Metallic nanostructures for efficient LED lighting

Light-emitting diodes(LEDs)are driving a shift toward energy-efficient illumination.Nonetheless,modifying the emission intensities,colors and directionalities of LEDs in specific ways remains a challenge often tackled by incorporating secondary optical components.Metallic nanostructures supporting plasmonic resonances are an interesting alternative to this approach due to their strong light–matter interaction,which facilitates control over light emission without requiring external secondary optical components.This review discusses new methods that enhance the efficiencies of LEDs using nanostructured metals.This is an emerging field that incorporates physics,materials science,device technology and industry.First,we provide a general overview of state-of-the-art LED lighting,discussing the main characteristics required of both quantum wells and color converters to efficiently generate white light.Then,we discuss the main challenges in this field as well as the potential of metallic nanostructures to circumvent them.We review several of the most relevant demonstrations of LEDs in combination with metallic nanostructures,which have resulted in light-emitting devices with improved performance.We also highlight a few recent studies in applied plasmonics that,although exploratory and eminently fundamental,may lead to new solutions in illumination.

Recent advances in development of vertical-cavity based short pulse source at 1.55 μm

This paper reviews and discusses recent developments in passively mode-locked vertical external cavity surface emitting lasers （ML-VECSELs） for short pulse generation at 1.55 gin. After comparing ML- VECSELs to other options for short pulse generation, we reviewed the results of ML-VECSELs operating at telecommunication wavelength and point out the chal- lenges in achieving sub-picosecond operation from a ML- VECSEL at 1.55 gm. We described our recent work in the VECSELs and semiconductor saturable absorber mirrors （SESAMs）, their structure design, optimization and characterization, with the goal of moving the pulse width from picosecond to sub-picosecond.

Self-organized metal-semiconductor epitaxial graphene layer on off-axis 4H-SiC（0001）

The remarkable properties of graphene have shown promise for new perspectives in future electronics, notably for nanometer scale devices. Here we grow graphene epitaxially on an off-axis 4H-SiC（0001） substrate and demonstrate the formation of periodic arrangement of monolayer graphene on planar （0001） terraces and Bernal bilayer graphene on （1120） nanofacets of SiC. We investigate these lateral superlattices using Raman spectroscopy, atomic force microscopy/ electrostatic force microscopy （AFM/EFM） and X-ray and angle resolved photoemission spectroscopy （XPS/ARPES）. The correlation of EFM and ARPES reveals the appearance of permanent electronic band gaps in AB-stacked bilayer graphene on （1120） SiC nanofacets of 150 meV. This feature is confirmed by density functional theory （DFT） calculations. The charge transfer between the substrate and graphene bilayer results in an asymmetric charge distribution between the top and the bottom graphene layers opening an energy gap. This surface organization can be thus defined as self-organized metal-semiconductor graphene.

Recent advances in germanium emission[Invited]

The optical properties of germanium can be tailored by combining strain engineering and n-type doping.In this paper,we review the recent progress that has been reported in the study of germanium light emitters for silicon photonics.We discuss the different approaches that were implemented for strain engineering and the issues associated with n-type doping.We show that compact germanium emitters can be obtained by processing germanium into tensile-strained microdisks.

High-finesse Fabry-Perot cavities with bidimensional Si_(3)N_(4) photonic-crystal slabs

Light scattering by a two-dimensional photonic-crystal slab(PCS)can result in marked interference effects associated with Fano resonances.Such devices offer appealing alternatives to distributed Bragg reflectors and filters for various applications,such as optical wavelength and polarization filters,reflectors,semiconductor lasers,photodetectors,bio-sensors and non-linear optical components.Suspended PCS also have natural applications in the field of optomechanics,where the mechanical modes of a suspended slab interact via radiation pressure with the optical field of a high-finesse cavity.The reflectivity and transmission properties of a defect-free suspended PCS around normal incidence can be used to couple out-of-plane mechanical modes to an optical field by integrating it in a free-space cavity.Here we demonstrate the successful implementation of a PCS reflector on a high-tensile stress Si_(3)N_(4) nanomembrane.We illustrate the physical process underlying the high reflectivity by measuring the photonic-crystal band diagram.Moreover,we introduce a clear theoretical description of the membrane scattering properties in the presence of optical losses.By embedding the PCS inside a high-finesse cavity,we fully characterize its optical properties.The spectrally,angular-and polarization-resolved measurements demonstrate the wide tunability of the membrane’s reflectivity,from nearly 0 to 99.9470±0.0025%,and show that material absorption is not the main source of optical loss.Moreover,the cavity storage time demonstrated in this work exceeds the mechanical period of low-order mechanical drum modes.This so-called resolved-sideband condition is a prerequisite to achieve quantum control of the mechanical resonator with light.