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EMITTER BASICS

EMITTER BASICS . Concept Light Emitter = optical electrical converter Light Radiation: electronic excitation in a semiconductor Nothing to do with incandescence Allows very high speed modulation Better spectrum (narrower, more stable) Parameters Operation Wavelength:  0 (nm)

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EMITTER BASICS

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  1. EMITTER BASICS • Concept • Light Emitter = optical electrical converter • Light Radiation: electronic excitation in a semiconductor • Nothing to do with incandescence • Allows very high speed modulation • Better spectrum (narrower, more stable) • Parameters • Operation Wavelength: 0 (nm) • Spectral Width (or BW):  (nm) • Optical Power into Fiber: Po (dBm) • Safe Margin: MS (dB). For the whole system, but assigned to the optical source

  2. EMITTER BASICS • Optical Emission Fundamentals • Emission:Free e- from the conduction band recombine with valence band holes, emitting photons. The wavelength of photons is set by the band gap (E1-E2) (Planck: h = 6.626·10-34J·s)

  3. EMITTER BASICS

  4. EMITTER BASICS • P-N Junction—A forward biased p-n junction

  5. LEDs AND LASERS • OpticalSources • LED • Light EmittingDiode • Laser Diode (LD) • Light AmplificationbyStimulatedEmission of Radiation Opt. Communic. LED Normal LED Opt. Communic. LD Industrial Laser

  6. NAJJAR M.

  7. LEDs AND LASERS • LEDs • Characteristics • Widespectrum() • Incoherentemission • Lowpower • Lowcost • Types • Surface LED • Edge LED • More radiation • More directional Δλ

  8. LEDs AND LASERS • LEDs • Actual Spectrum FWHM: Full Width at Half Maximum (Δλ)

  9. Characteristics of LEDs

  10. LEDs AND LASERS • Laser • OperationPrinciples • Anamplifieroscillating • Stimulatedemission → avalanche • Diode + resonantcavity (Fabry-Perot) → monochrome

  11. LEDs AND LASERS • Laser • Characteristics • Monochromaticspectrum (resonantcavity) • Coherent, more directional (stimulatedemission) • Highpower (avalanche) • Fastmodulation • Instability • Expensive Threshold Current Spontaneous emission = LED Stimulated emission = LD

  12. LEDs AND LASERS • Laser

  13. WithL : cavitylength P : mode order N: group indice

  14. LEDs AND LASERS • Laser • Instability • Withtemperature and power • Control isrequired (coolers + feedback)

  15. LEDs AND LASERS • LED Versus Laser

  16. PD BASICS • Concept • PD = PhotoDetector • Optical electrical converter • Absorption Fiber PD Free Space PD

  17. PD BASICS • OperationPrinciples • Oneabsorbed photoncreates a pair of free carriers • P-n junction, reverse biased • Depletionregion (without free carriers) • New photogenerated free carriers are pulled • DepletionRegion • Wide: many absorbed • photons • Narrow: highspeed

  18. PD PARAMETERS • Types of PDs (I) • PIN PDs: no avalanche, linear, lowsensitivity • Ip = R· po(photocurrent = responsivity · opticalpower) • AvalanchePDs = APDs: lowlinearity, highsensitivity • Multiplication Factor: M 40 times • It = Ip· M (total current = photocurrent · avalanche)

  19. PD PARAMETERS Dark current: The leakage current that flows through a photodiode with no light input. Thermally generated. Transit time: The time it takes a light-induced carrier to travel across the depletion region of a semiconductor. This parameter determines the maximum bit rate possible with a particular photodiode. Transit time is a function of depletion width and carrier drift velocity td= w/vd Light sensitivity: The minimum optical power a light detector can receive and still produce a usable electrical output signal.

  20. PD PARAMETERS • Photocurrent

  21. PD PARAMETERS • Responsivity (Sensitivity)

  22. PD PARAMETERS • PD Cut-Off Wavelength • One photon needs the gap energy to generate a pair

  23. Multiplication Coefficient (M) With V : polarisation tension.

  24. Phototransistor

  25. PD PARAMETERS • Types of PDs

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