Aveek Dutta

Role of epsilon-near-zero substrates in the optical response of plasmonic antennas

Radiation patterns and the resonance wavelength of a plasmonic antenna are significantly influenced by its local environment, particularly its substrate. Here, we experimentally explore the role of dispersive substrates, such as aluminum- or gallium-doped zinc oxide in the near infrared and 4H-silicon carbide in the mid-infrared, upon Au plasmonic antennas, extending from dielectric to metal-like regimes, crossing through epsilon-near-zero (ENZ) conditions. We demonstrate that the vanishing index of refraction within this transition induces a “slowing down” of the rate of spectral shift for the antenna resonance frequency, resulting in an eventual “pinning” of the resonance near the ENZ frequency. This condition corresponds to a strong backward emission with near-constant phase. By comparing heavily doped semiconductors and undoped, polar dielectric substrates with ENZ conditions in the near- and mid-infrared, respectively, we also demonstrate the generality of the phenomenon using both surface plasmon and phonon polaritons, respectively. Furthermore, we also show that the redirected antenna radiation induces a Fano-like interference and an apparent stimulation of optic phonons within SiC.

Surface-plasmon opto-magnetic field enhancement for all-optical magnetization switching

The demand for faster magnetization switching speeds and lower energy consumption has driven the field of spintronics in recent years. The magnetic tunnel junction is the most developed spintronic memory device in which the magnetization of the storage layer is switched by spin-transfer-torque or spin-orbit torque interactions. Whereas these novel spin-torque interactions exemplify the potential of electron-spin-based devices and memory, the switching speed is limited to the ns regime by the precessional motion of the magnetization. All-optical magnetization switching, based on the inverse Faraday effect, has been shown to be an attractive method for achieving magnetization switching at ps speeds. Successful magnetization reversal in thin films has been demonstrated by using circularly polarized light. However, a method for all-optical switching of on-chip nanomagnets in high density memory modules has not been described. In this work we propose to use plasmonics, with CMOS compatible plasmonic materials, to achieve on-chip magnetization reversal in nanomagnets. Plasmonics allows light to be confined in dimensions much smaller than the diffraction limit of light. This in turn, yields higher localized electromagnetic field intensities. In this work, through simulations, we show that using localized surface plasmon resonances, it is possible to couple light to nanomagnets and achieve significantly higher opto-magnetic field values in comparison to free space light excitation.

Nanostructured Transparent Conducting Oxide Films for Polarization Control with Plasmonic Metasurfaces

Transparent Conducting Oxides (TCOs) enable the realization of practical plasmonic and metamaterial devices at the telecommunication frequency due to their low optical loss and CMOS compatibility. By employing a conventional dry-etching process, we have fabricated GZO plasmonic waveplates, which convert linearly polarized light into circularly polarized light.

Surface-plasmon optomagnetic field enhancement for all-optical magnetization switching (Conference Presentation)

The demand for faster magnetization switching speeds and lower energy consumption has driven the field of spintronics in recent years. Whereas spin-transfer-torque and spin-orbit-torque interactions exemplify the potential of electron-spin-based devices and memory, the switching speed is limited to the ns regime by the precessional motion of the magnetization. All-optical magnetization switching, based on the inverse Faraday effect, has been shown to be an attractive method for achieving magnetization switching at ps speeds. Successful magnetization reversal in thin films has been demonstrated by using circularly polarized light. However, a method for all-optical switching of on-chip nanomagnets in high density memory modules has not been described. In this work we propose to use plasmonics, with CMOS compatible plasmonic materials, to achieve on-chip magnetization reversal in nanomagnets. Plasmonics allows light to be confined in dimensions much smaller than the diffraction limit of light. This in turn, yields higher localized electromagnetic field intensities. In this work, through simulations, we show that using surface plasmon resonances, it is possible to couple light to nanomagnets and achieve significantly higher opto-magnetic field values in comparison to free space light excitation for the same incident intensity. We use two well-known magnetic materials Bismuth Iron Garnet (BIG) and Gadolinium Iron Cobalt (GdFECo) and couple these nanomagnets to a plasmonic resonator made of Titanium Nitride. Our simulation results show 10 times enhancement in the opto-magnetic field for BIG and about 3 times for GdFeCo in the coupled structure compared to free-space excitation. Our simulations also show the possibility of having in-plane components of the opto-magnetic field in the coupled structure which might prove beneficial for switching in nanomagnets with canted magnetization.

