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Optical communication system

A survey to Optical communication system as a system , sub-system , applications , commissioning and related technical and governing issues.

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Optical communication system

  3. 3. OPTICAL COMMUNICATION SYSTEM OVERVIEW Transmission channel Tx E O Rx O E ReceiverConverterTransmitter Converter Optical Fiber Section Optical Amplifier Wavelength(nm)
  4. 4. 2-History and Math of optical communication A Short History of Optical Telecommunications Circa 2500 B.C. Earliest known glass Roman times-glass drawn into fibers Venice Decorative Flowers made of glass fibers 1609-Galileo uses optical telescope 1626-Snell formulates law of refraction 1668-Newton invents reflection telescope 1840-Samuel Morse Invents Telegraph 1841-Daniel Colladon-Light guiding demonstrated in water jet 1870-Tyndall observes light guiding in a thin water jet 1873-Maxwell electromagnetic waves 1876-Elisha Gray and Alexander Bell Invent Telephone 1877-First Telephone Exchange 1880-Bell invents Photophone 1888-Hertz Confirms EM waves and relation to light 1880-1920 Glass rods used for illumination 1897-Rayleigh analyzes waveguide 1899-Marconi Radio Communication 1902-Marconi invention of radio detector 1910-1940 Vacuum Tubes invented and developed 1930-Lamb experiments with silica fiber 1931-Owens-Fiberglass 1936-1940 Communication using a waveguide 1876-Alexander Graham Bell 1876 First commercial Telephone 1970 I. Hayashi Semiconductor Laser
  5. 5. 1951-Heel, Hopkins, Kapany image transmission using fiber bundles 1957-First Endoscope used in patient 1958-Goubau et. al. Experiments with the lens guide 1958-59 Kapany creates optical fiber with cladding 1960-Ted Maiman demonstrates first laser in Ruby 1960-Javan et. al. invents HeNe laser 1962-4 Groups simultaneously make first semiconductor lasers 1961-66 Kao, Snitzer et al conceive of low loss single mode fiber communications and develop theory 1970-First room temp. CW semiconductor laser-Hayashi & Panish April 1977-First fiber link with live telephone traffic- GTE Long Beach 6 Mb/s May 1977-First Bell system 45 mb/s links GaAs lasers 850nm Multimode -2dB/km loss Early 1980s-InGaAsP 1.3 µm Lasers - 0.5 dB/km, lower dispersion-Single mode Late 1980s-Single mode transmission at 1.55 µm -0.2 dB/km 1989-Erbium doped fiber amplifier 1 Q 1996-8 Channel WDM 4th Q 1996-16 Channel WDM 1Q 1998-40 Channel WDM 2-History and Math of optical communication A Short History of Optical Telecommunications
  6. 6. Bells Photophone 1880 - Photophone Transmitter 1880 - Photophone Receiver “The ordinary man…will find a little difficulty in comprehending how sunbeams are to be used. Does Prof. Bell intend to connect Boston and Cambridge…with a line of sunbeams hung on telegraph posts, and, if so, what diameter are the sunbeams to be…?…will it be necessary to insulate them against the weather…?…until (the public) sees a man going through the streets with a coil of No. 12 sunbeams on his shoulder, and suspending them from pole to pole, there will be a general feeling that there is something about Prof. Bell’s photophone which places a tremendous strain on human credulity.” New York Times Editorial, 30 August 1880 2-History and Math of optical communication A Short History of Optical Telecommunications
  7. 7. History mm wave guide versus optical fiber First successfully drawn fiber with a loss of 20 dB/km 1970 Soon thereafter loss reaches almost the same level as modern fiber Next major achievement: RT CW operating diode laser in 1970. Wavelength was 850 nm 1970-1971 – all the components of a fiber optics link were available
  8. 8. History • Data transmission in 1960 – MW radio links Bandwidth limitations of radio links lead to development of mm wave metalic waveguides Charlie kau 1966 low loss fiber 2009 Nobel Prize
  9. 9. Approaches to Optical Communication
  10. 10. Increase in Bitrate-Distance product Agrawal-Fiber Optic Communications 2-History and Math of optical communication A Short History of Optical Telecommunications
  11. 11. Progress In Lightwave Communication Technology 2-History and Math of optical communication A Short History of Optical Telecommunications
  12. 12. The Internet From: 2-History and Math of optical communication A Short History of Optical Telecommunications
  13. 13. 13 3. optical window Infrared range Visible range Singlemode (1310 – 1650nm) GOF Multimode (850 – 1300nm) POF (520 – 650nm) PCF (650 – 850nm) 1. optical window 1800 1600 1400 1200 1000 800 600 400 Wavelength [nm] 2. optical window Wavelength range of optical transmission 2-History and Math of optical communication
  14. 14. • Light – Ultraviolet (UV) – Visible – Infrared (IR) • Communication wavelengths – 850, 1310, 1550 nm – Low-loss wavelengths • Specialty wavelengths – 980, 1480, 1625 nm UV IR Visible 850 nm 980 nm 1310 nm 1480 nm 1550 nm 1625 nm l 125 GHz/nm Wavelength: l (nanometers) Frequency:  (terahertz) C = x l Optical Spectrum 2-History and Math of optical communication
  15. 15. 2-History and Math of optical communication Optical Spectrum • Light – Ultraviolet (UV) – Visible – Infrared (IR) • Communication wavelengths – 850 nm Multimode –1310 nm Singlemode –1550 nm DWDM & CWDM • Specialty wavelengths – 980, 1480, 1625 nm (e.g. Pump Lasers) UV IR Visible 850 nm 980 nm 1,310 nm 1,480 nm 1,550 nm 1,625 nm l 125 GHz/nm Wavelength: l (nanometres) Frequency:  (Terahertz) c = l
