C. De Tandt

Wet silicon bulk micromachined THz waveguides for low-loss integrated sensor applications

Wet Si bulk micromachining enables producing hexagonally shaped waveguides (WH) with superior performance and are applicable to low THz frequency range. We discuss the fabrication process, hexagonal cross-section analysis, and balance between loss mitigation and operational frequency band of WH.

Polarization-based reconfigurable optical interconnects in free-space optical processing modules

We demonstrate reconfigurable, data transparent optical interconnects between planes of optical thyristors using polarization-selective diffractive optical elements in combination with a liquid crystal based polarization controller. A reconfigurable fanout element and a switchable digital optical logical inverter are presented as examples of applications.

EXPERIMENTAL STUDY OF AN IN0.53GA0.47AS-INP RESONANT PLASMA WAVEGUIDE MODULATOR FOR MEDIUM-INFRARED LIGHT

We report on the first experimental study of a medium‐infrared waveguide modulator based on the coupling between a dielectric grating coupler and an In0.53Ga0.47As–InP waveguide, operating near cut off, and containing a resonant semiconductor plasma. The prototype designed for demonstrating this novel effect was grown by metalorganic chemical vapor deposition. The experimental results show low power (225 mW), low voltage (15 V) operation for obtaining a modulation depth of 30%. The overall transmission efficiency is, however, rather low (0.5%) due to the wet chemical etching techniques used for defining the grating structure.

Evanescent wave modulator for medium infrared wavelengths (8-12 μm)

We present a new modulation concept for medium infrared (8 - 12 μm) wavelengths. The operation principle of the presented modulator is based on evanescent wave absorption by means of a bulk, single or multiple quantum well structure. A sub-wavelength grating ensures efficient coupling of the optical field to the absorption medium. Modulation is then achieved by depletion of this absorption medium. We present an analysis of concept parameters and point out their respective advantages and disadvantages with respect to the modulation performance. In this context, we investigated the impact of different absorption media as bulk, single and multiple quantum well structures and found that single quantum well structures are best suited for modulation purposes. Simulations pointed out that an absolute modulation depth of the order of 60% can be achieved. We also investigated the impact of the diffraction order on the modulation performance. Furthermore, some preliminary experimental results on this modulation concept are presented and compared with simulations.

CO2 laser induced temperature profiles in n-GaAs: An analytical model probed with the Seebeck effect

An analytic model describing the distribution of the electron temperature created by absorption of an optical beam with a cylindrical symmetry in a layered structure was developed. Main attention was paid to the contribution of the lattice heating in the stationary and nonstationary regimes. It was shown that both the spatial distribution of the incident stationary beam and the temporal distribution of the incident pulses can be retrieved from the spatial and temporal electron temperature dependences near the illuminated surface. Electron temperature distributions can be measured using the thermoelectric effect. Experimental results of the spatial and temporal measurements of the thermoelectric voltage were compared with the theoretical calculations and a satisfactory agreement between experimental and theoretical results was found near the incident beam center for the quasistationary regime. The experimentally derived Seebeck detector’s responsivity equals 17.5μV∕Wcm−2.

Optical information processing planes with silicon technology

In this paper we report on progress made in optical logic planes consisting of hybrid electrically assisted thermo-optic resonators fabricated with standard Silicon technology. As a starting point, the features and shortcomings of a first generation of these bistable elements, based on double-sided polished Silicon wafers, are reviewed. Consecutively we demonstrate, both with modeling and experimental results, that some of the shortcomings of the first generation can be remedied using a Silicon on Sapphire based device. Finally we propose a novel structure, based on Silicon Implanted Oxide substrates, that combines the advantages of the two pervious structures. We show via a heat transfer model that these devices can display bistability at multi-microwatt optical bias power and that, when adequately dimensioned, crosstalk can be avoided such that they can be packed into dense arrays. Both these characteristics and their stability, wavelength flexibility, hybrid mode of operation, and the potentialities for microsecond switching times, can turn these low-cost devices into work- horses for prototype digital optical parallel computing circuitry.

Impact of deformation potential scattering on free-carrier induced optical nonlinearities: An experimental study in GaAs

We present results of the experimental determination of the optical nonlinearities induced by heating free electrons distributed in the multivalley conduction band of highly doped n-GaAs. We propose a very sensitive multilayer leaky waveguide structure for transverse magnetic polarized waves in order to drastically reduce the required optical intensities. We explain in depth the dependence of the optical nonlinearity on doping concentration and deformation potentials. For a doping concentration no of 7.6×1018 cm−3, we found a nonlinear refractive index value n2≈(1∓0.2)×10−6 cm2/W at λ=10.6 μm, by fitting nonlinear reflection measurements with an equivalent intervalley deformation potential value ΛLL=(1.0±0.30)×109 eV/cm.

Proposal for a high-speed resonant plasma modulator with subwatt power dissipation for use in medium-IR lidar applications

Environmental sensing and atmospheric monitoring are two of the main areas where LIDAR can be used to advance our understanding of global climate changes and the effects of industrial pollution. The spectrum from the UV to the far-IR are used to sense a variety of atoms and molecules. However most of the pollutants are hydrocarbons that have their fingerprint in the region of 8 to 12 rim. This wavelength region can be partially covered by C02 lasers. Besides, their wavelength can be extended by harmonic generation to cover the 4.6 to 5.4tm range1. Other C02 laser technology applications are wind-measurements and combustion dynamics . The required short pulses can be generated with intracavity and extra-cavity modulators. An attractive approach to achieving a short pulse tunable mid-IR light source utilizes a low power tunable CW laser combined with an external widebandwidth modulator. This paper describes the underlying physical principles of a high speed C02 modulator based on the plasma effect and the design towards low electrical power dissipation.

THz Bio-chemical Sensing Capabilities with High Performance SIW Based Sensor on nL-Volume Liquids in Capillary

Label-free and online bio-chemical detection proved to be possible with THz waves, which would open alternative ways to a myriad of applications in the chemical, biological and medical fields such as integrated micro-reactor monitors, PCR monitoring, faster and cheaper drug discovery. However some technological challenges need to be surmounted, especially low sensitivity and large sample quantity, before practical applications can be implemented. These challenges are tackled here by an integrated sensor approach, whereby a specially developed substrate integrated waveguide is used in combination with capillary tube to maximally exploit the dynamic range of the measurement system. The sensor performance is benchmarked with water/alcohol mixtures. A selection of measurements on biological substances is presented to demonstrate the bio-chemical sensing capabilities. The developed approach shows outstanding sensitivity performance for extremely small sample quantities.

An experimental study of the effects of various parameters on the resonant and efficiency of circular split-ring resonators

Single split-ring resonators has a great interest due to their refractive index facility. In this paper we provide a comprehensive study, supported with experimental data, that addresses the effect of the type of the substrate and the geometric parameters on the resonant frequency and the quality of the design. The measurements are carried out using quasi-optical technique in mm-wave frequency range. We also provide recommendations concerning the main factors that should be considered in designing split open ring resonators at mm-wave frequency range.