Optical fiber communication systems using WDM and DWDM

1. Optical fiber communication systems
using WDM and DWDM
Prepared By: Ahmed Shamel
Supervised By: Dr. En. Riyadh

2. OFC Systems using WDM and DWDM
 The use of wavelength-division multiplexing (WDM) has been resulted from the exponential
increase in users’ demand for higher bandwidth.
Advantages of using WDM:
 Increase channel capacity.
 Use of optical fibers to achieve higher speeds.
 Utilize wavelengths to multiplex00 users.
 Allow continuous channel allocation per user.
 Reliability and high performance-to-cost ratio
 Easy upgrading
Limitations of WDM:
 Inefficient usage of full capacity of the optical fiber.
 Capability of carrying signals efficiently over short distances only.

3.  Dense WDM (DWDM) is the improvement in optical fibers and narrowband lasers.
 DWDM is a fiber-optic transmission technique that employs light wavelengths to transmit data
parallel-by-bit or serial-by-character via the same single fiber optic cable .

4. Figure 1: Block Diagram of a DWDM System
Dense
Wavelength
Division
Demultiplexer
Dense
Wavelength
Division
Multiplexer
λ1
λ2
λn λn
λ2
λ1
TransmittersReceivers
Virtual
Fibers
EDFA
Optical Fiber

5. Basic Components & Operation
Transmitting Side
Lasers with precise stable
wavelengths
Optical Multiplexers
On the Link
Optical fiber
Optical amplifiers
Receiving Side
Photo detectors
Optical Demultiplexers

6. Wavelength selective WDM vs. Broadband WDM
Wavelength selective
 In The wavelength-routed WDM
technique Each source operates at a
separate, assigned wavelength.
 Usesmultiplexers and demultiplexers.
 The power from all sources is
combined (ideally) without loss.
Broadband WDM
 Broadcast-and-select technique
combines the powers of the sources at
the transmitting end and then divides
this total on the number of the
multiplexed signals. In these systems,
simple splitters and combiners are
used to combine and split the signals.
 Uses splitters and combiners.
 There is power loss.

8. Broadcast and select techniques
 Single-hop: No intermediate relaying nodes are used, a transmission of a
node on any wavelength of a WDM link can be received by any other
node on that same wavelength.
 The main topologies/techniques for Single-hop B&S are:
1. Star topology
2. Folded bus
3. Ring Topology
4. Mesh Topology.

9. Broadcast and select techniques Contd.
Multiple-hop: requires intermediate relaying nodes, usually nodes
are assigned channels on which they can transmit and receive, thus to
be able to reach all destinations, packets may have to travel through
several nodes.
 If both receivers and transmitters are fixed (or tunable only over a
restricted range), then it is unlikely that a random source will reach a
random destination directly, thus messages have to “hop” through
other intermediate nodes.

10. Angularly dispersive devices
 Angularly dispersive devices (e.g., prisms and gratings) are optical devices that transmit or
reflect light at an angle that depends on the wavelength of the incident light.
 The main parameters that describe such a device are:
1. excess loss: It is the loss (in dB) incurred by passing through the device in excess of the
expected 1/N splitting loss. Since these devices are, by their nature, wideband devices,
the excess loss should be specified as a function of the wavelength.
2. angular dispersion: is the measure of the angular spread dB between two beams that are
spatially coincident at the input with wavelengths separated by dx. The angular
dispersion is given by dB/dx.