Concita Sibilia

One-dimensional photonic crystal optical limiter

We explore a new passive optical limiter design using transverse modulation instability in the one-dimensional photonic crystal (PC) using x(3) materials. The performance of PC optical limiters strongly depends on the choice of the materials and the geometry and it improves as the duration of the incident pulse is extended. PC optical limiter performance is compared with that of a device made from homogeneous material. We identify three criteria for benchmarking the PC optical limiter. We also include a discussion of the advantages and disadvantages of PC optical limiters for real world applications.

Tuning thermal emission in metamaterials composed by oriented polar inclusions

We investigated a metamaterial composed by silicon carbide (SiC) subwavelength oriented wires, onto silicon substrate in the mid- to long- infrared range. A simple but versatile method was developed and implemented, combining homogenization techniques with the transfer matrix method for birefringent layered materials to model an effective medium layer where different inclusions content (filling factor) as well as different shape and orientation of inclusions (depolarization factors) are taken into account. The typical spectral features associated to oriented inclusions are thus exploited to design a selective emissivity feature, pertaining sharp resonances at infrared wavelengths. Taming and tuning the strength and the position of the phonon resonance of polar materials allows the design of versatile optical elements and infrared filters, in order to design an effective medium with specifically tuned emissive properties.

Spatial and spectral control of infrared thermal emission in VO2-based composite nanoantennas (Conference Presentation)

The possibility to control the infrared (IR) absorption and thermal emission on subwavelength scales has attracted large interest in the recent years thanks to the opportunities granted by nanostructured metamaterials. For example highly frequency selective and directional thermal emitters/absorbers have been proposed for a large variety of applications ranging from sensing and security to cooling and energy harvesting [1]. In order to introduce a control of the emissivity as a function of the temperature thermochromic and phase change materials have been considered. In particular Vanadium dioxide (VO2) has become a widely-studied material for applications such as metamaterials, smart windows and supercapacitors, thanks to its strong optical transmittance changes at the IR and THz regions and huge resistance jump [2]. The control mechanism is achieved by taking advantage of the metal-insulator phase transition of VO2 at its critical temperature (~68 °C). We numerically show the control of spatial and spectral features of the far field thermal emission pattern of nanoantenna arrays, composed of alternating Gold and VO2 rods, as a function of the temperature. In this work we performed a numerical study by modifying a previously developed model [3] based on the fluctuational electrodynamics approach and on the discretization of the resulting volume integral equation to calculate relative emissivity and spatial emission pattern of nanoparticle ensembles smaller than the thermal wavelength lam=hc/kBT [4]. The drastic changes of the VO2 refractive index across its metal-insulator phase transition produce strong differences in the behavior of the overall system by creating or destroying evanescent wave coupling between different elements of the nanoantenna. The study of IR thermal nano-emitters is crucial for the realization of coherent thermal nano-sources in the mid and far IR for sensing applications and thermal management as well as thermal logic gates on the nanoscale. References: [1] I. E. Khodasevych, L. Wang, A. Mitchell, and G. Rosengarten, Micro- and nano- structured surfaces for selective solar absorption, Adv. Opt. Mat. 3, 852 (2015). [2] Liu, M. et al. Phase transition in bulk single crystals and thin films of VO2 by nanoscale infrared spectroscopy and imaging. Phys. Rev. B 91, 245155 (2015). [3] M. Centini, A. Benedetti, M. C. Larciprete, A. Belardini, R. Li Voti, M. Bertolotti, C. Sibila, “Midinfrared thermal emission properties of finite arrays of gold dipole nanoantennas” Phys. Rev. B 92(20) 205411 (2015) [4] C. Wuttke and A. Rauschenbeutel, “Thermalization via Heat Radiation of an Individual Object Thinner than the Thermal Wavelength”, Phys. Rev. Lett. 111, 024301 (2013)

Second harmonic generation from metallic sub-wavelength slits and scatterers

We examine second harmonic generation from metallic sub-wavelength slits and scatterers. In the enhanced transmission regime, we find that the Coulomb contribution far exceed magnetic contributions to second harmonic generation.