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Abstract
We use a single-layer thick metallic metasurface to design the 0-,45- and 90-degree polarizers with transmission efficiencies exceeding 95% based on the bright electric dipole resonance and dark magnetic dipole resonance. In addition, we utilize a bilayer metallic metasurface (forming an efficient Fabry-Perot resonator) to propose a circularly polarizing dichroism waveplate (CPDW). The circular polarization dichroism (CPD = IRCP − ILCP.) in the transmission mode at 1.6 µm wavelength reaches 89% and the extinction ratio (ER = IRCP/ILCP) is 830:1. These four polarizing elements are integrated to form a full Stokes pixel that almost accurately measures arbitrary polarized light at λ0 = 1.6 µm (including elliptically polarized light).
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
The polarization of light contains a lot of useful information, and it has a broad prospects in photonic communications [1], satellite remote sensing [2] and bio-optical imaging and sensing [3]. The polarization imaging ideas are mainly divided into three categories: division of amplitude, division of aperture, and division of focal plane. Compared with division of amplitude and division of aperture, division of focal plane does not need to build complicated optical paths and is easier to integrate with semiconductor detectors [4]. However, due to the lack of the circularly polarizing dichroism waveplate (CPDW) with excellent performance, the existing polarization cameras can only effectively measure the first three components in the Stokes matrix [5–7]. Therefore, how to design a circular dichroism device with large circular dichroism, high extinction ratio, large bandwidth, and easy integration with semiconductor processing technology is now arousing extensive exploration.
Metasurface consisting of a planar array of meta-atoms with subwavelength period can flexibly and precisely control the phase and polarization information of light [8–10]. There have been many reports on the use of metasurface to design the circularly polarizing dichroism waveplate [11–17], and the geometric shapes of their unit cells can be two-dimensional Archimedean spirals [18,19], fishline-shaped metallic nanoparticles [20,21] and Z-shaped Si patches [22], etc. In addition, many circular polarizers made of three-dimensional chiral metamaterials [23–30] have also been reported. Although two-dimensional circular polarizers are easy to integrate with other optoelectronic devices, their extinction ratio may be not large enough, which limits the further development of full-Stokes imaging polarimetry [16,31–37].
In this article, we numerically demonstrate that a metallic metasurface composed of thick metal rod with a very small aspect ratio (depth/width ∼0.95) can be designed as a linear polarizer, and its excellent transmission and extinction ratio are closely related to the two resonance modes: a dark magnetic resonance [38] and a bright (electric dipole) ED response. To my best of knowledge, terminology like the bright and dark modes is first used to design plasmon polarizer. In traditional optics, the combination of a quarter-wave plate and a polarizer with a special orientation can have an extinction effect on left circularly polarized light [39]. We extract this idea and realize a high-performance circularly polarizing dichroism by adjusting the geometric parameters of the bilayer metallic metasurface. One metallic metasurface whose unit cell is U-shaped gold nanoparticle implements the function of phase retarder, and the other metallic metasurface whose unit cell is gold rod represents the 45-degrees polarizer. The full Stokes super pixel composed of four small pixels can achieve almost accurate measurement for arbitrary polarized light (including elliptically polarized light) at 1.6 µm wavelength. Moreover, this super pixel is likely to integrate with the infrared focal plane detector, which is expected to promote development of infrared polarization detectors.
2. Structure and analysis
Fig. 1. (a) shows a schematic diagram of four small pixel unit cells. All substrates are the SiO2. Numbers 1, 2, 3, and 4 represent 90-degree, 0-degree, 45-degree polarizers, and a circular dichroic device consisting of the SiO2 substrate, the U-shaped gold nanostructures submerged in SiO2 spacer and gold nanorods, respectively. (b) is a top view of a circular dichroic device consisting of a U-shaped structure and a rectangle. P1 = 850 nm, L1 = 690 nm, L2 = 70 nm, L3 = 700 nm, w1 = 240 nm, w2 = 60 nm, w3 = 200 nm, $\mathrm{\theta }$ =Pi/4. Figure 1(c) is a front view of a circular dichroic device. P1 = 850 nm. h1 = 85 nm, h2 = 1880nm, h3 = 230 nm. (d) and (e): the top and front views of a 90-degree polarizer, respectively. P1 = 850 nm, a1 = 640 nm, b1 = 240 nm, c1 = 230 nm. (f) and (g): the top and front views of a 45-degree polarizer, respectively. P1 = 850 nm, a2 = 700 nm, b2 = 200 nm, c2 = 230 nm, $\mathrm{\theta }$ =$\mathrm{\pi }/4$. The yellow for the gold, and other colors for the SiO2 layer.
