A novel sensing system based on single mode optical fiber in reflective configuration has been developed to measure the critical meniscus height (CMH) of low volumes of liquids, which is then used to calculate the contact angle. The sensing system has been designed especially for very low volumes of liquids (e.g. bioliquids) and the work has demonstrated that measurements are possible with a minimum liquid volume of 5 µL. The sensing system is based on monitoring the spectral variation induced by the difference in the refractive index regions surrounding the fiber tip, at the air-liquid or liquid-liquid interfaces. From the experiments performed in water, (by immersing and extracting the fiber sensor in the liquid sample), it can be concluded that the CMH forming on the fiber decreases as the temperature increases. The change of temperature (in this experiment from 22 to 60 ℃) does not influence the CMH of the sample used in the evaluation (P3 mineral oil), giving an indication of its thermal stability. In addition, a fixed fiber was used to measure the variation in the liquid level when another fiber is immersed in the liquid. The error in the liquid level obtained in the work was small, at 0.34 ± 0.04 %. Such a sensor, allowing accurate measurements with very small quantities is especially useful where liquid sample volumes are limited e.g. biologically sourced liquids or specialized, expensive industrial material in the liquid phase.

In this paper, fabrication and characterization of a Gallium co-doped Erbium fiber is presented, highlighting Gallium as a new potential co-dopant to be used in rare-earth doped fibers. This fiber was fabricated using standard MCVD and solution doping method. Fiber characterization setups for fluorescence lifetime, absorption and ASE spectrum are discussed in detail. We go on to show that fluorescence lifetime of 6.02 ms, NA of 0.12, cutoff wavelength of 1.4 μm and a peak absorption of 45 dB/m at 1550 nm is achievable using Gallium as the co-dopant for an Erbium doped fiber.

This is the accepted version of the paper.This version of the publication may differ from the final published version. City Research Online 1  Abstract-Graphene oxide is a very attractive material for refractive index and humidity sensing due to its unique twodimensional structure, which results in faster response times and improved sensitivity over alternative materials. In this paper, response of a graphene oxide-coated long period grating-based sensor to changes in relative humidity and external refractive index (as well as temperature to provide a correction for any changes) is reported. In fabricating the probes, an improved Hummer's method was used to synthesis the graphene oxide dispersion used as its basis, allowing coating of a functionalized long period grating by using a dip-coating technique. A consistent and stable response of the resonance dip intensity of the graphene oxide-coated long period grating was observed to the change in humidity, achieving a sensitivity of 0.15 dB / %RH with a linear correlation coefficient of 0.980 over the relative humidity range from 60%RH to 95%RH, at room temperature (25 ℃). A blue shift of the resonance band wavelength was recorded when the sensor was exposed to varying temperature conditions from 25 ℃ to 70 ℃ and the response was found to be linear, with a correlation coefficient of 0.997. When evaluating its performance as an external refractive index sensor, sensitivities of ~17dB/RIU in the lower refractive index region (1.33-1.38) and ~55 dB/RIU over the higher refractive index region (1.40-1.45) were achieved. The graphene oxide-coated long period grating sensor probe performed well, showing a good stability and repeatability over a number of test cycles in the performance evaluation carried out. Permanent repository link

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This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link ABSTRACTIn this paper, the response of a graphene oxide (GO) coated long period grating (LPG) to the change in temperature and in humidity is reported. To create the probe, an improved Hummer's method was used to synthesis the GO solution used as its basis, allowing coating of functionalized LPG by using a multi-layer dip coating technique. A consistent and stable response of the resonance peak intensity of the GO coated LPG was observed to the change in humidity, achieving a sensitivity of 0.15 dB / %RH with a linear correlation coefficient of 0.9804 over the relative humidity range from 60%RH to 95%RH at room temperature (25C). A blue shift of the resonance peak wavelength was recorded when the proposed sensor was exposed to varying temperature conditions from 25C to 70C and the response was found to be linear with a correlation coefficient of 0.9973. The GO coated LPG humidity sensor probe performed with a good stability and repeatability over a number of test cycles in this initial performance evaluation.