Innovative Visualization of Data Generated by Photonic Sensors

Fiber Bragg Gratings (FBGs) sensors consist of a set of Bragg reflectors capable of reflecting a single wavelength of light, directly proportional to the dimensions of the grating, and transmitting all the others. Analyzing the offset of the reflected wavelength from the rest state, it is possible to infer a temperature variation, a strain applied to the sensor, or more. Based on photons, this type of sensor is not susceptible to electromagnetic interferences, is lightweight, can be multiplexed on a single transmission line, and is a passive component. The main objective of this thesis is to create an innovative application, called FBG Data Analyzer, to display in real-time the data coming from a set of optical fiber sensors. This data is partially processed during acquisition and is shown in a comprehensive and human-readable manner. This thesis is part of a collaboration between the Department of Control and Computer Engineering (DAUIN) and the Department of Mechanical and Aerospace Engineering (DIMEAS) in the context of the Inter-Departmental Center for Photonic technologies. The application requirements include viewing the wavelength peaks trend in the time domain and possibly performing a spectrum analysis of those time series to detect oscillatory components by applying the Fast Fourier Transformation (FFT) algorithm to the selected signals. Another essential requirement is that, given an empirically determined coefficient, it is possible to correlate the variation of the wavelength peak value to the corresponding delta strain/temperature, where the variation is the difference between the value reflected by the resting FBG sensor and the one currently measured. The property just described is available in real-time thanks to the FBG Data Analyzer, while previously, it was only computed in post-analysis. The desktop application has been developed and tested on Windows using the Qt open-source framework. One of the reasons for its choice is the simplicity of porting the application to different operating systems. Most of the User Interface (UI) space is occupied by charts built on top of the QtCharts framework; they have been heavily customized and improved to meet the operators' needs. Given the rich presence of configuration parameters, an automatic saving system was implemented. It makes use of a JSON file which is also editable with an external editor. Physical sensor data is captured by the SmartScan by SmartFibres interrogator, which is the unit responsible for transforming wavelengths into digital values. The data is then sent to a software called Middleware, which processes this data and sends it either to a MongoDB database or via a TCP socket. Thanks to MongoDB's Change Stream feature, FBG Data Analyzer can obtain input data by actively waiting for changes to the current collection or by connecting to the TCP socket of the Middleware; the connection methods are mutually exclusive. During the development phase, the functionalities of the software were tested using an interrogator emulator capable of generating random wavelength peaks for the configured sensors. In the final phase, two types of tests were carried out. The first involved measurements of temperature variations induced through a climatic chamber, while the second regarded measurements of the strain applied to the wings and tail of a model aircraft. During the tests, CPU and RAM usage was closely monitored and remained at constant levels.