Abstract: Normal operation of complementary metal-oxide semiconductor (CMOS) devices entails the emission of picosecond pulses of light, which can be used to diagnose circuit problems. The pulses that are observed from submicron sized field effect transistors (FETs) are synchronous with logic state switching. Picosecond Imaging Circuit Analysis (PICA), a new optical imaging technique combining imaging with timing, spatially resolves individual devices at the 0.5 micron level and switching events on a 10 picosecond timescale. PICA is used here for the diagnostics of failures on two VLSI microprocessors.

Abstract: We measured the single-photon detection efficiency of NbN superconducting single-photon detectors as a function of the polarization state of the incident light for different wavelengths in the range from 488 nm to 1550 nm. The polarization contrast varies from ~% at 488 nm to~0% at 1550 nm, in good agreement with numerical calculations. We use an optical-impedance model to describe the absorption for polarization parallel to the wires of the detector. For the extremely lossy NbN material, the absorption can be kept constant by keeping the product of layer thickness and filling factor constant. As a consequence, the maximum possible absorption is independent of filling factor. By illuminating the detector through the substrate, an absorption efficiency of ~0% can be reached for a detector on Si or GaAs, without the need for an optical cavity.