Severing the link between modal order and group index using hybrid guided space-time modes

Shiri, Abbas; Abouraddy, Ayman F.

doi:10.48550/arxiv.2111.02617

Cited by 3 publications

(3 citation statements)

References 53 publications

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“…54(f)]. Uniquely, the intrinsic spatio-temporal structure of a hybrid ST mode allows overriding the constraints imposed by the planar waveguide boundary conditions, leading to a host of useful features: (1) the group index of a hybrid ST mode can be tuned continuously, independently of the waveguide structure; (2) hybrid ST modes are dispersion-free to all orders; and (3) each hybrid ST mode in a multimode planar waveguide can -in principle -be manipulated separately, and the group index of each tuned independently of those for the others [406].…”

Section: Hybrid St Modesmentioning

confidence: 99%

Space-time wave packets

Yessenov¹,

Hall²,

Schepler³

et al. 2022

Preprint

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Space-time' (ST) wave packets constitute a broad class of pulsed optical fields that are rigidly transported in linear media without diffraction or dispersion, and are therefore propagation-invariant in absence of optical nonlinearities or waveguiding structures. Such wave packets exhibit unique characteristics, such as controllable group velocities in free space and exotic refractive phenomena. At the root of of these behaviors is a fundamental feature underpinning ST wave packets: their spectra are not separable with respect to the spatial and temporal degrees of freedom. Indeed, the spatio-temporal structure is endowed with non-differentiable angular dispersion, in which each spatial frequency is associated with a single prescribed wavelength. Furthermore, deviation from this particular spatio-temporal structure yields novel behaviors that depart from propagation invariance in a precise manner, such as acceleration with an arbitrary axial distribution of the group velocity, tunable dispersion profiles, and Talbot effects in space-time. Although the basic concept of ST wave packets has been known since the 1980's, only very recently has rapid experimental development emerged. These advances are made possible by innovations in spatio-temporal Fourier synthesis, thereby opening a new frontier for structured light at the intersection of beam optics and ultrafast optics. Furthermore, a plethora of novel spatio-temporally structured optical fields (such as flying-focus wave packets, toroidal pulses, and ST optical vortices) are now providing a swathe of surprising characteristics, ranging from tunable group velocities to transverse orbital angular momentum. We review the historical development of ST wave packets, describe the new experimental approach for their efficient synthesis, and enumerate the various new results and potential applications for ST wave packets and other spatio-temporally structured fields that are rapidly accumulating, before casting an eye on a future roadmap for this field.

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Section: Hybrid St Modesmentioning

confidence: 99%

Space-time wave packets

Yessenov¹,

Hall²,

Schepler³

et al. 2022

Preprint

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“…These unique features of ST wave packets have con- sequently led to increasing interest in guided ST fields [24,[49][50][51]62]. In addition to the ST supermodes reported here, so-called 'hybrid ST modes' have been recently synthesized in single-mode [63] and multimode [64] planar waveguides. It is important to delineate here these two classes of guided ST fields: ST supermodes and hybrid ST modes in a planar waveguide.…”

Section: Discussionmentioning

confidence: 91%

Propagation-invariant space-time supermodes in a multimode waveguide

Shiri¹,

Webster²,

Schepler³

et al. 2022

Preprint

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When an optical pulse is spatially localized in a highly multimoded waveguide, its energy is typically distributed among a multiplicity of modes, thus giving rise to a speckled transverse spatial profile that undergoes erratic changes with propagation. It has been suggested theoretically that pulsed multimode fields in which each wavelength is locked to an individual mode at a prescribed axial wave number will propagate invariantly along the waveguide at a tunable group velocity. In this conception, an initially localized field remains localized along the waveguide. Here, we provide proof-of-principle experimental confirmation for the existence of this new class of pulsed guided fields, which we denote 'space-time supermodes', and verify their propagation invariance in a planar waveguide. By superposing up to 21 modes, each assigned to a prescribed wavelength, we construct space-time supermodes in a 170-micron-thick planar glass waveguide with group indices extending from ≈ 1 to ≈ 2. The initial transverse width of the field is 6 microns, and the waveguide length is 9.1 mm, which is ≈ 257× the associated Rayleigh range. A variety of axially invariant transverse spatial profiles are produced by judicious selection of the modes contributing to the ST supermode, including single-peak and multi-peak fields, dark fields (containing a spatial dip), and even flat uniform intensity profiles.

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“…The results reported here emphasize the possibilities emerging from interfacing the rapidly developing topic of ST wave packets [33] with nanophotonics. Recent efforts along these lines include exploiting nanophotonic structures for synthesizing ST wave packets [65], in addition to the propagation of ST wave packets in waveguides [66][67][68][69][70][71].…”

Section: Discussionmentioning

confidence: 99%