Date of Award

3-5-2007

Document Type

Thesis

Degree Name

Master of Science in Applied Physics

Department

Department of Engineering Physics

First Advisor

Thomas G. Alley, PhD

Abstract

The direct pumping of a Raman fiber amplifier (RFA) was attempted using an array of four 25W, fiber pigtailed diodes at 936nm, combined via a 7 channel fiber beam combiner. The initial attempt was conducted using a 1.8 km, 100 micron core, GRIN fiber with an NA of .29 and attenuation 3.6 dB/km at 936nm. While amplification was not achieved, over 200mW of conversion was shown, with 10.4W of pump power and 3.5W of seed. This corresponds to an average conversion efficiency of 2.2%. The subsequent effort utilized a 2km long, 200 micron core, GRIN fiber, with NA of .27 and attenuation of 2.8dB/km at pump wavelength. Again, amplification was not achieved, but a gain of 80mW was present, with 3.5W of seed power and 14W of pump. This corresponds to an average conversion efficiency of 0.6% and only 2.5% of the coupled seed power. The final experiment attempted to solve the problem of coupling efficiency and high Raman threshold by utilizing a 50/250 dual-clad fiber, with NAs of .28 and .46 for the core and inner cladding, respectively. Again, amplification was not realized, as only 100mW of gain was present, with 25W of pump and 4.2W of coupled seed power, corresponding to 36% of the coupled seed, and an average conversion efficiency of only 0.4%. Although amplification was not achieved for any of the three fibers, gain was shown possible in all, showing that directly pumping an RFA with a diode source is possible.

AFIT Designator

AFIT-GAP-ENP-07-01

DTIC Accession Number

ADA464846

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