1. Optical Transmission Systems

2. GOAL of the presentation Overview of Optical Component Technologies Basic understanding of certain key issues in Component Technologies Outline Set the Context Describe existing technologies Explain fundamental limits Describe practical considerations/tradeoffs

3. Light’s Dual Nature RaysWavesParticles Absorption Emission InterferenceRefraction Reflection Bandgap Conduction band Valence band n0n0 n1n1 n0n0

4. Why Optical ? High Bandwidth ( 500 Tbps) Low Attenuation (.25 dB/km) Low BER (10 -13 ) Light and occupies lesser space Flexible and Reliable Less crosstalk due to neutral photons Hard to eavesdrop Environmentally sound.

5. Bandwidth Comparison

6. All-Optical Network (Terabits  Petabits) TDM DWDM 0 5 10 15 20 25 30 35 40 Bandwidth 8  @OC-48 4  @OC-192 4  @OC-48 2  @OC-48 2  @1.2Gb/s (1310 nm, 1550 nm) 10 Gb/s 2.4 Gb/s 1.2 Gb/s 565 Mb/s 1.8 Gb/s 810 Mb/s 405 Mb/s Enablers EDFA + Raman Amplifier Dense WDM/Filter High Speed Opto-electronics Advanced Fiber 19821984198819941996199820002002199019861992 16  @OC-192 40 Gb/s 32  @OC-192 176  @OC-192 2004 2006 TDM (Gb/s) EDFA EDFA + Raman Amplifier 80  @ 40Gb/s Bandwidth Evolutionary Landmarks

7. Shannon’s Limit

8. Fiber Optic Transmission Bands Near Infrared Frequency Wavelength 1.6 229 1.0 0.8µm 0.6 0.41.81.4 UV (vacuum) 1.2 THz193461 0.2 353 Longhaul Telecom Regional Telecom Local Area Networks 850 nm 1550 nm 1310 nm CD Players 780 nm HeNe Lasers 633 nm

9. Optical Components 1. The Fiber A. Total Internal Reflection B. Multi Mode Fiber C. Single Mode Fiber D. Transmission Impairments Loss a. Rayleigh scattering b. Reflection c. Absorption Dispersion a. Chromatic Dispersion 1. Material Dispersion 2. Waveguide Dispersion b. Polarization Mode Dispersion Non-Linearities a. Stimulated Raman Scattering b. Stimulated Brillouin Scattering c. Four Wave Mixing d. Self Phase Modulation e. Cross Phase Modulation

10. Optical Components (Contd) 2. Couplers 3. Isolators 4. Circulators 5. Filters A. Diffraction Grating B. Reflection Grating C. Fabry Perot Filter D. Thin Film Dielectric Filter. E. Bragg Grating a. Short Period fiber bragg grating b. Long Period fiber bragg grating F. Mac Zhender Interferometer G. Arrayed Waveguide Grating H. Acoustoptic Tunable Filter

11. Optical Components (Contd) 6. Optical Amplifers A. Erbium Doped Fiber Amplifiers (EDFA) B. Raman Amplifiers (RA) C. Semiconductor Optical Amplifier (SOA) 7. Lasers A. MLM Fabry Perot B. Single Mode Lasers a. Distributed Bragg Reflector Laser (DBR) b. Distributed Feedback Laser (DFB) c. External Cavity Lasers 8. Modulators 9. Detectors A. PIN B. APD

12. Optical Components (Contd) 10. Optical Switches Photonic Switches A. Mechanical switches B. Electrooptic switches C. Thermooptic switches D. Semiconductor optical Amplifiers Lambda Switches A. Optoelectronic Method B. Semiconductor Optical Amplifier a. Cross Gain Modulation b. Cross Phase Modulation C. Four Wave Mixing

13. An Optical Network Dispersion Managed Fiber Medium Dispersion Fiber Tx WDMWDM OA Tunable DCM OA DCF Tunable DCM DWDMDWDM Dynamic PMD Compensation New Modulation Formats Forward Error Correction Impairment Tolerant Receiver C+L Band OA S Band OA Raman Amplifier Dynamic OADM..... 3000Km - 5000Km Rx PMDC Broadband PMD Compensation

14. 1. The Fiber Glass n = 1.5 Air n = 1.0 Light at this angle is refracted Light at this angle is reflected back into glass 11 22  1 =  2 For Total Internal Reflection

