CN113885115B

CN113885115B - Terahertz light beam deflector based on medium super surface and design method thereof

Info

Publication number: CN113885115B
Application number: CN202111218403.XA
Authority: CN
Inventors: 黄峰; 吴泽波; 陈佳强; 陈燕青; 王向峰
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2021-10-19
Filing date: 2021-10-19
Publication date: 2023-08-18
Anticipated expiration: 2041-10-19
Also published as: CN113885115A

Abstract

The invention provides a terahertz light beam deflector based on a dielectric super surface and a design method thereof, wherein silicon dioxide is used as a base material and a grating unit material of the light beam deflector; the unit structure of the beam deflector is constructed by using the periodic arrangement of two one-dimensional gratings; setting the polarization state, working frequency and incident angle of incident light; modulating the phase of incident light by designing the grating and substrate dimensions of a fixed thickness with the arrangement period as an optimization variable, and selectively scattering most of the incident light to the +1 diffraction order while suppressing the intensities of other diffraction orders; and adding a thickness optimization variable, and optimizing the size, the periodic arrangement and the substrate thickness of two gratings with different widths to finally obtain the terahertz light 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

Terahertz light beam deflector based on medium super surface and design method thereof

Technical Field

The invention belongs to the technical fields of terahertz, light field regulation and control and the like, and particularly relates to a terahertz light beam deflector based on a medium super surface and a design method thereof.

Background

Terahertz waves generally refer to electromagnetic waves having a band between millimeter waves of 0.1THz and far infrared rays of 10 THz. Terahertz waves have characteristics different from electromagnetic waves such as microwaves, infrared rays, X-rays and the like, and have remarkable research values in the aspects of broadband mobile communication, satellite communication, military radar, object imaging, environment monitoring, medical diagnosis and the like.

Light field regulation technology has attracted strong interest to vast scientific researchers in recent years. Virtually any photonic technology essentially performs a wide variety of manipulation of various physical parameters of the light field, including frequency, wavelength, time, amplitude, phase, polarization, etc., to effect loading, processing, and extraction of light information. The deflection control of the light beam is in a vital position, is a research focus in the optical field all the time, and has wide application in a plurality of fields such as industry, communication, biomedical, astronomical observation, national defense and military, and the like.

At present, a traditional super-surface light beam deflector applied to terahertz wave bands mostly adopts a series of sub-wavelength units with different sizes or directions to form a super-surface structure, each unit forms a specific phase mutation, and the whole structure forms a 0-2 pi phase gradient. When light is vertically incident, the unit array introduces a phase gradient, so that deflection of the emergent light angle can be realized. Most of the traditional beam deflectors can realize relatively small deflection, the device efficiency is obviously reduced under a large deflection angle, and the traditional super-surface device adopts metal as a unit material, so that the device efficiency is low due to metal loss. Therefore, the design of the terahertz light beam deflector with large deflection angle and high efficiency has very important significance.

Disclosure of Invention

In view of the above, in order to overcome the defects and shortcomings of the prior art, the present invention aims to provide a terahertz beam deflector based on a dielectric super-surface and a design method thereof, which adopts silicon dioxide as a substrate material and a grating unit material of the beam deflector; the unit structure of the beam deflector is constructed by using the periodic arrangement of two one-dimensional gratings; setting the polarization state, working frequency and incident angle of incident light; modulating the phase of incident light by designing the grating and substrate dimensions of a fixed thickness with the arrangement period as an optimization variable, and selectively scattering most of the incident light to the +1 diffraction order while suppressing the intensities of other diffraction orders; and adding a thickness optimization variable, and optimizing the size, the periodic arrangement and the substrate thickness of two gratings with different widths to finally obtain the terahertz light 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 adopts the following technical scheme:

a terahertz light beam deflector based on a medium super surface is 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 the 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 optimized variable.

Further, silicon dioxide is used as a base material and a grating unit material. The material has high transmittance in the terahertz wave band; refractive index n=1.98; terahertz wave is small in loss and easy to process.

