Mid-Infrared All-Spliced Cascaded Supercontinuum Generation

All-fiber mid-infrared (MIR) supercontinuum generation (SCG) has been a reality for more than a decade [1], [2], relying on mechanical butt-coupling to couple light between dissimilar fibers. In recent years, reports of all-spliced SCG has emerged due to advances in fusion splicing methods and instrumentation [3]–[5]. From a practical point of view, the all-spliced solution is favourable because it provides superior flexibility in terms of alignment and diameter mismatch, reduced Fresnel reflection, increased thermo-mechanical stability, and reduced chance of surface contamination and degradation. On the other hand, splicing dissimilar fibers also has a number of disadvantages. Firstly, the differences in thermal expansion coefficients causes stress gradients at the splice point during laser ON/OFF cycles, which may eventually lead to permanent damage. Secondly, there is no way to lower the intensity or reduce back reflection coupling by using angled facets or introducing a small air-gap [3]. It is particularly challenging in cascaded SCG, since the pump spectrum may extend into the high-loss region of the subsequent fibers in the cascade.