Tunable drop filters based on photonic crystal self-collimation ring resonators

Abstract

A tunable drop filter (TDF) based on two-dimensional photonic crystal (PC) self-collimation ring resonator (SCRR) is proposed. The PC consisting of square-lattice air cylinders in silicon has square-shaped equal frequency contours (EFCs) in the wavevector space at the frequencies between 0.172-0.188<i>c/a</i> for TE modes. The SCRR includes two mirrors and two splitters. The air holes inside the SCRR are infiltrated with a kind of liquid crystal whose ordinary and extraordinary refractive indices are 1.522 and 1.706, respectively. The effective refractive index <i>n</i>_eff of liquid crystal depends on the applied electric field. Simulated with the FDTD method, the transmission spectra at the drop port of SCRR are in the shape of sinusoidal curves with uniform peak spacing between 0.172-0.188<i>c/a</i>. Transmission peaks will shift to the lower frequencies when <i>n</i>_eff is increased. When <i>n</i>_eff changes from 1.522 to 1.706, the peaks will experience red-shift over 0.003<i>c/a</i>. So this SCRR can work as a tunable drop filter. For the operating wavelength around 1550nm, its dimensions are only tens of microns.