A Study Of Multi-channel Filter Based On Long Period Grating In Ti:LiNbO₃ Waveguide

Lithium niobate?LiNbO₃?crystal has become an ideal integrated platform for fabricating optical filters due to its excellent electro-optic and acousto-optic effects.Heretofore,a variety of applications based on a single mode Ti:LiNbO₃ waveguide have been reported.However,up to now,there has been seldom reported research on the application of a tunable multiwavelength filter based on multi-mode Ti:LiNbO₃,which has a promising prospect in the application of WDM system due to its strong filtering flexibility.Therefore,this study preliminarily explores the influence of temperature on the mode distribution of long-period gratings,and demonstrate a novel tunable multi-wavelength filter based on Ti:LiNbO₃ long-period waveguide grating,and lays a foundation for further research on multi-wavelength filters based on LiNbO3 waveguides.The main work and results accomplished:1.Fabricating a special structure of optical waveguide in the lithium niobate crystal by using the method of twice Ti-diffusion.And the buffer layer and the interdigital electrode with a specific period were prepared on the surface of the waveguide to complete the preparation of LPWG.Furthermore,two air-hole-type triangular-lattice photonic crystals?PhCs?cascaded in a Ti-diffused LiNbO₃ strip waveguide was also fabricated by FIB.2.Using a M-Z interference system to explore the effects of the composition on the electro-optic coefficient?_{3 3}and?₁₃of LiNbO₃ with a space electric field or a internal electric field of aluminum electrode.It was found that the EO coefficient decreased with the increase of the composition and reached the lowest when the Li₂O content was 49.5 mol%.3.The optical test system is constructed to characterize the photonic crystals and LPWG.The results of the photonic crystals are consistent with the theoretical values;and the data of LPWG band resistance under different driving voltage are as follows:?1?When the driving voltage is increased from 0V to 336V,the center wavelength of the LPWG??=675?m?we fabricated linear shifts to the longer wavelength about180nm due to the effect of photorefractive;?2?The contrast of the rejection band increases linearly with the driving voltage,and reached the maximum when the applied voltage is 303V?³0 dB?.However,if the driving voltage continues to increase,the band resistance of the resonant peak will decrease due to the over-coupling effect.4.A novel multi-wavelength filter based on Ti-diffused LiNbO₃ waveguide is designed by exploring the effects of local heating on long period gratings.The normalized transmission spectra for the TE polarization measured at 115V driving voltages but different device temperatures were given by an optical spectrum analyzer,three resonant peaks is clearly presented at 24.1?which is caused by the expected mode conversion,and the near-field images of the output light was also captured with an infrared camera to confirm the reason.The center wavelength of the three resonant peaks is almost constant and the contrast can be tuned linearly by 21dB with a temperature increases from 24.1?to 44.5?.Moreover,the center wavelengths of the three resonant peaks all drift to the right,and the center wavelength can be tuned over the O+E-band with a driving voltages control of 186V.