Optical Add Drop Multipleser Based On The Photorefractive Long-Period Waveguide Grating Coupler

Optical add-drop multiplexers (OADMs) act as one of the key network elements in the wavelength-division-multiplexed (WDM) optical networks. The OADM equipped with structures of long-period grating (LPG) has important applications in the new generation of high-speed communication system. It is a key node device to achieve high capacity, high integration and high speed optical network communication. Optical add-drop multiplexers based on photorefractive long-period waveguide gratings (LPWGs) coupler of lithium niobate (LiNbO3) has been researched in this thesis.Firstly, a photorefractive LPWG based on Ti-diffused LiNbO3waveguide is studied. The conditions of obtaining a single-mode waveguide when using the method of twice Ti-diffusion are theoretically analyzed. The mode effective indices of the core and different cladding are calculated by means of effective indices method. Then, we propose a solution by using amplitude mask method to fabricate photorefractive long-period gratings. For the operating mode of TM13, when the resonance wavelength is1553μm, the grating period Λ is74.28μm, and the grating coupling coefficient κ is91.79m-1. Meanwhile, the performance of the LPWGs has been analyzed, we got the minimum grating length of1.71cm and the FWHM is about4.6nm. Besides, we have carried out the work of fabricating waveguide devices on Ti:LiNbO3and preliminary experimental of fiber bonding, which will be the experimental foundation of making long-period grating in the future.Secondly, a photorefractive long-period waveguide gratings coupler based on LiNbO3waveguide is designed. The minimum grating length for100%coupling as2.42cm is obtained at the resonance wavelength of1553nm. For the initial conditions that the composite signal light only incident in a single waveguide, the transmission spectrum for the input waveguide and output waveguide at the place of100%coupling is obtained, the FWHM is about5.2nm and the side lobes are very small. Finally, the actual errors that may happen in the experiment have been discussed; the tolerance of grating length and the offset distance are calculated as0.37cm and0.21cm, respectively. The photorefractive long-period waveguide gratings coupler can be applied in the CWDM system. Finally, the structure and the theory for the optical add-drop multiplexers based on photorefractive LPWGs coupler have also been analyzed. We have made some change based on the structure of the coupler, designed the amplitude-mask, theoretically analyzed the add and drop spectrum, and discussed the influence of evanescent field to coupling efficiency.