| With the development of quantum communication,Big Data,Cloud Computing,Internet of Things,distributed feedback(DFB)semiconductor lasers with stable single-mode,narrow-linewidth,and high-accuracy-wavelength characteristic are indispensable.Compared with normal Fabry-Perot diode laser,periodic perturbation of refractive index(namely index-coupled DFB lasers)or gain/loss(namely gain-coupled DFB lasers)are fabricated in the waveguide or active layer to achieve single longitudinal mode.To solve the problem that index-coupled DFB lasers with a uniform refractive index have an inherent problem of lasing two degenerated modes,phase shift gratings,reconstruction-equivalent-chirp(REC)technology or high quality antireflection coating are introduced to obtain single longitudinal mode.Gain-coupled DFB(GC-DFB)lasers based on periodic gain(or loss)could effectively remove mode degeneration to achieve single longitudinal mode.Implementation of gain-coupled gratings require complex technology like epitaxial regrowth technology or electron beam lithography,making no difference with index-coupled DFB lasers and preventing them from widespread practical applications.Here,a regrowth-free gain-coupled-DFB laser based on periodic injection current with only i line lithography technology was proposed.The design,fabrication and test of the gain-coupled DFB lasers based on periodic injection current were all included in our research,1.Based on coupled wave theory and transmission matri,a theoretical model was built to analyze the gain-coupled DFB lasers based on periodic injection current.And commercial software PICS3 D,COMSOL Multiphysics,Matlab were used to calculate the theoretical and numerical transmission spectrum as a function of the wavelength,which could support the analysis,optimization of our devices.2.A single-longitudinal-mode regrowth-free gain-coupled DFB laser based on periodic injection current was demonstrated,fabricated by only low-cost i-line lithography without regrowth and nanoscale lithography.The commercial software PICS3 D was used to calculate the carrier density distribution and gain distribution.And the commercial software Comsol Multiphysics was used to calculate the total loss from the scattering loss and absorption from the surface metal.Hence,the optimized groove length and depth were obtained.Our uncoated devices with 1 mm cavity length could provide stable single longitudinal mode operation with the maximum CW output power up to 48.8 mW/facet at 971.31 nm at 250 mA,linewidth(<3.2 pm)and SMSR(>39 dB).And the SMSR is better3.It provided a novel method for easy DFB lasers fabrication: 4-μm-width periodic surface grooves acting as waveguide ridge were patterned only once by merely i-line lithography,which could simply the process and reduce the fabrication error.The maximum CW power of single facet in single-mode operation was 100.9 mW,with the record power conversion efficiency of 18.6%/facet,the slope efficiency of 0.53 W/A.The linewidth was below 2.84 nm with side mode suppression ratio over 43 dB.4.A single-mode purely gain-coupled distributed feedback laser is presented.It provides a novel practical low-cost method with easy fabrication process to realize single-mode diode lasers.The devices with 4μm ridge width and 2mm cavity length are fabricated based on asymmetric separate confinement heterostructure with two quantum wells.The measured maximum continuous-wave power of single-mode devices is 15.42 mW/facet at 971.97 nm at 200 mA without facet coating.The side-mode suppression ratio is over 30 dB,and the 3 dB spectrum width is less than 40 pm over the whole single-mode operation.5.A two-segment regrowth-free gain-coupled distributed feedback(DFB)laser monolithically integrated different gain contrast segments was proposed,realizing both wavelength-tunable(5nm)and wavelength stabilization characteristics,controlled by a single electrode only.It provides a novel method for low-cost practical gain-coupled DFB laser fabrication,which can be used in either/both wavelength-tunable applications such as sensing and detection,or/and wavelength stabilization fields such as pumping fiber lasers.Due to easy fabrication processing like I-line lithography and stable performance without regrowth or nanoscale gratings fabrication,the gain-coupled DFB lasers based on periodic injection current provides a method to fabricate practical gain-coupled distributed feedback lasers,which meet the requirement of the practical applications for widespread commercial applications like Li DAR,integrated optics and communication. |
