Franck Robin

Energy-Time Entanglement Preservation in Plasmon-Assisted Light Transmission

We report on experimental evidence of the preservation of the energy-time entanglement of a pair of photons after a photon-plasmon-photon conversion. This preservation is observed in two different plasmon conversion experiments, namely, extraordinary optical transmission through subwavelength metallic hole arrays and long range surface plasmon propagation in metallic waveguides. Plasmons are shown to coherently exist at two different times separated by much more than their lifetimes. This kind of entanglement involving light and matter is expected to be useful for future processing and storing of quantum information.

Investigation of the cleaved surface of a p–i–n laser using Kelvin probe force microscopy and two-dimensional physical simulations

We have investigated the cross-sectional electric field and potential distribution of a cleaved n+-InP/InGaAsP/p+-InP p–i–n laser diode using Kelvin probe force microscopy (KFM) with a lateral resolution reaching 50 nm. The powerful characterization capabilities of KFM were compared with two-dimensional (2D) physics-based simulations. The agreement between simulations and KFM measurements regarding the main features of the electric field and potential is very good. However, the KFM yields a voltage drop between n- and p-doped InP regions which is 0.4 times the one simulated. This discrepancy is explained in terms of surface traps due to the exposure of the sample to the air and in terms of incomplete ionization. This hypothesis is confirmed by the 2D simulations.

Detailed analysis of the influence of an inductively coupled plasma reactive-ion etching process on the hole depth and shape of photonic crystals in InP∕InGaAsP

The authors report on the fabrication of photonic crystals in the InP∕InGaAsP∕InP material system for applications at telecommunication wavelengths. To achieve low optical loss, the photonic crystal holes must demonstrate smooth sidewalls and should be simultaneously deep and cylindrical. The authors present the etching process of these structures based on a Cl2∕Ar∕N2 chemistry with an inductively coupled plasma reactive-ion etching system. A systematic analysis is provided on the dependency of the hole sidewall roughness, depth, and shape on the process parameters such as etching power, pressure, and chemical composition of the plasma. They found that a low plasma excitation power and a low physical etching are beneficial for achieving deep holes, whereas for the nitrogen content in the plasma, a delicate balance needs to be found. Nitrogen has a negative impact on the hole shape and surface roughness but is capable of preventing underetching below the mask by passivation of the sidewalls. With the autho...

Cantilevers with nano-heaters for thermomechanical storage application

We present the fabrication of thermomechanical cantilevers with nanometer-sized heaters used for data-storage application as implemented in the large two-dimensional cantilever array, known as the Millipede concept. Our goal is to explore how the power consumption of these cantilevers for the thermomechanical writing and reading process can be reduced by reducing the size of the heater structure. Such data are crucial for predicting the power consumption and data rate of storage devices using state-of-the-art CMOS manufacturing technology to achieve its associated minimum feature sizes. We describe the fabrication process and critical issues in connection with a complex device process that merges mix and match e-beam/optical lithography with the micro/nano electromechanical system (M/NEMS) fabrication technique. Fabricated cantilevers typically have a thickness of 100 nm, heater structures with lateral dimensions down to 180 nm, and critical feature alignment in the 50 nm range. We also present first experiments with such cantilevers, which highlight the scaling of the heater energy for the writing process provided by a nanometer-sized thermal constriction.

Optimization of a 60° waveguide bend in InP-based 2D planar photonic crystals

We present a novel design for a W1 (one missing row of holes) waveguide 60° bend implemented in a substrate-type InP/InGaAsP/InP planar photonic crystal based on a triangular array of air holes. The bend has been designed to provide high transmission over a large bandwidth. The investigated design improvement relies only on displacing holes while avoiding changing individual holes diameter in the interest of better process control (homogenous hole depth). Two-dimensional (2D) finite-element simulations were used to increase the relative transmission bandwidth from 18% to 40% of the photonic bandgap for unoptimized and optimized 60° bends, respectively. The 2D results were verified by means of rigorous three-dimensional (3D) finite-difference time-domain (FDTD) simulations. We show that excellent agreement between 2D and 3D simulations can be obtained, provided a small effective-index shift of −0.024(−0.74%) and an imaginary loss parameter (ϵ″=0.014) is introduced in the 2D simulations. To demonstrate the applicability of our improved design, the bend was fabricated and measured using the endfire technique. A bending loss of 3 dB is obtained for the optimized W1 waveguide bend compared to more than 8 dB in the unoptimized case.

