CN112578490A - Low-refractive-index large-angle deflection sparse grating for 3D printing - Google Patents

Low-refractive-index large-angle deflection sparse grating for 3D printing Download PDF

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Publication number
CN112578490A
CN112578490A CN201910939048.1A CN201910939048A CN112578490A CN 112578490 A CN112578490 A CN 112578490A CN 201910939048 A CN201910939048 A CN 201910939048A CN 112578490 A CN112578490 A CN 112578490A
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low
grating
refractive
index
sparse
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程洁嵘
董希谱
穆倩怡
常胜江
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Nankai University
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Nankai University
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1847—Manufacturing methods
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/002—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of materials engineered to provide properties not available in nature, e.g. metamaterials
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0012—Optical design, e.g. procedures, algorithms, optimisation routines
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1842—Gratings for image generation
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1866—Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

The invention relates to a 3D printed low-refractive-index large-angle deflection sparse grating, and belongs to the technical field of novel artificial electromagnetic materials and terahertz science. The structure of the invention comprises three layers, wherein the lowest layer is a metal substrate (1), the middle layer is a low-refractive-index medium layer (2), and the uppermost layer is a periodic sparse grating (3) formed by the same low-refractive-index medium. The low index medium has a refractive index of about 1.5 in the sub-terahertz wave band and low loss. By properly selecting the period of the sparse grating and the size of the internal grating ridge, the vertically incident sub-terahertz waves can be efficiently reflected to a large-angle direction close to the surface of the grating. The invention can be rapidly processed and molded by using a 3D printing technology, has low cost and compact structure, and provides a new scheme for the development of the sub-terahertz functional device from the aspects of a material system, a processing means and a design mechanism.

