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17 February 2010 A monolithic pump signal multiplexer for air-clad photonic crystal fiber amplifiers
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We report on the performance of a monolithic 6+1X1 fiber pump signal multiplexer for use in fiber amplifiers. The key component of this coupler design is an etched taper that transforms the low-numerical aperture large diameter pump radiation into a high numerical aperture small diamter format for injection into the pump cladding of an air-clad fiber while maintaining a constant refractive index profile in the core for efficient signal coupling. This taper was then fused onto the 6+1 fiber bundle at the large end and to the air-clad large mode area polarization maintaining photonic crystal fiber at the small end. We employed 6 pump delivery fibers in a 200/220/0.22 core/clad/NA format and a 25/250 polarization maintaining step index signal delivery fiber for the bundle. The large end of the taper had a cladding diameter of 650 μm while the small end had a cladding diameter of 300 μm to match the pump cladding diameter of the PCF which was 314 μm. The core within the taper had a constant diameter of 40 μm and NA of 0.07 achieved through a step index profile. The mode field diameter of the PCF was 54 μm. Signal coupling efficiency at 1550 nm was measured to be 90% with a polarization extinction ratio > 20dB while pump coupling efficiency was measured to be 87% at 1532nm. The low pump coupling efficiency was found to be due to pump delivery fibers that had a numerical aperture of 0.24, higher than the specification of 0.22. A simple calculation shows that with 0.22 NA pump fibers, the pump coupling efficiency would increase to 94%.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Benjamin G. Ward, Donald L. Sipes Jr., and Jason D. Tafoya "A monolithic pump signal multiplexer for air-clad photonic crystal fiber amplifiers", Proc. SPIE 7580, Fiber Lasers VII: Technology, Systems, and Applications, 75801C (17 February 2010);


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