Ultrafast all-optical switching in a continuous layer gap plasmon metasurface (Conference Presentation)

All-optical nanophotonic switches, not bound by the inherent RC delays of electronic circuits, have the potential to push data-processing speeds beyond the limits of Moore’s Law. This has lead to the investigation of light-matter interactions in nanostructured materials in several all-optical data processing applications. To have a true impact on the field of ultrafast data-transfer, it is important to demonstrate switching in the telecom frequency range. We have designed a continuous layer gap plasmon metasurface, comprising a layer of gold nanodisk resonators on a 20 nm film of ZnO deposited on an optically thick gold layer. The performance of the metasurface has been investigated through numerical studies, using the optical properties of as-grown gold and zinc oxide, characterized by ellipsometry. An on-off ratio of 10.6 dB has been observed in simulations. Experimental studies are underway. The findings of this research work will pave the pathway to the design of ultra-compact and ultrafast optical switches employing ultrafast, dynamically tunable metasurfaces.

Titanium nitride based hybrid plasmonic-photonic waveguides for on-chip plasmonic interconnects

Over the past few decades, photonic technologies have emerged as a promising technology for data communications. They offer advantages such as high data bandwidths at comparable or even lower power consumption than electronics. However, photonic integrated circuits suffer from the diffraction limit of light which is a major obstacle in achieving small device footprints and densely packed on-chip interconnects. In recent years, plasmonics has emerged as a possible solution for densely packed on-chip nanophotonic circuitry. The field of plasmonics deals with oscillations of free electrons in a metal coupled to an electromagnetic field. The large wave-vector associated with these oscillations enables light to be localized in volumes much smaller than the diffraction limit. Consequently, there have been many demonstrations of plasmonic interconnects for on-chip communications, using well known metals such as gold and silver. However these materials are not CMOS compatible and hence their use is not technologically feasible. The growing need for plasmonic materials which are robust, cost-effective, and CMOS-compatible has led to the study of alternate plasmonic materials. For the visible and near infrared ranges, transition metal nitrides have been shown to be suitable metals for plasmonic applications These materials have optical properties comparable to that of gold and are CMOS-compatible, hence, they can be easily integrated into a silicon platform for on-chip applications. In this work, we demonstrate titanium nitride based plasmonic interconnects in an all-solid state geometry which can be easily integrated on a silicon platform.

On-chip and planar optics with alternative plasmonic materials (Conference Presentation)

Plasmonic interconnects as well as metasurfaces manipulating the phase and amplitude of reflected and/or transmitted light, have attracted significant attention in the fields of planar optics and on-chip nanophotonics. The application space of plasmonics has recently been expanded by new materials classes including transparent conducting oxides (TCOs) and refractory transition metal nitrides (TMNs). These materials offer superior thermal stability, robustness, tailorability and CMOS compatibility, thus outperforming the conventional plasmonic components (e.g. gold and silver) in application-specific requirements. Here, we discuss recent progress in the areas of plasmonic interconnects, modulators and metasurfaces realized using TMNs and TCOs. Ultrafast nonlinear responses near the epsilon near zero (ENZ) region have been recently demonstrated for Al doped zinc oxide (AZO) (TCO). This has spurred the development of ultrafast, on-chip modulators with TCOs as an active material. Building from on our previous work on LRSPP waveguides with ultrathin Titanium Nitride (TiN) (5.5mm propagation length) and Zirconium Nitride (ZrN), we will report solid-state hybrid mode waveguides using TiN as well as a modulator based on this waveguide which provides all-optical tunability, low optical losses at the telecommunication window, and CMOS-compatibility. Successful integration of these alternative plasmonic components into the phase gradient metasurfaces platform without loss of performance have also been demonstrated. A metasurface employing ZrN brick antennas shows the photonic spin Hall Effect (PSHE), by reflecting the two circular polarizations in different directions. In another device, a metasurface based on nanostructures of Ga doped ZnO (TCO), functioning as a quarter-wave plate, have been realized.

