NL2030632A

NL2030632A - Square lattice metasurface resonator with adjustable optical rotation and polarization

Info

Publication number: NL2030632A
Application number: NL2030632A
Authority: NL
Inventors: Wang Siliang; Ren Zihua; Ren Xingang; Niu Kaikun; Shen Dongfang; Huang Zhixiang; Yang Lixia; Ci Qing
Original assignee: Univ Anhui
Priority date: 2021-09-09
Filing date: 2022-01-20
Publication date: 2023-03-20
Also published as: CN113741065B; CN113741065A; NL2030632B1

Abstract

The present disclosure discloses a square lattice metasurface resonator with adjustable optical rotation and polarization. The square lattice metasurface resonator includes multiple cross structures composed of two intersecting cuboids, wherein a length of the cross structures is 370nm, a width of the cross structures is 100nm, and a thickness of the cross structures is 320nm; the multiple cross structures are arranged side by side, and a distance between two adjacent cross structures is 475 nm; the square lattice metasurface resonator has four—fold rotational symmetry and has two independent response frequency points of bound states in continuum in a near—infrared waveband, whose material is silicon and refractive index in a near—infrared region is 3.58.

Description

SQUARE LATTICE METASURFACE RESONATOR WITH ADJUSTABLE OPTICAL

ROTATION AND POLARIZATION

TECHNICAL FIELD

The present disclosure relates to a field of computer tech- nology; in particular to a square lattice metasurface resonator with adjustable optical rotation and polarization.

BACKGROUND ART

Bound states in the continuum (BIC) are continuous states on the discrete spectrum and theoretically have a quality factor close to infinity. In practice, the quality factor of this BICs is often much lower than the theoretically predicted infinity, and is limited to around 10%. In addition to other factors, such as mate- rial absorption or a limited size of samples, the main limiting factor is that the scattering loss caused by manufacturing defects or misalignment in strong BIC modes excited in photonic crystal plates (PhCs) can be protected by the symmetry of the T point. In addition, a phase change such as a spectral response of quasi-BIC mode and special linear characteristics of sharp Fano resonance can be designed by modifying in-plane symmetry and out-of-plane symmetry or excitation conditions. By using the quasi-BIC mode with phase reversal characteristics to cause the phase change, a polarization azimuth angle is rotated up to 90° and the phase de- lay of the transmission increases suddenly. For the beam, the ar- bitrary polarization state o can be completely described by two parameters, namely a principal axis angle y and an ellipticity x.

The angle difference between rotation lines at two operating fre- quency points is very obvious, because the phase is reversed. As we all know, linearly polarized light can be expressed as the su- perposition of left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP). When linearly po- larized light passes through optical chiral materials such as chi- ral molecules or structures with helical characteristics, LCP and

RCP light will produce different phase delays. However, the chi-

ral-optical interaction is very weak in a simple structure with natural materials, so it is desirable to provide a simple and tun- able chiral structure with strong chiral-optical interaction.

For structures with a very large quality factor and multiple tunable resonances, it has obvious advantages in an application of optical rotation. A high quality factor indicates a narrow band- width response and high sensitivity, which means a substantial in- crease in light-matter interaction. At the same time, it is urgent to find a new tunable optical metasurface with simple structure and easy preparation.

SUMMARY

In order to solve the above technical problems, the embodi- ments of this specification are implemented as follows:

A square lattice metasurface resonator with adjustable opti- cal rotation and polarization provided in the embodiment of this specification includes multiple cross structures composed of two intersecting cuboids, wherein a length of the cross structures is 370nm, a width of the cross structures is 100nm, and a thickness of the cross structures is 320nm; the multiple cross structures are arranged side by side, and a distance between two adjacent cross structures is 475 nm; the square lattice metasurface resona- tor has four-fold rotational symmetry; a material of the square lattice metasurface resonator is silicon, whose refractive index in a near-infrared region is 3.58; the square lattice metasurface resonator has two independent response frequency points of bound states in continuum (BIC) in a near-infrared waveband.

Optionally, a transmission spectrum of the square lattice metasurface resonator in the near-infrared waveband presents a single-mode tunable property by adjusting in-plane symmetry and out-of-plane symmetry.

Optionally, a transverse magnetic wave is used to excite a

BIC mode, an eigenmode solver with finite element method is used to calculate a band structure and a quality factor (Q factor), a periodic boundary condition is added in a horizontal plane, and a matching layer is constructed in a vertical direction.

