Research On Phase-shifted Fiber Grating Based D-shape Polymer Electro-Optic Modulator

With the rapid development of information and the dramatic expansion of customers’ services demand, the high-speed optical fiber communication technology has become widely accepted, which makes the optical modulator also face higher requirements as one of the key components of fiber-optic communication systems. As a more potential organic nonlinear optical materials in terms of modulator fabrication, the organic electro-optic polymer material draws more attention. Electro-optic modulator has become one of the research hotspots of optical fiber communication systems and integrated optical systems, as one of the most effective externally modulated laser devices.In this paper, combining the phase-shift fiber Bragg grating with the extremely narrow transmission peak and organic electro-optic polymer materials, the phase-shift fiber Bragg grating based D-shape polymer electro-optic modulator (EOM) is designed and the theoretical analysis is given. We mainly studied the design of the waveguide structure of D-shape electro-optical modulator and optimization of phase-shifted fiber grating parameters. The main research contents are listed as follows:1. Based on the transfer matrix method for uniform fiber Bragg grating, phase shifted grating transfer matrix is derived. Furthermore, a detailed derivation for V-I transmission matrix of phase-shifted fiber grating is given, and the expression of reflectance and transmittance are obtained. Since the matrix in material interface by V-I method is the unit matrix which can be omitted, so the calculation process is easier and faster than the traditional transfer matrix method.2. Introduce electro-optic effect of EO polymer for two multi-cladding waveguide structures, including circularly symmetric structure and D-shape structure. The influence of structure parameters and organic electro-optic polymer materials on the effective index of PSFG is mainly investigated, including the distance of the polymer to the fiber core, the polymer thickness, the polymer refractive index. The results show that D-type multi-cladding waveguide structure can produce larger change of effective refractive index at a smaller voltage, which means it is easy to achieve high-speed signal modulation with relatively low driving voltage.3. Propose a Phase-shifted fiber grating based on the D-shape polymer electro-optic modulator and study the spectrum characteristics of the modulator with different shifted phases, phase positions and the refractive index modulation depths. The influence of grating length in modulation area and high-frequency modulation voltage on the spectrum is analyzed. Our research indicates, when the π phase shift is introduced in the middle of the fiber grating and larger refractive index modulation depth is given, the modulator can have a good modulation effect.