光电子学第4章(lpl-2014)_图文-课件（PPT-精）.ppt

ii) Gain Guide Cavities (GGC) Stripe Geometry Laser Metal Metal p.213 Active layer Carrier concentration profile z x y Metal Oxide -y y Current density profile Index profile 0 0 0 Gain/loss profile (c) (d) (e) (f) (g) (1) Effects to be considered : Gain guided confinement : gain within stripe width is higher Anti-guided effect : carrier concentration within stripe width is high Leakage loss : confinement effect is weak (2) The disadvantages for GGC higher multi-modes output linewidth larger kink occurred in P-J curve iii) Index Guided Cavities (IGC) Epitaxy longitudinal heterostructure Etching and regrowth lateral heterostructure Two direction confinement by lateral and longitudinal confinement index step Buried heterostructure laser (掩埋异质结激光器) Advantages : Disadvantages : complex fabrication Ⅱ. The Distributed Feedback Lasers (DFB LD 分布反馈器) In F-P cavity stationary wave condition: Can the cavity itself provide mode selection ? Multi-modes output for F-P LD the mode seperation: Periodic grating (周期光栅）is in confinement layer, close to active layer. DFB LD i) Bragg Reflection Bragg reflection equation Here, d is lattice constant is incident angle For DFB LD , d , The output spectrum of DFB LD The output spectrum of F-P LD iii) The advantages of DFB LD Linewidth low； Single mode not only at static state but also at dynamic state. Thermal reliability； Ⅲ. The Distribution Bragg Reflector ( DBR 分布布拉格反射器 ) Periodic reflecting stack is placed outside the active lasing region. Ⅳ. The surface Emitting Laser (面光射 LD) DBR Active Layer DBR Surface Emitting Laser 0.0 0.5 1.0 Wavelength Reflectivity GaAs/As DBR n-contact n-GaAs Substrate GaAs/AlAs DBR Active Region p.224 Typical structure of SEL Advantages: Disadvantages (or difficulties): difficulty to inject charge into the SEL device heating Ⅴ.