Telescope system based on metasurface

Abstract

The invention provides a telescopic system based on metasurfaces, which comprises a telescopic module formed by an objective lens unit and an eyepiece unit, the objective lens unit and the eyepiece unit are both formed by metasurfaces, and the metasurfaces of the objective lens unit and the eyepiece unit are arranged oppositely. In the telescope system based on the metasurface, the objective lens and the eyepiece designed based on the metasurface are small in size and micron in diameter, integration is facilitated, and in addition, the two functions of a Kepler telescope and a Galileo telescope can be achieved through one set of metasurface telescope structure. The method has important application value in the fields of aerospace earth observation, unmanned aerial vehicle-mounted miniaturized optical systems, guided missile guiding optical systems, medical in-vivo miniaturized imaging equipment and the like.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano optical technology, and in particular relates to a telescope system based on a metasurface. Background Art

[0002] At present, the design direction of telescope systems is mainly focused on using larger apertures to achieve higher imaging quality, which directly leads to increasingly complex optical systems and mechanical structures of telescopes, increasing costs, and brings many difficulties in assembly and mirror processing. In order to improve image quality and reduce system aberrations, aspheric mirrors have been widely used in telescope systems. For example, the primary and secondary mirrors of RC telescope systems are both hyperbolic mirrors, which can effectively eliminate spherical aberration and coma. However, compared with spherical mirrors, aspheric mirrors are more difficult to process and detect.

[0003] In addition, traditional telescope systems include Kepler telescopes, Galileo telescopes, Newtonian telescopes, and Cassegrain telescopes, etc. Their objective lenses and eyepieces have fixed performance and can only realize specific single systems. In addition, the mirror materials used in traditional telescopes are almost limited to glass, quartz, silicon carbide, etc., which limits the application value of telescope systems in miniaturized micro-nano devices, and at the same time limits the development of telescopes in the field of multifunctional devices and modern integrated optics. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a telescope system based on a metasurface to solve the problems of traditional telescope systems such as single function, large size and difficult integration.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A telescopic system based on a metasurface comprises a telescopic module consisting of an objective lens unit and an eyepiece lens unit, wherein both the objective lens unit and the eyepiece lens unit are formed of a metasurface, and the metasurfaces of the objective lens unit and the eyepiece lens unit are arranged opposite to each other.

[0007] Further:

[0008] The objective lens unit is an isotropic metasurface that satisfies the phase distribution of the focusing lens;

[0009] The eyepiece unit is an anisotropic metasurface, which presents the phase distribution of a focusing lens and the phase distribution of a diverging lens respectively when circularly polarized light of different rotation directions is incident;

[0010] The distance between the objective lens unit and the eyepiece unit is adjustable.

[0011] Further: the telescopic module has the following working modes:

[0012] Keplerian telescope mode: The distance between the objective lens unit and the eyepiece unit is the sum of their focal lengths, and the metasurface of the eyepiece unit presents the phase distribution of a focusing lens;

[0013] Galilean telescope mode: The distance between the objective lens unit and the eyepiece unit is the difference between their focal lengths, and the metasurface of the eyepiece unit presents the phase distribution of a divergent lens.

[0014] Furthermore: the substrate of the super surface in the objective lens unit and the eyepiece unit is ITO conductive glass, and the nanocolumns are made of titanium dioxide.

[0015] Furthermore: in the objective lens unit: a nanocolumn array is provided in a circular area on the surface of one side of the substrate, and the nanocolumns are periodically arranged in a square lattice. The period of the unit structure is 0.3μm. The nanocolumns are cylindrical structures with a height of 0.76μm and a radius of 50 to 110nm. Phase modulation is achieved by changing the radius of the nanocolumns.

[0016] Furthermore: in the eyepiece unit: a nanocolumn array is provided in a circular area on the surface of one side of the substrate, and the nanocolumns are periodically arranged in a square lattice. The period of the unit structure is 0.36μm. The nanocolumns are rectangular structures with a height of 0.76μm, a length of 0.26μm, and a width of 0.09μm. Phase modulation is achieved by changing the azimuth angle of the nanocolumns.

