| With the rapid development of optical communication,wavelength selective devices are playing an important role in optical communication systems.Tunable filters with excellent wavelength selective characteristics,play an important role in tunable laser,dense wavelength division multiplexing(DWDM),optical sensing etc.The current tunable filters are mainly composed of acousto-optic tunable filters,thermo tunable filters and electro-optic tunable filters.The electro-optic tunable filter with high tuning speed has attracted people's attention.In this paper,tunable filters based on LiNbO3 waveguide gratings are studied and proposed,taking advantage of the excellent electro-optic effect of LiNbO3 and the filtering properties of grating.The details are as follows:1.Single wavelength and multiple wavelength tunable filters are proposed based on the uniform phase shift Bragg gratings on LiNbO3.By using the electro-optic effect of lithium niobate crystal,the tuning of the resonant wavelength is realized by changing the voltages in the filter structure.The effect of applied voltage on the refractive index of LiNbO3 and resonant wavelength are analyzed.Besides,the factors that influence the tuning sensitivity,the number of wavelengths,the extinction ratio of the resonant wavelengths and the amplitude of the wavelengths are discussed.2.On the basis of the above filter structure,a reconfigurable multi-wavelength tunable filter is proposed.Both the number of resonant wavelengths and the wavelength spacing can be reconfigured by an encoding way.The characteristics of the filter with different coding modes are analyzed.3.The filtering characteristics of chirped grating and chirped phase shift grating are analyzed.Tunable filters are proposed based on chirped phase shift gratings on lithium niobate crystal by replacing the uniform Bragg gratings with chirped Bragg gratings in the above filters.The filtering characteristics of the filters are analyzed and discussed. |
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