Sensing characteristics of structural microfiber long-period gratings.

We present a detailed investigation into the sensing characteristics of a structural microfiber long-period grating (mLPG) sensor. By spirally winding a thinner microfiber to another thicker microfiber, periodic refractive index modulation is formed while the optical signal transmitted in the thicker microfiber is resonantly coupled out to the thinner microfiber, and then a 5-period four-port mLPG can be obtained with a device length of only ∼570 µm demonstrated a strong resonant dip of 25 dB. We studied the sensitivity characteristics of the four-port mLPG with surrounding strain, force, temperature and refractive index, and the obtained sensitivities were -6.4 pm/µÉ›, -8418.6 nm/N, 7.62 pm/°C and 2122 nm/RIU, respectively. With the advantages of high refractive index sensitivity and wide wavelength tunable range, the four-port mLPG has great potential in applications such as tunable filters and biochemical sensor.

ZIF-90-Derived Porous ZnO Coated Optical Microfiber Interferometer Sensor for Enhanced Humidity Sensing and Breath Monitoring.

Humidity plays an important role in many fields, and the realization of high sensitivity and fast response simultaneously for humidity detection is a great challenge in practical application. In this work, we demonstrated a high-performance relative humidity (RH) sensor made by supporting zeolitic imidazolate framework-90 (ZIF-90)-derived porous zinc oxide (ZnO) onto an optical microfiber Sagnac interferometer (OMSI). The ZIF-90-modified OMSI (ZIF-90-OMSI) sensor was in situ heated at different temperatures to obtain porous ZnO, and their humidity-sensing properties were investigated ranging from 25 to 80% RH. The experimental results showed that the porous ZnO fiber sensor prepared at 500 °C (Z500-OMSI) exhibited best humidity-sensing performance with a high sensitivity of 96.2 pm/% RH (25-45% RH) and 521 pm/% RH (50-80% RH) and ultrafast response/recovery time (62.37/206.67 ms) at 22.3% RH. These performances were attributed to the complete transformation of ZIF-90 to ZnO at 500 °C. The obtained Z500 not only retained the high porosity and specific surface area of ZIF-90 but also exhibited the exceptional hydrophilicity of ZnO. In addition, the signals of the proposed Z500-OMSI sensor changed with different breathing patterns, indicating the possibility for human respiration monitoring. This work provided a reliable candidate for an effective RH monitoring system with potential application in medical diagnoses, industrial production, environmental detection, and human health monitoring.