Total-space multi-focus super lens based on transverse dispersion and design method thereof

Abstract

The invention discloses a total-space multi-focus super lens based on transverse dispersion and a design method thereof.The super lens comprises a transparent substrate, a one-dimensional photonic crystal lamination layer and a double-layer nano brick unit structure, the one-dimensional photonic crystal lamination layer, a first nano brick and a second nano brick are sequentially arranged above the transparent substrate, and the first nano brick and the second nano brick are deposited below the transparent substrate; two mutually vertical sides of the transparent substrate are respectively used as an x axis and a y axis; the one-dimensional photonic crystal laminated layer is formed by alternately laminating a plurality of silicon layers and silicon dioxide layers, the thicknesses of the single silicon layer and the silicon dioxide layer are D1 and Dh respectively, and the period of the unit structure substrate is P; the included angle between the long axis of the first nano brick or the second nano brick and the x axis is the steering angle theta of the nano brick, and the value range of theta is [0, pi]; the first nano brick and the second nano brick both have the characteristics of a half-wave plate. By rotating the steering angle of the double-layer nano structure, when circularly polarized light with different wavelengths and polarization states enters the super lens, reflected waves and transmitted waves can be independently controlled.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-nano photonics, and particularly relates to an all-space multi-focus metalens based on transverse dispersion and a design method thereof. Background Art

[0002] A metasurface is a special two-dimensional metamaterial that can flexibly and effectively control the characteristics of electromagnetic waves such as phase, polarization, and amplitude at the sub-wavelength scale, and can create unique electromagnetic responses that do not exist in nature, so it is widely used in various fields. Therefore, the abrupt phase on the structural surface can be used to manipulate the wavefront of the reflected or transmitted wave, control the phase, amplitude, and polarization state of the electromagnetic wave, so as to achieve the purposes of focusing, beam deflection, and generating special beams.

[0003] A metalens is a planar lens in which sub-wavelength-sized structures are specifically distributed on a plane to achieve functions such as focusing and imaging. Its main working principle is based on the regulation of electromagnetic waves by the micro-nano structures on the material surface. By controlling the abrupt phase distribution on the surface, the control of the electromagnetic wave beam is realized, thereby changing its wavefront. Compared with traditional lenses, the metasurface lens has the advantages of light weight, small volume, and easy to achieve high modulation and integration.

[0004] The multi-focus full-surface metalens based on the principle of transverse dispersion is a new type of metasurface device that realizes the synchronous identification and reconstruction of spectral and polarization information by focusing light with different wavelengths and polarization states to different positions in space. Compared with the traditional microlens array, this multi-focus metalens has a larger numerical aperture (NA), which can provide better imaging performance and resolution. In addition, the design of the multi-focus metalens can also integrate geometric phase modulation technology and holographic principle to realize the regulation of spectral and polarization states, further promoting the progress and innovation of compact optical systems.

[0005] However, existing metasurfaces usually work in either pure reflection mode or pure transmission mode, leaving half of the electromagnetic space unused. Summary of the Invention

[0006] To solve the technical problems existing in the prior art, the present invention provides an all-space multi-focus metalens based on transverse dispersion and a design method thereof, which can not only work in both reflection and transmission spaces simultaneously, but also independently manipulate the reflected and transmitted electromagnetic waves. By rotating the steering angle of the double-layer nanostructure, the present invention can independently manipulate the reflected wave and the transmitted wave when circularly polarized light with different wavelengths and polarization states is incident on the metalens, and focus the light beam at different positions in the transmission and reflection spaces, realizing the synchronous identification and reconstruction of wavelength and polarization information.

[0007] The technical solution adopted by the present invention is:

[0008] The first invention of the present invention relates to a full-space multi-focus metalens based on lateral dispersion. It is characterized in that when circularly polarized light with different wavelengths and polarization states is incident on the metalens, in the reflection space and the transmission space, the lens can respectively form six foci with different spatial positions, and ultimately a total of twelve foci with different spatial positions can be formed in the full space. Based on the distribution of these foci in space, the measurement and analysis of the wavelength and polarization state of the incident light can be realized. Its structure includes a transparent substrate, a one-dimensional photonic crystal stack, and a double-layer nanobrick unit structure. The double-layer nanobrick unit structure includes a first nanobrick and a second nanobrick. The one-dimensional photonic crystal stack is sequentially arranged above the transparent substrate, the first nanobrick, and the second nanobrick is deposited below the transparent substrate. Taking two mutually perpendicular sides of the transparent substrate as the x-axis and the y-axis respectively, an xoy coordinate system is established.

