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1 Sources and detectors of light 1)Revision: semiconductors 2)Light emitting diodes (LED) 3)Lasers 4)Photodiodes for integrated optics and optical communications
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2 1) Revision: Energy band diagrams for metal… Metals characteristically have partially filled energy bands.
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3 … and semiconductor
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4 Generation of electron-hole pair
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5 Semiconductor statistics DOSFD area = area = p
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6 n-type semiconductor
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7 p-type semiconductor
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8 Intrinsic, n-type, and p-type semiconductor
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9 Degenerate semiconductor heavily doped n-type semiconductor donors form a band that overlaps the CB heavily doped p-type semiconductor
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10 E-k diagram band diagramE-k diagram
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11 Direct and indirect bandgap
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12 pn junction
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13 pn junction open circuitforward bias V 0
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14 2) Light emitting diodes (LED)
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15 Surface emitting LED
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16 How to get the light out?
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17 External and internal quantum efficiency Task: Estimate the external quantum efficiency of GaAs LED.
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18 Double heterostructure LED two junctions between materials with different bangaps
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19 LED materials direct bangap
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20 LED materials
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21 LED materials
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22 LED characteristics
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23 LED characteristics
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24 surface emitting LED (SLED) Edge-emitting LED (ELED) Double- heterosturuture light - LEDs are preferred for short haul applications - more economical - wider output spectrum, i.e. not suitable for wide bandwidth systems LEDs for optical fiber communications
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25 Coupling the radiation from a SLED into an fiber
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26 DH ELED
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27 Coupling the radiation from a ELED into an fiber
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28 3) Lasers - population inversion - optical feedback (optical cavity)
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29 Stimulated emission absorptionspontaneous emission Stimulated emission The emitted photon has the same energy, polarization, direction and phase as the incoming photon.
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30 Population inversion 1. (optical) pumping 2. rapid decay to the long-lived (metastable) state 3. population inversion4. Stimulated emission
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31 Stimulated emission: Optical amplifiers E.g.: Erbium doped fiber amplifier (EDFA)
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32 Erbium doped fiber amplifier (EDFA)
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33 Semiconductor optical amplifier (SOA) Fabry-Perot Traveling wave
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35 population inversion Laser diode (LD)
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36 DOS for electrons a holes in SCL under forward bias
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37 cleaved surface = mirror Optical feedback
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38 Laser oscillation conditions
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39 Laser oscillation conditions FP cavity must be the same in the steady state phase condition amplitude condition = = threshold condition
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40 stimulated emission spontaneous emission Optical power diode current
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41 Principle of a double heterostructure LD
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42 Example: DH stripe contact LD
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43 Example: A buried DH LD
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44 LD characteristics
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48 LDs for optical fiber communications
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50 DBR Laser
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51 Distributed feedback (DFB) laser
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52 Distributed feedback (DFB) laser
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53 Distributed feedback (DFB) laser
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54 Cleaved-coupled-cavity (C 3 ) laser
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55 Tunable lasers
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56 Quantum well devices
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57 Single quantum well (SQW)
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58 Multiple quantum well (MQW)
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59 Vertical cavity surface emitting laser (VCSEL)
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60 Vertical cavity surface emitting laser (VCSEL)
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61 Vertical cavity surface emitting laser (VCSEL)
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62 4) Photodiodes
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67 Absorption in direct and indirect semiconductor
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68 Responsivity
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69 p-i-n photodiode
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70 Avalanche photodiode electrode
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