Tilted fiber grating refractive index sensor and interrogation device.

摘要

This masters thesis presents a new way to measure the refractive index using Tilted Fiber Bragg Grating. We start by studying the properties of the TFBG spectrum in different surrounding refractive indices. We show that the notches of the TFBG spectrum displace as the surrounding refractive index changes. By picking up a particular notch (i.e. a particular mode) and tracking the shifts in the position of the center wavelength of this mode, we could generate curves by use of which one can determine the refractive index of the surrounding material. This property of the TFBG spectrum based on which the position of the modes displaces in response to the change in the surrounding refractive index is due to the fact that the tilt angle of the grating planes makes the light to couple to the cladding modes and because these cladding modes travel close to the cladding-external material surface, they can sense the change in the external material refractive index. Another interesting point mentioned in this research was that one does not need to worry about the shape of the mode used to measure the refractive index. This is true because as long as the modes have the same distance from Bragg resonance, they react exactly the same to the change in the external refractive index.;The second part of the thesis dealt with the Arrayed Waveguide Grating as a promising device to be used as the interrogator of the TFBG refractive index sensor. A very preliminary study was performed on the effect of fabrication errors on the performance of AWG. An optimum design based on the requirements of an ideal interrogator unit, in terms of crosstalk, channel spacing and device size was presented. This design was simulated and the results of the simulation were presented.