Heterogeneously integrated InGaP/Si waveguides for nonlinear photonics.

The heterogeneous integration of III-V semiconductors with the Silicon platform enables the merging of photon sources with Silicon electronics while allowing the use of Silicon mature processing techniques. However, the inherent sufficient quality of III-Vs' native oxides made imperative the use of deposited interfacial oxide layers or adhesives to permit the bonding. Here we present a novel approach enabling the heterogeneous integration of structured III-V semiconductors on silicates via molecular bonding at 150 °C, much below the CMOS degradation temperature, is presented.

GaInP nanowire arrays for color conversion applications.

Color conversion by (tapered) nanowire arrays fabricated in GaInP with bandgap emission in the red spectral region are investigated with blue and green source light LEDs in perspective. GaInP nano- and microstructures, fabricated using top-down pattern transfer methods, are derived from epitaxial GaInP/GaAs stacks with pre-determined layer thicknesses. Substrate-free GaInP micro- and nanostructures obtained by selectively etching the GaAs sacrificial layers are then embedded in a transparent film to generate stand-alone color converting films for spectrophotometry and photoluminescence experiments.

Gallium indium phosphide microstructures with suppressed photoluminescence for applications in nonlinear optics.

Gallium indium phosphide (GaInP), lattice matched to gallium arsenide, shows remarkable second-order nonlinear properties, as well as strong photoluminescence (PL) due to its direct band gap. By measuring the second-harmonic generation from the GaInP microwaveguide (0.2×11×1300  μm) before and after stimulating intrinsic photobleaching, we demonstrate that the PL could be strongly suppressed (-34  dB), leaving the nonlinear properties unchanged, making it suitable for low-noise applications.

Experimental quantification of surface optical nonlinearity in GaP nanopillar waveguides.

We report on surface second-order optical nonlinearity in single GaP nanopillars (nanowaveguides). The relative contribution of optical nonlinearity from the surface and the bulk is resolved by mode confinement analysis and polarization measurements. By investigating the thickness of nonlinear region at the surface of nanopillars, we estimated the nonlinear coefficient to be ~15 times higher at the surface with respect to the bulk.

Modal engineering of second-harmonic generation in single GaP nanopillars.

We report on modal dispersion engineering for second-harmonic generation (SHG) from single vertical GaP nanopillars/nanowaveguides, fabricated by a top-down approach, using optical modal overlap between the pump (830 nm) and SHG (415 nm). We present a modal analysis for the SHG process in GaP nanopillars and demonstrate efficient utilization of the longitudinal component of the nonlinear polarization density. Our SHG measurements show quantitatively the presented model.

Arbitrary interference curves by coincidence detection: theory and experiment.

We discuss how to use coincidence detection to generate unusual, nonsinusoidal interference curves by using not a single detector, but several in coincidence. The method works for both strong (classical) and weak (on the few-photon level) light, although in the latter case the detection becomes probabilistic with low efficiency. Using the method, one can tailor the coincidence measurement setup to obtain essentially any interference pattern.

Surface second-harmonic generation from vertical GaP nanopillars.

We report on the experimental observation and analysis of second-harmonic generation (SHG) from vertical GaP nanopillars. Periodic arrays of GaP nanopillars with varying diameters ranging from 100 to 250 nm were fabricated on (100) undoped GaP substrate by nanosphere lithography and dry etching. We observed a strong dependence of the SHG intensity on pillar diameter.

Junction-type photonic crystal waveguides for notch- and pass-band filtering.

Evolution of the mode gap and the associated transmission mini stop-band (MSB) as a function of photonic crystal (PhC) waveguide width is theoretically and experimentally investigated. The change of line-defect width is identified to be the most appropriate way since it offers a wide MSB wavelength tuning range. A high transmission narrow-band filter is experimentally demonstrated in a junction-type waveguide composed of two PhC waveguides with slightly different widths.

Experimental decoy-state quantum key distribution with a sub-poissionian heralded single-photon source.

We have experimentally demonstrated a decoy-state quantum key distribution scheme (QKD) with a heralded single-photon source based on parametric down-conversion. We used a one-way Bennett-Brassard 1984 protocol with a four states and one-detector phase-coding scheme, which is immune to recently proposed time-shift attacks, photon-number splitting attacks, and can also be proven to be secure against Trojan horse attacks and any other standard individual or coherent attacks. In principle, the setup can tolerate the highest losses or it can give the highest secure key generation rate under fixed losses compared with other practical schemes.