1. Training_Transmission_GB Page 1 Transmission September 2013

2. Training_Transmission_GB Page 2 Principle of optical communication Transmission channel Tx E O Rx O E Receiver Converter Transmitter Converter Optical transmission length is restricted by the attenuation or dispersion.

3. Training_Transmission_GB Page 3 The electromagnetic wave Electric wave Magnetic wave Propagation direction [Meter] Wavelength Time scale [Seconds] Period  Frequency = 1 /  Light is an electromagnetic wave and can be described with Maxwell’s equations.

4. Training_Transmission_GB Page 4 c = f * c: speed of light f: frequency : wavelength n = c 0 / c c 0 : v in Vakuum c: v in Medium What is light speed of light:Refraction index: in vacuum  300‘000 km/s1.0 in water  220‘000 km/s1.3 in glass  200‘000 km/s1.5 Light = electromagnetic wave (Wave-particle dualism) Visible spectrum for human eyes: Ultraviolett  380-780 nm  Infrared Wavelengths for data transmission in Glass Optical Fiber = invisible infrared: 850 nm, 1300 nm, 1550 nm, …

5. Training_Transmission_GB Page 5 (Speed of light in vacuum) Speed of light C (electromagnetic radiation) is: C 0 = f * (Wellenlänge x Frequenz) C 0 = 299793 km/s Velocity of electromagnetic wave Remarks: An x-ray-beam (l = 0.3 nm), a radar-beam (l = 10 cm ~ 3 GHz) or an infrared-beam (l = 840 nm) have the same velocity in vacuum

6. Training_Transmission_GB Page 6 Gamma x-ray UV InfraredMicrowaveRundfunk Visible light - electromagnetic radiation [www.wikipedia]

7. Training_Transmission_GB Page 7 Wavelength range - optical transmission Infrared range Visible range GOF Multimode (850 – 1300nm) POF (520 – 650nm) PCF (650 – 850nm) 1. optical window 18001600140012001000800 600 400 Wavelength [nm] 2. optical window 3. optical window Singlemode (1310 – 1650nm)

8. Training_Transmission_GB Page 8 When light or other electromagnetic waves hit a medium (e.g. air) a part of the light bounces back (reflection) the other strikes trough (refraction). Refraction & reflection of light

9. Training_Transmission_GB Page 9 Sun light [www.wikipedia] Refraction & reflection of light electromagnetic spectrum

10. Training_Transmission_GB Page 10 e.g. n air = 1,0003, n core = 1,5000 oder n sugar water = 1,8300 Change of velocity of light in matter Velocity of light (electromagnetic radiation) is: always smaller than in vacuum, it is C n (Velocity of Light in Matter) n = C 0 / C n n is defined as refractive index (n = 1 in Vacuum) n is dependent on density of matter and wavelength Refractive index

11. Training_Transmission_GB Page 11 Transmission

12. Training_Transmission_GB Page 12 Principle fiber optic transmission Optical fiber uses the effect of total reflection.

13. Training_Transmission_GB Page 13 Fiber structure Fiber optic is working with total reflection and therefore 2 materials with different density/refractive index are necessary: pure homogeneous refractive index within core Ø yy µm Ø xx µm

14. Training_Transmission_GB Page 14 Glass fiber index profile Core = continuous refraction index profile Core= several layers with unequal refraction index profiles Core = parabolic refraction index profile Step indexMulti-step indexGraded index

15. Training_Transmission_GB Page 15 Type of fiber Optical fiber Step Index (SI)Graded Index (GI) Single mode (SM)Multi mode (MM) 9/125µm (GOF) Low water peak Dispersion shifted Non zero dispersion shifted 980/1000 µm (POF) 500/750 µm (POF) 200/230 µm (PCF) 50/125 µm (GOF) 62.5/125 µm (GOF) 120/490 µm (POF) Diameter Refraction Index Profile

16. Training_Transmission_GB Page 16 n1n1 n2n2 Refractive index profile (Step index) ~ 680 Modes at NA = 0.2, d = 50  m & = 850 nm ~ 292 Modes at NA = 0.2, d = 50  m &  = 1300 nm Number of modes M = 0.5x(pxdxNA/l)2 n1n1 n2n2 n1n1 Same core density makes modes’ speed different (every mode travels for a different length) Multimode fiber (Step index) Input Output

17. Training_Transmission_GB Page 17 Multimode fiber (Graded index) Refractiv index profile (Graded index) ~150 Modes at NA = 0.2, d = 50  m & = 1300 nm Number of modes M = 0.25x(pxdxNA/l)2 n1n1 n1n1 n1n1 Input Output n1n1 n2n2 n2n2 Different core density makes modes’ speed same (every mode travels for about same length)

18. Training_Transmission_GB Page 18 Single mode fiber Refractive index profile (Step Index) Example: n1 =1.4570 and n2 = 1.4625 Remarks: One mode (2 polarizations) n1n1 n2n2 n1n1 n1n1 n2n2 Input Output if core is small enough only 1 mode can get transmitted.