Further, the one-dimensional grating structure is a reflective or transmissive diffraction grating. A reflective diffraction grating may be prepared using Au disposed below a silicon dioxide substrate as a reflective material.

Further, the design targets for modulating the phase of the incident light with the arrangement period as the optimization variable are: most of the incident light is scattered to the +1 diffraction order while suppressing the intensities of the other diffraction orders.

More preferably, the thickness and the width of the grating are further adjusted to control the phase delay of incident light passing through the whole array of the grating, and the size, the periodic arrangement and the substrate thickness of 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=λ/sin θ, where λ is the wavelength of incident light and θ is the deflection angle. For example, when the wavelength of incident light is 400 mu m, 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 preferable scheme thereof can realize large-angle deflection, have small loss, are easy to process and have high deflection efficiency. Most of the traditional beam deflectors can realize relatively smaller deflection, the efficiency of the device can be obviously reduced under a large deflection angle, and the traditional super-surface device adopts metal as a unit material, so that the efficiency of the device is low due to metal loss, and the development of high-performance imaging applications such as a molecular microscope is hindered. In contrast to such designs, the present invention utilizes a periodic arrangement of two one-dimensional gratings instead of a series of discrete elements used with conventional super-surface beam deflectors. The thickness and the width of the grating can control the phase delay of incident light passing through the whole array of the grating, and the ultra-surface terahertz beam deflector with specific angle deflection is obtained by modulating the phase of the incident light by optimizing the size of the grating and the size of the substrate, so that 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 attached drawings and detailed description:

FIG. 1 is a schematic diagram of the structure and principle of a transmissive terahertz beam deflector according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of the structure and principle of a reflective terahertz beam deflector according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of the diffraction efficiency versus deflection angle of a transmissive beam deflector according to an embodiment of the present invention at a fixed thickness and an optimized thickness.

FIG. 4 is a schematic diagram of the relationship between diffraction efficiency and deflection angle of a reflective beam deflector according to an embodiment of the present invention at a fixed thickness and an optimized thickness;

FIG. 5 is a schematic wavefront view of a transmissive beam deflector of an embodiment of the present invention at deflection angles of 20 and 70;

FIG. 6 is a schematic wavefront diagram of a reflective beam deflector of 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 patent more comprehensible, embodiments accompanied with figures are described in detail below:

the design of the beam deflector in this embodiment mainly comprises the following steps:

step S1: the unit structure of the beam deflector is constructed by using two one-dimensional gratings with different widths to be periodically arranged;

step S2: the designed polarized state of the incident light is TM polarized light, the wavelength of the incident light is 400 mu m, the corresponding working frequency is 0.75THz, and the incident angle is 0 degree;

step S3: designing a fixed thickness of the grating to be 200 mu m, and a fixed thickness of the substrate to be 300 mu m, modulating the phase of incident light by taking an arrangement period as an optimized variable, and selectively scattering most of the incident light to a +1 diffraction order while inhibiting the intensity of other diffraction orders;

step S4: and adding a thickness optimization variable, and calculating diffraction efficiency under different deflection angles by utilizing Matlab programming according to a strict coupled wave analysis method. And under the condition that constraint conditions are met, optimizing the designed structure. The incident light is normal and the desired light falls on the +1 diffraction order, when the grating period p=λ/sinθ. The structure sizes of the corresponding terahertz beam deflectors with the deflection angles of 20-70 degrees are optimized respectively, and finally the terahertz beam deflectors which can guide incident light to a very large deflection angle and have high deflection efficiency in a wide deflection angle range are obtained.

Fig. 1 and fig. 2 are schematic diagrams of a transmissive terahertz beam deflector and a reflective terahertz beam deflector according to embodiments of the present invention.

