DWDM BASICS

1. A presentation on
DWDM

2. Dense
Some times called stacked SDH/SONET
Wavelength
Division
Multiplexing
DWDM

3. …What is DWDM ?
A multi channel fiber optic transmission system in which
one fiber transmits No of client signals provided by
different Wavelength optical carriers

4. Why DWDM ?
a) Overcome fiber exhaust / lack of fiber availability
problems (Better utilization of available fiber)
d) Cost effective transmission
e) No O-E-O conversion delays
f) Wave length leasing instead of Bandwidth leasing
b) Space & Power savings at intermediate stations
c) Easier capacity expansion

5. …Why DWDM ?
LTE
LTE
LTE
LTE
LTE
LTE
LTE
LTE
Traditional Network with Repeaters, no WDM
75% fewer fibersWDM Network
with Repeaters
LTE
LTE
LTE
LTE
LTE
LTE
LTE
LTE
75% less equipmentWDM Network with
Optical Amplifiers
LTE
LTE
LTE
LTE
LTE
LTE
LTE
LTE

6. Any Disadvantages of this Technology ?
Yes of course…
a) Multi channel failure due to line failure
b) Requirements for more deliberate design of
Dispersion management,
gain profile management
& launched power due to broader Wavelength range
to be handled

7. WDM Classification:
WDM Classification is based on the Channel spacing
between 2 Wave lengths
Channel spacing > 200GHz is called CWDM
Channel spacing > 100 GHz is called WDM
Channel spacing < 100GHz is called DWDM
100 GHz is equal to 0.8 nm

8. Infrared Spectrum
O-Band E-Band S-Band C-Band L-Band
1260-1360nm
1460-1530nm
1530-1565nm
CWDM CWDM
Future
DWDM DWDM DWDM

9. Low-loss range
0.1
0.2
0.3
0.0
1300 1400 1500 1600 Wavelength (nm)
L
O
S
S
db/km C-Band L-Band

10. (nm)
1532.68
1533.47
1534.25
1535.04
1535.82
1536.61
1537.40
1538.19
1538.98
1539.77
1540.56
1541.35
1542.14
1542.94
1543.73
1544.53
1545.32
1546.12
1546.92
1547.72
1548.52
1549.32
1550.12
1550.92
1551.72
1552.52
1553.33
1554.13
1554.94
1555.75
1556.56
1557.36
1558.17
1558.98
1559.79
1560.61
1561.42
1562.23
1530.33
1531.12
1531.90
(THz)
195.7
195.6
195.5
195.4
195.3
195.2
195.1
195.0
194.9
194.8
194.7
194.6
194.5
194.3
194.2
194.1
194.0
193.9
193.8
193.7
193.6
193.5
193.4
193.3
193.2
193.1
193.0
192.9
192.8
192.7
192.6
192.5
192.4
192.3
192.2
192.1
192.0
191.9
196.0
195.9
195.8
C37
C36
C35
C34
C33
C32
C31
C30
C29
C28
C27
C26
C25
C24
C23
C22
C21
Tonech.
C20
C19
C18
C17
C16
C15
C14
C13
C12
C11
C10
C09
C08
C07
C06
C05
C04
C03
C02
C01
C40
C39
C38
Carrier
wavelength
Carrier
frequency
Channel
number
Note 1: Optical carriers are allocated on ITU-T 100 GHz (0.1 THz) grid in Rec. G. 692.
2: Tone channel is dedicated for operation & maintenance support.
Wavelength allocation in C-Band

11. Main Components in DWDM
1) Transponder
2) Omux/Odmux
3) Optical Amplifier
4) OADM
5) Regenerator

12. Client signals Client signalsWDM aggregate signals
IL-AMP
span
IL-AMP
#1
IL-AMP
#n
IL-AMP
#1
IL-AMP
#n
TERM
system
TERM
system
Intermediate
regenerator
(n-1)
IL-AMP spans
Wavelengthconversion
Opticalmux/demux
Wavelengthconversion
Opticalmux/demux
Opticalmux/demux
Ch-signalregeneration
Line system
…DWDM Components

