CN113885115A - Terahertz beam deflector based on dielectric super-surface and design method thereof - Google Patents
Terahertz beam deflector based on dielectric super-surface and design method thereof Download PDFInfo
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- CN113885115A CN113885115A CN202111218403.XA CN202111218403A CN113885115A CN 113885115 A CN113885115 A CN 113885115A CN 202111218403 A CN202111218403 A CN 202111218403A CN 113885115 A CN113885115 A CN 113885115A
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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
- G02B5/1861—Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
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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
- G02B5/1866—Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The invention provides a terahertz beam deflector based on a dielectric super surface and a design method thereof, wherein silicon dioxide is used as a substrate material and a grating unit material of the beam deflector; constructing a unit structure of the beam deflector by utilizing the periodic arrangement of two one-dimensional gratings; setting the polarization state, working frequency and incident angle of incident light; the phase of incident light is modulated by designing the size of a grating with fixed thickness and a substrate and taking an arrangement period as an optimization variable, and most of the incident light is selectively scattered to +1 diffraction order while the intensity of other diffraction orders is suppressed; and adding a thickness optimization variable, and optimizing the size, the periodic arrangement and the substrate thickness of the two gratings with different widths to finally obtain the terahertz beam deflector which can guide incident light to a very large deflection angle and has high deflection efficiency in a wide deflection angle range. The deflector can realize large-angle deflection, has small loss, is easy to process and has high deflection efficiency.
Description
Technical Field
The invention belongs to the technical field of terahertz and optical field regulation and control and the like, and particularly relates to a terahertz beam deflector based on a dielectric super-surface and a design method thereof.
Background
The terahertz wave generally refers to an electromagnetic wave having a band between a millimeter wave of 0.1THz and a far infrared ray of 10 THz. Terahertz waves have the characteristics different from electromagnetic waves such as microwaves, infrared rays, X rays and the like, and have significant research values in the aspects of broadband mobile communication, satellite communication, military radars, object imaging, environment monitoring, medical diagnosis and the like.
The light field regulation and control technology attracts the strong interest of the majority of researchers in recent years. In fact, any photonic technology essentially performs various controls on various physical parameters of an optical field, including frequency, wavelength, time, amplitude, phase, polarization, and the like, so as to realize loading, processing, and extraction of optical information. The deflection control of the light beam is in a crucial position, is always the research focus in the optical field, and has wide application in a plurality of fields such as industry, communication, biomedical treatment, astronomical observation, national defense and military.
At present, a series of sub-wavelength units with different sizes or directions are mostly adopted to form a super-surface structure, each unit forms specific phase mutation, and the whole structure forms a phase gradient of 0-2 pi. When light is vertically incident, the unit array introduces a phase gradient, and deflection of an emergent light angle can be realized. Most of the traditional light beam deflectors can only realize relatively small deflection, the efficiency of the device can be obviously reduced under a large deflection angle, and the traditional super-surface device takes metal as a unit material, so that the efficiency of the device is low due to metal loss. Therefore, the terahertz beam deflector with a large deflection angle and high efficiency is designed to have very important significance.
Disclosure of Invention
In view of the above, in order to overcome the defects and shortcomings in the prior art, the present invention aims to provide a terahertz beam deflector based on a dielectric super surface and a design method thereof, wherein silicon dioxide is used as a substrate material and a grating unit material of the beam deflector; constructing a unit structure of the beam deflector by utilizing the periodic arrangement of two one-dimensional gratings; setting the polarization state, working frequency and incident angle of incident light; the phase of incident light is modulated by designing the size of a grating with fixed thickness and a substrate and taking an arrangement period as an optimization variable, and most of the incident light is selectively scattered to +1 diffraction order while the intensity of other diffraction orders is suppressed; and adding a thickness optimization variable, and optimizing the size, the periodic arrangement and the substrate thickness of the two gratings with different widths to finally obtain the terahertz beam deflector which can guide incident light to a very large deflection angle and has high deflection efficiency in a wide deflection angle range. The deflector can realize large-angle deflection, has small loss, is easy to process and has high deflection efficiency.
The invention specifically adopts the following technical scheme:
the utility model provides a terahertz beam deflector based on medium super surface which characterized in that: firstly, constructing a unit structure of a beam deflector by utilizing the periodic arrangement of two one-dimensional gratings; based on the polarization state, working frequency and incident angle of incident light, the phase of the incident light is modulated by designing the grating with fixed thickness and the size of the substrate and taking the arrangement period as an optimization variable.
Further, silicon dioxide is used as a base material and a grating unit material. The material has high transmittance in the terahertz waveband; the refractive index n is 1.98; the terahertz wave has small loss and is easy to process.
Further, the one-dimensional grating structure is a reflective or transmissive diffraction grating. The reflective diffraction grating may be fabricated using Au disposed below a silicon dioxide substrate as the reflective material.
