A novel method of generation and synthesis of azimuthally E-polarized vortex beams is presented. ... more A novel method of generation and synthesis of azimuthally E-polarized vortex beams is presented. Along the axis of propagation such beams have a strong longitudinally polarized magnetic field where ideally there is no electric field. We show how these beams can be constructed through the interference of Laguerre-Gaussian beams carrying orbital angular momentum. As an example, we present a metasurface made of double-split ring slot pairs and report a good agreement between simulated and analytical results. Both a high magnetic-to-electric-field contrast ratio and a magnetic field enhancement are achieved. We also investigate the metasurface physical constraints to convert a linearly polarized beam into an azimuthally E- polarized beam and characterize the performance of magnetic field enhancement and electric field suppression of a realistic metasurface. These findings are potentially useful for novel optical spectroscopy related to magnetic dipolar transitions and for optical manipu...
The concept of magnetic nanoprobes (or magnetic nanoantennas) providing a magnetic near-field enh... more The concept of magnetic nanoprobes (or magnetic nanoantennas) providing a magnetic near-field enhancement and vanishing electric field is presented and investigated, together with their excitation. It is established that a particular type of cylindrical vector beams called azimuthally electric polarized vector beams yield strong longitudinal magnetic field on the beam axis where the electric field is ideally null. These beams with an electric polarization vortex and cylindrical symmetry are important in generating high magnetic to electric field contrast, i.e., large local field admittance, and in allowing selective excitation of magnetic transitions in matter located on the beam axis. We demonstrate that azimuthally polarized vector beam excitation of a photoinduced magnetic nanoprobe made of a magnetically polarizable nano cluster leads to enhanced magnetic near field with resolution beyond diffraction limit. We introduce two figures of merit as magnetic field enhancement and loca...
We investigate the power emitted by a transverse dipole at optical frequencies placed at a given ... more We investigate the power emitted by a transverse dipole at optical frequencies placed at a given distance from the interface between vacuum and a periodic bi-layered hyperbolic metamaterial (HM). We adopt the transmission line formalism for transverse electric (TE) and magnetic (TM) waves to determine the power spectrum emitted by the dipole towards the HM and the fraction of the power directed towards the isotropic half space, at various dipole distances from the interface. For small distances most of the power is directed into the HM, and we investigate the importance of layers’ thickness. These results are compared to similar ones in which a transverse dipole is placed above bulk silica-vacuum or bulk silver-vacuum interfaces.
2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2015
A novel birefringent transmitarray capable of local polarization conversion in infrared regime is... more A novel birefringent transmitarray capable of local polarization conversion in infrared regime is presented. In particular an incident beam with linear polarization can be transformed into a radially or azimuthally polarized vector beam and in general a wide continuum of polarization states are realizable on the higher order Poincare spheres. The transmitarray is composed of a rectangular array of double-layer double split-ring slot nanoantennas. The double layer element, chosen here, enables high transmission coefficient amplitude, thus increases the efficiency of conversion to the vector vortex beams. The array element exhibits anisotropy with respect to the field polarization on the transmitarray plane, where the transmission coefficients for two orthogonal linear polarizations are almost equal in magnitude and have almost a 180° phase difference. This transmission condition is crucial in the geometric phase control method employed here and it is satisfied in a certain frequency band. The local polarization transformation on the array is controlled through manipulating the angular orientation of the slot elements with respect to element centers. Locally the phase of circularly polarized transmitted waves are advanced or delayed with a phase equal to twice the rotation angle. This phase control method is purely geometrical and it is not frequency dependent. For a certain transmitarray, the generated beam's polarization map is also a function of incident beam polarization. We then study the interesting case of azimuthally E-polarized vortex beams which are a superposition of the Laguerre Gaussian (LG) beams carrying certain orbital angular momentum (OAM) states. Such beams have a strong longitudinally polarized magnetic field on the propagation axis of the beam where the total electric field vanishes. We demonstrate analytically and through numerical field calculations, the evolution of electric and magnetic fields as the beam propagates. These finding are particularly interesting in the view of optical spectroscopy systems related to dipolar transitions and for optical manipulation of particles with spin and orbital angular momenta.
