This paper describes an optical-fiber sensor developed for temperature measurement under the offshore oil well conditions. The sensor exploits the displacement of the optical absorption edge occurring in semiconductors under the influence of temperature variation as a result of temperature-induced energy shifting of conduction band extrema. The structure of the sensor and the measurement principle are described. The common-path reference measurement and node type error compensation technologies are developed. And the detailed theoretical analysis indicates that the proposed sensor system can effectively improve measurement errors caused by light fluctuation, difference and variation of the detector responsiveness, circuit magnification times, and so on. It approves that this sensor system can be applied under the long-term formidable conditions with fairly good measurement stability.

A free active element bulk-modulus-based fiber Bragg grating (FBG) sensor for down-hole pressure and temperature measurement is presented. With a differential measurement method and an isosceles triangle cantilever structure, problems of cross-sensitivity and chirped-signal in FBG sensors are solved. Simulation results indicate that the measurement sensitivity in measuring pressure and temperature is estimated to be ～8. 5 pm/MPa in a range from standard atmosphere pressure to 100 MPa and～27.5 pm/℃ from 20 to 200℃, respectively.

A novel fiber-optic sensor used for small intenal curved surface measurement is presented. A measurement principle based on beam reflection is described. Theoretically calculated curves and measured values are given. The results provide an essential theoretical and design basis for the measurement of curved surfaces with fiber-optic sensor. This sensor, which is composed of eight symmetrically cross-arranged receiving fibers and one centered emitting fiber, can accomplish distance measurement with high vertical resolution of 0.1