Canceling and inverting normal and anomalous group-velocity dispersion using space-time wave packets

Abstract

Angular dispersion can counterbalance normal group-velocity dispersion (GVD) that increases the wave-vector length in a dispersive medium. By tilting the wave vector, angular dispersion reduces the axial wave number in this case to match the pre-GVD value. By the same token, however, angular dispersion fails to counterbalance anomalous GVD, which in contrast reduces the wavevector length. Consequently, GVD-cancellation via angular dispersion has not been demonstrated to date in the anomalous dispersion regime. We synthesize here structured femtosecond pulsed beams known as 'space-time' wave packets designed to realize dispersion-cancellation symmetrically in either the normal-or anomalous-GVD regimes by virtue of non-differentiable angular dispersion inculcated into the pulsed field. Furthermore, we also verify GVD-inversion: reversing the GVD sign experienced by the field with respect to that dictated by the chromatic dispersion of the medium itself.

Propagation-invariant space-time supermodes in a multimode waveguide

“…The intrinsic challenges involved in synthesizing Xwaves have been recently resolved by the devleopment of so-called 'space-time' (ST) wave packets [25][26][27][28]: propagation-invariant [29][30][31][32][33][34], narrowband, paraxial pulsed beams whose group velocity can be tuned in free space [31,32,35,36] or transparent dielectrics [37]. A host of novel phenomena have been recently demonstrated using ST wave packets including anomalous refraction [38,39], ST Talbot effects [40] and dispersionfree propagation in dispersive media [41][42][43][44][45][46][47][48], to name a few [25]. The versatility of this new class of propagationinvariant pulsed beams suggests their suitability as a platform for synthesizing propagation-invariant supermodes in multimode waveguides.…”

Observation of ultrabroadband striped space-time surface plasmon polaritons

“…Recently a new class of propagation-invariant pulsed beams (diffraction-free and dispersion-free) have been investigated under the general rubric of 'space-time' (ST) wave packets, which require introducing a tight spectral association between the wavelengths and the spatial frequencies that conforms to a prescribed functional form [26][27][28][29][30][31][32][33]. Besides propagation invariance in free space [34][35][36], as well as in non-dispersive [37] or dispersive [38][39][40][41][42][43] dielectrics, ST wave packets feature a host of unique characteristics [32,33], including tunable group velocities [44,45] and anomalous refraction [46,47]. A critical feature of ST wave packets makes them particularly useful candidates for SPPs: their diffraction-free behavior is independent of dimensionality [33] (whether one [28] or two [48,49] transverse spatial coordinates are involved), making them excellent candidates for plasmonic applications that require maintaining transverse spatial localization in sensing and imaging.…”

Spectral reorganization of space-time wave packets in presence of normal group-velocity dispersion

“…Extensive studies have investigated the generation of STWPs in nonlinear dispersive media [33,34], but their propagation invariance was not verified. However, rapidly evolving developments in preparing STWPs via universal angular-dispersion synthesis [35] has very recently made it possible to confirm dispersion-free propagation of STWPs in dispersive media -in presence of either normal or anomalous GVD [36].…”