Suchandan Pal

Bragg grating-based fiber-optic laser probe for temperature sensing

A novel Bragg grating-based fiber-optic laser probe for temperature sensing using erbium-doped fiber as the active gain medium is reported. The combination of a chirped grating and a normal grating was used to form the laser cavity to achieve temperature-tunable laser action over a wide measurement range. The laser probe used a metal sheath to enhance its mechanical strength and contain the normal grating at the sensing point. The temperature dependence of the wavelength of the laser probe gives a sensitivity of 12.01 pm//spl deg/C and a repeatability of /spl plusmn/1.7/spl deg/C from room temperature to 300/spl deg/C.

Characteristics of potential fibre Bragg grating sensor-based devices at elevated temperatures

Fibre Bragg gratings (FBGs) of type I and IIA were fabricated in Ge-doped and B–Ge co-doped fibres using a 248 nm excimer laser and their performance characteristics were tested and compared with those of a chemical composition grating (CCG), written in a fluorine–germanium doped fibre, over a wide range of temperatures. Long-term testing (more than 600 h) involving a series of step-wise incremental temperature changes shows for the first time the potential of FBGs for high temperature measurement applications (up to and beyond 1100 °C), this depending on the type of FBG involved and the material and composition of the substrate fibre (the CCG was observed to be the most durable at very high temperatures). These gratings are likely to be useful for the simultaneous measurement of strain and temperature over these higher temperature ranges.

Strain-independent temperature measurement using a type-I and type-IIA optical fiber Bragg grating combination

A simple and effective technique for strain-independent temperature measurement has been demonstrated using the peak wavelengths of both type-I and type-IIA fiber Bragg gratings written without hydrogen loading in the same fiber, this having been specially fabricated with a high concentration of germanium in the core composition. The device is also capable of monitoring strain and temperature simultaneously and can be used to measure temperature over the range of 25–300u200a°C with a strain range of 0–500 μe, achieving a temperature-dependent sensitivity of 0.53 and 0.31 pm/°C for strain-independent temperature measurement with root mean square errors of 2.4 and 4.1u200a°C at 25 and 300u200a°C, respectively.

Bragg grating performance in Er–Sn-doped germanosilicate fiber for simultaneous measurement of wide range temperature (to 500 °C) and strain

A fiber-optic sensing scheme for the simultaneous measurement of strain and a wide range of temperatures has been investigated by combining the properties of the fiber Bragg grating (FBG) and the fluorescence from a rare-earth-doped photosensitive fiber. The temperature-dependent fluorescence peak power ratio of the two peaks occurring around 1535 nm and 1552 nm from the amplified spontaneous emission due to the 4I13/2↔4I15/2 transitions in Er3+-doped tin–germanosilicate fiber, with 980 nm pumping, and the dual functionality of the FBG were exploited in this scheme. The sensor is based on a single FBG written in a small length (∼10 cm) of the above fiber, which can be used for the simultaneous measurement of strain and temperature over ranges of 0–1150 μe and 22–500u200a°C, with root-mean-square errors of 36 μe and 6u200a°C, respectively.

Investigation of the photosensitivity, temperature sustainability and fluorescence characteristics of several Er-doped photosensitive fibers

Three different types of Er doped photosensitive fibers, germanium/erbium (Ge/Er) fiber, tin/germanium/erbium fiber (Sn/Er) and antimony/germanium/erbium fiber (Sb/Er) have been manufactured and studied for use in optical sensor systems. Their characteristics of photosensitivity, the temperature sustainability of fiber Bragg gratings (FBGs) written into these fibers and the fluorescence emission from the Er dopant were investigated and compared. It has been shown in this work that these fibers all show a satisfactory degree of photosensitivity to enable the fabrication of FBGs and a significant level of fluorescence emission within the 1550 nm band for sensor use. The high temperature sustainability of the FBGs written into these fibers was investigated and seen to be quite significant at temperatures as high as 850 °C, in particular for the Sn/Er and Sb/Er fibers. A fiber laser using the Sb/Er fiber as the gain medium was demonstrated, giving evidence of the strong fluorescence emission from the Er dopant. These fibers are all suitable for use in a variety of sensing applications for the simultaneous measurement of temperature and strain by means of monitoring both the fluorescence characteristics and the peak wavelength shift of the FBGs formed in fiber laser sensor application.

Bragg gratings written in Sn–Er–Ge-codoped silica fiber: investigation of photosensitivity, thermal stability, and sensing potential

Bragg gratings were fabricated in an Sn-Er-Ge-codoped silica fiber with a phase mask and ultraviolet radiation from a 248-nm KrF excimer laser. The photosensitivity of the fiber was examined by studying the initial growth rate of the gratings written into it. The thermal stability of the gratings was investigated and modeled in terms of both the refractive-index modulation and the effective refractive index of the fiber core. It was shown that the temperature-induced irreversible shift in the Bragg wavelength could not be predicted by the isothermal decay of the refractive-index modulation. Finally, the potential of the gratings written into the fiber is discussed in terms of their use in high-temperature-sensing applications.

Wide range of temperature and strain measurement using Bragg-grating-based fibre laser approach

A fiber laser-based sensor system has been developed to measure wide range of temperatures (22 - 500°C) and strain (0 - 1200με) using a normal and a chirped grating as optical feedback elements and Er3+-doped fiber as gain medium.