Alexander Cuadrado

Seebeck nanoantennas for solar energy harvesting

We propose a mid-infrared device based on thermocouple optical antennas for light sensing and energy harvesting applications. We numerically demonstrate that antennas are able to generate low-power dc signals by beneficing of the thermoelectric properties of the metals that constitute them. We theoretically evaluate the optical-to-electrical conversion efficiency for harvesting applications and finally discuss strategies to increase its performance. Thermocouple optical antennas therefore open the route toward the design of photovoltaic devices.

Seebeck nanoantennas for the detection and characterization of infrared radiation

Arrays of metallic thermocouples in the shape of spiral nanoantennas are proposed as infrared detectors, which use the thermoelectric properties of the metallic interfaces to generate electrical DC signals. The responsivity of these types of antennas is evaluated from both theoretical and numerical perspectives pointing out its potential as infrared sensors. Moreover, the same structures can be used to characterize the state of polarization of the optical near fields with a spatial resolution comparable to the wavelength.

Distributed bolometric effect in optical antennas and resonant structures

Universidad Autonoma de San Luis Potosi, Coordinacion para la Innovacion y,Aplicacion de la Ciencia y la Tecnologia, San Luis Potosi, Mexico 78210Abstract. Nanoantennas coupled to nanobolometers have been used as detectors of opticalradiation. They are typically manufactured using two different materials: one for the nano-antenna and another for the nanobolometer. However, those metals used to fabricate nano-antennas also present a bolometric response. Therefore, antenna-coupled detectors using thebolometriceffectdistributedalongthedevicewerecomparedwiththeresultspreviouslyreportedfor nanobolometers coupled with dipole antennas in the infrared regime. We modeled therelevant physical mechanisms and also simulated the simple case of a dipole antenna usinga multi-physics computational tool. The simulation results were compared with experimentalresults. The advantage in performance when using a dedicated material to enhance the bolo-metric effect, is balanced with the easiness of the fabrication of resonant structures involvingonly one material where the bolometric effect is distributed along the device.

Polarimetric pixel using Seebeck nanoantennas

Optical nanoantennas made of two metals are proposed to produce a Seebeck voltage proportional to the Stokes parameters of a light beam. The analysis is made using simulations in the electromagnetic and thermal domains. Each Stokes parameter is independently obtained from a dedicated nanoantenna configuration. S1 and S2 rely on the combination of two orthogonal dipoles. S3 is given by arranging two Archimedian spirals with opposite orientations. The analysis also includes an evaluation of the error associated with the Seebeck voltage, and the crosstalk between Stokes parameters. The results could lead to the conception of polarization sensors having a receiving area smaller than 10λ(2). We illustrate these findings with a design of a polarimetric pixel.

Multiphysics simulation for the optimization of optical nanoantennas working as distributed bolometers in the infrared

Abstract. The electric currents induced by infrared radiation incident on optical antennas and resonant structures increase their temperature through Joule heating as well as change their electric resistance through the bolometric effect. As the thermo-electric mechanism exists throughout a distributed bolometer, a multiphysics approach was adopted to analyze thermal, electrical, and electromagnetic effects in a dipole antenna functioning as a resonant distributed bolometer. The finite element method was used for electromagnetic and thermal considerations. The results showed that bolometric performance depends on the choice of materials, the geometry of the resonant structure, the thickness of an insulating layer, and the characteristics of a bias circuit. Materials with large skin depth and small thermal conductivity are desirable. The thickness of the SiO2 insulating layer should not exceed 1.2 μm, and a current source for the bias circuit enhances performance. An optimized device designed with the previously stated design rules provides a response increase of two orders of magnitude compared to previously reported devices using the same dipole geometry.

Robustness of antenna-coupled distributed bolometers

This Letter shows the effect of the geometrical and material properties of lead lines and connections on the robustness and reliability of optical antennas working as distributed bolometers. We analyze the operational limits of the biasing voltage using a mutiphysics finite element method. We demonstrate that, after evaluating the effect of the electromagnetic irradiance falling on the device, biasing voltage is the main limiting factor to maintain operative titanium optical antennas. Results have been experimentally verified by finding the biasing values needed to destroy optical antennas working as distributed bolometers. Structural damage has been identified from scanning electron microscopy images.

Antenna array connections for efficient performance of distributed microbolometers in the IR

Optical antennas and resonant structures have been extensively investigated due to its potential for electromagnetic detection and energy harvesting applications. However their integration into large arrays and the role of connection lines between individual antennas has drawn little attention. This is necessary if we want to exploit its potential constructively and to enable economical large-scale fabrication. In this contribution we point out some features that an efficient antenna array should address. Experimental measurements on aluminum microbolometers are compared to electromagnetic simulations, it is shown that the finite size of a real array and the interconnection lines interact and affect the global performance.

Size Dependence of the Directional Scattering Conditions on Semiconductor Nanoparticles

The resonant modes observed in semiconductor nanoparticles and the coherent interaction between them, producing directional light scattering, may be very interesting for CMOS integrated all-optical devices. In these systems, the control over the light scattering should be crucial, as well as the strength of this control. Fabrication parameters such as the size and shape of the nanoparticles and the optical properties of the environment can strongly affect to the emergence of these phenomena. In this letter, we numerically explore the size dependence of the directional scattering conditions of semiconductor nanoparticles. Several semiconductor materials and a large size range have been considered as a reference for further works. An interesting and unexpected linear behavior has been observed.

Steerable optical antennas by selective heating

Directional steerability can be obtained for an array of optical antennas through selective heating of the individual elements. Heating changes electrical conductivity of the heated element, which affects the phase of the generated currents. The variation in temperature can be obtained by modifying the biasing point of the individual elements of the array, which would allow fast reconfiguration. The numerical evaluation of the performance of an array of a reduced number of antennas (2 and 3) shows the feasibility of this approach.

An analytical model for the opto-thermo-mechanical conversion mechanisms in a MOEMS based energy harvester

The use of optical excitation in MEMS elements triggers several mechanisms that can be properly used for enhancing its mechanical response. This is particularly interesting when MEMS components are used as the transducer element on energy harvesting applications involving opto-mechanical conversion schemes. One of the pathways is based on the thermal response of the vibrating structures. In this contribution we have analyzed how a MEMS structure consisting on a clamped-clamped beam responds mechanically to the heating of the element. This heating is produced by the partial absorption of an incident radiation at the IR band. A thin metal layer evaporated on top of the suspended beam acts as the infrared light absorber. The gap forms an optical interferometer which couples the light absorption to the mechanical deflection of the CC-beam. This effect can be enhanced by a proper design of the whole mechanical geometry. Both, the optical absorbance and the energy conversion to the thermal domain of the MOEMS device are analyzed. Additionally, the transduction to the mechanical domain in the form of beam vibrations of the optical energy absorbed by the structure and transformed into heat is also modeled. This paper focus on the analytical model that is necessary to understand the involved physical mechanisms and the results obtained from the simulation of the device.