It is shown in Figs. 1 that the geometric parameters of the unit cells of the four proposed metasurfaces are specified respectively. However, the 0-degree polarizer is not shown, because it can be obtained by turning the 90-degree polarizer 90-degrees counterclockwise. The refractive index of the SiO2 layer in the near infrared is 1.46, and the dielectric constant of gold is derived from Ref. [40]. The finite element method is employed to analyze the optical properties of these metasurfaces. The direction of the incident light is from the SiO2 substrate to the air medium. We use the perfectly matched layer (PML) and the waveguides port as the boundary condition in the z-axis direction. In addition, the periodic boundary condition is applied along the x and y directions, and S-parameters of the transmitted light are extracted to get the corresponding amplitude and phase information.
Fig. 2. The influence of geometry parameters on the extinction ratio of the device. (a-d) correspond to the geometric parameters a1, b1, c1 and p1 of the 90-degree polarizer respectively, and the incident light is x-polarized light and y-polarized light. (e-h) correspond to the geometric parameters L1, L2, w1 and w2 of the circular polarizer respectively, and the incident light is left circularly polarized light and right circularly polarized light. The extinction ratio is proportional to the logarithm of the ratio of the transmittance of the device in two orthogonal directions.
The design tunability of device by scaling up or down the dimensions is very important to follow. Figure 2 shows the effect of some geometric parameters on the device performance. When one parameter is studied, the remaining parameters are consistent with those in Figs. 1. Figure 2(a) shows the effect of the gold rod length a1 on the extinction ratio of the 90 ° polarizer. It is seen that the resonant peak of the extinction ratio shifts sensitively towards longer wavelengths with the increased length a1, whereas a resonant valley at 1.28 µm induced by the Rayleigh resonance formed at the interface between metasurface and SiO2 substrate does not change. On the contrary, the resonant peak in Figs. 2(b) blue shifts as the width b1 increases. As shown in Figs. 2(c), when the height c1 is less than 330 nanometers. The resonance peak blue shifts as the height c1 increases. However, when the height c1 is greater than 330 nanometers, the resonance peak will split or broaden, and these phenomena may be due to the excitation of high-order electric dipole moments. Figure 2(d) shows that both the resonant peak and the resonant valley have redshifts as the period p1 increases. To reduce the difficulty of investigating the influence of geometrical parameters of circular polarizers on extinction ratio, we only discuss the geometric parameters of U-shaped nanostructures. Figure 2(e) shows that two resonant peaks with different intensities are both red-shifted as the arm length L1 increases, whereas it is seen in Figs. 2(f) that geometric parameter L2 has no effect on the extinction ratio of the circular polarizer. As shown in Figs. 2(g), the resonance peak near 1.6 µm will not be red shifted or blue shifted with the change of the arm width w1 except w1 of 540 nm. However, the peak intensity of the extinction ratio of the device will change significantly, which means that the parameter w1 must be carefully scanned for optimal performance during the simulation process. Figure 2(h) shows that when the arm width w2 is greater than 120 nm, the device performance is significantly reduced. In summary, Figs. 2(a)–2(d) indicates that polarizer with operation wavelengths from 1.3 to 1.85 µm can be obtained by simply varying geometric parameters of gold rod. Figures 2(e)–2(h) shows that it is difficult to obtain the design tunability of circular polarizer only considering the change of a single geometric parameter, and it may need to investigate the changes of several parameters at the same time to know what factors limit the extension of operation wavelength.
