High-reflectivity $Si_3N_4$ photonic-crystal membranes for optomechanics
Résumé
Nanomechanical resonators strongly coupled to the electromagnetic field are a promising resource for quantum-limited mass and force sensors, and as transducers for coupling otherwise incompatible quantum systems such as microwave and optical photons. In particular, suspended nanomem-branes obtained by chemical release of a high-tensile stress layer are an advantageous platform for such transducers, combining an extremely high mechanical quality factor and a low mass. We demonstrate the successful implementation of a photonic-crystal reflector on a high-tensile stress $Si_3N_4$ nanomembrane, enabling its direct coupling to a high-finesse optical cavity. This approach is particularly well suited for hybrid opto-electro-mechanical transducers, where the membrane motion is simultaneously coupled to an optical and a microwave cavity. We provide an illustration of the physical process underlying the high reflectivity by measuring the photonic crystal band diagram. Moreover, we introduce a clear theoretical description of the membrane scattering properties in the presence of optical losses. By embedding the photonic-crystal membrane inside a high-finesse cavity, we fully characterize its optical properties. The spectrally resolved measurements demonstrate the wide tunability of the membrane's reflectivity, from nearly 0 to 99.79 ± 0.02%, and show that the material absorption is not the main source of optical losses.
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