Metasurface-Based Ultrathin Beam Splitter with Variable Split Angle

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Letter

A metasurface-based ultra-thin beam splitter with variable split angle and power distribution Xingliang Zhang, Ruyuan Deng, Fan Yang, Chunping Jiang, Shenheng Xu, and Maokun Li ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.8b00626 • Publication Date (Web): 13 Jul 2018 Downloaded from http://pubs.acs.org on July 16, 2018

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A metasurface-based ultra-thin beam splitter with variable split angle and power distribution Xingliang Zhang,1 Ruyuan Deng,1 Fan Yang,1* Chunping Jiang,2* Shenheng Xu,1 and Maokun Li1 1

Department of Electronic Engineering, Tsinghua University, Beijing 100084, China

2

Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-

Bionics, Chinese Academy of Science, Suzhou 215123, China

ABSTRACT Metasurfaces are artificial electromagnetic surfaces that consist of subwavelength scatterers in an array configuration, exhibiting exceptional abilities to manipulate electromagnetic waves. Based on the metasurface concept, a novel beam splitter for a single-frequency same-polarization light is proposed in the visible spectrum. Using Metal-Dielectric-Metal (MDM) scattering unit cells, an array of the circular gold nanocylinders with two different diameters is designed and fabricated on the surface which introduces phase discontinuity on the scattering wavefronts. At 240 nm thick, the flat beam splitter can efficiently reflect an incident wave towards two predesigned directions. More importantly, the split angle and power distribution between these two beams can be readily controlled by setting a proper incident angle. Compared to conventional bulky optical components, the ability of this metasurface-based beam splitter would be very desirable in integrated optical systems. KEYWORDS: Metasurfaces, Beam splitter, Ultra-thin, Anomalous reflection, Visible spectrum

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Recently, metasurfaces, which are composed of subwavelength unit cells periodically or quasi-periodically arranged on a tiny chip, open a door to a number of novel devices and applications.1-15 These artificial

surfaces

exhibit

exceptional

abilities

to

manipulate

electromagnetic waves by altering amplitude, phase, and polarization states in desired manners. Through an elaborate arrangement of elements on the ultrathin surfaces, metasurfaces may provide full control over reflected and transmitted fields for a broad range of operational wavelengths ranging from microwave to the visible light.7-11,14-26 They have been previously shown to be of versatile functionality, low loss, ultrathin thickness and light weight. Since many conventional optical components such as lenses and wave plates are designed using volumetric materials, minimizing optical components is a necessity as integrating more and more components onto a single chip for large scale photonic integrated circuits are in demand.27 Although considerable efforts have been made, the photonic integration of conventional components is still quite challenging. The latest development of metasurfaces offers a new way to overcome the aforementioned limitations.7-11 With the progress of micro and nano fabrication, the metasurface-based optical components on a tiny chip can be achieved by using planar silicon processing techniques, which leads directly to achieving ultra-thin optical components. Beam splitters are essential components in photonic systems. A few beam splitters based on metasurfaces have already been presented in previous literatures.28-33 These metasurface-based beam splitters are either based on the frequency difference of the incident wave28-29 or based on the polarization difference of the incident wave30-33 which are applicable to multi-frequency or multi-polarization incident waves from microwave to the visible spectrum. However, for a single-frequency same-polarization incident wave, there are still less splitter designs in the visible spectrum due to design and processing difficulties. Also, beam splitters with variable split 2 ACS Paragon Plus Environment

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angle and power distribution are more necessary in photonic intergration systems due to the flexible and diversified capability of guiding the flow of light. In this paper, we first investigate a metasurface-based beam splitter for a single-frequency same-polarization light in the visible spectrum. Using Metal-Dielectric-Metal scattering unit cells, a 200×200 um2 flat beam splitter is designed, fabricated, and tested. The proposed beam splitter can efficiently reflect the incident light towards two predesigned directions. In contrast to a conventional bulky optical beam splitter, this beam splitter has an ultra-thin thickness (240 nm). Furthermore, the split angle and power distribution of the proposed device can be readily controlled, thus having great potentials in large-scale photonic integrated applications. The basic principle of designing metasurfaces is to introduce field discontinuity along the interface by spatially tailoring the geometries of the scattering unit cells. In general, such field discontinuity allows a full control over the wavefronts of the reflected or refracted beams with great opportunities for novel generation of optical devices, as demonstrated in Figure 1a. Therefore, the first step is to design a proper unit cell that possesses the ability of phase control. An elaborately designed unit cell is illustrated in Figure 1b. A simple composite MetalDielectric-Metal structure is proposed and is appropriate for the planar silicon-based nano processing, thus reducing the difficulty of processing at the nano-scale. Five parameters are used to characterize the geometry of the unit cell structure: p, d, h1, h2 and h3. Parameter p equals to 250 nm (p = 0.4 λ0 , λ0 = 632.8 nm), representing the period of unit cells. Parameter d is a variable, representing the diameter of cylinder on the top layer. By changing the dimeter, the desired compensatory reflective phase can be obtained. h1, h2 and h3 are the thicknesses of cylinder layer (50 nm), dielectric layer (50 nm), and ground layer (130 nm) respectively. The


