Photorefractive long-period waveguide grating filter in lithium niobate strip waveguide

To fabricate a long-period waveguide grating (LPWG) filter in a simple, reliable and low-cost way, a novel LPWG scheme based on photorefractive grating is designed and theoretically analyzed in a Ti-diffused strip waveguide embedded in a Ti-diffused planar LiNbO3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {LiNbO}_{3}$$\end{document} waveguide. By means of effective index method and coupled-mode theory, the processing conditions of the planar and the strip waveguide have been calculated. The minimum 100 % filtering length L=1.40\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$L=1.40$$\end{document} cm and the coupling coefficient κ=112.23m-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\kappa =112.23\,\hbox {m}^{-1}$$\end{document} are obtained. The photorefractive LPWG filter can be used in coarse wavelength division multiplexing system.