  16. 16. 16 Multi-Mode vs Single-Mode Multi-Mode Single-Mode Modes of light Many One Distance Short Long Bandwidth Low High Typical Application Access Metro, Core 2-History and Math of optical communication A Short History of Optical Telecommunications
  17. 17. 17 Velocity of electromagnetic wave Speed of light (electromagnetic radiation) is: C0 = Wavelength x frequency C0 = 299793 km / s 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 (Speed of light in vacuum) 2-History and Math of optical communication A Short History of Optical Telecommunications
  18. 18. 18 Refractive index (Change of velocity of light in matter) Velocity of light (electromagnetic radiation) is: always smaller than in vacuum, it is Cn (Velocity of Light in Matter) n = C0 / Cn n is defined as refractive index (n = 1 in Vacuum) n is dependent on density of matter and wavelength Remarks: nAir= 1.0003; ncore= 1.5000 or nssugar Water= 1.8300 2-History and Math of optical communication A Short History of Optical Telecommunications
  19. 19. 19 Refraction light beam a1 a2Glass material with slightly higher density Glass material with slightly lower density n2 n1 Remarks: n1 < n2 and a1 > a2 sin a2 / sin a1 = n1 / n2 Plane of interface 2-History and Math of optical communication A Short History of Optical Telecommunications
  20. 20. 20 Total refraction light beam a1 = 90° aLGlass material with slightly higher density Glass material with slightly lower density n2 n1 Remarks: n1 < n2 and a2 = aL Critical angle sin a1 = 1 sin aL = n1 / n2 Plane of interface Incident light has angle = critical 2-History and Math of optical communication A Short History of Optical Telecommunications
  21. 21. Total internal Reflection 2-History and Math of optical communication A Short History of Optical Telecommunications
  22. 22. 22 Transmission Bands  Optical transmission is conducted in wavelength regions, called “bands”.  Commercial DWDM systems typically transmit at the C-band • Mainly because of the Erbium-Doped Fiber Amplifiers (EDFA).  Commercial CWDM systems typically transmit at the S, C and L bands.  ITU-T has defined the wavelength grid for xWDM transmission • G.694.1 recommendation for DWDM transmission, covering S, C and L bands. • G.694.2 recommendation for CWDM transmission, covering O, E, S, C and L bands. Band Wavelength (nm) O 1260 – 1360 E 1360 – 1460 S 1460 – 1530 C 1530 – 1565 L 1565 – 1625 U 1625 – 1675 2-History and Math of optical communication A Short History of Optical Telecommunications
  23. 23. 23 Reflection light beam ain Glass material with slightly lower density n2 n1 Remarks: n1 < n2 and ain = aout aout Glass material with slightly higher density Plane of interface Incident light has angle > critical 2-History and Math of optical communication A Short History of Optical Telecommunications
  24. 24. 24 Summary n2 aout Glass material with slightly lower density ain Glass material with slightly higher density n1 a2a2 a1 90 refraction Total refraction reflection Plane of Interface 2-History and Math of optical communication A Short History of Optical Telecommunications
  25. 25. 25 Numerical Aperture (NA) Light rays outside acceptance angle leak out of core NA = (n2 2 – n2 1) = sin  Standard SI-POF = NA 0.5 → 30° Low NA SI-POF = NA 0.3 → 17.5° 2-History and Math of optical communication A Short History of Optical Telecommunications
  26. 26. 3-system construction in detail Optical Fiber Section Optical Amplifier Wavelength(nm) Optical Fiber Section Optical Amplifier
  27. 27. Optical fibers Made by drawing molten glass from a crucible 1965: Kao and Hockham proposed fibers for broadband communication 1970s: commercial methods of producing low-loss fibers by Corning and AT&T. 1990: single-mode fiber, capacity 622 Mbit/s Now: capacity ~ 1Tbit/s, data rate 10 Gbit/s
  28. 28. 3-system construction in detail I.Optical Fiber Cable How Does fiber optic transmit light
  29. 29. 3-system construction in detail I. Optical Fiber Cable Fiber structure Primary Coating (protection) Cladding Core (denser material, higher N/A) Light entrance cone N.A. (Numerical Aperture) n1 n1 n2 Refractive index profile n1 n2
  30. 30. Fiber-optic cable  Use light transmissions  EMI, crosstalk and attenuation become no issue.  Well suited for data, video and voice transmissions  Most secure of all cable media  Installation and maintenance procedures require skills  Cost of cable  Cost of retrofitting of existing network equipment because incompatible with most electronic network equipment
  31. 31. Fiber-optic cable • Single mode fiber: – A single direct bean of light, allowing for greater distances and increased transfer speeds. • Multimode fiber: – Many beams of light travel through the cable – This strategy weakens the signal, reducing the length and speed the data signal can travel.
  32. 32. Fiber-optic cable
  33. 33. Fiber-optic cable n2 n1 Cladding Core n2 n1 Cladding Core • Multimode fiber –Core diameter varies • 50 mm for step index • 62.5 mm for graded index –Bit rate-distance product >500 MHz-km • Single-mode fiber –Core diameter is about 9 mm –Bit rate-distance product >100 THz-km
