Design Of Fast Tunable Bragg Waveguide Grating Based On LiNbO₃

With the rapid development of optical communication technology, people have higherrequirements for the tunability of the optical devices. The traditional fiber grating with slowtuning has been greatly limited in high-speed optical communication and optical sensing field.However, waveguide grating can not only break through the limitation of structure of the fibergrating, but also has advantages of diversity and versatility of materials, and expand theapplied range of the grating greatly. Currently, tunable waveguide grating has been achievedin polymer, inorganic crystals, semiconductors and other materials. Especially, the tunablewaveguide grating based on electro-optical effect has overcame the drawbacks of slow tuningof fiber gratings, achieved a high tunable speed, and have been able to meet the technologyrequirements of the high capacity optical communications.In this paper, we propose a fast tunable single-mode waveguide Bragg gratings based onX-cut LiNbO3(LN), which enables the resonant wavelength fast tunable in a linear way. Onthis basis, we design a multi-parametric tunable waveguide grating filter, which the resonantwavelength and corresponding phase can be fast tuned independently and the output lightintensity can be controlled also. The details are described as follows:First, we elaborate the EO effect of LN and analyze emphatically the refractive indexdistribution of the APE waveguide, which its dispersion equation is also analyzed. Wedescribe the transfer matrix theory of wrinkle-order Bragg grating in detail, aiming atestablishing the theoretical foundation for the ensuing chapters.Second, we propose the fast tunable waveguide grating filter based on LN, which Braggwavelength can be fast tuned with a high sensitivity. Single-mode waveguide is designed toreduce the coupling loss with single-mode fiber. The distributed feedback coefficient of thegrating is amended theoretically considering the trapezoidal etched profile. The optimalwaveguide grating parameters is also obtained from the simulation analysis of thetransmission spectral characteristics.Third, a novel multi-parameter fast tunable Bragg grating filter is demonstrated, whichBragg wavelength and corresponding phase is tunable in a linear way by applied voltage with15.6pm/V wavelength tuning efficiency and0.2/V phase tuning efficiency. Moreover, thereflective intensity of the filter is controlled from maximum to zero.Fourth, to improve the performance of the intensity control, we present a scheme basedon phase delay device and a scheme based on electro-optic halfwave plate to enhance tuningspeed of the intensity.