The attached narrated power point presentation will help one get familiarized with the basic concepts of Wavelength Division Multiplexing as well as get introduced to WDM Networks. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.

1. 1
WDM Networks
MEC

2. 2
Contents
• Introduction.
• WDM Categories.
• Device Classifications.
• Performance Criteria.
• Broadcast-and-select Network.
• Wavelength Routing Network.
• Virtual Topology.
• Single-hop Network.
• Multi-hop Network.

3. 3
Wavelength Division Multiplexing
• Conceptually similar to Frequency Division
Multiplexing.
• Combines different carrier wavelengths onto
a single fiber at one end and separates them
at the other end.
• Simultaneous transmission of optical signals
over the same physical medium.
• Each source has a different peak wavelength.
• Common medium shared by different
wavelengths.
• Increase in information capacity of the
system.

4. 4
Wavelength Division Multiplexing
• A single optical source
uses only a small part
of available spectral
transmission band of a
fiber.
• Simultaneous use of
many spectral
channels.

5. 5
Unidirectional WDM System

6. 6
Bidirectional WDM System

7. 7
Multiplexer Categories
• Angularly dispersive devices.
– prisms.
- gratings.
• Filter based devices.
– multilayer thin film interference filters.
- single mode integrated optical devices.
• Passive WDM Devices.
– wavelength selectivity fixed.
• Active WDM Devices.
– can be actively switched/tuned according to
wavelength.

8. 8
Angularly Dispersive Devices
Wavelengths can be combined or separated.
Collimating Lens Focusing Lens
Linear Dispersion
Angular Dispersion

9. 9
Multi-thin Film Filter Reflector
Transparent at λ2 and reflects λ1.

10. 10
Tunable Filter
Different signals sent in individual frequency channels each
of bandwidth B. A tunable filter of passband B selects the
desired channel.

11. 11
Wavelength Tunable Filter
IB
Spectral Output variation altered
by changing the path length
through the crystal.
Reversible Optical Path
Length, use as MUX/DEMUX

12. 12
Performance Criteria
• Insertion Loss:
–Amount of power loss in fiber optic line
due to addition of a WDM coupling
device.
- Losses occurring at the connection
points of WDM element.
- Intrinsic losses within multiplexing
element.

13. 13
Performance Criteria
• Channel Width:
- Range of wavelength allocated to a
particular source.
- Channel widths of several tens of
nanometers required for laser diodes.
- LEDs have wider spectral output, 10-20
times larger channel widths required
when compared to laser diodes.

14. 14
Performance Criteria
• Cross Talk:
- Amount of signal coupling from one
channel to other.
- Tolerable levels depend on the
application.
- A -30dB level tolerable in general, but
-10dB not.

15. 15
WDM Networks
• Optical fiber networks use wavelength
division multiplexing (WDM) techniques.
• Classified as broadcast-and-select
networks or wavelength routing networks.
• Broadcast-and-select network:
- based on a star coupler.
- broadcast to all nodes.
- single-hop or multi-hop.

16. 16
Broadcast-and-Select Network

17. 17
Broadcast-and-Select Network
• Optical transmission broadcast to all other
nodes using fixed transmitters.
• Tunable receiver at the destination node
extracts desired signal from the entire
group of signals.
• All transmissions broadcast to all network
nodes.
• Most of the transmitted power depleted
on the receivers which do not use it.

18. 18
Wavelength Routing Network
• As the number of nodes increases, each
station receives a small fraction of overall
transmitted power.
• Wavelength routing network used to avoid
wastage of transmitted power.
• Each network node provided with restricted
connection(s) to the receiver(s).
• Signal routed to specific destination through
either a single node or using multiple nodes.

19. 19
Wavelength Routing
Physical connection Wavelength assignments Virtual topology
3 wavelengths used

20. 20
Wavelength Routing
• Uses three wavelengths (λ1, λ2 and λ3).
• Any network node can transmit or receive
a signal from another node within the
network.
• Wavelength implementation/path selection
known as routing and wavelength
assignment (RWA).
• Classified into single-hop or multi-hop.

21. 21
Wavelength Routing
• Node A can transmit to
node B using
wavelength λ1.
• Node A can
simultaneously receive
from node B using
wavelength λ2 only
through node E.
• No physical connection
between nodes C and E.

22. 22
Virtual Topology
• Virtual topology used to
describe only the enabled
wavelength paths.
• Only wavelength signals
identify interconnections
between nodes.
• No physical connection
between nodes C and E.
• Nodes can communicate via
virtual connection set up
using wavelengths λ1 and λ3.

23. 23
Single-hop Networks
• Allow direct communication between any
two nodes.
• Data remains entirely in the optical
domain.
• No conversion to electrical domain till it
reaches destination.

24. 24
Multi-hop Networks
• Transmission may take place through
intermediate nodes before reaching its
destination.
• Data can be switched electronically to the
next possible node at each intermediate
node, then retransmitted as optical signal.
• Conversion process inefficient, but
necessary if no common wavelength path
between two nodes.

25. 25
Thank You