Realization of ultrawide omnidirectional photonic band gap in multiple one-dimensional photonic crystals

Abstract

Theoretical and experimental investigations have shown that the omnidirectional photonic band gap (omni-PBG) of one-dimensional photonic crystals (1D PCs) can be enlarged by including multiple-periodic structures. These structures, consisting of Si–SiO2 alternating layers with multiple periods, Λ1, Λ2,…,ΛM, have great potential for ultrawide omnireflectors operating in the infrared frequency range. To confirm the effect of multiple periods in the 1D PCs, we prepared two types of 16-pair, Si∕SiO2 1D PCs with a single period of Λ1=426.9nm and Λ2=306.9nm, and one type of 16-pair 1D PC with double periods—the combination of eight-pair Λ1 and eight-pair Λ2. Theoretically, the normalized frequency range for omni-PBG (Δω) in double PC is enhanced by approximately twice that in the single PC. That is, Δω increases from 0.086 to 0.166, which corresponds to the wavelength range (Δλ) from 520to980nm for Λ=407.7nm. Measured reflectance (R) spectra are in a good agreement with the calculated results. For example, the R spectrum of Si∕SiO2 double 1D PC (8-pair Λ1+8-pair Λ2: Λ1=426.9nm, Λ2=306.9nm, and filling factor η=0.406) exhibits an ultrawide PBG over the wavelength range of 1050–2500nm for TE polarization at the incident angle of 5°.