Experimental Study of Thermal Decay of Fiber Bragg Grating and its Theoretical Modeling of Arrhenius Analysis

点击翻译按钮获取中文摘要

Optical spectrum of fiber Bragg grating (FBG) produced from hydrogen-loaded optical fiber is well known to evolve over a wide range after its fabrication by exposing to UV laser, that is, thermal decay. The purposes of this research are (1) to stabilize the optical spectrum by annealing thermal treatment so that the wavelength and reflectivity of the FBG do not vary at all, and (2) to understand the physics reason of the thermal decay. We have achieved following three major results.(1)We have proved that the evolution of short-period FBG wavelength after its fabrication is dominantly defined by out-diffusion of hydrogen molecules from the optical fiber. Quantitative agreement has been obtained with theoretical calculation of hydrogen diffusion in silica glass of the optical fiber.(2)In long-period FBG, the wavelength goes through a large upswing ranging over several tens to 100 nm and transmission minimum becomes deeper after its fabrication. Using theory of hydrogen diffusion and comp … More uter FBG simulation, we have revealed that the spectrum evolution is caused by quenching and re-filling of the hydrogen in the fiber core. The hydrogen in the core is dissociated by UV irradiation into atoms, and some H-atoms react with doped Ge in the fiber core forming Ge-OH bond and others return back to molecules by simple recombination, that is, the hydrogen is depleted in the fiber core, i.e. quenching. Then the surrounding cladding of the fiber supplies hydrogen to the core, i.e. re-filling. We have demonstrated that the spectrum evolution can be all explained by the quenching and re-filling.(3)Erdogan's theory has been extensively used for the analysis of thermal decay process of the short-period FBGs. To the best of our knowledge, no attempt has ever been made to apply the theory to long-period FBGs. Using the above result about the spectrum evolution by hydrogen quenching and re-filling, we have succeeded in applying the Erdgan's theory to long-period FBGs.We have published the first result to Journal of Lightwave Technology, and we have completed submitting our second result to Applied Optics. For the third result, we plan to publish soon. Less