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. 2019 May 31;5(5):eaau9593. doi: 10.1126/sciadv.aau9593

Fig. 1. Concept and principle of chip-scale broadband polarization diversity OAM generator on a silicon platform.

Fig. 1

(A) Zoom-in 2D subwavelength surface structure (superposed holographic fork gratings) region. (B and C) Illustration of holographic method producing fork gratings. The coupled interference between the vertically incident x-pol. (B) or y-pol. (C) OAM mode and the x-pol. (B) or y-pol. (C) TE0 in-plane guided mode forms a fork grating on top of the silicon waveguide with the fork opening direction along x (B) or y (C). (D to F) Superposed holographic fork gratings G(x, y) (D) formed by the superposition of two fork gratings of G1(x, y) with the fork opening direction along x (E) and G2(x, y) with the fork opening direction along y (F). (D) to (F) correspond to (A) to (C), respectively. (G to J) Superposed holographic fork gratings for generating broadband polarization diversity x-pol. OAM+1 (G), x-pol. OAM−1 (H), y-pol. OAM+1 (I), and y-pol. OAM−1 (J) under different incident conditions of −y-input x-pol. (G), y-input x-pol. (H), −x-input y-pol. (I), and x-input y-pol. (J) TE0 in-plane waveguide mode. x-Pol., x-polarization; y-Pol., y-polarization.