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S-72.227 Digital Communication Systems Fiber-optic Communications - Supplementary.

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Presentation on theme: "S-72.227 Digital Communication Systems Fiber-optic Communications - Supplementary."— Presentation transcript:

1 S Digital Communication Systems Fiber-optic Communications - Supplementary

2 Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

3 Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

4 Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

5 Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

6 Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

7 Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

8 Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

9 Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

10 Timo O. Korhonen, HUT Communication Laboratory EDFA - energy level diagram u Pump power injected at 980 nm causes spontaneous emission from E1 to E3 and there back to E2 u Due to the indicated spontaneous emission lifetimes population inversion (PI) obtained between E1 and E2 u The higher the PI to lower the amplified spontaneous emission (ASE) u Thermalization (distribution of Er 3+ atoms) and Stark splitting cause each level to be splitted in class (not a crystal substance) -> a wide band of amplified wavelengths u Practical amplification range 1525 nm nm, peak around 1530 nm Er 3+ levels E1 E2 E3 E nm 1480 nm 980 nm Fluoride class level (EDFFA) excited state absorption

11 Timo O. Korhonen, HUT Communication Laboratory Fundamental limits of silica fibers u C-band: supports early EDFA u C+L-band: support for EDFA’s of today u Raman amplifiers can be used over all bands - new (medium loss) bands are now applicable (as S & U bands) u New fibers can reduce loss at E & S bands (however, EDFA does not work here & Raman gain small) O-band Original E-band Extended S-band Short C-band Conventional L-band Long U-band Ultra-long Band Description Wavelength (nm) Wavelength (mm) Water spike Rayleigh scattering Infrared absorption Loss (dB/km) u Inter- and Intra-modal dispersion u Attenuation (Loss) u Non-linear effects –Four-wave mixing (FWM) –Stimulated Raman & Brillouin scattering (SRS,SBS) –Cross-phase & self-phase modulation (SPM,XPM) u Polarization fluctuations

12 Timo O. Korhonen, HUT Communication Laboratory Modulation of lasers

13 Timo O. Korhonen, HUT Communication Laboratory LD distortion coefficients u Let us assume that an LD transfer curve distortion can be described by where x(t) is the modulation current and y(t) is the optical power u n:the order harmonic distortion is described by the distortion coefficient and For the applied signal we assume and therefore

14 Timo O. Korhonen, HUT Communication Laboratory Link calculations u In order to determine repeater spacing on should calculate –power budget –rise-time budget u Optical power loss due to junctions, connectors and fiber u One should be able to estimate required margins with respect of temperature, aging and stability u For rise-time budget one should take into account all the rise times in the link (tx, fiber, rx) u If the link does not fit into specifications –more repeaters –change components –change specifications u Often several design iteration turns are required

15 Timo O. Korhonen, HUT Communication Laboratory Link calculations (cont.) u Specifications: transmission distance, data rate (BW), BER u Objectives is then to select –Multimode or single mode fiber: core size, refractive index profile, bandwidth or dispersion, attenuation, numerical aperture or mode- field diameter –LED or laser diode optical source: emission wavelength, spectral line width, output power, effective radiating area, emission pattern, number of emitting modes –PIN or avalanche photodiode: responsivity, operating wavelength, rise time, sensitivity FIBER: SOURCE: DETECTOR/RECEIVER:

16 Timo O. Korhonen, HUT Communication Laboratory The bitrate-transmission length grid SI: step index, GI: graded index, MMF: multimode fiber, SMF: single mode fiber

17 Timo O. Korhonen, HUT Communication Laboratory Using Mathcad to derive connection between fiber bandwidth and rise time

18 Timo O. Korhonen, HUT Communication Laboratory Ref: A.B.Carlson: Communication Systems, 3rd ed

19 Timo O. Korhonen, HUT Communication Laboratory Ref: A.B.Carlson: Communication Systems, 3rd ed


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