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Articles you may be interested inCharacteristics of doped optical fiber for fluorescence-based fiber optic temperature systems Rev. Sci. Instrum. 74, 5212 (2003); 10.1063/1.1623624 Analysis of dopant concentration effects in praseodymium-based fluorescent fiber optic temperature sensors Rev. Sci. Instrum. 71, 100 (2000)Nd 3+ -doped optical fiber temperature sensor using the fluorescence intensity ratio technique Rev. Sci. Instrum. 70, 4279 (1999); 10.1063/1.1150067 Determination of local high temperature excursion in an intrinsic doped fiber fluorescence-based sensor Rev. Sci. Instrum. 69, 2930 (1998); 10.1063/1.1149036Quasidistributed fluorescence-based optical fiber temperature sensor system Rev.The performance of the two most promising fluorescence-based temperature sensing techniques, namely the fluorescence intensity ratio ͑FIR͒ and fluorescence lifetime ͑FL͒ schemes, have been compared. Theoretical calibration graphs for the two methods illustrate the useful monotonic change of the response with temperature variation. Comparison of the responses and the sensitivities of the two schemes show that at very low temperatures the FIR method exhibits a significant variation with temperature, while the response of the FL method becomes constant with its sensitivity approaching zero. With increasing temperature, the FIR and the FL methods ͑with short relaxation times and shorter intrinsic lifetimes of the upper energy levels͒ share a similar sensitivity over a wide temperature range. The presence of a long relaxation time or a longer intrinsic lifetime of the upper level in the use of the FL method gives a less satisfactory response. Experimental data obtained for a range of dopant ions in various host materials are found to be consistent with the theoretical expectation, with each material having a specific energy gap difference. The sensitivities of each material are compared graphically which would allow the most appropriate sensor for an intended application to be selected.

A fiber-optic-based humidity sensor has been fabricated using a fiber Bragg grating (FBG) coated with a moisturesensitive polymer. The sensing concept exploits the inherent characteristics of the FBG and is based on the strain effect induced in the Bragg grating through the swelling of the polymer coating. A direct indication of the humidity level is given by the shift of the Bragg wavelength caused by the expansion of the sensing material. The FBG sensor used in this work has an approximate coating thickness of 33 m and was exposed to different humidity levels at room temperature. The sensitivity of the sensor was estimated to be about 4.5 pm/%RH at a wavelength of 1535 nm, this being obtained through a process of linear regression. The resulting uncertainty in the measurement is 4%RH and the response time of the sensor and the moisture expansion coefficient of polyimide were obtained from a series of experimental investigations and cross compared with the results of previous work.

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This paper reviews recent developments in the field of current measurement which employ a wide range of optical and fiber optic techniques. Depending on the current sensing mechanisms involved and the sensing materials used, optical current sensors (OCSs) may be categorized into four main groups: (i) OCSs employing optical fiber as their sensing elements, (ii) OCSs using bulk glass to sense the current, (iii) OCSs using electro-optic hybrid sensing devices, and (iv) OCSs using magnetic field sensing devices. The operational modes of a variety of OCSs have been grouped and discussed, and several examples given. It can be seen that as a result of an intensive and wide ranging research effort using various approaches, substantial progress in the differing aspects of the optical current sensing techniques considered, such as the sensing material used, the configurations of sensing elements introduced, and the detection schemes adapted, has been achieved during the past years. An overall view of the field shows it to be as an active and exciting research area, highlighting several recently introduced and novel sensing materials and configurations which provide impressive results in this field of instrumentation. Examples of applications for the electric power industry are discussed more extensively.

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