Before saturated absorption, graphene possesses optical nonlinear refractive index, which is a photoinduced refractive index effect. Taking advantage of this effect, a wavelength tunable filter is realized based on a graphene filled all optical fiber Fabry‐Pérot microcavity. Experimental results show that the interference wavelength of the filter exhibits linear red‐shift with the increase of the tunning optical power and tunning efficiency increases with the increase of cavity length and filled graphene thickness. In this study, the maximum wavelength vs power tunning efficiency can get 66 pm/mW. This filter has the advantages of high tunning efficiency, simple structure, antienvironmental interference good mechanical performance, and repeatability.

Large standoff magnetometry (LSM) is an emerging non-intrusive, above-ground, passive geo-magnetization flux leakage measurement technology to detect pipeline features or anomalies associated with elevated stresses. Although many promising field trial results have been reported in the past, its overall performance still has not reached sufficient consistency and reliability. This paper presents PG&E’s effort in gaining some fundamental understanding of the current LSM technology and its qualitative & quantitative performance. Specifically location accuracy of girth weld, casing end, dent and landslide damage is analyzed with references to inline inspection (ILI) and excavation data. In addition, basic physics of LSM stress quantification is examined using references of a full-scale finite element stress analysis on selected plain dents. The outcomes indicate advanced global navigation satellite system (GNSS) tool plus capability of identifying girth weld are important to achieve good anomaly location accuracy especially as LSM tends to report more indications than other inspection technologies in current practice. The LSM stress estimation and its comparison to pipe’s specified minimum yield strength (SMYS) may be only good quantitatively within magneto-elastic regime where localized stress concentration zones (SCZs) are under elastic stress loading only and without presence of residual plastic stress.

An optical fiber interferometric refractometer for alcohol gas concentration and low refractive index (RI) solution (with 1.33–1.38 RI range) measurement is theoretically and experimentally demonstrated. The refractometer is based on a single-mode thin-core single-mode (STS) interferometric structure. By embedding a suitably sized air cavity at the splicing point, high-order cladding modes are successfully excited, which makes the sensor more suitable for low RI solution measurement. The effect of the air cavity’s diameter on the sensitivity of alcohol gas concentration was analyzed experimentally, which proved that RI sensitivity will increase with an enlarged diameter of the air cavity. On this basis, the air cavity is filled with graphene in order to improve the sensitivity of the sensor; and the measured sensitivity of the alcohol gas concentration is −1206.1 pm/%. Finally, the characteristics of the single-cavity structure, graphene-filled structure and double-cavity structure sensors are demonstrated, and the linear RI sensitivities are −54.593 nm/RIU (refractive index unit), −85.561 nm/RIU and 359.77 nm/RIU, respectively. Moreover, these sensor structures have the advantages of being compact and easily prepared.

A soft highly sensitive tactile sensor based on an in-fiber interferometer embedded in polydimethylsiloxane (PDMS) structure is studied. Theoretical simulation obtains that the high order sensing modes and PDMS can improve the sensitivity. Experiments show that different order sensing modes, derived by fast Fourier transform (FFT) and inverse FFT methods, present different sensing performance. Corresponding to high order mode, 1.3593 nm/kPa sensitivity and 37 Pa (0.015 N) detection limit is obtained. Meanwhile, it also shows very good stability, reproducibility, and response time. This study not only demonstrates a tactile sensor with high sensitivity but also provides a novel sensing modes analysis method.

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