Extended single-mode photonic crystal fiber lasers

Abstract

We report on an ytterbium-doped photonic crystal fiber with a core diameter of 60 microm and mode-field-area of ~2000 microm(2) of the emitted fundamental mode. Together with the short absorption length of 0.5 m this fiber possesses a record low nonlinearity which makes this fiber predestinated for the amplification of short laser pulses to very high peak powers. In a first continuous-wave experiment a power of 320 W has been extracted corresponding to 550 W per meter. To our knowledge this represents the highest power per unit length ever reported for fiber lasers. Furthermore, the robust single-transverse-mode propagation in a passive 100 microm core fiber with a similar design reveals the potential of extended large-mode-area photonic crystal fibers.

Single-Mode Regime in Large-Mode-Area Rare-Earth-Doped Rod-Type PCFs

“…An important issue for these LMA PCFs is still to keep the excellent quality of the output beam, first of all by proper fiber designs that can assure the single-mode propagation. In fact, even if single-mode lasing has been experimentally demonstrated for Yb-doped rod-type fibers [8], [9], numerical simulations have previously shown that the single-mode regime of all-silica PCFs is significantly reduced when a core region as large as in rod-type fibers is considered [10]. This paper aims to provide guidelines on geometry and refractive index distribution in order to allow manufacturers to fabricate LMA DC doped PCFs that are single-mode, or effectively single mode at the lasing wavelength of interest, strongly related to the rare-earth element added in the fiber core.…”

“…Its value, in fact, increases with the doping, and manufacturers often attempt to match again the pure silica one by counter doping [9]. Slight variations, above or below the value for silica used in the cladding region, can considerably change the guidance characteristics of the modes, in particular of the higher order ones.…”

“…Slight variations, above or below the value for silica used in the cladding region, can considerably change the guidance characteristics of the modes, in particular of the higher order ones. A down-doped core surrounded by a photonic crystal cladding, for example, can guide due to the microstructure [9] and even lead to a short-wavelength cutoff for the fundamental mode [11]. By means of the finite-element method (FEM), we will, in this paper, analyze fibers with three different values of the doped core diameter, i.e., 35, 60, and 100 µm, showing, in particular, the mode effective index and the mode field distribution-doped region overlap versus the core refractive index.…”

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

“…This phenomenon is not desired because of reduction of beam quality. To overcome this problem, the numerical aperture must be reduced from standard values of 0.1 to a small value of 0.06 [6]. This value for the numerical aperture allows a core diameter of about 15 μm in the 1 μm wavelength region [6].…”

“…To overcome this problem, the numerical aperture must be reduced from standard values of 0.1 to a small value of 0.06 [6]. This value for the numerical aperture allows a core diameter of about 15 μm in the 1 μm wavelength region [6]. In this regard 2.3 m long ytterbium-doped air-clad large-modearea fibre lasers have been reported to deliver 80 W output power equivalent to the power density of 35 W/m [7].…”