h2 of 200nm; the reflective layer 3 is made of aluminum, with a thickness h3 of 200nm; TM polarized light with a wavelength range of 600 to 1000nm is used as the incident light source, and Fabry-Perot resonance is excited between the plasma nanoantenna array 1 and the reflective layer and within the working wavelength range.

[0028] In this embodiment, Figure 1 (a) Demonstrates the relationship between the side length and phase of a single pentagonal metal pillar when the height is 350nm, which can achieve a phase transition of almost 2π; Figure 1 (b) is the relationship curve between the side length and reflection intensity when the height of a single pentagonal metal column is 350nm. It can be seen that the reflection intensity value at this time is greater than 0.7. Therefore, by increasing the thickness and side length of the metal column, the complete 2π real phase transition can be further tuned.

[0029] Figure 2 As shown, the position of the LSPR can be changed by adjusting the side length of the nanodisk, so that the entire graph moves along the wavelength axis. The s-parameter analysis group is used to perform scanning calculations, and the reflection and phase results are obtained by scanning the height and side length of the nanorods. Figure 2 (a)-(b) respectively show the change of reflection intensity and phase with side length and wavelength when the thickness of the metal column is d=350nm; it can be seen that within these parameter ranges, when the wavelength is 600-1000nm, the design requirements are met. According to the scanning results, the height and wavelength to achieve the required transmission and phase characteristics are selected. The present invention sets the working wavelength to 1000nm.

[0030] Figure 3The curve shown is the relationship between the target phase and the distribution position of the metal column. After calculating the required nanorod side length according to the phase and side length data selected in the above steps, the nanorod side length is calculated according to the given Figure 3 The curve can determine the array arrangement of the unit to achieve the purpose of generating a specific phase value at a given spatial position. In order to focus the light, the light propagating from the metasurface to the focal plane must interfere constructively, so the phase shift at each point on the metasurface should satisfy the relationship of the expression of the phase difference; according to the unit side length and unit array arrangement determined above, the construction of the focusing lens can be further completed.

[0031] Furthermore, a circular hole composed of PEC (perfect electric conductor) is placed between the light source and the lens to limit the injection area to the circular metal area. Since the incident light is blocked by the PEC aperture, they show a clear field truncation; the numerical aperture plays a decisive role in the focusing performance in the lens design. The calculation of the numerical aperture is based on the formula:

[0032] NA = sin[tan -1 (D / 2f)]

[0033] (Where: D is the diameter, f is the focal length)

[0034] In this embodiment, the numerical aperture of the metalens is calculated to be about 0.421 based on the selected element diameter D of 40 μm and the focal length f of 43 μm. Then, the FDTD simulation is set, the light source is a plane wave, the three-axis boundary conditions are all PML, and the z-plane monitor is set to record the electric field information and energy information at the focal plane.

[0035] The far-field projection along the propagation axis z shows that the focal length of the metal is about 43um, as shown in Figure 4 (a) and Figure 4 As shown in (b), the calculated focal length deviates slightly from the target value of 50 μm, which is mainly attributed to the lens size limitation, which only allows a small number of nanorods to achieve a phase change of 2π over the lens radius. Increasing the size of the lens may help improve the results, and it can also be achieved by optimizing other parameters, such as the period. Figure 4 (c) shows the focusing effect, that is, a focal spot is finally obtained. According to the diffraction limit formula of the lens λ / 2NA, the diffraction limit of the present invention is about 1186nm. It is worth noting that when its diffraction limit is close to the wavelength, high-resolution imaging can be achieved for objects smaller than the illumination wavelength. The results show that the phase can be controlled by changing the side length of the nanorod array, but in many cases, other design requirements must be considered, such as phase profile and transmission efficiency. Therefore, to complete the design that meets the above requirements, other parameters such as height, period and refractive index may also need to be considered.

[0036] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A phase modulator with a plasma metasurface etalon structure, It is characterized in that The phase modulator of the plasma metasurface etalon structure comprises a plasma nano-antenna array, an isolation layer and a reflection layer, wherein the isolation layer is fixedly connected to the plasma nano-antenna array and is located above the plasma nano-antenna array, and the reflection layer is fixedly connected to the isolation layer and is located above the isolation layer; The plasma nanoantenna array is composed of a plurality of pentagonal metal columns, each of which is fixedly connected to the isolation layer and is periodically distributed above the isolation layer, with a period P of 1000 nm; The pentagonal side length w of each of the pentagonal metal pillars is 20 to 220 nm; The material of the isolation layer is silicon dioxide, and the thickness h2 is 200nm; The reflective layer is made of aluminum, and its thickness h3 is 200 nm. TM polarized light with a wavelength range of 600 to 1000 nm is used as the incident light source to induce Fabry-Perot resonance between the plasma nanoantenna array and the reflective layer and within the working wavelength range.

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