We present a study of nonlinearly governed all-optical switching of C-band femtosecond pulses using all-solid dual-core fibers with slight asymmetry between the cores. The fibers are made of a thermally matched pair of soft glasses ensuring high index contrast between the core and the cladding. Two dual-core fibers with lower and higher levels of dual-core asymmetry were examined by two different experimental approaches targeting nonlinear switching of 1560 nm, 75 fs solitonic pulses. When using the less asymmetric fiber, an effective self-switching of 1560 nm, 75 fs low-energy pulses was demonstrated; in the case of more asymmetric fiber, a cross-switching of identical pulses was achieved driven by 270 fs, 1030 nm control pulses. The fiber length was optimized in both cases by the cut-back method. The self-switching approach employed in the case of less asymmetric fiber resulted in 35 mm optimal length, at which the highest switching contrast of 20.1 dB with broadband character in the spectral range 1450-1650 nm was observed. The cross-switching in the more asymmetric fiber was performed with even higher switching contrasts exceeding 25 dB at more homogeneous spectral dynamics in the C-band at 14 mm optimal length. Both outcomes represent high application potential with some complementary advantages. The simpler self-switching scheme requires only a single sequence of pulses and subnanojoule switching energy levels. However, in applications where even higher switching contrasts are required, crossswitching can be performed by employing more complex experimental schemes with higher energy control pulses.
This paper reviews our latest achievements in the field of 2.1 um ultrafast Ho:fiber-based laser sources, including tunable all-fiber oscillators, diode-pumped optical preamplifier (booster), and high power fiber-based amplifiers. Pulse energy up to 1 mJ at the wavelength around 2.1 um was demonstrated out of picosecond ultrashort-pulse oscillator-amplifier system. On the application side, we report the volume modification of silicon using picosecond 2.1 μm laser system. We present both modelling and experimental results for the 2.1 μm ultrashort laser pulse interaction with silicon.
We demonstrate narrow band spectral intensity switching in dual-core photonic crystal fibers made of highly nonlinear glass under femtosecond excitation. The fibers expressed dual-core asymmetry, thus the slow and fast fiber cores were unambiguously distinguished according to their dispersion profiles. The asymmetry effect on the dual-core propagation in anomalous dispersion region was studied both experimentally and numerically. The experimental study was carried out using femtosecond laser amplifier system providing tunable pulses in range of 1500 nm - 1800 nm. The obtained results unveiled, that it is possible to improve nonlinearly the coupling between the two waveguides by excitation of the fast fiber core. The results were obtained in regime of high-order soliton propagation and were verified numerically by the coupled generalized nonlinear Schrödinger equations model. The spectral analysis of the radiation transferred to the non-excited core revealed the role of effects such as third order dispersion, soliton compression and spectral dependence of the coupling efficiency. The simulation results provide reasonable agreement with the experimentally observed spectral evolutions in the both fiber cores. Under 1800 nm excitation, narrow band spectral intensity switching was registered with contrast of 23 dB at 10 mm fiber length by changing the excitation pulse energy in sub-nanojoule range.
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