Higher-order mode supercontinuum generation in dispersion-engineered liquid-core fibers

Abstract

Supercontinuum generation enabled a series of key technologies such as frequency comb sources, ultrashort pulse sources in the ultraviolet or the mid-infrared, as well as broadband light sources for spectroscopic methods in biophotonics. Recent advances utilizing higher-order modes have shown the potential to boost both bandwidth and modal output distribution of supercontinuum sources. However, the strive towards a breakthrough technology is hampered by the limited control over the intra- and intermodal nonlinear processes in the highly multi-modal silica fibers commonly used. Here, we investigate the ultrafast nonlinear dynamics of soliton-based supercontinuum generation and the associated mode coupling within the first three lowest-order modes of accurately dispersion-engineered liquid-core fibers. By measuring the energy-spectral evolutions and the spatial distributions of the various generated spectral features polarization-resolved, soliton fission and dispersive wave formation are identified as the origins of the nonlinear broadening. Measured results are confirmed by nonlinear simulations taking advantage of the accurate modeling capabilities of the ideal step-index geometry of our liquid-core platform. While operating in the telecommunications domain, our study allows further advances in nonlinear switching in emerging higher-order mode fiber networks as well as novel insights into the sophisticated nonlinear dynamics and broadband light generation in pre-selected polarization states.

Adaptive liquid-core optical fibers for advanced soliton control

“…Here, we introduce the design principles and fabrication details of fiber-interconnectable, dispersionoptimized, step-index LCFs. We showcase the adaptive tuning potential of LCFs in three key applications: (1) controlling the soliton fission point [2], (2) wideband detuning of the soliton self-frequency shift at picojoule energy level (see Figure 1b) [3], and (3) tunable generation of femtosecond dispersive waves simultaneously at near-and short-wave infrared wavelengths [4]. Our results emphasize liquid-core optical fibers as a promising platform featuring low coupling losses, low pump requirements, flexible dispersion landscapes, and hence, the ability to boost adaptive operation control and nonlinear functionalities in all-fiber-integrated systems.…”

A Theoretical Study of the Supercontinuum Generation for the Photonic Crystal Fibre

“…The supercontinuum is created by nonlinearities operating on the ultra-shot as it passes through a ( PCF) with a highly nonlinear structure that separates into fundamental solitons, emitting dazzling white light. Induced Raman scattering allows the first-order solitons to migrate to the side of longer wavelengths as they pass through the fibre, resulting in a process known as induced Raman scattering (SSFS), with a much broader scope [18]. As shown in Fig 1 [19], the following behaviours indicate the mechanism of supercontinuum production via soliton fission based on the (GNLSE).…”

Numerical and Experimental Demonstration of Intermodal Dispersive Wave Generation

“…By providing light with an ultra-broad bandwidth at a high degree of coherence, supercontinua are of high interest for many applications, such as optical coherence tomography, [1] frequency comb generation, [2] frequency metrology, [3] or coherent Raman spectroscopy. [4] Supercontinuum generation (SCG) has been investigated numerically as well as experimentally in, for example, optical fibers, [5][6][7][8] photonic crystal fibers, [9][10][11][12][13] multi-material DOI: 10.1002/lpor.202100125 fibers, [14] liquid-core fibers, [15,16] and various integrated waveguides with different core materials. [17][18][19][20][21][22][23][24] One strategy for ultra-broad supercontinua involves higher-order soliton (HOS) fission in the anomalous dispersion regime associated with dispersive wave (DW) generation, phase-matched in the normal dispersion regime.…”

“…[ 26 ] While iXPM is solely a phase modulation between transverse modes, iFWM includes amplitude modulations, transferring energy between transverse modes. Many multi‐mode interactions were already investigated numerically as well as experimentally, such as multi‐mode SCG, [ 6,13 ] higher‐order mode SCG, [ 16 ] multi‐mode solitons, [ 5 ] iFWM, [ 27 ] all‐optical switching, [ 28 ] intermodal third‐harmonic generation, [ 23 ] geometric parametric instability, [ 29 ] soliton self‐mode conversion, [ 30 ] and beam self‐cleaning. [ 31 ] With the increased number of transverse modes in multi‐mode waveguides, the complexity of the nonlinear dynamics increases but enables new phase‐matching opportunities for frequency generation.…”

“…In contrast to previous generation of DWs in a different transverse mode via iFWM, [ 13,36 ] the effect of iDWG is solely due to phase modulation and no energy is transferred between transverse modes. Earlier simulations of SCG in liquid‐core fibers [ 16 ] may have contained traces of the new generation dynamics, however, this was neither investigated theoretically nor reported experimentally. Here, we report on experiments with accompanying numerical simulations proving the existence of iDWG and unraveling the underlying mechanism.…”