Nd-doped crystal waveguide lasers and amplifiers
This thesis presents the results of investigations into waveguide lasers and optical amplifiers fabricated in Nd-doped crystals. Laser operation of Nd3+ doped Ti:LiNbO3 around 900nm is reported. A threshold power of 26mW was obtained when the device was pumped with a Ti:Al2O3 laser operating around 814nm. The wavelength of the waveguide fundamental mode cut-off was altered by manipulation of the device fabrication parameters to induce higher propagation losses at the parasitic laser wavelength of 1.084µm and thus enhance lasing behaviour around 900nm. A 1.2W diode-pumped, Nd:Y3Al5O12 (Nd:YAG) waveguide optical amplifier has been demonstrated with a simple double pass geometry. Small signal gains as high as 28.4dB were observed along with extracted power efficiencies of up to 36%. Deviation from ideal performance is explained by reference to intense pumping effects and pump/signal overlap in the device. The coupling of diode-bars into planar waveguides for high power operation has been analysed. Using a lens array to couple the diode output into an Nd:YAG planar waveguide, an extremely compact, end pumped, device was constructed which had a slope efficiency of 40% with respect to incident pump power and a maximum output power of 1.5W for 6W of diode power. Fibre lens and proximity coupling scheme designs have also been examined. A Ti:Al2O3 face pumped LPE waveguide laser has been demonstrated. Nd:YAG on YAG, Nd:Gd3Ga5O12 on YAG and Nd:YAG on glass waveguides fabricated by thermal bonding have been studied. These structures had numerical apertures of 0.06, 0.74 and 0.82 respectively. The propagation losses, obtained from the laser performance, were found to be 0.7B/cm, 0.4dB/cm and 0.7dB/cm respectively.