Optical Multiplexing & Demultiplexing:
OPTICAL TELECOMMUNICATION NETWORKS
Phillip B. Oni (u96761)
AUTO3160 – OPTICS & SPECTROSCOPY
VAASA, Spring 2012.
Outline
 Introduction
 Multiplexing / Demultiplexing
 Optical Multiplexing
 Components of Optical Mux/Demux
 Application
 Advantages
 Shortcomings/Future Work
 Conclusion
 References
Introduction
 Optical transmission uses pulses of light to transmit information
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from one place to another through an optical fiber.
The light is converted to electromagnetic carrier wave, which is
modulated to carry information as the light propagates from one
end to another.
The development of optical fiber has revolutionized the
telecommunications industry.
Optical fiber was first developed in the 1970s as a transmission
medium.
It has replaced other transmission media such as copper wire
since inception, and it’s mainly used to wire core networks.
Today, optical fiber has been used to develop new high speed
communication systems that transmit information as light
pulses, examples are multiplexers.
Multiplexing & Demultiplexing
 Multiplexing
 What are Multiplexers?
Multiplexers are hardware components that combine multiple
analog or digital input signals into a single line of transmission.
 And at the receiver’s end, the multiplexers are known as demultiplexers – performing reverse function of multiplexers.

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Multiplexing is therefore the process of combining two or more
input signals into a single transmission.
At receiver’s end, the combined signals are separated into
distinct separate signal.
Multiplexing enhances efficiency use of bandwidth.
Multiplexer
http://en.wikipedia.org/wiki/File:Telephony_multiplexer_system.gif
Multiplexing Example
Triangular Signal
8
Amplitude--->
5
0
-5
-10
0
6
4
2
0
10
20
30
Time--->
Sampled Sinusoidal Signal
10
8
5
6
Amplitude--->
Amplitude--->
Quantization
 Digitization

Amplitude--->
 MATLAB simulation example:
Sinusoidal Signal
 Sampled in time:
10
0
-5
-10
0
10
20
Time--->
30
0
10
20
Time--->
Sampled Triangular Signal
30
0
10
20
Time--->
30
4
2
0
Multiplexing Example
 Multiplexed Signals
 Separation of signals
 Using time slots.
TDM Signal
8
6
4
Recovered Sinusoidal Signal
Amplitude--->
10
Amplitude--->
5
0
-5
-10
0
5
10
15
20
Time--->
Recovered Triangular Signal
25
2
0
-2
30
-4
Amplitude--->
8
6
-6
4
-8
2
0
0
5
10
15
Time--->
20
25
30
0
10
20
30
Time--->
40
50
60
Recovered Signal
Recovered Sinusoidal Signal
10
Amplitude--->
5
0
-5
-10
0
5
10
15
20
Time--->
Recovered Triangular Signal
25
30
0
5
10
25
30
Amplitude--->
8
6
4
2
0
15
Time--->
20
Optical Multiplexing
 Optical multiplexer and de-multiplexer are required
to multiplex and de-multiplex various wavelengths
onto a single fiber link.
 Each specific I/O will be used for a single
wavelength.
 One optical filter system can act as both multiplexer
and de-multiplexer
Laser 1
Laser 2
Multiplexer
Optical Fiber
De-multiplexer
Laser 3
Laser 4
Regenerator +
Receiver
Optical Multiplexing
 Optical multiplexer and de-multiplexer are basically
passive optical filter systems, which are arranged to
process specific wavelengths in and out of the transport
system (usually optical fiber).
 Process of filtering the wavelengths can be performed
using:
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
Prisms
Thin film filter
Dichroic filters or interference filters
 The filtering materials are used to selectively reflect a
single wavelength of light but pass all others
transparently.
 Each filter is tuned for a specific wavelength
Optical Multiplexing and Filtering
Credit: [LYNX Technik Inc.www.lynx-technik.com]
Components of Optical Multiplexer
 Combiner
 Tap Coupler
 ADD/DROP
 Filters
 Prisms
 Thin film
 Dichroic
 Splitter
 Optical fiber
Credit: [LYNX Technik Inc.www.lynx-technik.com]
Optical Multiplexing Techniques
 There are different techniques in multiplexing light signals onto a
single optical fiber link.
 Optical Multiplexing Techniques

