Experimental observation of above billion quality factor in silicon crystalline optical whispering gallery mode resonators

Silicon is a widely used material in modern microelectronics and photonics. Extremely low optical losses in near and mid-IR wavelengths made it a promising material for whispering gallery mode (WGM) optical microresonators. But, till now its potential was not fully utilized because of the best-obtained quality factor - about 2 x 10(7) - remained orders of magnitude below the material absorption limit. In this work we experimentally demonstrated a quality factor above 10(9) for the WGM in millimetres size crystalline silicon resonators. Materials with different residual conductivity were compared. Application of original semi-spherical silicon coupler allowed to obtain up to 35% resonance peaks contrast.