Near-infrared plasmonics with transparent conducting oxides (Conference Presentation)

As a result of the significant attention in searching for alternative plasmonic materials for real-life nanophotonic devices, transparent conducting oxides (TCOs) have been proposed as promising constituent building blocks for telecommunication wavelengths. They are eminently practical materials because they are CMOS-compatible, can be grown on many different types of substrates, patterned by standard fabrication procedures, and integrated with many other standard technologies. Due to the ability of TCO nanostructures to support strong plasmonic resonance in the near infrared (NIR), metasurface devices, such as a quarter wave plate, have been demonstrated whose properties can be easily adjustable with post processing such as thermal annealing. Additionally, TCOs can be used as epsilon near zero (ENZ) materials in the NIR. From our recent study of the behavior of nanoantennae sitting upon a TCO substrate, we found that TCOs serve as an optical insulating media due to the high impedance of TCOs at the ENZ frequency, enabling emission shaping. Finally, the optical properties of TCOs can be varied by optical or electrical means. Current research is focused on studying the ultrafast carrier dynamics in doped zinc oxide films using pump-probe spectroscopy. We have shown that aluminum doped zinc oxide films can achieve a 40% change in reflection with ultrafast dynamics (<1ps) under a small fluence of 3mJ/cm2. Consequently, TCOs are shown to be extremely flexible materials, enabling fascinating physics and unique devices for applications in the NIR regime.

New Materials for Plasmonics: Designs and Applications from Flat Optics to Quantum Nanophotonics

We will review the list of alternative plasmonic materials and provide a focused discussion on transition metal nitrides for refractory plasmonics. Nanostructures made of alternative plasmonic materials and their performance will be presented. Article not available.

Transparent conducting oxides as plasmonic component in near infrared (Presentation Recording)

The development of new plasmonic materials enables novel optical devices, and they in turn assist in the progress of optical communications. As a result of the significant attention in searching for alternative materials, transparent conducting oxides (TCOs) have been proposed as promising plasmonic compounds at telecommunication wavelengths [1]. They are eminently practical materials because they are CMOS-compatible, can be grown on many different types of substrates, patterned by standard fabrication procedures, and integrated with many other standard technologies. Due to the ability of TCO nanostructures to support strong plasmonic resonance in the NIR, metasurface devices, such as a quarter wave plate, have been demonstrated whose properties can be easily adjustable with post processing such as thermal annealing [2,3]. Additionally, TCOs can be used as epsilon near zero (ENZ) materials in the NIR. From our recent study of the behavior of nanoantennae sitting upon a TCO substrate, we found that TCOs serve as an optical insulating media due to the high impedance of TCOs at the ENZ frequency, enabling emission shaping. Finally, the optical properties of TCOs can be varied by optical or electrical means. Current research is focused on studying the ultrafast carrier dynamics in doped zinc oxide films using pump-probe spectroscopy. We have shown that aluminum doped zinc oxide films can achieve a 40% change in reflection with ultrafast dynamics (<1ps) under a small fluence of 3mJ/cm2. Consequently, TCOs are shown to be extremely flexible materials, enabling fascinating physics and unique devices for applications in the NIR regime. References [1] A. Boltasseva and H. Atwater, Science 331(6015), 290-291, 2011. [2] J. Kim et al, Selected Topics in Quantum Electronics, IEEE Journal of, 19, 4601907-4601907, 2013. [3] J. Kim et al, CLEO: QELS_Fundamental Science. Optical Society of America, 2014. This work was supported by ONR MURI N00014-10-1-0942