Date of Award

5-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

School of Materials Science and Engineering

Committee Member

Dr. Philip Brown, Committee Chair

Committee Member

Dr. John Ballato

Committee Member

Dr. Stephen Foulger

Abstract

Fabrication of rare earth (RE) doped optical fibers for use in fiber-based lasers and amplifiers is conventionally performed using a solution doping technique where RE salts (i.e., ErCl3) are dissolved in a solvent, introduced into the porous silica soot, dried and consolidated to form the active fiber core. This process does not allow for tailoring of the chemical environment about the RE. Alternatively, nanoparticle (NP) doping is more recent approach to incorporating rare earths into an optical fiber and have been shown to permit modification of the chemical environment around the RE in ways the enhance spectroscopic performance. This is due to the NP isolating the dopant from the host SiO2 glass by creating a protective “shell” surrounding the RE. The NP host should to have a lower phonon energy than the SiO2 (1100 cm^-1) matrix since the radiative and non-radiative processes influence lasing efficiencies. In this Thesis, lanthanum trifluoride (LaF3) was selected as the NP of choice since it possesses a low phonon energy (~350 cm^-1) and while the fluoride converts to an oxide during the fiber processing, a lower phonon energy environment still remains about the RE. More specifically, NP doping was performed for fabricating and studying erbium doped fibers, where Er3+-doped lanthanum fluoride (Er:LaF3) NPs were synthesized and their properties investigated to determine advantages for NP doping to conventional soluble salt doping. In addition, for this Thesis, different rare earth NP suspensions were produced and studied along with the effects of different host materials in those suspensions. Slope efficiencies in excess of 70% were realized for Er3+ nanoparticle doping in a multimode fiber-based master oscillator power amplifier (MOPA). This Thesis will discuss the systematic study of NP and fiber properties. More specifically, NP doped suspensions and fibers were characterized and discussed by their physical, chemical, and spectroscopic properties to develop an understanding as to how to tailor and HEL relevant performance parameters.

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