Finding Well-Coupled Optical Fiber Locations for Railway Monitoring Using Distributed Acoustic Sensing.

Distributed acoustic sensors (DAS) utilize optical fibers to monitor vibrations across thousands of independent locations. However, the measured acoustic waveforms experience significant variations along the sensing fiber. These differences primarily arise from changes in coupling between the fiber and its surrounding medium as well as acoustic interferences.

Psychotic symptoms in COVID-19 patients. A retrospective descriptive study.

Psychotic symptoms have been related to other coronavirus infections. We conducted a single-centre retrospective and observational study to describe new-onset psychotic episodes in COVID-19 patients. Ten patients infected by the novel coronavirus with psychotic symptoms and no previous history of psychosis were identified by the emergency and liaison psychiatry departments.

Compensation of nonlocal effects induced by the extinction ratio of pump pulses in Brillouin optical time-domain analysis sensors.

We demonstrate a technique to compensate the nonlocal effects that appear in Brillouin optical time-domain analysis sensors when pump pulses with limited extinction ratio are deployed. These recently discovered nonlocal effects are originated in the interaction between the probe wave and the pulse pedestal. Hence, their compensation method is based on deploying a modulation (dithering) of the optical frequency of the probe and pulse pedestal waves that provides a reduction of the effective interaction length between them.

Effects of pump pulse extinction ratio in Brillouin optical time-domain analysis sensors.

We report on two previously unknown non-local effects that have been found to impair Brillouin optical time-domain analysis (BOTDA) sensors that deploy limited extinction ratio (ER) pump pulses. The first one originates in the increased depletion of the pedestal of the pump pulses by the amplified probe wave, which in turn entails a reduced amplification of the probe and a measurement distortion. The second effect is due to the interplay between the transient response of the erbium-doped fiber amplifiers (EDFA) that are normally deployed to amplify the pump and the pedestal of the pump pulses.