Research On Optical Signal Processing Key Devices Based On The Nonlinear Effect Of Lithium Niobate Thin Film

Nonlinear optics is an important branch of modern optics,which can be applied in the fields of optical logic gate,optical interconnection,frequency conversion and wave（time）division multiplexing,etc.It has promoted the development of all-optical network communication and optical information computing and processing technology.With the research of photonic integrated circuit technology,the performance of nonlinear optical devices on chip is also improving,which can be integrated with other optical devices such as modulators and semiconductor lasers to realize the multifunctional structure of single chip.Lithium niobate（LN）is an excellent second-order nonlinear optical material with a wide transparent band and low absorption loss.In addition,driven by the marketization of lithium niobate thin film（LNTF）materials,it makes up for the defects of large device size and high power consumption caused by small relative refractive index difference of traditional LN bulk materials,and further promotes the development of micro nonlinear optical integrated chips.More and more nonlinear research on LN bulk materials have been transferred to LNTF materials and have shown better performance.In this thesis,the nonlinear optical devices are designed and studied for the LNTF materials’second order optical nonlinear effects.The main work of this thesis is as follows:1.The periodic polarization structure of x-cut LNOI ridge waveguide with thickness of 600 nm is studied.The effects of structural parameters such as etching depths and ridge widths on the nonlinear conversion efficiencies and poling periods are analyzed.When the waveguide section is small,the normalized conversion efficiency can reach 5558%W^-1cm^-2.A multi-channel band-stop filter based on the sum frequency generation effect is proposed and this filter functions of channel number reconfiguration,center frequency tuning and transmission equalization are realized by simulation.The minimum transmittance is-29.94 dB and the difference of transmittance after equalization is less than 0.1 dB.2.The optical parametric amplification processes of the difference frequency generation effect and the cascaded second-harmonic generation and difference frequency generation effect are investigated on the designed periodically poled lithium niobate（PPLN）waveguide,respectively.The effects of pump wavelength,waveguide structure,incident power and phase on the gain performance of each amplification process are analyzed.Finally,the typical characteristics of the above amplification processes,such as power variation over transmission length,gain limit and noise figure,are compared and analyzed.Due to the presence of constructive interference,the gain difference between phase sensitive and phase insensitive gain can reach 6 dB.3.Based on the different types of second-order optical nonlinear effects and the corresponding energy flow characteristics of LN materials,an optical parametric amplifier with polarization isolation using the difference frequency generation effect is designed.Utilizing the birefringence characteristics of LN materials and the quasi-phase matching techniques of different polarized lights,the optical parametric amplification process with high polarization isolation can be realized on a single PPLN waveguide by selecting the appropriate pump wavelengths and poling periods.The polarization isolation degree can be improved to the maximum extent,up to 30 dB,through the scheme of attenuation signal light by the sum frequency generation effect.