Design And Characterization Of High Order Surface Grating DBR Lasers

Semiconductor lasers are widely used in the fields of optical communications,gas detection,medical treatment,national defense and military.To realize the single-mode lasing,Bragg gratings are generally introduced in the epitaxial layer of semicoductor laser.Typical single-mode semiconductor lasers include distributed feedback（DFB）lasers and distributed Bragg reflector（DBR）lasers.Both of these lasers use a buried grating structure and require epitaxial regrowth,which is quite complicated.Therefore,this thessis focuses on high-order surface grating DBR lasers based on vertical coupling.The laser scheme,is regrowth free,can be fabricated with the standard photolithography,and thus has strong potential to realize low-cost high-reliability.By optimizing the structural parameters of the laser,a low-threshold single-mode high-order surface grating DBR laser was designed.In addition,the relative intensity noise（RIN）of the laser was measured and analyzed.The main research contents are:（1）Based on the analysis of Ga Sb semiconductor laser schemes generally used near 2μm,a new laser scheme based on the high-order surface grating DBR laser is developed.The Sadao-Adachi approximate model is used to calculate the refractive index of In Ga As Sb and Al Ga As Sb materials with different compositions,and the epitaxial material structure of the laser is designed.The ridge waveguide width has been set for the fundamental mode using the equivalent refractive index.（2）The scattering matrix method for grating analysis has been introduced and derived in detail.The scattering matrix model has been developed under Matlab.Based on this model,the grating parameters such as the period,etching depth,duty cycle,and length of the surface grating are simulated and optimized,and the optimal high-order surface grating structure with high reflection（～41%）and low loss(0.65cm^-1).Meanwhile,a time-domain traveling wave model is established to simulate the high-order surface grating laser.Based on the analysis of the influence of parameters such as grating structure and laser cavity length on the threshold current and output power of the laser,the 2.3μm single-mode high-order surface grating DBR laser has been designed for gas detection.The designed laser exhibits the threshold current of about 8 m A,the slope efficiency of about 0.14 m W/m A,and the output power of about 13m W at 100 m A.（3）The basic theory and spectral characteristics of the relative intensity noise（RIN）of semiconductor lasers are introduced.A set-up of measurement system is built for RIN test,and its accuracy is verified by comparing it with the commercial setup.Furthermore,the set-up for RIN test is used to characterize the fabricated high-order surface grating DBR lasers.Through detailed measurements,the relative intensity noise characteristics of the laser are analyzed by combining the output power and the side mode suppression ratio of the laser.The RIN of about-141.7 d B/Hz has been obtained experimentally for the laser,with the modulation bandwidth estimated of about 15 GHz.