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material of the top and ground layer is gold, and the dielectric layer is formed by magnesium fluoride (MgF2). Between the layers of different materials, 5-nm-thick titanium (Ti) film is utilized as an adhesion layer. The simulation results of the reflected phases (Figure 1c) obtained by the commercial software CST Microwave Studio (Computer Simulation Technology AG, Framingham, MA, USA) indicate that the proposed unit cell provides the functionality of phase control by varying the diameter of gold cylinders. From the phase response curve, we can see that the reflection phases under normal incidence are equal to -25° and -206°, when the diameters are 80 nm and 180 nm, respectively. The phase difference between these two unit cells approximately equals to 180°. Hence, these two unit cells can be utilized to construct a 1-bit array to realize the desired scattering pattern. Another important factor to consider is the reflection amplitude of unit cells, which has a direct impact on the efficiency of entire optical component. Figure 1d shows the reflective amplitude responses versus the diameters of gold cylinders. For the 1-bit design (d=80/180 nm), the reflective amplitudes are both more than 0.8, which means a high reflection efficiency for the proposed metasurface. The predesigned unit cells are then used to constitute a metasurface array, and a proper method of determining phase distribution is essential here. For a regular beam splitter such as a symmetrical dual-beam splitter or a symmetrical quadri-beam splitter, there are precise theoretical formulas to calculate the phase distribution according to the desired scattering patterns. For an irregular beam splitter, for example, a shaped-beam or an asymmetrical multibeam, an optimization algorithm is more appropriate to determine the phase distribution, such as the Genetic Algorithm (GA), or the particle swarm optimization (PSO) algorithm. It is worthwhile to point out that the metasurface-based beam splitter has more design flexibility, 4 ACS Paragon Plus Environment

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therefore it can deflect the incident light to arbitrary desired directions with an arbitrary beam splitting ratio, which is impossible for a conventional optical beam splitter. Here, we give an example of a basic dual-beam splitter design for concept proof. The incident light is designed to project onto a metasurface with a specific incident angle, and the deviation angle of reflected light with respect to the z-axis is exactly equal to the anomalous reflected angle determined by the generalized Snell’s law,22 λ

λ

θr1 = sin-1 (sinθi + 0 ) , θr2 = sin-1 (sinθi - 0 ) Γ Γ

(Eq.1)

In the Eq.(1), 0 , p, Γ, and θi represent the free-space wavelength, the period of a unit cell, the size of the gradient metasurface sequence, and the incident angle with respect to the z-axis, respectively. By changing the size of the gradient metasurface sequence and the incident angle, the required reflected angle can be achieved. Besides, by changing the incidence wavelength, the deflection angle will also be changed according to the Eq.(1). In addition, the operation bandwidth can be further extend by dispersion engineered spin-orbit interaction.34 The configuration of the proposed metasurface is exhibited in Figure 1a. By periodically arranging ‘-25°’ and ‘-206°’ unit cells in alternative columns, phase variations along the x-axis direction are generated. When the incident light projects onto a metasurface vertically, substituting λ0 = 632.8 nm, Γ = 1000 nm (n = 4, p = 250 nm), and θi =0° into Eq.(1), the deviation angles with respect to the z-axis are calculated as 39.26°. Since the phase gradient along the +xaxis and −x-axis are the same as each other, the reﬂection is directed to two symmetric angles with respect to the z-axis. When the incident light projects onto a metasurface obliquely, the deviation angles of reflected beams change accordingly with the variation of incident angles, and the two reflected beams are no longer symmetric according to Eq.(1). The reflected angles of two beams at different incident angles are listed in Supporting Information Table S1. The designed 5 ACS Paragon Plus Environment

