128 research outputs found
Giant anomalous self-steepening in photonic crystal waveguides
Self-steepening of optical pulses arises due the dispersive contribution of
the Kerr nonlinearity. In typical structures this response
is on the order of a few femtoseconds with a fixed frequency response. In
contrast, the effective Kerr nonlinearity in photonic crystal
waveguides (PhCWGs) is largely determined by the geometrical parameters of the
structure and is consequently tunable over a wide range. Here we show
self-steepening based on group-velocity (group-index) modulation for the first
time, giving rise to a new physical mechanism for generating this effect.
Further, we demonstrate that periodic media such as PhCWGS can exhibit
self-steepening coefficients two orders of magnitude larger than typical
systems. At these magnitudes the self-steepening strongly affects the nonlinear
pulse dynamics even for picosecond pulses. Due to interaction with additional
higher-order nonlinearities in the semiconductor materials under consideration,
we employ a generalized nonlinear Schr\"{o}dinger equation numerical model to
describe the impact of self-steepening on the temporal and spectral properties
of the optical pulses in practical systems, including new figures of merit.
These results provide a theoretical description for recent experimental results
presented in [Scientific Reports 3, 1100 (2013) and Phys. Rev. A 87, 041802
(2013)]. More generally, these observations apply to all periodic media due to
the rapid group-velocity variation characteristic of these structures.Comment: 7 pages, 4 figure
Soliton dynamics in the multiphoton plasma regime
Solitary waves have consistently captured the imagination of scientists,
ranging from fundamental breakthroughs in spectroscopy and metrology enabled by
supercontinuum light, to gap solitons for dispersionless slow-light, and
discrete spatial solitons in lattices, amongst others. Recent progress in
strong-field atomic physics include impressive demonstrations of attosecond
pulses and high-harmonic generation via photoionization of free-electrons in
gases at extreme intensities of 1014 Wcm2. Here we report the first
phase-resolved observations of femtosecond optical solitons in a semiconductor
microchip, with multiphoton ionization at picojoule energies and 1010 Wcm2
intensities. The dramatic nonlinearity leads to picojoule observations of
free-electron-induced blue-shift at 1016 cm3 carrier densities and self-chirped
femtosecond soliton acceleration. Furthermore, we evidence the time-gated
dynamics of soliton splitting on-chip, and the suppression of soliton
recurrence due to fast free-electron dynamics. These observations in the highly
dispersive slow-light media reveal a rich set of physics governing
ultralow-power nonlinear photon-plasma dynamics.Comment: 14 pages (main body and supplement), 11 figures - earlier draft;
http://www.nature.com/srep/2013/130122/srep01100/full/srep01100.htm
Physical origin of higher-order soliton fission in nanophotonic semiconductor waveguides
Supercontinuum generation in Kerr media has become a staple of nonlinear
optics. It has been celebrated for advancing the understanding of soliton
propagation as well as its many applications in a broad range of fields.
Coherent spectral broadening of laser light is now commonly performed in
laboratories and used in commercial white light sources. The prospect of
miniaturizing the technology is currently driving experiments in different
integrated platforms such as semiconductor on insulator waveguides. Central to
the spectral broadening is the concept of higher-order soliton fission. While
widely accepted in silica fibers, the dynamics of soliton decay in
semiconductor waveguides is yet poorly understood. In particular, the role of
nonlinear loss and free carriers, absent in silica, remains an open question.
Here, through experiments and simulations, we show that nonlinear loss is the
dominant perturbations in wire waveguides, while free-carrier dispersion is
dominant in photonic crystal waveguides
Interplay of plasma-induced and fast thermal nonlinearities in a GaAs-based photonic crystal nanocavity
We investigate the nonlinear response of GaAs-based photonic crystal cavities
at time scales which are much faster than the typical thermal relaxation rate
in photonic devices. We demonstrate a strong interplay between thermal and
carrier induced nonlinear effects. We have introduced a dynamical model
entailing two thermal relaxation constants which is in very good agreement with
experiments. These results will be very important for Photonic Crystal-based
nonlinear devices intended to deal with practical high repetition rate optical
signals.Comment: 10 pages, 8 figures, Phys Rev A (accepted
Shape Invariance in Supersymmetric Quantum Mechanics and its Application to Selected Special Functions of Modern Physics
We applied the methods of supersymmetric quantum mechanics to differential equations that generate well-known special functions of modern physics. This application provides new insight into these functions and generates recursion relations among them. Some of these recursion relations are apparently new (or forgotten), as they are not available in commonly used texts and handbooks. This method can be easily extended to explore other special functions of modern physics
Digital resonance tuning of high-Q/Vm silicon photonic crystal nanocavities by atomic layer deposition
We propose and demonstrate the digital resonance tuning of high-Q/Vm silicon
photonic crystal nanocavities using a self-limiting atomic layer deposition
technique. Control of resonances in discrete steps of 122 +/- 18 pm per hafnium
oxide atomic layer is achieved through this post-fabrication process, nearly
linear over a full 17 nm tuning range. The cavity Q is maintained in this
perturbative process, and can reach up to its initial values of 49,000 or more.
Our results are highly controllable, applicable to many material systems, and
particularly critical to matching resonances and transitions involving
mesoscopic optical cavities.Comment: 9 pages, 3 figure
Theory of Electro-optic Modulation via a Quantum Dot Coupled to a Nano-resonator
In this paper, we analyze the performance of an electro-optic modulator based
on a single quantum dot strongly coupled to a nano-resonator, where electrical
control of the quantum dot frequency is achieved via quantum confined Stark
effect. Using realistic system parameters, we show that modulation speeds of a
few tens of GHz are achievable with this system, while the energy per switching
operation can be as small as 0.5 fJ. In addition, we study the non-linear
distortion, and the effect of pure quantum dot dephasing on the performance of
the modulator.Comment: 9 pages, 7 figure
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