Second-harmonic generation using an a axis Nd : MgO : LiNbO3 single crystal fiber with Mg-ion indiffused cladding

We report the implementation of a low-loss core-cladding waveguide structur e of an a axis Nd:MgO:LiNbO3 single-crystal fiber with a step refractive in dex profile and the demonstration of a frequency-doubled laser made from su ch a cladded crystal fiber. The laser-heated pedestal grown a axis single-c rystal fiber, with an elliptical cross-sectional area of 200 x 150 mum, is further shown with a Mg ion indiffusion process. Electron probe microanalys is is used to measure the Mg ion concentration distribution in the Mg-diffu sed layer. After several trials, diffusion parameters suitable for achievin g a core-cladding waveguide structure with a step refractive index profile are obtained. The optical and structural properties of the cladded crystal fibers are also characterized. Room-temperature second-harmonic generation with such a cladded crystal fiber is demonstrated. At room temperature, cw green laser output with a power of 10 muW at the wavelength of 0.532 mum is achieved. The origin of the relatively low conversion efficiency is discus sed, (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-32 86(00)00710-8].