As shown in Figs. 3(a), it is obvious for the 90-degree polarizers that the extinction ratio reaches the maximum at the wavelength of 1.6 µm, which is 42dB. Here, $\textrm{ER} = 10\textrm{log}({{I_{TM}}/{I_{TE}}} ), {I_{TM}}\;\textrm{and}{I_{TE}}$ are transmission intensity for the TE and TM incident light, respectively. Figure 3(b) shows the transmittance and extinction ratio for the 45-degree polarizers. It can be concluded that the average extinction ratio is greater than 24dB in the wavelength range of 1350 nm to 2050 nm. The phenomena in Figs. 3(a) can be explained by the field distribution and current distribution depicted in Figs. 3(c${\sim} $i). It is seen from Figs. 3(c) that the fact that the sign of the electric charge at both ends of the metal bar is opposite indicates a pure electric dipole (ED) response. The field direction of the metal bar in Figs. 3(d), 3(g), 3(e) also shows that the unit cell of metasurface can be approximated as an electric dipole for the TE incident light. However, Figs. 3(h), 3(f), 3(i) shows that the gold rod can be regarded as a magnetic dipole for the TM incident light. In the case of the TE incidence at $\mathrm{\lambda } = 1.6$ µm resonant wavelength, it is seen that very strong electric field localization happens on the surface of the metal rod. In contrast, in the case of the TM incidence, negligible electric field localization can be found at all the different cross sections. It can be concluded that the electric dipole resonance is a bright mode which can have strong optical interaction with the TE incident light, which results in almost no energy existing in the transmission mode. Furthermore, the transmission valley at 1.08 µm for TE incident is supposed to be caused by surface plasmon polaritons (SPPs) mode between the gold rod and the SiO2 film. However, the magnetic dipole resonance is a dark mode, which has no blocking effect on the incident light and almost all the energy is transmitted, so a huge extinction ratio occurs, as witnessed in Figs. 3(a). Moreover, the bright and dark mode are widely used in the Fano Resonances to form asymmetric spectrum [41]. Table 1 shows the metal rod grating controlled by electric dipole and magnetic dipole mode may have more advantages in extinction ratio and efficiency than wire grating polarizer, and although dielectric coated metal grating [42] has an extinction ratio several orders of magnitude higher than other polarizers, the efficiency of less than 10% limits its promotion. In addition, considering that the optical resonance mode excited by metal rod grating is similar with the Fano resonance mode, the metasurface composed of thick metal rod may be designed as a sensor sensitive to the surrounding environment.
Fig. 3. Spectral response, field and current distributions of the linear polarizer. Figures 3(a) and 3(b): The transmittance and extinction ratio as a function of wavelength for 90-degree polarizer and 45-degree polarizer. (c): Charge density distribution and bulk current density of the metal rod for the TE light for 90-degree polarizer. (d-i): The field distribution of the cross section passing through the center of the metal rod for 90-degree polarizer at $\mathrm{\lambda } = 1.6$ µm. The white arrow presents the direction of the corresponding field, and the red represents the direction of the current.
Table 1. Performance of linear polarizer.
In classical optics, a combination of a quarter-wave plate and a polarizer with a special orientation can have a significant extinction effect on left circularly polarized light. This idea is applied to propose a bilayer metallic metasurface constructing a circular dichroic device. Thick metal rods, a counterpart of the 45-degree polarizer, and U-shaped nanoparticles, a counterpart of wave plate, make up the unit cells of the bilayer metasurface. Figures 4(a) and 4(b) show that the transmission intensity depending on the thickness of the SiO2 spacer (h2) and the geometric parameter (w1) for the RCP and LCP incident light, respectively. By finding a pair of parameters corresponding to the maximum value in Figs. 4(a) and the minimum value in Figs. 4(b), the optimal structure of the circular dichroism device can be determined. Figure 4(c) illustrates the transmittance and extinction ratio as a function of wavelength for the RCP and LCP incident light. In the range of 1550 nm to 1690 nm, the average transmittance for the right circularly polarized incident light reaches 0.85, whereas the average transmittance for the left circularly polarized incident light is lower than 0.1. In addition, it is particularly noteworthy that the extinction ratio reaches a maximum 33dB at ${\lambda _0} = 1595nm$, and average circular polarization dichroism (CPD) are 0.5 and 0.35 for operation bandwidth of (1250∼1350 nm) and (1900∼2300 nm), respectively. Therefore, the configuration shows a circularly polarizing dichroism waveplate operation.
Fig. 4. Spectral response and transmittance for the circular dichroic device. Figure 4(a) shows the transmittance as a function of w1 and h2 for the RCP incident light. (b): The transmittance for the LCP incident light. (c): The transmittance and extinction ratio as a function of wavelength for the RCP and LCP incident light. (d-g): The magnetic field distribution at 1.6 µm wavelength at different cross-sections of the SiO2 spacer with different circularly polarized incidences on a left-handed gold chiral structure. (h-k): The electric field distribution at 1.6 µm wavelength. The white dotted line is the outline of the metal.
