Strong Raman-induced noninstantaneous soliton interactions in gas-filled photonic crystal fibers

Abstract

We have developed an analytical model based on the perturbation theory in order to study the optical propagation of two successive intense solitons in hollow-core photonic crystal fibers filled with Raman-active gases. Based on the time delay between the two solitons, we have found that the trailing soliton dynamics can experience unusual nonlinear phenomena such as spectral and temporal soliton oscillations and transport towards the leading soliton. The overall dynamics can lead to a spatiotemporal modulation of the refractive index with a uniform temporal period and a uniform or chirped spatial period.Raman scattering involves the transfer of a small fraction of energy of an optical field to another field at longer wavelengths via inelastic scattering with optical phonons supplied by the medium. The Raman self-frequency redshift, first observed in conventional optical fibers [1][2][3], can continuously downshift the central frequency of a single pulse during propagation. With the invention of solid-silica-core photonic crystal fibers (PCFs) [4,5], this process has been demonstrated and extensively exploited in attaining a broad supercontinuum [6]. The main ingredients are the high confinement of light and tunability dispersion provided by these fibers. Gas-filled hollowcore (HC) PCFs with Kagome lattice have become a strong competitor for solid-silica-core PCFs [7,8]. Besides the latter benefits, a wide range of gases with different properties offers several opportunities to demonstrate new phenomena and applications using optical fibers [9][10][11][12][13][14][15][16][17][18][19][20].Raman scattering processes in gases are characterized by having very long molecular coherence relaxation (dephasing) time (∼ps), at least three orders of magnitude higher than silica glass. Within this time, the medium possesses a high non-instantaneous nonlinear response. A Raman-induced continuous downshift of the frequency of an ultrashort pulse propagating in a gas has been observed [21]. Moreover, a sinusoidal temporal modulation of the medium refractive index lagging the pulse has been detected by launching a delayed weak probe within the dephasing time [21][22][23]. Very recently, we have treated this modulation as a periodic temporal crystal [20] and we have proposed to use hydrogen-filled HC-PCFs to observe the analogue condensed matter physics phenomena, such as the Wannier-Stark ladder [24], the Bloch oscillations [25] and Zener tunneling [26]. In this Letter, we investigate the case when the delayed pulse is another strong fundamental soliton rather than a weak probe pulse as in [20]. The delayed soliton can be treated as a particle in a moving periodic potential induced by the * Corresponding author: m.saleh@hw.ac.uk leading soliton. Phenomena such as spectral and temporal soliton oscillations as well as upgrading the temporal crystal to a spatiotemporal one are predicted here.Pulse propagation in Raman-active gases is governed by the interplay between the Maxwell equations and the Bloch equations of an effective two...

Incoherent Shock and Collapse Singularities in Non-Instantaneous Nonlinear Media

“…Besides its fundamental interest, optical fibers and waveguides [29] turn out to be ideal testbeds for the experimental verification of our predictions, thanks to the easily tailorable Raman response function, as well as other recently investigated mechanisms involving liquid or gas-filled photonic crystal fibers (PCF), as well as surface plasmon polariton systems [30][31][32][33][34][35][36][37].…”

Soliton dynamics in gas-filled hollow-core photonic crystal fibers

“…we have found that a factor of 1 2 » might be used to correct the overestimated value of g 1 , resulting from using the zeroth-order Taylor approximation. The treatments of the dynamics of the trailing pulse 'probe' 2 y are presented in sections 3.1 and 3.2, when it is a weak long pulse and strong ultrashort soliton, respectively [53,54]. The study of the pump-probe dynamics will prove crucial in the future understanding of the essential building blocks of supercontinuum generation in Raman-active gases when excited by ultrashort pulses [69,75].…”

“…Gas-filled HC-PCFs with Kagome lattice have become a powerful alternative for solid-core PCFs especially for nonlinear applications [42]. The low-loss wide transmission window, the pressure-tunability dispersion, and the variety of different gases with special properties have offered several opportunities for demonstrating new nonlinear applications [43] such as Stokes generation with a drastical reduction in Raman threshold [44], high harmonic generation [45], efficient deep-ultraviolet radiation [46], ionization-induced soliton self-frequency blueshift [47][48][49][50], strong asymmetrical SPM, universal modulational instability (MI) [51], parity-time symmetry [52], and temporal crystals [53,54]. The subject of this review is to present in detail some of these applications, especially those which involve soliton dynamics.…”

Nonlinear interaction of vector solitons inside birefringent optical fibers

“…Depending on their relative amplitudes and phases, the two solitons may attract or repel each other. More recently, the effects of Raman scattering on two interacting optical solitons have been studied [6][7][8][9]. In all of these studies, optical pulses were assumed to remain linearly polarized during their propagation inside the optical fiber, and a scalar nonlinear Schrödinger (NLS) equation was used to describe the nonlinear interaction between two temporally separated solitons.…”