Phys. Rev. Applied 14, 064052 (2020)
Michael Scheucher, Khaled Kassem, Arno Rauschenbeutel, Philipp Schneeweiss, and Jürgen Volz
Optical fibers play a key role in many different fields of science and technology. In particular, fibers with a diameter of several micrometers are intensively used in photonics. For these applications, it is often important to precisely know and control the fiber radius. Here we describe a technique to determine the radius profile of an optical microstructure with ultrahigh precision from a single optical image. Using a basic microscopy setup, we demonstrate our method by measuring the axial radius variation along a 30-μm-diameter silica fiber with precision less than 0.3 Å. The axial resolution is tens of micrometers, and the measurement range is more than 0.5 mm. Our method relies on imaging the fiber’s whispering-gallery modes in which the speed of light propagating along the fiber axis is strongly reduced. Imaging those whispering-gallery modes, we infer the local radius variations of the optical microstructure with ultrahigh precision. Because of the performance and simplicity of implementation, we are convinced that our scheme has high potential for precision metrology and optical sensing.