OPTICAL TELECOMMUNICATION NETWORKS

Optical Multiplexing & Demultiplexing:

Phillip B. Oni (u96761)

AUTO3160 – OPTICS & SPECTROSCOPY

VAASA, Spring 2012.

Outline

IntroductionMultiplexing / DemultiplexingOptical MultiplexingComponents of Optical Mux/DemuxApplicationAdvantagesShortcomings/Future WorkConclusionReferences

Introduction

Optical transmission uses pulses of light to transmit information 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 de-multiplexers – performing reverse function of multiplexers.

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

MATLAB simulation example: Sampled in time:

Quantization Digitization

0 10 20 30-10

-5

0

5

10Sinusoidal Signal

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>

Time--->0 10 20 30

0

2

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8Triangular Signal

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>

Time--->

0 10 20 30-10

-5

0

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10Sampled Sinusoidal Signal

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Time--->0 10 20 30

0

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8Sampled Triangular Signal

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>Time--->

Multiplexing Example

Multiplexed Signals Separation of signals Using time slots.

0 10 20 30 40 50 60-8

-6

-4

-2

0

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8TDM Signal

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Time--->

0 5 10 15 20 25 30-10

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0

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10Recovered Sinusoidal Signal

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Time--->

0 5 10 15 20 25 300

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8Recovered Triangular Signal

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Time--->

Recovered Signal

0 5 10 15 20 25 30-10

-5

0

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10Recovered Sinusoidal SignalA

mpl

itude

--->

Time--->

0 5 10 15 20 25 300

2

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8Recovered Triangular Signal

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Time--->

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

Laser 3

Laser 4

Multiplexer Optical Fiber De-multiplexer

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: 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

CombinerTap Coupler

ADD/DROPFilters

Prisms Thin film Dichroic

SplitterOptical 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)

Separating wavelengths in time Wavelength division multiplexing (WDM)

Each channel is assigned a unique carrier frequency Channel spacing of about 50GHz

Coarse Wavelength Division Multiplexing (CWDM) Dense Wavelength Division Multiplexing

Uses a much narrower channel spacing, therefore, many more wavelengths are supported.

Code Division Multiplexing 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 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 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 delayMore services offeredIncrease return on investment (ROI)Low Bit Error Rate (BER)

Shortcomings

Fiber output loss + dispersion 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 photo-

detectors, 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 signalLess 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. 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