Ballistocardiography (BCG) is a non-invasive method to detect the heartbeat signal, which reflects the body recoils introduced by cardiac ejection. Compared with traditional heartbeat monitors, such as Electrocardiography (ECG), the BCG detection method can acquire heartbeat signals without any wearable devices, which is user-friendly. The device can be integrated into a cushion, which is convenient for users to monitor the heartbeat in long-term. In this paper, a BCG monitor based on the Mach-Zehnder interferometer (MZI) with a new phase modulation method is demonstrated. A low-cost and compact phase shifter is introduced to solve the problem of signal fading in the fiber-optic interferometer. The baseline drift produced from breath and noise can be removed by the phase modulation and accuracy BCG signal can be detected in the sitting position. Compared with existing BCG monitors, such as accelerometer-based and bathroom scales-based, our optical fiber interferometer-based BCG monitor has many merits including sensitivity, stable, and immune to electromagnetic interference (EMI). In conclusion, the BCG monitor based on optical fiber sensor has great potential in the long-term and real-time heartbeat monitoring.
A compact fiber-optic curvature sensor based on modal interferometer (MI) in few mode fiber (FMF) is presented and investigated both in theory and experiment. The proposed MI is simply constructed by splicing a 2-centimeter-long FMF between single mode fibers (SMFs) with built-in up-taper fusion mode, i.e., SMF-FMF-SMF structure is fabricated. Both the curvature sensing performance and temperature dependency are addressed, and the result shows that curvature within a range from 0 m-1 to 1.87 m-1 can be monitored without ambiguity and the temperature sensitivity can reach up to 111 pm/°C.
A vital signs monitor based on few-mode fiber (FMF) is presented in this paper. Two types of FMF, dual-mode fiber (DMF) and four-mode fiber are respectively utilized for vital signs monitoring. For DMF, core-offset distance between lead-in single mode fiber (SMF) and DMF was optimized numerically, the results of which agree very well with experiments and respiration ratio can be measured successfully with acceptable extinction ratio. For four-mode fiber, core-offset mode excitation method with optimized parameters is also utilized to excite four types of modes, LP01, LP11, LP21 and LP02, which realizes the modal interference enhancement and the extinction ratio can reach 10 dB. Breath signals can be also detected using this structure. As demonstrated in this paper, FMF-based sensor could provide a promising candidate for fiber-optic biomedical application.
KEYWORDS: Orthogonal frequency division multiplexing, Polarization, Signal detection, Digital signal processing, Photodetectors, Modulation, Single sideband modulation, Modulators, Receivers, Optical engineering
Polarization-interleave-multiplexed (PIM) with single-sideband orthogonal frequency-division multiplexing (SSB-OFDM) based on direct detection is proposed for short-reach applications transmitted up to 80 km in which the guard band can be shared for the two SSB signals with interleave electrical center frequencies. Based on two dual-drive Mach–Zehnder modulators with one single-end photodetector (PD), 100-Gb/s PIM-SSB-OFDM transmission over a 80-km standard single-mode fiber is successfully demonstrated. After 80-km transmission, the optical signal-to-noise ratio requirement is 29.1 dB with respect to the bit error rate threshold of 7% hard decision-forward error correction overhead.
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