A cost-efficient plastic optical fiber (POF) system for unobtrusive monitoring of human vital signs is presented. The system is based on speckle interferometry. A laser diode is butt-coupled to the POF whose exit face projects speckle patterns onto a linear optical sensor array. Sequences of acquired speckle images are transformed into one-dimensional signals by using the phase-shifting method. The signals are analyzed by band-pass filtering and a Morlet-wavelet-based multiresolutional approach for the detection of cardiac and respiratory activities, respectively. The system is tested with 10 healthy nonhospitalized persons, lying supine on a mattress with the embedded POF. Experimental results are assessed statistically: precisions of 98.8% ± 1.5% and 97.9% ± 2.3%, sensitivities of 99.4% ± 0.6% and 95.3% ± 3%, and mean delays between interferometric detections and corresponding referential signals of 116.6 ± 55.5 and 1299.2 ± 437.3 ms for the heartbeat and respiration are obtained, respectively.

This letter presents an optical fiber twist/torsion sensor that utilizes dissimilar polarization-preserving characteristics of standard single-mode and high-birefringence fibers. When only one polarization mode of the high-birefringence fiber is excited, spatial orientation of the E-field vector follows the fiber's principal axis orientation, even when the fiber is twisted around its longitudinal axis. This is contrary to a standard single-mode fiber (SMF), where the E-field vector maintains its spatial orientation regardless of the fiber torsional twist. The proposed sensor consists of a short section of standard SMF inserted in between two lead-in polarization-mainlining fibers. Only one mode of the lead-in fiber is excited at the input, while the ratio of both polarization modes is measured at the output side of the fiber assembly in order to determine the torsional twist of a standard SMF. This sensor can be used for measuring unambiguously twist/torsion angles of between ±95°. The sensor demonstrated very low temperature dependence.