Development of cavity ringdown long period grating pressure sensor.

• Main Author: Wong, Wei Chang.
• Other Authors: Chan Chi Chiu
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Chemical engineering::Biotechnology; DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: http://hdl.handle.net/10356/16602
• Institution: Nanyang Technological University

A new method of designing optical fiber pressure sensors by use of a cavity ring-down loop of long period grating (LPG) is reported. In order to determine the parameters of LPG that are best suit for experiment and pressure sensitivity, simulation of long period grating is done based on three-layer method by Erdogan. The full program is given and problems faced during the calculation are shown with proposed solutions. The simulated transmission spectrum shows good approximation the real model only if all the parameters of the fiber are known. This sensor measures the intensity of an input pulse as it is subjected to losses comprised of the fiber absorption loss, the fiber couplers insertion loss, the fiber scattering loss, attenuator loss, LPG transmission attenuation and deduction of erbium-doped fiber amplifier’s (EDFA) gain. The derivation of equations for the relationship between those losses of cavity ring-down and long period gratings with pressure is shown. The performances of the pressure sensor are demonstrated by applying different pressure levels to detect the decay constants. The experimental results show that this sensing setup can operate in the large pressure range, with a high sensitivity of 0.127(µs)-1•(MPa)-1. In addition, the relationship of pressure with long period grating is exhibited by usage of different transmission spectrums of LPG. The performances of the pressure sensor are demonstrated by applying different pressure levels to detect the decay constants. The experimental results show that this sensing setup can operate in the large pressure range, with a high sensitivity of 0.127(µs)-1•(MPa)-1. In addition, the relationship of pressure with long period grating is exhibited by usage of different transmission spectrums of LPG.