Greg W. Baxter

Comparison of fluorescence-based temperature sensor schemes: Theoretical analysis and experimental validation

The performance of the two most promising fluorescence-based temperature sensing techniques, namely the fluorescence intensity ratio (FIR) and fluorescence lifetime (FL) 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 levels) 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 hos...

High dynamic range temperature point sensor using green fluorescence intensity ratio in erbium-doped silica fiber

We propose a sensor based on the temperature dependant behavior of the two lines of green emission of the erbium ion. The ratio of the intensities of these two lines presents a very low dependance on pump wavelength and pump power fluctuations. The sensitivity of the ratio is 0.013//spl deg/C between room temperature and 600/spl deg/C. In addition, the measurement is self-calibrated. >

Nd3+-doped optical fiber temperature sensor using the fluorescence intensity ratio technique

An optical fiber temperature sensor employing the fluorescence intensity ratio using Nd3+-doped silica fiber and exhibiting high sensitivity is presented. The development and construction of the sensor, which requires relatively simple electronics and data analysis, is described together with its calibration over the −50 to +500 °C temperature range.

Single-mode 1.34-μm Nd:YVO 4 microchip laser with cw Ti:sapphire and diode-laser pumping

We report cw single-mode output at 1.34 microm in a Nd:YVO(4) microchip laser pumped separately with a Ti:sapphire laser and a diode laser in the region of 809 nm. The 0.5 mm x 1.0 mm x 1.0 mm Nd(3+)-doped YVO(4) crystal produced output powers as high as 60 mW with slope efficiencies as high as 40% and laser thresholds between 155 and 275 mW by use of a pumped volume of approximately 150-microm diameter and 0.5-mm length. Data are also presented for the lasers performance as a function of pump wavelength and for the spectral variation of the output with crystal temperature.

Simultaneous strain–temperature measurement using fluorescence from Yb-doped silica fiber

The effect of strain upon both the fluorescence intensity ratio and the fluorescence decay-time–temperature-sensing techniques has been studied using Yb-doped fiber. The measured variation with strain of the former method is consistent with no strain sensitivity, while the latter method demonstrates a linear dependence on strain. A single optical sensor element using both these fluorescence techniques thereby offers an attractive way of providing temperature compensation in a simultaneous strain and temperature monitoring system.

1.2-μm transitions in erbium-doped fibers: the possibility of quasi-distributed temperature sensors

We propose the principle of a high-dynamic, quasi-distributed temperature sensor based on the behavior of the 1.13- and the 1.24-µm emission lines in erbium-doped silica fibers. The ratio of fluorescent intensity of these lines presents a temperature dynamic of more than 11 dB between room temperature and 600 °C. As the lower level of these transitions is not the fundamental, the emission lines are absorption free, and no dependence of the intensity ratio of the two lines has been observed, with power and wavelength pump variations permitting the realization of self-calibrated quasi-distributed sensors.

A localized surface plasmon resonance-based optical fiber sensor with sub-wavelength apertures

An optical fiber refractive index sensor based on localized surface plasmon (LSP) resonances within resonant subwavelength apertures in a gold film is demonstrated. The excitation of LSPs within the apertures in the film on the optical fiber endfaces provided the basis of a compact refractive index sensor for liquids. A sensitivity of 755 ± 12 nm per refractive index unit was demonstrated for this sensor.

Blue light-emitting-diode-pumped point temperature sensor based on a fluorescence intensity ratio in Pr3+: ZBLAN glass

A fluorescence intensity ratio technique has been applied to Pr3+: ZBLAN glass, realising a point temperature sensor. We present data for a blue light emitting diode-pumped prototype which provides accurate and self-referenced measurements.

Analysis of dopant concentration effects in praseodymium-based fluorescent fiber optic temperature sensors

An analysis of concentration effects in praseodymium-doped glasses used as the sensor element of several fiber optic temperature sensors has been performed. Results show the dependence of a range of relevant parameters on concentration, and the determination of concentration-independent parameters used in the design of effective probe sensor elements with both doped and co-doped rare earth materials. Low concentrations of Pr3+, commensurate with an acceptable signal-to-noise ratio in the optical system, are preferable for the design of the most effective optical fiber fluorescence sensors based upon this species.

Er3+:Yb3+ doped fibre with embedded FBG for simultaneous measurement of temperature and longitudinal strain

A method for measuring temperature and strain simultaneously using a combination of the shift in a fibre Bragg grating and the fluorescence intensity ratio from Er3+:Yb3+ doped fibre is presented. This sensor scheme has the advantage of co-located measurement of temperature and strain as the Bragg grating is written into the Er3+:Yb3+ doped fibre. A number of these sensors were calibrated over temperature and strain ranges of 20–150 °C and 350–2530 μe, respectively, and the measurement data analysed using various techniques. Temperature and strain values inferred from the sensors during these calibrations showed rms errors in the order of 0.3 °C and 4.9 μe.