55 research outputs found
Small footprint optoelectrodes using ring resonators for passive light localization
The combination of electrophysiology and optogenetics enables the exploration of how the brain operates down to a single neuron and its network activity. Neural probes are in vivo invasive devices that integrate sensors and stimulation sites to record and manipulate neuronal activity with high spatiotemporal resolution. State-of-the-art probes are limited by tradeoffs involving their lateral dimension, number of sensors, and ability to access independent stimulation sites. Here, we realize a highly scalable probe that features three-dimensional integration of small-footprint arrays of sensors and nanophotonic circuits to scale the density of sensors per cross-section by one order of magnitude with respect to state-of-the-art devices. For the first time, we overcome the spatial limit of the nanophotonic circuit by coupling only one waveguide to numerous optical ring resonators as passive nanophotonic switches. With this strategy, we achieve accurate on-demand light localization while avoiding spatially demanding bundles of waveguides and demonstrate the feasibility with a proof-of-concept device and its scalability towards high-resolution and low-damage neural optoelectrodes
Bose-Einstein Condensation in Gap-Confined Exciton-Polariton States
The development of patterned multi-quantum well heterostructures in
GaAs/AlGaAs waveguides has recently allowed to achieve exciton-polariton
condensation in a topologically protected bound state in the continuum (BIC).
Remarkably, condensation occurred above a saddle point of the polariton
dispersion. A rigorous analysis of the condensation phenomenon in these
systems, as well as the role of the BIC, is still missing. In the present
Letter we theoretically and experimentally fill this gap, by showing that
polariton confinement resulting from the negative effective mass and the
photonic energy gap in the dispersion play a key role in enhancing the
relaxation towards the condensed state. In fact, our results show that
low-threshold polariton condensation is achieved within the effective trap
created by the exciting laser spot regardless of whether the resulting confined
mode is long-lived (polariton BIC) or short-lived (lossy mode). In both cases,
the spatial quantization of the polariton condensate and the threshold
differences associated to the corresponding state lifetime are measured and
characterized. For a given negative mass, a slightly lower condensation
threshold from the polariton BIC mode is found and associated to its suppressed
radiative losses as compared to the lossy one
Fabrication of Nanostructured GaAs/AlGaAs Waveguide for Low-Density Polariton Condensation from a Bound State in the Continuum
Exciton-polaritons are hybrid light-matter states that arise from strong
coupling between an exciton resonance and a photonic cavity mode. As bosonic
excitations, they can undergo a phase transition to a condensed state that can
emit coherent light without a population inversion. This aspect makes them good
candidates for thresholdless lasers, yet short exciton-polariton lifetime has
made it difficult to achieve condensation at very low power densities. In this
sense, long-lived symmetry-protected states are excellent candidates to
overcome the limitations that arise from the finite mirror reflectivity of
monolithic microcavities. In this work we use a photonic symmetry protected
bound state in the continuum coupled to an excitonic resonance to achieve
state-of-the-art polariton condensation threshold in GaAs/AlGaAs waveguide.
Most important, we show the influence of fabrication control and how surface
passivation via atomic layer deposition provides a way to reduce exciton
quenching at the grating sidewalls
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A New Experimental Platform for Operando Structural and Chemical Characterization at the ALS
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Fabrication of fluidic devices with 30 nm nanochannels by direct imprinting
In this work, we propose an innovative approach to the fabrication of a complete micro/nano fluidic system, based on direct nanoimprint lithography. The fabricated device consists of nanochannels connected to U-shaped microchannels by triangular tapered inlets, and has four large reservoirs for liquid input. A master silicon stamp with the multilevel structures is fabricated first, and then a negative replica is made, to be used as a stamp for ultraviolet nanoimprint lithography (UV-NIL). Afterwards, just one single UV-NIL step is necessary for patterning all the the micro and nanostructures. Furthermore, the devices are made of all-transparent materials, and the method allows flexibility for the type of substrates used. The active material (an inorganic-organic hybrid polymer) used for the fabrication of the device has been carefully chosen, so it has adequate surface properties (inert and hydrophilic) for its direct use for biological applications. Devices having 30 nm wide, 30 nm deep nanochannels have been fabricated, and the successful performance of the fluidic system and the continuity of the nanochannels have been proven by flow tests. © 2011 American Vacuum Society
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