No abstract

We demonstrate a method for quantitatively probing the local low-frequency dielectric constant of thin insulating films by nanoscale capacitance microscopy. The calibrated capacitance-distance curves are measured on the dielectric film and analyzed by using a tip-sample capacitance model here proposed. Applied to SiO2 films as small as 1×1μm2 area and 20–30nm thickness, the method gives a dielectric constant on the submicron scale in agreement with the value determined on the large scale. The observed precision is set by the capacitance noise level of the instrument and the tip radius.

Propagation of light beams through scattering or multimode systems may lead to the randomization of the spatial coherence of the light. Although information is not lost, its recovery requires a coherent interferometric reconstruction of the original signals, which have been scrambled into the modes of the scattering system. Here we show that we can automatically unscramble optical beams that have been arbitrarily mixed in a multimode waveguide, undoing the scattering and mixing between the spatial modes through a mesh of silicon photonics tuneable beam splitters. Transparent light detectors integrated in a photonic chip are used to directly monitor the evolution of each mode along the mesh, allowing sequential tuning and adaptive individual feedback control of each beam splitter. The entire mesh self-configures automatically through a progressive tuning algorithm and resets itself after significantly perturbing the mixing, without turning off the beams. We demonstrate information recovery by the simultaneous unscrambling, sorting and tracking of four mixed modes, with residual cross-talk of −20 dB between the beams. Circuit partitioning assisted by transparent detectors enables scalability to meshes with a higher port count and to a higher number of modes without a proportionate increase in the control complexity. The principle of self-configuring and self-resetting in optical systems should be applicable in a wide range of optical applications.

Bulk-heterojunction based organic photodetectors are fabricated by means of drop-on-demand inkjet printing with vertical topology, inverted structure, and small footprint (about 100 μm x 100 μm). Due to optimization of the deposition technique, an external quantum efficiency in excess of 80% at 525 nm and a -3dB bandwidth of a few tens of kHz is achieved.