We analyze the theoretical and physical properties of a CMOS compatible optical leaky wave antenn... more We analyze the theoretical and physical properties of a CMOS compatible optical leaky wave antenna (OLWA) integrated into a Fabry-Pérot resonator (FPR) at 193.4 THz (wavelength 0 = 1550 nm). The presented OLWA design is composed of a silicon (Si) dielectric waveguide sandwiched between two silica glass (SiO 2) domains, and it comprises periodic perturbations (cavities of vacuum). We first describe the radiation of the isolated OLWA whose radiation pattern is due to the excitation of a leaky wave, slowly decaying while traveling. The perturbations are indeed designed to obtain a leaky wave harmonic with very low attenuation and phase constants. Then, we integrate the same OLWA into a FPR where two leaky waves with the same wavenumber are travelling in opposite directions inside the resonator. We show that the radiation level at the broadside direction can be effectively controlled by modifying the optical properties of the Si waveguide through electron-hole excess carrier generation (found to be highly enhanced when it is integrated into a FPR). The design of the integrated OLWA is properly set to guarantee the constructive interference of the two radiated beams provided by the two leaky waves in the FPR. The modal propagation constant in the integrated OLWA can be then altered through excess carrier generation in Si, thus the antenna can be tuned in and out of the resonance thanks to the high FPR quality factor, and the LW modal dispersion relation. This allows for enhanced radiation level control at broadside, and preliminary results show up to 13 dB beam modulation.
Proceedings of the 2012 IEEE International Symposium on Antennas and Propagation, 2012
We propose a highly directive optical leaky wave antenna (OLWA) radiating at 1550 nm composed of ... more We propose a highly directive optical leaky wave antenna (OLWA) radiating at 1550 nm composed of a dielectric waveguide comprising periodic silicon (Si) perturbations. The antenna working principle is based on the excitation of a leaky wave guided mode in the perturbed waveguide. Here we study the radiation properties for two sets of perturbation dimensions, and show beam scanning capabilities of the antenna (radiation level and direction) at broadside by varying the free space wavelength. Moreover, the use of Si offers the electronic/optical tunability of its complex refractive index by excess electron-hole carrier density generation via current injection (electronic control) or optical absorption (optical control). Therefore, by changing the Si refractive index we vary the leaky wave attenuation constant and the input impedance of the antenna, which in turn allow for beam control capabilities. I.
We develop an electrodynamic model based on dyadic Green's functions for analyzing the near-field... more We develop an electrodynamic model based on dyadic Green's functions for analyzing the near-field interactions between a dipolar scatterer (DS) and a plasmonic nanosphere (PN) under external excitation, accounting for multipolar contributions in the evaluation of the scattered fields. In particular, we include all the radiative and nonradiative field interactions between the DS and the PN, particularly the physical mechanism of DS's self-coupling through the PN, which is either neglected or approximated in previous work. Our objective is to show under which conditions self-coupling is important for strong excitation-rate enhancement of the DS and provide a description of the system's properties. We analytically investigate the conditions under which the excitation rate of a DS, such as an organic dye or a quantum dot, is enhanced when located in close proximity to a PN. We show the existence of critical conditions in terms of polarizabilities and distances that lead to large enhancement based on self-coupling and how to predict it.
2014 IEEE Antennas and Propagation Society International Symposium (APSURSI), 2014
A leaky-wave antenna at optical frequencies is designed and integrated with a ring resonator at 1... more A leaky-wave antenna at optical frequencies is designed and integrated with a ring resonator at 1550 nm wavelength. The leaky wave is generated by using periodic perturbations in the integrated dielectric waveguide that excite the-1 spatial harmonic. The antenna consists of a dielectric waveguides with semiconductor corrugations, and it is compatible with CMOS fabrication technology. We show that integrating the leaky wave antenna in an optical ring resonator that is fed by directional couplers, we can improve the electronic control of the radiation through carrier injection into the semiconductor corrugations. I.
