Undoped and Yb-doped Lu3Al5O12 fibers single crystals have been grown by micro-pulling-down (mu-PD) technique. The crystals fibers diameter is determined by the melt meniscus section formed by the crystallization surface. Melt behaviours in the molten zone, meniscus length and thermal gradient have been studied by Ircon optical pyrometer and CCD camera. The longitudinal segregation coefficient (k) of the dopant (Yb3+) was measured by optical fluorescence and inductively coupled plasma (ICP). For laser measurement, the crystal fiber is longitudinally pumped by a fiber-coupled laser diode emitting a maximum output power of 100 W at 940 nm and the obtained result is encouraging. (C) 2009 Elsevier B.V. All rights reserved.