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metasurface covers a 200×200 um2 area and contains 640,000 unit cells in total, which is too large for numerical calculation. In order to reduce numerical calculation work and improve computation efficiency, a smaller array with the same element distribution is simulated to characterize the designed metasurface the size of which is 15×15 um2 containing 3600 unit cells. The distribution of unit cells follows the rules analyzed above, where two columns of ‘-25°’ unit cells and two columns of ‘-206°’ unit cells are distributed alternatively. The numerical simulation is processed in the Matlab platform (Mathworks, Natick, MA, USA) using the antenna array theory, and the detailed calculation method is depicted in Supporting Information. Under normal incidence, the simulated three-dimensional scattering pattern of the metasurface (15 × 15 um2) is depicted in Figure 2a. Two well-defined light beams are clearly formed, indicating the capability of beam splitting for visible light. The simulated reflection angles of the two reflected beams are both 39.21°, which has a good agreement with the calculated angle of 39.26° using theoretical formula depicted in Eq.(1). Under oblique incidence, three different oblique incident angles ( =5°, 10°, 15°) are applied to characterize the oblique incidence performance, and the simulated results compared with the normal incidence results are shown in Figure 2b. With the increase of the oblique incidence angle, the reflection angle of beam one (+x-axis direction) increases gradually, meanwhile the reflection angle of beam two (−x-axis direction) decreases gradually. Also with the incident angle increasing, the divergence angle of reflected beam one increases observably and the divergence angle of the reflected beam two decreases slightly. During the fabrication process, standard electron beam lithography and lift-off process are applied to fabricate the metasurface due to the extremely small feature size. Figure 3a-b shows 6 ACS Paragon Plus Environment

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the pictures of the fabricated metasurface sample from the camera (Nikon) and the scanning electron microscope (FEI, Quanta 400 FEG). The diameters of fabricated cylindrical elements are approximately 110 nm and 200 nm, which have some discrepancies to the designed sizes. The fabrication error has some influence on the reflection efficiency and the phase difference, but the metasurface still has the ability of beam splitting with the same reflection angles as predesigned values, as illustrated in Figure S3. The simulated result shows that the proposed metasurface has a good stability and robustness to split the beam. The reason is that the size of the gradient metasurface sequence (Γ) and the deviation angles of reflected beams don’t change according to the Eq.(1). We measure the fabricated metasurface using a custom-built experimental setup, and the schematic of setup is shown in Figure 4a. The sample is mounted on a platform with a positioning system, ensuring that the incidence light projects onto the center of the metasurface with a desired incident angle. The light source is a Helium-Neon laser (THORLABS, HNLS008R, 2 mW, 632.8 nm). Since the designed metasurface is polarization independent, it is not necessary to align the polarization direction of the laser.

The optical power detector

(THORLABS, PM120D, 50 nW-50 mW) and the camera (QHY 163M, pixel size of 3.8 um×3.8 um, 4656×3522 pixels) are used to detect and characterize the reflected light beams. The distance between laser and sample is 200 mm, and the camera is positioned 150 mm away from the sample to record the light intensity. The measured intensity distribution under normal incidence is shown in Figure S4. Then, the light intensity against different angles is obtained according to the geometrical relationship between the sample and the camera, and the result is presented in Figure 4b. It is shown that the two reflected beams are symmetric approximately under normal incidence. The measured half power beam width (HPBW) of the reflected beam one is 0.162° 7 ACS Paragon Plus Environment

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(39.158°~39.320°) and the measured HPBW of the reflected beam two is 0.156° (−39.324° ~ −39.160°). The beam widths of the reflected lights are very narrow since the electrical size of the designed metasurface is relatively large compared with the small working wavelength. The positions of the laser, the sample and the detectors are precisely positioned on the optical platform, the distances between them are precisely measured, and the reflection angles are obtained according to the geometrical relationship between them. The measured reflection angles of the two beams under normal incidence are both 39.25°, which are in agreement with the designed value (39.26°) and simulation value (39.21°). Then, we define the reflection efficiency as the ratio of the energy of the reflected two beams and the incident power received by the actual sample aperture of 200 × 200 um2. The reflected energy of two beams are detected by optical power detectors directly. Since the beam width of the laser is larger than the sample aperture, the measurement of the actual incident power needs a light-tight metal plate with a small hole of 200 × 200 um2. The probe of the power detector is closely attached to the holed metal plate in order to reduce the effects of diffraction, and the power detector is in the same location with the measured metasurface sample so that the energy passing through the small hole approximately equals to the incident power received by the actual metasurface sample of 200 × 200 um2. The measured light intensities of the two reflected beams under normal incidence are 1.350 uW and 1.362 uW, respectively, and the incident power received by the actual metasurface sample is 13.360 uW. Therefore, the reflection efficiency under normal incidence is about 20.30% according to the measured results. The loss of the reflection efficiency may arise from the phase discretization, quality of materials, fabrication error at nanoscale, and the measurement error. To further improve the deflection efficiency, we can improve the experimental accuracies, in


