Technology for Polymer Optical Fiber Bragg Grating Fabrication and Interrogation.

The aim of this project is to develop a new, high-quality interrogator for FBG sensor systems, which combines high performance with costeffectiveness. The work includes the fields of optical system design, signal processing, and algorithm investigation. We present an efficient and fast peak detection algorithm for FBGs, which avoids sudden shifts in the fitted wavelength and improves the wavelength fit resolution. We evaluate how detrimental the influence of higher-order modes is to the polarization stability and linearity of the strain and temperature response of a few-mode FBG sensor. We analyze and investigate errors and drawbacks, which are typical for spectrometer-based interrogators: undersampling, grating internal reflection, photo response nonuniformity, pixel crosstalk and temperature and long term drift. We propose a novel type of multichannel Digital Micromirror Device (DMD) based interrogator, where the linear detector is replaced with a commercially available DMD, which leads to cost reduction and better performance. Original optical design, which utilizes advantages of a retro-reflect optical scheme, has been developed in Zemax. We test the presented interrogator by measuring optical resolution, wavelength fit resolution, accuracy, temperature and polarization dependable wavelength shift and use it to measure the strain response of a fewmode and a highly multimode FBG in a polymer fiber.