In recent years, research in optics and photonics produced many forms of structured light for different applications, such as optical trapping, telecommunication, and imaging. Generating such beams usually requires challenging control of phase, amplitude, and polarization, and often more than one phase plate is needed. Mounting such optical elements leads to lengthy alignment procedures, worsened by tight tolerances and complex beam shapes. Here we present a method for fabricating two aligned metalenses on the two surfaces of a substrate, halving therefore the degrees of freedom for alignment. Such method is shown to work for a device capable of multiplying the topological charge of an OAM beam.
The ability to generate structured light with arbitrarily controlled polarization in a compact optical path has been a challenge over the last few years in the fields of optics and photonics. In this regard, our work proposes the design, fabrication, and characterization of new dielectric dual-functional meta-optics that generate orbital angular momentum beams with on-demand different vectorial behaviors acting only on the input polarization. The metaoptics are designed as an array of periodic subwavelength metastructures (so-called meta-atoms) composed of silicon nanofins on a silicon substrate, acting like half-wave plates that exploit both the geometric and dynamic phases. We prove the generation of dual-ring perfect vector beams and novel complex vectorial configurations: azimuthally-variant perfect vector beams and helico-conical vector beams. This design solution offers both compactness of the optical path and easy integration with other optical elements, suggesting intriguing applications in telecommunications, imaging, particle manipulation, and quantum information.
Over the past few years, the optics and photonics field has faced a challenge in developing the capability to produce structured light with arbitrary controlled polarization in a compact optical path. Our research addresses this challenge by presenting a novel approach involving the design of dielectric dual-functional metaoptics. These miniature, high-resolution metaoptics can generate custom elliptical orbital angular momentum beams with varied behaviors based on the input light's polarization. Our approach enhances the compactness of optical paths and facilitates seamless integration with other optical elements. Specifically, the proposed metaoptics exhibit suitability for applications in particle manipulation, microscopy, high-capacity communications, and security by contributing to complex structured light generation.
We describe the requirements and associated technology development plan for the communications data link from low mass interstellar probes. This work is motivated by several proposed deep space and interstellar missions with an emphasis on the Breakthrough Starshot project. The Starshot project is an effort to send the first low mass interstellar probes to nearby star systems and transmit back scientific data acquired during system transit within the time scale of a human lifetime. The about 104-fold increase in distance to nearby stars compared to the outer planets of our solar system requires a new form of propulsion to reach speeds of approximately 20% of the speed of light. The proposed use of a low mass sailcraft places strong constraints on the mass and power for the Starshot communications system. We compare the communications systems in current and upcoming solar system probes, New Horizons and Psyche, against the requirements for Starshot and define Figures of Merit for the communications capability in terms of data downlink rate multiplied by distance squared per unit mass. We describe current and future technology developments required for the on-board transmitter (signal generation, signal distribution, and beamforming) and for the near-Earth communications receiver (low-cost large aperture telescopes, high resolution spectrometers, and single photon counting detectors). We also describe a roadmap for technology development to meet the goals for future interstellar communications.
A novel optical architecture is designed and fabricated in order to overcome the limits of the traditional sorter based on log-pol optical transformation for the demultiplexing of optical beams carrying orbital angular momentum (OAM) of light. The proposed configuration simplifies the alignment procedure and significantly improves the compactness of the optical device. In addition, the integration of an optical fan-out provides higher resolution on OAM modes separation. Since the miniaturization level and the optical configuration require to operate beyond the paraxial approximation, a rigorous formulation of transformation optics in the non-paraxial regime is developed and applied for the first time. Samples have been fabricated as 256-level phase-only diffractive optics with high-resolution electron-beam lithography and tested for the demultiplexing of optical vortex superposition in a 8-bit free-space optical link. The results confirm the expected high efficiency and resolution in OAM sorting.
Label-free microscopy is a very powerful technique that can be applied to study samples with no need for exogenous fluorescent probes, keeping the main benefits of multiphoton microscopy, such as longer penetration depths and intrinsic optical sectioning while enabling serial multitechniques examinations on the same specimen. Among the many label-free microscopy methods, harmonic generation (HG) is one of the most intriguing methods due to its generally low photo-toxicity and relative ease of implementation. Today, HG and common two-photon microscopy (TPM) are well-established techniques, and are routinely used in several research fields. However, they require a significant amount of fine-tuning to be fully exploited, making them quite difficult to perform in parallel. Here, we present our designed multimodal microscope, capable of performing simultaneously TPM and HG without any kind of compromise thanks to two, separate, individually optimized laser sources with axial chromatic aberration compensation. We also apply our setup to the examination of a plethora of ex vivo samples to prove its capabilities and the significant advantages of a multimodal approach.