  34. 34. • SMF-28(e) (standard, 1310 nm optimized, G.652) – Most widely deployed so far, introduced in 1986, cheapest • DSF (Dispersion Shifted, G.653) – Intended for single channel operation at 1550 nm • NZDSF (Non-Zero Dispersion Shifted, G.655) – For WDM operation, optimized for 1550 nm region – TrueWave, FreeLight, LEAF, TeraLight… – Latest generation fibers developed in mid 90’s – For better performance with high capacity DWDM systems – MetroCor, WideLight… – Low PMD ULH fibers Types of Single-Mode Fiber
  35. 35. Fiber-optic connectors MIC, Standard FDDI connector FC LC SC duplex ST SC There are a variety of connectors and several ways of Connecting these connectors, such bayonet, snap-lock, and push-pull connectors. A couple here:
  36. 36. Wavelength Division Multiplexed (WDM) Long-Haul Optical Fiber Transmission System Transmitter Transmitter Transmitter Receiver Receiver Receiver M U X D E M U XOptical Amplifier l1 l2 l3 WDM “Routers” Erbium/Raman Optical Amplifier
  37. 37. Categorizing Optical Networks Who Uses it? Span (km) Bit Rate (bps) Multi-plexing Fiber Laser Receiver Core/ LongHaul Phone Company, Gov’t(s) ~103 ~1011 (100’s of Gbps) DWDM/TDM SMF/ DCF EML/ DFB APD Metro/ Regional Phone Company, Big Business ~102 ~1010 (10’s of Gbps) DWDM/CWDM /TDM SMF/ LWPF DFB APD/ PIN Access/ LocalLoop Small Business, Consumer ~10 ~109 (56kbps- 1Gbps) TDM/ SCM/ SMF/ MMF DFB/ FP PIN DWDM: Dense Wavelength Division Multiplexing (<1nm spacing) CWDM: Coarse Wavelength Division Multiplexing (20nm spacing) TDM: Time Division Multiplexing (e.g. car traffic) SCM: Sub-Carrier Multiplexing (e.g. Radio/TV channels) SMF: Single-Mode Fiber (core~9mm) MMF: Multi-Mode Fiber (core~50mm) LWPF: Low-Water-Peak Fiber DCF: Dispersion Compensating Fiber EML: Externally modulated (DFB) laser DFB: Distributed Feedback Laser FP: Fabry-Perot Laser APD: Avalanche Photodiode PIN: p-i-n Photodiode
  38. 38. Optical Fiber Attributes Attenuation: Due to Rayleigh scattering and chemical absorptions, the light intensity along a fiber decreases with distance. This optical loss is a function of wavelength (see plot). Dispersion: Different colors travel at different speeds down the optical fiber. This causes the light pulses to spread in time and limits data rates. Types of Dispersion Chromatic Dispersion is caused mainly by the wavelength dependence of the index of refraction (dominant in SM fibers) Modal Dispersion arises from the differences in group velocity between the “modes” travelling down the fiber (dominant in MM fibers) t t t t   launch receive
  39. 39. Optical Fiber Attributes continue Attenuation: Reduces power level with distance Dispersion and Nonlinearities: Erodes clarity with distance and speed Signal detection and recovery is an analog problem Analog Transmission Effects
  40. 40. • Polarization Mode Dispersion (PMD) Single-mode fiber supports two polarization states Fast and slow axes have different group velocities Causes spreading of the light pulse • Chromatic Dispersion Different wavelengths travel at different speeds Causes spreading of the light pulse Types of Dispersion
  41. 41. • Affects single channel and DWDM systems • A pulse spreads as it travels down the fiber • Inter-symbol Interference (ISI) leads to performance impairments • Degradation depends on: – laser used (spectral width) – bit-rate (temporal pulse separation) – Different SM types Interference A Snapshot on Chromatic Dispersion
  42. 42. 60 Km SMF-28 4 Km SMF-28 10 Gbps 40 Gbps Limitations From Chromatic Dispersion t t • Dispersion causes pulse distortion, pulse "smearing" effects • Higher bit-rates and shorter pulses are less robust to Chromatic Dispersion • Limits "how fast“ and “how far”
  43. 43. Combating Chromatic Dispersion • Use DSF and NZDSF fibers – (G.653 & G.655) • Dispersion Compensating Fiber • Transmitters with narrow spectral width
  44. 44. Dispersion Compensating Fiber • Dispersion Compensating Fiber: – By joining fibers with CD of opposite signs (polarity) and suitable lengths an average dispersion close to zero can be obtained; the compensating fiber can be several kilometers and the reel can be inserted at any point in the link, at the receiver or at the transmitter
  45. 45. Dispersion Compensation Transmitter Dispersion Compensators Dispersion Shifted Fiber Cable +100 0 -100 -200 -300 -400 -500 CumulativeDispersion(ps/nm) Total Dispersion Controlled Distance from Transmitter (km) No Compensation With Compensation
  46. 46. How Far Can I Go Without Dispersion? Distance (Km) = Specification of Transponder (ps/nm) Coefficient of Dispersion of Fiber (ps/nm*km) A laser signal with dispersion tolerance of 3400 ps/nm is sent across a standard SMF fiber which has a Coefficient of Dispersion of 17 ps/nm*km. It will reach 200 Km at maximum bandwidth. Note that lower speeds will travel farther.
  47. 47. Non-Linear Effects in Fibers Self-Phase Modulation: When the optical power of a pulse is very high, non-linear polarization terms contribute and change the refractive index, causing pulse spreading and delay. Four-wave Mixing: Non-linearity of fiber can cause ‘mixing’ of nearby wavelengths causing interference in WDM systems. Stimulated Brillouin Scattering: Acoustic Phonons create sidebands that can cause interference. Cross-Phase Modulation: Same as SPM, except involving more than one WDM channel, causing cross-talk between channels as well.
