Research On Nyquist Pulse Generation Based On Modulation

Sinc-type Nyquist pulse theoretically has the narrowest spectral width,and its spectral shape is close to rectangular,allowing data to be encoded with the smallest spectral width.While increasing the spectrum utilization rate,it also increases the channel capacity.There are important applications in WDM systems.In addition,Nyquist pulse can improve optical analog-todigital converters and optical filters because they can achieve ideal impulse signals.There are many experimental schemes for generating Nyquist pulse.One of the main methods is to use its spectral characteristics to generate a nearly rectangular optical frequency comb through an electro-optic modulator and the Nyquist pulse is mapped to the time domain.This thesis first studies a single Mach-Zehnder modulator,cascading two Mach-Zehnder modulators,a single dual parallel Mach-Zehnder modulator,cascading Mach-Zehnder modulator and dual parallel MachZehnder modulator solutions respectively to generate 3-line,9-line,5-line and 15-line optical frequency combs and corresponding Nyquist pulse.For different modulators,this article conducted modeling and simulation analysis.Based on the traditional cascaded two MZM modulator schemes,a frequency-doubled Nyquist pulse generation scheme based on modulator suppression of odd sidebands is proposed.The spacing and spectral width of the optical comb are doubled.The repetition rate of the pulse and the width of the pulse are also doubled,greatly improving the utilization of the RF signal.Based on the cascaded MZM modulator,this thesis proposes a flexible Nyquist pulse generation scheme based on multi-wavelength light source.The delay amount of different wavelengths of light is different through the dispersion compensation fiber.The second and third frequencies of the Nyquist pulse are generated.At the same time,a Nyquist pulse sequence with a rectangular and zigzag envelope is generated,which provides a solution towards high repetition rate and specific envelope shape for the generation of Nyquist pulse.Finally,the contents of the research are summarized,and our prospects for the research work after the Nyquist pulse is generated.