Ultrafast carrier dynamics in InP photonic crystals

Ultrafast time-resolved reflectivity investigations are performed on InP-based photonic crystals with a wide range of structural parameters. It is found that the structure plays a critical role in determining the recombination dynamics of the photo-injected charge carriers. For sufficiently large etched sidewall area densities the carrier lifetime is decreased to a level below 100 ps.

Realistic photonic bandgap structures for TM-polarized light for all-optical switching

We investigate manufacturable photonic crystal (PhC) structures with a large photonic bandgap for TM-polarized light. Although such PhC structures have been the object of only a limited number of studies to date, they are of central importance for ultra fast all-optical switches relying on intersubband transitions in AlAsSb/InGaAs quantum wells, which support only TM polarization. In this paper, we numerically study substrate-type PhCs for which the two-dimensional approximation holds and three-dimensional photonic-crystal slabs, both with honeycomb lattice geometry. Large TM PBGs are obtained and optimized for both cases. Two types of PhC waveguides are proposed which are able to guide TM modes. Their unique properties show the potential to apply as waveguiding structures in all-optical switches.

Fabrication of a hard mask for InP based photonic crystals: Increasing the plasma-etch selectivity of poly(methyl methacrylate) versus SiO2 and SiNx

We introduce cyclic reactive ion etching processes for SiO2 and SiNx hard masks where the fluorine-based etch steps are interleaved with N2 flushing steps in order to improve the selectivity to electron-beam resists. For SiO2 etching an etch-step duration of 30s resulted in a doubled selectivity of almost 4:1 between SiO2 and poly(methyl methacrylate) (PMMA) due to a reduced thermal load. We established the pattern transfer from a 200nm thick PMMA resist into a 600nm thick SiO2 layer for 200nm diameter holes. For SiNx etching we demonstrate improved sidewall verticality, an enhanced etch rate, and suppressed redeposition of etch byproducts for a cyclic process. With the use of an additional 30nm titanium intermediate layer we show an excellent overall selectivity between SiNx and PMMA of almost 5:1. This process is applied to the fabrication of planar photonic-crystal devices with 3.5μm deep holes in an InP based slab waveguide with an initial PMMA layer thickness of 220nm.

Simulation and evolutionary optimization of electron-beam lithography with genetic and simplex-downhill algorithms

Genetic and simplex-downhill (SD) algorithms were used for the optimization of the electron-beam lithography (EBL) step in the fabrication of microwave electronic circuits. The definition of submicrometer structures involves complex exposure patterns that are cumbersome to determine experimentally and very difficult to optimize with linear search algorithms due to the high dimensionality of the search space. An SD algorithm was first used to solve the optimization problem. The large number of parameters and the complex topology of the search space proved too difficult for this algorithm, which could not yield satisfactory patterns. A hybrid approach using genetic algorithms (GAs) for global search, and an SD algorithm for further local optimization, was unable to drastically improve the structures optimized with GAs alone. A carefully studied fitness function was used. It contains mechanisms for reduced dependence on process tolerances. Several methods were studied for the selection, crossover, mutation, and reinsertion operators. The GA was used to predict scanning patterns for 100-nm T-gates and gate profiles with asymmetric recess and the structures were fabricated successfully. The simulation and optimization tool can help shorten response times to alterations of the EBL process by suppressing time-consuming experimental trial-and-error steps.

A 110-GHz large-signal lookup-table model for InP HEMTs including impact ionization effects

We developed an efficient method to extract a large-signal lookup table model for InP high electron-mobility transistors that takes impact ionization into account. By measuring the device on a logarithmic frequency scale, we obtain high resolution at lower frequencies to accurately characterize impact ionization, and a sufficient number of data points at millimeter-wave frequencies to extract the nonquasi-static parameters. Model validation through linear and nonlinear device measurements and its application to monolithic-microwave integrated-circuit design are presented.