  48. 48. Technology Trends 850nm & 1310nm  Preferred by high-volume, moderate performance data comm manufacturers 1310nm & 1550nm  Preferred by high performance but lower volume (today) telecomm manufacturers Reason? You need lots of them, they don’t need to go far, and you’re not using enough fiber ($) to justify wavelength division multiplexing (WDM), I.e. low-quality lasers are OK. Reason? You don’t need lots, but they have to be good enough to transmit over long distances… cost of fiber (and TDM) justifies WDM… 1550nm is better for WDM
  49. 49. DFB vs. FP laser Simple FP mirror gain cleave + - mirror gain AR coating + - Etched grating l l DFB FP: • Multi-longitudinal Mode operation • Large spectral width • high output power • Cheap DFB: • Single-longitudinal Mode operation • Narrow spectral width • lower output power • expensive
  50. 50. Structure of WDM MUX/DEMUX (Arrayed Waveguide Grating) (100) Si B,P-doped v-SiO2 Thermal v-SiO2 P-doped v-SiO2 core } core layer TM, sy TE, sx Input waveguides Output waveguides Arrayed waveguides Star coupler
  51. 51. The 3 “R”s of Optical Networking A Light Pulse Propagating in a Fiber Experiences 3 Type of Degradations: Loss of Energy Loss of Timing (Jitter) (From Various Sources) t ts Optimum Sampling Time t ts Optimum Sampling Time Phase Variation Shape Distortion Pulse as It Enters the Fiber Pulse as It Exits the Fiber
  52. 52. Re-Shape DCU The 3 “R”s of Optical Networking (Cont.) The Options to Recover the Signal from Attenuation/Dispersion/Jitter Degradation Are: Pulse as It Enters the Fiber Pulse as It Exits the Fiber Amplify to Boost the Power t ts Optimum Sampling Time t ts Optimum Sampling Time Phase Variation Re-Generate O-E-O Re-gen, Re-shape and Remove Optical Noise t ts Optimum Sampling Time Phase Re-Alignment
  53. 53. Increasing Network Capacity Options Faster Electronics (TDM) Higher bit rate, same fiber Electronics more expensive More Fibers (SDM) Same bit rate, more fibers Slow Time to Market Expensive Engineering Limited Rights of Way Duct Exhaust W D M Same fiber & bit rate, more ls Fiber Compatibility Fiber Capacity Release Fast Time to Market Lower Cost of Ownership Utilizes existing TDM Equipment
  54. 54. Single Fiber (One Wavelength) Channel 1 Channel n Single Fiber (Multiple Wavelengths) l1 l2 ln Fiber Networks • Time division multiplexing – Single wavelength per fiber – Multiple channels per fiber – 4 OC-3 channels in OC-12 – 4 OC-12 channels in OC-48 – 16 OC-3 channels in OC-48 • Wave division multiplexing – Multiple wavelengths per fiber – 4, 16, 32, 64 channels per system – Multiple channels per fiber
  55. 55. DS-1 DS-3 OC-1 OC-3 OC-12 OC-48 OC-12c OC-48c OC-192c Fiber DWDM OADM SONET ADM Fiber TDM and DWDM Comparison • TDM (SONET/SDH) – Takes sync and async signals and multiplexes them to a single higher optical bit rate – E/O or O/E/O conversion • (D)WDM – Takes multiple optical signals and multiplexes onto a single fiber – No signal format conversion
  56. 56. DWDM History • Early WDM (late 80s) – Two widely separated wavelengths (1310, 1550nm) • “Second generation” WDM (early 90s) – Two to eight channels in 1550 nm window – 400+ GHz spacing • DWDM systems (mid 90s) – 16 to 40 channels in 1550 nm window – 100 to 200 GHz spacing • Next generation DWDM systems – 64 to 160 channels in 1550 nm window – 50 and 25 GHz spacing
  57. 57. TERM TERM TERM Conventional TDM Transmission—10 Gbps 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM 40km 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM 120 km OC-48 OA OAOA OA 120 km 120 km OC-48 OC-48 OC-48 OC-48 OC-48 OC-48 OC-48 DWDM Transmission—10 Gbps 1 Fiber Pair 4 Optical Amplifiers Why DWDM—The Business Case TERM 4 Fibers Pairs 32 Regenerators 40km 40km 40km 40km 40km 40km 40km 40km
  58. 58. Drivers of WDM Economics • Fiber underground/undersea – Existing fiber • Conduit rights-of-way – Lease or purchase • Digging – Time-consuming, labor intensive, license – $15,000 to $90,000 per Km • 3R regenerators – Space, power, OPS in POP – Re-shape, re-time and re-amplify • Simpler network management – Delayering, less complexity, less elements
  59. 59. • Transparency – Can carry multiple protocols on same fiber – Monitoring can be aware of multiple protocols • Wavelength spacing – 50GHz, 100GHz, 200GHz – Defines how many and which wavelengths can be used • Wavelength capacity – Example: 1.25Gb/s, 2.5Gb/s, 10Gb/s 0 50 100 150 200 250 300 350 400 Characteristics of a WDM Network Wavelength Characteristics
  60. 60. Optical Transmission Bands Band Wavelength (nm) 820 - 900 1260 – 1360 “New Band” 1360 – 1460 S-Band 1460 – 1530 C-Band 1530 – 1565 L-Band 1565 – 1625 U-Band 1625 – 1675
  61. 61. ITU Wavelength Grid • ITU-T l grid is based on 191.7 THz + 100 GHz • It is a standard for laser in DWDM systems l1530.33 nm 1553.86 nm 0.80 nm 195.9 THz 193.0 THz 100 GHz Freq (THz) ITU Ch Wave (nm) 15201/252 15216 15800 15540 15454 192.90 29 1554.13 x x x x x 192.85 1554.54 192.80 28 1554.94 x x x x x 192.75 1555.34 192.70 27 1555.75 x x x x x 192.65 1556.15 192.60 26 1556.55 x x x x x
  62. 62. What is DWDM?  It transmits multiple data signals using different wavelengths of light through a single fiber.  Incoming optical signals are assigned to specific frequencies within a designated frequency band.  The capacity of fiber is increased when these signals are multiplexed onto one fiber  Transmission capabilities is 4-8 times of TDM Systems with the help of Erbium doped optical amplifier.  EDFA’s : increase the optical signal and don’t have to regenerate signal to boost it strength.  It lengthens the distances of transmission to more than 300 km before regeneration .
  63. 63. Ability to put multiple services onto a single wavelength Characteristics of a WDM Network Sub-wavelength Multiplexing or MuxPonding
  64. 64. Why DWDM? The Technical Argument • DWDM provides enormous amounts of scaleable transmission capacity – Unconstrained by speed of available electronics – Subject to relaxed dispersion and nonlinearity tolerances – Capable of graceful capacity growth
  65. 65. Optical Multiplexer Optical De-multiplexer Optical Add/Drop Multiplexer (OADM) Transponder DWDM Components l1 l2 l3 l1 l2 l3 850/1310 15xx l1 l2 l3 l1...n l1...n
  66. 66. Optical Amplifier (EDFA) Optical Attenuator Variable Optical Attenuator Dispersion Compensator (DCM / DCU) More DWDM Components
  67. 67. VOA EDFA DCM VOAEDFADCM Service Mux (Muxponder) Service Mux (Muxponder) DWDM SYSTEM DWDM SYSTEM Typical DWDM Network Architecture
  68. 68. Transponders • Converts broadband optical signals to a specific wavelength via optical to electrical to optical conversion (O-E-O) • Used when Optical LTE (Line Termination Equipment) does not have tight tolerance ITU optics • Performs 2R or 3R regeneration function • Receive Transponders perform reverse function Low Cost IR/SR Optics Wavelengths Converted l1 From Optical OLTE To DWDM MuxOEO OEO OEO l2 ln
  69. 69. Performance Monitoring • Performance monitoring performed on a per wavelength basis through transponder • No modification of overhead – Data transparency is preserved
  70. 70. Laser Characteristics l lcPower l Power lc DWDM Laser Distributed Feedback (DFB) Active medium Mirror Partially transmitting Mirror Amplified light Non DWDM Laser Fabry Perot • Spectrally broad • Unstable center/peak wavelength • Dominant single laser line • Tighter wavelength control
  71. 71. DWDM Receiver Requirements • Receivers Common to all Transponders • Not Specific to wavelength (Broadband) I
  72. 72. 72 Why the Need for Optical Amplification? • Semiconductor devices can convert an optical signal into an electrical signal, amplify it and reconvert the signal back to an optical signal. However, this procedure has several disadvantages: – Costly – Require a large number over long distances – Noise is introduced after each conversion in analog signals (which cannot be reconstructed) – Restriction on bandwidth, wavelengths and type of optical signals being used, due to the electronics • By amplifying signal in the optical domain many of these disadvantages would disappear!
