Reflective dielectric chiral metasurface

Abstract

This disclosure provides a reflective dielectric chiral metasurface, comprising: a substrate layer for physical support; a reflective layer disposed on the substrate layer for receiving and reflecting circularly polarized light, wherein the circularly polarized light includes left-handed and right-handed circularly polarized light; and a dielectric micro / nanostructure layer disposed on the reflective layer for differentially scattering the left-handed and right-handed circularly polarized light to modulate the intensity of the circularly polarized light. The dielectric micro / nanostructure layer includes: an array of nanorod units, wherein the nanorod units in rows are staggered along the long axis of the nanorod units and the staggered directions are the same, forming a two-dimensional orthorhombic lattice periodic arrangement structure. This reflective dielectric chiral metasurface improves the output efficiency of the device, reduces the requirements for the fabrication process, and ensures the yield and mass production of the device.

Description

Technical Field

[0001] This disclosure relates to the field of micro-nano optical technology, and more particularly to a reflective medium chiral metasurface. Background Technology

[0002] Chiral materials exhibit unique responses to circularly polarized light due to their distinctive geometric properties. The circular dichroism effect refers to the different absorption intensities of left-handed and right-handed circularly polarized light by chiral materials. Based on this effect, chiral materials have a wide range of potential applications in detection, imaging, anti-counterfeiting, and communication. However, the circular dichroism effect of traditional chiral materials is too weak, resulting in very low intensity of the difference signal, which severely limits their application in these fields.

[0003] In recent years, utilizing metasurfaces to modulate the resonant modes of electromagnetic waves has become a research hotspot in the field of chiral optics. Metasurfaces are artificially fabricated one-dimensional or two-dimensional subwavelength micro / nanostructures whose electromagnetic properties can be controlled through various designs, including structural size and assembly methods, offering extremely high degrees of freedom. Furthermore, these structures possess a strong ability to control the amplitude, phase, and polarization characteristics of electromagnetic waves. In addition, as small-sized two-dimensional planar structures, metasurfaces are easy to integrate and compatible with existing processes. Therefore, compared to traditional chiral materials, chiral metasurfaces offer advantages such as stronger differential signal intensity, smaller device size, and higher production efficiency.

[0004] Currently, metals are still the primary material choice for chiral metasurfaces. Due to the Joule heating effect, these metasurfaces suffer from high losses and low output signal strength, placing high demands on signal detection systems. Furthermore, chiral metasurfaces require asymmetric structural units to achieve chirality. These asymmetric structural units have complex patterns and require high dimensional accuracy, posing challenges to fabrication processes.

[0005] In summary, chiral metasurfaces are an excellent alternative to traditional chiral materials, but many problems remain unresolved, severely limiting their practical applications. Therefore, it is urgent to find feasible methods to address the high losses caused by metal heat loss and the high precision requirements brought about by complex chiral patterns. Summary of the Invention

[0006] To address the problems of existing technologies, this disclosure provides a reflective dielectric chiral metasurface to solve the problems of high losses caused by metal heat loss and high precision requirements caused by complex chiral patterns.

[0007] This disclosure provides a reflective dielectric chiral metasurface, comprising: a substrate layer for physical support; a reflective layer disposed on the substrate layer for receiving and reflecting circularly polarized light, wherein the circularly polarized light includes left-handed and right-handed circularly polarized light; and a dielectric micro / nano structure layer disposed on the reflective layer for differentially scattering the left-handed and right-handed circularly polarized light to modulate the intensity of the circularly polarized light.

[0008] According to embodiments of this disclosure, the dielectric micro / nano structure layer includes: an array of nanorod units, wherein the nanorod units between rows are staggered along the long axis of the nanorod units and the staggered directions are the same, forming a two-dimensional rhombic lattice periodic arrangement structure.

[0009] According to embodiments of this disclosure, the nanorod unit has an axisymmetric structure.

[0010] According to embodiments of this disclosure, when circularly polarized light is incident along the normal direction of the reflective layer surface, the electric field distributions of left-handed and right-handed circularly polarized light are different when they resonate on the reflective layer surface. The electric field excited by the left-handed circularly polarized light forms an electric field coupling mode between the interlaced regions of the nanorod units, generating a circular dichroic signal.

[0011] According to embodiments of this disclosure, the circular dichroic signal exhibits a continuous frequency shift when the misalignment distance between nanorod units changes.

[0012] According to embodiments of this disclosure, the aspect ratio of the nanorod unit is 2 to 10.

[0013] According to embodiments of this disclosure, the length of the nanorod unit ranges from 100 nanometers to 10 micrometers, and the width ranges from 10 nanometers to 1 micrometer; the misalignment distance between adjacent nanorod units along the long axis direction is from 100 nanometers to 500 nanometers; and the spacing between adjacent nanorod units along the short axis direction is from 100 nanometers to 10 micrometers.

