Design and fabrication of fiber-Bragg-grating arrays

In this work the photolithographic method with the improvement of the stretch-and-write technique is applied for the design and the fabrication of fiber-Bragg gratings distributed on different lengths of fiber and with different operating wavelengths. A proper apparatus was set-up, which allows to easily change the fiber position behind the mask; moreover, by suitably setting the stage displacements, it is possible to stretch the fiber to a given strain value. In this condition all written gratings have the same peak wavelength corresponding to the utilized mask, but when the fiber is relaxed, the gratings compress and the peaks move towards shorter wavelengths. To the purpose to obtain grating arrays, working at pre-established wavelengths, strain calibration curves was obtained. Two different types of applications were investigated. Arrays of up to five gratings with different peak position and distributed over a 1 m length of fiber were fabricated and characterized for sensing purpose. Adjacent gratings spectrally concatenated were also produced in order to obtain pass-band filters to be applied in photonic systems. An interesting field of application of FBG arrays was considered for strain sensing in the automotive industry, to monitor Various critical components of vehicles. Another example of application was the construction of a pass-band filer applied to suppress the first side lobes of a laser diode spectrum.