Mode analysis of photonic crystal L3 cavities in self-suspended lithium niobate membranes

We report on a multimodal analysis of photonic crystal L3 cavities milled in lithium niobate free-standing membranes. The classical L3 cavity geometry is compared to an L3 cavity containing a second lattice superimposed on the primary one. Those two different geometries are investigated in terms of vertical radiation and quality (Q) factor for each mode of the cavities. Depending on the cavity geometry, some modes undergo an enhancement of their vertical radiation into small angles while other modes experience a higher Q factor. Experimental characterizations are corroborated by three-dimensional finite difference time domain simulations.