20 research outputs found
Patterned silicon substrates: a common platform for room temperature GaN and ZnO polariton lasers
A new platform for fabricating polariton lasers operating at room temperature
is introduced: nitride-based distributed Bragg reflectors epitaxially grown on
patterned silicon substrates. The patterning allows for an enhanced strain
relaxation thereby enabling to stack a large number of crack-free AlN/AlGaN
pairs and achieve cavity quality factors of several thousands with a large
spatial homogeneity. GaN and ZnO active regions are epitaxially grown thereon
and the cavities are completed with top dielectric Bragg reflectors. The two
structures display strong-coupling and polariton lasing at room temperature and
constitute an intermediate step in the way towards integrated polariton
devices
Direct observation of photonic Landau levels and helical edge states in strained honeycomb lattices
We report the realization of a synthetic magnetic field for photons and
polaritons in a honeycomb lattice of coupled semiconductor micropillars. A
strong synthetic field is induced in both the s and p orbital bands by
engineering a uniaxial hopping gradient in the lattice, giving rise to the
formation of Landau levels at the Dirac points. We provide direct evidence of
the sublattice symmetry breaking of the lowest-order Landau level wavefunction,
a distinctive feature of synthetic magnetic fields. Our realization implements
helical edge states in the gap between n=0 and n=1 Landau levels,
experimentally demonstrating a novel way of engineering propagating edge states
in photonic lattices. In light of recent advances in the enhancement of
polariton-polariton nonlinearities, the Landau levels reported here are
promising for the study of the interplay between pseudomagnetism and
interactions in a photonic system
Measuring topological invariants in polaritonic graphene
Topological materials rely on engineering global properties of their bulk
energy bands called topological invariants. These invariants, usually defined
over the entire Brillouin zone, are related to the existence of protected edge
states. However, for an important class of Hamiltonians corresponding to 2D
lattices with time-reversal and chiral symmetry (e.g. graphene), the existence
of edge states is linked to invariants that are not defined over the full 2D
Brillouin zone, but on reduced 1D sub-spaces. Here, we demonstrate a novel
scheme based on a combined real- and momentum-space measurement to directly
access these 1D topological invariants in lattices of semiconductor
microcavities confining exciton-polaritons. We extract these invariants in
arrays emulating the physics of regular and critically compressed graphene
sucht that Dirac cones have merged. Our scheme provides a direct evidence of
the bulk-edge correspondence in these systems, and opens the door to the
exploration of more complex topological effects, for example involving disorder
and interactions.Comment: Suppl. Mat. added; improved data/error analysi
Reconfigurable photon localization by coherent drive and dissipation in photonic lattices
7 pags., 4 figs.The engineering of localized modes in photonic structures is one of the main targets of modern photonics. An efficient strategy to design these modes is to use the interplay of constructive and destructive interference in periodic photonic lattices. This mechanism is at the origin of the defect modes in photonic bandgaps, bound states in the continuum, and compact localized states in flat bands. Here, we show that in lattices of lossy resonators, the addition of external optical drives with a controlled phase enlarges the possibilities of manipulating interference effects and allows for the design of novel types of localized modes. Using a honeycomb lattice of coupled micropillars resonantly driven with several laser spots at energies within its photonic bands, we demonstrate the localization of light in at-will geometries down to a single site. These localized modes are fully reconfigurable and have the potentiality of enhancing nonlinear effects and of controlling light-matter interactions with single site resolution.Ministerio de Ciencia, Innovación y Universidades (PGC2018-094792-B-100); Consejo Superior de Investigaciones CientÃficas (PTI-001);
Comunidad de Madrid (CAM 2020 Y2020/TCS-6545); Narodowe Centrum Nauki (DEC-2019/32/T/ST3/00332); Agence Nationale de la Recherche
(ANR-11-LABX-0007, ANR-16-CE30-0021, ANR-16-IDEX-0004 ULNE, ANR-QUAN-0003-05); European Research Council (820392, 865151, 949730),
