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Sources and detectors of light

Sources and detectors of light. Revision: semiconductors Light emitting diodes (LED) Lasers Photodiodes. for integrated optics and optical communications. 1) Revision: Energy band diagrams for metal…. Metals characteristically have partially filled energy bands. … and semiconductor.

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Sources and detectors of light

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  1. Sources and detectors of light • Revision: semiconductors • Light emitting diodes (LED) • Lasers • Photodiodes for integrated optics and optical communications

  2. 1) Revision: Energy band diagrams for metal… Metals characteristically have partially filled energy bands.

  3. … and semiconductor

  4. Generation of electron-hole pair

  5. Semiconductor statistics area = area = p DOS FD

  6. n-type semiconductor

  7. p-type semiconductor

  8. Intrinsic, n-type, and p-type semiconductor

  9. Degenerate semiconductor heavily doped n-type semiconductor heavily doped p-type semiconductor donorsform a band that overlaps the CB

  10. E-k diagram E-k diagram band diagram

  11. Direct and indirect bandgap

  12. pn junction

  13. pn junction open circuit forward bias V0

  14. 2) Light emitting diodes (LED)

  15. Surface emitting LED

  16. How to get the light out?

  17. External and internal quantum efficiency Task: Estimate the external quantum efficiency of GaAs LED.

  18. Double heterostructure LED two junctions between materials with different bangaps

  19. LED materials direct bangap

  20. LED materials

  21. LED materials

  22. LED characteristics

  23. LED characteristics

  24. LEDs for optical fiber communications - LEDs are preferred for short haul applications - more economical - wider output spectrum, i.e. not suitable for wide bandwidth systems light Double-heterosturuture light surface emitting LED(SLED) Edge-emitting LED(ELED)

  25. Coupling the radiation from a SLED into an fiber

  26. DH ELED

  27. Coupling the radiation from a ELED into an fiber

  28. 3) Lasers - population inversion - optical feedback (optical cavity)

  29. Stimulated emission absorption spontaneous emission Stimulated emission The emitted photon has the same energy, polarization, direction and phase as the incoming photon.

  30. Population inversion 2. rapid decay to the long-lived (metastable) state 1. (optical) pumping 4. Stimulated emission 3. population inversion

  31. Stimulated emission: Optical amplifiers E.g.: Erbium doped fiber amplifier (EDFA)

  32. Erbium doped fiber amplifier (EDFA)

  33. Semiconductor optical amplifier (SOA) Fabry-Perot Traveling wave

  34. Laser diode (LD) population inversion

  35. DOS for electrons a holes in SCL under forward bias

  36. Optical feedback cleaved surface = mirror

  37. Laser oscillation conditions

  38. Laser oscillation conditions FP cavity must be the same in the steady state phase condition amplitude condition = = threshold condition

  39. Optical power stimulated emission spontaneous emission diode current

  40. Principle of a double heterostructure LD

  41. Example: DH stripe contact LD

  42. Example: A buried DH LD

  43. LD characteristics

  44. LDs for optical fiber communications

  45. DBR Laser

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