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A compact hybrid structure of silica taper-assisted dual micro-bubbles is proposed and fabricated for broadband ultrasound sensing. UV-cured adhesive is dripped on silica taper to form dual elliptic microbubbles at preselected position. Scattering and reflected light in each microbubble converges at the two focal points of the ellipse to form two new point light sources, enhancing the emergence of high-order modes with strong multi-mode interference. The second microbubble with multi-mode interference further enhances the modulated light propagating from the first microbubble, realizing high contrast transmission spectrum. By exciting high-order harmonics of piezoelectric transducer (PZT) center at 3.7 MHz as ultrasound source, broad bandwidth acoustic signal from 3 kHz to 23.5 MHz is detected, owing to this hybrid structure with strong multi-mode interference along with polymer microbubbles with small Young’s modulus and small sizes. This unique dual-microbubble device makes attractive features for biomedical application and nondestructive test inspection. [ABSTRACT FROM AUTHOR]

We demonstrate a fiber-optic strain sensor based on a seven-core fiber (7-CF) for accurate extrusion bending and tensile strain sensing. The sensor structure we designed is the 7-CF spliced to a piece of multimode fiber on each side with a lateral core-offset and then conventionally fused to single mode optical fiber as the input and output ports. The experimental results indicate that the optimal curvature sensitivity of the sensor is achieved 25.96 nm/m−1, and the sensitivity of the tensile strain is 0.094 nm/ $\mu \varepsilon $ , which allows us to monitor bending and stretching strain respectively with high precision by the simple, low-cost, and effective sensor. [ABSTRACT FROM AUTHOR]

In this paper, a polymer polyhexamethylene biguanide (PHMB) based Fabry–Perot (FP) interferometric optical fiber sensor for carbon dioxide gas detection at atmospheric pressure is investigated and experimentally demonstrated. The absorption and release of CO2 gas molecules lead to the refractive index change of the PHMB. The length of CO2 sensitive FP cavity can be easily controlled by using the Czochralski method. The real-time measurement result shows that CO2 gas concentration with a sensitivity of 12.2 pm/ppm in a 0–700 ppm range can be achieved. [ABSTRACT FROM PUBLISHER]

An optical fiber Fabry–Perot interferometer (FPI) based on poly (ethyleneimine) (PEI)/ poly (vinyl alcohol) (PVA) blend membrane is proposed and realized experimentally as a sensor for the pressure of CO 2 in the atmosphere. The functional material layer based on PEI/PVA blend polymer exhibits reversible optical path difference change because of absorption and release of CO 2 gas molecules. The cavity of the FPI is fabricated by coating a 15-$\mu$m PEI/PVA blend film on the end-face of a cleaved single-mode fiber. An interference spectrum with fringe contrast of 19.5 dB and free spectra range of 33.15 nm is obtained. The proposed FPI sensor is sensitive to the changes of concentration of CO 2, as well as a sensitivity of 0.281 nm/ $\%$ within an interval which ranges from 7.6 $\%$ to 86.9 $\%$. [ABSTRACT FROM PUBLISHER]

A miniature optical fiber ultrasonic sensor based on the Fabry–Perot interferometer (FPI) is proposed and experimentally demonstrated. The cavity of the interferometer is based on a section of hollow core fiber coated with a 353ND diaphragm. A well-define interference pattern is achieved, and the spectral sideband filter technique is used to interrogate the sensor. Because the thin reflective diaphragm is extremely sensitive to sound pressure, the signal-to-noise ratio of the sensor response reaches to 31.22 dB with the pulse ultrasonic excitation of 300 kHz. A clear interface information can be distinguished in physical model imaging, and the longitudinal spatial resolution is 5 mm. This proposed sensor has the advantages of being simple to fabricate, ultracompact in size, cost effective, corrosion resistance, and being highly stable. [ABSTRACT FROM PUBLISHER]