What is the maximum differential group delay achievable by a space-time wave packet in free space?

Yessenov, Murat; Mach, Lam; Bhaduri, Basanta; Mardani, Davood; Kondakci, H. Esat; Atia, George K.; Alonso, Miguel A.; Abouraddy, Ayman F.

doi:10.1364/oe.27.012443

Cited by 74 publications

(102 citation statements)

References 74 publications

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“…Because the projection onto the (k z , ω c )-plane is no longer a straight line, the wave packet undergoes group velocity dispersion in free space (but not in the cavity), with group velocity v g = − 1 n 2 −1 c and dispersion coefficient k 2 = ∂ 2 kz ∂ω 2 = − n 2 n 2 −1 c 2 k o , so that v g in free space is negative. Negative-v g ST wave packets have been studied theoretically [39] and realized experimentally [24], and do not violate relativistic causality [40][41][42] We carried out our experiments using two FP cavities, each formed of symmetric Bragg mirrors sandwiching a 10-µm-thick layer of SiO 2 (index of n = 1.45 at a wavelength of λ = 800 nm, leading to a free spectral range of ∼ 22 nm) deposited via e-beam evaporation. The Bragg mirrors are formed of bilayers of SiO 2 and TiO 2 (thicknesses of 138 nm and 88 nm, and indices at λ = 800 nm of 1.45 and 2.28, respectively).…”

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Omni-resonant space–time wave packets

et al. 2020

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We describe theoretically and verify experimentally a novel class of diffraction-free pulsed optical beams that are 'omni-resonant': they have the remarkable property of transmission through planar Fabry-Pérot resonators without spectral filtering even if their bandwidth far exceeds the cavity resonant linewidth. Ultrashort wave packets endowed with a specific spatio-temporal structure couple to a single resonant mode independently of its linewidth. We confirm that such 'space-time' omni-resonant wave packets retain their bandwidth (1.6 nm), spatio-temporal profile (1.3-ps pulse width, 4-µm beam width), and diffraction-free behavior upon transmission through cavities with resonant linewidths of 0.3-nm and 0.15-nm. arXiv:1912.00092v1 [physics.optics]

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Omni-resonant space–time wave packets

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“…5d-iii,iv). Indeed, the propagation distance is dictated by the spectral uncertainty δλ and θ, almost independently of ∆x [57]. Therefore, in light of the typical plasmon decay lengths, the ST-SPP can be considered propagation-invariant for any ∆x, even for subwavelength widths.…”

Section: Propagation Of Subwavelength-width St-sppsmentioning

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Space–Time Surface Plasmon Polaritons: A New Propagation-Invariant Surface Wave Packet

et al. 2020

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We introduce the unique class of propagation-invariant surface plasmon polaritons (SPPs) representing pulsed surface wave packets propagating along unpatterned metal-dielectric interfaces and are localized in all dimensions -with potentially subwavelength transverse spatial widths. The characteristic features of such linear diffraction-free, dispersion-free 'plasmonic bullets' stem from tight spatio-temporal correlations incorporated into the SPP spectral support domain, and we thus call them 'space-time' SPPs. We show that the group velocity of space-time SPP wave packets can be readily tuned to subluminal, superluminal, and even negative values by tailoring the spatio-temporal field structure independently of any material properties. We present an analytical framework and numerical simulations for the propagation of space-time SPPs in comparison with traditional pulsed SPPs whose spatial and temporal degrees of freedom are separable, thereby verifying the propagation-invariance of the former.

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“…velocities tunable from 30c to −4c [58], group delays of ∼150 ps [59], propagation distances extending to 70 m [60,61], among other unique properties [62][63][64][65]. These attributes indicate the potential utility of ST wave packets in constructing an optical buffer.…”

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Demonstration of a Free-Space Optical Delay Line Using Space-Time Wave Packets

Yessenov

Abouraddy

2019

Frontiers in Optics + Laser Science APS/DLS

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An optical buffer having a large delay-bandwidth-product -a critical component for future all-optical communications networks -remains elusive. Central to its realization is a controllable inline optical delay line, previously accomplished via engineered dispersion in optical materials or photonic structures constrained by a low delay-bandwidth product. Here we show that space-time wave packets whose group velocity in free space is continuously tunable provide a versatile platform for constructing inline optical delay lines. By spatio-temporal spectral-phase-modulation, wave packets in the same or in different spectral windows that initially overlap in space and time subsequently separate by multiple pulse widths upon free propagation by virtue of their different group velocities. Delay-bandwidth products of ∼100 for pulses of width ∼1 ps are observed, with no fundamental limit on the system bandwidth. arXiv:1910.05616v1 [physics.optics] 12 Oct 2019The relentless increase in demand for communications bandwidth [1] has spurred developments in sub-systems that are critical for future optical networks, such as spatial-mode multiplexing [2-4] and ultrafast modulators [5]. A critical -but to date elusive -component is an optical buffer that alleviates data packet contention at optical switches by reordering the packets without an optical-to-electronic conversion [6]. Previous efforts addressing this challenge have exploited so-called 'slow light' [7,8], which refers to the reduction in the group velocity of a pulse traversing a selected material [9][10][11][12] or carefully designed photonic structure [13][14][15]. Despite the diversity of their physical embodiments [16], slow-light approaches typically rely on resonant optical effects and are thus limited by a delay-bandwidth product (DBP) on the order of unity.That is, the differential group delay with respect to a reference pulse traveling at c (the speed of light in vacuum) does not exceed the pulse width [17,18], which falls short of the requirements of an optical buffer [19]. Time-varying systems [20] can overcome this limit at the expense of increased implementation complexity. In one realization, a trapdoor mechanism in coupled resonators increases the storage time through externally controlled coupling [21] -but losses concomitantly increase in step with the delay. An alternate approach makes use of non-resonant recycling of orthogonal modes in a cavity [22]. A different strategy relies on transverse spatial structuring to reduce the group velocity in free space, but only a minute reduction below c has been detected to date [23,24]. Nevertheless, theoretical proposals suggest that pushing this approach to the limit may produce sufficiently large differential group delays for an optical buffer [25,26], but temporal spreading is associated with the propagation of these wave packets [27].Finally, a recent theoretical proposal suggests that optical non-reciprocity can help bypass the usual DBP limits [28], but doubts have been cast on this prospect [29,30].An alt...

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What is the maximum differential group delay achievable by a space-time wave packet in free space?

Cited by 74 publications

References 74 publications

Omni-resonant space–time wave packets

Omni-resonant space–time wave packets

Space–Time Surface Plasmon Polaritons: A New Propagation-Invariant Surface Wave Packet

Demonstration of a Free-Space Optical Delay Line Using Space-Time Wave Packets

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