DWDM Theory ZTE Corporation Transmission Course Team
DWDM Overview
Multiplexing Technology WDM TDM SDM
What is DWDM? Gas Station High Way Prowl Car
Definition l 1 l 2 l N l 1 l 2 l 1 l 2 l N OA l N OMU ODU Dense wavelength division multiplexing (DWDM) is a fiber optic transmission technique that employs light wavelengths to transmit data parallel-by-bit or serial-by-character.
Characteristics power dbm) wavelength interval : 1 ~ 10 nm 1530-1560nm wavelength
System Working Wavelength No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Central Frequency (THz) 192.1 192.2 192.3 192.4 192.5 192.6 192.7 192.8 192.9 193.0 193.1 193.2 193.3 193.4 193.5 193.6 193.7 Wavelength (nm) 1560.61 1559.79 1558.98 1558.17 1557.36 1556.55 1555.75 1554.94 1554.13 1553.33 1552.52 1551.72 1550.92 1550.12 1549.32 1548.51 1547.72 18 193.8 1546.92
continuation 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 193.9 194.0 194.1 194.2 194.3 194.4 194.5 194.6 194.7 194.8 194.9 195.0 195.1 195.2 195.3 195.4 195.5 195.6 195.7 195.8 195.9 1546.12 1545.32 1544.53 1543.73 1542.94 1542.14 1541.35 1540.56 1539.77 1538.98 1538.19 1537.40 1536.61 1535.82 1535.04 1534.25 1533.47 1532.68 1531.90 1531.12 1530.33 40 196.0 1529.55
Losses (db/km) 1.0 0.8 0.4 0.2 25 THz In use : In research : 0.1 1.2 1.3 1.4 1.5 1.6 1.7 Wavelength (µm) C-band : 1525~1565nm L-band : 1570~1620nm and S-band : 1400nm l 0
Difference between DWDM and SDH Transmitter Electrical Regenerator Receiver T l 1 R TDM: Electrical Regenerator for Single Wavelength Electrical Multiplex Electrical Demultiplex λ 1 λ 2 λ N λ 1 λ DWDM: Multi-wavelength on Single 2 Fiber, for Optic Amplification λ N Optical Multiplexer OA λ 1 λ 2 λ N Optical Demultiplexer
Relationship between DWDM and SDH Client and Server SDH DWDM
Relationship between DWDM and Other Services IP ATM SDH ATM IP Other SDH Open Optical Interface DWDM Physical Fiber
Characteristics of DWDM 32*2.5G 32*10G 8*2.5G 16*2.5G
DWDM Equipment Types OTM λ 1 λ 2 λ N λ 1 λ 2 λ N OADM λ i λ i λ k λ k OXC OXC
Optical Interface Criteria SDH DWDM G.957 G.691 155M 622M 2.5G 10G G.692 PDH
Transmission Characteristics
Types of Optic Fibers G.652 : A single-mode optical fiber that has a nominal zero-dispersion wavelength in the 1310 nm window. (dispersion-unshifted fiber) G.653 : Dispersion-shifted fiber, zero dispersion at 1550 nm window, easy to cause FWM. G.655 : Non-zero dispersion fiber; used in 1550 nm window. Less dispersion coefficient, dispersion limited transmission distance can be hundreds of km; prevent FWM
Attenuation (db/km) 1.0 0.8 0.4 0.2 Attenuation NZDF+ G.655+ NZDF- G.655- G.652 SMF EDFA Bandwidth G.653 DSF 20 10 0-10 Dispersion (ps/nm-km) 0.1 1.2 1.3 1.4 1.5 1.6 1.7-20 Wavelength (nm)
WDM Wavelength According to the characteristic of fibers and EDFA, the wavelength between 1525 nm and 1565 nm is used
Transport characteristics of optical fibers Attenuation Dispersion Non-linear Effect
Attenuation It is the reduction of signal strength or light power over the length of the light-carrying medium. Fiber attenuation is measured in decibels per kilometer (db/km).
Attenuation Absorbency Attenuation Intrinsic Absorbency Attenuation Impurity Absorbency Attenuation Scattering Attenuation
Dispersion T Optical signals of different wavelengths have different speeds in the optical fiber, and this will cause a phenomena called dispersion.
Influence of Dispersion 1 0 1 0 1 0 1 1 0 1 Input Output 1 0 1 0 1 0 1 1 0 1 Time Time
Kinds of Dispersion 1. Chromatic Dispersion 2. Polarization Mode Dispersion
Chromatic Dispersion It represents the fact that different colors or wavelengths travel at different speeds, even within the same mode. Chromatic dispersion is the result of material dispersion, waveguide dispersion, or profile dispersion.