[0009] The one-dimensional photonic crystal stack is formed by alternately stacking multiple silicon layers and silica layers, where the thicknesses of a single silicon layer and a silica layer are D l and D h , respectively, and the unit structure substrate period is P.

[0010] Define the long sides of the first nanobrick and the second nanobrick as the major axes, which are L1 and L2 respectively, the short sides as the minor axes, which are W1 and W2 respectively, and the height of both is H. The above structural parameters are all sub-wavelength levels. The angle between the major axis of the first or second nanobrick and the x-axis is the turning angle of the nanobrick, denoted as θ, and the value range of θ is [0, π].

[0011] Both the first nanobrick and the second nanobrick have the characteristics of a half-wave plate.

[0012] Furthermore, the materials of the first nanobrick and the second nanobrick are silicon.

[0013] Furthermore, the structural parameters L1, L2, W1, and W2 are optimized through electromagnetic simulation to meet the half-wave plate characteristics, and then the overall simulation of the metalens is performed to obtain the optical response characteristics.

[0014] Furthermore, there will be a phase modulation when the first nanobrick and the second nanobrick are penetrated by light, which is specifically manifested as:

[0015] When considering the reflection space, when a light beam with a wavelength of λ is incident on the metalens from bottom to top, it will pass through the bottom metasurface and then be reflected back, and will be modulated by the bottom metasurface again. When considering the transmission space, when the light beam is incident on the metalens, it will sequentially pass through the metasurface. Denote the phase distribution of the metalens in the reflection mode as The phase distribution in the transmission mode is denoted as The rotation angle of the second nanobrick is θ1, and the rotation angle of the first nanobrick is θ2. Their phase modulation satisfies the following relationship:

[0016]

[0017] Among them, x and y are the two-dimensional coordinates of each nanobrick, and f is the focal length of the metalens.

[0018] The second invention of the present invention relates to a design method of a full-space multi-focus metalens based on lateral dispersion, which is characterized by including the following steps:

[0019] Step 1, calculate the thicknesses D l and D h

[0020] According to the photonic crystal theory, calculate the thicknesses D l and D h ;

[0021] Step 2, construct the nano-unit structure

[0022] Optimize and simulate the double-layer nanobrick unit structure to optimize it into a half-wave plate, and obtain the size parameters of the optimized double-layer nanobrick unit structure, which are the lengths L1, L2, widths W1, W2, height H, and the unit structure substrate period P of the first nanobrick and the second nanobrick respectively;

[0023] Step 3, determine the working wavelength

[0024] Scan the overall structure through electromagnetic simulation software to determine the working wavelengths λ1, λ2, λ3 in the transmission space; the working wavelengths in the reflection space are λ4, λ5, λ6.

[0025] Step 4, measure and analyze the incident light wavelength and polarization state in the full space

[0026] Incident circularly polarized light with different wavelengths on the second nanobrick, and six spatially distinct foci can be formed respectively in the reflection space and the transmission space, where three foci are formed by LCP incident light and the other three foci are formed by RCP incident light. Finally, a total of twelve spatially different foci can be formed in the reflection and transmission spaces, that is, on the array composed of the double-layer nanobrick unit structure with variable rotation angles, the measurement of the incident light wavelength and polarization state in the full space is realized.

[0027] Furthermore, in Step 4, different wavelengths respectively correspond to six spatially distinct foci, and the positions of the foci can be represented in polar coordinates as:

[0028]

[0029] Among them, λ n represents the nth working wavelength, and r is the radius of the metalens. The polar angle with the focus

[0030] Furthermore, the coordinates (x center,n , y center,n ) of the nth focus in the rectangular coordinate system can be expressed as:

[0031]

[0032] The phase distribution of the metalens at different working wavelengths can be expressed as

[0033]

[0034] where λ is the wavelength of the incident light, x and y are the two-dimensional coordinates of each nanobrick, and f is the focal length of the metalens.

[0035] Furthermore, in step 4, multiple focusing phases with different wavelengths and corresponding foci at different positions are encoded on a single metalens. Then, the phase of the encoded metalens can be expressed as:

[0036]

[0037] where A n , are the amplitude and phase at the nth focus and the nth working wavelength, respectively.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] 1) The metalens composed of the double-layer nanostructure array with variable angles can achieve focusing at different positions in the transmission and reflection spaces. Therefore, it has a higher space utilization rate than the traditional metalens that is only limited to the half space (reflection or transmission space).

[0040] 2) The metalens produced by the present invention can operate at multiple wavelengths with low crosstalk during focusing. At the same time, the design method is ingenious and the structure used is simple. Therefore, the metalens designed by the present invention is easy to be integrated into imaging or display devices such as wearable near-eye displays, autonomous driving vehicles, and satellite imaging, reducing the volume and weight while ensuring the imaging quality, and adapting to the future development of miniaturization and microminiaturization.

