62 research outputs found
Quantum correlation of light scattered by disordered media
We study theoretically how multiple scattering of light in a disordered
medium can spontaneously generate quantum correlations. In particular we focus
on the case where the input state is Gaussian and characterize the correlations
between two arbitrary output modes. As there is not a single all-inclusive
measure of correlation, we characterise the output correlations with three
measures: intensity fluctuations, entanglement, and quantum discord. We found
that, while a single mode coherent state input can not produce quantum
correlations, any other Gaussian input will produce them in one form or
another. This includes input states that are usually regarded as more classical
than coherent ones, such as thermal states, which will produce a non zero
quantum discord
Superpixel-based spatial amplitude and phase modulation using a digital micromirror device
We present a superpixel method for full spatial phase and amplitude control
of a light beam using a digital micromirror device (DMD) combined with a
spatial filter. We combine square regions of nearby micromirrors into
superpixels by low pass filtering in a Fourier plane of the DMD. At each
superpixel we are able to independently modulate the phase and the amplitude of
light, while retaining a high resolution and the very high speed of a DMD. The
method achieves a measured fidelity for a target field with fully
independent phase and amplitude at a resolution of pixels per
diffraction limited spot. For the LG orbital angular momentum mode the
calculated fidelity is , using DMD pixels. The
superpixel method reduces the errors when compared to the state of the art Lee
holography method for these test fields by and , with a comparable
light efficiency of around . Our control software is publicly available.Comment: 9 pages, 6 figure
Phase-Retrieval with Incomplete Autocorrelations Using Deep Convolutional Autoencoders
Phase-retrieval techniques aim to recover the original signal from just the
modulus of its Fourier transform, which is usually much easier to measure than
its phase, but the standard iterative techniques tend to fail if only part of
the modulus information is available. We show that a neural network can be
trained to perform phase retrieval using only incomplete information, and we
discuss advantages and limitations of this approach
Quantum correlation of light scattered by disordered media
We study theoretically how multiple scattering of light in a disordered medium can spontaneously generate quantum correlations. In particular we focus on the case where the input state is Gaussian and characterize the correlations between two arbitrary output modes. As there is not a single all-inclusive measure of correlation, we characterise the output correlations with three measures: intensity fluctuations, entanglement, and quantum discord. We find that, while a coherent input state can not produce quantum correlations, any other Gaussian input will produce them in one form or another. This includes input states that are usually regarded as more classical than coherent ones, such as thermal states, which will produce a non-zero quantum discordWe are grateful to M. Paternostro, D. Browne, and M. Williamson for insightful discussions. JA acknowledges support by EPSRC (EP/M009165/1). JB acknowledges support from the Leverhulme Trust’s Philip Leverhulme Prize. IS acknowledges support from EPSRC (EP/L015331/1) through the Centre of Doctoral Training in Metamaterials (XM2)
Non-invasive imaging: Peeking through the curtain
Copyright © 2014 Nature Publishing Grou
A nanophotonic laser on a graph
Conventional nano-photonic schemes minimise multiple scattering to realise a
miniaturised version of beam-splitters, interferometers and optical cavities
for light propagation and lasing. Here instead, we introduce a nanophotonic
network built from multiple paths and interference, to control and enhance
light-matter interaction via light localisation. The network is built from a
mesh of subwavelength waveguides, and can sustain localised modes and
mirror-less light trapping stemming from interference over hundreds of nodes.
With optical gain, these modes can easily lase, reaching 100 pm
linewidths. We introduce a graph solution to the Maxwell's equation which
describes light on the network, and predicts lasing action. In this framework,
the network optical modes can be designed via the network connectivity and
topology, and lasing can be tailored and enhanced by the network shape.
Nanophotonic networks pave the way for new laser device architectures, which
can be used for sensitive biosensing and on-chip optical information
processing
Weak localization of light in superdiffusive random systems
L\'evy flights constitute a broad class of random walks that occur in many
fields of research, from animal foraging in biology, to economy to geophysics.
The recent advent of L\'evy glasses allows to study L\'evy flights in
controlled way using light waves. This raises several questions about the
influence of superdiffusion on optical interference effects like weak and
strong localization. Super diffusive structures have the extraordinary property
that all points are connected via direct jumps, meaning that finite-size
effects become an essential part of the physical problem. Here we report on the
experimental observation of weak localization in L\'evy glasses and compare
results with recently developed optical transport theory in the superdiffusive
regime. Experimental results are in good agreement with theory and allow to
unveil how light propagates inside a finite-size superdiffusive system
Wide field fluorescence epi-microscopy behind a scattering medium enabled by speckle correlations
Fluorescence microscopy is widely used in biological imaging, however
scattering from tissues strongly limits its applicability to a shallow depth.
In this work we adapt a methodology inspired from stellar speckle
interferometry, and exploit the optical memory effect to enable fluorescence
microscopy through a turbid layer. We demonstrate efficient reconstruction of
micrometer-size fluorescent objects behind a scattering medium in
epi-microscopy, and study the specificities of this imaging modality
(magnification, field of view, resolution) as compared to traditional
microscopy. Using a modified phase retrieval algorithm to reconstruct
fluorescent objects from speckle images, we demonstrate robust reconstructions
even in relatively low signal to noise conditions. This modality is
particularly appropriate for imaging in biological media, which are known to
exhibit relatively large optical memory ranges compatible with tens of
micrometers size field of views, and large spectral bandwidths compatible with
emission fluorescence spectra of tens of nanometers widths
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