19. Training_Transmission_GB Page 19 Step index and depressed step index n1n1 n2n2 n1n1 n2n2 Cladding with homogeneous refractive index OVD process Cladding with two refractive indexes MCVD process dependent Less macrobending Wide low attenuation spectrum Two zero dispersion points

20. Training_Transmission_GB Page 20 Optical characteristics

21. Training_Transmission_GB Page 21 Optical characteristics influences 1 2 3 Attenuation [dB] Dispersion Numerical Aperture (NA) [-] Power loss along the optical link Power loss along the optical link Pulse broadening and signal weakening Coupling loss LED/Laser  fiber fiber  fiber fiber  e.g. APD* Transmission distance Transmission distance Signal bandwidth & transmission distance Coupling capacitance Coupling capacitance TermEffectLimitation * Avalanche photodiode

22. Training_Transmission_GB Page 22 Attenuation

23. Training_Transmission_GB Page 23 Attenuation is the reduction of the optical power due to Attenuation Fiber Bending Connection Caused by absorption, scattering or a coupling. Value indication in decibel (dB) P in P out

24. Training_Transmission_GB Page 24 P 0 L = 10log ------- [dB] P 1 L: Pegel P 0 : power in P 1 : power out 1 dB =80 % Power 3 dB = 50 % Power 10 dB =10 % Power Decibel 1/2 3 dB 6 dB 0 dB 100% 50% 25% P in P out

25. Training_Transmission_GB Page 25 Attenuation Attenuation in DB remaining power in % 0.197.7 0.295.5 0.393.3 0.491.2 0.589.1 0.687.7 0.785.1 0.883.2 0.981.1 1.079.4 263.1 350.1 Attenuation in DB Verbleibende power in % 439.8 531.6 625.1 912.6 10 201.0 300.1 400.01 500.001 600.0001 700.00001 800.000001

26. Training_Transmission_GB Page 26 Attenuation contributors Fiber (material) Absorption Scattering Connection (fiber end to fiber end) intrinsic extrinsic Bending (fiber and cable) Micro bending Macro bending Kann nicht durch Installateur beeinflusst werden

27. Training_Transmission_GB Page 27 Fiber - attenuation (intrinsisch) Material absorption 3 to 5% of attenuation due to chemical doping process impurity Residual OH (water peak) absorb energy and transform it in heat/vibration greater at shorter wavelength Rayleigh Streuung 96 % of attenuation due to glass impurity reflects light in other direction depending on size of particles depends on wavelength (>800nm)

28. Training_Transmission_GB Page 28 Insertion loss - intrinsic Differences in Core diameter Numerical aperture Refractive index profile

29. Training_Transmission_GB Page 29 Insertion loss - extrinsic Due to Lateral offset Axial separation Axial tilt

30. Training_Transmission_GB Page 30 Insertion loss - extrinsic Due to: Fresnel reflection Surface roughness

31. Training_Transmission_GB Page 31 Dämpfung (extrinsisch) Micro-bending (can not be influenced by installer) Cable production process caused by imperfections in the core/cladding interface Macro-bending (can be influenced by installer) Bending diameter < 15x cable Ø Macro-bending is not only increasing the attenuation it also shortens lifetime of a fiber (micro cracks)

32. Training_Transmission_GB Page 32 800 1000 1200 1400 1600 wavelength [nm] 3.5 2.5 1.5 Attenuation [dB/km] 3. Window 1550 nm SiOH-absorptions Rayleigh-scattering (~ 1/   950 1240 1440 5. Window 4. Window 1625 nm Attenuation spectrum GOF 1. window 850 nm 2. window 1310 nm

33. Training_Transmission_GB Page 33 Dispersion

34. Training_Transmission_GB Page 34 Dispersion (fiber length dependency) Dispersion are all effects that considerably influence pulse „widening“ and pulse „flattening“. Input pulse L1L1 L 2 + L 2 L 1 + L 2 + L 3 Output pulse after L x The dispersion increases with longer fiber length and/or higher bit rate.

35. Training_Transmission_GB Page 35 Dispersion Moden Dispersion Profil Dispersion Chromatische Dispersion [ps/km * nm] Polarisations Moden Dispersion PMD [ps/  (km)] Multimode FaserSingle-mode Faser Dispersion is the widening and overlapping of the light pulses in a optical fiber due to time delay differences.

