The Effect of Mode Distribution on Evanescent Field Intensity: Applications in Optical Fiber Sensors

Abstract

This paper discusses the theoretical and experimental implications of changing the distribution of energy among the guided modes of an optical fiber. Particular emphasis is placed on optimizing the intensity of the evanescent field for near-infrared sensor applications. Both theoretical and experimental results show that, by the shifting of energy from low-to high-order modes, the evanescent field can be enhanced by as much as an order of magnitude. A second benefit of adjusting the mode distribution through mode scrambling is the generation of a stable mode distribution which is relatively insensitive to minor changes in the fiberoptic launch conditions. Therefore, mode scrambling can provide a more stable and more sensitive evanescent field sensor suitable for spectroscopic applications.