26 research outputs found
Theory of space-time supermodes in planar multimode waveguides
When an optical pulse is focused into a multimode waveguide or fiber, the
energy is divided among the available guided modes. Consequently, the initially
localized intensity spreads transversely, the spatial profile undergoes rapid
variations with axial propagation, and the pulse disperses temporally.
Space-time (ST) supermodes are pulsed guided field configurations that
propagate invariantly in multimode waveguides by assigning each mode to a
prescribed wavelength. ST supermodes can be thus viewed as spectrally discrete,
guided-wave counterpart of the recently demonstrated propagation-invariant ST
wave packets in free space. The group velocity of an ST supermode is tunable
independently -- in principle -- of the waveguide structure, group-velocity
dispersion is eliminated or dramatically curtailed, and the time-averaged
intensity profile is axially invariant along the waveguide in absence of
mode-coupling. We establish here a theoretical framework for studying ST
supermodes in planar waveguides. Modal engineering allows sculpting this
axially invariant transverse intensity profile from an on-axis peak or dip
(dark beam), to a multi-peak or flat distribution. Moreover, ST supermodes can
be synthesized using spectrally incoherent light, thus paving the way to
potential applications in optical beam delivery for lighting applications
Transverse spin angular momentum of space-time surface plasmon polariton wave packet
In addition to longitudinal spin angular momentum (SAM) along the axis of
propagation of light, spatially structured electromagnetic fields such as
evanescent waves and focused beams have recently been found to possess
transverse SAM in the direction perpendicular to the axis of propagation. In
particular, the SAM of SPPs with spatial structure has been extensively studied
in the last decade after it became clear that evanescent fields with spatially
structured energy flow generate threedimensional spin texture. Here we present
numerical calculations of the space-time surface plasmon polariton (ST-SPP)
wave packet, a plasmonic bullet that propagates at an arbitrary group velocity
while maintaining its spatial distribution. ST-SPP wave packets with complex
spatial structure and energy flow density distribution determined by the group
velocity are found to propagate with accompanying three-dimensional spin
texture and finite topological charge density. Furthermore, the spatial
distribution of the spin texture and topological charge density determined by
the spatial structure of the SPP is controllable, and the deformation
associated with propagation is negligible. ST-SPP wave packets, which can
stably transport customizable three-dimensional spin textures and topological
charge densities, can be excellent subjects of observation in studies of
spinphotonics and optical topological materials.Comment: 15 pages, 6 figure
Observation of ultrabroadband striped space-time surface plasmon polaritons
Because surface plasmon polaritons (SPPs) are surface waves characterized by
one free transverse dimension, the only monochromatic diffraction-free spatial
profiles for SPPs are cosine and Airy waves. Pulsed SPP wave packets have been
recently formulated that are propagation-invariant and localized in the
in-plane dimensions by virtue of a tight spectral association between their
spatial and temporal frequencies, which have thus been dubbed `space-time' (ST)
SPPs. Because of the spatio-temporal spectral structure unique to ST-SPPs, the
optimal launching strategy of such novel plasmonic field configurations remains
an open question. We present here a critical step towards realizing ST-SPPs by
reporting observations of ultrabroadband striped ST-SPPs. These are SPPs in
which each wavelength travels at a prescribed angle with respect to the
propagation axis to produce a periodic (striped) transverse spatial profile
that is diffraction-free. We start with a free-space ST wave packet that is
coupled to a ST-SPP at a gold-dielectric interface, and unambiguously identify
the ST-SPP via an axial beating detected in two-photon fluorescence produced by
the superposition of incident ST wave packet and the excited surface-bound
ST-SPP. These results highlight a viable approach for efficient and reliable
coupling to ST-SPPs, and thus represent the first crucial step towards
realization of the full potential of ST-SPPs for plasmonic sensing and imaging.Comment: 9 pages, 8 figure
Focus issue introduction: Advanced Solid-State Lasers (ASSL) 2014
The editors introduce the focus issue on Advanced Solid-State Lasers (ASSL) 2014, which is based on the topics presented at a congress of the same name held in Shanghai, China, from October 27 to November 1, 2014. This Focus issue, jointly prepared by Optics Express and Optical Materials Express, includes 28 contributed papers (21 for Optics Express and 7 for Optical Materials Express) selected from the voluntary submissions by attendees who presented at the congress and have extended their work into complete research articles. We hope this focus issue offers a useful snapshot of the variety of topical discussions held at the congress and will contribute to the further expansion of the associated research areas