This PDF file contains the front matter associated with SPIE Proceedings Volume 8808, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

Photon management is a key component in the development of efficient solar cells. Especially light-trapping concepts have a high potential to realize enhanced efficiencies. Here, we give an overview over several light trapping concepts for photon management in solar cells. These include basic as well as advanced light-trapping concepts. The theoretical limits of light path enhancement of the different concepts are given and experimental work on these topics is presented. The potential of 3D photonic crystals is discussed in the context of the corresponding approaches as well.

Theoretical efficiency limits are useful primarily because they provide a means for selecting which technologies to pursue, and they are a driving force for further progress. Yet implicit in such a process is the assumption that the upper limit provides a realistic estimate of potential performance. Real systems will never be perfect, but small deviations in material quality or optical design should yield only small deviations in performance. Shockley-Queisser efficiencies are not robust to small deviations. Although they provide a simple calculational tool, they obscure important internal dynamics. We examine these dynamics, resulting in a surprising conclusion: instead of considering external emission as a loss mechanism, it should actually be designed for. A solar cell must have almost perfect photon extraction, or it will fall far short of the Shockley-Queisser efficiency limit.

In this work we show the design of one-dimensional nanophotonic structures (photonic crystal gratings) for enhancement of extraction of light with specific wavelengths in light-emitting diodes (LEDs). The LEDs are made of silicon-rich oxide embedding silicon nanolayers with emission in the visible spectrum. The LED structure consists of a poly-silicon top layer 310 nm thick, a silicon-rich oxide layer with nanoparticles and a silicon substrate. The gratings are formed by grooves separated with periods ranging from 200 nm to 600 nm and widths 0.72 times the period engraved on the top layer. We have performed two dimensional finite-difference time-domain simulations to obtain the values for the internal and external quantum efficiency (EQE) in the normal direction in a spectral window from 400 nm to 500 nm. The results show that it is possible to achieve a strong enhancement in the EQE in the short wavelength region (400 nm) while it reaches 5-fold enhancement at longer wavelengths.

Photoluminescence from finite semiconductor nanowires is theoretically investigated. We show experimentally the directional emission of polarized light from single InP nanowires through Fourier microphotoluminescence, thus demonstrating semiconductor nanowires behave as efficient optical nanoantennas. Numerical calculations for finite nanowires confirm such enhanced and directional emission. We anticipate the relevance of these results for the development of nanowire photon sources with optimized efficiency and controlled emission.

We review the optical properties of carbon nanotubes (CNTs) and graphene and discuss how those properties can be used in photonic applications. In particular, we will give an overview of the benefits of using their highly nonlinear optical response in fiber lasers and other nonlinear fiber optic devices. Both graphene and CNTs exhibit high third order susceptibility and a broadband saturable absorption with sub-picosecond response. We will discuss the advantages and limitations of using the saturable absorption of carbon nanotubes and graphene for the passive mode-locking of fiber lasers, introduce the different methods that we have developed to integrate these materials in the fiber system and summarize the main contributions of these materials towards advancing fiber laser technology. In addition, these materials also exhibit an extremely high third order susceptibility which is responsible for nonlinear processes such as four wave mixing (FWM), Kerr focusing and third harmonic generation (THG) of great interest for optical switching and wavelength conversion. The large absorption of CNTs and graphene however limits the dimensions of these devices and, thus, their applicability. We review our efforts towards enhancing and exploiting the nonlinearity of CNT and graphene fiber optics devices.

Plasmonics mainly deals with light-matter interactions in metallic nanostructures. It has gathered interest since its discovery due to the benefits it provides when compared with photonics and electronics. It owes its popularity to the tremendous number of applications it serves for. In this paper, we review how plasmonic nanoparticles can be utilized in applications such as localized surface plasmon resonance based biosensing and enhancing performance of photodetectors.

