Ultrasensitive Measurement of Micronewton Force or Weak Dynamic Signal Based on PDMS Sealed Tapered Fiber Mach–Zehnder Interferometer

An ultrasensitive micronewton force optical sensor based on a tapered fiber Mach–Zehnder interferometer (MZI) embedded in polydimethylsiloxane (PDMS) is studied. Benefited from the methods of nonadiabatic tapering of a fiber combined with mode field mismatch between different fibers, both of which can excite high order modes, the sensor achieves a high sensitivity of up to 0.194 nm/mN and a low detection limit of
$103 ~\mu \text{N}$
. Meanwhile, this sensor possesses a longer effective interference length and a narrower free spectral range (FSR) than other microfiber optical sensors, allowing for more traceable intensity dips within the monitoring band. Consequently, a narrower band (
${C}$
-band) can be employed for monitoring purposes. Additionally, this approach also proves suitable for monitoring the dispersion turning point (DTP) within the
${C}$
-band, and a maximum sensitivity of 0.4091 nm/mN and a low detection limit of
$48.9 ~\mu \text{N}$
are obtained. Moreover, owing to its high sensitivity and rapid response time, the sensor can be effectively utilized for real-time monitoring of weak signals, for example, wrist pulse, showing its potential application as a wearable optical sensor in the field of human health monitoring.