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addition, draw on the experiences of metasurfaces with high efficiency, such as optical catenary structures35 and concentric apertures36. When the incident light projects onto the sample at oblique angles, the two beams have quite different properties compared with properties during normal incidence. The experimental and simulated reflection angles at different incident angles (5°, 10° and 15°) are shown in Figure 4c. For reflected beam one, the reflection angle increases from 39.25° to 63.25° when the incident angle increases from 0° to 15°. For reflected beam two, the reflection angle decreases from 39.25° to 22.39°. It is obvious that the reflected angles are affected by the incident angle and the reflective phase of the unit cells, and that the split angles can be readily controlled by setting a proper incident angle. The reflected light intensities of two reflected beams under oblique incidence are also measured, and the comparison of experimental and simulation results are shown in Figure 4d. As the incident angle increases gradually, the reflected energy of beam one decreases rapidly and the reflected energy of beam two increases slightly. The variation tendency of the reflected power is mainly determined by the scattering pattern of the unit cell. The scattering pattern of the unit cell is simulated in CST Microwave Studio and the results are shown in Figure S2. When the diameters of the circular cylinders are 110 nm and 200 nm, the unit cells have maximum scattering field intensity in normal direction, and the scattering field intensity decreases when observation direction deviates from the normal direction. For the reflected beam one, the reflection angle increases from 39.25° to 63.25° and the reflected beam gradually deviates from the normal direction, resulting in the rapid decrease of scattering field intensity. On the contrary, the reflection angle of beam two decreases from 39.25° to 22.39° and the reflected beam becomes gradually close to the normal direction, resulting in the slight


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increase of scattering field intensity. The experimental measurements are in good agreement with the simulation results. In conclusion, an optical metasurface has been designed as a beam splitter in the visible spectrum, and the functionality of the beam splitter has been numerically and experimentally demonstrated. The proposed beam splitter exhibits desirable abilities of separating an incident light of single-frequency same-polarization towards two predesigned directions. Furthermore, the split angle and power distribution between two beams can be readily controlled by setting a proper incident angle. Compared to conventional bulky optical components, the beam splitter has a small spatial size (200×200 um2) and ultrathin planar structure (240 nm), which is desirable for large-scale photonic integrated applications.

METHODS Fabrication: The metasurface sample was prepared by standard electron beam lithography and lift-off process. First, a 5-nm-thick titanium layer, a 130-nm-thick gold layer, and a 5-nm-thick titanium layer were deposited on a silicon substrate in sequence using electron-beam evaporation technology. Then, another 50-nm-thick magnesium fluoride layer was developed by optical coating technology to form a dielectric layer. The PMMA-A4 photoresist was deposited by spin coating and baked at 180 °C for 90 seconds. Before the e-beam exposure, a 10-nm-thick chromium (Cr) layer was deposited on photoresist using magnetron sputtering process in order to increase the conductivity of the photoresist. After electron beam exposure, the chromium layer was first removed by corrosive liquid (Ceric ammonium nitrate and nitric acid solution). The sample was then developed in a solution of isopropyl alcohol (IPA) and 4-Methyl-2-pentanone (MP) of IPA:MP = 3:1 for 120 seconds and subsequently rinsed with IPA for 30 seconds and blow-dried with nitrogen gun. After that, a 5-nm-thick titanium layer and a 50-nm-thick gold 10 ACS Paragon Plus Environment

