88,655 research outputs found
Hollow core fiber with an octave spanning bandgap
No full textWe thoroughly compare the out-of-plane bandgaps generated by three realistic two-dimensional lattices: a triangular and a square arrangement of holes and a triangular arrangement of rods. We demonstrate that, for any given hole diameter-to-pitch ratio d/Λ, the triangular arrangement of interconnected resonators generates the widest possible bandgap along the air line, and we propose a physical interpretation explaining these results. The design of a hollow core photonic bandgap fiber based on such a lattice and able to transmit light with sub-decibel-per-meter losses over an octave of frequencies is presented for the first time, to the best of our knowledge
Soliton spectral tunneling in dispersion controlled holey fibers
No full textWe design a number of index-guiding holey fibers with relatively simple structure which possess suitable dispersive properties for the observation of soliton spectral tunneling. Although the fabrication tolerances for these fibers are demanding, numerical simulations show that tunneling across a normal dispersion region of 150 nm width when pumped in the near infrared is in principle possible using just a few meters of these fibers
Multimode nonlinear fibre optics: theory and applications
No full textOptical fibres have been developed as an ideal medium for the delivery of optical pulses ever since their inception (Kao & Hockham, 1966). Much of that development has been focused on the transmission of low-energy pulses for communication purposes and thus fibres have been optimised for singlemode guidance with minimum propagation losses only limited by the intrinsic material absorption of silica glass of about 0.2dB/km in the near infrared part of the spectrum (Miya et al., 1979). The corresponding increase in accessible transmission length simultaneously started the interest in nonlinear fibre optics, for example with early work on the stimulated Raman effect (Stolen et al., 1972) and on optical solitons (Hasegawa & Tappert, 1973). Since the advent of fibre amplifiers (Mears et al., 1987), available fibre-coupled laser powers have been increasing dramatically and, in particular, fibre lasers now exceed kW levels in continuous wave (cw) operation (Jeong et al., 2004) and MW peak powers for pulses (Galvanauskas et al., 2007) in all-fibre systems. These developments are pushing the limits of current fibre technology, demanding fibres with larger mode areas and higher damage threshold. However, it is increasingly difficult to meet these requirements with fibres supporting one single optical mode and therefore often multiple modes are guided. Non-fibre-based laser systems are capable of delivering even larger peak powers, for example commercial Ti:sapphire fs lasers now reach the GW regime. Such extreme powers cannot be transmitted in conventional glass fibres at all without destroying them (Gaeta, 2000), but there is a range of applications for such pulses coupled into hollow-core capillaries, such as pulse compression (Sartania et al., 1997) and high-harmonic generation (Rundquist et al., 1998). For typical experimental parameters, these capillaries act as optical waveguides for a large number of spatial modes and modal interactions contribute significantly to the system dynamics.In order to design ever more efficient fibre lasers, to optimise pulse delivery and to control nonlinear applications in the high power regime, a thorough understanding of pulse propagation and nonlinear interactions in multimode fibres and waveguides is required. The conventional tools for modelling and investigating such systems are based on beam propagation methods (Okamoto, 2006). However, these are numerically expensive and provide little insight into the dependence of fundamental nonlinear processes on specific fibre properties, e.g., on transverse mode functions, dispersion and nonlinear mode coupling. For such an interpretation a multimode equivalent of the nonlinear Schrodinger equation, the standard and highly accurate method for describing singlemode nonlinear pulse propagation (Agrawal, 2001; Blow & Wood, 1989), is desirable. In this chapter, we discuss the basics of such a multimode generalised nonlinear Schrodinger equation (Poletti & Horak, 2008), its simplification to experimentally relevant situations and a few select applications. We start by introducing and discussing the theoretical framework for fibres with χ(3) nonlinearity in Sec. 2. The following sections are devoted to multimode nonlinear applications, presented in the order of increasing laser peak powers. A sample application in the multi-kW regime is supercontinuum generation, discussed in Sec. 3. Here we demonstrate how fibre mode symmetries and launching conditions affect intermodal power transfer and spectral broadening. For peak powers in the MW regime, self-focusing effects become significant and lead to strong mode coupling. The spatio-temporal evolution of pulses in this limit is the topic of Sec. 4. Finally, at GW peak power levels, optical pulses can only be delivered by propagation in gases. Still, intensities become so high that nonlinear effects related to ionisation must be taken into account. An extension of the multimode theory to include these extreme high power effects is presented in Sec. 5 and the significance of mode interaction is demonstrated by numerical examples pertaining to a recent experiment. Finally, we end this chapter with conclusions in Sec. 6
Spazieggiare
No full textIl saggio propone una lettura critica dell’intervento di interni proposto per l’aula della Scuola Cadorna, che prendendo le mosse dal lavoro di “progettazione partecipata” fatto dall’Architetto Linda Poletti con i bambini e le loro famiglie e e dallo studio di alcuni casi esemplari ha proposto una serie di modifiche all’aula esistente di piccola e media entità, che comprendono interventi murari e soluzioni d’arredo integrate e centrate sulla figura del bambino.
