Nanophotonic Research Articles

Hyperbolic-metamaterial antennas for broadband enhancement of dipole emission to free space

Dipole emitters used in nano optics and nanophotonics (e.g., fluorescent molecules or quantum dots) are weak radiators and thus detecting the radiation of a single emitter gets possible only if it is significantly enhanced. For this enhancement, one often utilizes resonant nanoantennas (Purcell's effect); this method, however, requires the exact knowledge of source location and radiation frequency which constitute a significant drawback. One known possibility for broadband location-insensitive radiation enhancement is to use a layer of the so-called hyperbolic metamaterial. However, the enhanced radiated energy is mainly directed into the volume of the lossy medium, where it is lost to heating. In this work, we suggest specific shapes of macroscopic hyperbolic metamaterial samples to open radiation windows for enhanced radiation to free space. We show that hyperbolic media slabs with properly shaped macroscopic grooves convert the evanescent waves produced by a dipole into waves traveling in free space, which results in the enhancement of useful radiation by one to two orders of magnitude. That level of enhancement of radiation into free-space which is also wideband and of non-resonant nature has not been reported up to now. These results may open possibilities for realization of broadband and directive antennas, where the primary radiators are randomly positioned fluorescent molecules or quantum dots.

Current-Voltage Characteristics of Copper Embedded PtSi/silicon-p Schottky Detector

A simple method for developing a Schottky IR sensors consisting of metal (pt)- semiconductor (Si-p) is demonstrated in this work. PtSi/Si-p structure is formed by depositing platinum layer over cleaned Si surface using e-beam and embedded by Copper thin film. Current-voltage (I-V) characterization of PtSi/Si with and without copper is made at 77 K. The I-V measurements are made in the presence and absence of electromagnetic wave with infrared source. The result shows a significant increase in photocurrent and higher sensitivity in copper embedded PtSi/Si structure comparing to the conventional PtSi/Si structure. The CuPt layer created over the PtSi layer increases the PtSi sensitivity by trapping infrared radiation. This sensor with small size and high sensitive for IR radiation can be utilized in infrared imageing sensors, nanoplasmonics and nano-Photonics elements.

Invited Presentation: Optical Properties of Carbon Nanotube/Chromophores Assemblies

The delocalized π-electronic system of carbon nanotubes allows them to link non-covalently to a lot of different organic molecules. In contrast to covalent functionalization, this weak interaction preserves most of the nanotubes intrinsic properties (photoluminescence or mobility for instance) but still leads to a strong enough coupling so as to give stable compounds and to induce new and efficient functionalities [1, 2]. We focus on nanotubes / chromophores compounds where the latter acts as an optical nano antenna that absorbs light and transfers its energy to the nanotube, allowing a uniform excitation of all the chiral species in the sample [3, 4, 5, 6, 7].In this presentation, we will focus on the latest developments of our research in this topic.

Tuning the Scattering Response of the Optical Nano Antennas Using Graphene

In this paper, we propose the tuning of the optical nano antenna in the visible spectrum using graphene. A dipole structure for the nano antenna is considered with the resonating wavelength at the VIS-NIR spectrum range. Resonance is determined using the scattering characteristics of the dipole antenna. Placing monolayer and bilayers of graphene sheets on top of the optical nano antenna will result in a change in the resonating wavelength. The input impedance of the resultant structures is calculated. The FDTD simulation results for resonance characteristics were verified with the experiment results. Such architecture of graphene on top of the dipole nano antennas can be used for different biological and chemical gas sensors.

Nanopatterning by laser interference lithography: applications to optical devices.

A systematic review, covering fabrication of nanoscale patterns by laser interference lithography (LIL) and their applications for optical devices is provided. LIL is a patterning method. It is a simple, quick process over a large area without using a mask. LIL is a powerful technique for the definition of large-area, nanometer-scale, periodically patterned structures. Patterns are recorded in a light-sensitive medium that responds nonlinearly to the intensity distribution associated with the interference of two or more coherent beams of light. The photoresist patterns produced with LIL are the platform for further fabrication of nanostructures and growth of functional materials used as the building blocks for devices. Demonstration of optical and photonic devices by LIL is reviewed such as directed nanophotonics and surface plasmon resonance (SPR) or large area membrane reflectors and anti-reflectors. Perspective on future directions for LIL and emerging applications in other fields are presented.

