Researchers designed a new sensor based on an S-tapered fiber probe (STFP) that can be used for high sensitivity refractive-index measurement. When light from a broadband source (BBS) enters the fiber's tapered area, a portion of the light interacts with the surrounding sample in a way that shifts the light's spectrum and the altered light is reflected back through the fiber to an optical spectrum analyzer (OSA) that monitors and records the change in spectrum, providing information about the sample's chemistry. See Chen et al. Optical Materials Express 8, 919-925 (2018).