Analysis of brillouin frequency shift and longitudinal acoustic wave in a silica optical fiber with a triple-layered structure

Abstract

We report a thorough analysis on the Brillouin frequency shift as a function of geometrical parameters in a silica optical fiber consisting of triple-layered structure, GeO 2-doped core, P 2 O 5 , and F co-doped inner cladding, and pure silica outer cladding. General characteristic equations for the Brillouin frequency shift were analytically derived and analyzed for various fiber parameters. In experiments, three-layered optical fibers were fabricated and their Brillouin frequency shifts were measured in the wavelength region of 1.55 m by a pump-probe technique. The longitudinal acoustic velocity in each layer was found significantly affected by the thermal stress as well as the dopant concentrations. We confirmed both in theory and experiment that the inner cladding of a three-layered optical fiber does provide a new degree of freedom in precise control of the Brillouin frequency shift.

Functional Fibers and Functional Fiber-Based Components for High-Power Lasers

“…The normal methods for SBS suppression include enhancing core mode size and acoustically engineered fiber designs that generally require complicated core doping profiles or cladding structures [321]. Another practical solution is controlling the Brillouin gain through fiber designing because fibers with different index profiles have different Brillouin gain spectra and therefore different SBS thresholds [321][322][323][324][325][326][327][328][329]. The acousto-optic effective area has been introduced to predict the SBS threshold in optical fibers with ununiform index profiles [330].…”