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Contents

1 Definition of Fiber 32 History of Optical Transmission 73 Loss of a Few Optical Media 11

4 Advantages and Disadvantages of Optical Fibers 135 Principle of Transmission with Light 156 Regenerator Spacing 197 Exercise 218 Solution 25

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1 Definition of Fiber

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In optical transmission an effect of total internal reflection is desired. This effectoccurs if two transparent media are arranged one above the other. The externalmedium must be "better" than the internal one.

The combination of glass and air would also fulfil this condition. However, oneachieves more favorable characteristics with two almost equally "good" types of glass.

A technically functional optical fiber (OF) consists of the following components:

The information-carrying glass (the core ) is covered

with a slightly "better" glass (the cladding ).

A protective layer of plastic (the coating ) is applied over the cladding.

This combination of core - cladding - coating is the fiber.

The fiber-glass factory delivers the fibers with a naturally colored coating.If fibers are processed into cables, they are colored for identification in the cablefactory according to the specifications of the customer.

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125

250

Potical fibres use din transmission applications have the following dimensions:

Diameter of the core approx.:8 mm, 50 mm, 62,5 mmDiameter with cladding:125 mmDiameter with the coating:250 mm

Fibre cross sectionandrefraction index.

Fig. 1

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2 History of Optical Transmission

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Use of light signals in the early epoch (such as signal fluch)

1626 Snell's law 1794 First telegraph line in France

1870 John Tydall demonstrated the light conductivity of a water jet

1880 Graham Bell developed the Opthophon (voice signals were sent via light but were effected by the whether)

1888 Demonstration of electromagnetic waves by Hertz

1897 Analysis of the waveguide

1934 Norman R. French patented an optical telephone system using glass rodsor something similar in order to transport voice signals.

1958 Arthur Schawlow and Charles H. Townes developed the laser.

1960 Theodor H. Maiman operated the laser the first time.

1962 First semiconductor laser by GE, IBM, MIT

1966 Charles H. Kao and George A. Hockham proposed the glass fiber asconductor.

1968 Optical wave guides with an attenuation of 1000 dB/km.

1970 Corning Glassworks produces an OWG with less than 20 dB/km at 633 nm.

1972 Attenuation of 4 dB/km at 850 nm and a bandwidth of 20 - 50 MHz/km isachieved.

1973 The first FO cables for telephone purposes are employed on militaryvessels.

1974 The concept for graded index fiber is introduced 500-1000 MHz/km.

1976 First system trials in the USA by Western Electric in Atlanta. Siemens startsa 2.1 km long test line in Munich.

1977 Field trial in Chicago over 2.5 km by Bell Systems.

Simultaneously in Long Beach over 9.5 km by General Telephone.

Siemens installs the first FO link for DBP in Berlin.

1981 Dispersion 4 ps/nm x km Beales GB

1983 Siecor delivers the first single mode fiber cable.

1984 In the laboratory, over 200 km spans are achieved at 1.55 m.

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1985 Dispersion-shifted fiber

1987 Foundation of the Siecor company in Neustadt with 80,000 km processedglass fiber. LA 140 LWL

1992 Siemens, together with Siecor, installs more than 3,000,000 km of cabledfiber in over 25 countries. SLA 4/SLA 16

1995 The cable factory Neustadt processes 500,000 km fiber into cables for thefirst time.

1996 Foundation of PT Trafindo Perkasa in Indonesia. The production startstemporarily with 70,000 km of fiber.

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3 Loss of a Few Optical Media

Medium

Pure Water Window glassOptical glassThick fogCity air in Dusseldorf Glass fibre 1970

Good fibre 1978Good fibre 1986

Optical Attenuation

100,00050,000

3,000500

1020

30,2

Penetration depth at 50% light gloss

33 mm66 mm

1,000 mm6,6 m

330 m165 m

1,000 m18,000 m

Fig. 2

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4 Advantages and Disadvantages of OpticalFibers

Advantages:l High transmission capacityl Low susceptibility to electromagnetic interference important for use in industrial

plants control lines in power plants in principle, no spacing requirements when runin parallel.

l Potential separation between transmitter and receiver (no ground loop)l Long distances between repeaters over 300 km is possible for sea cables large

production lengths therefore greater distances between couplings therefore fewer couplings therefore fewer installation errors.

l No line interference, no signal dispersionl Highly resistant to eavesdroppingl Short-circuit-free (no spark formation) important in areas where there is a risk of

explosions.l Light weight, highly flexible lighter equipment easier handling less volume for

shipping smaller cable reels lighter trailers smaller winches.l Smaller dimensions smaller cable diameter more effective utilization of cable

ducts.l No corrosion of fibers.l Unlimited material availability (SiO 2 is available in nearly limitless supply) 1 gram

of silicon corresponds to 10 kg of copper.#

Disadvantages:

l Installation technologyl high level of precision requiredl sophisticated devices necessary

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5 Principle of Transmission with Light

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Message transmission with light can be easily explained:

In the transmitter, the electrical signal is converted into a light signal in an electro-optical converter (e.g. a light emitting diode (LED) or a laser diode (LD)). To be moreprecise: The light intensity of the transmitting diode is modulated by the binary pulse-modulated diode current i 1, and light with the power P (0) is coupled with the opticalfiber. After traversing the optical fiber, the light is converted back into an electricalsignal in an opto-electric converter (e.g. photodiode) at the end of the transmissionroute. The optical transmission route therefore begins and ends with an electricalinterface whose data is normed independently of the transmission medium. There-fore, digital systems with fiber optics use, in principle, the same interfaces (CCITTrecommendations G. 703) they use for radio relay and multiplex units.

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i1

CCITT Interface

Light-emittingor laser code

opticaltransmitter

i2+

-Photodiode optical

receiver

Optical fibre

P (0)

P (L)

L Length of optical transmission routei1, i2 Laser diode or photodiode currentP(0), P(L) Optical transmit or receive power

Fig. 3

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6 Regenerator SpacingThe diagram shows regenerator spacing independently of transmission capacity andthe various transmission media.

An analog system (for example with 10,800 channels over a 2.6/9.5 coaxial cable)requires a repeater every 1.55 km.

A glass fiber can transmit more than three times as many channels across approx.100 km without a regenerator.

Maximum regenerator spacing

100

50

20

10

5

2

1 100 200 500 1000 2000 5000 10000 20000 50000

MM fibre

1500 nm

V300

V960

V2700

V3600coaxial pair 2.6/9.5 mm

V10800

LA 34 KX

LA 140 KX

LA 565 KX

8 Mbit/s 34 Mbit/s 140 Mbit/s565 Mbit/s622 2.5 Gbit/s

bit rate

SM fibre

Fig. 4

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7 Exercise

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Exercise

1. Name at least 5 decisive advantages of fiber-optic technology over standardcopper cable technology.

a)

b)

c)

d)

e)

2. In what year did the Corning Glassworks company succeed in manufacturing anoptical fiber with an attenuation of less than 20 dB/km (the beginning of fiber-optic technology)?

3. Describe the basic design of a fiber-optic transmission route!

4. Name the three elements of an optical fiber.

a)

b)

c)

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8 Solution

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Solution

1. a) high transmission capacity

b) low weight

c) large production lengths

d) not susceptible to electromagnetic influence

f) resistant to eavesdropping

2. 1970

3. telephone - electro-optical converter - fiber - electro-optical converter - telephone

4. a) core

b) cladding

c) coating

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