Further, the design objective of modulating the phase of incident light with the arrangement period as an optimization variable is: scattering most of the incident light to the +1 diffraction order while suppressing the intensity of the other diffraction orders.
Preferably, the phase delay of incident light passing through the grating alignment is further controlled by adjusting the thickness and the width of the grating, and the size, the period arrangement and the substrate thickness of the two gratings with different widths are optimized, so that the terahertz beam deflector with a large deflection angle is obtained.
Further, the one-dimensional grating structure is a reflective or transmissive diffraction grating; the arrangement period is as follows: p is λ/sin θ, where λ is the wavelength of the incident light and θ is the deflection angle. For example, when the wavelength of incident light is 400 μm, the corresponding working frequency is 0.75THz, and the deflection angle can reach 20-70 degrees through the design.
Compared with the prior art, the invention and the optimized scheme thereof can realize large-angle deflection, small loss, easy processing and high deflection efficiency. Most of the existing traditional light beam deflectors can only realize relatively small deflection, the device efficiency can be obviously reduced under a large deflection angle, and the traditional super-surface device takes metal as a unit material, so that the device efficiency is low due to metal loss, and the development of high-performance imaging application such as a molecular microscope is hindered. Compared with the design, the invention utilizes the periodic arrangement of two one-dimensional gratings to replace a series of discrete units used by the traditional super-surface beam deflector. The thickness and the width of the grating can control the phase delay of incident light passing through the whole line of the grating, the phase of the incident light is modulated by optimizing the size of the grating and the size of the substrate to obtain the super-surface terahertz beam deflector with specific angle deflection, and the terahertz beam deflector with large angle deflection and high deflection efficiency is obtained.
Drawings
The invention is described in further detail below with reference to the following figures and detailed description:
FIG. 1 is a schematic diagram of a structure and principle of a transmissive terahertz beam deflector according to an embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating a structure and principle of a reflective terahertz beam deflector according to an embodiment of the present invention;
fig. 3 is a schematic diagram illustrating a relationship between diffraction efficiency and deflection angle of a transmissive beam deflector at a fixed thickness and an optimized thickness according to an embodiment of the present invention.
FIG. 4 is a schematic diagram showing the relationship between the diffraction efficiency and the deflection angle of the reflective beam deflector according to the embodiment of the present invention under the fixed thickness and the optimized thickness;
FIG. 5 is a schematic diagram of the wavefront of a transmissive beam deflector at deflection angles of 20 and 70 according to an embodiment of the present invention;
fig. 6 is a schematic diagram of the wavefront of a reflective beam deflector according to an embodiment of the present invention at deflection angles of 20 ° and 70 °.
Detailed Description
In order to make the features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail as follows:
the design of the beam deflector in this embodiment mainly adopts the following steps:
step S1: constructing a unit structure of the beam deflector by utilizing the periodic arrangement of two one-dimensional gratings with different widths;
step S2: the designed polarization state of the incident light is TM polarized light, the wavelength of the incident light is 400 μm, the corresponding working frequency is 0.75THz, and the incident angle is 0 degree;
step S3: designing the fixed thickness of the grating to be 200 μm and the fixed thickness of the substrate to be 300 μm, modulating the phase of incident light with the arrangement period as an optimization variable, and selectively scattering most of the incident light to +1 diffraction order while suppressing the intensity of other diffraction orders;
step S4: and adding a thickness optimization variable, and calculating the diffraction efficiency under different deflection angles by utilizing Matlab programming according to a strict coupled wave analysis method. And optimizing the designed structure under the condition of meeting the constraint condition. The incident light is normal incidence and the light is required to fall on the +1 diffraction order, when the grating period p is λ/sin θ. Respectively optimizing the structural size of the corresponding terahertz beam deflector with the deflection angle of 20-70 degrees to finally obtain the terahertz beam deflector which can guide incident light to a very large deflection angle and has high deflection efficiency in a wide deflection angle range.
Fig. 1 and fig. 2 are schematic diagrams of a transmissive terahertz beam deflector and a reflective terahertz beam deflector in the embodiment of the present invention, respectively.
Fig. 3 and 4 show the diffraction efficiency versus deflection angle for a transmissive and reflective beam deflector at a fixed thickness and an optimized thickness, respectively. In the case where the operating frequency f is 0.75THz, the incident light is TM polarized light vertically incident, and the deflection angle is set in the range of 20 ° to 70 °. It can be seen from the figure that, when the beam deflector is of a transmission type, the diffraction efficiency of the beam deflector with a fixed thickness is lower as a whole, but is higher than that of the traditional beam deflector at a large deflection angle, and when the thickness of the grating and the thickness of the substrate are also taken as optimization variables to participate in optimization, the overall diffraction efficiency is greatly improved, particularly when the deflection angle is 30 degrees, the diffraction efficiency reaches up to 0.99, and the diffraction efficiency of the deflection angle within the range of 20 degrees to 70 degrees is kept above 0.8, which is much higher than that of the traditional beam deflector at the large deflection angle; when the beam deflector is of a reflection type, the deflection angle is less than 50 degrees, the diffraction efficiency of the two schemes reaches over 0.8, and particularly under the condition that the thickness participates in optimization, the diffraction efficiency of the designed beam deflector is close to 1 within the deflection angle range of 20-70 degrees.
