Search

We propose and experimentally investigate a spiral-polished single-multi-single-mode (SP-SMS) fiber sensor for the simultaneous measurement of strain and temperature. This special spiral shape on a multimode fiber is fabricated by a high-frequency CO2 laser, which excites higher order cladding modes in the interference process and leads to high strain sensitivity. Experimental results show that the strain sensitivity for the proposed structure in the transmission spectrum of two marked interference dips is − 17 pm/με and − 1 pm/με in the range of 0–600 με. Moreover, temperature sensitivities of 10 pm/℃ and 13.3 pm/℃ are obtained in the range of 30–150 ℃. Furthermore, the proposed sensor is inexpensive, is easy to fabricate and has a compact structure. [ABSTRACT FROM AUTHOR]

In this paper, a novel torsion sensor based on Mach-zehnder interferometer (MZI) is proposed and demonstrated. The proposed sensor is fabricated by the single-mode fiber (SMF) and multi-mode fiber (MMF) shear splicing, further employing CO 2 laser to modulate the MMF surface into triangular prism form. And compare the number of different triangular prism pairs structure on torsion sensitivity. By increasing the number of triangular prism pairs effectively improve the torsion sensitivity. The experimental results show that in the range of 0–9.617 rad/m, the highest sensitivity fiber sensor can be obtained with a sensitivity of 3.3133 nm/(rad/m). Meanwhile, the temperature characteristic of the sensor is investigated, which presents a sensitivity of 21.67 pm/℃ in the range from 30 ℃ to 100 ℃. Therefore, the temperature crosstalk is 0.0065 (rad/m)/℃, which results in a low temperature crosstalk. In addition, the structure also has the advantages of low cost and simple manufacturing process. [Display omitted] • A high sensitive torsion optical fiber sensor is achieved by using CO 2 laser polished method. • The highest torsion sensitivity of the UITP-SMS reaches 3.3133 nm/(rad/m). • A low-temperature crosstalk is obtained, which is 0.0065 (rad/m)/℃. • Low cost, simple structure and easy fabrication. [ABSTRACT FROM AUTHOR]

This paper presents a systematic review concentrating on the design and extensive applications of optical fiber sensors based on embedded long-period fiber gratings (LPFGs). First of all, the preparation procedures and the working principle is introduced in detail. Then, the applications of different types of sensors based on the embedded LPFG are investigated, which is explored to detect physical parameters such as temperature, strain, refractive index (RI), bending, torsion, liquid level. Also, the method for enhancing sensing performance is presented. Compared with LPFGs proposed in these years, the embedded LPFGs sensors with high selectivity and flexibility have proved to behave excellent sensing characteristic, especially in the recognition in bending and RI measurement. Furthermore, the sensors are briefly described according to the design scheme and sensing performance. Finally, the drawbacks of the sensors are analyzed and the future prospect is discussed. [ABSTRACT FROM AUTHOR]

• 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 new type of waved core fiber structure is proposed and experimentally demonstrated. • The highest sensitivity of the sensor reaches 125.5 pm/με within the measuring range of 0–200 με. • Simultaneous measurement for strain and temperature can be achieved. • Compact in length and high mechanical strength. Strain and temperature, as two important parameters to evaluate structural health, is increasingly paid numerous attentions for years. In this article, we developed and experimentally tested a highly sensitive strain sensor based on SMS structure with waved core multi-mode fiber (MMF), which has ability to monitor temperature simultaneously. By introducing a section of bent-core fiber into the portion of MMF, the higher-order cladding mode is excited to enhance the sensitivity. Furthermore, the portion of bent-core displays significant influence on effective refractive index (ERI) of the MMF section as strain applied, which brings about higher strain sensitivity. The experimental results display that the highest sensitivity of the sensor reaches 125.5 pm/με within 0–200 με and the measuring range achieves 0–1200 με. By demodulating two dips, simultaneous measurement for strain and temperature is achieved by solving the equation matrix. This simple method displays minor influence on mechanical property and enhances the strain sensitivity considerably. It is strongly believed the proposed sensor brings about a competitive choice in engineering fields. [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]