Optical Time Division Multiplexing (OTDM)
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Wavelength division multiplexing (WDM)
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Each channel is assigned a unique carrier frequency
Channel spacing of about 50GHz
Coarse Wavelength Division Multiplexing (CWDM)
Dense Wavelength Division Multiplexing
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
Separating wavelengths in time
Uses a much narrower channel spacing, therefore, many more wavelengths are
supported.
Code Division Multiplexing
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Also used in microwave transmission.
Spectrum of each wavelength is assigned a unique spreading code.
Channels overlap both in time and frequency domains but the code guide each
wavelength.
Applications
 The major scarce resource in telecommunication is
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bandwidth – users want transmit at more high rate and
service providers want to offer more services, hence, the
need for a faster and more reliable high speed system.
Reducing cost of hardware, one multiplexing system can
be used to combine and transmit multiple signals from
Location A to Location B.
Each wavelength, λ, can carry multiple signals.
Mux/De-Mux serve optical switching of signals in
telecommunication and other field of signal processing
and transmission.
Future next generation internet.
Advantages
 High data rate and throughput
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Data rates possible in optical transmission are usually in Gbps on
each wavelength.
Combination of different wavelengths means more throughput in
one single communication systems.
 Low attenuation

Optical communication has low attenuation compare to other
transport system.
 Less propagation delay
 More services offered
 Increase return on investment (ROI)
 Low Bit Error Rate (BER)
Shortcomings
 Fiber output  loss + dispersion
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Signal is attenuated by fiber loss and distorted by fiber dispersion
Then regenerator are needed to recover the clean purposes
 Inability of current Customer Premises Equipment
(CPEs) to receive at the same transmission rate of optical
transmitting systems.

Achieving all-optical networks
 Optical-to-Electrical conversion overhead

Optical signals are converted into electrical signal using photodetectors, switched and converted back to optical.

Optical/electrical/optical conversions introduce unnecessary time
delays and power loss.
 End-to-end optical transmission will be better.
Future Work
 Research in optical end user equipment
 Mobile phones, PC, and other handheld devices receiving and
transmitting at optical rate.
 Fast regeneration of attenuated signal
 Less distortion resulting from fiber dispersion.
 End-to-end optical components
 Eliminating the need for Optical-to-Electrical converter and
vise versa.
Conclusion
 Optical multiplexing is useful in signal processing
and transmission.
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Transporting multiple signals using one single fiber link
The growth of the internet requires fiber optic transmission to
achieve greater throughput.
Optical multiplexing is also useful in image processing and
scanning application.
 Optical transmission is better compare to other
transmission media because of its low attenuation
and long distance transmission profile.
THANK YOU
KIITOS
References
 Russell Steve. (2010) “The CWDM Fiber Primer” LYNX Technik Inc. <www.lynx-
technik.com> 8/05/2012
 Indumathi. T. S et al. (2009) "Evaluating Wavelength Routing Power of Dynamic
ROADM Networks (cat-I)" International Conference on Advanced Information
Networking and Applications Workshop.
 Saleh Bahaa E. A., Malvin Carl Teich. (1991) Fundamentals of photonics. Wiley:
New York. pg 799 – 832
 Watanabe, Shigeki. (2012) "All-Optical Data Frequency Multiplexing on Single-
Wavelength Carrier Light by Sequentially Provided Cross-Phase Modulation in
Fiber." IEEE Journal of Selected Topics in Quantum Electronics, Vol. 18, No. 2.
 Deng Lei. et al. (2012) "Fiber Wireless Transmission of 8.3 Gb/s/ch QPSK-OFDM
Signals in 75-110-GHz Band." IEEE Photonics Technology Letters, Vol. 24, NO. 5