Modeling And Numerical Research On Narrow-linewidth Semiconductor Lasers

Along with the development and application of optical communications and solid-state lidars,narrow-linewidth semiconductor lasers play an important role for their performance of low frequency noise and high-speed modulation.As an ideal optical source,narrow-linewidth lasers have compact footprint,low power assumption and long lifetime.The laser techniques for narrow-linewidth contain intracavity feedback technique and external cavity feedback technique.The intracavity technique focus on the optimization of distributed feedback lasers(DFB).And the external technique mainly includes the external cavity lasers with individual components and distributed feedback reflector lasers.This thesis proposes numerical research on the design,optimization and simulation of narrow-linewidth semiconductor lasers,and the device performance and physical process can be effectively analyzed by the self-consistent model.The narrower linewidth can be obtained by using the proposed model.The main contents are as follows:(1)Design of distributed feedback laser based on Moire grating.We discuss the narrow linewidth by suppressing the longitudinal spectral hole burning(LSHB).A distributed feedback laser based on Moire grating(DFM)is simulated by our proposed model.We analysis the structural parameters of Moire grating and coupling strength for suppressing the LSHB effects.The strong coupling coefficients generate serious LSHB and broaden the spectral linewidth.The longer cavity length can improve the linewidth.The simulation result shows that the DFM with κL=2.5,L=250 μm has 342.3 kHz spectral linewidth and 25 Gb/s large signal modulation speed compared with 574 kHz of DFB.The DFM with L=400 μm can reduce the linewidth to 199 kHz for effectively suppressing the LSHB.(2)Design of distributed feedback laser based on apodized laterally coupled grating(AG-DFB).We derive a physical model using transfer matrix and traveling wave equations.The LSHB can be suppressed by using the specific distributed coupling coefficients(κ)along with the laser cavity.We analyze the LSHB impact on spectral linewidth in different conditions of cavity length and coated facet.The parameters of κ profile are optimized by the model,such as the linear changing range and apodized length.The apodized grating width and etching depth are calculated by solving the effective index of guide mode in cross-section.The simulation result shows that the AG-DFB with L=400 μm has a 248 kHz linewidth and 30 Gb/s modulation speed,and the device with L=1mm has a 99.2 kHz linewidth.(3)III-V/Si external cavity lasers with narrow-linewidth and self-pulsing.Firstly.we present a narrow-linewidth tunable laser based on external cavity.The external cavity lasers can realize narrower linewidth according to the relation Δv∝1/L3 for large effective cavity length.We realize single mode and tunable wavelength based on vernier and thermo-optic effect of a dual-ring resonator.The device properties are simulated by the traveling wave model with digital filter such as L-I curve,spectral linewidth and tunable spectrum.The simulation result shows that the tunable range is 11nm and the spectral linewidth is 62.3 kHz.The thickness of bonding layer and alignment accuracy of III-V/Si taper is analyzed in simulation.In addition,we design a self-pulsing laser where the graphene assisted microring can generate the pulse-train for the strong nonlinear effects and saturable absorption(SA).The partly transmission element is formed by inducing air-holes in the coupling region of microring and bus-waveguide,in order to achieve the Fano interference.A III-V/Si integration is adhesively bonded by polymer.We optimize the radius and number of air-holes to enhance the Fano resonance and use the rate equations to evaluate the laser performance,such as photon distribution,carrier distribution,spectrum and pulse-trains.The repetition rate increases from 1 GHz to 3.12 GHz as the injection current from 12 mA to 20 mA.In summary,the innovation of this thesis is followed as:Firstly,we propose an improved 1D transfer matrix and traveling wave method for simulation of many complex structures of distributed feedback lasers.The structure contains the complex refractive index of Bragg grating,distributed coupling coefficients,HR-AR uniform grating DFB,AR-AR λ/4 phase-shift grating DFB.The lasing property can be calculated including 1D photon/carrier distribution,light-current curve(L-I),lasing spectrum,spectral linewidth,small signal response and large signal modulation,et al.The method playsan important role in opto-electronic design.Next,we present and optimize two novel distributed feedback lasers based on moire-grating and apodized laterally coupled grating using the proposed method.The structures enable to effectively suppress the serious LSHB,in order to realize the narrow spectral linewidth and high-speed modulation.These designs can meet the strict requirement in the optical transmission systems and lidars.Finally,we design an external cavity tunable laser with narrow-linewidth and a self-pulsing laser based on III-V/Si integration.The tunable narrow-linewidth laser can be optimized by the proposed traveling wave model based on digital filter.In the optimization of self-pulsing laser,a dynamic model is used to describe the waveguide-resonator coupling,and a multi-parameter fitting method is proposed for the physical model.