Full modal analysis of the Brillouin gain spectrum of an optical fiber

Abstract

We present a numerical study of stimulated Brillouin scattering in optical fibers based on a full modal analysis of the acoustic and optical properties. The computation of each acoustic mode supported by the fiber structure allows us a deep and detailed investigation of the characteristics of the Brillouin gain spectrum. We focus our attention on optical fibers acting as acoustic antiwaveguides where the biggest contribution to the Brillouin response often comes from very high-order modes but it is sometimes overlooked because of computational issues. Our analysis clearly highlights their role and their dependence on the physical and geometrical structure of the fiber. INTRODUCTIONFiber lasers are nowadays emerging as the most powerful solid-state laser technology because of their compactness, their reliable and efficient operation, and the high power levels attainable. However several issues degrading the laser performance arise and need to be tackled when increasing the light intensity in the fiber. Stimulated Brillouin scattering (SBS) is often the most detrimental effect for narrow-line lasers [1]. Moreover SBS sets a limit to the power which can be transmitted in a fiber communication system. On the other hand SBS can be conveniently employed for sensing applications and for all-optical signal elaboration. A great deal of research has thus been devoted to the design of fiber geometries in terms of their Brillouin response. The Brillouin gain spectrum (BGS) summarizes all the main properties characterizing a fiber from this point of view and hence is usually the object of the numerical investigations of SBS.Several approaches have been exploited for the computation of the BGS starting from the modal properties of the fiber [2,3]. The usual assumption is that the fiber can support a single optical mode so that only a limited set of axially-symmetric acoustic modes are evaluated. In this paper we present a numerical study of SBS in optical fibers based on a full modal analysis of the acoustic behaviour. The computation of the characteristics of each acoustic mode supported by the fiber structure allows a deep and detailed investigation of the BGS. This is particularly important in the case of optical fibers acting as acoustic antiwaveguides as higher-order modes often provide the biggest contribution to the Brillouin response.

Characterization of acousto-optical interaction in planar silica optical waveguide by the finite element method

“…The SBS gain can be calculated from the overlap integral of the optical field with the displacement vector profile, U(x,y) [17,18], or with the density variation profile [19]. The density variation profile holds strong correlation with the displacement vector profile and this normalized overlap [17,18] can be calculated as:…”

“…The density variation profile holds strong correlation with the displacement vector profile and this normalized overlap [17,18] can be calculated as:…”

Application of Distributed Optical Fiber Sensing Technology in Surrounding Rock Deformation Control of TBM-Excavated Coal Mine Roadway

“…Brillouin optical time domain reflectometry (BOTDR) is a fully distributed sensing technology for distributed strain and temperature measurement along all determined areas with only one optical fiber which is stimulated by laser pulses and therefore many discrete sensors can be replaced [15][16][17]. BOTDR provides fast and reliable measurements, and it also enables early detection of deformations that may affect the safety of mining operations, thereby allowing to schedule necessary works in advance to mitigate the potential risks.…”

Stimulated Brillouin scattering threshold in double-clad fibers with various cladding shapes

“…The acoustic response of such geometries is not known because their numerical characterizations are complicated. Even more difficulties occur when the fiber possess an acoustic antiwaveguide core since in that case the Brillouin response is often ruled by very high-order modes [2].We have recently developed a numerical tool which does not rely on any kind of symmetry of the fiber structure and is able to compute all the supported acoustic modes [3] in any arbitrary geometry. Here, we apply this tool to investigate the effect of the cladding shape of fiber on the SBS threshold power.…”

“…We have recently developed a numerical tool which does not rely on any kind of symmetry of the fiber structure and is able to compute all the supported acoustic modes [3] in any arbitrary geometry. Here, we apply this tool to investigate the effect of the cladding shape of fiber on the SBS threshold power.…”