Optical fiber taper coupling and high-resolution wavelength tuning of   microdisk resonators at cryogenic temperatures
  A system for studying microcavity resonators at cryogenic temperatures (~10 K) through evanescent coupling via optical fiber taper waveguides is reported, and efficient fiber coupling to AlGaAs microdisk cavities with embedded quantum dots is demonstrated. As an immediate application of this tool, we study high-resolution tuning of microdisk cavities through nitrogen gas adsorption, as first discussed by Mosor, et al. By proper regulation of the nitrogen gas flow and delivery of the gas to the sample surface, continuous tuning can be achieved with modest gas flows, and overall wavelength shifts as large as 4 nm are achieved. 
Kartik Srinivasan and Oskar Painter