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layer were deposited via E-beam evaporator. Finally, a lift-off process was implemented in acetone solution to form the required metasurface pattern. Simulation: Commercial software CST Microwave Studio and Matlab are used for the metasurface simulations. For the unit cell simulations in CST, periodic boundary condition and plane wave excitation are applied to simulate the reflective phase and magnitude responses in the infinite array environment. The material property of the gold in visible region is acquired from the Material Library of CST, which is called Gold (Johnson)(Optical). The material of magnesium fluoride is self-defined in CST according to the optical property in red light spectrum, whose relative dielectric permittivity is 1.9044. For the array simulations in Matlab, array theory is used to calculate the scattering field, and the details of computational formulas are explained in Supporting Information S2. SUPPORTING INFORMATION The calculated reflected angles using theoretical formula, calculation method of the scattering field using array theory, simulated scattering pattern of the practical fabricated metasurface, and measured reflected beams characteristic under normal incidence. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected] AUTHOR CONTRIBUTIONS X.Z., R.D., F.Y. and C.J. conceived the study; X.Z. performed the simulations, sample processing and measurements, and wrote the manuscript; R.D. performed the simulations and


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analyzed the mechanism; C.J. advised in processing the sample; C.J., S.X. and M.L. advised in preparing the manuscript. All authors discussed the results and commented on the manuscript. NOTES The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work was supported by the Beijing National Research Center for Information Science and Technology (BNRist) and the Nano Fabrication Facility in the Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO). Special thanks to Qingyu Ben Yang for proofreading on grammar and sentence clarity.


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REFERENCES (1) Yu, N.; Capasso, F., Flat optics with designer metasurfaces. Nature materials 2014, 13, 139-150. (2) Khorasaninejad, M.; Shi, Z.; Zhu, A. Y.; Chen, W.-T.; Sanjeev, V.; Zaidi, A.; Capasso, F., Achromatic metalens over 60 nm bandwidth in the visible and metalens with reverse chromatic dispersion. Nano letters 2017, 17, 1819-1824. (3) Yu, N.; Aieta, F.; Genevet, P.; Kats, M. A.; Gaburro, Z.; Capasso, F., A broadband, background-free quarter-wave plate based on plasmonic metasurfaces. Nano letters 2012, 12, 6328-6333. (4) Wang, S.; Wu, P. C.; Su, V.-C.; Lai, Y.-C.; Chu, C. H.; Chen, J.-W.; Lu, S.-H.; Chen, J.; Xu, B.; Kuan, C.-H., Broadband achromatic optical metasurface devices. Nature Communications 2017, 8, 187. (5) Arbabi, A.; Horie, Y.; Ball, A. J.; Bagheri, M.; Faraon, A., Subwavelength-thick lenses with high numerical apertures and large efficiency based on high-contrast transmitarrays. Nature communications 2015, 6, ncomms8069. (6) Pors, A.; Nielsen, M. G.; Eriksen, R. L.; Bozhevolnyi, S. I., Broadband focusing flat mirrors based on plasmonic gradient metasurfaces. Nano letters 2013, 13, 829-834. (7) Lin, D.; Fan, P.; Hasman, E.; Brongersma, M. L., Dielectric gradient metasurface optical elements. science 2014, 345, 298-302. (8) Zheng, G.; Mühlenbernd, H.; Kenney, M.; Li, G.; Zentgraf, T.; Zhang, S., Metasurface holograms reaching 80% efficiency. Nature nanotechnology 2015, 10, 308-312. (9) Sun, S.; Yang, K.-Y.; Wang, C.-M.; Juan, T.-K.; Chen, W. T.; Liao, C. Y.; He, Q.; Xiao, S.; Kung, W.-T.; Guo, G.-Y.; Zhou, L.; Tsai, D. P., High-Efficiency Broadband Anomalous Reflection by Gradient Meta-Surfaces. Nano Letters 2012, 12, 6223-6229. (10) Li, Z.; Palacios, E.; Butun, S.; Aydin, K., Visible-frequency metasurfaces for broadband anomalous reflection and high-efficiency spectrum splitting. Nano letters 2015, 15, 1615-1621. (11) Wu, P. C.; Tsai, W.-Y.; Chen, W. T.; Huang, Y.-W.; Chen, T.-Y.; Chen, J.-W.; Liao, C. Y.; Chu, C. H.; Sun, G.; Tsai, D. P., Versatile polarization generation with an aluminum plasmonic metasurface. Nano letters 2016, 17, 445-452. (12) Ni, X.; Ishii, S.; Kildishev, A. V.; Shalaev, V. M., Ultra-thin, planar, Babinet-inverted plasmonic metalenses. Light: Science & Applications 2013, 2, e72. (13) Tang, D.; Wang, C.; Zhao, Z.; Wang, Y.; Pu, M.; Li, X.; Gao, P.; Luo, X., Ultrabroadband superoscillatory lens composed by plasmonic metasurfaces for subdiffraction light focusing. Laser & Photonics Reviews 2015, 9, 713-719. (14) Sun, S.; He, Q.; Xiao, S.; Xu, Q.; Li, X.; Zhou, L., Gradient-index meta-surfaces as a bridge linking propagating waves and surface waves. Nature materials 2012, 11, 426.