Optionally, a range of an optical rotation of the square lat-

tice metasurface resonator is 0° to 180°.

Optionally, an attenuation of the quality factor of the square lattice metasurface resonator changes exponentially with a change of an absolute value of a normalized vector.

Optionally, a line shape of Fano resonance is flexibly ad- jJusted by controlling the in-plane symmetry and the out-of-plane symmetry of a metasurface structure with a quasi-BIC mode.

Optionally, linearly polarized light can be transmitted through the square lattice metasurface resonator at two resonant wavelengths, so that the BIC becomes the quasi-BIC mode, in the quasi-BIC mode, a red shift and a blue shift occur.

Optionally, a polarization state of the square lattice metasurface resonator is adjustable, which is changed from linear polarization to elliptical polarization.

The above-mentioned at least one technical solution adopted in the embodiment of this specification can achieve the following beneficial effects:

The square lattice metasurface resonator provided by the pre- sent disclosure has simple structure and composition, convenient crystal preparation, high feasibility in actual experiments and production, which is easier to achieve numerical simulation re- sults and with a higher practical value.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are used to provide a further understanding of the present disclosure and constitute a part of the present disclosure. The exemplary embodiments and descriptions of the present disclosure are used to explain the present disclo- sure, and do not constitute an undue limitation of the present disclosure. In the attached figures:

FIG. 1 is a structure diagram of a square lattice metasurface resonator with adjustable optical rotation and polarization;

FIG. 2(a) is a band structure of a C4 structure;

FIG. 2(b) is a distribution diagram of a quality factor Q, and illustrations (i) and (ii) are respectively electric field distributions in TM1 and TM2 modes at T point;

FIG. 2(c) is a distribution diagram of a quality factor Q un-

der different displacements in x direction;

FIG. 2(d) is a distribution diagram of a quality factor Q un- der displacements of both x and y directions at the same time;

FIG. 3(a) is a transmission spectrum distribution diagram of wavelengths under different displacements in x direction;

FIG. 3 (kb) is an electric field distribution of TM2 mode at T point when dx=60nm;

FIG. 3(c) is an electric field distribution of TMl mode at T point when dx=60nm;

FIG. 4(a) is a transmission spectrum distribution diagram of different wavelengths with a same displacement in x and y direc- tions;

FIG. 4 (b) is an electric field distribution of TM2 mode at T point when dx= dy= 60nm;

FIG. 4(c) is an electric field distribution of TM1 mode at T point when dx= dy= 60nm;

FIG. 5(a), FIG. 5(b), FIG. 5{c) and FIG. 5(d) are optical ro- tation (gray line) / transmission amplitude (black line) of TM1 and TM2 modes;

FIG. 5(e) and FIG. 5(f) are corresponding ellipticities (c, fj), an illustration is an elliptical polarization state, and cor- responding displacements are 5nm, 30nm and 60nm respectively.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to make the purpose, technical solutions, and ad- vantages of the present disclosure clearer, the technical solu- tions of the present disclosure will be described clearly and com- pletely in conjunction with specific embodiments of the present disclosure and the corresponding drawings. Obviously, the de- scribed embodiments are only a part of the embodiments of the pre- sent disclosure, rather than all the embodiments. Based on the em- bodiments in the present disclosure, all other embodiments ob- tained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present disclosure.

In the present disclosure, a silicon square lattice metasur- face resonator with four-fold rotational symmetry (C4) is innova- tively proposed, and a finite element method (FEM) is used to cal-

culate a designed structural model. Under the excitation of TM linear polarization along x-direction, a C+, metasurface structure can be observed in a near-infrared waveband with dual BIC modes.

The symmetry is broken by adjusting displacements of the C4, crys- 5 tal structure along x and y axes, and a feature mode is calculat- ed. The study found that linearly polarized light can be transmit- ted through the metasurface at two resonance wavelengths, and at this time, BIC becomes a quasi-BIC mode. A transmission spectrum and an electric field mode under different structures are calcu- lated, and the mode on the transmission spectrum is independently adjustable without interfering with each other, presenting a sin- gle-mode tunability of dual quasi-BIC. The dual quasi-BIC mode metasurface with the single-mode tunability can be further applied in anti-interference optical devices. Furthermore, a Poynting vec- tor of the structure is calculated to find that electromagnetic wave propagation has a phase delay phenomenon in xoy plane, and the two quasi-BIC modes reveal completely different optical rota- tion changes. Then through the combination of linearly polarized light and Fano resonance, an outgoing beam has controllable opti- cal rotation in all four quadrants, in other words, a range of op- tical rotation covers 0° to 180°. The optical rotation metasurface with dual quasi-BIC characteristics designed in this project has achieved a breakthrough in the field of optical rotation polariza- tion control of metasurfaces, and is expected to be applied in the fields of nonlinear optics, holographic imaging, quantum infor- mation and biosensing.

