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Source: Master 7_

WDM and DWDM Multiplexing

Multiplexing

• Multiplexing
  • (^) a process where multiple analog message signals or digital data

streams are combined into one signal over a shared medium

• Types
  • (^) Time division multiplexing
  • (^) Frequency division multiplexing
• Optically
  • (^) Time division multiplexing
  • (^) Wavelength division multiplexing

Problem: Demand for massive increases in capacity Immediate Solution: Dense Wavelength Division Multiplexing Longer term Solution: Optical Fibre Networks Problems and Solutions

Wavelength Division

Multiplexing

 (^) Multiple channels of information carried over the same fibre, each using an individual wavelength  (^) A communicates with X and B with Y as if a dedicated fibre is used for each signal  (^) Typically one channel utilises 1320 nm and the other 1550 nm  (^) Broad channel spacing, several hundred nm  (^) Recently WDM has become known as Coarse WDM or CWDM to distinguish it from DWDM Wavelength Division Multiplexer Wavelength Division Demultiplexer  1 A  2 B

X

Y

Fibre

WDM Overview

 Multiple channels of information carried over the same fibre, each using an individual

wavelength

 Attractive multiplexing technique

 (^) High aggregate bit rate without high speed electronics or modulation  (^) Low dispersion penalty for aggregate bit rate  (^) Very useful for upgrades to installed fibres  (^) Realisable using commercial components, unlike OTDM

 Loss, crosstalk and non-linear effects are potential problems

Wavelength Division Multiplexer Wavelength Division Demultiplexer  1 A  2  3

B

C

X

Y

Z

Fibre

WDM Overview

Wavelength multiplexer types include:

 Fibre couplers

 Grating multiplexers

Wavelength demultiplexer types include:

 Single mode fused taper couplers



Grating demultiplexers

 Tunable filters

Grating

Multiplexer

Demultiplex

er

Grating Grin Rod Lens Fibres

WDM Multiplexers/Demultiplexers

WDM systems require sources at different wavelengths

Irish researchers at U.C.D. under the ACTS program are developing

precision tunable laser sources

Objective is to develop a complete module incorporating:

 (^) Multisection segmented grating Distributed Bragg Reflector Laser diode  (^) Thermal and current drivers  (^) Control microprocessor  (^) Interface to allow remote optical power and wavelength setting ACTS BLISS AC069 Project Tunable Sources

Buffered Fibre on Reels

Optical Transmitters

Early DWDM: CNET WDM Experimental Setup

Dense Wavelength

Division Multiplexing

Multiple channels of information carried over the same fibre, each using an

individual wavelength

Unlike CWDM channels are much closer together

Transmitter T

communicates with Receiver R

as if connected by a

dedicated fibre as does T

and R

and so on

Wavelength Division Multiplexer Wavelength Division Demultiplexer  1 T  2  N

T

TN

R

 N

R

RN

Source: Master 7_

 1  2 ...  N

Fibre

Simple DWDM System

Multiplexer Optical Output Spectrum for an 8 DWDM

channel system, showing individual channels

Source: Master 7_ Sample DWDM Signal

1.1 Tbits/sec total bit rate (more than 13 million telephone channels)

55 wavelengths at 20 Gbits/sec each

1550 nm operation over 150 km with dispersion compensation

Bandwidth from 1531.7 nm to 1564.07 nm (0.6 nm spacing)

Terabit Transmission using DWDM

Expansion Options