Nonlinear Distortion Analysis of Directly Modulated ... - 연세대학교

V. SummaryIn analog fiber-optic link, the direct laser modulation method is verysimple and cost-effect. However, the direct laser modulation causes nonlineardistortion, which degrade system performance. In the thesis, the lasernonlinear distortion is analyzed and a new distortion suppression method isproposed.First, the laser nonlinear distortion is investigated by using Volterra seriesexpansion of the laser rate equations. Based on this analytic distortion model,the usual distortion characteristics are observed. Then, as one previouslyreported distortion suppression method, optical injection locking is introduced.This technique has many advantages such as low chirp, narrow linewidth, andnoise reduction besides the distortion suppression by relaxation oscillationfrequency increase. To find the characteristics of optical injection locking, thesystem matrix from the rate equation that contains external light injection isused. From the computer simulation, the validity of nonlinear distortionsuppression by optical injection locking is proved. Moreover, the stablelocking range dependence on laser parameters is observed. It is found that thelarge gain suppression factor and bias current can extend the stable lockingrange, and the large linewidth enhancement factor and differential gain canshrink the stable locking range. The distortion suppression for optical injectionwavelength and power is also analyzed by the injection locked laser frequencyresponse simulation and IMD2 suppression experiment. The results show thatwhen the detuning frequency is small, the relaxation oscillation frequencyincrease is dominant and when large, the damping is grown. When optical56