Theoretical Study Of Long-Period Channel Waveguide Gratings

By comparing with long-period fiber grating(LPFG) in material selection and fabrication technology, and by referencing the-state-of-art of long-period waveguide grating(LPWG), we demonstrate the feasibility and advantages of LPWG over LPFG.To overcome the geometry and material constraints of a fiber, we propose to fabricate a long-period grating(LPG) in/on channel waveguide, so that various kinds of geometric shapes and various kinds of materials can be alternatively used to optimize the performance of the LPG. In this dissertation, we present a theoretical analysis of the general working principle, structure parameters and optical characteristics of long-period channel waveguide grating(LPCWG). Therefore, we firstly introduce the light propagation theory in slab waveguide, establish the theory model of LPCWG, and derive the general expressions for coupling coefficient and transmission coefficient of LPCWG on the basis of coupled-mode theory and phase-matching condition. For analyzing the structure and characteristics of LPCWG, we design its structure model and fabrication process, which Benzo-Cyclobutene (BCB) was selected as channel waveguide material and Polymethylmethacrylate (PMMA) as cladding material. For solving the eigenvalue equation of channel waveguide by Marcatili method, the C programme was produced to determine the mode index, the electromagnetic field distributing of guided mode, and the coupling coefficients of TE–TE mode coupling and TM–TM mode coupling.Through the discussion of the relationship among structure parameters of LPCWG, we obtain single mode condition of channel waveguide and the other effects for LPCWG, determine the structure parameters and optical characteristics. In additional, we mainly analyze the polarization sensitivity of resonance wavelength, and present the polarization insensitive condition. So we can design LPCWG with polarization-insensitive resonance wavelength by selecting given parameter properly.