Uno spazio progettato per loro, a loro misura e con la loro attiva collaborazione aperto a essere definito e ri-definito dai suoi utenti a seconda delle loro necessità. Un’aula in cui i bambini possano, usando le parole di Argan “spazieggiare”, sperimentando quel processo mediante il quale «l’uomo riconosce e definisce una relazione tra se stesso e il mondo, delimita una “zona d’esperienza” entro la quale la propria personalità è, comunque, “attiva”»
Wavelength conversion in a short length of a solid lead-silicate fibre
No full textWe experimentally demonstrate a four-wave-mixing-based wavelength conversion scheme at 1.55 µm using a 1.1-m length of highly nonlinear, dispersion tailored W-type lead–silicate optical fibe
Designing dispersion- and mode-area-decreasing holey fibers for soliton compression
No full textWe investigate numerically the adiabatic compression of solitons at 1.55 µm in holey fibers which exhibit simultaneously decreasing dispersion and effective mode area. Compression factors >10 are achieved for optimum fiber parameters
Opportunities and Challenges for Long-Distance Transmission in Hollow-Core Fibres
No full textRecently NANF fiber prototypes have shown a steady decrease in loss. Theory predicts they could eventually outperform conventional fibers, in both loss and optical bandwidth. We investigate their potential impact on long-haul optical communication systems. (c) 2021 The Author(s
Mid-IR coherent supercontinuum generation in all-solid step-index soft glass fibers
No full textWe numerically demonstrate that normal dispersion femtosecond pumping of tailored soft glass step-index fibers can generate highly coherent mid-IR supercontinuum light with two octaves bandwidth, suitable for recompression to few-cycle pulse durations
Dataset for article: Polarization stable hollow core fiber interferometer with Faraday rotator mirrors
No full textThis dataset supports the publication:
R. SLAVIK, D. DOUSEK, D. SUSLOV, M. KOMANEC. S. ZVANOVEC, F. POLETTI, AND D.J. RICHARDSON, Polarization stable hollow core fiber interferometer with Faraday rotator mirrors, PHOTONICS TECHNOLOGY LETTERS 2021 </span
Nonlinear optical mode coupling by ionization in an Ar-filled capillary with high-power short-pulse excitation
No full textHigh-power ultrashort laser pulses at near-infrared wavelengths propagating in gas-filled capillaries can form a compact source of XUV/soft X-ray radiation by high-harmonic generation (HHG) [1]. Maximization of the frequency conversion efficiency requires a detailed understanding of the atomic interaction mechanism as well as the propagation properties of both the near-infrared pump in the presence of a partially ionized gas and of the generated XUV. Here we focus on the numerical simulation of pulse propagation in a parameter regime dominated by plasma effects and by the nonlinear properties of ionization, and compare the results with experimental observations
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