Mode-Field Matched Pump-Signal Combiner for High Power Fiber Laser in Advanced Manufacturing

Abstract

Stable output and beam profile at high power laser operation is a prime requirement for precision high-end manufacturing. The stability of laser charateristics during power scaling in a single-oscillator is limited by several unavoidable non-linear effects. Hence, kW-level power scaling through multiple amplification stages or using signal combination are feasible solutions. In a master oscillator power amplifier (MOPA) architecture, pump-signal combiner with high pump coupling efficiency and low loss signal transmission maintaining seed beam quality during coupling from a single mode fiber into a large mode area fiber, is an important component. In this respect, an effective method of fabricating mode-field matched pump-signal combiner has been presented employing a section of intermediate fiber, having adiabatically tapered core and uniform cladding, along with a conventional signal fiber (termed hybrid signal fiber) inside the input fiber bundle to obtain effective mode-field matching of signal light in between the input fiber bundle and the output fiber. Additionally a taper-less signal combiner design has been proposed for scaling laser power through incoherent combination. The reduced-clad signal fiber with low loss core guidance supports bundling of the input fibers inside an economic low-OH silica tube to obtain good transmission efficiency and beam profile.