Pieter G. Kik

Plasmonics—A Route to Nanoscale Optical Devices

The further integration of optical devices will require the fabrication of waveguides for electromagnetic energy below the diffraction limit of light. We investigate the possibility of using arrays of closely spaced metal nanoparticles for this purpose. Coupling between adjacent particles sets up coupled plasmon modes that give rise to coherent propagation of energy along the array. A point dipole analysis predicts group velocities of energy transport that exceed 0.1c along straight arrays and shows that energy transmission and switching through chain networks such as corners (see Figure) and tee structures is possible at high efficiencies. Radiation losses into the far field are expected to be negligible due to the near-field nature of the coupling, and resistive heating leads to transmission losses of about 6 dB/lm for gold and silver particles. We analyze macroscopic analogues operating in the microwave regime consisting of closely spaced metal rods by experiments and full field electrodynamic simulations. The guiding structures show a high confinement of the electromagnetic energy and allow for highly variable geometries and switching. Also, we have fabricated gold nanoparticle arrays using electron beam lithography and atomic force microscopy manipulation. These plasmon waveguides and switches could be the smallest devices with optical functionality.

Observation of coupled plasmon-polariton modes in Au nanoparticle chain waveguides of different lengths: Estimation of waveguide loss

Near-field interactions between closely spaced Au nanoparticles were characterized by studying the spectral position of the extinction bands corresponding to longitudinal (L) and transverse (T) plasmon-polariton modes of Au nanoparticle chains. Far-field spectroscopy and finite-difference time-domain simulations on arrays of 50 nm diameter Au spheres with an interparticle spacing of 75 nm both show a splitting DeltaE between the L and T modes that increases with chain length and saturates at a length of seven particles at DeltaE = 65 meV. We show that the measured splitting will result in a propagation loss of 3 dB/15 nm for energy transport. Calculations indicate that this loss can be reduced by at least one order of magnitude by modifying the shape of the constituent particles.

Surface Plasmon Nanophotonics

SURFACE PLASMON NANOPHOTONICS.- NEAR-FIELD AND FAR-FIELD PROPERTIES OF NANOPARTICLE ARRAYS.- THEORY OF LIGHT TRANSMISSION THROUGH PERIODICALLY STRUCTURED NANO-APERTURES.- DEVELOPMENT AND NEAR-FIELD CHARACTERIZATION OF SURFACE PLASMON WAVEGUIDES.- NUMERICAL SIMULATIONS OF LONG-RANGE PLASMONIC TRANSMISSION LINES.- SURFACE PLASMON POLARITON GUIDING IN PHOTONIC BANDGAP STRUCTURES.- SUBWAVELENGTH-SCALE PLASMON WAVEGUIDES.- OPTICAL SUPERLENS.- OPTICAL FIELD ENHANCEMENT WITH PLASMON RESONANT BOWTIE NANOANTENNAS.- NEAR-FIELD OPTICAL EXCITATION AND DETECTION OF SURFACE PLASMONS.- PRINCIPLES OF NEAR-FIELD OPTICAL MAPPING.- OVERVIEW OF SIMULATION TECHNIQUES FOR PLASMONIC DEVICES.- PLASMON HYBRIDIZATION IN COMPLEX NANOSTRUCTURES.- SENSING PROTEINS WITH ADAPTIVE METAL NANOSTRUCTURES.- INTEGRATED OPTICS BASED ON LONG-RANGE SURFACE PLASMON POLARITONS.- LOCALIZED SURFACE PLASMONS FOR OPTICAL DATA STORAGE BEYOND THE DIFFRACTION LIMIT.- SURFACE PLASMON COUPLED EMISSION.

Strong exciton-erbium coupling in Si nanocrystal-doped SiO2

Silicon nanocrystals were formed in SiO2 using Si ion implantation followed by thermal annealing. The nanocrystal-doped SiO2 layer was implanted with Er to a peak concentration of 1.8 at. %. Upon 458 nm excitation the sample shows a broad nanocrystal-related luminescence spectrum centered around 750 nm and two sharp Er luminescence lines at 982 and 1536 nm. By measuring the excitation spectra of these features as well as the temperature-dependent intensities and luminescence dynamics we conclude that (a) the Er is excited by excitons recombining within Si nanocrystals through a strong coupling mechanism, (b) the Er excitation process at room temperature occurs at a submicrosecond time scale, (c) excitons excite Er with an efficiency >55%, and (d) each nanocrystal can have at most ~1 excited Er ion in its vicinity.