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(15) Holloway, C. L.; Kuester, E. F.; Gordon, J. A.; O'Hara, J.; Booth, J.; Smith, D. R., An overview of the theory and applications of metasurfaces: The two-dimensional equivalents of metamaterials. IEEE Antennas and Propagation Magazine 2012, 54, 10-35. (16) Yang, H.; Cao, X.; Yang, F.; Gao, J.; Xu, S.; Li, M.; Chen, X.; Zhao, Y.; Zheng, Y.; Li, S., A programmable metasurface with dynamic polarization, scattering and focusing control. Scientific reports 2016, 6, 35692. (17) Deng, R.; Mao, Y.; Xu, S.; Yang, F., A single-layer dual-band circularly polarized reflectarray with high aperture efficiency. IEEE Transactions on Antennas and Propagation 2015, 63, 3317-3320. (18) Liu, S.; Cui, T. J.; Xu, Q.; Bao, D.; Du, L.; Wan, X.; Tang, W. X.; Ouyang, C.; Zhou, X. Y.; Yuan, H., Anisotropic coding metamaterials and their powerful manipulation of differently polarized terahertz waves. Light: Science and Applications 2016, 5, e16076. (19) Liu, L.; Zhang, X.; Kenney, M.; Su, X.; Xu, N.; Ouyang, C.; Shi, Y.; Han, J.; Zhang, W.; Zhang, S., Broadband metasurfaces with simultaneous control of phase and amplitude. Advanced Materials 2014, 26, 5031-5036. (20) Grady, N. K.; Heyes, J. E.; Chowdhury, D. R.; Zeng, Y.; Reiten, M. T.; Azad, A. K.; Taylor, A. J.; Dalvit, D. A.; Chen, H.-T., Terahertz metamaterials for linear polarization conversion and anomalous refraction. Science 2013, 1235399. (21) Cong, L.; Xu, N.; Zhang, W.; Singh, R., Polarization control in terahertz metasurfaces with the lowest order rotational symmetry. Advanced Optical Materials 2015, 3, 1176-1183. (22) Yu, N.; Genevet, P.; Kats, M. A.; Aieta, F.; Tetienne, J.-P.; Capasso, F.; Gaburro, Z., Light propagation with phase discontinuities: generalized laws of reflection and refraction. science 2011, 334, 333-337. (23) Ni, X.; Emani, N. K.; Kildishev, A. V.; Boltasseva, A.; Shalaev, V. M., Broadband light bending with plasmonic nanoantennas. Science 2012, 335, 427-427. (24) Mousavi, S. H.; Kholmanov, I.; Alici, K. B.; Purtseladze, D.; Arju, N.; Tatar, K.; Fozdar, D. Y.; Suk, J. W.; Hao, Y.; Khanikaev, A. B., Inductive tuning of Fano-resonant metasurfaces using plasmonic response of graphene in the mid-infrared. Nano letters 2013, 13, 1111-1117. (25) Yao, Y.; Shankar, R.; Kats, M. A.; Song, Y.; Kong, J.; Loncar, M.; Capasso, F., Electrically tunable metasurface perfect absorbers for ultrathin mid-infrared optical modulators. Nano letters 2014, 14, 65266532. (26) Dabidian, N.; Kholmanov, I.; Khanikaev, A. B.; Tatar, K.; Trendafilov, S.; Mousavi, S. H.; Magnuson, C.; Ruoff, R. S.; Shvets, G., Electrical switching of infrared light using graphene integration with plasmonic Fano resonant metasurfaces. Acs Photonics 2015, 2, 216-227.