The mid-infrared (mid-IR), as the spectral range where all finite temperature biological and mechanical objects emit thermal radiation, and where numerous molecular species have strong vibrational absorption resonances, is of significant importance for both security and sensing applications. The design of materials with engineered absorption resonances, which by Kirchoff’s Law, should give strongly selective emission at the design resonance upon thermal excitation, allows for the control of the spectral character of the material’s thermal emission. Designed as a thin film coating, these structures can be applied to grey-body emitters to shift the grey-body thermal emission into predetermined spectral bands, altering their appearance on a thermal imaging system. Here we demonstrate strongly selective mid-infrared absorption and thermal emission from three classes of subwavelength thin-film materials. First, we demonstrate selective thermal emission from patterned, commerciallyavailable steel films, via selective out-coupling of thermally-excited surface modes. Subsequently, we show nearperfect absorption (and strongly selective thermal emission) for wavelengths between 5 - 9μm with patterned metal-dielectric-metal structures. Finally, we demonstrate strong absorption from large area, unpatterned, thinfilm high-index dielectric coatings on highly-doped Si substrates, tunable across the mid-IR (5 - 12μm). Our results are compared to numerical simulations, as well as analytical models, with good agreement between experiments and models.

This paper reviews the first demonstrations of broadband graphene terahertz modulators as well as recent progress on reconfigurable terahertz devices using graphene. Although atom-thick, single layer graphene is capable of efficiently tuning terahertz absorption meanwhile introducing negligible insertion loss. Recent developments in terms of transmission-mode and reflection-mode electro-absorption modulators are reviewed. Moreover, an application of these devices is presented and discussed: arrays of graphene electro-absorption modulators as electrically reconfigurable patterns for terahertz cameras.

Photonic crystals provide superb opportunities for tailoring of the photonic density of states. This ability can in turn be explored to control radiation into far-field, enhance fluorescent light emission, as well as optimize laser emission. In order to make these phenomena useful for large macroscopic devices, large-area nano-fabrication techniques have to be successfully implemented. In this talk, I will present some of our recent theoretical and experimental progress in exploring these opportunities.

Topological insulators are a new phase of matter, with the striking property that conduction of electrons occurs only on the surface. In two dimensions, surface electrons in topological insulators do not scatter despite defects and disorder, providing robustness akin to superconductors. Topological insulators are predicted to have wideranging applications in fault-tolerant quantum computing and spintronics. Recently, large theoretical efforts were directed towards achieving topological insulation for electromagnetic waves. One-dimensional systems with topological edge states have been demonstrated, but these states are zero-dimensional, and therefore exhibit no transport properties. Topological protection of microwaves has been observed using a mechanism similar to the quantum Hall effect, by placing a gyromagnetic photonic crystal in an external magnetic field. However, since magnetic effects are very weak at optical frequencies, realizing photonic topological insulators with scatterfree edge states requires a fundamentally different mechanism - one that is free of magnetic fields. Recently, a number of proposals for photonic topological transport have been put forward. Specifically, one suggested temporally modulating a photonic crystal, thus breaking time-reversal symmetry and inducing one-way edge states. This is in the spirit of the proposed Floquet topological insulators, where temporal variations in solidstate systems induce topological edge states. Here, we propose and experimentally demonstrate the first external field-free photonic topological insulator with scatter-free edge transport: a photonic lattice exhibiting topologically protected transport of visible light on the lattice edges. Our system is composed of an array of evanescently coupled helical waveguides arranged in a graphene-like honeycomb lattice. Paraxial diffraction of light is described by a Schrödinger equation where the propagation coordinate acts as ‘time’. Thus the waveguides' helicity breaks zreversal symmetry in the sense akin to Floquet Topological Insulators. This structure results in scatter-free, oneway edge states that are topologically protected from scattering.

We report slow light measurements in hollow core photonic crystal waveguides. We show that reshaping the slot into a comb allows increasing the confinement of light and engineering the dispersion of the waveguides. Cut-back measurements in such waveguides exhibits losses that are comparable to those of standard W1 photonic crystal waveguides in slow light regime and to those of a refractive slot waveguides in fast light regime, meanwhile the nonlinear effective area and the modal volume are strongly reduced. Such hollow core waveguides can introduce new functionalities to silicon and ultra-high nonlinearities when infiltrated by adequate materials.