The technical solutions provided by the embodiments of the present disclosure will be described in detail below with refer- ence to the accompanying drawings.

As shown in FIG. 1, a metasurface with C,, symmetry is a cross structure composed of two intersecting cuboids, whose material is silicon, and refractive index in a near-infrared region is ng = 3.58. Geometric parameters of the metasurface are shown in FIG. 1.

A period is P=475nm, length and width are respectively L=370nm and

W=100nm, and thickness is D=320nm. Herein, transverse magnetic (TM) waves are used to excite the BIC mode, and an eigenmode solv- er with finite element method is used to calculate a band struc-

ture and Q factor. A periodic boundary condition is added in a horizontal xoy plane, and a perfect matching layer (PML) is con- structed in a vertical z direction.

Calculating a band and Q value of the metasurface

As shown in FIG. 2{a), the band structure of the proposed Cay structure in a wavelength range of 910nm to 935nm is analyzed, and a normalized wave vector is k=-0.08-0.08. Above a light cone, the

Ca, structure can simultaneously support two BIC modes at T point, namely TM1 mode and TM2 mode.

At the same time, in FIG. 2(b), it can be seen that a quality factor Q corresponding to the TM1 and TM2 modes both achieved their peak values at T point. For the wave vector k#0, the TM2 mode has a higher quality factor Q compared to the TM1 mode, and at k=0, that is, at the T point, the quality factor Q of the TM1 mode is an order of magnitude higher than the quality factor of

TM2 mode. According to the viewpoint of topology theory, a near- field profile shows the different properties of the topological charge. When the number of topological charges in the momentum space is +1, the quality factor Q is shown as a secondary attenua- tion that increases with k of a single isolation topology’s charge state, that is (Qx1/k“). With the change of Bailey curvature of a topological Brillouin zone, the number of topological charges in

TM2 presents multiple topological states of charge, so the attenu- ation of the quality factor Q changes exponentially with a change of an absolute value of a normalized k vector.

In FIG. 2(c), the quality factor Q of the two BIC modes of

TM1 and TM2 increases with the displacement along x direction, and the quality factor Q of the TMI mode is always higher than the quality factor Q of the TM2 mode. In the case of displacement along x and y directions at the same time (FIG. 2(d)), except for the peak value of Q quality factor in the TM1 mode around 65nm, the quality factor Q values of the two modes at other displacement points are not much different. In subsequent studies, the BIC modes of different topological charge states will show a huge dif- ference in a peak shift direction and a polarization phase rota- tion range of the transmitted light in the physical phenomena caused by the changes in in-plane symmetry and out-of-plane sym-

metry.

For the electric field E propagating in z direction in a pe- riodic port, a background field scattering matrix is defined as C, and for the scattering matrix under quasi-BIC: ae

S=C+- s i(0-0,)+1/7 7) wherein, © and w, are uniformly defined by the period and ge- ometric size of the metasurface, and 1 is related to a character- istic quantity & of a disturbance system:

T=O/0, «1/6? (2)

Therefore, it is determined that the scattering matrix in the system can be uniquely determined by the parameter ò, and a dis- turbance factor ò can be precisely controlled by adjusting geomet- ric parameters. This property can be deeply understood from the phenomenon that the C4 symmetric structure is destroyed.

Calculation of the transmission spectrum when the symmetry is destroyed along the x direction

Without inherent loss or symmetry destruction, the symmet- rical protection BIC mode of the TM1 and TM2 wavebands will not be able to couple to external radiation. As crossed rectangular units along the C; axis and C: axis, have displacements of dx and dy in the x and y directions along C; axis and C: axis, respectively,

Cas geometric symmetry destruction will convert the BIC mode to the quasi-BIC mode (super cavity mode). The change of Q quality factor with displacement dx and dy is shown in FIG. 2. At the same time, the spectra corresponding to the TM1 and TM2 modes reveal the different physical mechanisms underlying the two quasi-BIC modes under the p-polarized electric field when the symmetry is destroyed along the x direction.

FIG. 3(a) shows a transmission spectrum of C4, symmetric geom- etry structure with different displacements dx along the x direc- tion. It can be seen from the figure that two resonance peaks cor- respond to the two quasi-BIC modes of TM1 and TM2, respectively.