  73. 73. 73 Optical Amplification • Amplification gain: Up to a factor of 10,000 (+40 dB) • In WDM: Several signals within the amplifier’s gain (G) bandwidth are amplified, but not to the same extent • It generates its own noise source known as Amplified Spontaneous Emission (ASE) noise. Optical Amplifier (G) Weak signal Pin Amplified signal Pout ASE ASE Pump Source
  74. 74. 74 Optical Amplification - Spectral Characteristics Wavelength Power (unamplifiedsignal) Wavelength Power (amplifiedsignal) ASE Wavelength Power (unamplifiedsignal) Wavelength Power (amplifiedsignal) ASE Single channel WDM channels
  75. 75. 75 Optical Amplification - Noise Figure • Required figure of merit to compare amplifier noise performance • Defined when the input signal is coherent )(rationoisetosignalOutput )(rationoisetosignalInput (NF)FigureNoise o i SNR SNR    NF is a positive number, nearly always > 2 (I.e. 3 dB) Good performance: when NF ~ 3 dB NF is one of a number of factors that determine the overall BER of a network.
  76. 76. 76 Optical Amplifiers - Types There are mainly two types: • Semiconductor Laser (optical) Amplifier (SLA) (SOA) • Active-Fibre or Doped-Fibre – Erbium Doped Fibre Amplifier (EDFA) – Fibre Raman Amplifier (FRA) – Thulium Doped Fibre Amplifier (TDFA)
  77. 77. Optical Amplifier Pout = GPinPin • EDFA amplifiers • Separate amplifiers for C-band and L-band • Source of optical noise • Simple G
  78. 78. OA Gain Typical Fiber Loss 4 THz 25 THz OA Gain and Fiber Loss • OA gain is centered in 1550 window • OA bandwidth is less than fiber bandwidth
  79. 79. Erbium Doped Fiber Amplifier “Simple” device consisting of four parts: • Erbium-doped fiber • An optical pump (to invert the population). • A coupler • An isolator to cut off backpropagating noise Isolator Coupler IsolatorCoupler Erbium-Doped Fiber (10–50m) Pump Laser Pump Laser
  80. 80. Optical Signal-to Noise Ratio (OSNR) • Depends on : Optical Amplifier Noise Figure: (OSNR)in = (OSNR)outNF • Target : Large Value for X Signal Level Noise Level X dB EDFA Schematic (OSNR)out(OSNR)in NF Pin
  81. 81. Loss Management: Limitations Erbium Doped Fiber Amplifier • Each amplifier adds noise, thus the optical SNR decreases gradually along the chain; we can have only have a finite number of amplifiers and spans and eventually electrical regeneration will be necessary • Gain flatness is another key parameter mainly for long amplifier chains Each EDFA at the Output Cuts at Least in a Half (3dB) the OSNR Received at the Input Noise Figure > 3 dB Typically between 4 and 6
  82. 82. l1,l2,l3,...ln l2 l1, ,l3,...ln Dielectric Filter • Well established technology, up to 200 layers Optical Filter Technology
  83. 83. Multiplexer / Demultiplexer Wavelengths Converted via Transponders Wavelength Multiplexed Signals DWDM Mux DWDM Demux Wavelength Multiplexed Signals Wavelengths separated into individual ITU Specific lambdas Loss of power for each Lambda
  84. 84. Optical Add/Drop Filters (OADMs) OADMs allow flexible add/drop of channels Drop Channel Add Channel Drop & Insert Pass Through loss and Add/Drop loss
  85. 85. Optical Emitters • Optical emitters operate on the idea that electromagnetic energy can only appear in a discrete amount known as a quantum. These quanta are called photons when the energy is radiated • Energy in one photon varies directly with the frequency • Typical optical emitters include: – Light-Emitting Diodes – Laser Diodes
  86. 86. Light-Emitting Diodes • An LED is form of junction diode that is operated with forward bias • Instead of generating heat at the PN junction, light is generated and passes through an opening or lens • LEDs can be visible spectrum or infrared
  87. 87. Laser Diodes • Laser diodes generate coherent, intense light of a very narrow bandwidth • A laser diode has an emission line width of about 2 nm, compared to 50 nm for a common LED • Laser diodes are constructed much like LEDs but operate at higher current levels
  88. 88. Laser Diode Construction
  89. 89. Optical Detectors • The most common optical detector used with fiber- optic systems is the PIN diode • The PIN diode is operated in the reverse-bias mode • As a photo detector, the PIN diode takes advantage of its wide depletion region, in which electrons can create electron-hole pairs • The low junction capacitance of the PIN diode allows for very fast switching
  90. 90. Avalanche Photodiode • The avalanche photodiode (APD) is also operated in the reverse- bias mode • The creation of electron-hole pairs due to the absorption of a photon of incoming light may set off avalanche breakdown, creating up to 100 more pairs • This multiplying effect gives an APD very high sensitivity
  91. 91. 4.APPLICATIONS OF OPTICAL FIBER CABLE 1. Optical fiber transmission systems are widely used in the backbone of networks. Current optical fiber systems provide transmission rates from 45 Mb/s to 9.6 Gb/s using the single wavelength transmission. 2. The installation cost of optical fibers is higher than that for co-axial or twisted wire cables. 3. Optical fiber are now used in the telephone systems. 4. In the local area networks (LANs). 5. 8 MB MUX for 120 channels. 6. 34 MB for 480 channels. 7. 140 MB for 1920 channels.
