We investigate in this paper the potential of carbon nanotubes for infrared bolometers. A method to obtain
CNT film layer and technological processes to obtain matrix of devices are presented. The electrical
characterization of samples establishes the quality of our technology i.e. low contact resistance, and weak
dispersion between devices. The potential of carbon nanotubes films as bolometric material is investigated by
measuring the thermal dependence of their resistance and by comparison with amorphous silicon (one of the
leading material for bolometric applications). Optical measurements of CNT films in the infrared and THz
ranges show a relatively high absorption for a few hundreds nanometers thick material. Eventually the
infrared (8-12 μm) photo-response of a first demonstrator is presented and discussed.
We propose a novel interpretation of stray light, which is modeled using a scattering process. For this, a description and simulations based on the bidirectional scattering distribution function (BSDF) are developed. We focus on the particular example of a window closing an optical cavity. Such a window is known to introduce a stray light component that is experimentally very subtle to handle. Our idea is motivated by the uncomfortable observation that for years, the usual estimation of this parasitic contribution (be it for absolute or relative measurements, for visible or IR applications, for field or laboratory experiments, etc.) was based on the rather imprecise and obviously incorrect assumption (nevertheless today a widely used rule of thumb) that the optical window can be approximated by a graybody emitting in its transparency range. This statement obviously goes against Kirchhoff's law of radiation, and can thus not be physically sound. Various typical experimental situations are explored with our model, and a comparison is made with results given by the rule of thumb. This shows some cases of relative concordance. However, the scatter-based model should provide an individually more accurate estimation, as shown by some examples.
A structure based on the free-carrier-induced electrorefractive effect in Si/SiGe modulation-doped quantum wells, placed in the intrinsic region of a PIN diode has been proposed. Effective index variation produced by carrier depletion under a reverse bias leads to a phase modulation of a guided wave. The measured variation of the effective index is typically 2.10-4 for a 0V to 6V variation of the reverse bias voltage. This study is focused on the integration of modulation doped SiGe/Si quantum-well optical modulator in SOI submicron rib waveguides with optical losses lower than 0.4dB/cm. The influence of the geometrical parameters, of layer doping and of the metallic contacts has been determined through numerical simulations and optimized modulation structures are defined. The obtained factor of merit LχVχ is then of 1.26 V.cm which can be favorably compared with the best published results obtained with other optimized modulators.
SOI microwaveguides and associated devices (splitters, turns,...) are used for light distribution. Rib SOI geometries obtained by shallow etching of the silicon film offer definite advantages for the integration of active devices while fulfilling efficiency and compactness. Propagation losses of such waveguides are one order of magnitude smaller than for single mode strip waveguides. Rib-based compact and low loss optical signal distribution from one input to up to 1024 output points has been demonstrated. Light injection in submicron SOI waveguides is discussed. The indirect bandgap of silicon is not in favor of light emission and modulation. Realization of silicon sources and efficient high speed silicon-based modulators is a real challenge. For light detection, germanium can be grown on silicon and Ge photodetectors with -3dB bandwidths up to 30 GHz have been demonstrated.