Self-referenced reflective intensity modulated fiber optic displacement sensor

A simple referencing technique is presented for a fiber optic reflective di splacement sensor. Two receiving fibers are arranged side by side to operat e in the negative and positive slopes of the output signal. The ratio of th e two outputs provides common mode rejection. A theoretical model of the ne w referencing technique is developed and verified experimentally. The linea r operating range of the sensor depends on the numerical aperture of the fi bers and the diameter of the second receiving fiber. The minimum detectable displacement of a representative sensor is 1.57 nm/root Hz in the audio fr equency range, which agrees well with the theoretical value. The measured d ynamic range of the sensor is 111 dB. Alternative sensor structures to redu ce the size and to increase linear range and resolution are discussed. (C) 1999 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(99)024 02-2].