Optical metasurface filter for tunable edge orientation enhancement and working method

Abstract

According to the optical metasurface filter and method for tunable edge directional enhancement, the angle of the metasurface can be rotated in a simple mechanical tuning mode, tuning of the edge enhancement direction of an amplitude or phase sample is achieved, edge filtering in different directions is achieved in an efficient and compact mode, and the optical metasurface filter and method have the advantage of chip-level ultrafast optical calculation. The invention discloses a polarization-sensitive vertical edge detection filter which is constructed by a metasurface and an optical 4F system. The metasurface (10) comprises an amorphous silicon cuboid nano brick unit (1) and a silicon dioxide substrate (2), each amorphous silicon cuboid nano brick unit has a fixed square lattice constant Px = Py = 300nm, a height H = 365nm and designed L = 129nm and W = 90nm, and the amorphous silicon cuboid nano brick units are periodically arranged on the silicon dioxide substrate; the phase is changed by changing the orientation angle theta of the amorphous silicon cuboid nano brick unit, and required phase distribution is completed.

Description

Technical Field

[0001] The present invention relates to the technical field of optics, and in particular to an optical metasurface filter for tunable edge-directional enhancement, and a working method of the optical metasurface filter for tunable edge-directional enhancement. Background Art

[0002] Fast and reliable directional edge imaging technology has potential application prospects in artificial intelligence, machine vision, biomedical image recognition and other fields. Edge detection is usually achieved through digital signal calculations by computers. However, they consume a lot of energy and time. In recent years, optical simulation computing has provided new opportunities for fast and reliable image edge information processing with its advantages of strong parallel processing capabilities, fast computing speed, low energy consumption or even close to zero. To this end, many image edge detection methods and filters based on optical computing have been gradually realized, but the current filter functions are relatively single and most of them cannot be applied to some situations where only edges in a certain direction are required.

[0003] With the in-depth study of radial Hilbert transform, two new directional edge detection methods have been verified based on classical imaging technology: the sine function method and the spiral phase superposition method. Among them, the spiral phase superposition method mainly controls the edge enhancement direction by superimposing the spiral phase of the topological charge and introducing relevant parameters, that is, directional edge enhancement is achieved in a given direction. However, so far, directional edge enhancement based on the above method is mainly achieved through spiral phase plate liquid crystal spatial light modulators. Their large structure and limited resolution will hinder their widespread application in modern miniaturized and integrated systems. In addition, compared with the electrically adjustable mode of the spatial light modulator, the traditional mechanical modulation method is relatively stable. Therefore, it is very attractive to build a simple, miniaturized, stable and adjustable directional edge enhancement system. Summary of the invention

[0004] In order to overcome the defects of the prior art, the technical problem to be solved by the present invention is to provide an optical metasurface filter for tunable edge directional enhancement, which can rotate the angle of the metasurface in a simple mechanical tuning manner to achieve tuning of the edge enhancement direction of the amplitude or phase sample, allowing edge filtering in different directions in an efficient and compact manner, and has the advantages of chip-level ultrafast optical computing.

[0005] The technical solution of the present invention is: the optical metasurface filter for tunable edge directional enhancement is a polarization-sensitive vertical edge detection filter constructed by a metasurface and an optical 4F system, wherein the metasurface (10) comprises: an amorphous silicon cuboid nanobrick unit (1) and a silicon dioxide substrate (2); each amorphous silicon cuboid nanobrick unit has a fixed square lattice constant, and the corresponding silicon dioxide substrate width and length are both Px =P y =300nm, the height of the amorphous silicon rectangular nanobrick unit is H=365nm, and the designed length L=129nm and width W=90nm, the amorphous silicon rectangular nanobrick units are periodically arranged on the silicon dioxide substrate; the phase is changed by changing the orientation angle θ of the amorphous silicon rectangular nanobrick unit to achieve the required phase distribution.

[0006] A method for operating an optical metasurface filter for tunable edge-directed enhancement is also provided, comprising the following steps:

[0007] (1) Establish a database of polarization conversion efficiency and determine the structural dimensions of amorphous silicon cuboid nanobrick units based on the imaging band range of 600 to 800 nm;

[0008] (2) Obtaining the phase distribution of the metasurface based on the spiral phase superposition method for:

[0009]

[0010] Wherein, angle(·) represents the angle component of the formula in the brackets, α is a constant value, the spiral phase φ=arctan(y / x), and x and y represent the horizontal and vertical coordinates on the plane of the metasurface, respectively;

[0011] (3) The rotation angle of the nanobrick is set according to the required phase distribution, and the set amorphous silicon rectangular nanobrick units are arranged on a silicon dioxide substrate.

[0012] Beneficial technical effects brought by the present invention: The present invention provides a tunable filter for edge-directional enhancement based on a metasurface, which uses a simple mechanical tuning method to rotate the angle of the metasurface to achieve tuning of the edge enhancement direction of the amplitude or phase sample. This method allows edge filtering in different directions to be achieved in an efficient and compact manner, and has the advantages of chip-level ultrafast optical computing. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A simple functional schematic diagram of the optical metasurface filter for tunable edge-directional enhancement of the present invention.