[0017] Furthermore: the telephoto module is provided with a distance adjustment mechanism to adjust the distance between the objective lens unit and the eyepiece unit.

[0018] Further: Also including:

[0019] Illumination module: used to generate circularly polarized light to illuminate the observed object;

[0020] Imaging module: used to capture the imaging results from the telephoto module.

[0021] Furthermore: the illumination module includes an illumination unit, a linear polarizer, and a quarter wave plate, wherein the light beam emitted by the illumination unit is converted into circularly polarized light via the linear polarizer and the quarter wave plate in sequence; the relative angle position between the linear polarizer and the quarter wave plate is adjustable, and the adjustment range includes the position where the fast axes of the two are 45° and -45°.

[0022] Furthermore: the imaging module includes a collecting lens, a lens unit, and an imaging unit, wherein the light beam from the telescope module is transmitted to the imaging unit after passing through the collecting lens and the lens unit in sequence; the imaging unit is a CCD camera.

[0023] The beneficial effects of the present invention are:

[0024] (1) The present invention provides a telescope system based on a metasurface, which adopts isotropic and anisotropic titanium dioxide medium metasurfaces to replace traditional lens materials, and designs a metasurface objective lens with polarization independence and a metasurface eyepiece with polarization sensitivity. The system has a very small size, with a diameter of micrometer level, which is conducive to integration and provides a technical basis for integration with other equipment. Therefore, it has important application value in the fields of aerospace earth observation, unmanned aerial vehicle miniaturized optical systems, missile guidance optical systems, and medical in vivo miniaturized imaging equipment.

[0025] (2) The telescope system based on the metasurface of the present invention is composed of only two planar metasurfaces, and no additional lens group is required, so the structure is simple and reliable. On this basis, by adjusting the distance between the objective lens unit and the eyepiece unit, and using circularly polarized light of different rotation directions, the functions of the Keplerian telescope and the Galilean telescope can be realized with a set of metasurface telescope structures, thereby enhancing the functionality of the same telescope system hardware device.

[0026] (3) The present invention uses titanium dioxide as the metasurface functional unit material, which has a refractive index of 2.58 at a wavelength of 633nm and a loss of almost 0, and can ensure sufficient light transmittance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a structural diagram of a telescopic system according to an embodiment of the present application;

[0028] Figure 2 This is a schematic diagram of a telescope module in the telescopic system of the present invention;

[0029] Figure 3 The structure diagram of the metasurface unit in the embodiment of the present application, wherein (a) is the objective lens unit, and (b) is the eyepiece lens unit;

[0030] Figure 4 is the relationship between the size of the isotropic metasurface nanopillars and the phase and transmittance of the transmitted light;

[0031] Figure 5 This is the relationship between the size and transmittance of the anisotropic metasurface nanopillars;

[0032] Figure 6 This is a focusing effect diagram of the objective lens unit of the embodiment of the present application;

[0033] Figure 7 This is a focusing effect diagram of the eyepiece unit of the embodiment of the present application under LCP incidence;

[0034] Figure 8 Phase distribution diagram of the eyepiece unit under LCP and RCP incidence respectively according to the embodiment of the present application.

[0035] Reference numerals:

[0036] 1-illumination unit; 2-linear polarizer; 3-quarter wave plate; 4-observation object;

[0037] 31-objective lens unit; 32-eyepiece unit; 5-collecting objective lens; 6-lens unit;

[0038] 7-imaging unit; 100-substrate; 200-objective lens nanocolumn; 300-eyepiece nanocolumn. DETAILED DESCRIPTION

[0039] Embodiments of the present invention are described in detail below, examples of the illustrated embodiments 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.