[0041] 3) The metalens produced by the present invention has an all-dielectric structure, which is more economical compared to the metalens structure that uses metal to achieve reflection. Description of the Drawings

[0042] Figure 1 is a schematic diagram of the unit structure of the metalens of the present invention;

[0043] Figure 2a andFigure 2b They are respectively the reflectivity and transmittance scanning diagrams of the unit structure of the present invention;

[0044] Figure 3 It is a schematic diagram of multi-wavelength focusing in the transmission and reflection space of the present invention;

[0045] Figure 4a It is a schematic diagram of the theoretical phase focusing distribution when the wavelengths are 600nm, 650nm, and 700nm and the incident light is left-handed in the present invention;

[0046] Figure 4b It is a schematic diagram of the theoretical phase focusing distribution when the wavelengths are 600nm, 650nm, and 700nm and the incident light is right-handed in the present invention. Specific embodiments

[0047] The following will describe in detail the specific embodiments of the embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention.

[0048] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0049] The present invention will be described in detail below with reference to the accompanying drawings and in combination with exemplary embodiments.

[0050] Embodiment 1

[0051] Referring to Figure 1 , a full-space multi-focus metalens based on lateral dispersion of the present invention includes a transparent substrate, a one-dimensional photonic crystal stack, and a double-layer nanobrick unit structure. The double-layer nanobrick unit structure includes a first nanobrick and a second nanobrick; the one-dimensional photonic crystal stack is sequentially arranged above the transparent substrate, the first nanobrick, and the second nanobrick is deposited below the transparent substrate. Taking two mutually perpendicular sides of the transparent substrate as the x-axis and y-axis respectively, an xoy coordinate system is established accordingly;

[0052] The one-dimensional photonic crystal stack is formed by alternately stacking multiple silicon layers and silica layers, where the thicknesses of a single silicon layer and a silica layer are D l and D h respectively, and the period of the unit structure substrate is P;

[0053] Define the long sides of the first nanobrick and the second nanobrick as the major axes, which are L1 and L2 respectively, the short sides as the minor axes, which are W1 and W2 respectively, and the height of both is H; the above structure parameters are all sub-wavelength levels; the angle between the major axis of the first or second nanobrick and the x-axis is the turning angle of the nanobrick, which is θ, and the value range of θ is [0, π];

[0054] Both the first nanobrick and the second nanobrick have the characteristics of a half-wave plate.

[0055] In this embodiment, the materials of the first nanobrick and the second nanobrick are silicon.

[0056] In this embodiment, the structural parameters L1, L2, W1, and W2 are optimized by electromagnetic simulation to meet the characteristics of a half-wave plate, and then the overall simulation of the metalens is performed to obtain the optical response characteristics.

[0057] In this embodiment, there will be a phase modulation when the first nanobrick and the second nanobrick are penetrated by light, specifically manifested as:

[0058] When considering the reflection space, when a light beam with a wavelength of λ is incident on the metalens from bottom to top, it will pass through the bottom metasurface and then be reflected back, and will be modulated by the bottom metasurface again; when considering the transmission space, when the light beam is incident on the metalens, it will pass through the metasurface in sequence; the phase distribution of the metalens in the reflection mode is denoted as The phase distribution in the transmission mode is denoted as The rotation angle of the second nanobrick is θ1, and the rotation angle of the first nanobrick is θ2, and their phase modulation satisfies the following relationship:

[0059]

[0060] where x and y are the two-dimensional coordinates of each nanobrick, and f is the focal length of the metalens.

[0061] Embodiment 2

[0062] Reference Figures 2a to 4b , a design method of a full-space multi-focus metalens based on transverse dispersion according to the present invention, includes the following steps:

[0063] Step 1, calculate the thicknesses D l and D h

[0064] According to the photonic crystal theory, calculate the thicknesses D l and D h ;

[0065] Specifically, in this embodiment, according to the photonic crystal theory, D l = 60 nm, D h = 120 nm;

[0066] Step 2, construct the nano-unit structure

[0067] By optimizing and simulating the double-layer nanobrick unit structure to optimize it into a half-wave plate, the size parameters of the optimized double-layer nanobrick unit structure are obtained, which are the lengths L1 and L2, widths W1 and W2, height H, and the unit structure substrate period P of the first nanobrick and the second nanobrick respectively.

