1. UPM, DIAC. Open Course. March 2010 8. EMITTERS AND PDs 8.1 Emitter Basics 8.2 LEDs and Lasers 8.3 PD Basics 8.4 PD Parameters 8.5 Catalogs

2. 8-2 8.1 EMITTER BASICS (I) 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: P o (dBm) – Safe Margin: M S (dB). For the whole system, but assigned to the optical source

3. 8-3 8.1 EMITTER BASICS (II) 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 (E 1 -E 2 ) (Planck: h = 6.626·10 -34 J·s)

4. 8-4 8.1 EMITTER BASICS (III) P-N Junction —A forward biased p-n junction

5. 8-5 8.2 LEDs AND LASERS (I) Optical Sources – Laser Diode (LD) Light Amplification by Stimulated Emission of Radiation – LED Light Emitting Diode Normal LED Industrial LaserOpt. Communic. LD Opt. Communic. LED

6. 8-6 8.2 LEDs AND LASERS (II) LEDs (I) – Characteristics Wide spectrum (  ) Incoherent emission Low power Low cost – Types Surface LED Edge LED – More radiation – More directional Δλ

7. 8-7 8.2 LEDs AND LASERS (III) LEDs (II) – Actual Spectrum FWHM: Full Width at Half Maximum (Δλ)

8. 8-8 8.2 LEDs AND LASERS (IV) Laser (I) – Operation Principles An amplifier oscillating Stimulated emission → avalanche Diode + resonant cavity (Fabry-Perot) → monochrome

9. 8-9 8.2 LEDs AND LASERS (V) Laser (II) – Conditions High photon density Population inversion N1N1 N2N2 E2E2 E1E1 N 1 >N 2 Thermal equilibrium N1N1 N2N2 E2E2 E1E1 N 1 <N 2 Population inversion (no equilibrium) PUMPING

10. 8-10 8.2 LEDs AND LASERS (VI) Laser (III) – Characteristics Monochromatic spectrum (resonant cavity) Coherent, more directional (stimulated emission) High power (avalanche) Fast modulation Instability Expensive Spontaneous emission = LED Stimulated emission = LD Threshold Current

11. 8-11 8.2 LEDs AND LASERS (VII) Laser (IV) – Actual Spectrum

12. 8-12 8.2 LEDs AND LASERS (VIII) Laser (V) – Instability With temperature and power Control is required (coolers + feedback)

13. 8-13 8.2 LEDs AND LASERS (IX) Laser (VI) – Peltier Coolers

14. 8-14 8.2 LEDs AND LASERS (X) LED Versus Laser LEDLASER  (nm) Wide (50-100)Narrow (0.5-5) P o (mW)Low (1)High (5-20) Coupling (dB)10-130-1 BW (GHz)Small (0.01-0.1)Huge (0.5-2) CostCheapExpensive HardwareEasyComplex Fiber TypeMultimodeSinglemode

15. 8-15 8.3 PD BASICS (I) Concept – PD = PhotoDetector – Optical electrical converter – Absorption Fiber PD Free Space PD

16. 8-16 8.3 PD BASICS (II) Operation Principles – One absorbed photon creates a pair of free carriers – P-n junction, reverse biased Depletion region (without free carriers) New photogenerated free carriers are pulled Depletion Region Wide: many absorbed photons Narrow: high speed

17. 8-17 8.4 PD PARAMETERS (I) Photocurrent

18. 8-18 8.4 PD PARAMETERS (II) Responsivity (Sensitivity)

19. 8-19 8.4 PD PARAMETERS (III) PD Cut-Off Wavelength – One photon needs the gap energy to generate a pair

20. 8-20 8.4 PD PARAMETERS (IV) Actual PDs

21. 8-21 8.4 PD PARAMETERS (V) Types of PDs (I) – PIN PDs: no avalanche, linear, low sensitivity I p = R· p o (photocurrent = responsivity · optical power) – Avalanche PDs = APDs: low linearity, high sensitivity Multiplication Factor: M  40 times I t = I p · M (total current = photocurrent · avalanche)

22. 8-22 8.4 PD PARAMETERS (VI) Types of PDs (II) PIN ParameterSymbolUnitSiGeInGaAs Wavalengthλnm400-1100800-16501100-1700 ResponsivityRA/W0.4-0.60.4-0.50.75-0.95 Dark currentIDID nA1-1050-5000.5-2.0 Rise timetrtr ns0.5-10.1-0.50.05-0.5 BandwidthBGHz0.3-0.70.5-31-2 Bias voltageVBVB V55-105 APD ParameterSymbolUnitSiGeInGaAs Wavalengthλnm400-1100800-16501100-1700 AvalancheM-20-40050-20010-40 Dark currentIDID nA0.1-150-50010-50 Rise timetrtr ns0.1-20.5-0.80.1-0.5 Gain·BandwidthM·BGHz100-4002-1020-250 Bias voltageVBVB V140-40020-4020-30

23. 8-23 8.4 PD PARAMETERS (VII) Quality Versus Received Power

24. 8-24 8.5 CATALOGS (I)

25. 8-25 8.5 CATALOGS (II)

26. 8-26 8.5 CATALOGS (III)

27. 8-27 8.5 CATALOGS (IV)

28. 8-28 8.5 CATALOGS (V)

29. 8-29 8.5 CATALOGS (VI)

30. 8-30 8.5 CATALOGS (VII)

31. 8-31 8.5 CATALOGS (VIII)

32. 8-32 8.5 CATALOGS (IX)

33. 8-33 8.5 CATALOGS (X)

34. 8-34 8.5 CATALOGS (XI)

35. 8-35 8.5 CATALOGS (XII)

36. 8-36 8.5 CATALOGS (XIII)