This work will present the technological processes necessary to experimentally obtain plasmonic metasurfaces for developing flat optical components or diffractive optical elements (DOE) which have reflexion functionalities. This class of metasurfaces offers the possibility to manipulate the beam shape using an array of metallic nanoscale elements patterned on a substrate.<p> </p> The main feature of these structures is that one can manipulate the phase behavior by modifying some of the geometrical parameters of the nano-antennas in order to achieve the required phase shift values for the desired applications. The first important step in experimentally obtaining a plasmonic metasurface structures is the electron beam lithography (EBL) followed by the lift-off method. Due to the small sizes of the gold nano-antennas and tight periodicity of the array a number of impediments can emerge in experimentally obtaining such geometries which can be overcome by the parameter optimization of the employed technologies.
The diffraction patterns (DPs) from helical phase distributions were intensively studied due to their peculiar capability of carrying orbital angular momentum. In the present study, we investigated the combination between a helical phase distribution and another distribution: axicon in our case. Such phase distributions were digitally embedded into holographic masks (HMs). The reconstruction step is performed by simulating the propagation through these HMs, using scalar diffraction theory, Fraunhofer approximation. The spatial intensity arrangement of the DPs is investigated linked with the radial and azimuthal constructive parameters values of the diffractive phase structures embedded in the HMs and transferred in these DPs. Keywords: helical phase distribution
In this paper we will present two technological processes necessary to experimentally obtain diffractive optical elements (DOE) operating in reflection which generate optical beams presenting orbital angular momentum. This class of DOE, also known as spiral phase plates (SPP), are three-dimensional structures consisting in disks where the variation of their thickness is directly proportional with the azimuthal angle Φ. In this case a beam of light applied on the SPP surface acquires an angular orbital momentum (OAM) and a vortex – like configuration. The first technique is the 3D electron beam lithography (EBL). The materials utilized in this case are the positive electronresist PMMA 35 K which has a deposition thickness of 500 nm and the negative electronresist SU8. To obtain the three dimensional structure, the PMMA and SU-8 films were configured by different exposure doses such that after development process each exposure corresponds to a defined thickness of the electronresist. The calibration curve between exposure dose and the height of the structure was determined. The second technique investigated here is photolithography. In this case a photoresist layer was exposed through a mask presenting regions with various levels of transmittance in order to obtain different levels of heights.
We generated holographic masks starting with the interference between the reference beam and the signal beam, which is diffracted by the object. We investigate additive and multiplicative combinations between conical and helical phase distributions as compound objects to be inserted in the signal beam. We explored experimentally the dynamics of the diffracted intensity patterns, in two and three dimensions, after these holographic masks are addressed onto a programmable spatial light modulator. The diffracted intensity spatial arrangement contain information about constructive parameters used for holographic masks generation and exhibit asymmetric shapes and peaks along the optical axis in all analyzed compound objects. We introduce a reading mask in the optical path and, by analyzing changes of the spatial distribution in the final diffracted intensity arrangement, is possible to read the values of the constructive parameters. The generation of these reading masks in each case is discussed.
This work presents a numerical analysis using the finite difference time domain (FDTD) method of the optical
properties (modal characteristics, dispersion, propagation length, and optical confinement) exhibited by a particular class of plasmonic waveguides named dielectric loaded surface plasmon (DLSP) devices. The DLSP systems investigated here consist in ridge like waveguides realized from PMMA with typical cross section areas of 100x100 nm configured on the top of a silver substrate. The FDTD simulations show that in the visible range an optimal compromise between a high degree of optical confinement and an adequate propagation length of around 10 μm can be achieved. This indicates that in this spectral range the proposed DLSP waveguides could possesses applications in various sensing and optical signal processing devices.
The aim of this research is to calculate the refractive index of transparent atmospheric aerosols, which have biological
origin, using a digital holographic microscopy technique (DHM). The samples are collected on filters, using miniature
impactors for particles with dimensions smaller than 10μm (on even one axis), from a height of over 20 meters, in
Magurele, a rural location near the urban and industrial agglomeration of the capital city, Bucharest. Due to their organic
or inorganic origin, each atmospheric aerosol particle has different size, shape and optical properties which have a
determinant role in LIDAR measurements. We record on a CCD camera hundreds of holograms which contain the
diffraction pattern from every aerosol particle superposed with the reference wave. Digitally, we scan the entire volume
of one particle with nanometric resolution (using an algorithm based on the Fresnel approximation). The calibration was
done using an object with known dimensions fabricated by e-beam lithography and some complementary measurements
were done in confocal microscopy. Our analysis separates four main classes of atmospheric aerosols particles (wires,
columns, spherical fragments, and irregular). The predominant class in the investigated period is the first one, which has
biological origin and the refractive index was calculated starting from the phase shift introduced by them in the optical
path and models for their cylindrical shape. The influence of spatial filtering in the reconstructed object images was
In this paper we present simulation of transmission / reflection spectra of polymeric rectangular and hexagonal
photonic crystals (PC) as well as the propagation of radiation in a hexagonal PC - based waveguide. The polymeric PC
are periodic structures consisting in square arrays of holes configured in suspended membranes of PMMA with different
diameters and pitch (100 nm diameter with 500 nm, respectively 800 nm pitch; 200 nm diameter with 500 nm pitch; 400
nm diameter with 700 nm pitch).
For fabrication, we propose the bi-layer EBL technique based on simultaneous patterning of a bottom
sacrificial layer (LOR 5A - Microchem Corporation) and a positive electron resist (PMMA of different molecular
weights). Characterization of nanostructures was performed using SEM imaging and AFM measurements .
Microring resonators will be one of the most important components of the next generation of optical communications. In this work, we have analyzed from theoretical perspective a new proposed microring resonator structure based on the wafer-bonding technique which implies the vertical coupling between the passive bus waveguide and the active ring resonator. We have investigated the possibility to obtain the monomode operation of the active ring waveguide for certain ring radius values by the selective attenuations of the higher order modes and the obtaining of the desired coupling efficiency by varying the technological parameters like the layers thickness, etching depth, bus waveguide width and the offset (misalignment between the ring and the bus waveguide). Depending on the fabrication method, the misalignment between the ring resonator and the bus waveguide may vary within a significant range. Therefore, we considered a much wider bus waveguide in the coupling region in order to minimise the effects of misalignment.