243 research outputs found
Multiplication and division of the orbital angular momentum of light with diffractive transformation optics
We present a method to efficiently multiply or divide the orbital angular
momentum (OAM) of light beams using a sequence of two optical elements. The
key-element is represented by an optical transformation mapping the azimuthal
phase gradient of the input OAM beam onto a circular sector. By combining
multiple circular-sector transformations into a single optical element, it is
possible to perform the multiplication of the value of the input OAM state by
splitting and mapping the phase onto complementary circular sectors.
Conversely, by combining multiple inverse transformations, the division of the
initial OAM value is achievable, by mapping distinct complementary circular
sectors of the input beam into an equal number of circular phase gradients. The
optical elements have been fabricated in the form of phase-only diffractive
optics with high-resolution electron-beam lithography. Optical tests confirm
the capability of the multiplier optics to perform integer multiplication of
the input OAM, while the designed dividers are demonstrated to correctly split
up the input beam into a complementary set of OAM beams. These elements can
find applications for the multiplicative generation of higher-order OAM modes,
optical information processing based on OAM-beams transmission, and optical
routing/switching in telecom.Comment: 28 pages, 10 figure
Grating-Coupled Surface Plasmon Resonance (GC-SPR) Optimization for Phase-Interrogation Biosensing in a Microfluidic Chamber.
Surface Plasmon Resonance (SPR)-based sensors have the advantage of being label-free, enzyme-free and real-time. However, their spreading in multidisciplinary research is still mostly limited to prism-coupled devices. Plasmonic gratings, combined with a simple and cost-effective instrumentation, have been poorly developed compared to prism-coupled system mainly due to their lower sensitivity. Here we describe the optimization and signal enhancement of a sensing platform based on phase-interrogation method, which entails the exploitation of a nanostructured sensor. This technique is particularly suitable for integration of the plasmonic sensor in a lab-on-a-chip platform and can be used in a microfluidic chamber to ease the sensing procedures and limit the injected volume. The careful optimization of most suitable experimental parameters by numerical simulations leads to a 30–50% enhancement of SPR response, opening new possibilities for applications in the biomedical research field while maintaining the ease and versatility of the configuration
Total angular momentum sorting in the telecom infrared with silicon Pancharatnam-Berry transformation optics
Parallel sorting of orbital angular momentum (OAM) and polarization has
recently acquired paramount importance and interest in a wide range of fields
ranging from telecommunications to high-dimensional quantum cryptography. Due
to their inherently polarization-sensitive optical response, optical elements
acting on the geometric phase prove to be useful for processing structured
light beams with orthogonal polarization states by means of a single optical
platform. In this work, we present the design, fabrication and test of a
Pancharatnam-Berry optical element in silicon implementing a log-pol optical
transformation at 1310 nm for the realization of an OAM sorter based on the
conformal mapping between angular and linear momentum states. The metasurface
is realized in the form of continuously-variant subwavelength gratings,
providing high-resolution in the definition of the phase pattern. A hybrid
device is fabricated assembling the metasurface for the geometric phase control
with multi-level diffractive optics for the polarization-independent
manipulation of the dynamic phase. The optical characterization confirms the
capability to sort orbital angular momentum and circular polarization at the
same time.Comment: 15 pages, 10 figure
Test of mode-division multiplexing and demultiplexing in free-space with diffractive transformation optics
In recent years, mode-division multiplexing (MDM) has been proposed as a
promising solution in order to increase the information capacity of optical
networks both in free-space and in optical fiber transmission. Here we present
the design, fabrication and test of diffractive optical elements for
mode-division multiplexing based on optical transformations in the visible
range. Diffractive optics have been fabricated by means of 3D high-resolution
electron beam lithography on polymethylmethacrylate resist layer spun over a
glass substrate. The same optical sequence was exploited both for input-mode
multiplexing and for mode sorting after free-space propagation. Their high
miniaturization level and efficiency make these optical devices ideal for
integration into next-generation platforms for mode-division (de)multiplexing
in telecom applications.Comment: 4 pages, 1 extended references page, 6 figures. arXiv admin note:
substantial text overlap with arXiv:1610.0744
Multiphoton Label-Free ex-vivo imaging using a custom-built dual-wavelength microscope with chromatic aberrations compensation
Label-Free Multiphoton Microscopy is a very powerful optical microscopy that
can be applied to study samples with no need for exogenous fluorescent probes,
keeping the main benefits of a Multiphoton approach, like longer penetration
depths and intrinsic optical sectioning, while opening the possibility of
serial examinations with different kinds of techniques. Among the many
variations of Label-Free MPM, Higher Harmonic Generation (HHG) is one of the
most intriguing due to its generally low photo-toxicity, which enables the
examination of specimens particularly susceptible to photo-damages. HHG and
common Two-Photon Microscopy (TPM) are well-established techniques, routinely
used in several research fields. However, they require a significant amount of
fine-tuning in order to be fully exploited and, usually, the optimized
conditions greatly differ, making them quite difficult to perform in parallel
without any compromise on the extractable information. Here we present our
custom-built Multiphoton microscope capable of performing simultaneously TPM
and HHG without any kind of compromise on the results thanks to two, separate,
individually optimized laser sources with full chromatic aberration
compensation. We also apply our setup to the examination of a plethora of ex
vivo samples in order to prove the significant advantages of our approach
A versatile quantum walk resonator with bright classical light
In a Quantum Walk (QW) the "walker" follows all possible paths at once
through the principle of quantum superposition, differentiating itself from
classical random walks where one random path is taken at a time. This
facilitates the searching of problem solution spaces faster than with classical
random walks, and holds promise for advances in dynamical quantum simulation,
biological process modelling and quantum computation. Current efforts to
implement QWs have been hindered by the complexity of handling single photons
and the inscalability of cascading approaches. Here we employ a versatile and
scalable resonator configuration to realise quantum walks with bright classical
light. We experimentally demonstrate the versatility of our approach by
implementing a variety of QWs, all with the same experimental platform, while
the use of a resonator allows for an arbitrary number of steps without scaling
the number of optics. Our approach paves the way for practical QWs with bright
classical light and explicitly makes clear that quantum walks with a single
walker do not require quantum states of light
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