The special circular dichroism of this configuration can be also expressed by handedness of structure. A combination of ‘U-shaped’ nanoparticles and a gold bar whose long axis has a deflection angle of 45 degrees to the X axis is chiral in structure. Figures 4(d)–4(g) and Figs. 4(h)–4(k) show the field distribution of corresponding cross-section. In the case of LCP incidence at 1.6 µm resonant wavelength, it is seen that very strong standing wave occurs within the SiO2 spacer due to the strong coupling interaction when the handedness of incident circular polarization and the handedness of structure matches, and it can be explained by Fabry-Perot (FP) resonances between ‘U-shaped’ nanoparticles and a gold bar, satisfying $2{k_z}{h_1} + 2{\mathrm{\Phi }_R} = 2m\pi $, where m is an integer and ${\mathrm{\Phi }_R}$ is the phase picked up by the waveguide mode by reflection at each of the openings. In addition, ${\mathrm{\Phi }_R}$ can be expected to satisfy $2{\mathrm{\Phi }_R} \approx{-} 2\pi$ due to the strong impedance mismatch between the SiO2 spacer and the metal metasurfaces. Figures 4(d) and 4(f) indicates that there are three periods for absolute value of the magnetic field intensity (The absolute operator can reduce the size of period by half). Figures 4(h) and 4(j) shows there are three periods for absolute value of the electric field intensity, so ${k_z}{h_1} = 1.5\ast 2\pi $ and m=2. Moreover, it is seen in Fig. 4(j) that a strong local field enhancement coupled with adjacent units occurs near the U-shaped gold nanoparticles. We speculate that the FP resonance cavity composed of a U-shaped metasurface induced by special strong local electric field coupling, a metasurface at the upper layer and the SiO2 spacer can have an extinction effect on the left polarized light at 1.6 µm wavelength. It is evident that transmission valley happens at 1.6 µm resonance wavelength corresponding to m=2 FP resonance. Furthermore, transmission valley at 1.32 µm and 1.98 µm are expected to correspond to m=3 and m=1 FP resonance, respectively. In contrast, in the case of RCP incidence, negligible optical response can be seen, which implies that no strong coupling interaction occurs in the case of opposite handedness of the chiral structure and polarized incidence. It is seen in TableFigure 2 that the circular polarizer we designed has the highest extinction ratio.
Table 2. Performance of the circular polarizer.
Angle of incidence and numbers of unit cell of metasurface are crucial for practical use in imaging polarimetry. Figure 5 investigates the influence of incident light angle and unit cell number on the performance of nanostructures. To simplify the research problem, we only discuss the case where the incident plane of light lies in the x-z and y-z planes. Figure 5(a) shows the functional relationship between the extinction ratio and the wavelength is almost the same when the incident angle is less than 10 degrees, and the resonant peak of the extinction ratio redshifts with the increase of the incident angle when the incident angle is greater than 10 degrees. Figures 5(b)–5(d) indicates that the intensity of resonance peak near 1.6 µm decreases with the increase of incident angle when the incident angle is less than 10 degrees, whereas the resonant peak of the extinction ratio is broadened or split when the incident angle is greater than 10 degrees, which will greatly reduce the performance of the device. The first element n in the symbol (n, N) in Figs. 5(e) and 5(f) represents n unit cells in the x-direction dimension, and the second element N represents N unit cells in the y-direction dimension, where n can be any integer, and N represents infinity. Scattering boundary conditions are used on both sides of the dimensional direction corresponding to n, and periodic boundary conditions are used on both sides of the dimensional direction corresponding to N. As shown in Figs. 5(e) and 5(f), In all the curves, the extinction ratio increases with the increase of the number of cells, and the slope of (n,n) is smaller than the slope of the other two curves. We can boldly predict that when n is equal to 100 (the device footprint is 85 by 85 µm), the device will have good performance.
Fig. 5. Extinction Ratio (ER) for angle of incident and numbers of unit. The extinction ratio in Figs. 5(e,f) does not add a logarithmic operator, The incident angle is the angle between wave vector and Z axis. (a): ER for the 90 ° polarizer, the incident plane is the x-z plane. (b): ER for the 90 ° polarizer, the incident plane is the y-z plane. (c): ER for the circular polarizer, the incident plane is the x-z plane. (d): ER for the circular polarizer, the incident plane is the y-z plane. (e): ER for the 90 ° polarizer. The incident light wavelength is 1.6 µm. (f): ER for the circular polarizer. The incident light wavelength is 1.6 µm. The number of cells in Figs. 5(e,f) is only limited by the computing capacity of our server during the simulation process.
