We investigate graphene-based optical absorbers that exploit guided mode resonances (GMRs) attaining theoretically perfect absorption over a bandwidth of few nanometers (over the visible and ...near-infrared ranges) with a 40-fold increase of the monolayer graphene absorption. We analyze the influence of the geometrical parameters on the absorption rate and the angular response for oblique incidence. Finally, we experimentally verify the theoretical predictions in a one-dimensional, dielectric grating by placing it near either a metallic or a dielectric mirror, thus achieving very good agreement between numerical predictions and experimental results.
A one-dimensional dielectric grating, based on a simple geometry, is proposed and investigated to enhance light absorption in a monolayer graphene exploiting guided mode resonances. Numerical ...findings reveal that the optimized configuration is able to absorb up to 60% of the impinging light at normal incidence for both TE and TM polarizations resulting in a theoretical enhancement factor of about 26 with respect to the monolayer graphene absorption (≈2.3%). Experimental results confirm this behavior showing CVD graphene absorbance peaks up to about 40% over narrow bands of a few nanometers. The simple and flexible design points to a way to realize innovative, scalable and easy-to-fabricate graphene-based optical absorbers.
A label-free localized surface plasmon resonance (LSPR)-based biosensor exploiting gold nanorods (GNRs) is proposed and demonstrated. For this aim, 35 ± 5 nm long and 20 ± 4 thick GNRs spaced by a ...few nanometers thick polyelectrolytes (PE) from a gold thin film was analyzed and synthesized. The morphology of the GNRs, the plasmon properties of GNRs, swelling of PE layers and the wettability of the surfaces were characterized by transmission and scanning electron microscopy, spectroscopic reflectivity and contact angle measurements, respectively. Indeed, when immersed in a phosphate buffer saline solution, the GNRs-PE-gold system shows an optical shift of the LSPR wavelength. This shift was found to correspond to a vertical swelling of about 2 nm, demonstrating the extreme sensitivity of the biosensor. Finally, we show that LSPR measurements can be used to detect dynamic resonance changes in response to both thickness and buffer solution, while the hydrophobic behavior of the surface can be exploited for reducing the number of liquid analytes in clinical biosensing application.
We investigate the linear response of single and multiple graphene sheets embedded in quarter-wave one-dimensional photonic crystals (PhCs) in terms of absorption and losses. In particular, we show ...that it is possible to achieve near-perfect narrowband absorption when a single monolayer graphene is sandwiched between two PhC mirrors with optimized pair numbers. The simulations reveal that the resonant wavelength and the total absorption frequency may be tuned by tilting the angle of incidence of the impinging source. We also show that the losses, related to the dielectric materials constituting the one-dimensional PhC, can degrade the optical performance of the device. Conversely, by arranging the same dielectric slabs in a different order (supercell), it is possible to achieve a broadband absorption that is almost constant over a wide range of angle of incidence. In this configuration, the absorption and the bandwidth can be tuned by varying the supercell geometry. These features make these devices attractive for different applications ranging from tunable and saturable absorbers for short-pulse lasers to graphene-based photodetectors.
We demonstrate a very compact multifunctional photonic-crystal demultiplexer on high index contrast InP-membrane for coarse WDM applications. Polarization diversity is implemented using 2D-grating ...couplers. The performance of the device is evaluated using integrated p-i-n photodetectors. Polarization diversity from fiber to detector-without intermediate functional device-results in a minimal polarization dependent loss (PDL) of 0.2 dB. This value increases to 1.1 dB when including the photonic-crystal demultiplexer.
•Different plasmonic resonances can be excited in 2D gold square nanopatch arrays.•The fabricated devices are insensitive to light polarization.•A plasmonic biosensor with a sensitivity and a figure ...of merit of 630nm/RIU and 21, respectively, is presented.•Color variation is a quick tool to predict refractive index changes.•The 2D gold nanopatch arrays can be exploited for Surface Enhanced Raman Scattering with an enhancement factor up to 2×105.
