Integrated optical devices in rare-earth-doped LiNbO3
This thesis describes the fabrication and characterisation of rare-earth-doped Ti:LiNbO3 channel waveguide devices. Rare-earth-doped integrated optical sources in LiNbO3 are expected to play key roles in optical communication and sensor systems, due to their potential of mass production at reduced cost and their ability to perform several signal processing functions on a single chip. The fabrication of neodymium-diffused Ti:LiNbO3 waveguide devices is described in detail, and their spectroscopic and laser characteristics are given. Laser results for emission at 1084nm and ~900nm are presented, the latter for the first time. Room temperature lasing has been demonstrated for the first time in these devices. Y-branch resonator cavities have been analysed using a transfer matrix approach, and their tuning and wavelength selective properties have been studied. The latitude offered by the planar configuration was then demonstrated through the fabrication of Y-branch laser devices in Nd-diffused LiNbO3, with on-chip electro-optic modulators. The potential of multiple-cavity structures for added functionality has been demonstrated by tuning and Q-switching these devices. Diode pumped operation of these devices has been demonstrated. A detailed spectroscopic analysis, using the Judd-Ofelt theory, has been carried out in the Er:LiNbO3 system for the first time. Results are presented on the lifetimes and quantum efficiencies of various energy levels. ESA transition strengths have been calculated and qualitative comparisons have been made with Er-doped glass to evaluate the efficiency of the 980nm pumping scheme in Er:LiNbO3. Er-diffused Ti:LiNbO3 waveguides have been fabricated and characterised. The versatility of the diffusion technique for the incorporation of rare-earth ions in LiNbO3 has been demonstrated by the fabrication of locally-diffused Er:Ti:LiNbO3 devices. Net gain has been measured in these waveguides, pumped at 1480nm, and the measurement techniques employed and the results obtained are presented. Comparisons have been made of the pump power requirements for gain threshold in planar and locally diffused waveguides, and it is shown that gain localisation may potentially allow the realisation of low threshold waveguide lasers in this system.