A fiber optic tachometer is described that uses the Faraday effect in a ferrite to modulate light from a multimode fiber. A yttrium iron garnet (YIG) crystal is used as the magnetooptic modulator. A permanent magnet is placed near the crystal, such that a nearby rotating steel toothed wheel changes the magnetic field inside the crystal, causing modulation of the intensity of the 1.3-µm light. Modulation depths up to 50% have been achieved with signal-to-noise ratios of over 15 dB. A single multimode fiber connects the remote sensor head to the LED light source and detector.
© 1989 Optical Society of America
Brian J. Zook and Clifford R. Pollock, "Fiber optic tachometer based on the Faraday effect," Appl. Opt. 28, 1991-1994 (1989)