[0068] Specifically, in this embodiment, the size parameters of the optimized double-layer silicon nanobrick are: the lengths are L1 = 120 nm and L2 = 125 nm, the widths are W1 = 70 nm and W2 = 60 nm, the heights are H1 = 150 nm and H = 500 nm, and the unit structure substrate period is P = 300 nm.

[0069] Step 3, determine the working wavelength

[0070] By scanning the overall structure including with an electromagnetic simulation software, determine the working wavelengths λ1, λ2, λ3 in the transmission space; the working wavelengths in the reflection space are λ4, λ5, λ6.

[0071] Specifically, in this embodiment, by scanning the double-layer nanostructure with an electromagnetic simulation software, determine that the working wavelengths in the transmission space are λ1 = 450 nm, λ2 = 500 nm, and λ3 = 550 nm; the working wavelengths in the reflection space are λ4 = 600 nm, λ5 = 650 nm, and λ6 = 700 nm.

[0072] Step 4, measure and analyze the incident light wavelength and polarization state in the full space

[0073] Incident circularly polarized light with different wavelengths onto the second nanobrick, and six spatially distinct foci can be formed respectively in the reflection space and the transmission space. Among them, three foci are formed by LCP incident light, and the other three foci are formed by RCP incident light. Eventually, a total of twelve spatially different foci can be formed in the reflection and transmission spaces, that is, on the array composed of the double-layer nanobrick unit structure with variable rotation angles, the measurement of the incident light wavelength and polarization state in the full space is realized.

[0074] In this embodiment, in step 4, different wavelengths respectively correspond to six spatially distinct foci, and the positions of the foci can be represented in polar coordinates as:

[0075]

[0076] Among them, λ n represents the nth working wavelength, t is the radius of the metalens, is the polar angle of the focus.

[0077] In this embodiment, the coordinates (x center,n , y center,n ) of the nth focus in the rectangular coordinate system can be expressed as:

[0078]

[0079] Phase distribution of the metalens at different working wavelengths can be expressed as

[0080]

[0081] where λ is the wavelength of the incident light, x and y are the two-dimensional coordinates of each nanobrick, and f is the focal length of the metalens.

[0082] In this embodiment, in step 4, multiple focusing phases with different wavelengths and corresponding foci at different positions are encoded on one metalens. Then, the phase of the encoded metalens can be expressed as:

[0083]

[0084] where A n 、 are the amplitude and phase at the nth focus and the nth working wavelength, respectively.

[0085] From Figure 2a and Figure 2b it can be seen that in the transmission space, the unit structure exhibits excellent transmission performance at wavelengths of 450 nm, 500 nm, and 550 nm, and the transmittance is greater than 0.6. In the reflection space, the unit structure exhibits high reflectivity at wavelengths of 600 nm, 650 nm, and 700 nm, and the reflectivity is greater than 0.5. This result indicates that whether in the reflection space or the transmission space, the designed unit structure can achieve efficient optical response, thus ensuring the high-efficiency characteristics of the overall device.

[0086] The nano-unit structure of the present invention can generate different phase responses to left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP) respectively. Therefore, an array of metalenses can simultaneously act as a positive lens and a negative lens. Since the probabilities of randomly selecting the structure "0" (not selected) and "1" (selected) are equal, these two structures for controlling RCP and LCP are respectively controlled by random combination. As Figure 3 、 Figure 4a and Figure 4b shown, when circularly polarized light with different wavelengths λ is incident on the lower-layer nano-structure array, six spatially distinct foci can be respectively formed in the reflection space and the transmission space, where three foci are formed by LCP incident light and the other three foci are formed by RCP incident light. Finally, a total of twelve spatially different foci can be formed in the reflection and transmission spaces, that is, on the array composed of double-layer nano-structures with variable rotation angles, the measurement of the incident light wavelength and polarization state in the entire space is realized.

[0087] The present invention can achieve independent manipulation of reflected waves and transmitted waves at multiple wavelengths and form twelve foci with different spatial positions in the transmission and reflection spaces. Based on the distribution of these foci in space, it is possible to measure and analyze the wavelength and polarization state of incident light. This breakthrough in multi-focus control technology has brought unprecedented opportunities to application fields such as spectral analysis and polarization detection technology.