We investigate the directive radiation at 1550 nm from an optical leaky wave antenna (OLWA) with ... more We investigate the directive radiation at 1550 nm from an optical leaky wave antenna (OLWA) with semiconductor perturbations made of silicon (Si). We study the radiation pattern dependence on the physical dimensions, number of perturbations and carrier densities in these semiconductor perturbations through optical excitations at a visible wavelength, 625 nm. In this detailed theoretical study we show the correlation between the pump power absorbed in the perturbations, the signal guided in the waveguide and the radiation through leakage. To overcome the limited control of the radiation intensity through excess carrier generation in Si, we present a new design with the OLWA integrated with a Fabry-Pérot resonator (FPR). We provide analytical and numerical studies of the enhanced radiation performance of the OLWA antenna inside the FPR, and derive closed-form formulas accounting for LW reflection at the edges of the FPR. A discussion on the constructive and destructive radiation by the direct and reflected leaky waves in the FPR resonator is provided. Results shown in this paper exhibit 3 dB variation of the radiation and pave the way for further optimization and theoretical developments.
We investigate a novel implementation of hyperbolic metamaterial (HM) at far-infrared frequencies... more We investigate a novel implementation of hyperbolic metamaterial (HM) at far-infrared frequencies composed of stacked graphene sheets separated by thin dielectric layers. Using the surface conductivity model of graphene, we derive the homogenization formula for the multilayer structure by treating graphene sheets as lumped layers with complex admittances. Homogenization results and limits are investigated by comparison with a transfer matrix formulation for the HM constituent layers. We show that infrared iso-frequency wavevector dispersion characteristics of the proposed HM can be tuned by varying the chemical potential of the graphene sheets via electrostatic biasing. Accordingly, reflection and transmission properties for a film made of graphene-dielectric multilayer are tunable at terahertz frequencies, and we investigate the limits in using the homogenized model compared to the more accurate transfer matrix model. We also propose to use graphene-based HM as a super absorber for near-fields generated at its surface. The power emitted by a dipole near the surface of a graphene-based HM is increased dramatically (up to 5 × 10 2 at 2 THz), furthermore we show that most of the scattered power is directed into the HM. The validity and limits of the homogenized HM model are assessed also for near-fields and show that in certain conditions it overestimates the dipole radiated power into the HM.
A novel method of generation and synthesis of azimuthally E-polarized vortex beams is presented. ... more A novel method of generation and synthesis of azimuthally E-polarized vortex beams is presented. Along the axis of propagation such beams have a strong longitudinally polarized magnetic field where ideally there is no electric field. We show how these beams can be constructed through the interference of Laguerre-Gaussian beams carrying orbital angular momentum. As an example, we present a metasurface made of double-split ring slot pairs and report a good agreement between simulated and analytical results. Both a high magnetic-to-electric-field contrast ratio and a magnetic field enhancement are achieved. We also investigate the metasurface physical constraints to convert a linearly polarized beam into an azimuthally E- polarized beam and characterize the performance of magnetic field enhancement and electric field suppression of a realistic metasurface. These findings are potentially useful for novel optical spectroscopy related to magnetic dipolar transitions and for optical manipu...
The concept of magnetic nanoprobes (or magnetic nanoantennas) providing a magnetic near-field enh... more The concept of magnetic nanoprobes (or magnetic nanoantennas) providing a magnetic near-field enhancement and vanishing electric field is presented and investigated, together with their excitation. It is established that a particular type of cylindrical vector beams called azimuthally electric polarized vector beams yield strong longitudinal magnetic field on the beam axis where the electric field is ideally null. These beams with an electric polarization vortex and cylindrical symmetry are important in generating high magnetic to electric field contrast, i.e., large local field admittance, and in allowing selective excitation of magnetic transitions in matter located on the beam axis. We demonstrate that azimuthally polarized vector beam excitation of a photoinduced magnetic nanoprobe made of a magnetically polarizable nano cluster leads to enhanced magnetic near field with resolution beyond diffraction limit. We introduce two figures of merit as magnetic field enhancement and loca...