Orbital angular momentum (OAM) states of light have been recently considered in new mode-division multiplexing techniques in order to increase the bandwidth of today’s optical networks. Many optical architectures have been presented and exploited in order to sort the different OAM channels. Here we present a diffractive version of the sorting technique based on log-pol optical transformation and we further improve the miniaturization level by integrating the two components into a single diffractive optical element. Samples have been fabricated with high-resolution electronbeam lithography and characterized in the optical range. The presented design is promising for integration into nextgeneration optical platforms performing optical processing of OAM modes, for applications both in free-space and optical fibers.
The orbital angular momentum (OAM) of light offers a promising solution to today’s overwhelming demand of bandwidth and has known an increasing attention as a new degree of freedom in the telecom field. Here we present the design, fabrication and optical characterization of miniaturized phase-only diffractive optical elements (DOE) for OAM beams generation, multiplexing and sorting. Samples have been fabricated with high-resolution electron-beam lithography and exhibit high fabrication quality. Different DOE designs are presented for the sorting of optical vortices with different steering geometries in far-field and applications in free-space and optical fibers.
Nanoporous TiO2 anatase film has been investigated as sensitive layer in Surface Plasmon Resonance sensors for the
detection of hydrogen and Volatile Organic Compounds, specifically methanol and isopropanol. The sensors consist of a
TiO2 nanoporous matrix deposited above a metallic plasmonic grating, which can support propagating Surface Plasmon
Polaritons. The spectral position of the plasmonic resonance dip in the reflectance spectra was monitored and correlated
to the interaction with the target gases.
Reversible blue-shifts of the resonance frequency, up to more than 2 THz, were recorded in response to the exposure to
10000 ppm of H2 in N2 at 300°C. This shift cannot be explained by the mere refractive index variation due to the target
gas filling the pores, that is negligible.
Reversible red-shifts were instead recorded in response to the exposure to 3000 ppm of methanol or isopropanol at room
temperature, of magnitudes up to 14 THz and 9 THz, respectively. In contrast, if the only sensing mechanism was the
mere pores filling, the shifts should have been larger during the isopropanol detection.
We therefore suggest that other mechanisms intervene in the analyte/matrix interaction, capable to produce an injection
of electrons into the sensitive matrix, which in turn induces a decrease of the refractive index.
The preparation, optical characterization and plasmonic biosensing properties of self-standing nanoporous gold leaves are presented. Respect to the bulk gold, the material shows metallic behaviour at higher wavelengths and a lower imaginary part of the dielectric constants. The plasmonic properties in the near infrared range have been investigated probing the resonance shift after a self-assembling monolayer functionalization. Due to a great increase of the active surface the presence of an organic molecule adsorbed on its surface leads to important optical responses. This demonstrates how nanoporous gold reveals benefits for better reaction efficiency and detection sensitivity and how plasmonic properties in the near-IR range can assure employment in plasmonic devices.
A design of spiral phase plates for the generation of multiring beams carrying orbital angular momentum (OAM) is presented. Besides the usual helical profile, these phase plates present radial π-discontinuities in correspondence of the zeros of the associated Laguerre polynomials. Samples were fabricated by electron beam lithography over glass substrates coated with a polymethylmethacrylate resist layer. The optical response was analyzed and the purity of the generated beams was investigated in terms of Laguerre-Gaussian modes contributions. The far-field intensity pattern was compared with theoretical models and numerical simulations, while the expected phase features were confirmed by interferometric analysis with a Mach-Zehnder setup. The high quality of the output beams confirms the applicability of these phase plates for the generation of high-order OAM beams with nonzero radial index. An application consisting of the design of computer-generated holograms encoding information for light beams carrying phase singularities is presented and described. A numerical code based on an iterative Fourier transform algorithm has been developed for the computation of phase-only diffractive optical element for illumination under OAM beams. Numerical analysis and preliminary experimental results confirm the applicability of these devices as high-security optical elements for anticounterfeiting applications.
