3D optical micro-resonators by curving nanostructures using intrinsic stress

We propose a new approach for the 3D control of light in real 3D optical micro-resonators that can be assimilated to 'cages', where photons are efficiently trapped. The main attractive feature of this photon cages lies in their ability to result in a considerable enhancement of the electromagnetic field in the central part of the cage, that is in the air region, opening the way to new sensing or trapping of nanoparticles in fluidic (gas or liquid) ambiances. Fabrication of three dimensional structures consists in exploiting the process of elastic relaxation of patterns formed in pre-stressed multi-layer structures. The final shape of these objects can be predetermined by the distribution of the deformations in the various semiconductor layers, imposed during their epitaxial growth, before their freestanding from the substrate by selective etching. We will present the basic concepts and fabrication we exploit to confine photons in air using spherical structures based on progressive relaxation of pre-stressed InGaP/InAsP bilayer films. It is worthwhile to notice that the formed microstructures exhibit patterns with dimensions compatible with optical operation in the visible/NIR wavelength range.