Fabrication and Characterization of Waveguides in Potassium Gadolinium Tungstate

• Main Author: Merchant, Clark Adrien
• Other Authors: Aitchison, J. Stewart
• Format: Others
• Language: en_ca
• Published: 2008
• Subjects: Waveguides; Raman; Microreflectivity; crystals; 0544
• Online Access: http://hdl.handle.net/1807/11236

This thesis describes the fabrication and characterization of waveguides in the nonlinear, Raman-active optical crystal potassium gadolinium tungstate (KGW). Ion implantation and femtosecond laser writing techniques are used for the first time to fabricate waveguides in this material. The light ion implanted waveguides using hydrogen ions showed unexpected refractive index increases in the damage regions of approximately 0.3% of the nominal refractive index values for three of the four polarization orientations, with only the highest refractive index polarization exhibiting a refractive index decrease of approximately 0.2%. Waveguides fabricated using high-energy carbon, oxygen and fluorine ion irradiations resulted in strongly confining waveguides with wide amorphous damage regions. Carbon ion irradiation of KGW showed the most promise, with sharp step-like waveguides with a maximum refractive index change of delta-n=0.2 with excellent preservation of the Raman properties in the waveguide core. Microreflectivity measurements on the carbon ion irradiated sample revealed unexpected intermittent refractive index changes in the core region, a feature not detected using standard characterization techniques found in the literature. The oxygen ion irradiation of KGW also generated strongly confining waveguides with a maximum refractive index change of delta-n=0.17, however the Raman performance was shown to be reduced to less than 50% in the waveguide cores. Fluorine ion irradiations of KGW resulted in amorphous regions fabricated in the surface regions, offering promise for masking techniques for creating two-dimensional structures. The waveguides written using femtosecond laser writing processes were used to write buried channel waveguides using compressive stresses to form the waveguide. These waveguides exhibited low-losses down to to 2.0 dB/cm in the telecommunications spectrum, with high coupling efficiency to SMF fiber, and excellent Raman properties in the waveguide core. These channel waveguides also successfully showed SRS generation into the 1.8-1.9 \mu m infrared region using a high power picosecond pump source in the telecommunications band. The use of the microreflectivity and micro-Raman spectroscopy measurement techniques were demonstrated to be valuable characterization tools for each of the fabrication methods.