The work of design, fabrication and characterization of spiral phase plates for the generation of Laguerre-Gaussian (LG) beams with non-null radial index is presented. Samples were fabricated by electron beam lithography on polymethylmethacrylate layers over glass substrates. The optical response of these phase optical elements was measured and the purity of the experimental beams was investigated in terms of Laguerre-Gaussian modes contributions. The farfield intensity pattern was compared with theoretical models and numerical simulations, while the expected phase features were confirmed by interferometric analyses. The high quality of the output beams confirms the applicability of these phase plates for the generation of high-order Laguerre-Gaussian beams. A novel application consisting in the design of computer-generated holograms encoding information for light beams carrying phase singularities is shown. A numerical code based on iterative Fourier transform algorithm has been developed for the computation of the phase pattern of phase-only diffractive optical element for illumination under LG beams. Numerical analysis and preliminary experimental results confirm the applicability of these devices as high-security optical elements.
In this work, we study how the Orbital Angular Momentum of a Plasmonic Vortex (an SPP carrying OAM) can be probed by the LSPR of nanoantennae conveniently integrated inside a Plasmonic Vortex Lens. We show that the turning “on” or “off” of the antennae acts as a fingerprint of the OAM of the PV and we discuss a particularly meaningful case. The integrated structure is fabricated and experimentally characterized in the near field. The results are in good agreement with the simulations and seem to prove the capability to transfer OAM properties control at the nanoscale.
Wireless communication amounts to encoding information onto physical observables carried by electromagnetic (EM) fields, radiating them into surrounding space, and detecting them remotely by an appropriate sensor connected to an informationdecoding receiver. Each observable is second order in the fields and fulfills a conservation law. In present-day radio only the EM linear momentum observable is fully exploited. A fundamental physical limitation of this observable, which represents the translational degrees of freedom of the charges (typically an oscillating current along a linear antenna) and the fields, is that it is single-mode. This means that a linear-momentum radio communication link comprising one transmitting and one receiving antenna, known as a single-input-single-output (SISO) link, can provide only one transmission channel per frequency (and polarization). In contrast, angular momentum, which represents the rotational degrees of freedom, is multi-mode, allowing an angular-momentum SISO link to accommodate an arbitrary number of independent transmission channels on one and the same frequency (and polarization). We describe the physical properties of EM angular momentum and how they can be exploited, discuss real-world experiments, and outline how the capacity of angular momentum links may be further enhanced by employing multi-port techniques, i.e., the angular momentum counterpart of linear-momentum multiple-input-multiple-output (MIMO).
In recent years, we developed two very high speed single photon photometers, Aqueye and Iqueye, as prototypes for “quantum” photometers for the Extremely Large Telescopes of the next decade. These instruments, based on single photon avalanche photodiodes and a 4-fold split-pupil concept, have been successfully used to obtain data of the highest quality on optical pulsars. Subsequently, we performed an attempt to utilize the Orbital Angular Momentum and associated Optical Vorticity to achieve high performance stellar coronagraphy. Presently, we are making a synergic effort in building Aqueye Plus, a new instrument for the 1.8 m telescope of the Asiago - Cima Ekar Observatory, which combines both functions, namely high speed simultaneous multicolor photon counting photometry and stellar coronagraphy. The innovative capability of Aqueye Plus is to take advantage of the two parallel outputs (NIM and TTL) of the four high time accuracy photon counting sensors. The NIM output preserves the best timing capability, while the TTL output drives a deformable 32-element mirror in a sort of quadrant detector to correct for defocus and tip/tilt aberrations of the stellar image on the phase mask discontinuity. This paper describes the Aqueye Plus instrument main characteristics and its foreseen performance.
We have designed Aqueye+, an instrument for the Copernicus 182 cm Asiago Telescope, with two channels, one devoted to ultrafast photometry based on four single photon avalanche photodiodes, the second dedicated to stellar coronagraphy based on innovative optical vortex coronagraph system. The OVC requires a very good image quality, therefore an adaptive optic system AO was designed for the instrument. The peculiarity of this AO system is that there is no wavefront sensors, but the feedback for the deformable mirror is instead given by the photometric channel of Aqueye+.