15. The Acceptance Cone

16. Multimode fiber Pulse broadening due to multi-path transmission. Bitrate x Distance product is severely limited!

17. Doping profile designed to minimize “race” conditions (“outer” modes travel faster due to lower refractive index!) Most common designs: 62.5/125 or 50/125  m, NA ~ 0.2 Bitrate x Distance product: ~ 1 Gb/s km r Gradient-Index (GI) Fiber

18. Step-Index type with very small core Single-Mode Fiber (SMF) n r 1.465 1.460

19. Transmission Impairments

20. Rayleigh Scattering

21. Reflection

22. Absorption

23. Transmission Impairments 900 1100 1300 15001700 0.5 1.0 1.5 2.0 2.5 OH Absorption Attenuation (dB/km) Wavelength (nm) “Optical Windows” 23 1 Main cause of attenuation: Rayleigh scattering in the fiber core 4 5 AllWave TM eliminates the 1385nm water peak

24. Loss - 1 st Order

25. Chromatic Dispersion

26. Cause of Chromatic Dispersion Material Dispersion β = nω/c n 2 (ω ) = 1 + χ(ω) P(r, ω) = έ χ(r,ω)E (r,ω) Waveguide Dispersion Power distribution between core and cladding

27. Dispersion Limits

28. Dispersion Compensation Dispersion Compensation Fiber Fiber Bragg Gratings

29. Polarization Mode Dispersion

30. PMD – The Networking Killer 20 % of installed fiber useless => 10 G 75 % of installed fiber useless => 40 G Leads to increased PDL Limits transmission to 25 km!! Two PMD Solutions 1.Optical mitigation 2.Electrical mitigation

31. PMD Compensation

32. Non-Linearities - SBS and SRS

33. Cause of Non-Linearity P = έ [ χ 1. E + χ 2. E.E + χ 3.E.E.E +…] For high values of E, the third order term becomes significant.

34. Scattering Compensation Ways to reduce SBS penalty Power below threshold Increase line width of the source Use Phase modulation schemes Ways to reduce SRS penalty Keep the channels densely packed Keep power below threshold.

35. Four Wave Mixing

36. FWM Compensation Unequal channel spacing Increased channel spacing Reduced power below threshold Use spatial walk off – introduce time delay

37. Non-Linearties (Contd) Self Phase Modulation Refractive index dependance on the power of a signal Cross Phase Modulation Refractive index dependance on the power of another signal

38. Effects of Nonlinearites

39. Multiple Channels vs Single Channel

40. Tools to combat Impairments Power / Channel Dispersion Compensation Channel Spacing Wavelength / Frequency Choice

41. 2. Couplers

42. Couplers (Contd.) Applications: 1.3 dB couplers – for Broadcast and Select networks 2.Taps for monitoring purposes 3.Optical Switches 4.Mac Zhender Interferometers 5.Lambda selective multiplexers and demultiplexers 6.Combine pump and signals in EDFAs

43. 3. Isolators

44. 4. Circulators

45. 5. Filters Fabry Perot Filter

46. Diffraction Grating

47. Bragg Grating

48. Mac Zhender Grating

49. Thin Film Dielectric Grating

50. Arrayed Waveguide Grating

51. Acuostooptic Tunable Filter

52. 6. Optical Amplifiers EDFA

53. EDFA (Contd.)

55. SNR

56. All Optical System Capacity

57. Raman Amplification

58. Raman Amplifiers Used as Pre-amplifier in the reverse direction Same pump laser as EDFA Higher gains Larger Bandwidth Distributed and hence lower noise figure’ Lower P launched – reduced nonlinearities

59. Benefits of Raman

60. Semiconductor Optical Amplifier

61. 7. Lasers MLM Fabry Perot Laser

62. SLM Lasers

63. External Cavity Lasers

64. External Cavity Lasers (Contd. )

65. 8. External Modulators

66. 9. Photodetectors

67. A Photodiode

68. 10. Optical Switches Photonic Switches (MEMS)

69. Electrooptic Switch

70. Lamda Switch

71. An Optical Network - Revisited Dispersion Managed Fiber Medium Dispersion Fiber Tx WDMWDM OA Tunable DCM OA DCF Tunable DCM DWDMDWDM Dynamic PMD Compensation New Modulation Formats Forward Error Correction Impairment Tolerant Receiver C+L Band OA S Band OA Raman Amplifier Dynamic OADM..... 3000Km - 5000Km Rx PMDC Broadband PMD Compensation

72. Conclusion