This work reports the development of a low cost in-line color sensor for turbid liquids based on the transmission and scattering phenomena of light from RGB and IR LED sources, gathering multidimensional data. Three different methodologies to discriminate color from the turbidity influence are presented as a proof of concept approach. They are based in regression models, expectation maximization Gaussian mixtures and artificial neural networks applied to labeled measurements. Each methodology presents advantages and disadvantages which will depend on the intended implementation. Regression models revealed to be best suited for standard or occasional measurements, the EM Gaussian mixture will perform better for well-known controlled range of colors and turbidities and the neural networks have easy implementation and potential suited for real-time IoT platforms.

All-optical wavelength conversion is one of the major research topics in the optical networks area. Problems due to electrical conversion can be easily eliminated, such as thermic noise; its transparency to the shape of the signal and to the bit rate, makes this type of conversion an attractive solution. The ‘Four Wave Mixing’(FWM) process is one of these alloptical techniques. Theoretical calculation of efficiency as a function of the various parameters involved on the conversion, give us one idea how to optimize a FWM systemand to achieve the best efficiency of conversion, in a DSF fiber. In this work we present the formulation and study the phenomena as a function of its main parameters.

In this paper, the coupling of a single source injected in a single-mode fiber to all the cores of a multi-core fiber is theoretically studied. The power transfer between the core and the cladding of a fiber is promoted by long-period gratings. To promote the power transfer between the fibers, we considered cladding modes with similar effective refractive index. The results show that the coupling is possible, but the design still needs to be optimized to maximize the power transfer.

We theoretically demonstrate a long-period grating (LPG) based single-mode fiber to multi-core fiber coupler. The coupling efficiency achieved was 24% of the input power, evenly distributed by all cores, using LPGs of length 4 cm.

A novel plastic optical fiber (POF) sensor was investigated to monitor total suspended solids (TSS) concentration continuously, offering insights into wastewater treatment bioreactors without disturbing them. First, off-line experiments with both anaerobic and aerobic sludge (in concentrations ranging between 0.1 and 8.6 g TSS L−1) were used to establish the exponential relationship of the sensor’s transmitted optical power with TSS concentrations. Attenuation coefficients differed clearly with the type of sludge (1.227– 1.274 and 0.456–0.679 for anaerobic and aerobic biomass, respectively) and, in the case of the aerobic sludge, with its coloring. The POF sensor was further used for online monitoring of sludge settling profiles inside a sequencing batch reactor (SBR) that was being operated under a Bfeast-famine^ regime. The turbidity profiles agreed very well with the Boltzmann equation. The Boltzmann dx parameter revealed clear differences in the steepness of the settling gradients, which could be explained by the changes in the applied organic loading rates (OLR). OLR in the range of 1.34–1.53 g COD L−1 day−1 resulted in steeper settling gradients than OLR in the range of 2.13–3.12 g COD L−1 day−1 (dx: 0.42–0.50 vs. 0.90–1.36). Thus, the POF sensor not only revealed elevated potential for prediction of biomass concentration but also for becoming an integral part of real-time automation systems in order to diminish repeated sampling and off-line analysis to control the withdrawal phase based on seasonal sludge settling profiles.

A new optical system with wavelengthencoding/time-spreading Optical Code Division Multiple Access (O-CDMA) is proposed. Using orthogonal polarizations we can have a simple encoding and decoding of two independent channels and achieve differential detection. The resulting system has a constant null decision threshold and therefore a superior performance when compared with a system with direct detection.

In this study, the implementation of an optical accelerometer unit based on fiber Bragg gratings, suitable to monitor structures with frequencies up to 45 Hz, is reported. The developed optical system was used to estimate the structure eigenfrequencies of a steel footbridge, with a total length of 300 m, over the Sao Pedro Creek, located at University of Aveiro Campus, in Portugal. The acceleration records measured with this solution are compared with those obtained by traditional commercial electronic devices, revealing a root-mean-square error of 2.53 x 10(-5) G.

This paper presents a structural health monitoring system for monitoring, with reduced visual impact, one historical building structural. The system is based on fiber Bragg gratings and comprises 19 displacement sensors and 5 temperature sensors. All the sensors were custom made according to the monitoring points' characteristics. The results obtained over the first year of monitoring are presented. The objective of this work is to gather data that will bring a deeper knowledge of how this structure behaves and to help planning the recovering interventions in this historical building.