We demonstrate the fabrication of a 2D periodic arrangement of gold square nano-patches on both silicon and borosilicate glass substrates whose optical properties can be exploited for both linear and nonlinear applications. The comparison between numerical and experimental results, combined with high-resolution scanning electron microscopy images highlights the importance of the geometry and the fine shape in the determination of the square gold nano-patches optical properties.
Spin-coated layers of zinc(II) tetra-4-(2,4-di-tert-amylphenoxy)phthalocyanine (ZnPctamyl) and copper(II) tetrakis(p-tert-butylphenyl)porphyrin (CuPtphen) have been synthesized and used as solid ...state chemically interacting materials deposited in thin film form for the detection of alcohols, amines, ketones, alkanes, and pyridines for applications in food quality control. The UV−Vis variations obtained by the exposure of the sensing layers to the mentioned analytes in controlled atmosphere have been analyzed and compared with those deriving by a single thin film obtained by mixing the two metal complexes in an appropriate ratio. A multichannel monitoring of the main bands of the sensing layer due to the interaction with the analyte vapors became the basis to construct a set of independent sensors located on a single sensing element. The effects in the variation of the absorption bands of the blend system are compared with the variations in absorbance observed with the two sensing layers fabricated separately with each single compound. The interaction between some volatile organic compound species and the heterogeneous sensing layer shows a different behavior in the responses with respect to the results obtained with each single compound.
In this paper, we study an unconventional kind of quasi-three-dimensional (3-D) photonic crystal (PhC) with circular lattice pattern: it consists of air holes in a GaAs material (n=3.408) along ...circular concentric lines. This particular PhC geometry has peculiar behavior if compared with the traditional square and triangular lattices, but it is difficult to model by using conventional numerical approaches such as wave expansion method. The resonance and the radiation aspects are analyzed by the 3-D finite-element method (FEM). The model, based on a scattering matrix approach, considers the cavity resonance frequency and evaluates the input-output relationship by enclosing the photonic crystal slab (PhCS) in a black box in order to define the responses at different input-output ports. The scattering matrix method gives important information about the frequency responses of the passive 3-D crystal in the 3-D spatial domain. A high sensitivity of the scattering parameters to the variation of the geometrical imperfection is also observed. The model is completed by the quality factor (Q-factor) estimation. We fabricated the designed circular photonic crystal over a slab membrane waveguide embedding InAs/GaAs quantum dots emitting around 1.28 mum. Good agreement between numerical and experimental results was found, thus validating the 3-D FEM full-wave investigation.
Immunosensors are devices that exploit immobilized antibodies to promote the binding of specific analytes related to diseases of medical importance, such as cancer or cardiac dysfunctions. Label-free ...immunosensors have an important role, due to their simplicity and fast read-out. Here, the proof of concept for an immunosensor based on a 2-D photonic crystal silicon nitride membrane is presented. The device has been fabricated by means of a well-tuned nanofabrication protocol, achieving a high-quality photonic pattern on a large-area membrane (1 mm × 1 mm), and it has been tested for the detection of interleukin-6, getting protein detection at pg/mL concentrations.
Two dimensional photonic band gap structures on GaAs/AlGaAs, Si
3N
4 and Si/SiO
2 has been fabricated using a 30
keV gallium ion beam. This process is being developed as a viable alternative for fast ...prototyping of high quality 2D photonic crystal devices. The feasibility of high-resolution (down to 80
nm) unit cell fabrication has been demonstrated as well as the longitudinal depth of the holes (more than 600
nm) over a pattern area of 100
×
100
μm and smaller, using FIB milling as well as FIB gas assisted etching. During milling fluorine gas was added in the sample chamber to control the interior shape of the holes and also to reduce the formation of Ga spherical calotte shaped dots. The in-plane photoluminescence emission of some fabricated devices has been optically characterized by exciting the in plane cavities from the top surface of the device by picosecond laser pulses. As expected, by virtue of its higher back mirror reflectivity leading to lower cavity losses, the 2D photonic crystal cavity showed the occurrence of amplified spontaneous emission.
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