13. Transponder
A device that takes an optical signal, performs electrical
3R regeneration & re-transmits the signal in optical form
In to Wavelength grid as per G.192
It allows any Wavelength as input to DWDM
For every input Wavelength, one transponder is required
Its very useful for Wavelength leasing, as customer can
Send any wavelength

14. Omux/Odmux
Various Transponder outputs (Wavelengths) will be
provided as Inputs to Mux. Each input is equipped with
A selective filter of certain Wavelength. The output of
these filters are coupled to a Single Mode fiber
At the Receiver end, these Wavelengths are separated
again by a Demux & directs them to individual
Transponders
Both Mux & Demux are identical components,
only difference is that they are driven in opposite
direction

15. OMUX

16. Transmit
Amplifier
(TXA)
OMUX
Aggregate Signal
over n-channels with
wavelengths ranging
from λ1 to λn.
Channel spacing is
100 GHz and even.
Channel
#1
#2
#3
#(n-1)
#(n-2)
#n
Wavelength
λ1
λ2
λ3
λ(n-1)
λ(n-2)
λn
λ1 λ2 λnλ(n-1)
100 GHz
ClientOMUX

17. Optical Amplifier
Where do we require Optical Amps ?
a) Booster/Post Amp
Boosts the signal at Transmitter end to compensate
relatively low output power of laser transmitters
b) Line Amp
Used at regular intervals to compensate fiber
transmission loss
c) Pre Amp
Boosts signal prior to Optical detectors to increase the
Rx sensitivity

18. …Optical Amplifier
Tx Rx
PreamplifierTx Rx
Line
amplifier
Tx Rx
Booster/Post Amplifier

19. OADM
Hence A special type of Mux is designed called
Optical Add/Drop Mux
With an Add/drop facility, new channels can be added to
& others can be dropped off the transmission link
In general, not all transmission channels have the same
start & destination
This Add/Drop function is completely in Optical form

20. …OADM

21. Regenerator
Regenerator is nothing but an Amplifier, with addition of
3R function
Since noise level also amplifies along with original signal
in an ordinary amplifier, it requires to supress this noise
at intermediate stations
Regeneration requires at every 600kms distance

22. Amplifier Vs Regenerator

23. What is 3R generation ?
Re-amplification – 1R
Re-shaping – 2R
Correcting noise & dispersion
Remove noise from a digital signal & shape it in to
clear 1’s & 0’s
Boost up the received weak signals to transmit further
It is done by Optical Amps
Done by DCF & OEO

24. Re-timing – 3R
Synchronizing with Network clock
Adjusting the precise location of 1’s & 0’s in a detected
signal in order to match them to the bit rate of system
By using PLL & optical clock recovery

25. ALCATEL DWDM
Metropolitan
National &
Metropolitan
International& National

26. 1626 LM
• Up to 96 channels at 10 Gb/s in extended C band with 50 GHz
spacing
• 1686 WM and 1640 WM upgrade
• Line optical fibre amplifiers
• 4x2.5 Gb/s concentrator (TRBC)
• Enhanced FEC
• Point-to-point and ring configurations
• Bi-directional G709 10 Gb/s transponders
• Tunable laser over 2 channels and the whole
C-Band
• Q3 and TL1 management interfaces
• 1+N Optical channel protection with external OCP
• Optical supervisory channel
• Performance Monitoring

27. 1696 MS
 32+32 bidir channels in one rack
 8ch.+8ch.+8ch.+8ch. modular HUB node
 1ch., 2ch., 4ch. and 8ch. low loss OADM
 Low cost optical amplifiers
 New 4Any concentrator (4xANY_P)
 CPE mechanical
 Point-to-point and ring configurations
 Multi-rate and 10Gb/s transponders
 Tunable laser over 2 channels
 Q3 and TL1 management interfaces
 1+1 Optical channel protection (O-SNCP)
 Optical supervisory channel
 Performance Monitoring

28. DWDM
• 1640WM : a core DWDM system supporting up
to 160 channels (upgradeable up to 240 channels)
and working at different standard synchronous bit-
rates from 2.5Gb/s to 40Gb/s.
• 1686WM : a regional and metropolitan DWDM
system – scalable up to 32 channels – supporting
different bit-rates from 100Mb/s to 10Gb/s.