ece228 lecture 11 [Compatibility Mode]

ece228 lecture 11 [Compatibility Mode] - Bowers ECE 228A...

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Bowers ECE 228A Laser Design Lecture #11 John Bowers ECE 228A Read Chapter 3
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Bowers ECE 228A Semiconductor Optical Source Basics Current injection Semiconductor p- junction n junction Light generation aser ED No Optical Feedback Optical Feedback Laser LED
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Bowers ECE 228A Semiconductor Lasers • Laser = Gain medium + optical cavity asing occurs with population inversion or when gain Lasing occurs with population inversion or when gain exceeds losses x : Double Heterostructure laser Ex : Double Heterostructure laser I bias Light Contact layer p-InP Cleaved facets Light n-InGaAsP N-InP
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Bowers ECE 228A Optical and quantum confinement A heterostructure is a p-n junction between materials with dissimilar andgaps bandgaps Used to confine: Carriers (efficiency) and Photons (waveguide) ergy P-type N-type ectron En e Injected electrons ------ +++++++ El Injected holes ex Optical Mode Optical gain active Ind n Optical waveguiding Refr a 1 n 2 n 2
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Bowers ECE 228A Solve Wave Equation for Symmetric Guide ] ) , , ( Re[ ) , , , ( e z y x E t z y x e t i 2 2 2 2 0 0  E k E E E where / c n k 0 0 / 1 c 0 0 n
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Bowers ECE 228A Symmetric 3 Layer Guide Solve wave equation Sinusoidal solutions and exponential solution Match boundary conditions at interface pply boundary condition at infinity Apply boundary condition at infinity 2 2 2 2 n k k n 1 2 2 2 2 2 0 x n 2 d 1 0 n k n 1 2 tan d k k x x
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Bowers ECE 228A Symmetric 3 Layer Guide Solve wave equation Sinusoidal solutions and exponential solution Match boundary conditions at interface pply boundary condition at infinity Apply boundary condition at infinity 2 2 2 2 n k k n 1 2 2 2 2 2 0 x n 2 d 1 0 n k n 1 2 tan d k k x x
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Bowers ECE 228A Symmetric 3 Layer Guide n 1 Plot graphically 2 2 2 2 2 2 2 2 0 2 x n k k n 2 n 1 d 1 0 tan x d k k n k   2 2 2 2 ) ( tan 2 x x k n n k d k k 1 2 0 2 x x k x d/2 
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Bowers ECE 228A Symmetric 3 Layer Guide n 1 Asymmetric solutions 2 2 2 2 2 2 2 2 0 2 x n k n k k n 2 n 1 d 1 0 cot x x d k k 2 2 1 2 2 2 0 ) ( cot 2 x x x k n n k d k k ) ( 2 1 2 2 2 0 2 n n k d k x d/2  Single mode condition
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Bowers ECE 228A Lateral mode calculation Effective Index Method 1. Do transverse calculation (y) – Neglect variation in lateral direction(x) – Calculate effective index n in each region 2. Do lateral calculation 1.Neglect variation in transverse direction(y) 2.Calculate effective index of mode. This method is reasonably accurate when 1.The width is much larger than the thickness ateral>transverse) (lateral>transverse) 2.The lateral confinement is relatively weak.
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Bowers ECE 228A Modes • Transverse (vertical) – Virtually all lasers have single transverse mode; simple to obtain, only requires ability to grow thin layers (0.2 micron—not all that thin) • Lateral modes – Most laser waveguides sustain multiple lateral modes (1 to 2 micron is above the single mode limit) asers of width below 1.5 micron tend to lase single
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This note was uploaded on 05/20/2010 for the course ECE ece228 taught by Professor Johnbowers during the Spring '10 term at UCSB.

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ece228 lecture 11 [Compatibility Mode] - Bowers ECE 228A...

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