[0014] Figure 2 The schematic diagram of the structure of an amorphous silicon cuboid nanobrick unit and a silicon dioxide substrate of the super surface of the present invention.

[0015] Figure 3 It is a schematic diagram of the structure of the experimental system of the present invention for the optical metasurface filter with tunable edge-directional enhancement.

[0016] Figure 4 Graph showing the experimental results of the amplitude and phase samples in the present invention.

[0017] Figure 5 This is a simulation result diagram of the amplitude sample in the present invention under a wide band.

[0018] Figure 6 The present invention is a flow chart of the working method of the optical metasurface filter for tunable edge-directional enhancement. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0020] It should be noted that the term "comprises" and any variations in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or equipment.

[0021] like Figure 1-3 As shown, the optical metasurface filter for tunable edge directional enhancement is a polarization-sensitive vertical edge detection filter constructed by a metasurface and an optical 4F system. The metasurface 10 includes: an amorphous silicon cuboid nanobrick unit 1 and a silicon dioxide substrate 2; each amorphous silicon cuboid nanobrick unit has a fixed square lattice constant, and the corresponding silicon dioxide substrate width and length are both P x =P y =300nm. The height of the amorphous silicon cuboid nanobrick unit is H=365nm, and the designed length L=129nm and width W=90nm, and the amorphous silicon cuboid nanobrick units are periodically arranged on the silicon dioxide substrate; the phase is changed by changing the orientation angle θ of the amorphous silicon cuboid nanobrick unit to achieve the required phase distribution.

[0022] Preferably, an experimental system is constructed by the optical metasurface filter, and the experimental system includes in sequence: a laser 3, a first polarizer 41, a first wave plate 51, an objective lens 6, a pinhole 7, a first lens 81, a sample 9, a second lens 82, an optical metasurface filter 10, a third lens 83, a second wave plate 52, a second polarizer 42, and a camera.

[0023] like Figure 6 As shown, a working method for an optical metasurface filter for tunable edge-directional enhancement is also provided, which comprises the following steps:

[0024] (1) Establish a database of polarization conversion efficiency and determine the structural dimensions of amorphous silicon cuboid nanobrick units based on the imaging band range of 600 to 800 nm;

[0025] (2) Obtaining the phase distribution of the metasurface based on the spiral phase superposition method for:

[0026]

[0027] Wherein, angle(·) represents the angle component of the formula in the brackets, α is a constant value, the spiral phase φ=arctan(y / x), and x and y represent the horizontal and vertical coordinates on the plane of the metasurface, respectively;

[0028] (3) The rotation angle of the nanobrick is set according to the required phase distribution, and the set amorphous silicon rectangular nanobrick units are arranged on a silicon dioxide substrate.

[0029] Beneficial technical effects brought by the present invention: The present invention provides a tunable filter for edge-directional enhancement based on a metasurface, which uses a simple mechanical tuning method to rotate the angle of the metasurface to achieve tuning of the edge enhancement direction of the amplitude or phase sample. This method allows edge filtering in different directions to be achieved in an efficient and compact manner, and has the advantages of chip-level ultrafast optical computing.

[0030] Preferably, in step (3), when the phase α=0, for amplitude objects, the system based on the metasurface implements edge filtering in all vertical directions; by rotating the metasurface, the system based on the metasurface implements edge filtering in different directions.

[0031] Preferably, in step (3), when the phase α=0, for a phase object with a phase distribution range of 0 to π, the system based on the metasurface implements edge filtering in the left vertical direction; by rotating the metasurface, the system based on the metasurface implements single edge filtering in different directions.

[0032] Preferably, in step (3), when the phase α=0, for a phase object with a phase distribution range of π to 2π, the system based on the metasurface implements edge filtering in the right vertical direction; by rotating the metasurface, the system based on the metasurface implements single edge filtering in different directions, and is different from the filtering edge of the phase object with a phase distribution range of 0 to π.

[0033] The specific embodiments of the present invention are described in detail below.

[0034] The present invention provides a tunable filter for edge-directed enhancement based on a metasurface, which uses a simple mechanical tuning method to change the rotation angle of the metasurface, thereby realizing the switching of the edge enhancement direction of the amplitude or phase sample. This method allows edge filtering of samples in different directions to be realized in an efficient and compact manner, which has considerable advantages in the fields of optical computing and biological imaging.

[0035] The phase distribution of the metasurface in this embodiment can be expressed as:

[0036]

[0037] Wherein, phase φ = arctan (y / x), x and y represent the coordinates of the x and y directions on the plane of the metasurface, respectively. The functional schematic diagram of the tunable filtering system constructed by the metasurface is shown in the figure below: Figure 1 As shown. When the incident light is E in When, after Figure 1 The modulated output light E of the system shown out The theoretical expression should be:

[0038]

[0039] Where FT and IFT represent Fourier transform and inverse Fourier transform, respectively. In terms of effect, specifically, when the incident light is right-handed circularly polarized (RCP) and the rotation angle of the metasurface is 0°, the vertical edge of the amplitude sample will be enhanced. When the incident light is right-handed circularly polarized (RCP) and the rotation angle of the metasurface is 90°, the horizontal edge of the amplitude sample will be enhanced (e.g. Figure 1 shown).