With the increase of the displacement dx along the x direction, the quasi-BIC mode shows an adjustable characteristic of a Fano resonance line shape, which provides a new idea for polarization control, that is, phase reversal caused by multiple Fano resonanc- es can make a phase of the transmitted light move freely between 0-180°. TM1 and TM2 have quasi-BIC modes with different topologi- cal charges in the momentum space, which leads to different de- grees of attenuation of the Q factor. Thus, it can be observed that as dx increases, a resonant frequency of the TMI mode shows a clear blue shift, while the resonant frequency of the TM2 mode shows a slight red shift, which indicates that destroying the sym- metry along the x direction and adding the disturbance factor will reduce the coupling between the two quasi-BIC modes. In addition, the quasi-BIC mode in the TM1 and TM2 frequency bands of the Cg, geometry structure can show anti-interference characteristics in a narrow frequency band even when the C: axis symmetry is destroyed.

This property is expected to play a role in optical circuit switching equipment, especially for application scenarios such as multi-mode channel switching.

Electric field distributions of TM1 and TM2 modes are shown in FIG. 3(b), and an arrow direction indicates the direction of

Poynting energy flow. It can be seen that a near-field distribu- tion of the quasi-BIC mode is similar to the near-field distribu- tion of the BIC mode. After the structure symmetry is destroyed, the BIC mode can be changed to the quasi-BIC mode, so that obvious resonance peaks can be observed in the transmission spectrum.

Herein, monochromatic beams defined by E(r, t) and H(r, t) in free space and their standard complex representations are given:

E(r‚1) =Re[ E(r)e™ (3)

N Niet

H(r,?) = Re| H(r)e™ | (4)

The definition of Poynting's energy flow can be written in

Gaussian units: s=cg(ExH) (5) wherein, g=(47)

Correspondingly, two variables x and ¢ which characterize the polarization state of an optical activity metasurface can also be expressed as: cg ¢=—=[Ex(VxH)-Hx (7 xE)] 02 (6) cg r=—=|E-VxE+H -VxH] @ 2 (7)

Furthermore, symmetry equations obtained from continuum equa- tions can express a close relationship between flow density and the polarization state of the optical rotation.

As shown in FIG. 3(a), it can be seen intuitively that the increase in the displacement dx along the x direction will reduce the quality factor 9, the BIC mode will change to the quasi-BIC mode, and the Fano resonance peak will also change accordingly, which shows that by controlling the in-plane symmetry and out-of- plane symmetry of the metasurface structure with the quasi-BIC mode, the line shape of the Fano resonance can be flexibly adjust- ed, thereby further explaining the mechanism of asymmetric reso- nance shape caused by the mutual interference of resonance re- sponse (even a polar state) and edge state.

Calculation of the transmission spectrum when symmetry is de- stroyed at the same time along the x and y directions (dx = dy)

When the displacements dx and dy along the x and y directions are equal (FIG. 1(b)), the transmission spectrum of the proposed

C4, symmetric structure is shown in FIG. 4(a). The resonance peak caused by the TM2 mode is almost fixed at 923 nm, while the quasi-

BIC mode of the TM1 waveband shows the blue shift characteristic.

The destruction of symmetry will cause single-mode adjustment. Be- cause of multi-mode manipulation, it has broad application pro- spects in the direction of optical circuit devices and crystal fi- bers. A spectral distance between the two resonances can be con- trolled through this independent tunability, so as to further re- alize the precise control of the phase by adjusting the Fano line shape of an incident wave.

Then, as shown in FIG. 1, the displacement conditions are changed and the rectangular silicon units of the C+ unit are moved in the x and y directions to create a displacement dx=dy along the x and y directions. The finite element method is used once again to perform numerical simulation on the transmission spectrum to analyze the metasurface, and the result is shown in FIG. 4(c). It is worth noting that, in the case of less than 40nm, a transmis- sion line under the condition of dx=dy shows very good single-mode adjustability. The resonance response caused by the quasi-BIC mode of the TM2 waveband is fixed at the frequency point of 923nm, and the resonance response caused by the quasi-BIC mode of TM1 wave- band is blue-shifted over the wider band of 900nm-916nm. The sin- gle-channel sensitive adjustment is a very promising feature. Be- cause of the avoidance of multi-mode mutual interference during the adjustment process, it is widely used in optical circuit switching devices and crystal fibers. In addition, the spectral distance between two resonance responses is controlled through this independent controllability, thereby further adjusting the

Fano line shape and phase of the incident wave.

