Knowledge of the distribution of the aspect ratios (ARs) in a chemically-synthesized colloidal solution of Gold Nano Rods (GNRs) is an important measure in determining the quality of synthesis, and consequently the performance of the GNRs generated for various applications. In this work, an algorithm has been developed based on the Bellman Principle of Optimality to readily determine the AR distribution of synthesized GNRs in colloidal solutions. This is achieved by theoretically fitting the longitudinal plasmon resonance of GNRs obtained by UV-visible spectroscopy. The AR distribution obtained from the use of the algorithm developed have shown good agreement with those theoretically generated one as well as with the previously reported results. After bench-marking, the algorithm has been applied to determine the mean and standard deviation of the AR distribution of two GNRs solutions synthesized and examined in this work. The comparison with experimentally derived results from the use of expensive Transmission Electron Microscopic images and Dynamic Light Scattering technique shows that the algorithm developed offers a fast and thus potentially cost-effective solution to determine the quality of the synthesized GNRs specifically needed for many potential applications for the advanced sensor systems.

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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.

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A fiber ring laser sensor setup utilizing FBGs (Fiber Bragg Gratings) for simultaneous measurement of ambient temperature and relative humidity (RH) is presented. Two FBGs are incorporated as tunable filters for a dual-wavelength laser emission, where one FBG was coated with Polyimide (PI) in order to achieve sensitivity to RH changes, while the other bare FBG was used for temperature sensing. An increase in RH would induce a strain on the grating, which results in a variation in the resonance wavelength of the PI-coated FBG. This causes a shift in the laser emission wavelength. Being insensitive to RH changes, the bare FBG was employed to measure temperature. The dual-wavelength fiber ring laser sensor created thus allows to determine simultaneous measurement of RH and temperature. The RH sensitivities observed by the PI coated FBG to RH and temperature are 3.6 pm/%RH and 12.15 pm/°C respectively. The temperature sensitivity of the bare FBG was observed to be 9.6 pm/°C. The main advantage of the proposed setup is an optical signal to noise ratio (OSNR) higher than 55 dB and a 3 dBbandwidth less than 0.02 nm, which points out efficient capabilities for both precise sensing and remote detection applications.

The thermally coupled green band emission from excited Er 3+ ions has been used in the past to create optical thermometers, by doping the material in various types of media, particularly glasses.Glasses are known to be excellent hosts for Er 3+ ions: however, high temperatures (>900 K) are usually required for doping these ions into glasses and a non-linear temperature response is often produced. In this work, the frequently encountered drawbacks of glass-based temperature sensors have been addressed by developing a temperature sensor created at a lower temperature (543 K), by dip-coating chemically synthesized upconverting nanoparticles (UCNP -NaYF4:(18%) Yb 3+ , (2%) Er 3+ ) embedded in polydimethylsiloxane (PDMS) onto the tip of a 1000 μm optical fibre, to create the actual fibre probe. The sensor shows an excellent linear response (R 2 = 0.991) over a very useful temperature range of 295 K -473 K, with a sensitivity of 2.9 ×10 -3 K -1 , a temperature resolution of ± 2.7 K and response time of ~ 5 seconds. Additionally, a probe was investigated where a pure upconverting nanoparticle powder was coated on the tip of optical fibre and its spectral and temperature response was obtained (and cross compared with that of UCNP-PDMS composite). The results obtained from the probe development work show that the UCNP-PDMScoated optical fibre temperature sensor developed offers a better alternative to more conventional Er 3+ doped glass-based temperature sensors, in terms of the thermal budget, the synthesis process and the ease of coating, creating as a result, a very linear device response.

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A novel sensor for measuring viscoelastic properties of sodium alginate (SA) in distilled water of concentration (1.0, 1.5, 2.0, 2.5, and 3.0 w/w%) has been tested. The sensor used is an FBG (Fiber Bragg Grating) fibre optic sensor. It has seen that there is a linear response in terms of area of the peak as the concentration of SA increases and the FWHM increases linearly with a small error bar, indicating the precision of the present sensor. The system proposed will substitute the mechanical Maxwell method for measuring viscoelasticity of polymers, with a mechano-optic sensor.