Photonic crystal (PC) devices in the InP/InGaAsP/InP planar waveguide system exhibiting narrow bandwidth
features were investigated for use as ultrasmall and tunable building blocks for photonic integrated circuits at
the telecom wavelength of 1.55 μm. The H1 cavity, consisting of a single PC-hole left unetched, represents
the smallest possible cavity in a dielectric material. The tuning of this cavity by temperature was investigated
under the conditions as etched and after the holes were infiltrated with liquid crystal (LC), thus separating the
contributions of host semiconductor and LC-infill. The shift and tuning by temperature of the MiniStopBand
(MSB) in a W3 waveguide, consisting of three rows of holes left unetched, was observed after infiltrating the PC
with LC. The samples finally underwent a third processing step of local wet underetching the PC to leave an
InGaAsP membrane structure, which was optically assessed through the ridge waveguides that remained after
the under etch and by SNOM-probing.
The filling is reported of the air holes of an InP-based two-dimensional photonic crystal with solid polymer and with liquid crystal 5CB. The polymer filling is obtained by thermal polymerization of an infiltrated liquid monomer, trimethylolpropane triacrylate. The filling procedure for both the monomer and liquid crystal relies on the capillary action of the liquid inside the ~ 200 nm diameter and < 2.5 μm deep air holes. The solid polymer infiltration result was directly inspected by cross-sectional scanning electron microscopy. It was observed that the holes are fully filled to the bottom. The photonic crystals were optically characterized by transmission measurements around the 1.5 μm wavelength band both before and after infiltration. The observed high-frequency band edge shifts are consistent with close to 100% filling, for both the polymer and the liquid crystal. No differences were observed for filling under vacuum or ambient, indicating that the air diffuses efficiently through the liquid infiltrates, in agreement with estimates based on the capillary pressure rise.