[0040] like Figure 1 and Figure 2 The telescope system shown in the figure has a core composed of a telescope module consisting of an objective lens unit 31 and an eyepiece lens unit 32. Both the objective lens unit 31 and the eyepiece lens unit 32 are composed of a metasurface, wherein:

[0041] 1. Objective lens unit

[0042] like Figure 3 As shown in (a), the metasurface constituting the objective lens unit 31 includes: a substrate 100 and an objective lens nanocolumn 200. In this embodiment, the substrate 100 is made of ITO (indium tin oxide) conductive glass. An array of objective lens nanocolumns 200 is arranged in a circular area on one side of the substrate 100, and each objective lens nanocolumn 200 is periodically arranged in a square lattice, and the period P1 of the unit structure is 0.3 μm.

[0043] The metasurface constituting the objective lens unit 31 is an isotropic metasurface, wherein the objective lens nanocolumn 200 is a cylindrical structure made of titanium dioxide, and each objective lens nanocolumn 200 has the same height and different radius. By changing the radius of each objective lens nanocolumn 200, a phase modulation of 0 to 2π is achieved. The entire objective lens unit 31 metasurface satisfies the phase distribution of the focusing lens:

[0044]

[0045] Wherein, (x, y) is the coordinate position of the nanorod in the array, λ is the wavelength of the incident light, and f1 is the focal length of the focusing lens, that is, the focal length of the objective lens unit 31 .

[0046] This embodiment uses the finite time-domain difference (FDTD) method to calculate the influence of the radius and height change of the cylindrical nanorod on the phase and transmittance of the output light. The results are as follows: Figure 4As shown, (a) and (b) are the radius of the nanocolumn on the horizontal axis, the height of the nanocolumn on the vertical axis, (a) and (c) are the effects on the phase, and (b) and (d) are the effects on the transmittance. In order to obtain full phase modulation of 0 to 2π and ensure uniform and high transmittance. Finally, this embodiment sets the height h1 of the objective lens nanocolumn 200 to 0.76μm and the radius r to 50 to 110nm. The radius of each objective lens nanocolumn 200 is determined according to the phase distribution formula of the focusing lens and the corresponding relationship between the radius and the phase.

[0047] 2. Eyepiece unit

[0048] like Figure 3 As shown in (b), the metasurface constituting the eyepiece unit 32 includes: a substrate 100 and an eyepiece nanocolumn 300. An array of eyepiece nanocolumns 300 is arranged in a circular area on one side of the substrate 100, and each eyepiece nanocolumn 300 is periodically arranged in a square lattice, and the period P2 of the unit structure is 0.36 μm.

[0049] The metasurface constituting the eyepiece unit 32 is an anisotropic metasurface, wherein the eyepiece nanocolumns 300 are rectangular structures and made of titanium dioxide. Phase modulation of 0 to 2π is achieved by changing the azimuth angle of each eyepiece nanocolumn 300. The phase distribution introduced by the rectangular nanocolumns is polarization sensitive, so the phase distribution of the entire eyepiece unit 31 metasurface changes with the switching of the rotation direction of the circularly polarized light; wherein the phase distribution of the circularly polarized light of a certain rotation direction is shown as satisfying the phase distribution of the focusing lens, and the phase distribution of the circularly polarized light of another rotation direction is shown as satisfying the phase distribution of the divergent lens.

[0050] Specifically in this embodiment:

[0051] 1) When the incident light is LCP (left-handed circularly polarized light), the eyepiece unit 31 is a focusing lens, and the corresponding phase distribution is:

[0052]

[0053] 2) When the incident light is RCP (right-hand circularly polarized light), the eyepiece unit 31 is a diverging lens, and the corresponding phase distribution is:

[0054]

[0055] Where (x, y) is the coordinate position of the nanorod in the array, λ is the wavelength of the incident light, and f2 is the focal length.

[0056] The relationship between the azimuth angle and phase of the cuboid nanorod is:

[0057]

[0058] The azimuth angle of each eyepiece nanorod 300 is set according to the above phase distribution formula and the relationship between the azimuth angle and the phase.

