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 multiply 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. 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, whereas 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 beam transmission, and optical routing/switching in telecom.

A compact diffractive sorter for high-resolution demultiplexing of orbital angular momentum beams.

The design and fabrication of a compact diffractive optical element is presented for the sorting of beams carrying orbital angular momentum (OAM) of light. The sorter combines a conformal mapping transformation with an optical fan-out, performing demultiplexing with unprecedented levels of miniaturization and OAM resolution. Moreover, an innovative configuration is proposed which simplifies alignment procedures and further improves the compactness of the optical device. Samples have been fabricated in the form of phase-only diffractive optics with high-resolution electron-beam lithography (EBL) over a glass substrate. A soft-lithography process has been optimized for fast and cheap replica production of the EBL masters. Optical tests with OAM beams confirm the designed performance, showing excellent efficiency and low cross-talk, with high fidelity even with multiplexed input beams. This work paves the way for practical OAM multiplexing and demultiplexing devices for use in classical and quantum communication.

Design, fabrication and characterization of Computer Generated Holograms for anti-counterfeiting applications using OAM beams as light decoders.

In this paper, we present the design, fabrication and optical characterization of computer-generated holograms (CGH) encoding information for light beams carrying orbital angular momentum (OAM). Through the use of a numerical code, based on an iterative Fourier transform algorithm, a phase-only diffractive optical element (PO-DOE) specifically designed for OAM illumination has been computed, fabricated and tested. In order to shape the incident beam into a helicoidal phase profile and generate light carrying phase singularities, a method based on transmission through high-order spiral phase plates (SPPs) has been used. The phase pattern of the designed holographic DOEs has been fabricated using high-resolution Electron-Beam Lithography (EBL) over glass substrates coated with a positive photoresist layer (polymethylmethacrylate). To the best of our knowledge, the present study is the first attempt, in a comprehensive work, to design, fabricate and characterize computer-generated holograms encoding information for structured light carrying OAM and phase singularities. These optical devices appear promising as high-security optical elements for anti-counterfeiting applications.

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 output-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.

Compact sorting of optical vortices by means of diffractive transformation optics.

The orbital angular momentum (OAM) of light has recently attracted a growing interest as a new degree of freedom in order to increase the information capacity of today's optical networks, both for free-space and optical fiber transmission. Here we present our work of design, fabrication, and optical characterization of diffractive optical elements for compact OAM mode division demultiplexing based on optical transformations. Samples have been fabricated with 3D high-resolution electron beam lithography on a polymethylmethacrylate resist layer spun over a glass substrate. Their high compactness and efficiency make these optical devices promising for integration into next-generation platforms for OAM modes processing in telecom applications.

Diffractive optics for combined spatial- and mode- division demultiplexing of optical vortices: design, fabrication and optical characterization.

During the last decade, the orbital angular momentum (OAM) of light has attracted growing interest as a new degree of freedom for signal channel multiplexing in order to increase the information transmission capacity in today's optical networks. Here we present the design, fabrication and characterization of phase-only diffractive optical elements (DOE) performing mode-division (de)multiplexing (MDM) and spatial-division (de)multiplexing (SDM) at the same time. Samples have been fabricated with high-resolution electron-beam lithography patterning a polymethylmethacrylate (PMMA) resist layer spun over a glass substrate. Different DOE designs are presented for the sorting of optical vortices differing in either OAM content or beam size in the optical regime, with different steering geometries in far-field. These novel DOE designs appear promising for telecom applications both in free-space and in multi-core fibers propagation.

Resonance properties of thick plasmonic split ring resonators for sensing applications.

We investigate in detail the optical response of dense split ring resonator (SRR) arrays as a function of their thickness, for normally impinging light in the VIS-NIR spectral range. We find that, for sufficiently tall SRRs, several vertical Fabry-Perot resonances can be excited, which may interact with the well-known horizontal SRR resonant paths. Furthermore, we analyze the possibility to exploit these nanostructures to detect bio-chemical quantities. In particular, we find that the coexistence of vertical and horizontal resonances yields an increased sensitivity. Well ordered, large arrays of thick SRRs are obtained by exploiting a fabrication process based on X-Ray Lithography. A very good agreement is found between numerical and measured transmittances. A preliminary detection test evidences the potential of this geometry as a sensing platform.

Integrated architecture for the electrical detection of plasmonic resonances based on high electron mobility photo-transistors.

We report the design of an integrated platform for on-chip electrical transduction of the surface plasmon resonance supported by a nanostructured metal grating. The latter is fabricated on the active area of a GaAs/AlGaAs photo-HEMT and simultaneously works as the electronic gate of the device. The gold plasmonic crystal has a V-groove profile and has been designed by numerical optical simulations. By showing that the numerical models accurately reproduce the phototransistors experimental response, we demonstrate that the proposed architecture is suitable for the development of a new class of compact and scalable SPR sensors.

Relationships among injuries treated in an emergency department that are caused by different kinds of animals: epidemiological features.

OBJECTIVE: To analyse animal-related injury features treated in an emergency department. METHODS: Inspection of all reports concerning animal-related injuries treated in the emergency department in 1998-1999, researched through non-codified diagnosis. RESULTS: A total of 988 patients (1.66% of annual emergency department visits) were treated in the emergency department for animal-related injuries. Prevalence of the causing agent was as follows: insects 53.1% (74.9% not identified), mammals 30.9%, marine fauna 7.4%, arachnids 7.1%, reptiles 0.51%, birds 0.51% and intestinal parasites 0.4%. Sex prevalence was also noted: male 59.6%. Age most affected was III-IV decades. Month prevalence: August, except for arachnids, cats and reptiles. Mammals cause a number of lesions higher than any other group from November to May, while insect-related lesions are prevalent from June to October. In dog-related injuries, the upper right extremity prevails over the left (63%, P<0.001). Bites included 28.7% of all cases; cats caused only bite lesions in 50% of cases, and dogs in 95%. Allergic reactions were observed in 18.6% of patients with insect and marine fauna injuries. Vespids show the highest allergic reaction/injury ratio (44%). Hospital admittance was 2.7% of all animal-related injury visits (7.9 cases/100 000 residents). CONCLUSIONS: Insects are the prevalent injuring animals but most are not identified; thus, dogs account for most injuries among identified animals (25.2% of total cases). Insects cause most hospitalizations because of allergic and infective complications (erysipelas). Mammalian and bird injuries being excluded, the diagnosis of 'animal lesion' was defined 'probable' in 11.7%; in some cases, a dermatologist's consultation is required. In serious allergic reactions, adrenaline is rarely used.