Optical Science and Engineering ETDs

Publication Date

6-22-2015

Abstract

This work presents theoretical, numerical, and experimental investigations of power scaling of core-pumped single-frequency Raman fiber amplifiers operating at 1178 nm. A numerical model was developed that accounts for stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) in relation to the fiber mode field diameter, length, seed power, and available pump power in both co-pumped and counter-pumped configurations. The backward travelling Stokes light is initiated from both spontaneous Brillouin and spontaneous Raman processes. In order to mitigate the SBS process for further power scaling, a multi-step longitudinal temperature distribution along the gain fiber was employed and optimized. Although higher amplifier efficiency is obtained with higher seed power, the output power diminishes at SBS threshold if the same length of fiber is considered. However, if the fiber length is optimized for a given seed power, more power can be extracted; thus indicating further power scaling is expected by constructing a two-stage amplifier system. As an initial experimental step, a commercial off-the-shelf (COTS) fiber is used to obtain 10 W of single-frequency output power through the application of a multi-step thermal gradient in a counter-pumped configuration. A cutback experiment performed on the COTS fiber indicated a linear relation between signal output and pump power at SBS threshold; a result that showed agreement with the theoretical predictions. In addition, 18 W of output was achieved in the single-stage amplifier by designing and utilizing an acoustically tailored fiber for SBS suppression. Further power scaling was demonstrated by constructing a counter-pumped two-stage amplifier system as predicted by the numerical model. In comparing co- and counter-pumped systems, it was shown that while the latter preserves the single-frequency characteristic of the seed laser, the former leads to spectral broadening of the amplified signal output.

Degree Name

Optical Science and Engineering

Level of Degree

Doctoral

Department Name

Optical Science and Engineering

First Advisor

Diels, Jean-Claude

First Committee Member (Chair)

Dajani, Iyad

Second Committee Member

Thomas, James

Third Committee Member

Arissian, Ladan

Document Type

Dissertation

Language

English

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