华中科大光纤通信Chapter 4 Optical Receivers (including Chapter 5).ppt

OE, HUST Chapter 4 Optical receivers Basic Concept Common Photodetectors Receiver Design Receiver Noise Receiver Sensitivity Sensitivity Degradation Configuration Requirements high sensitivity fast response low noise low cost high reliability Simulation 4.1 Basic Concepts 4.1.1 Detector Responsivity Stimulated absorption: photon an electron-hole pair Photon current: , R: responsivity Quantum efficiency: 4.1.2 Rise time and Bandwidth Chapter 4 Optical receivers Basic Concept Common Photodetectors Receiver Design Receiver Noise Receiver Sensitivity Sensitivity Degradation 4.2 Common photodetectors 4.2.1 p-n photodiodes a reverse biased p-n junction 4.2.2 p-i-n photodiodes i-layer → high resistance → large electric field → the depletion region throughout it → drift component dominates over the diffusion component → Double-heterostructure design 4.2.3 Avalanche Photodiodes Basic concepts Impact ionization: an accelerating electron can acquire sufficient energy to generate a new electron-hole pair. a photon a single primary electron many secondary electrons holes i-layer: absorption p-layer: multiplication through impact ionization impact-ionization coefficients: ( : electrons; : holes ) depend on material and on the electric field. Multiplication factor the current flow within multiplication layer assuming that: , the electric field across the gain region is uniform ( are constants), only electrons cross the boundary to enter the n-region. Avalanche process: intrinsically noisy, gain factor fluctuates around an average value. Responsivity Bandwidth APD structures Reach-through APD SAM-APD (Separate Absorption Multiplication) SAGM-APD (Separate Absorption Grading Multiplication)