Activating photonic crystal membrane nanocavities by infiltrating with liquid crystals or luminescent colloidal nanocrystals

Liquid crystal (LC, Merk 5 CB) is infiltrated into active, InAs quantum dots embedded, InGaAsP membrane type nanocavities to investigate the possible effect of the LC orientation on active cavity tuning. The tuning is demonstrated thermally and thermo-optically. The thermal tuning showed that the cavity modes can be tuned in opposite directions and exhibits a sudden change at the clearing temperature. The mechanism relies on the existence of both ordinary and extraordinary refractive indices of the liquid crystal due to its molecular alignment inside the voids. It shows that the electric field distribution of cavity modes can have a substantial component parallel to the LC director. The average electric field orientation with respect to the LC orientation can be mode dependent, so that different modes can be dominated by either branch of the LCs refractive index. Thermo-optic tuning of the modes is obtained when the power of the excitation laser is increased from 40 µW to 460 µW. A large and a reversible blueshift of more than 10 nm of the cavity modes is observed which is attributed to temperature induced liquid transport. InGaAsP type of nanocavities, without InAs quantum dots were infiltrated with PbSe colloidal quantum dots to obtain a comparison of internal light sources either in the semiconductor or in the holes.