Abstract

Recent results in laser beam delivery and ultra-short pulse (USP) compression using hypocycloid-core Kagome hollow-core photonic crystal fibers (HC-PCFs) [1] proved that this type of optical fiber is an excellent candidate as a photonic component for these applications. For example, it has been demonstrated that the fiber guides up to 1 mJ of 600 fs long pulses with no damage, and by a simple choice of gas and fiber dispersion, the authors achieved both USP guidance with no pulse broadening nor narrowing, guidance with self-phase modulation (SPM) spectral broadening, and finally guidance with over 10-fold self-compression using solitonic dynamics. However, these compression results necessitated both fiber gas-loading-system and tailored fiber-fabrication, which are not necessarily accessible to the broader research community. Here, we report on a set of results of self-compression of a USP laser based on a commercially available Kagome fiber (PMC-C-YB-7C from GLOphotonics [2]) and with no need of gas loading management. The compression relies on pulse dynamics near the photoionization threshold, which shows a strong and abrupt self-compression via the formation of a soliton at a well-defined pulse energy value and then its breakup at higher energy values [3]. By simply adjusting the fiber length from 10 cm to 4 m, we achieved compression of an initial 600 fs from Yb-doped USP-laser down to ~20 fs (a compression ratio ~30) over an energy span of 10 - 500 µJ. Figure 1(a) shows a summary of calculated (dotted curves) and measured (solid curves) pulse duration evolution with input energy for different fiber lengths. All curves show a “step shape” corresponding to this sudden compression, and the input energy value at which the self-compression occurs increases with shortening fiber length. A typical experimental FROG [4] evolution of such dynamic is shown in Figure 1 (c) for the case of 2 m fiber length resulting in a spectral broadening, a soliton red-shift and a strong pulse compression as the energy is increased. For this conditions, the maximum compression occurs at an energy around 60 µJ. For higher energy, the pulse breaks up via soliton fission.

© 2017 IEEE