Radiation Collimation of Polarized LED with All-Dielectric Nanostructures

In order to improve the light-field coupling efficiency of a polarized light emitting diode (LED), a composite device with an integrated all-dielectric nanostructure is designed based on a one-dimensional photonic crystal and a subwavelength dielectric grating. The all-dielectric nanostructure model for collimating polarized beams is established by using the finite-difference time-domain (FDTD) method. The influence of structure parameters of the photonic crystal and the dielectric grating on the light-field regulation of the polarized LED is studied systematically. The physical mechanism of collimation characteristics affected by photonic crystal thickness, photonic crystal period, dielectric grating period, dielectric grating height and dielectric grating linewidth is analyzed. The optimized nanostructures are composed of TiO2 nano-gratings with a period of 550 nm, a linewidth of 160 nm and a depth of 120 nm, and a photonic crystal structure composed of two pairs of Al2O3/SiO2 films (the thickness of each layer is 80 nm). Calculation results show that the designed all-dielectric nanostructure can control the divergence angle of the polarized LED within the range of -6(o)-6(o) in the green light band, and achieve the far-field collimation of the light radiation, with the light extraction efficiency greater than 77%. The far-field radiation intensity of the designed structure is 6.6 times higher than that of the bare LED in the vertical direction (with a divergence angle of 0(o)).