Transcript fiber
S-72.3320 Advanced Digital Communication (4 cr) Fiber-optic Communications - Supplementary Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed. Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed. Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed. Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed. Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed. Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed. Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed. Timo O. Korhonen, HUT Communication Laboratory G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed. EDFA - energy level diagram Fluoride class level (EDFFA) E4 excited state absorption 980 nm E3 32 1 s Er3+ levels E2 1530 nm 980 nm 1480 nm 21 10ms E1 Pump power injected at 980 nm causes spontaneous emission from E1 to E3 and there back to E2 Due to the indicated spontaneous emission lifetimes population inversion (PI) obtained between E1 and E2 The higher the PI to lower the amplified spontaneous emission (ASE) Thermalization (distribution of Er3+ atoms) and Stark splitting cause each level to be splitted in class (not a crystal substance) -> a wide band of amplified wavelengths Practical amplification range 1525 nm - 1570 nm, peak around 1530 nm Timo O. Korhonen, HUT Communication Laboratory 100 Fundamental limits of silica fibers O-band E-band S-band C-band L-band U-band Original 1260-1360 Extended 1360-1460 Short 1460-1530 Conventional 1530-1565 Long 1565-1625 Ultra-long 1625-1675 Water spike 10 Loss (dB/km) Band Description Wavelength (nm) 50 5 1 0.5 0.1 Rayleigh scattering Infrared absorption 0.8 1.0 1.2 1.4 1.6 1.8 Wavelength (mm) C-band: supports early EDFA C+L-band: support for EDFA’s of today Raman amplifiers can be used over all bands new (medium loss) bands are now applicable (as S & U bands) New fibers can reduce loss at E & S bands (however, EDFA does not work here & Raman gain small) Timo O. Korhonen, HUT Communication Laboratory Inter- and Intra-modal dispersion Attenuation (Loss) Non-linear effects – Four-wave mixing (FWM) – Stimulated Raman & Brillouin scattering (SRS,SBS) – Cross-phase & self-phase modulation (SPM,XPM) Polarization fluctuations Modulation of lasers Timo O. Korhonen, HUT Communication Laboratory LD distortion coefficients Let us assume that an LD transfer curve distortion can be described by y (t ) a1 x(t ) a2 x 2 (t ) a3 x 3 (t ) where x(t) is the modulation current and y(t) is the optical power n:the order harmonic distortion is described by the distortion coefficient A H n 20log10 n A1 and y(t ) A0 A1 cost A2 cos 2t A3 cos3t... For the applied signal we assume x(t ) cos t and therefore 2 a2 A2 a1 x(t ) a1 cos t H 2 20log10 A 20log10 3a 4a 3 1 1 a2 x 2 (t ) cos 2 (t ) (a2 / 2)(1 cos 2 t ) a3 H 20log A3 20log a3 x 3 (t ) (a3 / 4)(3cos t cos3 t ) 2 10 3 A 3 a 4 a 1 3 1 a a 3a a y (t ) 2 3 a1 cos t 2 cos 2 t 3 cos3 t 2 4 2 4 Timo O. Korhonen, HUT Communication Laboratory A1 A2 Link calculations In order to determine repeater spacing on should calculate – power budget – rise-time budget Optical power loss due to junctions, connectors and fiber One should be able to estimate required margins with respect of temperature, aging and stability For rise-time budget one should take into account all the rise times in the link (tx, fiber, rx) If the link does not fit into specifications – more repeaters – change components – change specifications Often several design iteration turns are required Timo O. Korhonen, HUT Communication Laboratory Link calculations (cont.) Specifications: transmission distance, data rate (BW), BER Objectives is then to select FIBER: – Multimode or single mode fiber: core size, refractive index profile, bandwidth or dispersion, attenuation, numerical aperture or modefield diameter SOURCE: – LED or laser diode optical source: emission wavelength, spectral line width, output power, effective radiating area, emission pattern, number of emitting modes DETECTOR/RECEIVER: – PIN or avalanche photodiode: responsivity, operating wavelength, rise time, sensitivity Timo O. Korhonen, HUT Communication Laboratory The bitrate-transmission length grid 1-10 m <10 Kb/s 10-100 Kb/s 100-1000 Kb/s 1-10 Mb/s 10-50 Mb/s 50-500 Mb/s 500-1000 Mb/s >1 Gb/s 10-100 m 100-1000 m 1-3 km 3-10 km 10-50 km 50-100 km >100 km VII V I V II III IV BL 100 Mb/s I Region: VI SLED with SI MMF II Region: 100 Mb/s BL 5 Gb/s LED or LD with SI or GI MMF III Region: BL 100 Mb/s ELED or LD with SI MMF IV Region: 5 Mb/s BL 4 Gb/s ELED or LD with GI MMF V Region: 10 Mb/s BL 1 Gb/s LD with GI MMF VI Region: 100 Mb/s BL 100 Gb/s LD with SMF VII Region: 5 Mb/s BL 100 Mb/s LD with SI or GI MMF SI: step index, GI: graded index, MMF: multimode fiber, SMF: single mode fiber Timo O. Korhonen, HUT Communication Laboratory Using Mathcad to derive connection between fiber bandwidth and rise time exp g( t ) t 2 2 2 G( f ) 2 2 2 exp 2 f 2 g( 0) 2 1 2 2 th exp 2 2 2 2 ln ( 2 ) th 2 ln ( 2 ) th 2 ln ( 2 ) 1 G( 0 ) 1 2 2 1 ( 2( ) ) f 3dB exp 2 f 3dB 2 2 2 4 2 2 ln ( 2 ) substitute ln ( 2 ) t h Timo O. Korhonen, HUT Communication Laboratory 1 2 th 0 f 3dB yeilds 2 ln ( 2 ) ln ( 2 ) 0.221 t FWHM 2 t h ( 2( ) ) 2 ln ( 2 ) 1 2 ln ( 2 ) ( 2( ) ) 1 t ln ( 2 ) h 2 1 2 4 0 Timo O. Korhonen, HUT Communication Laboratory Ref: A.B.Carlson: Communication Systems, 3rd ed Timo O. Korhonen, HUT Communication Laboratory Ref: A.B.Carlson: Communication Systems, 3rd ed