Thermal Effects on Modal Properties of Dual-Core Yb-Doped Fibers

Abstract

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Heat Load Influence on Supermodes in Yb-Doped Four-Core Fibers

“…The characteristics of the Yb-doped 4-core fibers studied in this analysis are analogous to the ones of the dual-core fibers considered in [16]. In particular, for each core the diameter is fixed to 19 µm and the refractive index is properly modified to obtain the V -parameter equal to 1.735, 2.2 and 2.4, while keeping fixed the silica refractive index for the cladding, thus providing an intrinsically single-mode behaviour at the signal wavelength of 1032 nm.…”

“…1(left), the four Yb-doped cores are placed at the vertices of a square of side d, varied in the range between 20 µm and 65 µm. The outer part of the 4-core fiber cross-section is the same described in [16]. In particular, we consider an outer diameter sufficiently large to render the fiber unbendable, a so-called rod-type fiber.…”

“…In this work the influence of thermal effects on the supermode propagation in multicore fibers with four Yb-doped cores, arranged in a square with variable side dimension, that is with different optical coupling conditions, is numerically analyzed through the finite element method (FEM). Being the scaling of the total active core area essential for increasing the pulse energy and the peak power in fiber-based amplifiers [9], the study recently done for Yb-doped dual-core fibers [16] is extended to the case of four active cores in the fiber cross-section. Since the thermally-induced refractive index change in the doped cores provides a tighter field confinement of the supermodes, the beaviour of effective area and single-mode regime is analyzed as a function of the total heat load generated as sideeffect of the amplification process [17].…”

Thermo-optic instabilities in asymmetric dual-core amplifiers

“…The scalar mode fields m have been estimated as the dominant polarization components of full-vectorial solutions obtained with a commercial full-vector modal solver based on the finite element method [15,17,18], with subsequent renormalization according to Eq. (7).…”

“…We neglect thermo-optic modifications to the transverse mode profiles, which may have some impact on the quantitative results, leading to an overestimate of the intercore coupling. However, a recent finite-element study indicated that the mode profiles in the structure considered were not strongly modified at thermal loads of a few tens of W/m [15], which is the regime we are considering in most of the simulations.…”