FIGS. 5 and 6 are wavefronts in the x-z plane at deflection angles of 20 and 70 for transmissive and reflective beam deflectors, respectively, according to embodiments of the present invention, with the abscissa and ordinate representing the length in the x and z directions, respectively, expressed as multiples of the wavelength; arrows indicate the incident direction and the deflection direction, respectively; the contour lines are field strengths; the geometric position of the terahertz beam deflector is shown in the square frame. It can be seen that when transmissive, the incident light is deflected in the direction of propagation behind the device as designed. Substituting the optimized structural parameters into p ═ lambda/sin theta to reversely deduce the simulated deflection angle, and concluding that the simulated deflection angle is matched with the initially set deflection angle, the transmitted light beam is indeed deflected to a preset angle efficiently, which shows that the optimization process is effective, and the designed light beam deflector can indeed realize the high-efficiency large deflection angle emission of the light beam; when the reflecting type light beam deflecting device is in a reflecting type, the reflecting light can be seen to deflect at a certain angle, the measured and obtained reversely-deduced deflection angle is matched with the set deflection angle, and the designed reflecting type light beam deflecting device is proved to meet the requirement.
Table 1 shows the optimized structural parameters of the transmissive beam deflector in the design example of the present invention. It can be found that the periods at the same deflection angle are substantially equal because the period p ═ λ/sin θ, the period being dependent only on the incident light wavelength and the deflection angle.
Table 2 shows the optimized structural parameters of the reflective beam deflector in the design example of the present invention. The grating periods at each deflection angle of the transmissive and reflective beam deflectors are substantially the same. And it was found that the thickness of the grating of the reflective beam deflector is always much thinner in the deflection angle range of 20 deg. -70 deg. than the thickness of the grating of the transmissive beam deflector, because the light interacts twice with the super-surface.
The present invention is not limited to the above-mentioned preferred embodiments, and other various types of terahertz beam deflectors based on dielectric super-surface and design methods thereof can be obtained by anyone who can derive the teaching of the present invention.
Claims (6)
1. The utility model provides a terahertz beam deflector based on medium super surface which characterized in that: firstly, constructing a unit structure of a beam deflector by utilizing the periodic arrangement of two one-dimensional gratings; based on the polarization state, working frequency and incident angle of incident light, the phase of the incident light is modulated by designing the grating with fixed thickness and the size of the substrate and taking the arrangement period as an optimization variable.
2. The terahertz beam deflector based on the dielectric super surface as claimed in claim 1, wherein: silicon dioxide is used as a substrate material and a grating unit material.
3. The terahertz beam deflector based on the dielectric super surface as claimed in claim 1, wherein: the one-dimensional grating structure is a reflection type or transmission type diffraction grating.
4. The design method of the terahertz beam deflector based on the dielectric super surface as claimed in claim 1, wherein: the design objective of modulating the phase of incident light with the arrangement period as an optimization variable is as follows: scattering most of the incident light to the +1 diffraction order while suppressing the intensity of the other diffraction orders.
5. The design method of the terahertz beam deflector based on the dielectric super surface as claimed in claim 1, wherein: and further controlling the phase delay of incident light passing through the grating alignment by adjusting the thickness and the width of the grating, and optimizing the size, the period arrangement and the substrate thickness of the two gratings with different widths to obtain the terahertz beam deflector with a large deflection angle.
6. The design method of the terahertz beam deflector based on the dielectric super surface as claimed in claim 1, wherein: the one-dimensional grating structure is a reflection type or transmission type diffraction grating; the arrangement period is as follows: p is λ/sin θ, where λ is the wavelength of the incident light and θ is the deflection angle.
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| CN202111218403.XA CN113885115B (en) | 2021-10-19 | 2021-10-19 | Terahertz light beam deflector based on medium super surface and design method thereof |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114512816A (en) * | 2022-03-01 | 2022-05-17 | 电子科技大学 | High-efficiency reflective terahertz wave beam deflection device |
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2021
- 2021-10-19 CN CN202111218403.XA patent/CN113885115B/en active Active
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| CN114512816B (en) * | 2022-03-01 | 2023-04-18 | 电子科技大学 | High-efficiency reflective terahertz wave beam deflection device |
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