2,192 research outputs found
Observation of robust flat-band localization in driven photonic rhombic lattices
We demonstrate that a flat-band state in a quasi-one-dimensional rhombic
lattice is robust in the presence of external drivings along the lattice axis.
The lattice was formed by periodic arrays of evanescently coupled optical
waveguides, and the external drivings were realized by modulating the paths of
the waveguides. We excited a superposition of flat-band eigenmodes at the input
and observed that this state does not diffract in the presence of static as
well as high-frequency sinusoidal drivings. This robust localization is due to
destructive interference of the analogous wavefunction and is associated with
the symmetry in the lattice geometry. We then excited the dispersive bands and
observed Bloch oscillations and coherent destruction of tunneling.
{\textcopyright} 2017 Optical Society of America.Comment: 5 pages, 7 figure
Technological Leapfrogging as a Source of Competitive Advantage
This paper examines technological leapfrogging industries characterized by long term investments in perennial crops. Threshold farm size and economic valuation are used to evaluate adoption of harvester innovations. Less than 1 percent of Polish farmers are able to adopt overhead harvesters and sunk costs limit the ability of rapid adjustments in U.S. technology.Research and Development/Tech Change/Emerging Technologies,
Ultrafast laser inscription of mid-IR directional couplers for stellar interferometry
We report the ultrafast laser fabrication and mid-IR characterization (3.39
microns) of four-port evanescent field directional couplers. The couplers were
fabricated in a commercial gallium lanthanum sulphide glass substrate using
sub-picosecond laser pulses of 1030 nm light. Straight waveguides inscribed
using optimal fabrication parameters were found to exhibit propagation losses
of 0.8 dB/cm. A series of couplers were inscribed with different interaction
lengths, and we demonstrate power splitting ratios of between 8% and 99% for
mid-IR light with a wavelength of 3.39 microns. These results clearly
demonstrate that ultrafast laser inscription can be used to fabricate high
quality evanescent field couplers for future applications in astronomical
interferometry.Comment: 4 pages, 4 figure
State-recycling and time-resolved imaging in topological photonic lattices
Photonic lattices - arrays of optical waveguides - are powerful platforms for
simulating a range of phenomena, including topological phases. While probing
dynamics is possible in these systems, by reinterpreting the propagation
direction as "time," accessing long timescales constitutes a severe
experimental challenge. Here, we overcome this limitation by placing the
photonic lattice in a cavity, which allows the optical state to evolve through
the lattice multiple times. The accompanying detection method, which exploits a
multi-pixel single-photon detector array, offers quasi-real time-resolved
measurements after each round trip. We apply the state-recycling scheme to
intriguing photonic lattices emulating Dirac fermions and Floquet topological
phases. In this new platform, we also realise a synthetic pulsed electric
field, which can be used to drive transport within photonic lattices. This work
opens a new route towards the detection of long timescale effects in engineered
photonic lattices and the realization of hybrid analogue-digital simulators.Comment: Comments are welcom
Modulation-assisted tunneling in laser-fabricated photonic Wannier-Stark ladders
We observe Wannier-Stark localization in curved photonic lattices, realized
using arrays of evanescently coupled optical waveguides. By correctly tuning
the strength of inter-site coupling in the lattice, we observe that
Wannier-Stark states become increasingly localized, and eventually fully
localized to one site, as the curvature of the lattice is increased. We then
demonstrate that tunneling can be successfully restored in the lattice by
applying a sinusoidal modulation to the lattice position, an effect that is a
direct analogue of photon-assisted tunneling. This precise tuning of the
tunneling matrix elements, through laser-fabricated on-site modulations, opens
a novel route for the creation of gauge fields in photonic lattices.Comment: 5 pages. Comments are welcom
Observation of pair tunneling and coherent destruction of tunneling in arrays of optical waveguides
We report on the experimental realization of a photonic system that simulates
the one-dimensional two-particle Hubbard model. This analogy is realized by
means of two-dimensional arrays of coupled optical waveguides, fabricated using
femtosecond laser inscription. By tuning the analogous "interaction strength",
we reach the strongly-interacting regime of the Hubbard Hamiltonian, and
demonstrate the suppression of standard tunneling for individual "particles".
In this regime, the formation of bound states is identified through the direct
observation of pair tunneling. We then demonstrate the coherent destruction of
tunneling (CDT) for the paired particles in the presence of an engineered
oscillating force of high frequency. The precise control over the analogous
"interaction strength" and driving force offered by our experimental system
opens an exciting route towards quantum simulation of few-body physics in
photonics.Comment: 4 pages, 4 figures, Appendi
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