139 research outputs found
Assessment method for photo-induced waveguides
A method to probe the guiding characteristics of waveguides formed in
real-time is proposed and evaluated. It is based on the analysis of the time
dependent light distribution observed at the exit face of the waveguide while
progressively altering its index profile and probed by a large diameter optical
beam. A beam propagation method is used to model the observed dynamics. The
technique is applied to retrieve the properties of soliton-induced waveguides
Large self-deflection of soliton beams in LiNbO3
We report the observation of large self-deflection of 2-D bright photorefractive solitons in LiNbO(3) crystal under a dc applied field. Beam deflection as large as 300 mu m after a 7 mm. propagation distance is reported, leading to formation of curved 2-D waveguides. We attribute this large deflection to the low level of impurity acceptors present in the samples, as confirmed by numerical results from a time-dependent photorefractive model
Domain evolution of BaTiO3 ultrathin films under electric field: a first-principles study
A first-principles-derived method is used to study the morphology and
electric-field-induced evolution of stripe nanodomains in (001) BaTiO3 (BTO)
ultrathin films, and to compare them with those in (001) Pb(Zr,Ti)O3 (PZT)
ultrathin films. The BaTiO3 systems exhibit 180o periodic stripe domains at
null electric field, as in PZT ultrathin films. However, the stripes alternate
along [1-10] in BTO systems versus [010] in PZT systems, and no in-plane
surface dipoles occur in BTO ultrathin films (unlike in PZT materials).
Moreover, the evolution of the 180o stripe domains in the BaTiO3 systems, when
applying and increasing an electric field along [001], involves four regions:
Region I for which the magnitude of the down dipoles (i.e., those that are
antiparallel to the electric field) is reduced, while the domain walls do not
move; Region II in which some local down dipoles adjacent to domain walls
switch their direction, resulting in zigzagged domain walls - with the overall
stripe periodicity being unchanged; Region III in which nanobubbles are
created, then contract along [110] and finally collapse; and Region IV which is
associated with a single monodomain. Such evolution differs from that of PZT
ultrathin films for which neither Region I nor zigzagged domain walls exist,
and for which the bubbles contract along [100]. Discussion about such
differences is provided.Comment: 19 pages, 4 figures, 27 references, submitted to Phys. Rev.
Magnetically controlled exciton transfer in hybrid quantum dot-quantum well nanostructures
A magnetophotoluminescence study of the carrier transfer with hybrid
InAs/GaAs quantum dot(QD)-InGaAs quantum well (QW) structures is carried out
where we observe an unsual dependence of the photoluminescence (PL) on the GaAs
barrier thickness at strong magnetic field and excitation density. For the case
of a thin barrier the QW PL intensity is observed to increase at the expense of
a decrease in the QD PL intensity. This is attributed to changes in the
interplane carrier dynamics in the QW and the wetting layer (WL) resulting from
increasing the magnetic field along with changes in the coupling between QD
excited states and exciton states in the QW and the WL
Aharonov-Bohm interference in quantum ring exciton: effects of built-in electric fields
We report a comprehensive discussion of quantum interference effects due to
the finite structure of excitons in quantum rings and their first experimental
corroboration observed in the optical recombinations. Anomalous features that
appear in the experiments are analyzed according to theoretical models that
describe the modulation of the interference pattern by temperature and built-in
electric fields.Comment: 6 pages, 7 figure
Optical spatial solitons at the interface between two dissimilar periodic media: Theory and experiment
Discrete spatial solitons traveling along the interface between two dissimilar one-dimensional arrays of waveguides were observed for the first time. Two interface solitons were found theoretically, each one with a peak in a different boundary channel. One evolves into a soliton from a linear mode at an array separation larger than a critical separation where-as the second soliton always exhibits a power threshold. These solitons exhibited different power thresholds which depended on the characteristics of the two lattices. For excitation of single channels near and at the boundary, the evolution behavior with propagation distance indicates that the solitons peaked near and at the interface experience an attractive potential on one side of the boundary, and a repulsive one on the opposite side. The power dependence of the solitons at variable distance from the boundary was found to be quite different on opposite sides of the interface and showed evidence for soliton switching between channels with increasing input power
Wavelength, power and pulse duration influence on spatial soliton formation in AlGaAs
This work presents the dependence of spatial soliton formation in AlGaAs slab waveguide versus significant parameters such as wavelength, light power, and pulse duration. Comparison between theory and experiments reveals the importance of multiphoton absorption to understand the soliton behavior. Experimental measurements establish some limits of soliton formation such as usable wavelengths and pulse durations
Large self-deflection of soliton beams in LiNb03
We report the observation of large self-deflection of 2-D bright photorefractive solitons in LiNbO3 crystal under a dc applied field. Beam deflection as large as 300 m after a 7 mm propagation distance is reported, leading to formation of curved 2-D waveguides. We attribute this large deflection to the low level of impurity acceptors present in the samples, as confirmed by numerical results from a time-dependent photorefractive model
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