[0014] According to embodiments of this disclosure, the nanorod unit is a dielectric material with an absorption rate of less than 10% at the operating wavelength.

[0015] According to embodiments of this disclosure, the reflective layer is made of a metallic material with a reflectivity higher than 80% at the operating wavelength.

[0016] According to embodiments of this disclosure, the thickness of the substrate layer ranges from 300 micrometers to 500 micrometers, the thickness of the reflective layer ranges from 100 nanometers to 500 nanometers, and the thickness of the dielectric micro / nano structure layer ranges from 100 nanometers to 300 nanometers.

[0017] The reflective chiral metasurface provided according to the embodiments of this disclosure has at least the following beneficial effects:

[0018] By setting up a dielectric micro / nano structure layer, when near-infrared circularly polarized light is incident perpendicularly along the normal direction of the chiral metasurface, the circularly polarized light interacts with the dielectric micro / nano structure layer, differentially scattering the left-handed and right-handed circularly polarized light, thereby achieving intensity modulation of the circularly polarized light.

[0019] Furthermore, the dielectric micro / nanostructure layer consists of arrayed nanorod units. These nanorod units are staggered but aligned in the same direction, resulting in high flexibility. By adjusting the relative positions of the nanorods, the wavelength of the circular dichroic signal can be continuously adjusted, enabling the reflective dielectric chiral metasurface to have a wide range of applications. Moreover, the dielectric micro / nanostructure layer, composed of staggered nanorod units, has a simple basic structure, low precision requirements, low processing difficulty, high yield, and is easy to integrate into chip systems.

[0020] Furthermore, the nanorod unit is made of a dielectric material with an absorption rate of less than 10% at the operating wavelength, resulting in low insertion loss and high efficiency of the reflective dielectric chiral metasurface.

[0021] Furthermore, by rationally designing the structure and size of nanorod units, the loss of the chiral metasurface of the reflective medium can be further reduced, thereby improving efficiency and accuracy. Attached Figure Description

[0022] Figure 1 The schematic diagram illustrates the three-dimensional structure of the reflective medium chiral metasurface provided in the embodiments of this disclosure.

[0023] Figure 2A The diagram schematically illustrates the electric field intensity distribution inside a chiral metasurface structure when left-handed circularly polarized light propagating along the normal direction is incident on the structure, as provided in the embodiments of this disclosure.

[0024] Figure 2B The diagram schematically illustrates the electric field intensity distribution inside a chiral metasurface structure when right-handed circularly polarized light propagating along the normal direction is incident on the structure, as provided in the embodiments of this disclosure.

[0025] Figure 3 The schematic diagram illustrates the structure of the dielectric micro / nano structure layer provided in the embodiments of this disclosure.

[0026] Figure 4 The illustration schematically shows a scanning electron microscope (SEM) image of a reflective dielectric chiral metasurface provided in an embodiment of the present disclosure.

[0027] Figure 5 The circular dichroism spectrum of the reflective dielectric chiral metasurface provided in the embodiments of this disclosure is schematically shown.

[0028] Figure 6The diagram illustrates the variation of the circular dichroism spectrum of the reflective chiral metasurface provided in the embodiments of this disclosure with the change of the staggered distance between the nanorods. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0030] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0031] In this disclosure, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0032] In the description of this disclosure, it should be understood that the terms "longitudinal", "length", "circumferential", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the subsystem or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure.

[0033] Throughout the accompanying drawings, identical elements are represented by the same or similar reference numerals. Conventional structures or constructions have been omitted where they may cause confusion in understanding this disclosure. Furthermore, the shapes, dimensions, and positional relationships of the components in the drawings do not reflect actual size, scale, or actual positional relationships. Additionally, any reference numerals placed between parentheses in the claims should not be construed as limiting the claims.

[0034] Similarly, to simplify this disclosure and aid in understanding one or more of the various aspects of the disclosure, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together in a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present disclosure. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0035] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0036] Figure 1 The schematic diagram illustrates the three-dimensional structure of the reflective medium chiral metasurface provided in the embodiments of this disclosure.

[0037] like Figure 1 As shown, the reflective dielectric chiral metasurface includes a substrate layer 1, a reflective layer 2, and a dielectric micro / nano structure layer 3.

[0038] Specifically, substrate 1 provides physical support. Reflective layer 2, disposed on substrate 1, receives and reflects circularly polarized light, including left-handed and right-handed circularly polarized light. Dielectric micro / nano structure layer 3, disposed on reflective layer 2, differentially scatters the left-handed and right-handed circularly polarized light to modulate its intensity.

[0039] Figure 2A The diagram schematically illustrates the electric field intensity distribution inside a chiral metasurface structure when left-handed circularly polarized light propagating along the normal direction is incident on the structure, as provided in the embodiments of this disclosure.

