A three-color wavelength selective focusing superlens and its preparation method

Abstract

This invention relates to a three-color wavelength-selective focusing superlens and its fabrication method. Specifically, it is a method based on continuous-domain quasi-bound metasurface manipulation of optical circular polarization states to achieve multispectral wavefront modulation. This method enables selective focusing of monochromatic / three-color selective wavelength light in the visible light band and provides guidance for applications in augmented reality display systems. The selective manipulation of wavelength focusing with nanometer precision is achieved through metasurface nonlocal mode design. The introduction of continuous-domain quasi-bound states breaks through the frequency domain manipulation scale limit, greatly improving the manipulation scale of the spectral wavefront. It features thinness, high quality factor, and high robustness, and can be applied to the design of optical components in augmented reality display systems. Given the current widespread use of local metasurfaces for thinner AR components, this invention, based on continuous-domain quasi-bound state nonlocal metasurface design, has broad market prospects.

Description

Technical Field

[0001] This invention relates to a three-color wavelength selective focusing superlens and its fabrication method. Specifically, it is a method based on continuous domain quasi-bound metasurface manipulation of optical circular polarization states to achieve multispectral wavefront modulation. This method can achieve selective focusing of monochromatic / three-color selective wavelength light in the visible light band and provides guidance for applications in augmented reality display systems. Background Technology

[0002] Metalenses, also known as metalenses, are two-dimensional planar lens structures composed of an arrangement of dielectric pillar microstructures with subwavelength thickness. Metalenses allow for flexible control of light polarization, phase, and amplitude properties by adjusting parameters such as the shape, rotation direction, and height of the microstructures. Furthermore, metalenses offer advantages such as thinner size, lighter weight, and easier integration, providing a new solution for achieving compact, integrated optical systems.

[0003] In recent years, Augmented Reality (AR) and Virtual Reality (VR) have received increasing attention in both academia and industry. Comfortable wearability of AR / VR display devices is fundamental to their commercial applications, thus placing high demands on device form factor. The key to reducing device size lies in adopting lighter and more compact optical solutions. Planar optical solutions, including diffractive optics and metasurface optics, hold great promise in addressing this challenge. Superlenses, as ultrathin planar optical elements, overcome the bulkiness and limited functionality of refractive and traditional diffractive optical elements, and can be used to replace optical elements in AR / VR display devices, such as polarizers, beam splitters, and optical combiners. Simultaneously, the flexible phase manipulation capabilities of superlenses provide great flexibility for achieving unconventional imaging functions, such as chiral imaging and edge detection.

[0004] However, the following drawbacks of current superlenses still need to be addressed:

[0005] The superlens has limited spectral control capabilities, allowing only wide-bandwidth wavefront shaping. This results in energy loss across the entire wavelength range after the incident light passes through the superlens, leading to low efficiency.

[0006] Due to the chromatic dispersion characteristics of lenses and the properties of materials, it is impossible to realize large-area achromatic metalenses with sizes exceeding millimeters.

[0007] Superlenses can only image with zero field of view, which cannot meet the human eye's requirement of a 124° wide field of view. Summary of the Invention

[0008] The purpose of this invention is to provide a three-color wavelength-selective focusing superlens and its fabrication method, enabling the focusing and imaging of monochromatic / three-color selective wavelength light through continuous-domain quasi-bounded state resonant modulation of white light incident signals across the entire wavelength range supported by a dielectric nanostructure. This superlens produces a wavefront shaping effect only for selected visible light wavelengths, while other wavelengths have no modulation effect.

[0009] The technical solution of the present invention is as follows:

[0010] A three-color wavelength selective focusing superlens comprises several upper dielectric nanostructures, a SiO2 substrate, and several lower dielectric nanostructures; the three colors refer to red, green, and blue.

[0011] The aforementioned upper dielectric nanostructures are arranged at equal intervals on the upper surface of the SiO2 substrate by etching, and satisfy the quasi-bound state physical conditions in the continuous domain at the red light wavelength, which is used to control the red light focusing.

[0012] The aforementioned several lower-layer dielectric nanostructures are arranged at equal intervals on the lower surface of the SiO2 substrate by etching, and satisfy the quasi-bound state physical conditions in the continuous domain at blue and green light wavelengths, which is used to control the focusing of blue and green light.

[0013] The material of the upper dielectric nanostructure is titanium dioxide or gallium nitride. The upper dielectric nanostructure is cuboid in shape, with a length of 160-200 nm, a width of 80-100 nm, and a thickness of 240-300 nm.

