Compact acousto-optic filter with beam expanders constituted by photonic crystal rows of airholes

A compact acousto-optic (AO) filter with multireflector (MR) beam expanders constituted by 32 photonic crystal rows of airholes in LiNbO(3) waveguide has been proposed and numerically studied by the two-dimensional finite-difference-time-domain method. The diameter and position of every row of holes are gradually varied along MR beam expanders in order to provide high efficiency and good sidelobe suppression. Device sizes are 70 μm × 150 μm, with an FWHM bandwidth of 4.4 nm, a tuning range of 110 nm, internal loss of -3 dB, and sidelobes of -20 dB, thus providing a unique value of 0.6 μm(2) for the product FWHM bandwidth by an AO length. It is intended for use in fiber optics telecommunications and sensing.