WDM principles

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WDM principles

  1. 1. WDM Principles February 2014 1 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  2. 2. How to increase network capacity? Space Division Multiplexing (SDM) • Add fiber & equipment • Time & Cost Time Division Multiplexing (TDM) • PDH/SDH (STM16->STM-64(10G)>STM-256(40G) • Cost & Complexity Wavelength Division Multiplexing (WDM) • Economical, mature & quick 2 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  3. 3. What’s WDM? • A technology that utilizes the properties of refracted light to both combine and separate optical signals based on their wavelengths within the optical spectrum • Different signals with specific wavelength are multiplexed into a fiber for transmission 3 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  4. 4. What’s WDM? , Contd., Gas Station Free Way Petrol Car Freeway Petrol Car Gas Station Gray Car Colored Car Driveway : Fiber : Supervisory Signal : Optical relay : Client Service : Service in different channels (wavelength) : Optical wavelength 4 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  5. 5. Advantages of WDM • Ultra high capacity • Data transparency transmission – Doesn’t change the structure or any byte in the frame for the client signal • Long haul transmission • Compatible with existing optical fibers • High performance-to-cost-ratio (unit traffic cost) – However, projects get long time to break-even • High networking flexibility, economy and reliability • Smooth expansion 5 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  6. 6. WDM system key technologies • Optical multiplexer (MUX) and demultiplexer • Optical Amplifier (Amp) • Supervisory channel • Optical Source 6 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  7. 7. Optical Multiplexer Unit: Multiplex several services with different wavelength into one main path signal Optical Amplifier: Amplifies the optical signal 1 A P A OLA nm OSC Optical Transponder Unit: Access the client services & convert the wavelength compiled with ITU standard OTU1 P P OA n A P P OA OTUn Optical Line Amplifier O M U 2 1 A 1, 2..n P OTU2 System structure 1, 2..n A OTU1 Optical De-multiplexer Unit: De-multiplex one main path signal into several individual signals nm OSC O D U 2 n OTU2 OTUn OSC Optical Supervisory Channel: Terminate & Re-generation. Not amplification. A P Active Passive 7 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  8. 8. OTU- Optical Transponder Unit Optical to Electrical conversion O Non-color E (Not defined by ITU-T) E O Ex:1310 nm short reach SMF 1550 nm long reach SMF Wavelength conversion 850 nm MMF Electrical to Optical conversion Color (Defined by ITU-T) Ex:1: 1550.51 nm 2 :1551.23 nm Can’t use these in WDM without OTU SMF-Single Mode Fiber MMF-Multi Mode Fiber 8 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  9. 9. Loss • Passive => Loss (power reduction) – Ex:- Input power to the MUX 0 dB. Output power from the MUX -6 dB. Therefore the loss is 6 dB • Loss can be due to splicing, distance, bending, aging, connectors Source: http://www.thefoa.org/tech/lossbudg.htm Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU 9
  10. 10. Transmission Modes • Single fiber unidirectional – 2 optical fibers • Single fiber bidirectional – Only 1 optical fiber – Ex:- CWDM, to reduce cost Coarse WDM 10 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  11. 11. Application modes • Open system – NO special requirements for multiplex terminal optical interface – Only requirement is that these interfaces meet the optical interface standards defined in ITU-T • Integrated system – Doesn’t adopt wavelength conversion technology – Requires that the wavelength of the optical signal at the multiplex terminal confirms to the specifications for the WDM system 11 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  12. 12. c=f • c = velocity of light in a vacuum = 3 x 108 m/s (constant) • f = frequency (Hz) •  = wavelength (m) • f1/ • Refractive index n = c / v • v = speed of light in a material • In an optical fiber, since the n of core is higher than n of cladding the light refracts 12 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  13. 13. Fiber cable types • G.652 • G.653 – Main application: submarine • G.655 – Best fiber for WDM – Expensive 13 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  14. 14. Single vs. multi mode Source: http://osd.com.au/multimode-versus-singlemode/ High Attenuation (3 dB/km) High dispersion Expensive today (because of less demand) Attenuation = 0.22 dB.km (G.652 @ 1550nm) No mode dispersion Mode=Path of light 14 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  15. 15. WDM network topologies • Point to Point • Ring • Mesh Cost  Complexity  Reliability  15 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  16. 16. CWDM vs. DWDM DWDM CWDM Source: http://www.cable360.net/tech/strategy/businesscases/30007.html CWDM- Coarse WDM, DWDM-Dense WDM Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU 16