3. Result and discussions
In the preceding sections, we have discussed the extinction capabilities of the corresponding optics components, and we have thoroughly studied the optical properties of the thick gold rod. In this section, we demonstrate the full-Stokes imaging polarimetry using the nanoparticles dimensions of Sec. 2. To our knowledge, four pixels can measure all the polarization information of the polarized light in classic optics, and their corresponding Jones matrices are $\left[ {\begin{array}{cc} 1&0\\ 0&0 \end{array}} \right], \left[ {\begin{array}{cc} 0&0\\ 0&1 \end{array}} \right], \left[ {\begin{array}{cc} {0.5}&{0.5}\\ {0.5}&{0.5} \end{array}} \right]$ and $\left[ {\begin{array}{cc} {0.5\ast i}&{0.5}\\ {0.5\ast i}&{0.5} \end{array}} \right]$, respectively. In addition, $\left[ {\begin{array}{cc} {0.5\ast i}&{0.5}\\ {0.5\ast i}&{0.5} \end{array}} \right] \ast \left[ {\begin{array}{c} 1\\ { - i} \end{array}} \right] = 0^{\ast} \left[ {\begin{array}{c} 1\\ { - i} \end{array}} \right]$, which indicates that the polarizing element corresponding to this jones matrix has a complete extinction effect on left circularly polarized light. Therefore, this imaging polarimetry systems can determine the Stokes vector $\textrm{S} = [{{S_0},\; \; {S_1},\; \; \; {S_2},\; \; {S_3}} ]$, where the components are calculated as ${S_0} = I, {S_1} = {I_x} - {I_y}, {S_2} = 2{I_{{{45}^0}}} - {S_0}, {S_3} = 2{I_{CPDW}} - {S_0}.$ Here I is the total intensity and ${I_x}, {I_y}, {I_{{{45}^0}}}$ and ${I_{CPDW}}$ are the transmitted light intensities for corresponding polarizing components, respectively. It is worth noting that the measurement scheme of four pixels may make complementary pairs of pixels have different efficiencies, so we prefer to use 6 pixels to measure full-Stokes parameters for practical application.
To verify the correctness of the circular dichroic device we designed in Section 2, we used the TE and TM incident light to excite the bilayer metallic metasurface to obtain corresponding Jones matrix. It is assumed that the Jones matrix of the polarization element is $\left[ {\begin{array}{cc} {{T_{xx}}}&{{T_{xy}}}\\ {{T_{yx}}}&{{T_{yy}}} \end{array}} \right]$, which can be obtained by extracting the S-parameters. As shown in Figs. 6(a), the absolute values of four elements of the Jones matrix are equal to 0.47 at 1.6 µm wavelength. Moreover, the cross-polarization conversion efficiency is as high as 22%, which is only 3% less than the theoretical maximum conversion efficiency of thin metallic metasurface [46]. Figure 6(b) shows the phase difference depending on wavelengths. When the wavelength is 1.6 µm, $\textrm{arg}$(${T_{xx}}/{T_{xy}}$) and $\textrm{arg}$(${T_{yx}}/{T_{yy}}$) are both $\mathrm{\pi }/2$, and $\textrm{arg}$(${T_{xx}}/{T_{yx}}$) is zero. From the two figures above, we can draw the conclusion that the Jones matrix of the circular dichroic metasurface we designed is $\left[ {\begin{array}{cc} {0.47\ast i}&{0.47}\\ {0.47\ast i}&{0.47} \end{array}} \right]$. Except for the amplitude reduction caused by ohmic loss and negligible reflection, its Jones matrix is the exactly same as one that is the combination of a quarter-wave plate and a 45-degree polarizer in classic optics. Therefore, this polarizing element will have an excellent extinction effect on left circularly polarized light at 1.6 µm wavelength.
Fig. 6. Jones matrix parameters for the circular dichroism devices. (a): Transmission as a function of wavelength, the yellow dotted line corresponds to the intersection of the absolute values of the four components of the Jones matrix. (b): Phase difference as a function of wavelength.
