Effects of twisting and bending on LP_21 mode propagation in optical fiber

Abstract

Twisting and bending characteristics of low-multimode LP21 mode propagation in optical fibers is presented for the first time. Theoretical fiber mode modeling, combining geometrical rotation with opto-elastic effects, demonstrates that the propagation of the LP21 mode is bending-effect-immune. Experimental testing verifies that the LP21 mode specklegram rotates 0.9112 of the fiber twist angle in a fused silica fiber, independent of any fiber bending. This characteristic allows for the LP21 mode to be highly applicable in fiber specklegram sensors.

Fiber-optic bend sensor using LP_21 mode operation

“…The distinctive propagation properties of LP 21 mode have been reported previously, with an intensity distribution (specklegram) which only rotates linearly with fiber twist angle, but independent of bending angle [9]. The distinctive propagation properties of LP 21 mode have been reported previously, with an intensity distribution (specklegram) which only rotates linearly with fiber twist angle, but independent of bending angle [9].…”

“…Previously, the obtained propagation properties of pure LP 21 mode both experimentally and theoretically have been published [9]. The LP 21 specklegram remains unchanged under fiber bending and or in kilometer-long fiber; under fiber twisting, the specklegram rotates by an angle linearly proportional to the twist angle due to both opto-elastic and geometrical effects.…”

Optical manipulation of biological particles using LP21mode in fiber

“…The LP 21 mode has a unique four-lobed centrosymmetric intensity distribution. From Maxwell's equations, LP 21 mode can be written as a superposition of HE 31 and EH 11 [13]:…”

“…We demonstrate the manipulation of biological particles using a single beam in LP 21 mode, with a low-order fiber optic transmission mode [13]. With an intrinsic four-lobed intensity distribution and high coherence, we demonstrate that an LP 21 mode beam can be focused to form an optical chuck, allowing the capture and reorganization of biological particles inside clusters, as well as both translation and rotation of the particle by simply rotating a segment of fiber in the optical train.…”

Variational Approximations for ${\rm LP}_{l1}$ Modes of Graded-Index Few-Mode Fibers

“…FMFs find application largely in astronomical telescopes [5], [6] for improving their performance. Besides this, FMF also finds application in sensors [7] where the LP 21 mode is utilized. In this letter, because of the uses of LP 11 and LP 21 modes as stated above, we have proposed two parameter variational fields for the LP l1 modes of a graded-index few-mode fiber.…”