Optical microscope and tapered fiber coupling apparatus for a dilution refrigerator

We have developed a system for tapered fiber measurements of optomechanical resonators inside a dilution refrigerator, which is compatible with both on-and off-chip devices. Our apparatus features full three-dimensional control of the taper-resonator coupling conditions enabling critical coupling, with an overall fiber transmission efficiency of up to 70%. Notably, our design incorporates an optical microscope system consisting of a coherent bundle of 37 000 optical fibers for real-time imaging of the experiment at a resolution of similar to 1 mu m. We present cryogenic optical and optomechanical measurements of resonators coupled to tapered fibers at temperatures as low as 9 mK. (C) 2015 AIP Publishing LLC.