Région Hauts-de-France
Topological gap solitons in a 1D non-Hermitian lattice
Nonlinear topological photonics is an emerging field aiming at extending the
fascinating properties of topological states to the realm where interactions
between the system constituents cannot be neglected. Interactions can indeed
trigger topological phase transitions, induce symmetry protection and
robustness properties for the many-body system. Moreover when coupling to the
environment via drive and dissipation is also considered, novel collective
phenomena are expected to emerge. Here, we report the nonlinear response of a
polariton lattice implementing a non-Hermitian version of the
Su-Schrieffer-Heeger model. We trigger the formation of solitons in the
topological gap of the band structure, and show that these solitons demonstrate
robust nonlinear properties with respect to defects, because of the underlying
sub-lattice symmetry. Leveraging on the system non-Hermiticity, we engineer the
drive phase pattern and unveil bulk solitons that have no counterpart in
conservative systems. They are localized on a single sub-lattice with a spatial
profile alike a topological edge state. Our results demonstrate a tool to
stabilize the nonlinear response of driven dissipative topological systems,
which may constitute a powerful resource for nonlinear topological photonics
Homoepitaxial nonpolar (10-10) ZnO/ZnMgO monolithic microcavities: Towards reduced photonic disorder
Nonpolar ZnO/ZnMgO-based optical microcavities have been grown on (10-10) m-plane ZnO
substrates by plasma-assisted molecular beam epitaxy. Reflectivity measurements indicate an exponential
increase of the cavity quality factor with the number of layers in the distributed Bragg reflectors.
Most importantly, microreflectivity spectra recorded with a spot size in the order of 2 lm show
a negligible photonic disorder (well below 1 meV), leading to local quality factors equivalent to those
obtained by macroreflectivity. The anisotropic character of the nonpolar heterostructures manifests
itself both in the surface features, elongated parallel to the in-plane c direction, and in the optical
spectra, with two cavity modes being observed at different energies for orthogonal polarizations
Homoepitaxial nonpolar (10-10) ZnO/ZnMgO monolithic microcavities: Towards reduced photonic disorder
Nonpolar ZnO/ZnMgO-based optical microcavities have been grown on (10-10) m-plane ZnO
substrates by plasma-assisted molecular beam epitaxy. Reflectivity measurements indicate an exponential
increase of the cavity quality factor with the number of layers in the distributed Bragg reflectors.
Most importantly, microreflectivity spectra recorded with a spot size in the order of 2 lm show
a negligible photonic disorder (well below 1 meV), leading to local quality factors equivalent to those
obtained by macroreflectivity. The anisotropic character of the nonpolar heterostructures manifests
itself both in the surface features, elongated parallel to the in-plane c direction, and in the optical
spectra, with two cavity modes being observed at different energies for orthogonal polarizations
Type-III and Tilted Dirac Cones Emerging from Flat Bands in Photonic Orbital Graphene
The extraordinary electronic properties of Dirac materials, the two-dimensional partners of Weyl semimetals, arise from the linear crossings in their band structure. When the dispersion around the Dirac points is tilted, one can predict the emergence of intricate transport phenomena such as modified Klein tunneling, intrinsic anomalous Hall effects, and ferrimagnetism. However, Dirac materials are rare, particularly with tilted Dirac cones. Recently, artificial materials whose building blocks present orbital degrees of freedom have appeared as promising candidates for the engineering of exotic Dirac dispersions. Here we take advantage of the orbital structure of photonic resonators arranged in a honeycomb lattice to implement photonic lattices with semi-Dirac, tilted, and, most interestingly, type-III Dirac cones that combine flat and linear dispersions. Type-III Dirac cones emerge from the touching of a flat and a parabolic band when synthetic photonic strain is introduced in the lattice, and they possess a nontrivial topological charge. This photonic realization provides a recipe for the synthesis of orbital Dirac matter with unconventional transport properties and, in combination with polariton nonlinearities, opens the way to study Dirac superfluids in topological landscapes