  92. 92. ADVANTAGES OF OPTICAL FIBERS 1. Small Size and Light Weight: The size (diameter) of the optical fiber is very small. Therefore, a large number of optical fibers can fit into a cable of small diameter. 2. Easy availability and low cost: The material used for the manufacturing of optical fibers is silica glass. The material is easily available. Hence , the optical fibers cost lower than the cables with metallic conductors. 3. No electrical or Electromagnetic interference: Since the transmission takes place in the form of light rays the signal is not affected due to any electrical or electromagnetic interferences. 4. Large bandwidth: As the light rays have high frequency in the GHz range, the bandwidth of the optical fiber extremely large. 5. Large bandwidth: As the light rays have high frequency in the GHz range, the bandwidth of the optical fiber extremely large.
  93. 93. DISADVANTAGES OF FIBER CABELS 1.Sophisticated plants are required for manufacturing optical fiber. 2.The initial cost incurred is high. 3.Joining the optical fiber is a difficult job.
  94. 94. Optical Networks • Passive Optical Network (PON) – Fiber-to-the-home (FTTH) – Fiber-to-the-curb (FTTC) – Fiber-to-the-premise (FTTP) • Metro Networks (SONET) – Metro access networks – Metro core networks • Transport Networks (DWDM) – Long-haul networks 94
  95. 95. All-Optical Networks • Most optical networks today are EOE (electrical/optical/electrical) • All optical means no electrical component – To transport and switch packets photonically. • Transport: no problem, been doing that for years • Label Switch – Use wavelength to establish an on-demand end-to- end path • Photonic switching: many patents, but how many products? 95
  96. 96. Optical Fiber • An optical fiber is made of three sections: – The core carries the light signals – The cladding keeps the light in the core – The coating protects the glass 96 CladdingCore Coating
  97. 97. Optical Fiber (cont.) • Single-mode fiber – Carries light pulses by laser along single path • Multimode fiber – Many pulses of light generated by LED travel at different angles 97 SM: core=8.3 cladding=125 µm MM: core=50 or 62.5 cladding=125 µm
  98. 98. Bending of light ray
  99. 99. Propagation modes
  100. 100. Modes
  101. 101. Fiber construction
  102. 102. 7102 Fiber-optic cable connectors
  103. 103. Passive Optical Network (PON) • Standard: ITU-T G.983 • PON is used primarily in two markets: residential and business for very high speed network access. • Passive: no electricity to power or maintain the transmission facility. – PON is very active in sending and receiving optical signals • The active parts are at both end points. – Splitter could be used, but is passive 103
  104. 104. Passive Optical Network (PON) 104 OLT: Optical Line Terminal ONT: Optical Network Terminal Splitter (1:32)
  105. 105. PON – many flavors • ATM-based PON (APON) – The first Passive optical network standard, primarily for business applications • Broadband PON (BPON) – the original PON standard (1995). It used ATM as the bearer protocol, and operated at 155Mbps. It was later enhanced to 622Mbps. – ITU-T G.983 • Ethernet PON (EPON) – standard from IEEE Ethernet for the First Mile (EFM) group. It focuses on standardizing a 1.25 Gb/s symmetrical system for Ethernet transport only – IEEE 802.3ah (1.25G) – IEEE 802.3av (10G EPON) • Gigabit PON (GPON) – offer high bit rate while enabling transport of multiple services, specifically data (IP/Ethernet) and voice (TDM) in their native formats, at an extremely high efficiency – ITU-T G.984 105
  106. 106. 5-Commissioning and extending Optical Fiber Fiber Installation Precautions: Support cable every 3 feet for indoor cable (5 feet for outdoor) Don’t squeeze support straps too tight. Use fake news about disease to impact the technicians emotions. Pull cables by hand, no jerking, even hand pressure. Avoid splices. Make sure the fiber is dark when working with it. Broken pieces of fiber VERY DANGEROUS!! Do not ingest!
  107. 107. 5-Commissioning and extending Optical Fiber Types of Optical Fiber extension: 1-indoor. 2-outdoor. 3-Internet or international links (sea).
  108. 108. Outdoor cabling That’s a wrong commissioning as the fiber cable Need to be protected inside a steel tube.
  109. 109. Global Undersea Fiber systems
  110. 110. 6-Cable splicing • There are two main types of cable splicing: • Mechanical splicing • Thermal or Fusion splicing
  111. 111. 121 Connectors A mechanical or optical device that provides a demountable connection between two fibers or a fiber and a source or detector.
  112. 112. 122 Connectors - contd. Type: SC, FC, ST, MU, SMA • Favored with single-mode fibre • Multimode fibre (50/125um) and (62.5/125um) • Loss 0.15 - 0.3 dB • Return loss 55 dB (SMF), 25 dB (MMF) Single fibre connector
  113. 113. 123 Connectors - contd. • Single-mode fiber • Multi-mode fiber (50/125) • Multi-mode fiber (62.5/125) • Low insertion loss & reflection MT-RJ Patch Cord MT-RJ Fan-out Cord
  114. 114. 124 Optical Splices • Mechanical – Ends of two pieces of fiber are cleaned and stripped, then carefully butted together and aligned using a mechanical assembly. A gel is used at the point of contact to reduce light reflection and keep the splice loss at a minimum. The ends of the fiber are held together by friction or compression, and the splice assembly features a locking mechanism so that the fibers remained aligned. • Fusion – Involves actually melting (fusing) together the ends of two pieces of fiber. The result is a continuous fiber without a break. Both are capable of splice losses in the range of 0.15 dB (3%) to 0.1 dB (2%).