[0040] Figure 2B The diagram schematically illustrates the electric field intensity distribution inside a chiral metasurface structure when right-handed circularly polarized light propagating along the normal direction is incident on the structure, as provided in the embodiments of this disclosure.

[0041] like Figures 2A-2BAs shown, the working principle of this reflective chiral metasurface is as follows: When near-infrared circularly polarized light is incident perpendicularly along the normal direction of the chiral metasurface, the circularly polarized light interacts with the dielectric micro / nano structure layer 3, forming a resonance. The electric field distributions of left-handed and right-handed circularly polarized light are different when they resonate on the chiral metasurface. The electric field excited by left-handed circularly polarized light overlaps between the interlaced regions of the nanorods, forming additional electric field coupling, while right-handed circularly polarized light does not exhibit a similar phenomenon. Due to the different resonance intensities of the generated electric fields, the chiral metasurface has different reflectivities for left-handed and right-handed circularly polarized light, thereby achieving intensity modulation of the circularly polarized light. This difference in reflectivity between left-handed and right-handed circularly polarized light is called the circular dichroism signal.

[0042] Figure 3 The schematic diagram illustrates the structure of the dielectric micro / nano structure layer provided in the embodiments of this disclosure.

[0043] Figure 4 The illustration schematically shows a scanning electron microscope (SEM) image of a reflective dielectric chiral metasurface provided in an embodiment of the present disclosure.

[0044] like Figure 3 and Figure 4 As shown, the dielectric micro / nano structure layer 3 includes an array of nanorod units, wherein the nanorod units between rows are staggered along the long axis of the nanorod units and the staggered directions are the same, forming a two-dimensional rhombic lattice periodic arrangement structure.

[0045] For example, the direction parallel to the major axis is the X direction, and the direction parallel to the minor axis is the Y direction, with the nanorod units arranged in a staggered manner along the Y direction.

[0046] In this embodiment, the nanorod unit has an axisymmetric structure. Preferably, the aspect ratio of the nanorod unit is 2 to 10. The length of the nanorod unit ranges from 100 nanometers to 10 micrometers, and the width ranges from 10 nanometers to 1 micrometer. Along the long axis (Y-direction) of the nanorod unit, the misalignment distance between adjacent nanorod units is 100 nanometers to 500 nanometers. Along the short axis (X-direction) of the nanorod unit, the spacing between adjacent nanorod units is 100 nanometers to 10 micrometers.

[0047] According to embodiments of this disclosure, as the number of nanorods in the interlaced regions increases, more additional electric field coupling is formed, making the difference in reflectivity of the chiral metasurface for left-handed and right-handed circularly polarized light even greater. The reflectance spectra R of the chiral metasurface under left-handed and right-handed circularly polarized light illumination obtained from testing are shown below. lcp R rcp The circular dichroism of this metasurface can be calculated:

[0048]

[0049] The larger the CD signal, the greater the difference in reflection intensity between left-handed and right-handed circularly polarized light. A greater intensity difference means that the detector can tolerate more background noise when identifying different signals, and thus has greater application value in fields such as detection, imaging, anti-counterfeiting, and communication.

[0050] According to embodiments of this disclosure, the spectral characteristics can be altered by adjusting the structural parameters of the dielectric micro / nano structure layer 3. Specifically, when the misalignment distance between adjacent nanorods along the Y direction changes, the overlapping region of the electric fields excited by circularly polarized light changes, and the wavelength corresponding to the maximum circular dichroism signal also changes. Based on this phenomenon, the wavelength of the maximum circular dichroism signal can be continuously tuned. Multiple wavelengths can adapt to various application scenarios, further increasing the application scenarios of this chiral metasurface, while simultaneously enabling wavelength resolution of circularly polarized light, thus broadening its application range.

[0051] Furthermore, the reflective layer is made of a metallic material with a reflectivity higher than 80% at the operating wavelength. The nanorod units are made of a dielectric material with an absorptivity of less than 10% at the operating wavelength. The thickness of the substrate layer ranges from 300 micrometers to 500 micrometers, the thickness of the reflective layer ranges from 100 nanometers to 500 nanometers, and the thickness of the dielectric micro / nanostructure layer ranges from 100 nanometers to 300 nanometers.

[0052] To more clearly illustrate the reflective chiral metasurface provided in this disclosure, a specific example is given below. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this disclosure.

[0053] In this example, the silicon substrate 1 has a thickness of 500 micrometers, the reflective layer 2 has a thickness of 100 nanometers, and the dielectric micro / nanostructure layer 3 is formed by etching on a dielectric film with a thickness of 150 nanometers. The nanorods are 1000 nanometers long and 200 nanometers wide, and are arranged as periodic units in a two-dimensional rhombic lattice, spaced 1000 nanometers apart along the X-axis and 150 nanometers apart along the Y-axis, with a misalignment distance of 300 nanometers between adjacent nanorods along the Y-axis. The reflective layer 2 is made of aluminum, and the dielectric micro / nanostructure layer 3 is made of silicon nitride.

