Arrayed Waveguide Grating-Based Interrogation System for Safety Applications and High-Speed Measurements

This thesis is focused on the design of two interrogation systems for Fiber Bragg Grating (FBG) sensors based on the Wavelength Domain Multiplexing (WDM) by means of the Arrayed Waveguide Grating (AWG) device. The FBG sensors have been employed in a large number of environments thanks to their intrinsic characteristics. To design a measurement system based on the Fiber Optic Sensor (FOS) technology, it is mandatory to make use of an optoelectronic system with the aim to "read" the wavelength shifting performed by the sensors. This latter is named interrogation system and, actually, sets a limit on the employability of the FBG sensors, due to its cost, design complexity and low reliability in some contests. For this reasons, the researchers are constantly looking on new technologies for the design of innovative interrogation systems. The AWG device seems to provide characteristics which cannot be reached with other devices and, due to its passivity, gives the possibility to increase the system speed to let the FBG sensors to be employed also for the detection of high-speed phenomena. Furthermore, thanks to the robustness and reliability of AWG device, is possible to turn an interrogation system into a full analog monitoring system employable in a safety scenario, such as industrial processes or other kind of environments, in which digital processing does not ensure enough reliability

Simulation of an Optical-to-Digital Converter for High Frequency FBG Interrogator

In this paper, design and simulations of an optoelectronic circuit for the conversion of the optical signal, coming from an interrogation system for FBG sensors, into a digital signal, is presented. The approach is divided into an optical introduction of the interrogation system, an analog section and, finally, digital considerations. The analog processing part is mainly based on the realization of a double stage transimpedance amplifier to obtain, in the working conditions, the best performances required in terms of high gain and wide bandwidth. The output voltage from the analog section is then converted to digital via a 12-bit ADC and sent to an FPGA that processes the defined algorithm in order to obtain the needed optical-electrical linear conversion. The circuit simulations, digital stability and other consideration, including the stability to optical power variability obtained by the numerically simulated interrogation system, are performed, highlighting the peculiarities of this new type of high frequency FBG interrogator