Fabrication Of Grating Type Terminal Filters And Mechanism Of Fs-Laser Induced Fiber Gratings

Optical access network technology is one of the important means of accessing. With the development of fiber Optical access network technology, passive optical network(PON) which has the advantage of less upfront investment,easy maintenance, flexible structure and so on is more and more important. However, the current monitor signal is in the passive optical network communications band, which is not conducive to the transmission of communication signals. The network fails can not be find timely in most cases, which is not conducive to maintaining a good network stability. The optical time domain reflectometry and grating type terminal filters combines the a signal with the wavelength of1650nm can be used by achieved to monitor the all-optical network PON real-time which has the advantage of low-cost. This technology is treated as an important direction of the development of optical access network. But the temperature stability of fiber grating is poor.Bragg wavelength and the intensity modulated of refractive index will be changed at high temperatures, which can affect the reliability of network monitoring systems.In this paper, through the theoretical analysis of FBGs and fabricating the grating type terminal filters with the wavelength of1650nm, the temperature stability of fiber grating was researched. The main work is as follows:(1) The basic theory of fiber gratings are described based on the coupled-mode theory. The different types of gratings, the different writing method, and the performance of chirped grating performance was studied. The characteristics of different fiber gratings were simulated with Matlab.(2) Hydrogen loaded G.657, G.652and non-hydrogen loaded Ps-GeB-125were used to fabricated the FBGs using a KrF excimer laser. The3dB bandwidth of grating type terminal filters is5.4nm and the center wavelength of the grating type terminal filters is1651nm. The grating type terminal filter is suitable for the network monitoring system terminal filter.(3) The influence of the laser pulse energy, spot uniformity and the fiber type on the temperature stability of the grating was analyzed based on large number of experiments. The results obtained show that the temperature stability of gratings can be improved by increasing the photosensitivity of fibers and the laser pulse energy. what’s more, the uniformity of the laser spot also has some influence on the temperature stability of the grating.(4) The mechanism of femtosecond grating was analyzed in view of the good temperature stability of the FBGs fabricated by fs-laser. Because of the restrictions of experimental conditions, we did not fabricate grating type terminal filters by fs-laser in experiments.