Theoretical Research On Gas Sensing By Bragg Fiber

Starting from the algorithm and characteristics of Bragg fiber, we investigate the field distribution and the effective index of Bragg fiber with loss in the core. And a new type of optical fiber gas sensor is proposed. Hollow Bragg fiber is used as the absorption cell of optical fiber gas sensor. We calculate the relative sensitivity of hollow Bragg fiber gas sensor, and what we discussed in this paper would be helpful to provide some theoretical suggestion for a high sensitivity all-fiber gas sensor. The main contents are as follows:1) The general principles of optical fiber gas sensor have been introduced. The advantages of hollow Bragg fiber gas sensor have been presented by comparing with other gas sensors.2) The guiding principle, modal properties and experimental development of Bragg fiber, especially three kinds of calculation methods for Bragg fiber: the transfer matrix method, the asymptotic method and the Galerkin method have been introduced.3) Using analysis method and perturbation method, we got the relative sensitivity of hollow Bragg fiber gas sensor, which is about 20 times better than that for the solid core photonic crystal fiber gas sensor. The results show that the field is centralized in the core and sensitive to the gas loss. The advantages of this new type of optical fiber gas sensor are high sensitivity, short response time and simple structure. This gas sensor can measure different kinds of gas with different wavelength laser.