[0040] like Figure 2 As shown, the metasurface includes a silicon dioxide (SiO2) substrate and a plurality of amorphous silicon (α-Si) cuboid nanobrick units arranged on the substrate, each of which has a fixed square lattice constant P x =P y =300nm and height H=365nm, as well as designed L=129nm and W=90nm, which are periodically arranged on the silicon dioxide substrate. By changing the orientation angle θ of the amorphous silicon cuboid nanobrick unit, the phase can be changed to achieve the required phase distribution.

[0041] The value of the orientation angle θ is calculated based on half of the required phase value, where the size of the amorphous silicon cuboid nanobrick unit is calculated based on maximizing its polarization conversion efficiency under incident light of 600 to 800 nm.

[0042] An experimental system for optical metasurface filters with tunable edge-directed enhancement Figure 3 As shown. The experimental system mainly consists of a laser 3 (wavelength of 671nm), a first polarizer 41, a first wave plate 51, an objective lens 6 (×40), a pinhole 7 (25μm), a first lens 81, a sample 9, a second lens 82, an optical metasurface filter 10, a third lens 83, a second wave plate 52, a second polarizer 42, and a camera. The focal lengths of the first, second, and third lenses are 200nm, 100nm, and 200nm, respectively.

[0043] like Figure 4 As shown in the figure, the first row shows the edge detection results of the system when the sample is an amplitude object; the second row shows the edge detection results of the system when the sample is a phase object. Both the output result graph and the normalized intensity distribution of the system show that the system has a tunable edge-oriented enhancement effect on the sample object.

[0044] Figure 5 It shows the simulation output results and normalized intensity distribution diagram of the system when the sample object is an amplitude object and the wavelength of the incident light is changed (the wavelengths in the first to third rows are 604nm, 671nm, and 760nm, respectively). It can be clearly found that the working band of the filter system is at least 156nm.

[0045] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. Optical metasurface filter for tunable edge-directed enhancement, characterized in that: The invention relates to a polarization-sensitive vertical edge detection filter constructed by a metasurface and an optical 4F system. The metasurface (10) comprises: an amorphous silicon cuboid nanobrick unit (1) and a silicon dioxide substrate (2). Each amorphous silicon cuboid nanobrick unit has a fixed square lattice constant, and the corresponding silicon dioxide substrate width and length are both P x =P y =300nm, the height of the amorphous silicon rectangular nanobrick unit is H=365nm, and the designed length L=129nm and width W=90nm, the amorphous silicon rectangular nanobrick units are periodically arranged on the silicon dioxide substrate; the phase is changed by changing the orientation angle θ of the amorphous silicon rectangular nanobrick unit to achieve the required phase distribution.

2. The optical metasurface filter for tunable edge-directional enhancement according to claim 1, characterized in that: An experimental system is constructed by using the optical metasurface filter, and the experimental system comprises in sequence: a laser (3), a first polarizer (41), a first wave plate (51), an objective lens (6), a pinhole (7), a first lens (81), a sample (9), a second lens (82), an optical metasurface filter (10), a third lens (83), a second wave plate (52), a second polarizer (42), and a camera.

3. The working method of the optical metasurface filter for tunable edge-oriented enhancement according to claim 1, characterized in that: It includes the following steps: (1) Establish a database of polarization conversion efficiency and determine the structural dimensions of amorphous silicon cuboid nanobrick units based on the imaging band range of 600 to 800 nm; (2) Obtaining the phase distribution of the metasurface based on the spiral phase superposition method for: Wherein, angle(·) represents the angle component of the formula in the brackets, α is a constant value, the spiral phase φ=arctan(y / x), and x and y represent the horizontal and vertical coordinates on the plane of the metasurface, respectively; (3) The rotation angle of the nanobrick is set according to the required phase distribution, and the set amorphous silicon rectangular nanobrick units are arranged on a silicon dioxide substrate.

4. The working method of the optical metasurface filter for tunable edge-oriented enhancement according to claim 3, characterized in that: In the step (3), when the phase α=0, for amplitude objects, the system based on the metasurface implements edge filtering in all vertical directions; by rotating the metasurface, the system based on the metasurface implements edge filtering in different directions.

5. The working method of the optical metasurface filter for tunable edge-oriented enhancement according to claim 1, characterized in that: In the step (3), when the phase α=0, for a phase object with a phase distribution range of 0 to π, the system based on the metasurface implements edge filtering in the left vertical direction; by rotating the metasurface, the system based on the metasurface implements single edge filtering in different directions.

6. The working method of the optical metasurface filter for tunable edge-oriented enhancement according to claim 1, characterized in that: In the step (3), when the phase α=0, for a phase object with a phase distribution range of π to 2π, the system based on the metasurface implements edge filtering in the right vertical direction; by rotating the metasurface, the system based on the metasurface implements single edge filtering in different directions, and the filtering edge is different from that of a phase object with a phase distribution range of 0 to π.

Images