Two-dimensional hexagonal symmetry diffraction pattern by SiO₂ photonic structures fabricated by hot embossing

Using synthesized sol-gel nanoimprint resist, large-area, ordered SiO₂ cylindrical and stripe photonic nanostructures with constant aspect ratio have been fabricated by a single-step soft stamp hot embossing nanoimprint. Different from the traditional hot embossing nanoimprint technique, in our imprint process, the external force applied to the soft stamp is provided just by using our hand. Since the stress can be well released, the stamp can be easily released after the hot stage cooling down. So the optical window (K9 glass) substrates with imprinted two-dimensional SiO₂ cylindrical photonic nanostructures show good light diffraction property. Also, our experiment demonstrates that with the imprinted sample annealing at 200°C, the density of SiO₂ will be increased and the diffraction efficiency can be further enhanced. In addition, the light splitting characteristic can still keep good for a larger (6 inch) substrate, which has a certain radian. This illustrates that this nanoimprint method can be compatible with the fluctuation of the imprinted substrates. Furthermore, as the distance between two adjacent feature nanostructures is in sub-micro scale, hexagonal symmetry diffraction pattern by the cylindrical photonic structures was realized at normal incidence of monochromatic laser (λ=532nm). The diffraction efficiency of first order is about 11.2%. Morever, the diffraction pattern and the intensity of the first diffraction order can be modulated just by changing the incident angle of the input laser.