[0014] The material of the lower dielectric nanostructure is titanium dioxide or gallium nitride. The shape of the lower dielectric nanostructure is a cuboid with a length of 160-200 nm, a width of 80-100 nm, and a thickness of 240-300 nm.

[0015] The rotation angle θ1(r) of the upper dielectric nanostructure satisfies the following formula:

[0016]

[0017]

[0018] In the above formula, Represents the red light optical phase, r represents the superlens radius, and λ represents the red light optical phase. B θ1 represents the red light wavelength, f represents the focal length, and θ1 represents the rotation angle of the upper medium nanostructure.

[0019] The rotation angle θ2(r) of the lower dielectric nanostructure satisfies the following formula:

[0020]

[0021]

[0022]

[0023] In the above formula, Represents the optical phase of green light. Represents the optical phase of blue light, r represents the radius of the superlens, and λ represents the optical phase of blue light. G Represents the wavelength of green light, λ B θ represents the blue light wavelength, f represents the focal length, and θ2 represents the rotation angle of the underlying nanostructure.

[0024] A method for fabricating a three-color wavelength selective focusing superlens, the method comprising the following steps:

[0025] The first step is to deposit a thin film of titanium dioxide or gallium nitride on the surface of a SiO2 substrate by chemical vapor deposition. Then, a planar pattern of the upper dielectric nanostructure is prepared on the thin film by electron beam etching. Finally, a three-dimensional pattern of the upper dielectric nanostructure is processed by inductively coupled plasma etching (ICP).

[0026] The second step involves depositing a thin film of titanium dioxide or gallium nitride on the lower surface of a SiO2 substrate using chemical vapor deposition. Then, a planar pattern of the underlying dielectric nanostructure is prepared on the thin film using electron beam etching. Finally, a three-dimensional pattern of the underlying dielectric nanostructure is fabricated using inductively coupled plasma etching (ICP) to obtain a three-color wavelength selective focusing superlens.

[0027] Beneficial effects

[0028] (1) The superlens of the present invention is used to achieve focused imaging of light of a set wavelength color;

[0029] (2) The superlens of the present invention only produces a wavefront shaping effect on visible light with a selected resonant wavelength, while other wavelengths have no modulation effect. In this scalable nonlocal superlens design, by designing a single-layer nonlocal surface, the wavefront can be modulated by satisfying the quasi-bound state physical conditions in the continuous domain at different wavelengths, and the wavefront shape remains unchanged even when the quasi-bound state physical conditions in the continuous domain are not satisfied.

[0030] (3) By superimposing the wavefront shaping effects of multiple nonlocal metasurfaces, this invention can achieve different functions at multiple design wavelengths, such as multifunctional beam guiding and orbital angular momentum manipulation. Traditional photonic devices rarely provide fine spatial control and sharp spectral control over the incident wavefront. In the tri-color wavelength-selective focusing superlens design presented in this invention, a single basic unit supports high-quality monochromatic / tri-color continuous-domain quasi-bound state resonance modes;

[0031] (4) The device proposed in this invention achieves spatial dimension and spectral control of light by modulating quasi-bound states in a continuous domain, and realizes monochromatic / tricolor selective wavelength resonance of the focused light of the superlens without affecting the resonance frequency. This phase encoding method for spatial variations in the continuous domain can realize multispectral wavefront shaping and independent control of multiple quasi-bound states in the continuous domain.

[0032] (5) The visible light band tri-color wavelength selective focusing superlens proposed in this invention can serve as an alternative to optical elements in augmented reality systems. Using our designed tri-color wavelength selective focusing superlens, display information can be projected onto the observer's eye at selected tri-color selective wavelengths, while allowing an unobstructed wide field of view of the real world. This design allows the non-local superlens to display contextual information covering the entire eyepiece and providing a wide field of view, without requiring additional polarizers or beam splitters to attenuate real-world light.

[0033] (6) This invention is the first to realize a monochromatic / tricolor selective wavelength lens for the visible light band based on a continuous-domain quasi-bound metasurface, and applies it to a visible light augmented reality system. By utilizing the nonlocal mode design of the metasurface, the selective control of the superlens' nano-precision wavelength focusing is achieved. The introduction of continuous-domain quasi-bound states breaks through the limit of frequency domain manipulation scale, greatly improving the manipulation scale of the spectral wavefront. It features thinness, high quality factor, and high robustness, and can be applied to the design of optical components in augmented reality display systems. Given the current widespread use of local metasurfaces to achieve thinner AR components, this invention's nonlocal metasurface design based on continuous-domain quasi-bound states has broad market prospects.