One attractive application of slow light is tuning the delay of optical pulses. It is achieved by controlling the chirping of photonic crystal waveguides whose photonic band exhibits a flat band sandwiched by the opposite dispersion characteristics. We call the so-obtained tunable slow light dispersion-compensated (DC) slow light. In these years, we have fabricated the devices using CMOS-compatible process, demonstrated the delay tuning of sub-ps pulses with a tuning resolution over 100, and applied it to varying the demodulation rate of DQPSK receiver. The other attractive application of slow light is enhancing the nonlinearity. It is achieved by the particular design of photonic crystal waveguides, which exhibits a straight photonic band with a small slope, producing low-dispersion (LD) slow light. We have demonstrated strong two-photon absorption (TPA), self-phase modulation and four-wave mixing in Si-based devices at fiber communication wavelengths. In this presentation, we demonstrate two advanced devices that utilize both DC and LD slow light. One is the on-chip optical correlator and the other is the all-optical ultrafast delay tuning. In the former, the delay scanner based on DC slow light and nonlinear-enhanced TPA photodiode based on LD slow light were integrated. The auto-correlator action was confirmed for ps pulses. In the latter, the delay of the DC signal pulse was tuned through the intensity and timing of the LD control pulse with a maximum tuning range and response time of 10 ps. It potentially achieves the retiming of disordered pulses by using LD pulses as a clock.

We review recent demonstration of stimulated Brillouin scattering in a chalcogenide photonic chip and its application to optical and microwave signal processing tasks. The interaction between light and sound via stimulated Brillouin scattering (SBS) was exploited in chalcogenide photonic circuits to achieve on-chip SBS slow and fast light, microwave photonic filters, and dynamic gratings using travelling-wave geometry. Using a ring-resonator geometry, photonic-chip based Brillouin laser was demonstrated.

Si/Chalcogenide glass - hybrid slot waveguide designs are theoretically investigated to facilitate efficient degenerate four wave mixing. The TE-field of the mode concentrates inside the infiltrated slot leading to a nonlinear figure of merit >1. A periodic refractive index change is introduced to create a photonic band gap with associated negative dispersion in the second band. This negative dispersion compensates for the usual positive dispersion from waveguide and materials so that phase matching (group velocity dispersion = 0) can be achieved. Changing the periodicity of the index variation the phase matching frequency can be tuned across the whole near infrared allowing a flexible design of the hybrid photonic components.

A nonlinear electromagnetic scattering problem is studied in the presence of bound states in the radiation continuum (or resonances with the vanishing width). It is shown that the solution is not analytic in the nonlinear susceptibility and the conventional perturbation theory fails due to strong evanescent fields that necessarily occur if the scattering system has resonances with the vanishing width. A non-perturbative approach is developed. It is then applied to the system of two parallel periodic subwavelength arrays of dielectric cylinders with a second order nonlinear susceptibility. This scattering system is known to have bound states in the radiation continuum. In particular, it is demonstrated that, for a wide range of values of the nonlinear susceptibility, the structure converts over 40% of the incident fundamental harmonic flux into the outgoing second harmonic flux when the distance between the arrays is as low as a half of the incident radiation wavelength. The effect is non-perturbative and solely attributed to the presence of bound states in the radiation continuum. The example demonstrates that bounds states in the radiation continuum can be used to substantially enhance and control optically nonlinear effects in nanophotonic devices.

A layered waveguide supported hybrid modes between a surface plasmon and a confined guided mode is studied. The condition for the strong coupling regime are described. The Green function is obtained and decomposed along the continuous and discrete spectrum.

In this works, rare earth ion doped core and core-shell Y₂O₃ phosphors have been extensively studied for many applications due to the high stability and emission range and intensity. The core-shell Y2O3: (RE= Eu, Dy, Tb) nanoparticles are synthesized using a two-step process in which 100-150 nm Y₂O₃ core particles are synthesized using a molten salt synthesis and the shell is deposited using a sol-gel process The core-shell architecture was designed for enhanced luminescence efficiency with long emission lifetimes. Specifically, a multi-shell architecture was necessary to spatially separate Dy³⁺, Eu³⁺ and Tb³⁺ within the phosphor to circumvent the energy transfer to the surface quenching sites. First, the crystallinity of Y₂O₃nanophosphors was characterized using X-ray analysis. RE-doped Y₂O₃ core nanoparticles have a good compositional homogeneity. We have also recorded emission spectra and measured fluorescence lifetime. After coating passive shell layer, emission spectra and measured emission lifetimes were compared with those form Y₂O₃ nanophosphor core system and the effectiveness of these core-shell phosphors were successfully assessed.