We theoretically suggest ultra-sparse 1D and 2D arrays of high-index dielectric wires as broadband, omnidirectional reflectors and polarizers. Using diffraction potential arguments and numerical simulations, we show the proposed device for 1D array supports a high-extinction polarizing function. For an optimized 1D SrTiO3-wire array, a TE reflection resonance has a remarkably wide bandwidth while the TM wave almost freely passes through the array in the entire zero-order spectral domain. Based on the theoretically observed performance of the 1D array, we design fully conical omnidirectionality in the reflection for the 2D extension at the center wavelength of the fundamental-mode resonance condition. We briefly discuss possibility of the proposed 1D and 2D wire grid architectures for space-variant beam transforming optics and vector beam generations. Applications to THz photonic components and other long-wave devices such as radio-wave telescopes and satellite antenna are envisioned.
We experimentally demonstrate a robust Si-photonic waveguide architecture that realizes dynamically encircling an exceptional point (EP) in the optical domain and broadband asymmetric modal transmission as an essential consequence. The structure consists of a pair of coupled channel waveguides and an adjacent slab-waveguide patch that enable precise lithographic controls on the phase velocities and radiation rates of the guided photonic modes. Complex modal index and inter-mode coupling constant profiles required for the encircling-an-EP parametric control are precisely coded in the geometry of those elements. The device created on this basis induces the symmetry-exchanging adiabatic state flip for one transmission direction and symmetry-preserving anti-adiabatic state-jump for the transmission in the opposite direction. In fabrication, we use a state-of-the-art electron-beam lithography for creating mm-long devices with nm-scale transversal precision. A comprehensive spectral measurement for the intensity and phase distributions of the transmitted optical states is obtained with a specially designed phase-sensitive infrared microscopy integrated with a tunable diode-laser system and spectrum analyzer. On this basis, we confirm in the experiment the highly asymmetric modal transmission persisting over a broad spectral band exceeding 100 nm in the telecommunications window around 1,550 nm. Hence, we establish a substantive experimental step toward broadband non-reciprocal photonic devices based on the unique non-Hermitian dynamics.
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