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• A highly sensitive strain optical fiber sensor is achieved by means of side-polishing and high-temperature oxyhydrogen flame heating. • The highest strain sensitivity of the M-LPFG reaches to −19.05 pm/ με. • A compact length is obtained, which is 5 mm. • Low cost, simple structure and easy fabrication. Optical sensors for strain measurement have been significantly concerned due to their unique characteristics of quick response, anti-electromagnetic interference and compact size. In this article, a brand-new type of "M"-shaped core long-period fiber grating (M-LPFG) based on core-modulated method is proposed and experimentally testified. By means of side-polishing and high-temperature oxyhydrogen flame heating, the cladding of fiber tends to be circular and the core will bend slightly towards the polished area. The micro-bending core is suffered strong refractive index modulation and this phenomenon also excites the evanescent field adequately. By analyzing the simulated light transmission and the transmission spectrum, considerable degree of micro-bending core is achieved. In the experiment, the proposed sensor with 10 periods (5 mm) displays a high strain sensitivity of −19.05 pm/ με with range of 0–500 με, and the temperature sensitivity of which is obtained as 51.16 pm/°C. Due to relatively small influence on cladding and self-circularity of structure, the M-LPFG possesses a high mechanical strength. With the above advantages of high sensitivity, compact size, low-cost and strong mechanical strength, the method of fabricating M-LPFG has great potential in strain measurement. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate an optical fiber torsion sensor based on symmetrically polished single-multi-single mode (SP-SMS) fiber structure. The polished structure enhances the torsion response effectively, which is fabricated by a high-frequency CO 2 laser. Experimental results show that the high sensitivity of the proposed torsion sensor reaches 1.032 nm/(rad m−1) in the range from − 10.261 rad/m to 10.261 rad/m. Meanwhile, the temperature response of the sensor is also investigated, which is 21 pm/°C in the range from 30 °C to 150 °C. Moreover, the structure has the features of low cost, simple fabricating method and small temperature crosstalk. Schematic diagram of the symmetrically polished SMS fiber structure (SP-SMS). The geometrical shape of the sensor is prepared by a high-frequency CO 2 laser, which enhances the torsion sensitivity of the structure. The structure achieves a high sensitivity of 1.032 nm/(rad m−1). Meanwhile, small temperature-torsion crosstalk of 0.03 (rad m−1)/°C is achieved. The fabricating method of the structure has the advantages of is non-contact and scalable. Hence, the proposed structure provides a new idea to the design of the fiber torsion sensor. [Display omitted] • The highest torsion sensitivity of the SP-SMS reaches to 1.032 nm/(rad m−1). • The low temperature-torsion crosstalk is obtained, which is 0.03 (rad m−1)/°C. • Low cost, compact structure and easy fabrication. [ABSTRACT FROM AUTHOR]

• A high sensitive curvature optical fiber sensor is achieved by using CO 2 laser polished method. • The highest bending sensitivity of the AP-LPFG reaches to 30.85 nm/m−1. • A compact length is obtained, which is 7.39 mm. • Low cost, simple structure and easy fabrication. In this paper, we experimentally propose and theoretically investigate a two-dimensional vector curvature sensor based on asymmetrically polished long period fiber grating (AP-LPFG). This sensor is fabricated by a high-frequency CO 2 laser in order to polish periodic asymmetrical V-shaped grooves on a single mode fiber (SMF). Such grooves efficiently enhances the bending sensitivity of sensor and shorten the length of the structure to 7.39 mm. Experimental results show that the sensitivity of AP-LPFG reaches 30.85 nm/m−1 in the direction of the X-axis and −0.97 nm/m−1 in the direction of the Y-axis. Meanwhile, the temperature response of AP-LPFG is carried out, which is 76 pm/℃ in range of 30-160℃. Moreover, the AP-LPFG has the features of compact length and simple structure, which shows the potential in curvature sensing. [ABSTRACT FROM AUTHOR]

A simple fiber sensor for dual-parameters measurement of curvature and temperature is proposed and demonstrated, which is prepared by sandwiching a section of deformed multimode fiber (D -MMF) into two single-mode fibers (SMFs). This structure is processed by CO 2 laser etching and hydrogen-oxygen flame melting method. The micro-bent core of MMF constructs in-fiber composite interference, which effectively improves the bending sensitivity of the structure. It is found that the dips at 1310 nm and 1376 nm in the interference spectrum show different curvature and temperature responses. The curvature sensitivities of two dips are up to − 23.2 nm/m−1 and − 11.64 nm/m−1 in the range of 0–1.1733 m−1. Moreover, the temperature sensitivities of two monitored dips are − 52.1 pm/°C and − 19.7 pm/°C, respectively. [Display omitted] • A high sensitive curvature optical fiber sensor is achieved by using CO 2 laser polished method and hydrogen-oxygen flame heating stretching. • The highest curvature sensitivity of the D-MMF reaches to − 23.2 nm/m−1 • Dual parameters measurement of curvature and temperature. • Low cost, compact structure and easy fabrication. [ABSTRACT FROM AUTHOR]