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A compact all-fiber optical anemometer based on a fiber Bragg grating inscribed in a metal-filled microstructured optical fiber (MOF) is presented. Six-hole MOF (SHMOF) with a suspended core is fabricated to engineer the evanescent field of the fundamental guided mode, and low-melting-point alloy is filled in the micro-holes to achieve highly efficient light-heat conversion. Such a metal-filled SHMOF can strongly absorb pumping light at 1450 nm to generate heat and forms a fiber-optic “hot wire.” The Bragg grating at 850 nm is inscribed in the core of SHMOF and acts as an in-fiber sensor for monitoring wind-speed dependent temperature of the “hot wire.” Experimental results show the sensitivity of the fiber-optic anemometer is as high as ∼0.091 nm/(m/s) at wind speed of around 2 m/s. Such a compact anemometer is promising as a low-power-consumption optical flow-meter for remote sensing and on-chip integration.

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.

The authors review their recent advances in the development of optical fiber Bragg grating (FBG) sensor technologies. After a brief review of the fiber grating sensors, several newly developed FBG sensors are described. With the continuous development of fiber materials, microstructures and post-processing technologies, FBG sensors are still creative after the first demonstration of permanent gratings thirty years ago.

An all-fiber optical anemometer with high light-heat conversion efficiency by using an in-house microstructured optical fiber Bragg grating (MOFBG) is presented. Low-molten-temperature BiSnIn alloy was successfully infiltrated into 11- cm length of a six-hole microstructured optical fiber which was inscribed with a fibre Bragg grating (FBG) centered at ~848 nm. Light launched into the MOFBG was strongly absorbed by the metal to generate heat, while the FBG was utilized to monitor temperature change due to surrounding wind speed. The sensitivity of the laser-heated MOFBG anemometer was measured to be ~0.1 nm/(m/s) for wind speed ranged from 0.5 m/s to 2 m/s. The efficiency of the anemometer, defined as effective sensitivity per pump power, is 8.7 nm/(m/s*W).

We thermally regenerated long-period fiber gratings at 850°C. Two strong seed gratings 10cm apart interfere near 1550nm. The regenerated grating has narrow interference fringes above 20% deep and stable up to 1000°C ideal for high-temperature sensors. © 2014 OSA.

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. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this

By applying a suitable quadratic temperature distribution at a temperature within the viscoelastic softening region for silica, a regenerated chirped grating with bandwidth of 9.8 nm is produced from a uniform grating using post strain-tuning under load. Simulated and experimental results are in good agreement. © 2013 Optical Society of America.

We present an optical fiber bend sensor with enhanced resolution based on the principle of a Mach-Zehnder interferometer in transmission. The sensor is based on two identical Long-Period Gratings separated by approximately 100 mm in a D-shaped single-mode optical fiber. The sensor provides a narrow resonance bandwidth compared to a typical resonance from a Long-Period Grating. The sensor was recoated with low refractive index polyimide and embedded on a fiber-glass base plate before it was characterized as a bending sensor.

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.

A fiber-optic anemometer based on fiber Bragg gratings (FBGs) is presented. A short section of cobalt-doped fiber was utilized to make a fiber-based "hot wire" for wind speed measurement. Fiber Bragg gratings (FBGs) were fabricated in the cobalt-doped fiber using 193 nm laser pulses to serve as localized temperature sensors. A miniature all-optical fiber anemometer is constructed by using two FBGs to determine the dynamic thermal equilibrium between the laser heating and air flow cooling through monitoring the FBGs' central wavelengths. It was demonstrated that the sensitivity of the sensor can be adjusted through the power of pump laser or the coating on the FBG. Experimental results reveal that the proposed FBG-based anemometer exhibits very good performance for wind speed measurement. The resolution of the FBG-based anemometer is about 0.012 m/s for wind speed range between 2.0 m/s and 8.0 m/s.