Fig. 3 and 4 are the diffraction efficiency versus deflection angle for a transmissive and reflective beam deflector, respectively, at a fixed thickness and an optimized thickness. At the operating frequency f=0.75 THz, the incident light is TM polarized light normally incident, and the deflection angle range is set to 20 ° -70 °. As can be seen from the graph, when the light beam deflector with fixed thickness is transmissive, the diffraction efficiency is lower as a whole, but is higher than that of the traditional light beam deflector with large deflection angle, and when the grating thickness and the substrate thickness are also used as optimization variables to participate in optimization, the whole diffraction efficiency is greatly improved, especially when the deflection angle is 30 degrees, the diffraction efficiency is up to 0.99, and the diffraction efficiency of the deflection angle in the range of 20 degrees to 70 degrees is kept above 0.8, which is much higher than that of the traditional light beam deflector with large deflection angle; when the deflection angle is less than 50 degrees, the diffraction efficiency of both schemes reaches more than 0.8, and especially 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 show the wavefront in the x-z plane for a 20℃and 70℃deflection angle for a transmissive and reflective beam deflector, respectively, in accordance with an embodiment of the present invention, wherein the abscissa indicates the length in the x and z directions, expressed as a multiple of the wavelength; arrows indicate the incident direction and the deflection direction, respectively; the contour is the field strength; the box is the geometry of the terahertz beam deflector. As can be seen from the figure, the incident light is deflected in the direction of propagation after the device has been designed, when it is transmissive. Substituting the optimized structural parameters into p=lambda/sin theta to reversely push the simulated deflection angle, and concluding that the result is consistent with the deflection angle which is set at the beginning, the transmitted light beam is truly and efficiently deflected to a preset angle, which proves that the optimization process is effective, and also that the designed light beam deflector can truly realize the high-efficiency large deflection angle emergence of the light beam; when the reflection type beam deflector is reflective, the reflected light can be seen to deflect at a certain angle, and the reversely-simulated deflection angle obtained by measurement is matched with the set deflection angle, so that the designed reflection type beam deflector is proved to meet the requirements.

Table 1 shows the optimized structural parameters of the transmission beam deflector in the design example of the present invention. The periods at the same deflection angle can be found to be substantially equal because the period p=λ/sin θ, the period being related only to the wavelength of the incident light and the deflection angle.

Table 2 shows the optimized structural parameters of the reflective beam deflector according to the design example of the present invention. The grating period at each deflection angle of the transmissive and reflective beam deflectors is substantially the same. And the grating thickness of the reflective beam deflector is found to be much thinner than the grating thickness of the transmissive beam deflector in the deflection angle range of 20 ° -70 ° as the light will interact twice with the super surface.

The present invention is not limited to the above-mentioned best mode, any person can obtain other various terahertz beam deflectors based on the super surface of the medium and its design method under the teaching of the present invention, and all equivalent changes and modifications made according to the scope of the present invention should be covered by the present invention.

Claims

1. A terahertz light beam deflector based on a medium super surface is 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 the incident light, modulating the phase of the incident light by designing the grating with fixed thickness and the size of the substrate and taking the arrangement period as an optimized variable;

silicon dioxide is used as a base material and a grating unit material;

the design targets for modulating the phase of the incident light with the arrangement period as the optimization variable are: and scattering most of incident light to a +1 diffraction order, inhibiting the intensity of other diffraction orders, controlling the phase delay of the incident light passing through the whole array of the gratings by adjusting the thickness and the width of the gratings, and optimizing the size, the periodic arrangement and the substrate thickness of two gratings with different widths to obtain the terahertz light beam deflector with a large deflection angle.

2. The terahertz beam deflector based on the super surface of a medium according to claim 1, wherein: the one-dimensional grating structure is a reflective or transmissive diffraction grating.

3. The method for designing the terahertz beam deflector based on the medium super surface according to claim 1, wherein the method comprises the following steps: the one-dimensional grating structure is a reflective or transmissive diffraction grating; the arrangement period is as follows: p=l/sinq, where l is the wavelength of the incident light and q is the deflection angle.