Demonstration of ultra-low NA rare-earth doped step index fiber for applications in high power fiber lasers

Abstract

Abstract:In this paper, we report the mode area scaling of a rare-earth doped step index fiber by using low numerical aperture. Numerical simulations show the possibility of achieving an effective area of ~700um 2 (including bend induced effective area reduction) at a bend diameter of 32cm from a 35μm core fiber with a numerical aperture of 0.038. An effective single mode operation is ensured following the criterion of the fundamental mode loss to be lower than 0.1dB/m while ensuring the higher order modes loss to be higher than 10dB/m at a wavelength of 1060nm. Our optimized modified chemical vapor deposition process in conjunction with solution doping process allows fabrication of an Yb-doped step index fiber having an ultra-low numerical aperture of ~0.038. Experimental results confirm a Gaussian output beam from a 35μm core fiber validating our simulation results. Fiber shows an excellent laser efficiency of ~81% and a M 2 less than 1.1. 2015 Optical Society of AmericaOCIS codes: (060.2280) Fiber design and manufacturing; (140.3510) Fiber lasers.

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Highly efficient Yb-free Er-La-Al doped ultra-low Na large mode area single-trench fiber laser

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