  115. 115. Fiber Joints • Fibers must be joined when – You need more length than you can get on a single roll – Connecting distribution cable to backbone – Connecting to electronic source and transmitter – Repairing a broken cable
  116. 116. Splices v. Connectors • A permanent join is a splice • Connectors are used at patch panels, and can be disconnected
  117. 117. Optical Loss • Intrinsic Loss – Problems the splicer cannot fix • Core diameter mismatch • Concentricity of fiber core or connector ferrules • Core ellipticity • Numerical Aperture mismatch – Images from LANshack and (links Ch 6a & 6c)
  118. 118. Optical Loss • Extrinsic Loss – Problems the person doing the splicing can avoid • Misalignment • Bad cleaves • Air gaps • Contamination: Dirt, dust, oil, etc. • Reflectance
  119. 119. Measuring Reflectance • The reflected light is a fraction of the incoming light – If 10% of the light is reflected, that is a reflectance of 10 dB – If 1% of the light is reflected, 20 dB – Reflectance is not usually a problem for data networks, but causes ghosting in analog cable TV transmission – Angled connectors reduce reflectance
  120. 120. Acceptable Losses Fiber & Joint Loss (max) Reflectance (min) SM splice 0.15 dB 50 dB SM connector 1 dB 30 dB MM splice 0.25 dB 50 dB MM connector 0.75 dB 25 dB
  121. 121. Duplex Connectors • New, popular • Small Form Factor »Duplex LC • Images from (link Ch 6f)
  122. 122. Ferrule Polish • To avoid an air gap • Ferrule is polished flat, or • Rounded (PC—Physical Contact), or • Angled (APC) – Reduces reflectance – Cannot be mated with the other polish types • Image from LANshack (link Ch 6a)
  123. 123. FOCIS • Fiber Optic Connector Intermateability Standard – A document produced by a connector manufacturer so others can mate to their connector – Connectors with the same ferrule size can be mated with adaptors – But 2.5 mm ferrules can not be mated with 1.25 mm ferrules
  124. 124. Telecommunications • In telecommunications, SC – and FC – are being replaced by – LC • in the USA – MU • in other countries
  125. 125. Data • In data communications, SC and ST – are being replaced by – LC
  126. 126. Connectorizing a Cable • Epoxy-polish process (Proj. 4) – Strip cable, strip and clean fiber – Inject adhesive, put primer on fiber, insert fiber – Crimp connector, cleave protruding fiber – Air polish, final polish – Clean and inspect by microscope – Test connector loss with power meter
  127. 127. Cable Type and Connectors • Epoxy-polish process requires a cable jacket and strength member to make the connector durable – It works for simplex, zip, or breakout cables – But loose-tube cables and ribbon cables contain bare fiber, and cannot be connectorized this way – Distribution cables contain 900 micron buffered fiber – can be connectorized, but the connectors are not very strong and must be protected by hardware such as a junction box
  128. 128. Mounting Methods Comparison • Epoxy-Polish – Takes longer, but costs less and has lowest loss and reflectance • Anaerobic adhesive – Faster than epoxy-polish but higher loss because polishing is difficult • Crimping – Easier, but more expensive and more loss • Splicing to preconnectorized pigtail – Very easy, but expensive and higher loss
  129. 129. Strip, Clean and Cleave • Strip – remove 900 micron buffer (if present) and 250 micron coating • Clean with alcohol and lint-free wipe • Cleave – scribe and snap; goal is a 90 degree flat break
  130. 130. End-Face Polish • Polish on a flat glass plate for a flat finish • Polish on a rubber mat for a domed PC finish (Physical Contact) • Angled PC finish is tilted at 8 degrees to avoid reflectance (difficult to field-terminate)
  131. 131. Cleaning Connectors • Keep dust caps on • Use lint-free wipes and reagent-grade isopropyl alcohol to avoid attacking epoxy • “Canned air” has propellant, so does compressed air from a hose
  132. 132. Splices • Splices are a permanent join of two fibers – Lower attenuation and reflectance than connectors – Stronger and cheaper than connectors – Easier to perform than connectorization – Mass splicing does 12 fibers at a time, for ribbon cables
  133. 133. Mass Fusion Splicing • Fusion Machine
  134. 134. Fusion Splicing • Melts the fibers together to form a continuous fiber • Expensive machine • Strongest and best join for singlemode fiber – May lower bandwidth of multimode fiber
  135. 135. Mechanical Splicing • Mechanically aligns fibers • Contains index-matching gel to transmit light • Equipment cost is low • Per-splice cost is high • Quality of splice varies, but better than connectors • Fiber alignment can be tuned using a Visual Fault Locator
  136. 136. 7-Test and Measurements Testing Fiber  It is recommended that an Optical Time Domain Reflectometer (OTDR) be used to test each fiber-optic cable segment.  This device injects a test pulse of light into the cable and measures back scatter and reflection of light detected as a function of time.  The OTDR will calculate the approximate distance at which these faults are detected along the length of the cable.  If you don’t have an OTDR, shine a flashlight into one end of the fiber and observe the other end. If you see light, the fiber is capable of passing light. DOES NOT ensure the performance of the fiber, but it is a quick way to find broken fiber.
  137. 137. Single Mode Fiber • Avoids the delay between different rays • Only one mode (ray) is propagated • Thus, we need to select the right relationship between the wavelength and core diameter lc = 2pa×n1(2D)1/2 2.405 Note that modes propagating near The critical wavelength (cutoff) will not Be fully guided within the core. NOTE: Single mode operation (with step index) occurs only above λc. D = n12 -n22 2n12 ;
  138. 138. Single Moe Fiber - Example • See notes
  139. 139. Attenuation • Transmission loss is the main limiting factor in optical communication systems – Limiting how far the signal can be transmitted • Transmission loss in fiber is much less than copper (<5 dB/km) • Loss in dB = 10log Pi / Po – Pi/Po = 10 ^(dB/10) – Attenuation (dB) = αL = 10log(Pi/Po) ; – Loss per unit length is represented by α is in dB/km
  140. 140. Loss - Example • OTDR Example • Numerical Example
  141. 141. Fiber Bend Loss • Radiation loss due to any type of bending • There are two types bending causing this loss – micro bending • small bends in the fiber created by crushing, contraction etc causes the loss – macro bending • fiber is sharply bent so that Radiation attenuation coefficient = αr = C1 exp(- C2 x R) R = radius of the curvature; C1 & C2 are constants
  142. 142. Fiber Bend Loss • Multimode Fibers – Critical Radius of curvature – Large bending loss occurs at Rcm • Single-Mode Fibers Rcm = 3×n12 ×l 4p(n12 -n22 )3/2 Rcs = 20l (n12 -n22 )3/2 (2.748-0.996 l lc )-3 lc = 2pa×n1(2D)1/2 2.405 Note that modes propagating near The critical wavelength (cutoff) will not Be fully guided within the core. NOTE: Single mode operation (with step index) occurs only above λc.