Optical rotation polarization control of Fano metasurface

According to the equation derived from a Jones matrix, it can be known that according to the geometric structure of the C4, crys- tal shown in FIG. 1, the structure has different displacements on a fast axis and a slow axis. Therefore, the C4 crystal has optical rotation, which is actually a kind of birefringent crystal. When the linearly polarized light in the x direction is incident on an optical rotation medium, the optical axis will produce completely different rotation angles at the two frequency points of the BIC mode in the near-infrared region, and has tunable characteristics.

Because a linearly polarized wave is incident from the x direc- tion, a simple xoy coordinate system is defined herein, as shown in FIG. 1, the angle of ¢ which is a rotation angle of the polar- ized light and the ellipticity x constitutes two main parameters, which define the polarization ellipse. The angle p is the rotation angle of the polarized light, and together with the ellipticity x constitute the two main parameters that define the polarization ellipse.

The general expression is:

IVe cos(p) —sin(g) || cos(y) | | cos(@)cos(y)~isin(@)sin(y) 25 : 5) - ns cos(¢) | sin( 4 Bh oe cos( x) +1icos(g)sin( D) (14)

Therefore, the changes of a principal axis angle (optical ro- tation) and ellipticity under different dx and dy conditions are calculated, and a curve image is drawn as shown in FIG. 5.

When the displacement dx along the x direction changes from 5nm to 60nm and the displacement along the y direction is fixed at (dy=60nm), the resonant frequency of the TM1 waveband is red- shifted 926.7nm from the wavelength of 922nm, and the optical ro- tation angle increases first and then decreases in the range of 25°~55, indicating that the electric field polarization direction falls into [g=0°-90°] quadrants I and III. Unlike the TM1 mode, the resonant frequency of the TM2 waveband has the blue shift in the wavelength range of 897.5nm to 887.8nm. The reason for this phenomenon can be attributed to: these two quasi-BIC modes have different topological charge distributions, which also cause dif- ferent responses of optical rotation. Due to the light-matter in- teraction caused by the TM2 mode, the optical rotation decreases from 175° to 135°, which indicates that the electric field polari- zation direction falls into [p= 90°-180°] quadrants II and IV.

When the displacement change exists in the y direction, that is, the displacement of dy changes from 5nm to 60nm and the fixed displacement dx=60nm, the optical rotation and transmittance show different optical rotation trends, and the response wavelength of the TM1 waveband is blue-shifted from 926nm to 921nm, The light angle is first reduced from 65° to 30°, and then increased to 45°.

The transmittance is as high as 0.8 at the displacement of dy=5nm.

When the displacement of dy is increased, the resonance peak of the TM2 waveband shifts from 897.5nm to 887.8nm. For the TM2 mode, with the displacement dy=5 to 60 nm increment, the optical rota- tion angle gradually decreases from 180° to 145°, and the trans- mittance increases from 0 to 0.5. Therefore, the multi-BIC mode can adjust the optical activity, which provides a lot of freedom to manipulate the optical rotation of linearly polarized light over the entire quadrant.

The ellipticity x is also extracted and displayed in the fig- ure. The results show that even for different rotation angles, the

TM1 mode maintains a strong linear characteristic. When linearly polarized light passes through the metasurface, the transmitted light is still linear. For the TM2 mode, the ellipticity with a small displacement of dy=5nm is x=55°, and then the ellipticity decreases to 0° as the displacement dy increases, which will gen- erate LCP and RCP light, thereby providing circular dichroism res- olution. By breaking the symmetry of the C,, metasurface along the x and y directions, the metasurface with different in-plane sym- metry and out-of-plane symmetry when linearly polarized light is incident at the BIC response frequency point, the transmittance, the principal axis angle (9) and the ellipticity (x) defined in the process of optical rotation have different laws. The huge dif- ference is caused by the different topological charge states of

BIC. By controlling the number of topological charges, the states of combination and separation of topological charges are further extended to light field control. And this phenomenon is expected to extend to the direction of circular dichroism control and non- linear optical control, and provide a theoretical and practical basis for light field control in the field of optical communica- tions in the future.

