  Real-time vital sign monitoring is gaining immense significance not only in
the medical field but also in personal health management. Facing the needs of
different application scenarios of the smart and healthy city in the future,
the low-cost, large-scale, scalable, and distributed vital sign monitoring
system is of great significance. In this work, a seamlessly integrated contact
and contactless vital sign monitoring system, which can simultaneously
implement respiration and heartbeat monitoring, is proposed. In contact vital
sign monitoring, the chest wall movement due to respiration and heartbeat is
translated into changes in the optical output intensity of a fiber Bragg
grating (FBG). The FBG is also an important part of radar signal generation for
contactless vital sign monitoring, in which the chest wall movement is
translated into phase changes of the radar de-chirped signal. By analyzing the
intensity of the FBG output and phase of the radar de-chirped signal, real-time
respiration and heartbeat monitoring are realized. In addition, due to the
distributed structure of the system and its good integration with the
wavelength-division multiplexing optical network, it can be massively scaled by
employing more wavelengths. A proof-of-concept experiment is carried out.
Contact and contactless respiration and heartbeat monitoring of three people
are simultaneously realized. During a monitoring time of 60 s, the maximum
absolute measurement errors of respiration and heartbeat rates are 1.6
respirations per minute and 2.3 beats per minute, respectively. The measurement
error does not have an obvious change even when the monitoring time is
decreased to 5 s.
