We present thermally regenerated fiber Bragg gratings in air-hole microstructured fibers for high-temperature, hydrostatic pressure measurements. High-temperature stable gratings were regenerated during an 800°C annealing process from hydrogen-loaded Type I seed gratings. The wavelength shifts and separation of grating peaks were studied as functions of external hydrostatic pressure from 15 to 2400 psi, and temperature from 24°C to 800°C. This Letter demonstrates a multiplexible pressure and temperature sensor technology for high-temperature environments using a single optical fiber feedthrough. © 2011 Optical Society of America OCIS codes: 060.2370, 060.4005, 120.5475, 120.6780. Sensors that operate at high temperatures are needed for a wide range of applications in the energy, automobile, and aerospace industries. For example, fast, accurate, and reliable interrogation of gas pressure information ensures safe and efficient operations of gas turbine, coal boilers, and power plants, where the operating temperatures range from 400°C to more than 1000°C. Optical fiber sensors have always been considered good candidates for harsh environment applications. A single Fabry-Perot interferometer implemented on a fiber tip can perform pressure or temperature sensing beyondCompared with fiber interferometer sensors, fiber Bragg gratings (FBGs) offer greater multiplexing capability [2], and continuous efforts have been made to improve the operating temperature of FBGs. These may involve modifying the chemical composition of the fiber core [3], and using an ultrafast laser to form a Type II damaged grating [4]. Previously, we reported a high-temperature pressure fiber sensor in which the grating was inscribed in an air-hole microstructure fiber with an ultrafast laser [5]. The Type II FBG shows stable and reproducible pressure sensing operation over 800°C. But further optimization of grating linewidth and suppression of the strong laser-induced birefringence are needed to allow better pressure sensing range and accuracy. The relatively large in-line loss with Type II permanent damage also limits sensor multiplexing.Recently, a new type of high-temperature FBG was reported, in which grating structures are regenerated after the Type I seed gratings are erased during a hightemperature annealing process [6][7][8][9][10]. Unlike chemical composition gratings, it has been shown that the regeneration process is independent from dopants in fiber cores [8] and photosensitization processes, such as hydrogen loading [10]. This versatility opens up hightemperature stabilization to other material systems and allows postregeneration of unloaded gratings, including arrays of online draw tower gratings [10]. By carefully controlling the strength of the seed grating and annealing procedures, high-temperature gratings with ∼35% reflectivity and narrow linewidth can be regenerated [7]. Stable operating temperature up to 1295°C was reported for regenerative gratings [8]. The ultrahigh temperature stability, good grating qualities, and rela...