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

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

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· J·s)

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

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

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

LEDs AND LASERS (III) LEDs (II) – Actual Spectrum FWHM: Full Width at Half Maximum (Δλ)

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

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

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

LEDs AND LASERS (VII) Laser (IV) – Actual Spectrum

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

LEDs AND LASERS (IX) Laser (VI) – Peltier Coolers

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) BW (GHz)Small ( )Huge (0.5-2) CostCheapExpensive HardwareEasyComplex Fiber TypeMultimodeSinglemode

PD BASICS (I) Concept – PD = PhotoDetector – Optical electrical converter – Absorption Fiber PD Free Space PD

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

PD PARAMETERS (I) Photocurrent

PD PARAMETERS (II) Responsivity (Sensitivity)

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

PD PARAMETERS (IV) Actual PDs

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)

PD PARAMETERS (VI) Types of PDs (II) PIN ParameterSymbolUnitSiGeInGaAs Wavalengthλnm ResponsivityRA/W Dark currentIDID nA Rise timetrtr ns BandwidthBGHz Bias voltageVBVB V APD ParameterSymbolUnitSiGeInGaAs Wavalengthλnm AvalancheM Dark currentIDID nA Rise timetrtr ns Gain·BandwidthM·BGHz Bias voltageVBVB V

PD PARAMETERS (VII) Quality Versus Received Power

CATALOGS (I)

CATALOGS (II)

CATALOGS (III)

CATALOGS (IV)

CATALOGS (V)

CATALOGS (VI)

CATALOGS (VII)

CATALOGS (VIII)

CATALOGS (IX)

CATALOGS (X)

CATALOGS (XI)

CATALOGS (XII)

CATALOGS (XIII)