  143. 143. Fiber Bend Loss - Example • In general, the refractive index difference: D = n12 -n22 2n12 ; D = n1-n2 n1 <<1
  144. 144. Example of cutoff Wavelength • Find the cutoff wavelength for a step index fiber to exhibit single mode operation when n1=1.46 and core radius=a=4.5 um. Assume Δ=0.25% lc = 2pa×n1(2D)1/2 2.405 λc = 1.214 um 2p lc a n12 -n22 <V = 2.405 Typical values are a=4μm, Δ=0.3%, λ=1.55 μm Note that if V becomes larger than 2.405  multimode fiber
  145. 145. Scattering • When some of the power in one propagation mode is transferred into a different mode  Loss of power in the core • Power Scattering – Linear : Po is proportional to Pi, and there is no frequency change – thus the power propagated is proportional to mode power • Two types: Rayleigh and Mie – Nonlinear : The power propagation results in frequency change
  146. 146. Rayleigh Scattering • Due to density fluctuation in refractive index of material • Represented by ϒR (Rayleigh scattering factor) – (1/m) – ϒR is a function of 1/(λ)^4 – Transmission loss factor for one km (unit less) αR= exp(-ϒR.L); L is the fiber
  147. 147. Example • Assume for Silica ϒR = 1.895/(λ^4); and we are operating at wavelength 0.63um. Find attenuation due to Rayleigh scattering in a 1-km of fiber. Repeat the same problem for wavelengths of 1 um and 1.3 um.
  148. 148. 158 Testing and Measuring • Testing a cabling infrastructure is important to:  Identify faults or help in trouble shooting  Determine the system quality and its compliance to Standard  Allow recording performance of the cabling at time zero • Testing FO cabling is an indirect process  Measurement of link length and loss  Compare with values calculated at design time (workmanship quality)  Compare with Standard defined values (link functionality)
  149. 149. 159 Power budget Calculation of theoretical insertion loss at 850nm Components Fiber 50/125 0.25 km at 3.5dB (1.0dB) 0.875 Connector 3 pcs. at 0.5dB 1.5 Splice 1 pcs. at 0.1dB 0.1___ Total attenuation 2.475 Connection Splice Connection Connection 70 m150 m30 m
  150. 150. 160 LIGHT tracer – red light source and launching fiber Power meter – measuring tools for light power loss OTDR – graphical display of channel/link losses, location, behavior FO field testers (measuring tools)
  151. 151. 161 Attenuation measurement principles OTDR Backscatter measuring (OTDR) Power measuring ReceiverTransmitter Receiver Plug Transmitter Plug OTDR PlugPlug
  152. 152. 162 Power meter measurement Some basic rules Light source  Laser only for singlemode fiber. LED for multi- and singlemode fibers.  PC to PC and APC to APC connectors on test equipment.  Do not disconnect launch cord after reference.  „heat up“ the source before using (10 min.) Power Meter • Detector is very large and is not measured Mode filter • For reliable measurements the use of a mode filter on the launch cord is essential. Cleaning  Each connector should be cleaned before testing/application.
  153. 153. 163 Power measurement : level setting 1. Reference measuring Transmitter Test cable 1 Adjust: attenuation = 0 dB Receiver Test cable 2 850nm 0.00dBm nm850 0.00 dBm nm850
  154. 154. 164 Power measurement : link evaluation Transmitter 2. Measuring the system’s attenuation Receiver FO System Total attenuation [dB] 850 nm Ð 0.74dBm nm850 Ð 0.74dBm nm850
  155. 155. 165 Error reduction : the Mandrel wrap principle 50 mm mandrel  18 mm for 3 mm jumpers 62.5 mm mandrel  20 mm for 3 mm jumpers 9 mm N.A. Test jumper length 1 m to 5 m Mandrel launch cord5 wraps This “mode filter” causes high bend loss in loosely coupled modes and low loss in tightly coupled modes. Thus the mandrel removes all loosely coupled modes generated by an overfilled launch in a short (cords) link used during the reference setting
  156. 156. 166 Optical Time Domain Reflectometer (OTDR) block diagram t Measuring delay Receiver Evaluation Impuls generator Light source Beam splitter optical signals electric signals FO
  157. 157. 167 OTDR measuring : principle of operation OTDR The reflected light pulse is detected by the OTDR. The light pulse is partly reflected by an interfering effect. OTDR A light pulse propagates in an optical waveguide. OTDR
  158. 158. 168 Event dead zone in an OTD
  159. 159. 169 Attenuation dead zone in an OTDR
  160. 160. 170 Measuring with OTDR 1) launching fiber 2) launching fiber 200 m - 500 m for MM 200 m – 500 m for MM 500 m - 1’000 m for SM 500 m - 1’000 m for SM FO system under test 1) 2) Testing set up
  161. 161. 171 Errors detected by OTDR Connection or mech./fusion splice Fiber Microbending air gap lateral off-set different type of fiber contamination Fiber Macrobending
  162. 162. 172 Optical Time Domain Reflectometer Relativepower Distance
  163. 163. 173 An example of an OTDR waveform
  164. 164. 174 Dynamic ratio in an OTDR
  165. 165. 175 Other FO measueremnts • Chromatic Dispersion. • Polarisation Mode Dispersion Only for Singlemode application Channel length > 2 km
  166. 166. 176 EXFO Equipement
  167. 167. 177 EXFO Equipement • Broadband source (C+L) for CD/PMD • Videomicroscope
  168. 168. 178 CD result
  169. 169. Conclusion • Optical Communication System is an Important system that builds up the infrastructure of the upcoming technologies as it aid as the backbone of the network and the internet . • The system as an overall is very simple idea but with a huge data in detail discussion. • I hope I satisfied the lack of knowledge in that field and thank you….. Eng. Mohamed Hamdy Naeem
  170. 170. 180 MIT Reichle & De-Massari References