Research On Electro-Optic Tunable LiNbO₃ Optical Waveguide F-P Cavity

Fabry-Perot cavity has important research value in optical communication.And in order to meet higher communication needs,tunable F-P cavity is more promising.In terms of manufacture,it can compensate fabrication error.Furthermore,in terms of function,it can be used as a wavelength-selected switch.At present,three methods,i.e.tuning the effective refractive index of material,the length of F-P cavity or the incident wavelength,can be used to realize tunable function of F-P cavity.Taking into account the simple driving control,fast response speed and easy integration,the first method is accepted.In order to realize electro-optical tunable function,F-P cavity need to be fabricated using electro-optical material with larger electro-optical coefficients.Lithium niobate(LiNbO3,LN)crystal is our best choice due to its higher electro-optic coefficient and mature waveguides processing.And LN waveguide has good end-face flatness after being polished,which can form high quality F-P cavity after being plated a certain reflection coefficient of dielectric film.Thus,electro-optical tunable LN waveguide F-P cavity is investigated in this dissertation.The main content of the dissertation include:First,as for the design,the basic structure,the working principle,the output characteristics,and the tuning properties of the proposed electro-optical tunable LN waveguide F-P cavity are analyzed firstly.Then,the single mode transmission condition,which is decided by the diffusion depth and width of the LN waveguide,are investigated.Subsequently,the reflection coefficient of dielectric films is investigated so as to achieve an optimal output spectrum.At last,according to the selected LN wafer and waveguide dimensions,the tuning electrode is designed.Secondly,according to the design parameters,the mask used to fabricate the waveguide and the electrode are designed.Then,the single-mode straight waveguide is fabricated by annealed proton exchange technology.And the tunable electrode is fabricated by using lift-off technology.After coating dielectric films(reflection coefficient is 80%-85%)on both polished ends of the waveguide,electro-optical tunable LN waveguide F-P cavity is fabricated successfully.At last,the performance of the fabricated F-P cavity is characterized.Specific experimental work include:(1)Investigating how to realize a low loss single-mode straight LN waveguide.According to the best experimental parameters concluded,a length of 1.50 cm straight waveguide with the insertion loss of 3.81 dB is fabricated successfully;(2)Fabricating a 1.5-cm length LN waveguide tunable F-P cavity and characterizing its performance.The suppression degree of output spectrum is 3.20 dB and the free spectral range is 0.06 nm.When driving voltage is 10 V,the center wavelength shifted 0.03 nm.