Tubular optical microcavities based on rolled-up photonic crystals

Abstract

The self-rolling of micro-structured membranes via the stress-engineering method opens new ways to create 3D photonic micro-objects with original designs and optical properties. This article validates this approach by producing 3D hollow micro-resonators based on rolled-up 2D photonic crystal membrane mirrors, capable of trapping light in 3D and in air. We fabricated the 3D tubular microresonators with 10 μm–20 μm diameters by rolling photonic crystal membranes using stress-engineering technique on the prestressed InGaP/InP bilayer. We also added a design feature to lift the microtubes vertically and facilitate optical measurements, but also to attach the structures to the substrate. The dispersion of the planar 2D photonic crystal membrane was optimized to exhibit high reflectivity (>95%) at normal incidence over a large spectral band (100 nm) in the near-infrared domain (1.5 μm–1.6 μm). The cylindrical cavity model and numerical simulations predicted the presence of quasi-pure radial cavity modes with a strong concentration of light over nearly 3% of the photonic microtubes’ cross section. We demonstrated experimentally the presence of those modes through scanning near-field optical microscopy measurements. Using a bowtie nanoantenna, we selectively detected and mapped transverse electric modes in the hollow core of photonic microtubes. Spatially resolved cartographies allowed for the identification of the modes in good agreement with theoretical predictions. This work brings theoretical and experimental proof of concept of light cages based on rolled-up photonic crystal membranes. It also opens the path to the realization of original photonic microstructures as combinations of a specific photonic crystal design and a targeted 3D form.