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Register a new userDelocalized SPM rogue waves in normal dispersion cascaded supercontinuum generation
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Added by
Rasmus Eilk{\\ae}r Hansen
Publication date
2020
fields
Physics
and research's language is
English
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In the numerical modelling of cascaded mid-infrared (IR) supercontinuum generation (SCG) we have studied how an ensemble of spectrally and temporally distributed solitons from the long-wavelength part of an SC evolves and interacts when coupled into the normal dispersion regime of a highly nonlinear chalcogenide fiber. This has revealed a novel fundamental phenomenon - the generation of a temporally and spectrally delocalized high energy rogue wave in the normal dispersion regime in the form of a strongly self-phase-modulation (SPM) broadened pulse. Along the local SPM shape the rogue wave is localized both temporally and spectrally. We demonstrate that this novel form of rogue wave is generated by inter-pulse Raman amplification between the SPM lobes of the many pulses causing the initially most delayed pulse to swallow the energy of all the other pulses. We further demonstrate that this novel type of rogue wave generation is a key effect in efficient long-wavelength mid-IR SCG based on the cascading of SC spectra and demonstrate how the mid-IR SC spectrum can be shaped by manipulating the rogue wave.
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We present a numerical study of the evolution dynamics of ``optical rogue waves, statistically-rare extreme red-shifted soliton pulses arising from supercontinuum generation in photonic crystal fiber [D. R. Solli et al. Nature Vol. 450, 1054-1058 (2007)]. Our specific aim is to use nonlinear Schrodinger equation simulations to identify ways in which the rogue wave dynamics can be actively controlled, and we demonstrate that rogue wave generation can be enhanced by an order of magnitude through a small modulation across the input pulse envelope and effectively suppressed through the use of a sliding frequency filter.
Supercontinuum generation is a highly nonlinear process that exhibits unstable and chaotic characteristics when developing from long pump pulses injected into the anomalous dispersion regime of an optical fiber. A particular feature associated with this regime is the long-tailed rogue wave-like statistics of the spectral intensity on the long wavelength edge of the supercontinuum, linked to the generation of a small number of rogue solitons with extreme red-shifts. Here, we apply machine learning to analyze the characteristics of these solitons at the edge of the supercontinuum spectrum, and show how supervised learning can train a neural network to predict the peak power, duration, and temporal delay of these solitons from only the supercontinuum spectral intensity without phase information. The network accurately predicts soliton characteristics for a wide range of scenarios, from the onset of spectral broadening dominated by pure modulation instability to near octave-spanning supercontinuum with distinct rogue solitons.
Supercontinuum (SC) generation via femtosecond (fs) pumping in all-normal-dispersion (ANDi) fiber is predicted to offer completely coherent broadening mechanisms, potentially allowing for substantially reduced noise levels in comparison to those obtained when operating in the anomalous dispersion regime. However, previous studies of SC noise typically treat only the quantum noise, typically in the form of one-photon-per-mode noise, and do not consider other technical noise contributions, such as the stability of the pump laser, which become important when the broadening mechanism itself is coherent. In this work, we discuss the influence of the amplitude and pulse length noise of the pump laser, both added separately and combined. We show that for a typical mode-locked laser, in which the peak power and pulse duration are anticorrelated, their combined impact on the SC noise is generally smaller than in isolation. This means that the supercontinuum noise is smaller than the noise of the mode-locked pump laser itself, a fact that was recently observed in experiments but not explained. Our detailed numerical analysis shows that the coherence of ANDi SC generation is considerably reduced on the spectral edges when realistic pump laser noise levels are taken into account.
We present numerical results of supercontinuum (SC) generation in the mid-IR spectral region, specifically addressing the molecular fingerprint window ranging from 2.5 to 25 um. By solving the Generalized Nonlinear Schrodinger Equation (GNLSE) in a chalcogenide waveguide, we demonstrate low-power SC generation beyond 10 um from a pump at 5 um. Further, we investigate the short-pulse and CW regimes, and show that a simple linear dispersion profile, applicable to a broad range of chalcogenide media, is sufficient to account for the broad SC generation, and yield rich pulse dynamics leading to the frequent occurrence of rogue wave events. Results are encouraging as they point to the feasibility of producing bright and coherent light, by means of single low-power tabletop laser pumping schemes, in a spectral region that finds applications in such diverse areas as molecular spectroscopy, metrology and tomography, among others, and that is not easily addressable with other light sources
Ability to selectively enhance the amplitude and maintain high coherence of the supercontinuum signal with long pulses is gaining significance. In this work an extra degree of freedom afforded by varying the dispersion profile of a waveguide is utilized to selectively enhance supercontinuum. As much as 16 dB signal enhancement in the telecom window and 100 nm of wavelength extension is achieved with a cascaded waveguide, compared to a fixed dispersion waveguide. Waveguide tapering, in particular with increasing width, is determined to have a flatter and more coherent supercontinuum than a fixed dispersion waveguide when longer input pulses are used. Furthermore, due to the strong birefringence of an asymmetric silicon waveguide the supercontinuum signal is broadened by pumping simultaneously with both quasitransverse electric (TE) and quasi-transverse magnetic (TM) mode in the anomalous dispersion regime. Thus, by controlling the dispersion for the two modes selective signal generation is obtained. Such waveguides offer several advantages over optical fiber as the variation in dispersion can be controlled with greater flexibility in an integrated platform. This work paves the way forward for various applications in fields ranging from medicine to telecom where specific wavelength windows need to be targeted.
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