Linear Optical Sampling Enabled Ultrafast Laser Characterization And Analysis

Ultrafast lasers are widely used in optical communication,sensing,and industrial processing.Due to the bandwidth constraints of optoelectronic devices,the experimental verifications related to the analysis of ultrafast lasers suffer from accurately accessing its full-field information.The linear optical sampling(LOS)system integrates coherent detection and all-optical sampling theory,it enables ultra-high equivalent sampling rate with low-rate and low-bandwidth optoelectronic devices for the full-field information characterization of ultrafast optical pulses.The LOS is innovatively applied to ultrafast laser characterizations,circumventing the limitations of conventional characterization methods.Combined with nonlinear Fourier transform,LOS system enables ultrafast laser characterization and analysis,which has significant theoretical and practical values.When the operation wavelength range is expanded,the input optical power dynamic range of fiber optical frequency comb(FOFC)based LOS system is limited.In this thesis,we explore sources of characterization error of balance detection and propose the biased balance detection scheme,in order to enhance the dynamic range of input optical power in the FOFC-based LOS system.Next,by precisely tuning the repetition rate difference between the sampling optical pulse and the ultrafast pulse under test,a LOS system with ultra-high equivalent sampling rate has been realized.As a result,the nonlinear frequency spectrum of ultrafast pulses can be accurately assessed.Finally,a LOS-based ultrafast fiber laser operating state monitoring system is developed to realize an accurate acquisition of the full-field information of multiple soliton states simultaneously.The innovative research outcomes are summarized as follows:(1)The constraints between the peak power of the sampling pulse source and the power of signal under test is obtained in the FOFC-based LOS system with unideal balanced photodector(BPD).Theoretical investigations indicate that,the input optical power dynamic range is jointly determined by the peak power of the FOFC and the imbalance ratio of the BPD.Biased balance detection scheme is proposed.By increasing the peak power of the FOFC or the imbalance ratio of the BPD to ensure accurate peak extraction,the extension of the input optical power dynamic range can be achieved.A LOS-based high-speed optical modulation analyzer is developed by using 400 MHz BPD and 4×1.25 GSa/s analog-to-digital converter(ADC).For QPSK signal characterization,when the imbalance ratio of the BPD is enhanced from 1.03 to 1.06,the input optical power dynamic range is enhanced from 0.75 m W to 1.20 m W.Precise characterizations of 32 Gbaud PDM-QPSK are achieved within the wavelength range of 1550-1570 nm.The error vector magnitude deviation is less than 2% compared with that of commercial optical modulation analyzer.(2)By simultaneously monitoring the phase fluctuations of the ultrafast pulse under test and the sampling optical pulse,the sampling error of LOS with high equivalent sampling rate is digitally compensated.Thus,the full-field information of ultrafast optical pulses can be accurately accessed.Two passively mode-locked fiber lasers are experimentally developed to act as the ultrafast fiber laser under test and the sampling pulse source,respectively.By finely tuning the repetition rate difference,a 55.56 TSa/s equivalent sampling rate arising in the LOS system can be secured,where only 400 MHz BPD and 4×5GSa/s ADC are used.Thus,the full-field information of 1.71 ps ultrafast pulse is accurately evaluated,and the concept of soliton distillation has been experimentally verified for the first time,which proves that the LOS system with ultra-high equivalent sampling rate can provide a nonlinear frequency spectrum analysis tool for ultrafast laser.(3)The LOS-based ultrafast fiber laser operating state monitoring system,with an equivalent sampling rate of more than 10 TSa/s and an optical spectral resolution of less than0.01 nm,is developed,where only 400 MHz BPD and 4×10 GSa/s ADC are utilized.An ultrafast fiber laser mode-locked by the carbon nanotube is developed,its operation condition can be reconfigurable to achieve several kinds of ultrafast laser outputs,including standard single soliton,soliton with the energy exchange sideband,tightly bound state soliton molecules,loosely bound state soliton molecules,triple pulses and quadra pulses.Based on biased balance detection scheme,through compressing the spectrum and improving the spectral overlap,the LOS-enabled fiber laser monitoring system can realize multiple functions of commercial autocorrelator,optical spectrum analyzer,and high-speed oscilloscope simultaneously.