  17. 17. Since f  1 / , channel spacing can be denotes as both distance and frequency CWDM vs. DWDM, cont., Types CWDM DWDM Channel spacing (Grid) 20 nm (fixed) 100 GHz/ 50 GHz/ 25 GHz 1311~1611 nm (All bands) C-band: 1529nm~1561nm L-band: 1570nm~1603nm 18 x 10 Gbps 192 x 10 Gbps Laser Un-cooled Laser Cooled Laser Cost 70% 100% 100 km (max) 5000 km Band Capacity (max) Application As CWDM works in all 5 bands, amplification is NOT possible 17 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  18. 18. Linear and non-linear effects • Linear ( distance) – Attenuation – Dispersion • Non-Linear – Four Way Mixing (FWM) • Chromatic • Polarization 18 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  19. 19. Attenuation Lowest loss band Water peak Source: http://osd.com.au/multimode-versus-singlemode/ 19 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  20. 20. Dispersion • Physical phenomenon of signal distortion caused when various modes carrying signal energy or different frequencies of the signal have different group velocity and disperse from each other during propagation • Digital modulation -> carrier frequency+ multiple other frequencies -> different speeds -> Inter Symbol Interference (ISI) -> Bit errors • Color 2 types – Mode dispersion • – Dominant in MMF Chromatic dispersion (CD) • • Dominant in SMF Ex:- Rainbow – • Light through water traverse at different speeds Dispersion affects the own channel Source: http://www.bubblews.com/news/2058509-somewhere-over-the-rainbow 20 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  21. 21. Chromatic dispersion A phenomenon that the phase velocity and group velocity of light propagating in a transparent medium depend on the optical frequency. A related quantitative measure is the Group Velocity Dispersion (GVD) Source: https://www.upc.edu/patents/TO/ict-and-electronic-technologies/chromatic-dispersion-1.jpg 21 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  22. 22. Chromatic dispersion, cont., G.655: little dispersion to avoid FWM G.652: widely used, need DCF for high rate transmission Dispersion coefficient G.653 17 ps/nm/km 4.5 ps/nm/km 1310 1550 Wavelength/nm 22 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  23. 23. Dispersion Compensation Fiber (DCF) DCM (Dispersion Compensation Module) . Usually placed at bottom of rack Source: http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=5719 Dispersion-> DCF ->Dispersion longer fiber distance -> attenuation  -> Optical Amplifiers -> noise  -> S/N If the total accumulated dispersion (ps/nm) is less than 800 for 10 Gbps/STM-64, then DCM is not required 23 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  24. 24. Polarization Mode Dispersion (PMD) • Resulting from different propagation velocities of 2 states of cross polarization of optical signal in fiber • Can’t avoid • Due to – Manufacturing process – Installation/usage (temperature, vibration, bending (DCM) Source: http://www.fiberoptics4sale.com/wordpress/optical-fiber-dispersion/ • Both PMD and CD are sensitive at higher bit rates 24 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  25. 25. Optical source • Key requirements – Large dispersion tolerance value – Standard and stable wavelength • ITU-T recommends the maximum deviation of the channel frequency to be <=10% of channel spacing 25 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  26. 26. Modulators • Direct • Electro-Absorption (EA) External – Ex:- for 40 G • Mach-Zehnder (M-Z) External – Ex:- for 40 G • Coherent – Ex:- for 100 G – No DCM required 26 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  27. 27. Comparison of modulators Types Direct EA M-Z Coherent Max. dispersion tolerance (ps/nm) 1200-4000 7200-12800 >12800 40000 Cost moderate expensive Very expensive Very expensive good better best best Wavelength stability 27 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  28. 