Applications of Fiber Bragg Gratings for Optical Communication Systems and Optical Sensor Systems

Abstract

This thesis is concerned with research into the development of a range of fiber Bragg gratings (FBGs) based devices for optical sensor system and optical communications. The research can be divided into two main themes. The first theme area concerns optical communication systems by the use of uniform FBGs mounted on an S-shape plate with a specially designed device in order to compensate dispersion slope (DS) for ultra high speed WDM or OTDM systems. The second concerns optical sensor systems by the use of uniform FBGs mounted on an S-shape plate with a radio-frequency-modulated refractive semiconductor optical amplifier (RSOA) so as to measure curvature for cost effective sensor systems. In addition, I fabricated and demonstrate long period fiber gratings inscribed in a specially designed photonic crystal fiber by inducing an arc charge for curvature sensor.

Firstly, a novel method for tunable dispersion slope compensation is proposed and experimentally demonstrated in the first theme. I use two uniform fiber Bragg gratings (FBGs), a spatially designed S-bending stage and 4-port circulator. Two FBGs are mounted on each surface of a metal plate along the calculated quadratic curve. The DS can be tuned by adjusting a nonlinear strain along two uniform FBGs without changing second order dispersion as well as the central wavelength. In the experiment, a DS tuning range from -13.9 to -54.8 ps/nm2 is achieved with the bandwidth of larger than 2.0 nm.

In second theme, a novel temperature-insensitive FBG bending sensor based on intensity-modulated RF signal measurement is realized using two FBGs attached to the opposite sides of a cantilever plate. The sensitivity of the RF signal intensity is 0.38 mV/m-1. The proposed sensor system has important advantages including low cost, ability to observe the direction of bending, and temperature-independent property. Moreover, a photonic crystal fiber (PCF) with two large air holes outside the holey cladding region is fabricated to induce an effective long periodic grating (LPG) in the core by an electric arc discharge. I believe that the two large air holes lead to the asymmetric perturbation in the core under the electric arc discharge, thereby introducing the coupling to the first higher-order mode. The transmission characteristics of the PCF with the LPG for the external perturbation such as strain, curvature, and temperature are also investigated. It is found that the shift of resonance peak in the transmission spectrum depends on the bending direction. The curvature of 8.55 m-1 results in the center wavelength shifts of 1.8, 4.3, and 11 nm for a vertical, diagonal, and horizontal direction of the curvature to the large air-hole alignment, respectively.