Description

Low-refractive-index large-angle deflection sparse grating for 3D printing
Technical Field
The invention relates to a 3D printed low-refractive-index large-angle deflection sparse grating, and belongs to the technical field of novel artificial electromagnetic materials and terahertz science.
Background
Terahertz waves refer to a section of electromagnetic waves with the frequency between 0.1THz and 10 THz. The related technology has good application prospect in the fields of safety inspection, biological imaging, wireless communication and the like. But compared with the visible light wave band, the functional devices in the wave band are not only few in types, but also heavy in structure. For example, commercial terahertz lenses have low numerical aperture and low focusing efficiency, and the development of various terahertz imaging, sensing and spectroscopy systems is severely restricted.
In recent years, rapidly developing metasurfaces offer highly integrated, highly flexible, planar, lightweight solutions for manipulating the amplitude, phase and polarization characteristics of electromagnetic waves. The electromagnetic wave response can be controlled point by point through the sub-wavelength structural unit. To increase the resolution and the degree of freedom of beam steering, the size of the structural unit is required to be small, and the locality of the optical field is required to be strong. This is typically achieved by plasma resonance of the metal super-surface or electric and magnetic dipole resonance of the high index dielectric super-surface.
The particularity of these super-surfaces in the terahertz band is that: on one hand, the metal is close to a perfect conductor, the resonance locality is very weak, the unit size cannot be far smaller than the wavelength, and the wave front control of large phase gradients such as large-angle deflection is restricted; on the other hand, only high-resistance silicon is used for the transparent high-refractive-index medium of terahertz, and the terahertz, particularly the sub-terahertz wave of 0.1-0.3THz, has longer wavelength and higher requirement on the thickness of the silicon-based super surface, which brings great difficulty to processing and preparation.
The low-refractive-index dielectric material is weak in beam binding capacity and poor in spatial regulation and control performance, and is rarely used for super-surface design. However, a large amount of low-refractive-index and low-loss polymers exist in the sub-terahertz waveband, such as polymethylpentene (TPX), Polyethylene (PE), polypropylene (PP), polylactic acid (PLA) and the like, various low-cost complex microstructures can be rapidly processed by using a 3D printing technology, and the defects of the metal and medium super-surface in the terahertz waveband can be effectively overcome. Therefore, the research on the sub-terahertz super-surface device based on the low-refractive-index medium has important scientific value, the weak binding defect of the device to a light field is overcome, the beam deflection of a large angle is realized, a lens with a high numerical aperture is expected to be further developed, and the resolution and the integration degree of a sub-terahertz imaging system are improved.
Disclosure of Invention
The purpose of the invention is as follows: the invention provides a low-refractive-index large-angle beam deflection super-surface based on a 3D printing technology, and large-angle beam deflection with higher efficiency is realized in a certain frequency range by optimally designing an internal grating structure with sparse super-surface.
In order to achieve the purpose, the structure of the invention comprises three layers, wherein the lowest layer is a metal substrate (1), the middle layer is a low-refractive-index medium layer (2), and the uppermost layer is a periodic sparse grating (3) formed by the same low-refractive-index medium.
Further, the low refractive index material in the present invention needs to have a small absorption coefficient in the operating band, for example, the refractive index of polylactic acid in the sub-terahertz band is 1.57 and the loss is small.
Further, the low-refractive-index medium layer (2) and the grating (3) are formed in one step through 3D printing.
Furthermore, the metal substrate is a layer of aluminum foil and is tightly attached to the back of the 3D printed sample.
The basic function of this structure is to efficiently reflect normally incident sub-terahertz beams to large angular directions close to the grating surface.
In order to realize the function, the specific design steps of the periodic grating and the medium substrate are as follows:
(1) according to the operating wavelength lambda and the deflection angle thetarDetermining the period of the grating as Λ =2 λ/sin (θ)r) Wherein the incident angle is thetai=0, the polarization direction of the beam is x, and the +2 th order diffraction direction of the grating corresponds.
(2) Each period comprises two grid structures, and the structures are uniformly distributed along the y direction.
(3) The system optimizes 5 parameters including the width W1, W2, the distance L1, the thickness H1 and the thickness H2 of the uniform dielectric layer of the two gates.
(4) The optimized objective function maximizes the efficiency for the +2 order diffraction order.
(5) The constraints for optimization are that the minimum value of W1, W2, L1 is larger than the minimum printable size of the 3D printer, the sum of W1, W2 and L1 is smaller than the grating period Λ, and the upper limit of H1 and H2 is 5 λ to avoid excessive device thickness.
(6) The optimized algorithm is a gradient descent method, a Newton method or a genetic algorithm and the like.
(7) The optimized iteration number is determined by solving the difference between the field intensity of the +2 th order diffraction order and the perfect field intensity 1 through a strict coupled wave analysis method.
The invention has the beneficial effects that: only two gratings are contained in each period, the structure is sparse, the size is large, the processing is easy, the 3D printing forming speed is high, the cost is low, and the structure is light and thin; large-angle deflection of 80 degrees of sub-terahertz waves can be realized through optimization, and the theoretical deflection efficiency is more than 80%; a new scheme is provided for the development of the terahertz super-surface functional device from the aspects of a material system, a processing means and a design mechanism; the large-angle deflection function which is difficult to realize by the traditional optical element is realized, and a feasible research foundation is laid for further realizing the terahertz large-numerical-aperture lens, improving the imaging resolution and the like.
Drawings
Fig. 1 is a schematic structural and functional diagram of a low-refractive-index dielectric super-surface for realizing large-angle beam deflection according to an embodiment of the present invention.
Fig. 2 is a structural diagram of a structural unit of a low-refractive-index dielectric super-surface for realizing large-angle beam deflection and an optimization parameter schematic diagram according to an embodiment of the present invention.
FIG. 3 is a diagram showing an implementation 70 of an embodiment of the present invention with an infinite periodic array and uniform plane wave incidenceo、75oAnd 80oThe distribution of energy at each diffraction order upon deflection.
FIG. 4 is a diagram of an implementation 70 of an embodiment of the present inventiono、75oAnd 80oThe reflected magnetic field distribution at the time of degree deflection.
FIG. 5 is an angular distribution of energy under a Gaussian beam illumination of limited size according to an embodiment of the present invention.
FIG. 6 is a 3D printed sample object diagram according to an embodiment of the present invention.
FIG. 7 is a graph of the angular distribution of the electric field intensity measured at a frequency of 0.14 THz and a distance of 30cm from the sample for a different deflection angle of a super-surface sample printed in 3D according to example 3 of the present invention.
The figure shows that: the grating structure comprises a metal substrate 1, a low-refractive-index dielectric layer 2 and a low-refractive-index periodic sparse grating 3.

