Figure 2 (IMAGE)

Pohang University of Science & Technology (POSTECH)

Figure 2

Caption

Demonstration of a low?loss silicon metasurface platform. a) The unit cell configuration of rectangular pillars composed of hydrogenated amorphous silicon (a?Si:H) on a glass substrate. The conversion efficiency η can be defined by the intensity ratio of transmitted right?handed circularly polarized light (RCP) to the incident left?handed circularly polarized light (LCP). η is calculated by varying the period p, height h, length l, and width w. b) The maximum η variation according to the TP. The blue rectangles, green circles, and red triangles represent measured data at the wavelengths of 450, 532, and 635 nm, respectively. c) The calculated η of the optimized geometrical structures with a?Si:H deposited at TP = 200 °C, PC = 25 mTorr, WRF = 800 W, and γ  = 7.5. The blue, green, and red circles relate to the optimized η at the wavelengths of 450, 532, and 635 nm, respectively. d) The relationship between the value of the extinction coefficient (k) and maximum η. The black rectangles are the calculated maximum η at measured k at the wavelengths of 450, 532, and 635 nm with various deposition conditions. The solid line shows a fitting curve with (k2 + Ak + B)-1, where A = 7.04, and B = ?8.49 with the goodness of fit of R2 = 0.92. e) Schematic of the geometric metasurface. Under normal LCP incidence, the propagation direction of the transmitted RCP light deviates by a deflection angle θ from the normal direction. f) SEM images of the fabricated metasurfaces optimized for: i) λ = 450 nm, ii) λ = 532 nm, and iii) λ = 635 nm. g) Oblique SEM images show the defects within the fabrication steps for metasurfaces optimized for i) λ = 450 nm, ii) λ = 532 nm, and iii) λ = 635 nm. h) Captured images of the transmitted light on the screen with different incident wavelength λ. Bright spots at the center and right side are the zeroth?order beam and transmitted cross?polarized beam, respectively. Dark spots on the left side are due to the imperfect circular polarization state. i) λ = 450 nm, ii) λ = 532 nm, and iii) λ = 635 nm.

Credit

Junsuk Rho (POSTECH), WILEY

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