chapter 6

chapter 6 - Click to edit Master subtitle style 5/13/10 THE...

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Unformatted text preview: Click to edit Master subtitle style 5/13/10 THE FIBER FORUM JOSEPH C. PALAIS PRESENTED BY 5/13/10 Joseph C. Palais 6.1 22 Chapter 6 Optical Sources and Amplifiers 5/13/10 Joseph C. Palais 6.1 33 Section 6.1 Light-Emitting Diodes An LED is a pn junction semiconductor. It emits light in the infrared or visible spectrum when forward biased. p n LED i V + - 5/13/10 Joseph C. Palais 6.1 44 LIGHT EMITTING DIODES p n Energy Level Diagram for V = 0 (zero bias) Wg Conduction Band Valence Band- - - - - - - + + + + + + Hole Energy Electron Energy 5/13/10 Joseph C. Palais 6.1 55 P N Energy Level Diagram for V > 0 (forward bias) Wg Conduction Band Valence Band- - - - - - - - - - - - -- - - - - - - - - - + + + + + + + + + + + + Hole Energy hf = Wg Electron Energy Wg = bandgap energy Its value depends on the semiconductor used. LIGHT EMITTING DIODES 5/13/10 Joseph C. Palais 6.1 66 The re le ase d e ne rgy t a ke s t he form of a phot on.-19-34 1 1.6 10 , 6.626 10 eV J h J s = = ( 6 .1 ) hf W g 2245 g W c h = c h W g = LIGHT EMITTING DIODES Now Wg is in joules and is in meters 5/13/10 Joseph C. Palais 6.1 77 Suppose W g is give n in e V. Com put e t he out put w ave le ngt h. 1.24 g W = ( 6 .2 ) w it h W g in e V and in m . LIGHT EMITTING DIODES 34 8 19 6.626 10 (3 10 ) ( ) 1.6 10 g g hc W W eV -- = = 6 1.24 10 ( ) g m W eV - = 5/13/10 Joseph C. Palais 6.1 88 Material ( m) Wg (eV) GaAs 0.9 1.4 AlGaAs 0.8 - 0.9 1.4 - 1.55 InGaAs 1.0 - 1.3 0.95 - 1.24 InGaAsP 0.9 - 1.7 0.73 - 1.35 GaInP 0.64 - 0.68 1.82 - 1.94 Com m on Charact e rist ics LIGHT EMITTING DIODES Click to edit Master subtitle style 5/13/10 THE FIBER FORUM JOSEPH C. PALAIS PRESENTED BY 5/13/10 Joseph C. Palais 6.2 1010 Section 6.2 LED Operating Characteristics 5 Output Power (mW) Input Current (mA) Linear Region Nonlinear Region There is no output power for reverse bias (negative current). 100 5/13/10 Joseph C. Palais 6.2 1111 Section 6.2 LED Operating Characteristics Ideally, optical power increases linearly with input current. This is approximately true over what is labeled the linear region on the preceding graph. 5/13/10 Joseph C. Palais 6.2 1212 Proof: Le t i = curre nt ( coulom bs/se cond) N = num be r of charge s pe r se cond e nt e ring t he junct ion. The n ( / ) i N electron s e = LED OPERATING CHARACTERISTICS ( / ) ( / ) i Coulombs s N e Coulombs electron = 5/13/10 Joseph C. Palais 6.2 1313 If a fract ion & of t he se cha rge s re com bine t o e m it phot ons, t he out put pow e r is = e i W P g LED OPERATING CHARACTERISTICS = = ion recombinat energy s ions recombinat W N P g ) ( s energy NW P g / = (6.3) 5/13/10 Joseph C. Palais 6.2 1414 If Wg is in eV, this simplifies to i W g = P w he re W g is in e V and P is in W at t s. Thus, t he line ar de pe nde nce is prove n....
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chapter 6 - Click to edit Master subtitle style 5/13/10 THE...

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