2,270 research outputs found
Optical sensing with Anderson-localised light
We show that fabrication imperfections in silicon nitride photonic crystal
waveguides can be used as a resource to efficiently confine light in the
Anderson-localised regime and add functionalities to photonic devices. Our
results prove that disorder-induced localisation of light can be utilised to
realise an alternative class of high-quality optical sensors operating at room
temperature. We measure wavelength shifts of optical resonances as large as
15.2 nm, more than 100 times the spectral linewidth of 0.15\,nm, for a
refractive index change of about 0.38. By studying the temperature dependence
of the optical properties of the system, we report wavelength shifts of up to
about 2 nm and increases of more than a factor 2 in the quality factor of the
cavity resonances, when going from room to cryogenic temperatures. Such a
device can allow simultaneous sensing of both local contaminants and
temperature variations, monitored by tens of optical resonances spontaneously
appearing along a single photonic crystal waveguide. Our findings demonstrate
the potential of Anderson-localised light in photonic crystals for scalable and
efficient optical sensors operating in the visible and near-infrared range of
wavelengths.Comment: 10 pages, 3 figure
Disordered Cellulose-based Nanostructures for Enhanced Light-scattering
Cellulose is the most abundant bio-polymer on earth. Cellulose fibres, such
as the one extracted form cotton or woodpulp, have been used by humankind for
hundreds of years to make textiles and paper. Here we show how, by engineering
light matter-interaction, we can optimise light scattering using exclusively
cellulose nanocrystals. The produced material is sustainable, biocompatible
and, when compared to ordinary microfibre-based paper, it shows enhanced
scattering strength (x4) yielding a transport mean free path as low as 3.5 um
in the visible light range. The experimental results are in a good agreement
with the theoretical predictions obtained with a diffusive model for light
propagation
Sensitivity and spectral control of network lasers
Recently, random lasing in complex networks has shown efficient lasing over more than 50 localised modes, promoted by multiple scattering over the underlying graph. If controlled, these network lasers can lead to fast-switching multifunctional light sources with synthesised spectrum. Here, we observe both in experiment and theory high sensitivity of the network laser spectrum to the spatial shape of the pump profile, with some modes for example increasing in intensity by 280% when switching off 7% of the pump beam. We solve the nonlinear equations within the steady state ab-initio laser theory (SALT) approximation over a graph and we show selective lasing of around 90% of the strongest intensity modes, effectively programming the spectrum of the lasing networks. In our experiments with polymer networks, this high sensitivity enables control of the lasing spectrum through non-uniform pump patterns. We propose the underlying complexity of the network modes as the key element behind efficient spectral control opening the way for the development of optical devices with wide impact for on-chip photonics for communication, sensing, and computation
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