We present fiber Bragg grating pressure sensors in air-hole microstructured fibers for high-temperature operation above 800°C. An ultrafast laser was used to inscribe Type II grating in two-hole optical fibers. The fiber Bragg grating resonance wavelength shift and peak splits were studied as a function of external hydrostatic pressure from 15 psi to 2000 psi. The grating pressure sensor shows stable and reproducible operation above 800°C. We demonstrate a multiplexible pressure sensor technology for a high-temperature environment using a single fiber and a single-fiber feedthrough. © 2010 Optical Society of America OCIS codes: 060.2370, 060.4005, 120.5475, 120.6780. Pressure sensors operated at high temperature above 500°C have many important applications in the energy industry. They ensure safe and efficient energy production during operations of gas turbines, coal boilers, nuclear power plants, and others. The hightemperature environment presents unique challenges to sensing systems. It not only requires robust sensor elements but also demands reliable packaging and wiring techniques rated for high-temperature environments.Fiber-based optical sensors have been considered good candidates for applications within harsh environments. For example, high-temperature pressure sensors based on a Fabry-Perot interferometer (FPI) have been successfully demonstrated [1,2], and fiber pressure sensors with operating temperatures up to 800°C have been achieved using sapphire fibers [1]. On the other hand, conventional fiber Bragg grating (FBG) sensors are generally considered unsuitable for high-temperature operation. Although FBG pressure sensors have been fabricated using UV laser writing, their operational temperature was limited to below 300°C owing to the poor thermal stability of the UV-induced refractive index change [3,4].In contrast to interferometer-based fiber sensors, FBG-based sensors are readily multiplexible, and the fabrication and the packaging of FBG sensors are relatively simple. They can be produced reliably and in large quantities using a phase mask writing technique. These highly desirable advantages have resulted in significant efforts to improve the hightemperature stability of FBG sensors. In particular, the adaptation of novel fibers, such as nitrogen-doped fiber [5], or novel fabrication techniques, such as ultrafast laser writings [6], has potentially improved the operational temperature of fiber grating devices to be on par with FPI-based sensors, approaching or exceeding 800°C.In this Letter, we apply femtosecond-pulsed ultrafast laser writing to produce high-temperature stable FBG in two-hole fibers for pressure sensing. This work demonstrates a significant improvement of the operational temperature of FBG pressure sensors in air-hole microstructured fiber to over 800°C. A large number of high-temperature FBG pressure sensors in microstructured fibers can be fabricated in one fiber using a simple phase mask approach. The multiplexed fiber sensor array in a single fiber can be serviced by...
An ultrafast thulium-doped fiber laser with large net normal dispersion has been developed to produce dissipative soliton and noise-like outputs at 1.9 μm. The mode-locked operation was enabled by using single-wall carbon nanotubes as saturable absorber for all-fiber configuration. Dissipative soliton in normal dispersion produced by the fiber laser oscillator was centered at 1947 nm with 4.1-nm FWHM bandwidth and 0.45 nJ/pulse. The output dissipative soliton pulses were compressed to 2.3 ps outside the laser cavity.
An all-fiber passively mode-locked thulium-doped fiber ring oscillator is constructed using optically deposited few layer graphene micro-sheets as the saturable absorber (SA). The mode-lock operation was achieved by 130-mW pump power at 1.5-μm. The fiber oscillator produces 2.1-ps soliton pulse output with 80-pJ per pulse energy. The 3-dB bandwidth of the laser output was measured as 2.2-nm. The RF signal-to-noise ratio of 50-dB and sub 20-Hz 3-dB bandwidth of the laser output confirms the stable laser operation with low time jittering. This paper shows that graphene can be an effective saturable absorber for the development of mid-IR fiber mode-locked laser.
This Letter presents an all-fiber mode-locked thulium-doped fiber ring oscillator based on nonlinear polarization evolution (NPE). Pumped by an erbium-doped fiber amplified spontaneous emission source, the construction of the laser cavity consisting of only fiber optic components can operate under two different regimes of solitary and noiselike (NL) pulses. Autocorrelation measurements are performed to extract features of these two regimes.
An optical hot-wire flow sensing grid is presented using a single piece of self-heated optical fiber to perform distributed flow measurement. The flow-induced temperature loss profiles along the fiber are interrogated by the in-fiber Rayleigh backscattering, and spatially resolved in millimeter resolution using optical frequency domain reflectometry (OFDR). The flow rate, position, and flow direction are retrieved simultaneously. Both electrical and optical on-fiber heating were demonstrated to suit different flow sensing applications.
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