[0034] (7) This invention designs a visible light band monochromatic / tricolor selective wavelength superlens based on a continuous-domain quasi-bound metasurface. This superlens can focus light at a selected monochromatic / tricolor design wavelength while allowing light from other bands to pass through normally, thus avoiding energy loss across the entire wavelength range and improving energy utilization. This makes it possible to fabricate this type of superlens over large areas. Furthermore, this superlens projects the display information carried by the tricolor selective wavelengths onto the observer's eye, while allowing unobstructed wide-range viewing angles of the real world, thus expanding the display field of view. In summary, the tricolor wavelength selective focusing superlens we proposed can be widely used in AR / VR display devices. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the planar structure of the red, green and blue selective wavelength superlens in the visible light band of the present invention;

[0036] Figure 2 This is a schematic diagram of a planar structure of a monochromatic selective wavelength superlens in the visible light band, according to a specific embodiment of the present invention.

[0037] Figure 3 This is a schematic diagram of a visible light band three-color selective wavelength superlens micro / nano structure unit according to a specific embodiment of the present invention;

[0038] Figure 4 This is a diagram showing the Pancharatnam-Berry Phase-nanostructure rotation relationship of a continuous-domain quasi-bound state selective wavelength superlens in a specific embodiment of the present invention.

[0039] Figure 5 The polarization conversion rate spectra of monochromatic and bichromatic selective wavelength continuous domain quasi-bound state superlenses in specific embodiments of the present invention are shown.

[0040] Figure 6 The polarization conversion rate spectrum of the three-color continuous domain quasi-bound state selective wavelength superlens in a specific embodiment of the present invention;

[0041] Figure 7 This is the focusing optical field of a monochromatic selective wavelength continuous domain quasi-bound state selective wavelength superlens in a specific embodiment of the present invention;

[0042] Figure 8 This is the focusing light field of the dual-color selective wavelength continuous domain quasi-bound state selective wavelength superlens in a specific embodiment of the present invention;

[0043] Figure 9 This is the focusing light field of the three-color selective wavelength continuous domain quasi-bound state selective wavelength superlens in a specific embodiment of the present invention;

[0044] Figure 10 This is a normalized light intensity distribution at the focusing peak of a three-color selective wavelength continuous domain quasi-bound state selective wavelength superlens in a specific embodiment of the present invention. Detailed Implementation

[0045] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0046] The design of visible-light band monochromatic / tricolor selective wavelength superlenses based on continuous-domain quasi-bound metasurfaces is achieved through micro / nano structure design and fabrication. In this embodiment, the sample structure of the visible-light band tricolor selective wavelength superlens is as follows: Figure 1 As shown: The sample includes a dielectric nanostructure 1, a SiO2 substrate 2, and a dielectric nanostructure 3, wherein dielectric nanostructures 1 and 3 are located on the upper and lower surfaces of the SiO2 substrate, respectively. The visible light band monochromatic selective wavelength superlens sample structure is shown below. Figure 2 As shown: It includes a dielectric nanostructure and a SiO2 substrate, wherein the dielectric nanostructure is located on the upper surface of the SiO2 substrate.

[0047] The rotation angle θ1(r) of the dielectric nanostructure 1 satisfies the following formula:

[0048]

[0049]

[0050] In the above formula, Represents the red light optical phase, r represents the superlens radius, and λ represents the red light optical phase. B θ1 represents the red light wavelength, f represents the focal length, and θ1 represents the rotation angle of the upper medium nanostructure.

[0051] The rotation angle θ2(r) of the dielectric nanostructure 2 satisfies the following formula:

[0052]

[0053]

[0054]

[0055] In the above formula, Represents the optical phase of green light. Represents the optical phase of blue light, r represents the radius of the superlens, and λ represents the optical phase of blue light. G Represents the wavelength of green light, λ B θ2 represents the blue light wavelength, f represents the focal length, and θ2 represents the rotation angle of the underlying nanostructure. Because the lens dispersion is continuous, simultaneous focusing of two wavelengths can be achieved by controlling only a single wavelength.

[0056] The following describes a method for preparing experimental samples for visible-band monochromatic / tricolor selective wavelength superlenses based on continuous-domain quasi-bound metasurfaces, including the following steps:

[0057] Step 1: Use an organic solvent to ultrasonically clean the SiO2 substrate, following the sequence of ethanol (cleaning time 10-15 min) → deionized water (cleaning time 10-20 min). Finally, use a nitrogen gun to blow away the remaining deionized water on the substrate to obtain a clean SiO2 substrate.

