RESUMEN
Multimode optical fibers have recently reemerged as a viable platform for addressing a number of long-standing issues associated with information bandwidth requirements and power-handling capabilities. As shown in recent studies, the complex nature of such heavily multimoded systems can be effectively exploited to observe altogether novel physical effects arising from spatiotemporal and intermodal linear and nonlinear processes. Here, we study for the first time, accelerated nonlinear intermodal interactions in core-diameter decreasing multimode fibers. We demonstrate that in the anomalous dispersion region, this spatiotemporal acceleration can lead to relatively blue-shifted multimode solitons and blue-drifting dispersive wave combs, while in the normal domain, to a notably flat and uniform supercontinuum, extending over 2.5 octaves. Our results pave the way towards a deeper understanding of the physics and complexity of nonlinear, heavily multimoded optical systems, and could lead to highly tunable optical sources with very high spectral densities.
RESUMEN
We show that germanium-doped graded-index multimode silica fibers can exhibit relatively high conversion efficiencies (â¼6.5%) for second-harmonic generation when excited at 1064 nm. This frequency-doubling behavior is also found to be accompanied by an effective downconversion. As opposed to previous experiments carried out in single- and few-mode fibers where hours of preparation were required, in our system, these χ(2) related processes occur almost instantaneously. The efficiencies observed in our experiments are, to the best of our knowledge, among the highest ever reported in unprepared fibers.
RESUMEN
We demonstrate that the pump's spatial input profile can provide additional degrees of freedom in tailoring at will the nonlinear dynamics and the ensuing spectral content of supercontinuum generation in highly multimoded optical fibers. Experiments and simulations carried out at 1550 nm indicate that the modal composition of the input beam can substantially alter the soliton fission process as well as the resulting Raman and dispersive wave generation that eventually lead to supercontinuum in such a multimode environment. Given the multitude of conceivable initial conditions, our results suggest that it is possible to pre-engineer the supercontinuum spectral content in a versatile manner.
RESUMEN
We demonstrate that frequency generation in multimode parabolic-index fibers can be precisely engineered through appropriate fiber design. This is accomplished by exploiting the onset of a geometric parametric instability that arises from resonant spatiotemporal compression. By launching the output of an amplified Q-switched microchip laser delivering 400 ps pulses at 1064 nm, we observe a series of intense frequency sidebands that strongly depend on the fiber core size. The nonlinear frequency generation is analyzed in three fiber samples with 50 µm, 60 µm, and 80 µm core diameters. We further demonstrate that by cascading fibers of different core sizes, a desired frequency band can be generated from the frequency lines parametrically produced in each section. The observed frequency shifts are in good agreement with analytical predictions and numerical simulations. Our results suggest that core scaling and fiber concatenation can provide a viable avenue in designing optical sources with tailored output frequencies.
RESUMEN
We observe efficient supercontinuum generation that extends into the visible spectral range by pumping a low differential mode group delay graded index multimode fiber in the normal dispersion regime. For a 28.5 m long fiber, the generated spectrum spans more than two octaves, starting from below 450 nm and extending beyond 2400 nm. The main nonlinear mechanisms contributing to the visible spectrum generation are attributed to multipath four-wave mixing processes and periodic spatio-temporal breathing dynamics. Moreover, by exploiting the highly multimodal nature of this system, we demonstrate versatile generation of visible spectral peaks in shorter fiber spans by altering the launching conditions. A nonlinearly induced mode cleanup was also observed at the pump wavelength. Our results could pave the way for high brightness, high power, and compact, multi-octave continuum sources.