[0088] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A full-space multi-focus metalens based on lateral dispersion, characterized in that: It includes a transparent substrate, a one-dimensional photonic crystal stack and a double-layer nanobrick unit structure, wherein the double-layer nanobrick unit structure includes a first nanobrick and a second nanobrick; a one-dimensional photonic crystal stack and a first nanobrick are sequentially arranged on the transparent substrate, and the second nanobrick is deposited below the transparent substrate, and the two perpendicular sides of the transparent substrate are respectively an x-axis and a y-axis, thereby establishing an xoy coordinate system; The one-dimensional photonic crystal stack is formed by alternating multiple silicon layers and silicon dioxide layers, wherein the thickness of a single silicon layer and a single silicon dioxide layer is D l and D h , the unit structure base period is P; The long sides of the first nanobrick and the second nanobrick are defined as the major axis, which are L1 and L2 respectively, and the short sides are defined as the minor axis, which are W1 and W2 respectively, and the heights are both H; the above structural parameters are all at the sub-wavelength level; the angle between the long axis of the first or second nanobrick and the x-axis is the steering angle of the nanobrick, which ranges from [0 to π]; Both the first nanobrick and the second nanobrick have the characteristics of a half-wave plate.

2. A full-space multi-focus metalens based on lateral dispersion as claimed in claim 1, characterized in that: The materials of the first nanobrick and the second nanobrick are silicon.

3. A full-space multi-focus metalens based on lateral dispersion as claimed in claim 1, characterized in that: The structural parameters L1, L2, W1, and W2 are optimized by electromagnetic simulation to satisfy the half-wave plate characteristics, and then the overall simulation of the metalens is performed to obtain the optical response characteristics.

4. A full-space multi-focus metalens based on lateral dispersion as claimed in claim 1, characterized in that: The first nanobrick and the second nanobrick will have a phase modulation after being passed by light, which is specifically manifested as follows: When the reflection space is considered, when a light beam with a wavelength of λ is incident on the metalens from bottom to top, it will pass through the underlying metasurface and then be reflected back and modulated by the underlying metasurface again; when the transmission space is considered, when the light beam is incident on the metalens, it will pass through the metasurfaces in sequence; the phase distribution of the metalens in the reflection mode is recorded as The phase distribution in transmission mode is recorded as The rotation angle of the second nanobrick is θ1, and the rotation angle of the first nanobrick is θ2. Their phase modulation satisfies the following relationship: Where x and y are the two-dimensional coordinates of each nanobrick, and f is the focal length of the metalens.

5. A design method for a full-space multi-focus metalens based on lateral dispersion, characterized in that: The steps include: Step 1: Calculate the thickness D of the silicon layer and silicon dioxide layer l and D h The thickness D of the silicon layer and silicon dioxide layer of the one-dimensional photonic crystal stack is calculated based on the photonic crystal theory. l and D h ; Step 2: Constructing the nanostructure By optimizing and simulating the double-layer nanobrick unit structure to optimize it into a half-wave plate, the size parameters of the optimized double-layer nanobrick unit structure are obtained, which are the length L1, L2, width W1, W2, height H of the first nanobrick and the second nanobrick, and the unit structure base period P; Step 3: Determine the operating wavelength The whole structure is scanned by electromagnetic simulation software to determine the working wavelengths λ1, λ2, and λ3 in the transmission space; the working wavelengths in the reflection space are λ4, λ5, and λ6. Step 4: Measure and analyze the wavelength and polarization state of the incident light in the entire space When circularly polarized light is incident on the second nanobrick at different wavelengths, six focal points with different spatial positions can be formed in the reflection space and the transmission space respectively, three of which are formed by the LCP incident light and the other three are formed by the RCP incident light. Finally, a total of twelve focal points with different spatial positions can be formed in the reflection and transmission space. That is, on the array composed of the double-layer nanobrick unit structure with variable rotation angle, the measurement of the wavelength and polarization state of the incident light in the whole space can be realized.

6. The design method of a full-space multi-focus metalens based on lateral dispersion as claimed in claim 4, characterized in that: In step 4, different wavelengths correspond to six focal points with different spatial positions, where the positions of the focal points can be expressed in polar coordinates as follows: Among them, λ n represents the nth operating wavelength, r is the radius of the superlens, is the polar angle of the focus.

7. The design method of a full-space multi-focus metalens based on lateral dispersion as claimed in claim 5, characterized in that: The coordinates of the nth focus in the rectangular coordinate system (x center,n ,y center,n ) can be expressed as: Phase distribution of metalens at different working wavelengths It can be expressed as Where λ is the wavelength of the incident light, x and y are the two-dimensional coordinates of each nanobrick, and f is the focal length of the metalens.

8. The design method of a full-space multi-focus metalens based on lateral dispersion as claimed in claim 4, characterized in that: In step 4, multiple focusing phases with different wavelengths and corresponding focal points at different positions are encoded on a metalens, and the phase of the encoded metalens can be expressed as: Among them, A n , are the amplitude and phase at the nth focus and nth operating wavelength respectively.

Images