[0058] Step 2: 240 / 270 / 300 nm TiO2 was deposited onto the SiO2 substrate obtained in the previous step using chemical vapor deposition (CVD) on a molten silicon dioxide wafer. After cooling, PMMA A4 adhesive (2000 rad / s, 45 s) was spin-coated onto the upper surface, and the wafer was dried at 180 °C for 2 min. The designed structural shapes were then patterned using an electron beam etching (EBL) system. After exposure, the anti-charge layer was removed by rinsing with deionized water, and the device was developed in a cooled 3:1 isopropanol deionized water solution for 2 minutes, followed by rinsing with deionized water for 30 seconds. These devices were etched in a fluorine-based inductively coupled plasma etcher. The dielectric nanostructures 1 and 3 were finally obtained by immersing the wafer in N-methyl-2-pyrrolidone at 80 °C for 5 hours to remove the PMMA etching mask.

[0059] The following is the measurement procedure for the focusing efficiency of the visible light band monochromatic / tricolor selective wavelength superlens based on the continuous domain quasi-bound metasurface: In this invention, the test of the visible light band monochromatic / tricolor selective wavelength superlens based on the continuous domain quasi-bound metasurface is carried out in the superlens imaging optical path. After the visible light supercontinuum laser is emitted, it is refracted by the optical aperture and the semi-transparent and semi-reflective mirror, and then passed through a 20X objective lens and the designed superlens. The power of the beam before and after passing through the superlens is measured by a power meter to obtain the focusing efficiency.

[0060] Example 1

[0061] A monochromatic / tricolor lens for the visible light band on a nonlocal single-crystal substrate was designed and numerically demonstrated, producing wavefront shaping effects only for selected visible light wavelengths. The design required realizing the function of a superstructure array unit lens operating at red, green, and blue wavelengths. This metasurface was etched into a TiO2 thin film covered with a SiO2 antireflective layer via rectangular holes. The tricolor-selective wavelength transmission medium nanostructure array mode was calculated using finite-difference time-domain simulation and an incoherent transfer matrix method (see...). Figure 1 ) and monochromatic selective wavelength transmission medium nanostructure array mode (see Figure 2 The morphology of a single structural unit is shown in [reference needed]. Figure 3 .

[0062] Two bilayer dielectric nanostructure samples were prepared following the steps described above. The first sample is a rectangular dielectric nanostructure 1 with a length of 165 nm, a width of 50 nm, and a height of 250 nm (from bottom to top); the second sample is a 300 nm thick SiO2 substrate; and the third sample is a rectangular dielectric nanostructure 3 with a length of 170 nm, a width of 80 nm, and a height of 240 nm (see...). Figure 1 ); A 300 nm thick SiO2 substrate 1 from bottom to top, and a rectangular dielectric nanostructure 2 with a length of 170 nm, a width of 80 nm, and a height of 240 nm (see Figure 2The superlens sample employs the Pancharatnam-Berry Phase design method. Based on the correspondence between the rotation angle of the rectangular nanostructure and the Berry phase, the full-phase modulation of the superlens in the 0-2p range is achieved through the rotation angle design of the nanostructure (see...). Figure 4 The numerical simulation results of its circularly polarized light conversion efficiency (see...) Figure 5 The results show that, for the upper surface structure, the transmissivity of the red band around the spectral peak of 648 nm is close, achieving the highest circular polarization conversion efficiency and realizing focused imaging at a single wavelength. For the lower surface structure, selective wavelength focusing of green and blue light is achieved, with spectral peaks at 522 nm and 470 nm, respectively. Corresponding structure arrays were micro- or nano-fabricated on the upper and lower surfaces of the SiO2 substrate, respectively, enabling focused imaging of red, green, and blue colors at selective wavelengths (see...). Figure 6 ).

[0063] The designed continuous-domain quasi-bound state visible light band three-color selective wavelength superlens focuses the light field on its upper surface (see...). Figure 7 The results show that for the red light band, the lens exhibits a significant focusing effect near the wavelength peak of 648 nm, while no significant focusing phenomenon is observed at non-selective wavelengths such as 640 nm and 660 nm. The focused light field on the lower surface of the designed continuous-domain quasi-bound state visible light band three-color selective wavelength superlens is shown in [reference needed]. Figure 8 The results show that for the blue and green light bands, there are significant focusing effects near the wavelength peaks of 470nm and 522nm, respectively, while no significant focusing phenomenon is observed at non-selective wavelengths such as 440nm and 560nm. The focused light field of the integrated superlens (see...) Figure 9 The results show that, within the visible light region of 400-700 nm, the designed superlens exhibits significant focusing effects only at selected wavelengths of 470 nm, 530 nm, and 650 nm in the blue, green, and red bands, respectively. The interaction between the two superlens layers on the upper and lower surfaces leads to a slight shift in the peak wavelengths of green and red light. The normalized intensity distribution corresponding to the peak values ​​of the three color characteristics shows that the energy is concentrated in the central region (see...). Figure 10 With a radius narrower than 1mm and a focal shift within 2mm, it achieves good focusing imaging effect for three colors.

