ABSTRACT
The nonlinear limits of conventional single-mode bers were well recognized in the 1990s during earlier efforts to scale the peak powers of pulsed ber lasers. These earlier efforts focused on lowering the numerical aperture (NA) and optimizing the refractive index prole of optical bers to increase the effective mode area [1, 2]. The emergence of photonic crystal bers (PCFs) in the late 1990s gave new impetus to the mode area scaling of single-mode optical bers. The observation of the “endlessly single-mode” nature of PCFs at small hole sizes in 1996 [3] led to an early realization of the dispersive nature of a photonic crystal cladding [4], which limits the increase of normalized frequency V at short wavelengths. It was quickly realized that the scalability of Maxwell’s equation allows for single-mode operation at very short wavelengths in a small core to be directly translated into single-mode operation in a large core at longer wavelengths [5]. This led to a rapid progress in scaling of core diameters of single-mode PCFs, culminating in the 100-μm core diameter demonstrated in 2006 [6].
