A small-size, high-precision fiber Bragg grating interrogator was developed for continuous plethysmograph monitoring. The interrogator employs optical edge filters, which were integrated with a broad-band light source and photodetector to demodulate the Bragg wavelength shift. An amplifier circuit was designed to effectively amplify the plethysmograph signal, obtained as a small vibration of optical power on the large offset. The standard deviation of the measured Bragg wavelength was about 0.1 pm. The developed edge filter module and amplifier circuit were encased with a single-board computer and communicated with a laptop computer via Wi-Fi. As a result, the plethysmograph was clearly obtained remotely, indicating the possibility of continuous vital sign measurement.

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The simultaneous measurement of temperature and pressure using the reflected light of two high birefringent fibers is studied. These two fibers are spliced and twisted 45 degrees. The resulting spectrum contains the interference caused by the birefringence of each fiber, and the differential and sum of the frequency. The obtained spectrum is processed with a band-pass filter to get the spectrum of each fiber. The pressure and the temperature are demodulated using the peak-tracking method. As a result, the pressure and the temperature sensitivity of these individual fibers are obtained as 3.2nm/MPa and -1.6nm/K for the PANDA fiber, and 3.2nm/MPa and negligible temperature sensitivity for the PM-PCF. This method produces an easily encapsulated, highly sensitive temperature and pressure sensor without any additional type of sensor.