Claims (9)

1. The low-refractive-index large-angle beam deflection sparse grating based on the 3D printing technology is characterized by comprising three layers, wherein the lowest layer is a metal substrate (1), the middle layer is a low-refractive-index medium layer (2), and the uppermost layer is a periodic sparse grating (3) formed by the same low-refractive-index medium.
2. The low refractive index high angle beam deflection sparse grating based on 3D printing technology of claim 1, wherein the low refractive index material is selected to have a low absorption coefficient in the sub-terahertz operating band, and a refractive index of about 1.5 or higher.
3. The low-refractive-index large-angle beam deflection sparse grating based on the 3D printing technology as claimed in claim 1, wherein the low-refractive-index medium layer (2) and the grating (3) are formed in one step by 3D printing.
4. The low-refractive-index large-angle beam deflection sparse grating based on the 3D printing technology as claimed in claim 1, wherein the metal substrate is a layer of aluminum foil and is attached to the back of the 3D printed sample.
5. The low refractive index large angle beam deflection sparse grating based on 3D printing technology as claimed in claim 1, characterized in that the grating period is expressed by the expression Λ =2 λ/sin (θ)r) Determining, wherein Λ is grating period, λ is working wavelength, and θrThe incident angle is 0, which is the deflection angle of the reflected light, and the deflection angle corresponds to the 2 nd diffraction order direction of the periodic grating.
6. The grating period of claim 5, comprising only two grating ridge structures.
7. In the grating period as claimed in claims 5 and 6, the width, spacing and thickness of two grating ridges are optimized by combining the strict coupled wave algorithm and the optimization algorithm, so that the 2 nd diffraction order has the highest efficiency.
8. In the parameter optimization process according to claim 7, the width and the pitch of the ridges are larger than the minimum size that can be processed by the 3D printer, and the optimization algorithm may be selected from a gradient descent method, a newton method, a genetic algorithm, or the like.
9. The low-refractive-index large-angle beam deflection sparse grating based on the 3D printing technology as claimed in claim 1, wherein the optimally designed sparse grating structure is rapidly formed by 3D printing.
CN201910939048.1A 2019-09-30 2019-09-30 Low-refractive-index large-angle deflection sparse grating for 3D printing Pending CN112578490A (en)

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Cited By (4)

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Publication number Priority date Publication date Assignee Title
CN113341562A (en) * 2021-06-21 2021-09-03 南开大学 Design method of high-numerical-aperture super lens based on non-local diffraction regulation
CN113885115A (en) * 2021-10-19 2022-01-04 福州大学 Terahertz beam deflector based on dielectric super-surface and design method thereof
CN114397754A (en) * 2021-12-31 2022-04-26 中山大学 Design method of high-numerical-aperture super-structured lens and high-numerical-aperture super-structured lens
CN117741965A (en) * 2024-02-20 2024-03-22 中国科学院长春光学精密机械与物理研究所 Design method of high-precision image position alignment system based on double telecentric lenses

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Publication number Priority date Publication date Assignee Title
CN113341562A (en) * 2021-06-21 2021-09-03 南开大学 Design method of high-numerical-aperture super lens based on non-local diffraction regulation
CN113885115A (en) * 2021-10-19 2022-01-04 福州大学 Terahertz beam deflector based on dielectric super-surface and design method thereof
CN113885115B (en) * 2021-10-19 2023-08-18 福州大学 Terahertz light beam deflector based on medium super surface and design method thereof
CN114397754A (en) * 2021-12-31 2022-04-26 中山大学 Design method of high-numerical-aperture super-structured lens and high-numerical-aperture super-structured lens
CN114397754B (en) * 2021-12-31 2023-06-30 中山大学 Design method of high-numerical-aperture super-structure lens and high-numerical-aperture super-structure lens
CN117741965A (en) * 2024-02-20 2024-03-22 中国科学院长春光学精密机械与物理研究所 Design method of high-precision image position alignment system based on double telecentric lenses
CN117741965B (en) * 2024-02-20 2024-04-16 中国科学院长春光学精密机械与物理研究所 Design method of high-precision image position alignment system based on double telecentric lenses

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Application publication date: 20210330