Photonic properties of two-dimensional photonic crystals based on monolayer of dielectric microspheres

The optical properties of two-dimensional (2D) photonic crystal (PhC) slabs based on self-assembled monolayer of dielectric microspheres are studied. The in-plane transmission spectra of 2D array of dielectric spheres with triangular lattice are investigated using the finite-difference-time-domain (FDTD) method. The structures studied are monolayer of dielectric spheres infiltrated with air ('opals') and air spheres infiltrated with dielectric material ('inverse opals'), with glass substrate sustaining the monolayer of spheres. The transmission spectra are calculated for different values of refractive index contrasts between the spheres and the infiltrated material and for different values of filling fractions (compactness of the spheres). As the refractive index is varied, compact spheres are assumed; and as the filling fraction is varied, the refractive index of the dielectric spheres or the dielectric matrix is fixed to be 2.5. For compact opal structure on glass substrate, a narrow photonic band gap (PBG) is observed in the transmission spectra for dielectric spheres with refractive index higher than around 1.9. When the refractive index is fixed at 2.5, the PBG is observed for more compact spherical arrangement and disappears for more separated spheres. While for inverse opal structure on glass substrate, using non-compact spheres enlarges the width of PBG which is not observed for compact spherical arrangement. The application of the study is to realize organic PhC microcavity laser.