We investigate the power emitted by a transverse dipole at optical frequencies placed at a given ... more We investigate the power emitted by a transverse dipole at optical frequencies placed at a given distance from the interface between vacuum and a periodic bi-layered hyperbolic metamaterial (HM). We adopt the transmission line formalism for transverse electric (TE) and magnetic (TM) waves to determine the power spectrum emitted by the dipole towards the HM and the fraction of the power directed towards the isotropic half space, at various dipole distances from the interface. For small distances most of the power is directed into the HM, and we investigate the importance of layers’ thickness. These results are compared to similar ones in which a transverse dipole is placed above bulk silica-vacuum or bulk silver-vacuum interfaces.
2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2015
A novel birefringent transmitarray capable of local polarization conversion in infrared regime is... more A novel birefringent transmitarray capable of local polarization conversion in infrared regime is presented. In particular an incident beam with linear polarization can be transformed into a radially or azimuthally polarized vector beam and in general a wide continuum of polarization states are realizable on the higher order Poincare spheres. The transmitarray is composed of a rectangular array of double-layer double split-ring slot nanoantennas. The double layer element, chosen here, enables high transmission coefficient amplitude, thus increases the efficiency of conversion to the vector vortex beams. The array element exhibits anisotropy with respect to the field polarization on the transmitarray plane, where the transmission coefficients for two orthogonal linear polarizations are almost equal in magnitude and have almost a 180° phase difference. This transmission condition is crucial in the geometric phase control method employed here and it is satisfied in a certain frequency band. The local polarization transformation on the array is controlled through manipulating the angular orientation of the slot elements with respect to element centers. Locally the phase of circularly polarized transmitted waves are advanced or delayed with a phase equal to twice the rotation angle. This phase control method is purely geometrical and it is not frequency dependent. For a certain transmitarray, the generated beam's polarization map is also a function of incident beam polarization. We then study the interesting case of azimuthally E-polarized vortex beams which are a superposition of the Laguerre Gaussian (LG) beams carrying certain orbital angular momentum (OAM) states. Such beams have a strong longitudinally polarized magnetic field on the propagation axis of the beam where the total electric field vanishes. We demonstrate analytically and through numerical field calculations, the evolution of electric and magnetic fields as the beam propagates. These finding are particularly interesting in the view of optical spectroscopy systems related to dipolar transitions and for optical manipulation of particles with spin and orbital angular momenta.
We analyze the theoretical and physical properties of a CMOS compatible optical leaky wave antenn... more We analyze the theoretical and physical properties of a CMOS compatible optical leaky wave antenna (OLWA) integrated into a Fabry-Pérot resonator (FPR) at 193.4 THz (wavelength 0 = 1550 nm). The presented OLWA design is composed of a silicon (Si) dielectric waveguide sandwiched between two silica glass (SiO 2) domains, and it comprises periodic perturbations (cavities of vacuum). We first describe the radiation of the isolated OLWA whose radiation pattern is due to the excitation of a leaky wave, slowly decaying while traveling. The perturbations are indeed designed to obtain a leaky wave harmonic with very low attenuation and phase constants. Then, we integrate the same OLWA into a FPR where two leaky waves with the same wavenumber are travelling in opposite directions inside the resonator. We show that the radiation level at the broadside direction can be effectively controlled by modifying the optical properties of the Si waveguide through electron-hole excess carrier generation (found to be highly enhanced when it is integrated into a FPR). The design of the integrated OLWA is properly set to guarantee the constructive interference of the two radiated beams provided by the two leaky waves in the FPR. The modal propagation constant in the integrated OLWA can be then altered through excess carrier generation in Si, thus the antenna can be tuned in and out of the resonance thanks to the high FPR quality factor, and the LW modal dispersion relation. This allows for enhanced radiation level control at broadside, and preliminary results show up to 13 dB beam modulation.
Proceedings of the 2012 IEEE International Symposium on Antennas and Propagation, 2012
We propose a highly directive optical leaky wave antenna (OLWA) radiating at 1550 nm composed of ... more We propose a highly directive optical leaky wave antenna (OLWA) radiating at 1550 nm composed of a dielectric waveguide comprising periodic silicon (Si) perturbations. The antenna working principle is based on the excitation of a leaky wave guided mode in the perturbed waveguide. Here we study the radiation properties for two sets of perturbation dimensions, and show beam scanning capabilities of the antenna (radiation level and direction) at broadside by varying the free space wavelength. Moreover, the use of Si offers the electronic/optical tunability of its complex refractive index by excess electron-hole carrier density generation via current injection (electronic control) or optical absorption (optical control). Therefore, by changing the Si refractive index we vary the leaky wave attenuation constant and the input impedance of the antenna, which in turn allow for beam control capabilities. I.