28. S (signal) OA Amplifier • Compensates the loss • Any analog signal system has noise. Optical signal is also analog • More Amps-> more accumulated noise (N)->S/N->BIR – Amp keeps Signal (S) constant. • Solution: re-generation • Amplification and regeneration gives unlimited distance, theoretically 28 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  29. 29. Amplifier types • EDFA - Erbium Doped Fiber Amplifier – Widely used • RFA - Raman Fiber Amplifier – Uses non-linearity effect – Uses high power class 4 laser • Use APC (Angular Physical Contact) connectors instead of PC – Ex:-LC/APC (Lucent Connector), SC/APC, FC/APC – 20 km distance • Need to maintain splice loss <0.1dB within 1st 10 km and <0.2dB within next 10 km – Low noise – Low gain efficiency (10~12 dB) 29 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  30. 30. EDFA Source: http://www.tlc.unipr.it/bononi/ricerca/edfa.html Source: http://spie.org/x33612.xml 30 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  31. 31. Raman Source: http://www.globalspec.com/RefArticleImages/157D4FA155A471EB0023715782A949C2_04_04_DWDM-10.jpg 31 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  32. 32. Optical Multiplexer and demultiplexer • TFF - Thin Film Filter – when no. of channels<16 • AWG - Arrayed Waveguide Grating – when no. of channels>=16 – expensive 32 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  33. 33. TFF 0.1 dB loss. Therefore max. of 16 channels Has the lowest power Source: http://www.fiberoptics4sale.com/wordpress/what-is-multilayer-dielectric-thin-film-filter/ 33 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  34. 34. AWG All have the same power Source: http://docstore.mik.ua/univercd/cc/td/doc/product/mels/cm1500/dwdm/dwdm_ovr.htm 34 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  35. 35. Supervisory technologies • OSC - Optical Supervisory Channel – Often used in backbone systems – Uses OTN (G.709) framing (similar to SDH) on OUT board – Costly • ESC - Electrical Supervisory Channel – Often used in metropolitan systems – OTU is mandatory at every site • OLA sites don’t have OUT. Therefore can’t mange OLAs with ESC 35 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  36. 36. Related ITU-T recommendations • • • • • • G.652 - SMF G.655 - Dispersion-shifted SMF G.661/G.662/G.663 - OAs G.671 - Passive optical components G.957 - SDH optical interfaces G.691 - Optical interfaces for single channel STM64, STM-256 systems & other SDH systems with OA G.692 - Optical interfaces for multi-channel systems with OA G.709 - OTN interfaces • G.975 - FEC for submarine systems 36 Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU
  37. 37. About the Author 37 Eng. Anuradha Udunuwara is a Chartered Engineer by profession based in Sri Lanka. He has over a decade industry experience in strategy, architecture, engineering, design, plan, implementation and maintenance of CSP Networks using both packet-switched (PS) and Circuit-Switched (CS) technologies, along with legacy to NGN migration. Eng. Anuradha is a well-known in the field of CSP industry, both locally and internationally. Graduated from University of Peradeniya, Sri Lanka in 2001 with an honors in Electrical & Electronic Engineering, Eng. Anuradha is a corporate member of the Institution of Engineers Sri Lanka, a professional member of British Computer Society, a member of Institution of Electrical & Electronic Engineers, a member of Institution of Engineering & Technology (formerly Institution of Electrical Engineers), a member of the Computer Society of Sri Lanka, a life member of Sri Lanka Association for the Advancement of Science, a senior member of the Carrier Ethernet Forum, a member of the Internet Society, a member of the Internet Strategy Forum, a member of the Internet Strategy Forum Network, a member & a senior contributor of the Ethernet Academy, a member of the NGN/IMS forum and a member of the Peradeniya Engineering Faculty Alumni Association. He is also an ITIL foundation certified and the only MEF-CECP in the country. In his spare time Anuradha enjoys spending time with his family, playing badminton, photography, reading and travelling. Anuradha Udunuwara | udunuwara@ieee.org | www.linkedin.com/in/anuradhau | @AnuradhU

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