Fiber-optic bend sensor using LP_21 mode operation

Abstract

A novel fiber-optic bending sensor based upon the propagation of LP21 mode is demonstrated. The sensor, comprised of an S-bend fiber on an elastic film, measures LP21 mode specklegram rotation, which increments linearly with bending angle by the stress-optic effect. The sensor is capable of experimentally achieving a sensitivity as high as 4.13 rad/m(-1). The theoretical analysis of the sensor, which is a combination of fiber coupled-mode theory and elastic-optic theory, validates the accuracy of the sensor. The sensor is also shown to be temperature-immune, and can detect both bending direction and bending angle with a large dynamic range. Furthermore, the sensor implementation incorporates inexpensive single-mode fiber at 650 nm for few-mode operation, enabling low-loss transmission and compatibility with existing interfaces.

All-fiber spatial rotation manipulation for radially asymmetric modes

“…Recently, generation of cylindrical vector beam (CVB) by coherent superposition of two spatially orthogonal LP modes with high polarization purity has been demonstrated 12 . Fiber specklegram sensors (FSS) using LP 21 mode rotation 13 and orbital angular momentum (OAM) generation by two spatially orthogonal LP modes with fixed phase delay 14, 15 have been also reported. For those applications, fine and reliable adjustment of the spatial orientation of high order modes has become a basic necessity.…”

Fiber optic temperature sensor based on image processing of intermodal interference pattern

“…Among others, statistical mode sensors [1] and (more recently) few-mode fiber sensors [2,3] have been developed. Interference pattern analysis has mainly so far been applied to vibration, bend [4] and strain sensing [5].…”

Two-dimensional refractive index and stresses profiles of a homogenous bent optical fiber

“…Optical fibers are well known to be common elements in the field of optical communications, data transmission, and sensing devices [1][2][3]. Optical fiber were reported to suffer mechanical bending [4][5][6], twisting [5], and elongation through drawing [7] during applications.…”

“…These mechanical processes generate a birefringence inside the optical fiber material. The induced birefringence, however, is preferred in some sensor applications [1][2][3]. In the fields of telecommunications and data transition, bending and twisting are known to cause signal attenuation [8,9].…”