[0059] In this embodiment, COMSOL Multiphysics software is used to calculate the relationship between the length and width of the nanorods and the transmittance of the emitted light. The results are as follows: Figure 5 As shown, the height h2 of the nanocolumn is set to 0.76 μm. Taking into account the processing feasibility and transmittance, in this embodiment, the length l and width w of the eyepiece nanocolumn 300 are set to 0.26 μm and 0.09 μm respectively, corresponding to Figure 5 The transmittance of the circle in the middle is 96%.

[0060] 3. Telescope module

[0061] In this embodiment, the radius of the objective lens unit 31 determined by the above-mentioned material size parameters is 20 μm, and the focal length f1 is 70 μm; the radius of the eyepiece unit 32 is 7 μm, and the focal length f2 is 14 μm.

[0062] This embodiment uses FDTD software to simulate the focusing effect of the objective lens unit 31 and the eyepiece unit 32. Figure 6 The figure shows the focusing effect of the objective lens unit 31, which shows that the parallel light beam can be converged at a specified focal position. (a) is the focusing effect under the xy coordinate, and (b) is the focusing effect under the xz coordinate. Figure 7 The figure shows the focusing effect of the eyepiece unit 32 when the LCP light is incident. Figure 8 Shown are the focusing phase and divergence phase presented by the eyepiece unit 32 under LCP and RCP incidence respectively.

[0063] like Figure 2 As shown, when forming a telescope module, the super surfaces (the side with the nano-pillar functional structure) of the objective lens unit 31 and the eyepiece lens unit 32 are arranged opposite to each other, and the structural centers of the two are coaxial, wherein the objective lens unit 31 is located on the side close to the observed object. When in use:

[0064] 1) Under the incident light of LCP, the distance D1 between the objective lens unit 31 and the eyepiece lens unit 32 is adjusted to the sum of their focal lengths D1 = f1 + f2. At this time, the telescope module works in the Kepler telescope mode.

[0065] 2) Under the incident RCP light, the distance D2 between the objective lens unit 31 and the eyepiece lens unit 32 is adjusted to the sum of their focal lengths D2 = f1 - f2. At this time, the telescope module works in the Galilean telescope mode.

[0066] Therefore, by adjusting the distance between the objective lens unit 31 and the eyepiece unit 32 and working under circularly polarized light of different rotation directions, two telescope modes, namely the Keplerian telescope and the Galilean telescope, can be realized, thereby increasing the functionality of the telescope module.

[0067] 4. Telescope system

[0068] like Figure 1 As shown, this embodiment provides a telescopic system to realize the imaging function based on the telescope module in practice. It includes an illumination module, the telescopic module, and an imaging module. Among them:

[0069] Illumination module: used to generate circularly polarized light (LCP or RCP) to illuminate the object. Specifically, it includes illumination unit 1, linear polarizer 2, and quarter wave plate 3. The conventional light beam emitted by illumination unit 1 is converted into linear polarized light by linear polarizer 2, and then the linear polarized light is converted into circular polarized light by quarter wave plate 3; when the fast axes of quarter wave plate 3 and linear polarizer 2 are 45°, LCP is output; when the fast axes of the two are -45°, RCP is output.

[0070] In this embodiment, the illumination module irradiates from behind the observation object 4, and the circularly polarized light is transmitted through the observation object 4 and enters the telescope module, and the telescope module then transmits the processed light beam to the imaging module.

[0071] The telephoto module is provided with a distance adjustment mechanism for adjusting the distance between the objective lens unit 31 and the eyepiece unit 32 to change the working mode of the telephoto module.

[0072] Imaging module: used to collect the light beam from the telephoto module and output the imaging result. Specifically includes a collecting lens 5, a lens unit 6, and an imaging unit 7. The collecting lens 5 and the lens unit 6 can be conventional optical lenses, which are used to receive the light beam from the telephoto module and amplify it and transmit it to the imaging unit 7; the imaging unit 7 can be a CCD camera, which is used to capture the imaging result.

[0073] In the description of the present invention, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying 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 should not be understood as a limitation on the present invention.