The present disclosure intends to propose a new type of opti- cal path control element and further enhance the polarization con- trol ability of the metasurface. Based on a BIC topology charge theory, a new type of C4 metasurface structure with two independ- ent BIC response frequency points in the near-infrared waveband is proposed. In summary, its advantages are as follows: 1. The C4, metasurface has two BIC modes with different topo- logical charges in the near-infrared waveband. By controlling the in-plane symmetry and out-of-plane symmetry of the structure, the

Fano linearity can be well tuned, and further the mechanisms of the resonance response (dipole state) and the boundary state in- terfering with each other to produce the asymmetric resonance shape are explained and verified. 2. By adjusting the in-plane symmetry and the out-of-plane symmetry, the transmission spectrum of the metasurface in the near-infrared waveband presents a single-mode tunable property, that is, for multiple resonant peaks, only one of the peak posi- tions is tuned while leaving the rest of the peak positions sta- tionary. Through this independent tunability to control the spec-

tral distance between the two resonance peaks, this metasurface has the potential to be used in the fields of optical circuit de- vices and optical circuit switches. 3. The quasi-BIC mode is innovatively applied to the field of polarization control of optical rotation, which greatly enhances the controllability of the phase rotation of the transmitted light, and the optical rotation expands from 0-90° to 0-180°, and at the same time, the extremely high Q value also means the super sensitive response and high transmission efficiency of light, which provides a new idea for the phase control of the polariza- tion state of the light field. 4. The proposed C4, structure has simple composition, conven- ient crystal preparation, high feasibility in actual experiments and production, which is easier to achieve numerical simulation results, and has high practical value.

The present disclosure uses a two-dimensional metasurface to control the polarization and phase of light, and at the same time, the metasurface can also act as an optical circuit device such as an optical switch. After the incident linearly polarized light passes through the designed metasurface medium, it will have the property of total transmission in a specific waveband, and with the change of the metasurface structure (dx dy), the frequency point of the total transmission can be adjusted and has a single mode adjustability, used to design optical path control devices with good performance. On the exit surface, the incident light will undergo polarization phase adjustment (optical rotation) at the corresponding response frequency point. The difference of the change effect depends on a degree of change of dx and dy and the choice of mode (TM1 and TM2), which makes the light field control very flexible, and can conveniently output different phase infor- mation at different adjustable frequency points for imaging dis- play and sensing in the near-infrared waveband.

It should also be noted that the terms “comprise”, “include” or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, product or equipment includ- ing a series of elements not only includes those elements, but al- so includes other elements that are not explicitly listed, or in-

clude elements inherent to such process, method, product or equip- ment. If there are no more restrictions, the elements defined by the sentence “including a...” do not exclude the existence of oth- er identical elements in the process, method, product or equipment that includes the element.

The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embod- iment focuses on the differences from other embodiments. In par- ticular, as for the system embodiment, since it is basically simi- lar to the method embodiment, the description is relatively sim- ple. For related parts, please refer to the part of the descrip- tion of the method embodiment.

The above descriptions are only embodiments of the present disclosure, and are not intended to limit the present disclosure.

For those skilled in the art, the present disclosure can have var- ious modifications and changes. Any modification, equivalent re- placement, improvement, etc. made within the spirit and principle of the present disclosure shall be included in the scope of the claims of the present disclosure.

Claims

CONCLUSIONS

A square grating meta-surface resonator with adjustable optical rotation and polarization, comprising a plurality of cross structures composed of two intersecting cubes, where a length of the cross structures is 370 nm, a width of the cross structures is 100 nm and a thickness of the cross structures is 320 nm; wherein the plurality of cross structures are arranged side by side and a distance between two adjacent cross structures is 475 nm; wherein the square lattice metasurface resonator has quadruple rotational symmetry; wherein a material of the square lattice meta-surface resonator is silicon, the refractive index of which in a near-infrared region is 3.58; wherein the meta-surface square-lattice resonator has two independent response frequency points of bound states in continuum in a near-infrared waveband.

A square grating metasurface resonator according to claim 1, wherein a transmission spectrum of the square grating metasurface resonator in the near-infrared waveband exhibits a tunable property in single mode by in-plane symmetry and symmetry off-plane adjustment.

The square grating metasurface resonator according to claim 1, wherein a range of optical rotation of the square grating metasurface resonator is 0° to 180°.

A square grating meta-surface resonator according to claim 1, wherein a line shape of Fano resonance is flexibly adjusted by controlling in-plane symmetry and out-of-plane symmetry of a meta-surface structure with a quasi-BIC mode -

len.

5. Metasurface resonator with a square lattice according to con-

claim 1, wherein a polarization state of the square grating metasurface resonator is adjustable, which is changed from linear polarization to elliptical polarization.