Due to the ohmic loss of the metallic metasurface, the derivation formula of the corresponding Stokes vector will change. The Jones matrix of these four small pixels can be expressed as $\left[ {\begin{array}{cc} {{p_1}}&0\\ 0&0 \end{array}} \right], \left[ {\begin{array}{cc} 0&0\\ 0&{{p_2}} \end{array}} \right], \;0.5 \left[ {\begin{array}{cc} {{p_3}}&{{p_3}}\\ {{p_3}}&{{p_3}} \end{array}} \right], \;0.5 \left[ {\begin{array}{cc} {{p_4}\ast i}&{{p_4}}\\ {{p_4}\ast i}&{{p_4}} \end{array}} \right]$, respectively. where ${p_1}\; ,{p_2}\; ,{p_3}$ and ${p_4}$ are real numbers. The components of the Stokes parameter are defined as:
Here, ${I_1}, {I_2},\; {I_3}$ and ${I_4}$ are the transmission intensities of linearly polarized light interacting with 0-degree, 90-degree, and 45-degree polarizers and circular dichroic devices, respectively. (See the literature [39] for the detailed derivation process.) For convenience, S1, S2, and S3 are normalized to S0. We used the linearly polarized light that is represented by L and $\mathrm{\theta }$ to illuminate the four small pixels. Here, L is the quotient of the projection of the electric field amplitude in the X and Y directions, and $\mathrm{\theta }$ is the phase difference between the electric field in the Y-axis and X-axis directions. The transmitted light intensities obtained by integrating the power flux over a transmission port are brought into Eqs. (1)–(4) to derive the full Stokes parameter. Figure 7 demonstrates the theoretical and numerical solution of the full Stokes parameters, it is seen that the full Stokes pixel we designed has an almost accurate detection for 1.6 µm linearly polarized light. It extends our detection field to circularly polarized light that cannot distinguished by traditional infrared detection devices, which greatly enhances our detection dimension.Fig. 7. Results of theory and numerical solution of the Stokes parameters for different linearly polarized incidence. Light yellow for theoretical value, and Pale blue for numerical solution of FEM.
A quantitative comparison is necessary by extracting the average errors for S1, S2 and S3. The theoretical Stokes parameter is represented by (${D_0},{D_1},{D_2},{D_3}$), and the Stokes parameter obtained by the finite element algorithm is (${S_0},{S_1},{S_2},{S_3}$). Moreover, errors for the degree of linear and circular polarizations are defined as $\left|{\left|{\sqrt {S_1^2 + S_2^2} /{S_0} - \sqrt {D_1^2 + D_2^2} /{D_0}} \right|} \right|$ and $|{|{{S_3}/{S_0} - {D_3}/{D_0}} |} |$, respectively. Here, $|{|\textrm{x} |} |$ indicates that the absolute value operator acts on the element x. Figure 8 shows largest error of linear polarization occurs in the case of left circularly polarized incident light, which is 6.7%. In addition, largest error of circular polarization occurs in the case of y polarized incident light, which is 5.1%. If the square of absolute value in literature [31] is used to calculate the error, the error result will be lower. Such a low error polarimetric is likely to be widely used in the field of biosensor and communication.
Fig. 8. the error for degree of linear and circular polarizations. The magnitude of the errors in Figs. 8 is the real error multiplied by 100. The incident light is represented by the symbol (L,$\mathrm{\theta }$), L and $\mathrm{\theta }$ follow the definition rules in Figs. 7. Number 1∼12 on the horizontal axis represents the incident light corresponding to (1:0,0), (0:1,0), (1:1,0), (1:1,0), (1:-1,0), (1:1,$- \frac{\pi }{2}$), (1:1, $\frac{\pi }{2}$), (1:3, $\frac{\pi }{6}$), (1:3, $\frac{\pi }{4}$), (1:3, $\frac{\pi }{3}$), (1:5, $\frac{\pi }{6}$), (1:5, $\frac{\pi }{4}$), (1:5, $\frac{\pi }{3}$) respectively.
4. Conclusion
In conclusion, we utilize the single-layer metallic metasurface consisting of the thick gold rod and the SiO2 film to realize the function of 0- degree, 45-degree and 90-degree polarizer, and they all have an average extinction ratio of 33dB in transmission at $\mathrm{\lambda } \approx 1.6$ µm with an operation bandwidth of 100 nm. In addition, a circularly polarizing dichroism waveplate (CPDW) is proposed by using the bilayer metallic metasurface consisting of the SiO2 substrate, the U-shaped gold nanostructures submerged in SiO2 spacer and gold nanorods, and the circular polarization dichroism ($\textrm{CPD} = {I_{RCP}} - {I_{LCP}}$) in the transmission mode at 1.6 µm wavelength reaches 89% and the extinction ratio ($\textrm{ER} = {I_{RCP}}/{I_{LCP}}$) is 830:1. We also numerically demonstrate that the full Stokes large pixel composed of four small pixels can almost accurately measure arbitrary polarized light at 1.6 µm wavelength. We believe that the large pixel designed by us may be easy to integrate with infrared detector, which can extend our detection dimension from intensity to polarization.
Funding
National Key Research and Development Plan (No.2016YFB0402402); Supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB43010000).
Disclosures
The authors declare no conflicts of interest.
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