[0074] The present invention is not limited to the above-mentioned embodiments. Any obvious improvement, substitution or deformation that can be made by those skilled in the art without departing from the essential content of the present invention belongs to the protection scope of the present invention.

Claims

1. A telescope system based on a metasurface, characterized in that: The invention comprises a telescopic module composed of an objective lens unit (31) and an eyepiece lens unit (32), wherein the objective lens unit (31) and the eyepiece lens unit (32) are both composed of a super surface, and the super surfaces of the objective lens unit (31) and the eyepiece lens unit (32) are arranged relative to each other.

2. The telescopic system based on a metasurface according to claim 1, characterized in that: The objective lens unit (31) is an isotropic metasurface that satisfies the phase distribution of the focusing lens; The eyepiece unit (32) is an anisotropic metasurface, which presents a phase distribution of a focusing lens and a phase distribution of a diverging lens respectively when circularly polarized light of different rotation directions is incident; The distance between the objective lens unit (31) and the eyepiece lens unit (32) is adjustable.

3. The telescopic system based on a metasurface according to claim 2, characterized in that: The telescope module has the following working modes: Keplerian telescope mode: the distance between the objective lens unit (31) and the eyepiece unit (32) is the sum of their focal lengths, and the metasurface of the eyepiece unit (32) presents a phase distribution of a focusing lens; Galileo telescope mode: the distance between the objective lens unit (31) and the eyepiece unit (32) is the difference between their focal lengths, and the metasurface of the eyepiece unit (32) presents a phase distribution of a divergent lens.

4. The telescopic system based on a metasurface according to claim 1, characterized in that: The substrate of the super surface in the objective lens unit (31) and the eyepiece unit (32) is ITO conductive glass, and the nanocolumns are made of titanium dioxide.

5. The telescopic system based on a metasurface according to claim 1, characterized in that: In the objective lens unit (31), a nanocolumn array is provided in a circular area on the surface of one side of the substrate, and the nanocolumns are periodically arranged in a square lattice. The period of the unit structure is 0.3 μm. The nanocolumns are cylindrical structures with a height of 0.76 μm and a radius of 50 to 110 nm. Phase modulation is achieved by changing the radius of the nanocolumns.

6. The telescopic system based on a metasurface according to claim 1, characterized in that: In the eyepiece unit (32), a nanocolumn array is provided in a circular area on the surface of one side of the substrate, and the nanocolumns are periodically arranged in a square lattice. The period of the unit structure is 0.36 μm. The nanocolumns are rectangular parallelepiped structures with a height of 0.76 μm, a length of 0.26 μm, and a width of 0.09 μm. Phase modulation is achieved by changing the azimuth angle of the nanocolumns.

7. The telescopic system based on a metasurface according to claim 3, characterized in that: The telephoto module is provided with a spacing adjustment mechanism for adjusting the spacing between the objective lens unit (31) and the eyepiece unit (32).

8. The telescopic system based on a metasurface according to claim 3, characterized in that: Also includes: Illumination module: used to generate circularly polarized light to illuminate the observed object; Imaging module: used to capture the imaging results from the telephoto module.

9. The telescopic system based on a metasurface according to claim 8, characterized in that: The illumination module comprises an illumination unit (1), a linear polarizer (2), and a quarter wave plate (3), wherein the light beam emitted by the illumination unit (1) is converted into circularly polarized light via the linear polarizer (2) and the quarter wave plate (3) in sequence; the relative angle position between the linear polarizer (2) and the quarter wave plate (3) is adjustable, and the adjustment range includes a position where the fast axes of the two are 45° and a position where -45°.

10. The telescopic system based on a metasurface according to claim 8, characterized in that: The imaging module comprises a collecting objective lens (5), a lens unit (6), and an imaging unit (7), wherein a light beam from the telephoto module is sequentially transmitted through the collecting objective lens (5) and the lens unit (6) to the imaging unit (7); the imaging unit (7) is a CCD camera.

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