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Advantages for sensor applications of long-period gratings (LPGs) in special optical fibers are reported. Two consecutive LPGs separated by 60 to 100 mm interfere to improve the resolution and reduce noise in a highly doped fiber with inner cladding and in a D-shaped fiber. These gratings provide good contrast to increase the resolution for sensing applications, with or without access to the surroundings along the fiber. The mode profiles of the devices were characterized experimentally to gain deeper insight into the improved functionality. [ABSTRACT FROM AUTHOR]

An active optical fiber gas sensor was developed in a cobalt-doped single mode fiber. This fiber can be heated up to a few hundred degrees Celsius by a heating laser, and a fiber Bragg grating (FBG) was fabricated inside this fiber as a thermometer. The Bragg wavelength of the FBG is sensitive to the thermal conductivity of the gas surrounding the fiber and can be used to monitor the concentration of a special gas once we know in advance the kind of gas. The proposed sensor is ideal for detecting explosive or corrosive gases in some practical application scenarios, such as gas pipeline, coal mine, flow meters, and so on. We have measured the methane concentration ranging from 0% to 4.8% (5% is its explosion limit) as a demonstration. [ABSTRACT FROM PUBLISHER]

A microstructured optical fiber (MOF) Bragg grating is presented for microfluidic sensing applications. The MOF is specially designed to be with a large amount of microholes for developing ultrasensitive sensors based on inner coating and surface effects. With the fabrication of fiber Bragg grating (FBG), such an MOF sensor has been demonstrated for monitoring the fluid flowing through microholes. Experimental results reveal that the sensitivity of the sensor depends on both the refractive-index range of measurement and the order of fiber modes. The temperature dependency of the sensor has also been measured and compared with that of conventional FBGs. [ABSTRACT FROM AUTHOR]

Poly(dimethylsiloxane) (PDMS) is one of the most popular polymer materials for microfluidic devices. However, it still remains a challenge to rapidly fabricate PDMS microfluidic devices with micrometer-scale feature sizes. In this paper, we present gray-scale digital photolithography technology for direct patterning of large-area high-resolution PDMS microstructures for biomicrofluidic applications. With the positive- and negative-tone photosensitive PDMS (photoPDMS), we rapidly fabricated various PDMS microstructures with complex geometries by using a one-step patterning process. The positive-tone PDMS was used to pattern large-area microfluidic chips, while the negative-tone PDMS was utilized to fabricate high-resolution on-chip microstructures and components. In particular, a large-area microfluidic chip of 5.5  ×  2.8 cm2 with complex three-dimensional (3D) staggered herringbone mixers was fabricated from the positive-tone PDMS by using a single-step optical exposure process; a small microfluidic chip with a feature size as small as 5 µm was prepared with the negative-tone PDMS. Furthermore, 3D surface engineering of PDMS microchannels was demonstrated to customize extracellular microenvironments for investigating cell migration. [ABSTRACT FROM AUTHOR]