Improved large-mode-area endlessly single-mode photonic crystal fibers

Abstract

We numerically study the possibilities for improved large-mode area endlessly single mode photonic crystal fibers for use in high-power delivery applications. By carefully choosing the optimal hole diameter we find that a triangular core formed by three missing neighboring air holes considerably improves the mode area and loss properties compared to the case with a core formed by one missing air hole. In a realized fiber we demonstrate an enhancement of the mode area by ∼ 30 % without a corresponding increase in the attenuation.Applications requiring high-power delivery call for single-mode large-mode area (LMA) optical fibers. While standard-fiber technology has difficulties in meeting these requirements the new class[1] of all-silica photonic crystal fibers (PCF) has a big potential due to their endlessly single-mode properties [2] combined with (in principle) unlimited large effective areas.[3] For recent reviews we refer to Refs. 4, 5.The cladding structure of these PCFs consists of a triangular array of air holes of diameter d and pitch Λ corresponding to an air-filling fraction f = π/(2 √ 3)(d/Λ) 2 . The presence of the air holes results in a strongly wavelength dependent effective index n eff of the cladding and in the short and long wavelength limits we have lim λ≪Λ n eff = n si , lim λ≫Λ n eff = f × n air + (1 − f ) × n si ≡n.

Multimode Nonlinear Fibre Optics: Theory and Applications

“…In the bulk interpretation this corresponds to the situation where nonlinear focusing and diffraction are perfectly balanced, thereby generating a stationary spatial soliton. It may seem that this modal description of self-focusing is only possible in multimode fibres but breaks down in singlemode fibres, for example in large-mode area photonic crystal fibres designed for endlessly single mode operation (Mortensen et al, 2003). However, in this case the role of the higher order bound modes of a multimode fibre is taken over by the cladding modes, and it is the FWM-induced power exchange between the guided mode of a singlemode fibre and its cladding modes which provides a modal interpretation of self-focusing.…”

Numerical modelling of self-heating effects on guiding modes of high-power photonic crystal fibre lasers

“…The solution of above equation gives the displacement vector components (u x , u y , u z ). The first derivatives of displacement vector components define the strain tensor components as (4) Using the generalized Hooke's law [25], σ ij = C ijkl ε kl , where σ ij are the stress tensor components and C ijkl are the stiffness tensor components, one can calculate the stress components. In the plane strain approximation which is used for longlength warmed up systems with a zero temperature gradient along the z direction, the nonzero components of the strain tensor are ε 1 = ε xx , ε 2 = ε yy , and ε 6 = ε xy .…”

“…The ratio of the hole diameter (d) to the hole-to-hole distance (Λ) plays a crucial role in determining the optical properties of photonic crystal fibres (PCFs). It has been proved that for a ratio of d/Λ = 0.45 the one-hole missing PCF acts as a single-mode fibre regardless of the wavelength of the propagating light [3][4][5]. In fibre lasers, to suppress unwanted nonlinear effects when scaling the delivered powers, one can increase the core area.…”

Highdno/dTLiquid Crystals and their Applications in a Thermally Tunable Liquid Crystal Photonic Crystal Fiber

“…We have demonstrated a highly tunable large-core single-mode photonic bandgap fiber, which has a core diameter of 25 mm, an effective mode area of 440 mm 2 and a high tuning sensitivity near room temperature [13]. This is achieved using UCF-1 and a three-rod core PCF [22].…”