We develop an electrodynamic model based on dyadic Green's functions for analyzing the near-field... more We develop an electrodynamic model based on dyadic Green's functions for analyzing the near-field interactions between a dipolar scatterer (DS) and a plasmonic nanosphere (PN) under external excitation, accounting for multipolar contributions in the evaluation of the scattered fields. In particular, we include all the radiative and nonradiative field interactions between the DS and the PN, particularly the physical mechanism of DS's self-coupling through the PN, which is either neglected or approximated in previous work. Our objective is to show under which conditions self-coupling is important for strong excitation-rate enhancement of the DS and provide a description of the system's properties. We analytically investigate the conditions under which the excitation rate of a DS, such as an organic dye or a quantum dot, is enhanced when located in close proximity to a PN. We show the existence of critical conditions in terms of polarizabilities and distances that lead to large enhancement based on self-coupling and how to predict it.
2014 IEEE Antennas and Propagation Society International Symposium (APSURSI), 2014
A leaky-wave antenna at optical frequencies is designed and integrated with a ring resonator at 1... more A leaky-wave antenna at optical frequencies is designed and integrated with a ring resonator at 1550 nm wavelength. The leaky wave is generated by using periodic perturbations in the integrated dielectric waveguide that excite the-1 spatial harmonic. The antenna consists of a dielectric waveguides with semiconductor corrugations, and it is compatible with CMOS fabrication technology. We show that integrating the leaky wave antenna in an optical ring resonator that is fed by directional couplers, we can improve the electronic control of the radiation through carrier injection into the semiconductor corrugations. I.
We investigate the directive radiation at 1550 nm from an optical leaky wave antenna (OLWA) with ... more We investigate the directive radiation at 1550 nm from an optical leaky wave antenna (OLWA) with semiconductor perturbations made of silicon (Si). We study the radiation pattern dependence on the physical dimensions, number of perturbations and carrier densities in these semiconductor perturbations through optical excitations at a visible wavelength, 625 nm. In this detailed theoretical study we show the correlation between the pump power absorbed in the perturbations, the signal guided in the waveguide and the radiation through leakage. To overcome the limited control of the radiation intensity through excess carrier generation in Si, we present a new design with the OLWA integrated with a Fabry-Pérot resonator (FPR). We provide analytical and numerical studies of the enhanced radiation performance of the OLWA antenna inside the FPR, and derive closed-form formulas accounting for LW reflection at the edges of the FPR. A discussion on the constructive and destructive radiation by the direct and reflected leaky waves in the FPR resonator is provided. Results shown in this paper exhibit 3 dB variation of the radiation and pave the way for further optimization and theoretical developments.
We investigate a novel implementation of hyperbolic metamaterial (HM) at far-infrared frequencies... more We investigate a novel implementation of hyperbolic metamaterial (HM) at far-infrared frequencies composed of stacked graphene sheets separated by thin dielectric layers. Using the surface conductivity model of graphene, we derive the homogenization formula for the multilayer structure by treating graphene sheets as lumped layers with complex admittances. Homogenization results and limits are investigated by comparison with a transfer matrix formulation for the HM constituent layers. We show that infrared iso-frequency wavevector dispersion characteristics of the proposed HM can be tuned by varying the chemical potential of the graphene sheets via electrostatic biasing. Accordingly, reflection and transmission properties for a film made of graphene-dielectric multilayer are tunable at terahertz frequencies, and we investigate the limits in using the homogenized model compared to the more accurate transfer matrix model. We also propose to use graphene-based HM as a super absorber for near-fields generated at its surface. The power emitted by a dipole near the surface of a graphene-based HM is increased dramatically (up to 5 × 10 2 at 2 THz), furthermore we show that most of the scattered power is directed into the HM. The validity and limits of the homogenized HM model are assessed also for near-fields and show that in certain conditions it overestimates the dipole radiated power into the HM.
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