A polarization-independent diffractive optical element (DOE) consisting of dual photonic crystal (PhC) slabs was proposed for unidirectional light transmission at telecom wavelengths. Employing rigorous coupled wave analysis (RCWA) together with genetic algorithm (GA), the contrast ratios of designed DOE with 10nm precision at normal incidence from opposite directions reached to 33.6 dB and 32.2 dB with transmittance differences of 84.57% and 87.63% at wavelengths of 1310 nm and 1550 nm, respectively. The presented DOE showed great promising for applications in optical communication.
A 2D supercell grating was proposed to work as a polarization beam splitter (PBS) at normal incidence, which directed TE-polarized light to (0, ±1) order and TM-polarized light to (±1, 0) order. The diffraction efficiency of targeted transmitting orders reached 71.32% and the extinction ratio exceeded 19.97 dB for TE- or TM- polarized illumination with 1550nm wavelength. Meanwhile, the (0, 0) order was well suppressed. The proposed 2D supercell grating is suitable for compact polarization systems.
Two issues that hindering fast developments of diffractive waveguides based on surface relief grating (SRG) for augmented reality (AR) applications: light leakage at out-coupler and low light efficiency. A layer of subwavelength metal wire grid on commonly used protective glass sheet above diffractive waveguide was designed to prohibit the light leakage and reflect them back to AR waveguide for recycling light usage. One-dimensional (1D) SRG based AR waveguide was analyzed under TE-polarized illumination at 532nm wavelength with 30° field-of-view (FOV). It was demonstrated that 80% efficiency improvement and 9% intensity uniformity increasement could be obtained with completely prohibited light leakage by nanostructures glass cover, compared with that on planar protective glass.
The optical properties of the methylammonium lead iodide (CH3NH3PbI3) - Germanium (Ge) heterojunction with a layer of periodical nanoparticles was investigated to achieve broadband light harvesting by 3D Finite Element Method (FEM). The constructed heterojunction device showed a broad bandwidth from 300nm to 1600nm. Under the AM(1.5) illumination, the maximal energy absorbed by the heterojunction device was 776.64W/m2 after optimizing thickness of perovskite and Ge, as well as radius of metallic or dielectric nanospheres (Au, Ag, Al, Si3N4, TiO2, Ta2O5). The improved optical performance was further demonstrated by comparing calculated electric fields and charge carrier generation rates of the optimized heterojunction with periodical nanoparticles layer with that of corresponding flat device.
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