The operation of an incoherent optical frequency-domain reflectometer for monitoring the continuous Rayleigh backscatter in a multimode optical fiber is presented. A simple but effective model to predict the value of beat frequencies arising in the system when excited by a linearly frequency-swept amplitude modulation has been developed. We have verified the model’s predictions by experimental measurement of beat frequencies and modulation depth indices of different lengths of standard graded-index multimode optical fiber. Demonstration of the system sensitivity to the detection of microbending loss is then discussed. In particular the detection of loss in a hydrogel-based water-sensing cable allows an alternative interrogation to conventional optical time-domain reflectometry techniques to be implemented. We demonstrate that the incoherent optical frequency-domain reflectometer is capable of detecting and locating sections of increased loss in a multimode optical fiber, and we discuss the fundamental limits on spatial resolution and dynamic range.
© 2000 Optical Society of America
S. Gareth Pierce, Alistair MacLean, and Brian Culshaw, "Optical Frequency-Domain Reflectometry for Microbend Sensor Demodulation," Appl. Opt. 39, 4569-4581 (2000)