Katarzyna Krupa

Intermodal modulational instability in graded-index multimode optical fibers

We report on the experimental observation of an intermodal noise-seeded modulational instability process (MI) taking place in the normal dispersion regime of a few-mode graded-index optical fiber. Strong power dependence of the MI spectra is observed, with a peak gain modulation frequency that scales as the square root of the injected light power. These observations are in excellent agreement with the predictions of a bimodal-MI model.

Zero focusing via competing nonlinearities in beta-barium-borate crystals

We investigate nonlinear focusing behavior of light beams propagating in beta-barium-borate crystals under mismatched second-harmonic generation. We clearly identify experimentally multiple self-focusing and defocusing regions against the orientation angle and the condition where competing quadratic and cubic nonlinearities perfectly compensate each other (zero-focusing point).

All-normal dispersion supercontinuum generation in the near-infrared by Raman conversion in standard optical fiber

We demonstrate all-normal dispersion supercontinuum generation in the 1080 nm-1600 nm range by propagating subnanosecond pulses in a high numerical aperture standard optical fiber. The extreme saturation of the Raman gain provides a flat spectrum in the considered range, making this broadband source particularly suitable for coherent Raman spectroscopy. This unusual regime of supercontinuum generation (Raman gain saturation regime) is investigated through an experimental spectrotemporal study. The possibility of operating spectrometer-free time-coded coherent Raman spectroscopy is introduced.

Static and dynamic measurements of active MEMS by Twyman-Green interferometry: case of AlN-based microactuators

This study presents static and dynamic characterisation by Twyman Green interferometry of two active MEMS actuators driven by a thin film transducer of aluminium nitride (AlN). Firstly, we report on the testing results of thin film AlN/Si piezoelectric micro-machined ultrasonic transducers. These devices are expected to exhibit sensing capabilities for monitoring fluid property changes. The goal of second case study is the development of reliable AlN driven cantilevers working as actuation elements in Micro-Electro-Mechanical Systems (MEMS).

Cascaded intermodal four-wave mixing in a few-mode fiber

During the last few years, intensive works on multimode fibers allowed for the observation of a series of complex and novel nonlinear spatiotemporal phenomena such as: multimode solitons, geometric parametric instability, supercontinuum generation, and self-induced beam cleaning [1-4]. Among these phenomena, intermodal four-wave mixing (IMFWM) demonstrated larger frequency shifts in comparison with single-mode fibers. In this work, we studied IMFWM in a few-mode graded-index fiber (GRIN-FMF) pumped in the normal dispersion regime at 1064 nm. We report parametric sidebands detuned by hundreds of THz from the pump.

Visible Supercontinuum Generation by Dual-Wavelength Pumping in Multimode Rectangular Optical FibersVisible Supercontinuum Generation by Dual-Wavelength Pumping in Multimode Rectangular Optical Fibers

We study supercontinuum generation in a multimode microstructured optical fiber by dual-wavelength pumping. We demonstrate significant blue extension of the spectrum in relatively short fiber length by exploiting cross-phase modulation between high order modes.

Reliability study of AlN-driven microcantilevers based on interferometric measurements of their static and dynamic behaviours

Microelectromechanical systems (MEMS) are exposed to a variety of environmental conditions, making the prediction of operational reliability difficult. In this contribution, we investigate the environmental effects on the static and dynamic properties of piezoelectrically actuated MEMS microcantilevers where aluminium nitride (AlN) is used as actuation material. The environmental effects to be considered include thermal and humid cycling, as well as harsh electrical loading performed under standard weather conditions. Investigated properties are defined for the static behaviour (i.e. determined initial deflection, out-of-plane displacement vs. constant voltage) and dynamic behaviour (i.e. determined 1st resonance frequency, vibration amplitude at 1st resonance mode) of AlN-based microcantilevers. The metrology tool is a Twyman Green interferometer, operating in both stroboscopic regime and time-average interferometry mode. The initial deflection and the frequency changes of the first resonance mode of microcantilevers are monitored during the accelerated thermal aging, the humidity tests, as well as harsh electrical loading and fatigue tests. Finally, the resonant fatigue tests, accelerated by application of a high voltage are accomplished to evaluate the lifetime of microcantilevers. For constant values of voltage higher than 15 V, a delamination of top electrode of AlN transducer is observed.