We present a novel noncontact optical method for absolute measurement of refractive index and thickness of optically transparent media. The method is based on a simple dual-confocal fiber-optic sensor design. It includes two independent confocal channels consisting of two identical apertureless fiber-optic-type confocal microscopes constructed by use of a single 2×2 fiber coupler. A geometrical-ray model is used to obtain the analytical dependence between the sample's refractive index and its thickness. The measurement method provides high accuracy in spatially locating the specific imaging points that correspond to the backreflected intensity peaks of the confocal responses. Thus, a simultaneous measurement of the sample refractive index and thickness is achieved.
© 2002 Optical Society of America
(060.2350) Fiber optics and optical communications : Fiber optics imaging
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(120.4640) Instrumentation, measurement, and metrology : Optical instruments
(170.1790) Medical optics and biotechnology : Confocal microscopy
(180.5810) Microscopy : Scanning microscopy
Ilko K. Ilev, Ronald W. Waynant, Kimberly R. Byrnes, and Juanita J. Anders, "Dual-confocal fiber-optic method for absolute measurement of refractive index and thickness of optically transparent media," Opt. Lett. 27, 1693-1695 (2002)