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(27) Smit, M.; Van der Tol, J.; Hill, M., Moore's law in photonics. Laser & Photonics Reviews 2012, 6, 113. (28) Hasani, H.; Tamagnone, M.; Capdevila, S.; Moldovan, C. F.; Maoddi, P.; Ionescu, A. M.; Peixeiro, C.; Mosig, J. R.; Skrivervik, A. K.; Perruisseau-Carrier, J., Tri-Band, polarization-independent reflectarray at terahertz frequencies: design, fabrication, and measurement. IEEE Transactions on Terahertz Science and Technology 2016, 6, 268-277. (29) Li, Z.; Palacios, E.; Butun, S.; Aydin, K., Visible-frequency metasurfaces for broadband anomalous reflection and high-efficiency spectrum splitting. Nano letters 2015, 15, 1615-1621. (30) Khorasaninejad, M.; Zhu, W.; Crozier, K., Efficient polarization beam splitter pixels based on a dielectric metasurface. Optica 2015, 2, 376-382. (31) Niu, T.; Withayachumnankul, W.; Upadhyay, A.; Gutruf, P.; Abbott, D.; Bhaskaran, M.; Sriram, S.; Fumeaux, C., Terahertz reflectarray as a polarizing beam splitter. Optics express 2014, 22, 16148-16160. (32) Farmahini-Farahani, M.; Mosallaei, H., Birefringent reflectarray metasurface for beam engineering in infrared. Optics letters 2013, 38, 462-464. (33) Ma, H. F.; Liu, Y. Q.; Luan, K.; Cui, T. J., Multi-beam reflections with flexible control of polarizations by using anisotropic metasurfaces. Scientific reports 2016, 6, 39390. (34) Pu, M.; Zhao, Z.; Wang, Y.; Li, X.; Ma, X.; Hu, C.; Wang, C.; Huang, C.; Luo, X., Spatially and spectrally engineered spin-orbit interaction for achromatic virtual shaping. Scientific reports 2015, 5, 9822. (35) Pu, M.; Li, X.; Ma, X.; Wang, Y.; Zhao, Z.; Wang, C.; Hu, C.; Gao, P.; Huang, C.; Ren, H., Catenary optics for achromatic generation of perfect optical angular momentum. Science Advances 2015, 1, e1500396. (36) Guo, Y.; Pu, M.; Zhao, Z.; Wang, Y.; Jin, J.; Gao, P.; Li, X.; Ma, X.; Luo, X., Merging geometric phase and plasmon retardation phase in continuously shaped metasurfaces for arbitrary orbital angular momentum generation. Acs Photonics 2016, 3, 2022-2029.


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Figures: Figure 1:

Figure 1. (a) Schematic of a metasurface-based beam splitter for visible light. (b) Schematic of the unit cell. (c) Simulated reflective phase responses versus the diameter of the element. (d) Simulated reflective magnitude responses versus the diameter of the element.


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Figure 2:

Figure 2. Simulated scattering pattern of the metasurface (15×15 um2) at the designed diameters of 80/180 nm: (a) Normalized three-dimensional scattering pattern of the metasurface under normal incidence. (b) Simulation results of normalized two-dimensional scattering patterns (xoz-plane) with the incident angles from 0° to 15°. The light intensities of oblique incidences are normalized to the intensity of normal incidence.


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Figure 3:

Figure 3. Photograph and top-view scanning electron microscope (SEM) images of the fabricated sample:(a) Photograph of the sample by camera (Nikon). (b) SEM image of the metasurface sample.


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Figure 4:

Figure 4. Experimental setup and the measured results: (a) Schematic of experimental setup. (b) The measured distribution of light intensities in different angles under normal incidence. (c) Experimental and simulated results of the reflection angle at different incident angles. (d) Experimental and simulated results of the reflected light energy at different incident angles. The light energy at oblique incidences are normalized to the energy of beam one at normal incidence.


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For Table of Contents Use Only: Title: A metasurface-based ultra-thin beam splitter with variable split angle and power distribution Authors: Xingliang Zhang, Ruyuan Deng, Fan Yang, Chunping Jiang, Shenheng Xu, and Maokun Li Descriptions: We select two graphics to be used as TOC Graphic. The left one is a schematic graphic of our design, which shows that the designed metasurface can manipulate visible light of single-frequency same-polarization at nano-scale. The right one shows the important characteristic of the designed metasurface that the deflection angle can be readily controlled by changing the incident angle. The ability of this device would be very desirable in integrated optical systems, and this study may help further research into the miniaturized optical components for large-scale photonic integrated applications.


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Metasurface-Based Ultrathin Beam Splitter with Variable Split Angle

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