Research On Optical Arbitrary Waveform Generation (OAWG) Based On Tunable Lithium Niobate Waveguide Grating

Optical Arbitrary Waveform Generation（OAWG）can realize arbitrary waveform specified by users and overcome electronics bottleneck.Ability to generate large-bandwidth,arbitrarily shaped waveforms in optical serve many applications,among which are bandwidth-efficient telecommunications,parallel signal processing and pattern recognition,remote sensing.In recent years,the real and dynamic OAWG system has drawn many scholars’ attention.In this paper,we design a simple waveform generation device-second order differentiator based on long period waveguide grating（LPWG）according to electro-optic effect of LiNbO₃ and combining transfer matrix method.Two kinds of optical arbitrary waveform generators based on tunable waveguide gratings array are proposed according to pulse shaping based on Fourier synthesis and electro-optic effect of LiNbO₃.The three waveform generators are based on x-cut lithium niobate（LiNbO₃）.The main work in this thesis includes the following parts:（1）The research backgrounds of OAWG and tunable waveguide grating,several basic methods of OAWG are introduced.The characteristics of LiNbO₃,two analysis methods of waveguide grating based on LiNbO₃ and principle of pulse shaping based on Fourier synthesis are introduced in detail.（2）A second-order differentiator based on LPWG is designed.The feasibility of the second-order differentiator based on the long-period waveguide grating is verified using the transfer matrix method and MATLAB.The influence of various parameters on the structure was analyzed.（3）Optical arbitrary waveform generation based on two arrays of tunable apodized waveguide Bragg gratings（WBGs）is proposed.Due to the electro-optic effect of LiNbO₃,the central wavelength of each grating in the two gratings arrays can be tuned by the voltages added on gratings to match wavelengths of the input light source.The amplitude and phase of the input light source can be controlled by the voltages added on waveguides.Optical pulses with different waveforms,such as rectangular and Gaussian optical pulses with different periods,are obtained;Because of tunability of the grating array,the voltages can also compensate for the amplitude,phase distortion of output waveform and distortion of central wavelength of each grating;Finally the distortions of the output waveform caused by the voltage variations on the waveguides and the gratings in the two gratings arrays are analyzed.And the tolerable range of voltage variation is obtained,in which the distortion of the output waveform is small.（4）Optical arbitrary waveform generation based on an array of tunable apodized WBGs is proposed.The properties of OAWG are analyzed using transfer matrix method.Due tothe electro-optic effect of LiNbO₃,amplitude and phase of incident light source are controlled via adjusting voltages on gratings and waveguides.Consequently,optical pulses with different waveforms are generated,such as Gaussian pulses with different delays,triangular waveform and Gaussian pulses with different amplitudes;The amplitude of output waveform can also be linearly controlled by adjusting voltage array added on gratings proportionally;In addition,voltages can compensate for amplitude and phase distortion;Furthermore,the effect of voltage variations on waveform generation is discussed.And the tolerable range of voltage variation is obtained,in which the distortion of the output waveform is small.