Size-dependent electron-hole exchange interaction in Si nanocrystals

Silicon nanocrystals with diameters ranging from [approximate]2 to 5.5 nm were formed by Si ion implantation into SiO2 followed by annealing. After passivation with deuterium, the photoluminescence (PL) spectrum at 12 K peaks at 1.60 eV and has a full width at half maximum of 0.28 eV. The emission is attributed to the recombination of quantum-confined excitons in the nanocrystals. The temperature dependence of the PL intensity and decay rate at several energies between 1.4 and 1.9 eV was determined between 12 and 300 K. The temperature dependence of the radiative decay rate was determined, and is in good agreement with a model that takes into account the energy splitting between the excitonic singlet and triplet levels due to the electron-hole exchange interaction. The exchange energy splitting increases from 8.4 meV for large nanocrystals ([approximate]5.5 nm) to 16.5 meV for small nanocrystals ([approximate]2 nm). For all nanocrystal sizes, the radiative rate from the singlet state is 300–800 times larger than the radiative rate from the triplet state.

Concentration quenching in erbium implanted alkali silicate glasses

A comparison is made of photoluminescence properties of six sodalime and alkali-borosilicate glasses implanted with Er to concentrations as high as 1.4 × 1021 at./cm 3. Clear photoluminescence (PL) spectra around 1.54 l~m, due to the 4113/2 ~ 4It5/2 transition in Er 3+ are observed, of which the shape depends on the host glass composition. PL lifetimes in the range of 0.9-12.6 ms are found, depending on glass and Er concentration. In borosilicate glass, implantation-induced defects remain after annealing and cause quenching of the Er luminescence due to a direct coupling to the Er. Such defects are not present in Er-implanted sodalime glass after annealing. In both types of glass the luminescence lifetime decreases strongly with concentration due to a concentration quenching effect in which energy migration takes place due to energy transfer between Er ions, followed by quenching at hydroxyl groups. Concentration quenching via this mechanism is less strong in the borosilicates than in the sodalime glasses, but because of the quenching effect of implantation-induced defects in borosilicates these glasses are not suitable for optical doping by ion implantation.

Exciton–erbium interactions in Si nanocrystal-doped SiO2

The presence of silicon nanocrystals in Er doped SiO2 can enhance the effective Er optical absorption cross section by several orders of magnitude due to a strong coupling between quantum confined excitons and Er. This article studies the fundamental processes that determine the potential of Si nanocrystals as sensitizers for use in Er doped waveguide amplifiers or lasers. Silicon nanocrystals were formed in SiO2 using Si ion implantation and thermal annealing. The nanocrystal-doped SiO2 layer was implanted with different doses of Er, resulting in Er peak concentrations in the range 0.015–1.8 at. %. All samples show a broad nanocrystal-related luminescence spectrum centered around 800 nm and a sharp Er luminescence line at 1536 nm. By varying the Er concentration and measuring the nanocrystal and Er photoluminescence intensity, the nanocrystal excitation rate, the Er excitation and decay rate, and the Er saturation with pump power, we conclude that: (a) the maximum amount of Er that can be excited via exc...

Erbium-Doped Optical-Waveguide Amplifiers on Silicon

Thin-film integrated optics is becoming more and more important in optical-communications technology. The fabrication of passive devices such as planar optical waveguides, splitters, and multiplexers is now quite well-developed. Devices based on this technology are now commercially available. One step to further improve this technology is to develop optical amplifiers that can be integrated with these devices. Such amplifiers can compensate for the losses in splitters or other optical components, and can also serve as pre-amplifiers for active devices such as detectors. In optical-fiber technology, erbium-doped fiber amplifiers, are used in long-distance fiber-communications links. They use an optical transition in Er 3+ at a wavelength of 1.54 μ m for signal amplification, and their success has set a standard of optical communication at this wavelength. Using the same concept of Er doping, planar-waveguide amplifiers are now being developed. For these devices, silicon is often used as a substrate, so that optoelectronic integration with other devices in or on Si (electrical devices, or Si-based light sources, detectors, and modulators) may become possible. Figure 1 shows an example of a silicon-based optical integrated circuit5 in which a 1 × 4 splitter is combined with an amplifying section.

Gain limiting processes in Er-doped Si nanocrystal waveguides in SiO2

Erbium-doped Si nanocrystal based optical waveguides were formed by Er and Si ion implantation into SiO2. Optical images of the waveguide output facet show a single, well-confined optical mode. Transmission measurements reveal a clear Er related absorption of 2.7 dB/cm at 1.532 μm, corresponding to a cross section of 8×10−20 cm2. The Si nanocrystals act as sensitizers for Er but under high doping conditions (∼50 Er ions per nanocrystals) no pump-induced change in the Er related absorption is observed under optical pumping (λ=458 nm), which is ascribed to an Auger quenching effect. For very high pump powers, a broad absorption feature is observed, attributed to free carrier absorption.

Excitation and deexcitation of Er3+ in crystalline silicon

Temperature dependent measurements of the 1.54 μm photoluminescence of Er implanted N codoped crystalline Si are made. Upon increasing the temperature from 12 to 150 K, the intensity quenches by more than a factor thousand, while the lifetime quenches from 420 to 3 μs. The quenching processes are described by an impurity Auger energy transfer model that includes bound exciton dissociation and a nonradiative energy backtransfer process. Electron and hole trap levels are determined. Direct evidence for a backtransfer process follows from spectral response measurements on an Er-implanted Si solar cell.