Plasmonics and Nanophotonics

Plasmonics and Nanophotonics

Optical Solitons in Photonic Nano Waveguides with an Improved Nonlinear Schrödinger's Equation

Optical Solitons in Photonic Nano Waveguides with an Improved Nonlinear Schrödinger's Equation

DNA as nanophotonic scaffolds

DNA as nanophotonic scaffolds

Introduction to Micro- and Nanooptics

Introduction to Micro- and Nanooptics

Editorial: APCOT 2012 Special Issue

The sixth Asia-Pacific Conference on Transducers and Micro/Nano Technologies (APCOT 2012) was held between 4th and 7th of July in Nanjing, China. It was technically co-sponsored by IEEE Nanjing Section. Annually, the conference provides an opportunity for engineers from the diverse worlds of academia, industry and research institutions to share the latest developments in the field. The topics covered were similarly varied, ranging from sensor technology and microsystems (both physical and biological) to optical MEMS and nano devices.

PECVD based silicon oxynitride thin films for nano photonic on chip interconnects applications

Thin silicon oxynitride (SiOxNy) films were deposited by low temperature (∼300°C) plasma enhanced chemical vapour deposition (PECVD), using SiH4, N2O, NH3 precursor of the flow rate 25, 100, 30sccm and subjected to the post deposition annealing (PDA) treatment at 400°C and 600°C for nano optical/photonics on chip interconnects applications. AFM result reveals the variation of roughness from 60.9Å to 23.4Å after PDA treatment with respect to the as-deposited films, favourable surface topography for integrated waveguide applications. A model of decrease in island height with the effect of PDA treatment is proposed in support of AFM results. Raman spectroscopy and FTIR measurements are performed in order to define the change in crystallite and chemical bonding of as-deposited as well as PDA treated samples. These outcomes endorsed to the densification of SiOxNy thin films, due to decrease in SiN and SiO bonds strain, as well the OH, NH bonds with in oxynitride network. The increase in refractive index and PL intensity of as deposited SiOxNy thin films to the PDA treated films at 400°C and 600°C are observed. The significant shift of PL spectra peak positions indicate the change in cluster size as the result of PDA treatment, which influence the optical properties of thin films. It might be due to out diffusion of hydrogen containing species from silicon oxynitride films after PDA treatment. In this way, the structural and optical, feasibility of SiOxNy films are demonstrated in order to obtain high quality thin films for nano optical/photonics on chip interconnects applications.

Indirect optical absorption in silicon via thin-film surface plasmon

Optical excitations in semiconductors have been extensively studied in the dipole limit, neglecting the spatial variation of the exciting field. This is a very good approximation in most cases. However, when approaching the regime of nano optics and plasmonics, optical fields of extreme spatial confinement is found, e.g., surface plasmon polaritons (SPPs). Here we investigate the optical absorption of a SPP bound to an Ag thin-film embedded in Si at photon energies below the direct band gap of Si. In this regime, all absorbtion processes in Si must be assisted by a source of crystal momentum to overcome the momentum mismatch of the indirect transition. While phonon-assisted processes are the obvious example, the optical wave vector can also supply the needed momentum, provided the optical field displays sufficient spatial variation. We apply a simple model for the electric field and a band theoretical model response function for Si, including both frequency and wave vector dependence, and find that absorption in the Si medium relative to the Ag film may be increased significantly due to indirect transitions facilitated by the optical wave vector.