[0064] This invention presents, for the first time, a visible-light band monochromatic / tricolor selective wavelength superlens based on a continuous-domain quasi-bound state metasurface, and numerical simulations demonstrate a metasurface optical device with a nonlocal wavefront. This nonlocal metasurface device allows independent control of the resonant wavelength (through structural unit geometry), quality factor (through perturbation intensity), and wavefront (through the spatial distribution of geometric phase) at multiple wavelengths (through cascaded surfaces and adding independent perturbations to individual surfaces). It also leverages its high-quality factor monochromatic / tricolor selective wavelength advantage to achieve wavefront shaping for light-matter interactions. This concept of wavefront shaping based on a continuous-domain quasi-bound state metasurface is also applicable to waveguide integrated surfaces, and has broad application prospects in the future augmented reality display technology field. This invention provides a nanoscale, highly sensitive, and robust design method for visible-light band monochromatic / tricolor selective wavelength superlenses based on a continuous-domain quasi-bound state metasurface, applicable not only to rectangular nanostructures but also to other types of dielectric metasurfaces. With the rapid development of optoelectronic information devices and micro-nano photonic devices in the modern universe, the demand for design solutions for lightweight and high-performance optoelectronic devices is becoming increasingly strong. This invention has a strong supporting impetus and reference value for their future development.

[0065] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. Those skilled in the art should understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.

Claims

1. A three-color wavelength selective focusing superlens, characterized in that: This focusing superlens comprises several upper dielectric nanostructures, a SiO2 substrate, and several lower dielectric nanostructures; the three colors refer to red, green, and blue. The aforementioned upper dielectric nanostructures are arranged at equal intervals on the upper surface of the SiO2 substrate by etching, and satisfy the quasi-bound state physical conditions in the continuous domain at a wavelength of 650 nm, which is used to control the focusing of red light at 650 nm. The aforementioned lower dielectric nanostructures are arranged at equal intervals on the lower surface of the SiO2 substrate by etching, and satisfy the quasi-bound state physical conditions in the continuous domain at wavelengths of 470 nm and 530 nm, which are used to control the focusing of blue light at 470 nm and green light at 530 nm. The material of the upper dielectric nanostructure is titanium dioxide or gallium nitride. The material of the lower dielectric nanostructure is titanium dioxide or gallium nitride. The upper medium nanostructure is in the shape of a cuboid, with a length of 170 nm, a width of 80 nm, and a thickness of 240 nm; The lower medium nanostructure is rectangular in shape, with a length of 165 nm, a width of 50 nm, and a thickness of 250 nm.

2. The tricolor wavelength selective focusing superlens according to claim 1, characterized in that: The rotation angle of the upper dielectric nanostructure Satisfy the following formula: in, Represents 650 nm optical phase. r Represents the radius of the superlens. Represents a wavelength of 650 nm. f Represents focal length. This represents the rotation angle of the upper dielectric nanostructure; The corner of the lower dielectric nanostructure Satisfy the following formula: in, Represents the optical phase at a wavelength of 530 nm. r Represents the radius of the superlens. Represents a wavelength of 530 nm. f Represents focal length. This represents the rotation angle of the underlying medium nanostructure.

3. A method for preparing a tricolor wavelength selective focusing superlens as described in claim 1, characterized in that... The steps of this method include: The first step is to deposit a thin film of titanium dioxide or gallium nitride on the surface of the SiO2 substrate. Then, the planar shape pattern of the upper dielectric nanostructure is prepared on the thin film by electron beam etching. Finally, the three-dimensional pattern of the upper dielectric nanostructure is processed by inductively coupled plasma etching. The second step involves depositing a thin film of titanium dioxide or gallium nitride on the lower surface of a SiO2 substrate. Then, a planar pattern of the underlying dielectric nanostructure is prepared on the thin film by electron beam etching. Finally, a three-dimensional pattern of the underlying dielectric nanostructure is processed by inductively coupled plasma etching to obtain a three-color wavelength selective focusing superlens.

4. The method for preparing a three-color wavelength selective focusing superlens according to claim 3, characterized in that: A thin film of titanium dioxide or gallium nitride is deposited on the upper or lower surface of a SiO2 substrate by chemical vapor deposition.

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