36. Training_Transmission_GB Page 36 Moden Dispersion Stufen Index Profile Laufzeitunterschiede der Moden in der Faser Schneller Moden pflanzen sich entlang der optischen Achse fort. Langsamere Moden (größerer Einstrahlungswinkel) sind länger und dadurch langsamer MM Faser mit Stufen Index (SI) Profil V = Konstanter Brechungsindex Große Laufzeitdifferenz → niedrige Bandbreite z.B. PMMA SI-POF, DS-POF

37. Training_Transmission_GB Page 37 Modal dispersion Step index profile Delay of modes in the fiber Lowest-order mode propagates along the optical axis. Highest-order mode  extended length  lowest speed MM Fiber with step index (SI) profile V = constant refractive index Large propagation delay → low bandwidth e.g. PMMA SI-POF, DS-POF

38. Training_Transmission_GB Page 38 Modal dispersion Parabolic index profile Increase speed of rays near margin Time differences between low and high order modes is minimizes MM Fiber with graded index (GI) profile V 2 >V 1 parabolic index “no” propagation delay → high bandwidth e.g. GI-GOF, GI-POF

39. Training_Transmission_GB Page 39 Chromatic dispersion Singlemode chromatic dispersion Dominant type of dispersion in SM fibers and is caused by wavelength dependent effects. Chromatic dispersion is the cumulative effect of material and waveguide dispersion Multimode chromatic dispersion As waveguide dispersion is very low compared to material dispersion it can be disregarded.

40. Training_Transmission_GB Page 40 SMF-28 @ 1310 nm ≤ 3.5 ps/nm*km SMF-28 @ 1550 nm ≤ 18 ps/nm*km Chromatische Dispersion = Summe von Material- und Wellenleiter Dispersion Material Dispersion Abhängigkeit der Lichtbrechung von der Wellenlänge (Laufzeitunterschied) Wellenleiter Dispersion Abhängigkeit unterschiedlichen Geschwindigkeiten im Kern und Mantel von der Wellenlänge (Pulsverbreiterung)

41. Training_Transmission_GB Page 41 Grenzwellenlänge (Cut-off ) Nur relevant für Singlemodefasern Unterste Wellenlänge, bei welcher nur ein Mode ausbreitungsfähig ist Ist von einigen Faktoren abhängig, aber hauptsächlich vom Kerndurchmesser Je kleiner der Kerndurchmesser, desto kürzer die Cut-off Wellenlänge Beispiel: SM Grenzwellenlänge 1200nm  über 1200nm: 1 Mod  unter 1200nm: mehrere Moden ausbreitungsfähig

42. Training_Transmission_GB Page 42 Delay (PMD) Polarisationsmoden-Dispersion (PMD) „slow axis" n y „fast axis“ n x < n y y x PMD occurs in SM fibers high bit rate systems >40Gb/s systems with a very small chromatic dispersion A mode in SM fiber has two orthogonal polarizations n x : magnetisches Feld, n y : elektrisches Feld

43. Training_Transmission_GB Page 43 Bandwidth length definition = Kapazität der Datenübertragung Längenabhängig aufgrund Dispersion Pulse widening limits bandwidth B and the maximum transmission rate Mbps Pulse widening is approx. proportional to the fiber length L Approximation for bandwidth-length product: B x L = BLP 500MHz x 1km = 500MHz*km BLP L 500MHz*km 0.5km B == = 1000MHz

44. Training_Transmission_GB Page 44 Numerical aperture

45. Training_Transmission_GB Page 45 Numerical Aperture (NA) Light rays outside acceptance angle leak out of core NA = (n 2 0 – n 2 1 ) = sin  Standard SI-POF= NA 0.5 → 30° Low NA SI-POF= NA 0.3 → 17.5° Light rays guided in core

46. Training_Transmission_GB Page 46 Waveguide dispersion 2w 0 Beam waste Numerical Aperture: NA = sin  = (n 2 2 - n 1 2 ) 0.5 =  w 0 Example: NA = 0.17 and Q = 9.8° 80% of light in core 20% of the light in cladding 2w 0 Verlust Akzeptanzwinkel  Mode field diameter 2w 0 Waveguide dispersion occurs when the mode filed is entering into the cladding. It is wavelength and fiber size dependent.

47. Training_Transmission_GB Page 47 Large value of NA mean large value of acceptance angle (  Large value of NA means more light power/modes in the fiber More modes mean higher mode dispersion (lower bandwidth) Large values of NA mean lower bending induced attenuation of the fiber NA and transmission performance Remarks: Two Fibers with NA = 0.2 & 0.4 Fiber with NA = 0.2 has 8-times more bending induced attenuation than NA = 0.4 Fiber