Going Green with Nanophotonics

Going Green with Nanophotonics

Tomography of the modulus and phase of an infrared focused beam for nanophotonic characterization measurements

Tomography of the modulus and phase of an infrared focused beam for nanophotonic characterization measurements

Honorary Chairman Dieter Bimberg

AbstractDieter H. Bimberg was born in Schrozberg/Germany on 10 July, 1942. He received the Diploma in physics and the Ph.D. degree from Goethe University Frankfurt in 1968 and 1971, respectively. From 1972 to 1979 he held a Principal Scientist position at the Max Planck Institute for Solid State Research in Grenoble/France and Stuttgart/Germany. In 1979 he was appointed as Professor of Electrical Engineering, Technical University of Aachen. Since 1981 he has held the Chair of Applied Solid State Physics at Technical University (TU) Berlin. Since 1990 he has been Executive Director of the Solid State Physics Institute at TU Berlin. From 1994 to 2006 he was Chairman of the DFG Collaborative Research Center (CRC) “Growth Related Properties of Nanostructures”. In 2007 he founded the DFG‐CRC on “Semiconductor Nano Photonics” which will operate until 2018. He has chaired the bmb+f “National Center of Competence on Nano‐Opto‐electronics” since 1998 and the joint board of the Federal Government Nanotechnology Centers of Competence since 2006. He holds guest professorships at Technion, Haifa (twice), University of California, Santa Barbara, and Hewlett‐Packard, Palo Alto/CA. His honors include the Japanese Prize of Applied Physics in 1988 and the Russian State Prize in Science and Technology in 2002. He is honorary Member of the A. F. Ioffe Physico‐Technical Institute of the Russian Academy of Sciences. Since 2004 he has been full member of the German National Academy of Sciences “Leopoldina” and a Fellow of the American Physical Society. In 2009 he was elected Fellow of the Institute of Electrical and Electronics Engineers (IEEE). Dieter Bimberg has authored more than 1000 papers, 20 patents, and 6 books. The number of his citations is over 24000 and his Hirsch index is 68. His research interests include physics and technology of nano¬structures and nanostructured devices like quantum‐dot lasers and amplifiers, wide‐gap semiconductor heterostructures, GaN‐based lasers, ultrahigh‐speed photonic devices, single electron devices, and quantum cryptography (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Trapped rainbow techniques for spectroscopy on a chip and fluorescence enhancement

We report on the experimental demonstration of the broadband "trapped rainbow" in the visible range using arrays of adiabatically tapered optical nano waveguides. Being a distinct case of the slow light phenomenon, the trapped rainbow effect could be applied to optical signal processing, and sensing in such applications as spectroscopy on a chip, and to providing enhanced light-matter interactions. As an example of the latter applications, we have fabricated a large area array of tapered nano-waveguides, which exhibit broadband "trapped rainbow" effect. Considerable fluorescence enhancement due to slow light behavior in the array has been observed.

Editorial - Special Issue on Nano Photonics

Editorial - Special Issue on Nano Photonics

Winter College to focus on nano-optics, plasmonics

Winter College to focus on nano-optics, plasmonics

Engineering the Input Impedance of Optical Nano Dipole Antennas: Materials, Geometry and Excitation Effect

An optical nano dipole antenna is analyzed by means of its input impedance as well as the matching properties of the antenna topology and material configuration. A comparison of this classical microwave driving method with plane wave excitation is accomplished, contrasting the resonances in the input impedance and optical cross sections for several setups, and analyzing the spectral response shape. It is found that for all structures analyzed, a simple linear expression can be defined characterizing the relation between total dipole length and resonant wavelength. The fact that this linear relationship remains valid for different excitation models, for most widely used antenna materials (Au, Ag, Cu, and Al) and even in the presence of substrates is important with respect to practical designs. To our knowledge, such an extensive study has not been performed before.

Efficient transmission of crossing dielectric slot waveguides

Transmission properties of two crossing dielectric slot waveguides (Si-Air-Si) are investigated using the finite difference in time domain method. Results show that the low transmission of this system mainly results from the reflection and radiation loss rather than the crosstalk. Using a simple method of filling up the crossing slots locally, the reflection, radiation losses and crosstalk are all greatly suppressed. With moderate parameters in this paper, the transmission efficient increases from 35.0% to more than 97% in a wide range of wavelength around 1.55 mm. The results and method presented in this paper may be very useful in the application of slot waveguide in micro and nano photonics.