10. SYSTEM DESIGN 10.1 Fundamentals 10.2 Power Budget 10.3 Time Budget 10.4 Sections 10.5 WDM

10.1 FUNDAMENTALS (I) Factors and Decisions FACTOR CONSIDERATIONS / CHOICES Topology Point to point / Distribution or Network (bus, ring, star…) OF type Singlemode / Multimode Dispersion Regenerators / Compensators Nonlinear effects TX power, OF characteristics, wavelengths Operating λ Typical values: 780; 850; 1310; 1550; 1625 nm TX power In dBm Optical source LED / LD PD threshold (sensitivity) Photodetector PIN / APD Code - Modulation Usually: mBnB – ASK BER Typical: 10-9 – 10-12 S/N (“OSNR”) In dB (depends on BER) Nº of connectors / losses In short links they may be dominant Nº of splices / losses Only relevant in long haul links Environmental requirements Humidity, temperature, sunlight... Mechanical requirements Indoor / Outdoor. Flammability PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.1 FUNDAMENTALS (II) Goal —ensuring BER requirements Power Budget Calculate system losses Check if PD receives enough signal strength Too much signal is harmful Nonlinear effects PD saturation Time Budget Calculate all temporal parameters OF dispersion Devices’ response time Check if resultant BW is enough to cope with rate requirements Calculations for several sections Calculations for WDM PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.1 FUNDAMENTALS (III) Sections / Repeaters Regeneration Section (L): Maximum run between a source and a PD (TX and RX) Regenerator (RR): Decides on every symbol, and regenerates it May be wrong, but noise dissappears PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial) Sections ▪ Do not accumulate noise… ▪ Do accumulate errors (BER)

10.1 FUNDAMENTALS (IV) Block Diagram (point to point) TX RR RX L REGENERATION SECTION TX RR RX L CONNECTOR PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial) SPLICE Electric signal LASER Optical signal Opt. signal PD Elect. signal (processing) LASER Opt. signal PD Elect. signal COMMUNICATION ENDS ARE JOINT VIA “M” REGENERATION SECTIONS. EACH SECTION HAS A LENGTH “L”

10.2 POWER BUDGET (I) Calculation (per Regeneration Section!) PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.2 POWER BUDGET (II) Graphical Interpretation PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.2 POWER BUDGET (III) PD Threshold PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.3 TIME BUDGET (I) Calculation (per Regeneration Section!) (I) Calculate OF total dispersion, ΔtOF Evaluate OF BW (3 dB), and its characteristic time, tOF Read from catalogs source and PD rise times (tTX , tRX) PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.3 TIME BUDGET (II) Calculation (per Regeneration Section!) (II) Add all time contributions (quadratic sum). System time is obtained Estimate system BW, or data rate PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.4 SECTIONS Concept Calculations For each section, power and time budget Attenuation and dispersion are not accumulated from one section to another (regeneration) Errors are accumulated. Total BER increases Calculations We disregard the probability of errors being corrected in other sections Total BER: sum of every section BER (M sections) PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.5 WDM (I) Calculations (I) All calculations have been made for one carrier (one λ) With WDM system capacity increases Total RbT is divided by carrier number Rb↓ → little dispersion (for each carrier) Rb↓ → PD threshold, So, improves (↓dBm) (for each carrier) Dispersion compensation Needed (for L and Rb large) It is done for each carrier (MUX device) Nonlinear effects must be taken into account High power into fiber Several carriers → FWM Source power is distributed among all carriers Sources and amplifiers (e.g. EDFAs) cannot launch more power W launched into OF are divided by WDM carrier number PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.5 WDM (II) Calculations (II) Optical amplifiers (EDFA’s) degrade S/N OSNR: optical signal to noise ratio A minimum OSNR is required (depending on BER) This limits the number of amplifiers OSNR (dB) per regeneration section, per carrier Pfi (dBm): power into fiber, per carrier A (dB): attenuation for one span bettween two EDFA’s Fa (dB): EDFA noise figure N: nº of spans in a regeneration section PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.5 WDM (III) Diagram L RR RR EDFA EDFA REGENERATION SECTION SPAN PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial) EDFA EDFA RR RR P2 = 0 dBm G = 25 dB P1 = -25 dBm Example A = 25 dB P0 = 0 dBm

10.5 WDM (IV) Graphical Interpretation PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.5 WDM (V) Quality Graphics (I) PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)

10.5 WDM (VI) Quality Graphics (II) PESO - Menos de la décima parte que coaxial INCONVENIENTES - No es capaz de llevar la alimentación (como hace el coaxial)