Chirp The directly modulated signal will cause more chirp and more dispersion. T
Dispersion Tolerance Parameter of dispersion tolerance for laser source (Ds) Dispersion parameter for optical fiber (D) Longest transmission distance: Ds/D Example If Ds = 12800 ps/nm, SMF G.652 dispersion is D = 20 ps/km/nm and then the longest transmission distance of this optical source is 640km.
Polarization Mode Dispersion This problem occurs because the fiber is not consistent along its length. Due to bending and twisting, as well as temperature changes, the fiber core is not exactly circular. The result is that the modes in the fiber exchange power with each other in a random fashion down the fiber length, which result in different group velocities; the signal breaks up. In effect, the light travels faster on one polarization plane than another.
Nonlinear Effects 1. Brillouin Scattering 2. Stimulated Raman Scattering 3. Four Wave Mixing 4. Self-phase Modulation 5. Cross-phase Modulation 6. Intermodulation (Mixing)
Causes of Nonlinearities 1. Refractive index of the glass 2. Scattering phenomena
Key Technology of DWDM
DWDM system Optical Transmitter OLA Optical Receiver Ch 1 Input Ch N OTU1 OTUn 1 OMU ODU 1 OTU1 OTUn Ch 1 Output Ch N OSC OSC OSC EMS
Bidirection OTM OTM OTU OTU O M U OBA OLA OPA O D U OTU OTU OTU OTU O D U OPA OLA OBA O M U OTU OTU
Important Technologies of WDM Laser source Optical Mutiplexer and Demultiplexer Optical Transceiver EDFA Supervision of WDM system
Laser Source Parameters Fixed wavelength The tolerance of dispersion Kinds Modulate directly Modulate indirectly
Modulate Directly Electric Signal Optical Signal Shortcomings : cause the chirp, dispersion.
Modulate indirectly Modulator Output Electrical Signal Reduce the chirp
Main Problem Fixed Wavelength Tolerance of Dispersion G.652 SMF, near 1550 nm window, dispersion is 20 ps/km nm For 350 km, 500 km and 640 km, the tolerance is 7200 ps/nm, 10000 ps/nm and 12800 ps/nm respectively
Muliplexer and Demultiplexer Multiplexer Demultiplexer Fiber
OTU OTU wavelength conversion electrical regeneration supervision information of B1 and J0 OTU includes OTUT, OTUG and OTUR 2.5G OTU, 10G OTU, multi-service OTU OTU With FEC & No FEC
OTU technology The major function of the OTU board is to employ the optical/electrical/optical conversion mode to realize wavelength conversion. SDH Transmission Receiving Unit Transmission Unit Output Supervision 1. Dispersion tolerance 2. Fixed standard wavelength Supervision Card
Transmission OTU G.957 S1 OTU R1 S2 S3 O M U OA OA OA O D U R2 R3 Sn Rn
Regenerator OTU S1 S1 S2 S3 O M U OA OA O D U O M U OA OA O D U S2 S3 Sn Sn
Receive OTU R1 G.957 S1 OTU S2 S3 O M U OA OA OA O D U R2 R3 Sn Rn
continuation According to transmission distance OTUD (short) Ds = 1800ps/nm : OTUEM (middle) Ds = 7200ps/nm : OTUEL (long) Ds=12800ps/nm : < 90km 90km-360km 360km-640km
Erbium Doped Fiber Amplifier 1 1 2 O M U OBA n OLA OLA OPA O M U 2 n EDFA include Optical Booster Amplifier (OBA) - high optical output power Optical Line Amplifier (OLA) - compensate the loss of the transmission line Optical Pre Amplifier (OPA) - low noise
EDFA Parameters Output Power Channel Gain - the ratio of input optical power to output optical power. Gain Evenness - maximum gain in the amplify band. Noise Coefficient - the ratio of input OSNR to output OSNR
Noise is mainly caused by OA.
Optical Supervision Control (OSC) OMU OBA OLA OLA OLA OPA ODU OSC OSC OSC OSC OSC ODU OMU OPA OLA OLA OLA OBA
O B A osc O L A O L A O P A OMU OBA OLA OLA OLA OPA ODU OSC OSC OSC OSC OSC ODU OMU OPA OLA OLA OLA OBA
OSC 1510nm Signal speed : 2.048Mb/s Receiving sensitivity : Transmission power : -48dbm 0 ~ -7 dbm