A novel compact architecture implementing grating-coupled surface plasmon resonance (GCSPR) based on polarization modulation in conical mounting is presented. In this system a plasmonic grating is azimuthally rotated in order to support the excitation of high-sensitivity surface plasmon polaritons (SPPs). At SPP resonance, a scan of the incident polarization is performed before and after the binding event and the phase term of the output trend is exploited as sensing parameter. The mechanical complexity of the SPR system is significantly reduced and a resolution down to 10-7 refractive index units is assured. In this work a numerical study of the polarization-based grating-coupled SPR technique is performed and analyzed with Chandezon’s method. Therefore an experimental test on an assembled prototype is presented and applied to the detection of binding events on the grating surface (avidin/biotin reaction, DNA/PNA probes).
We report our results on arrays of transparent metal coated wedges for plasmonic nanofocusing. FIB milling and
chemical etching were used for the fabrication. FEM simulations were used to design the system. The design, fabrication
and characterization of wedge structures are presented. The structure shows plasmonic properties in the optical spectral
range, with excitation and propagation of surface plasmon polaritons at the wedge tip. The particular designs proposed
allow the condensation of plasmonic waves at the wedge tips leading to the nanofocusing effects.
The optical vortex coronagraph (OVC) is an innovative instrument that can be applied to both space and groundbased
telescopes for direct imaging of planets around bright stars. OVC rejects the light of the on-axis star without
altering that of off-axis sources, means of a spiral phase plate (SPP) used as a phase modyfing device (PMD).
We present the fabrication process made by lithographic nanofabrication and tests for the characterization of
two different high-quality SPPs.
In this paper we report results obtained in the design and fabrication of diffractive optical elements (DOEs) with minimum feature size down to tens of nanometers by the use of e-beam and x-ray lithography. The DOEs are patterned using e-beam lithography and replicated by x-ray lithography. Since in our days there is an increased interest for extreme ultraviolet and x-ray microscopy our work has been focused toward the fabrication of DOEs mainly for these applications. Different types of zone plates (ZPs) were fabricated for x-ray beam focusing: high resolution ZPs for high resolution beam focusing, multilevel phase ZPs to increase the diffraction efficiency in the desired order and high aspect ratio ZPs for hard x-rays. Recently we have extended the concept of the ZPs to a more general category of DOEs which beside simple focusing can perform new optical functions in the range of x-rays. In particular, the intensity of the beam after the DOE can be distributed with almost complete freedom. We have designed and fabricated DOEs that focus the beam in an array of spots disposed either in plane or along the optical axis. This type of DOEs has been tested successfully in x-ray differential interference contrast microscopy. The possibility to introduce a specified phase shift between the generated spots is demonstrated in this paper by preliminary results obtained from computer simulations and experiments performed in visible light.
Diffractive optical elements (DOE’s) can be used to manipulate the amplitude, the phase and the polarization of light beams. They can operate over a wide range of wavelength from UV to x-ray radiation. Interest in DOE’s has grown rapidly in recent years since they are smaller and lower in size and weight than conventional optical elements and in addition allow optical functions impossible to reach with other refractive or reflective optical elements. In this paper we report results obtained in DOE’s design and fabrication at the LILIT Nanolithography beam line developed at the national laboratory TASC-INFM. Among the design methods we have used, the phase retrieval iterative algorithm approach is presented in more detail here. There are also presented aspects involved in the fabrication of high-resolution zone plates for focusing soft x-rays. The fabrication process is based on e-beam lithography and etching techniques similar to those used in the microelectronic technology, allowing structures sized down to few tens of nanometers. Experimental results are presented for some applications of our DOE’s: laser beam shaping, optical tweezers array generation and x-ray microscopy.
Some considerations on the design of computer generated phase elements applied to the intensity redistribution of Gaussian light beams are presented in this paper. The computer generated phase elements are designed using an iterative transform algorithm for Fresnel domain. Parameters which influence the performances of these algorithms and the computation time are discussed. Results obtained by computer simulations are presented for three different Gaussian beam shaping (flat-top, 2 shifted gaussians, acronym.)
High resolution and high efficiency Zone Plate for X-rays in the energy range of 300 eV and 12 KeV fabricated by means of electron beam and X-ray lithography are presented. Regarding the high resolution regime zone plate with 40 nm outermost zone and thickness of 0.2 micrometer are shown. For high efficiency performances, multilevel zone plate and continuous profile were fabricated to provide an increase of efficiency at the first diffraction order and to suppress higher ones. The combination of the two lithography allows a powerful design flexibility at several energy regimes.
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