[0054] Figure 5 The circular dichroism spectrum of the reflective dielectric chiral metasurface provided in the embodiments of this disclosure is schematically shown.

[0055] like Figure 5As shown, when near-infrared circularly polarized light is incident perpendicularly along the normal direction of the chiral metasurface, the electric fields excited by the left-handed circularly polarized light coincide between the interlaced regions of the nanorods, forming additional electric field coupling. However, right-handed circularly polarized light does not exhibit a similar phenomenon. Due to the different resonance intensities of the generated electric fields, the chiral metasurface exhibits different reflectivities for left-handed and right-handed circularly polarized light. This difference in reflectivity between left-handed and right-handed circularly polarized light is termed circular dichroism. The maximum circular dichroism signal of 23.75% is obtained at 738 nm.

[0056] Figure 6 The diagram illustrates the variation of the circular dichroism spectrum of the reflective chiral metasurface provided in the embodiments of this disclosure with the change of the staggered distance between the nanorods.

[0057] like Figure 6 As shown, when the misalignment distances between the nanorods are 100, 200, 300, 400, and 500 nm, the wavelengths corresponding to the maximum signal in the circular dichroism spectrum are 824, 776, 751, 724, and 699 nm, respectively. As the misalignment distance gradually increases, the wavelength corresponding to the maximum signal in the circular dichroism spectrum continuously decreases.

[0058] This example clearly demonstrates that the reflective chiral metasurface provided in this disclosure utilizes a simple nanorod structure, coupled with an electric field through an interlaced arrangement, to generate chirality. While reducing fabrication complexity, it still retains relatively high circular dichroism signal intensity. Furthermore, the structure of this invention offers high flexibility; adjusting the relative positions of the nanorods allows for modulation of the response wavelength, enabling use in various environments. Additionally, the structural design based on silicon nitride and aluminum materials results in a strong overall output optical signal and low loss, further meeting application requirements.

[0059] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A reflective dielectric chiral metasurface, characterized in that, The application relates to a circularly polarized light modulation device, which comprises the following layers: a substrate layer for physical support; a reflection layer arranged on the substrate layer and used for receiving and reflecting circularly polarized light, wherein the circularly polarized light comprises left-handed circularly polarized light and right-handed circularly polarized light; a medium micro-nano structure layer arranged on the reflection layer and used for differentially scattering the left-handed circularly polarized light and the right-handed circularly polarized light to regulate the intensity of the circularly polarized light; the medium micro-nano structure layer comprises nanorod units arranged in an array; when the circularly polarized light is incident along the normal direction of the surface of the reflection layer, the electric field distribution of the left-handed circularly polarized light and the right-handed circularly polarized light is different when the circularly polarized light resonates on the surface of the reflection layer; the electric field excited by the left-handed circularly polarized light forms an electric field coupling mode between the staggered areas of the nanorod units, and a circular dichroism signal is generated; when the staggered distance between the nanorod units changes, the circular dichroism signal appears continuous frequency shift, and with the gradual increase of the staggered distance, the wavelength corresponding to the maximum signal in the circular dichroism signal continuously decreases; the nanorod units in the rows are staggered and arranged in the same direction along the long axis of the nanorod units, and form a two-dimensional rhombic lattice periodic arrangement structure. The nanorod unit is an axisymmetric structure. The length-width ratio of the nanorod unit is 2-10. The length of the nanorod unit ranges from 100 nanometers to 10 micrometers, and the width ranges from 10 nanometers to 1 micrometer. The staggered distance between adjacent nanorod units along the long axis of the nanorod unit is 100 nanometers to 500 nanometers; and the interval between adjacent nanorod units along the short axis of the nanorod unit is 100 nanometers to 10 micrometers. The material of the nanorod unit is a dielectric material with an absorption rate of less than 10% at the working wavelength. The material of the reflection layer is a metal material with a reflectivity higher than 80% at the working wavelength. The thickness of the substrate layer ranges from 300 micrometers to 500 micrometers, the thickness of the reflection layer ranges from 100 nanometers to 500 nanometers, and the thickness of the medium micro-nano structure layer ranges from 100 nanometers to 300 nanometers.

2. The reflective meta-chiral super-surface of claim 1, wherein, ​ 3. The reflective meta-chiral super-surface of claim 1 or 2, wherein, ​ 4. The reflective meta-chiral super-surface of claim 3, wherein, ​ ​ 5. The reflective meta-chiral super-surface of claim 1 or 2, wherein, ​ 6. The reflective meta-chiral super-surface of claim 1, wherein, ​ 7. The reflective meta-chiral super-surface of claim 1, wherein, ​

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