Giovanna Calò

Tunability of Photonic Band Gap Notch Filters

A notch filter based on an index confined photonic band gap waveguide is proposed. The dropping of an electromagnetic wave having a specific wavelength is obtained by opportunely designing a periodically corrugated overlay. The selective filtering properties of the proposed structure are identified by using a computer code based on the bidirectional beam propagation method with the aid of the method of lines. The optimized design of a notch filter, characterized by a full-width half-maximum (FWHM) bandwidth of 2 nm, is given. The tunability is reached by exploiting the electroclinic effect of smectic-A * liquid crystals.

Broadband Mach–Zehnder Switch for Photonic Networks on Chip

In this paper, we propose a broadband silicon Mach-Zehnder switch (MZS) for wavelength division multiplexing applications on photonic networks on chip. The proposed reconfigurable switch is based on a single-stage three-waveguide interferometric configuration in which the phase shift is achieved via a p-i-n diode. The device is analyzed by the coupled-mode theory and by the finite-difference beam propagation method. The proposed configuration leads to a considerable increase in the bandwidth with respect to the conventional MZS. For example, the two-waveguide MZS with a gap g=0.30 μm between the two coupled waveguides exhibits bandwidth Δλ = 60 nm, crosstalk CT = - 15 dB, and insertion loss IL = 1.1 dB. Conversely, a bandwidth Δλ = 115 nm is achieved for the three-waveguide configuration to parity of the other parameters.

Wavelength Routers for Optical Networks-on-Chip Using Optimized Photonic Crystal Ring Resonators

In this paper, we propose an optical 1 × 2 passive wavelength router (λ-router), based on photonic crystal ring resonators. The router, as basic building block to be assembled into higher order routing matrices, exploits a broadband crossing between two photonic crystal waveguides and a photonic crystal ring resonator. Moreover, we analyze the behavior of a 4 × 4 λ-router configuration obtained by assembling eight 1 × 2 routers. The design criteria are pointed out, and the numerical results, obtained by the finite-difference time-domain and the plane-wave expansion methods, are reported. The 4 × 4 λ-router has a footprint of 30 μm × 30 μm, and it is capable of connecting four transmitters with four receivers with a maximum crosstalk between the ports equal to -13.9 dB.

Active WDM Filter on Dilute Nitride Quantum Well Photonic Band Gap Waveguide

A defective Photonic Band Gap device based on dilute nitrides is proposed as a high performance active wavelength fllter for wavelength division multiplexing applications. The analyzed structure is made of GaInNAs-GaInAs multi quantum well ridge waveguides in which a geometrical defect in the periodic lattice induces selective transmission spectral regions centered at difierent wavelengths inside the photonic band gap. The multi-channel fllter performances are evaluated as a function of both the defect length and the injected current value. The analysis is performed by using proprietary codes, based on the Bidirectional Beam Propagation Method with the Method of Lines introducing the rate equations. Highly selective 11-channel active fllter with minimum value of the bandwidth at half-height ¢‚ = 0:105nm with gain G = 16:51dB has been assessed.

Study of gain in photonic bandgap active InP waveguides

The parametric analysis of an active InP-based buried waveguide is proposed to optimize the amplification of the electric field at a given operation wavelength. The waveguide exploits a one-dimensional photonic crystal (PhC), the periodicity of which is perturbed by an active defective region. The analysis of the gain spectrum, as a function of the geometrical and electrical parameters, has been performed using proprietary codes, based on the bidirectional beam propagation method with method of lines, introducing rate equations to take into account the interaction of the matter with the photons. It is shown that the variations in the number of layers of the one-dimensional PhC, of the injection current, and of the length of the active defect strongly influence the behavior of the gain. A simple example of an active photonic switch is proposed as an application of the outlined design criteria.

Efficient plasmonic nanostructures for thin film solar cells

Recent scientific publications have highlighted the possibility of enhancing solar conversion efficiency in thin film solar cells using surface plasmon (SP) waves and resonances. One main strategy is to deposit layers of metal nanoparticles on the top of a thin film silicon solar cell which can increase light absorption and consequently the energy conversion in the frequency range where the silicon intrinsic absorptance is low. In this paper, we investigate the effects produced on the light absorption and scattering by silver nanoparticles, arranged in a periodic pattern, placed on the top of amorphous silicon (α-Si) thin layer. We propose different geometry of metal objects, quantifying the scattering (back and forward) determined by the nanoparticles in dependence of their shapes and Si thickness. The analysis reveals that the thickness of the substrate has huge influence on the scattering, in particular on the back one, when the nanoparticles have corners, whereas it seems less dramatic when rounded profiles are considered (nanospheres).

WDM Performances of Two- and Three-Waveguide Mach-Zehnder Switches Assembled into 4x4 Matrix Router

The performance comparison of two conflgurations of broadband Mach-Zehnder Switches exploiting, respectively, two and three waveguides, assembled into 4 £ 4 matrices is reported in this paper. The simulations are performed by the Finite Element Method and the Finite Difierence Beam Propagation Method. In particular, we have found that, to parity of maximum insertion loss, about equal to 1dB for the single switch and 3dB for the 4£4 matrix, the proposed three-waveguide conflguration exhibits an almost doubled bandwidth ¢‚ = 115nm, making it suitable for e-cient routing of the Wavelength Division Multiplexing signals over photonic Networks on Chip.

Modification of the scattering of silver nanoparticles induced by Fabry–Pérot resonances rising from a finite Si layer

In this paper we theoretically give evidence of the enhancement of scattering phenomena related to single metal nanoparticles having different shapes and located on a silicon layer having finite thickness, thus resembling a thin film solar cell. The study has been carried out in order to deeply understand how the presence of corners (nanobrick) or rounded edges (nanosphere) and the contact surfaces between the metal nanoparticle and the semiconductor affect the scattering when a finite Si layer is considered right below the nanoparticles. Arrays of such silver nanoparticles have also been investigated through a proprietary finite-difference time-domain-based code. The comparison with a typical configuration, where the semiconductor layer is semi-infinite, leads us to note that, in dependence on the shape and size of the nanoparticles, the finite layer, which acts as a Fabry–Perot resonant cavity, is able to exceptionally twist the forward and backward scattering. In particular the forward scattering in all cases is enhanced, whereas the backward scattering seems to be more sensitive to the interference induced by resonances rising in the finite dielectric layers, since it exhibits opposite effects depending on the nanoparticle shapes.

Field localization in Bragg waveguide assisted by metal layers

The surface plasmons (SPs) capability to affect the field localization within a Bragg structure is discussed in this paper. The effects induced by the presence of a silver layer on the formation of a resonant mode are analyzed as well, showing that SPs do actually aid the formation of an enhanced resonant mode, which is not able to localize when SPs are not well supported by the metal. The numerical analysis highlights the dramatic ability of a SP to localize light at certain wavelengths, even though the mechanism is affected by losses, which have been estimated replacing silver with a perfectly electric conductor layer.

Integrated Vivaldi plasmonic antenna for wireless on-chip optical communications

In this paper we propose a novel hybrid optical plasmonic Vivaldi antenna for operation in the standard C telecommunication band for wavelengths in the 1550 nm range. The antenna is fed by a silicon waveguide and is designed to have high gain and large bandwidth. The shape of the radiation pattern, with a main lobe along the antenna axis, makes this antenna suitable for point-to-point connections for inter- or intra-chip optical communications. Direct port-to-port short links for different connection distances and in a homogeneous environment have also been simulated to verify, by comparing the results of a full-wave simulation with the Friis transmission equation, the correctness of the antenna parameters obtained via near-to-far field transformation.