ece228 lecture 12

ece228 lecture 12 - Bowers ECE 228A Laser Design Lecture...

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Bowers ECE 228A Laser Design Lecture #12 John Bowers ECE 228A Read Chapter 3 No class on Thursday. ake up Friday May 21 Make up Friday, May 21
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Bowers ECE 228A Project Model a directly modulated fiber optic transmission system – Assume square wave modulation at 10 GHz – Use the rate equations to calculate the light amplitude and phase input to e fiber the fiber. – Include the fiber dispersion and Kerr effect. – Assume a PIN photodetector. Calculate the capacitance and transit time response. – Calculate the received eye diagram for zero bias and bias at threshold. – Add appropriate dispersion compensation (what is it?) and recalculate the eye diagram. – Assumptions: Laser: 5 quantum well laser with InGaAs quantum wells, clad with 1.3 m bandgap InGaAsP. For a quantum well thickness of 10 nm, with 10 nm barriers, calculate the lasing wavelength (ignore coupling between the wells (i.e. assume infinitely thick barriers). For a separate confinement layer thickness of 50 nm on each side of the 5 quantum well active region, calculate the transverse confinement factor (assuming infinitely wide active region). For a 2 mm wide stripe, calculate the total confinement factor assuming InP cladding and using the effective index calculation. Calculate the mirror loss, total loss, threshold gain, threshold carrier density, threshold current, quantum efficiency, and slope efficiency for the five quantum well InGaAsP laser with internal quantum efficiency 0.8, 500 m length, 95% and 30% power reflectivity facets, internal loss 10 cm-1, material lifetime 1 ns, material gain: g(N)=2000 cm-1 ln (N/2x1018 cm-3). Fiber: SMF-28 (dispersion zero at 1310 nm) 100 km long Photodetector: InGaAs PIN with 1 m intrinsic layer thickness. Area: 200 m 2 . Series resistance: 5 W.
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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 Lasers of width below 1.5 micron tend to lase single
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ece228 lecture 12 - Bowers ECE 228A Laser Design Lecture...

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