Direct Diode Pumped Raman Fiber Amplifier Based on a Multimode Graded Index Fiber
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING AND MANAGEMENT/DEPT OF ENGINEERING PHYSICS
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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 dBkm 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 2.8dBkm 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 50250 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.
- Lasers and Masers
- Fiber Optics and Integrated Optics