当前位置:首页 >> 工学 >>

Optical Fiber Communication chapter1


Optical Fiber Communication
Ge Hua E-mail:gehua@mail.whut.edu.cn TEL:13349951640

2013-7-11

The Sch. Of Information Engineering, WHUT

1

Textbook:

Optical Fiber Communication
Gerd Keiser (Third Edition) McGraw-Hill Companies 高等教育出版社

Reference:

1、Fiber-Optic Communications Technology
D.K.Mynbaev 科学出版社

2、 Underingstanding Fiber Optics
Jeff Hecht(赫克特) (Fourth Edition) 电子工业出版社

3、光纤通信
原荣著
2013-7-11

电子工业出版社
2

The Sch. Of Information Engineering, WHUT

Website:

1、www.lightreading.com 2、lw.pennet.com www.lightwaveonline.com 3、www.c-fol.net

2013-7-11

The Sch. Of Information Engineering, WHUT

3

The main content of this course
Chapter1 Introduction Chapter2 optical fibers:structure,waveguiding,fabrication Chapter3 signal degradation in optical fibers Chapter4 optical source Chapter6 photodetectors Chapter10 WDM concepts and components Chapter11 optical amplifiers

Chapter12 optical network
Chapter13 measurements
2013-7-11 The Sch. Of Information Engineering, WHUT 4

Chapter1 Introduction

2013-7-11

The Sch. Of Information Engineering, WHUT

5

OUTLINE
Historical Perspective The character of optical fiber Communication Systems

Optical Communication Systems

2013-7-11

The Sch. Of Information Engineering, WHUT

6

1.1 Historical Perspective
1.1.1 Need For Optical Communication 1.1.2 The evolution of fiber optic systems

1.1.3 Optical Network

2013-7-11

The Sch. Of Information Engineering, WHUT

7

1.1.1 Need For Optical Communication
The motivation behind each new communication form is: a、improve the transmission fidelity b、increase the data rate. So more information could be send

c、increase the transmission distance between relay stations
d、increase the transmission capacity

2013-7-11

The Sch. Of Information Engineering, WHUT

8

2013-7-11

The Sch. Of Information Engineering, WHUT

9

1、Before the 19th century

Very low information rate
Optical means:
signal lamps
fire signal by Greeks in the 18th century

Acoustical means: horns

2013-7-11

The Sch. Of Information Engineering, WHUT

10

2、The era of electrical communication The invention of the telegraph by Samuel F.B.Morse in 1838
the bit rate B could be increased to ~10b/s by use of new coding techniques, such as Morse code. the use of intermediate delay station allow communication over long distances(~1000km)

The invention of the telephone in 1876
brought a major change inasmuch as electric signals were transmitted in analog form through a continuously varying electric current

2013-7-11

The Sch. Of Information Engineering, WHUT

11

Coaxial cable system
the first system put into service in 1940, a 3-MHz system capable of transmitting 300 voice channels or a single television channel The bandwidth of such systems is limited by the frequencydependent cable losses, which increase rapidly for frequencies beyond 10 MHz

Microwave communication system
the first microwave system operating at the carrier frequency of 4 GHz was put into service in 1948.

2013-7-11

The Sch. Of Information Engineering, WHUT

12

1.1.2 The evolution of fiber optic systems
transmission of information in an optical format is carried out not by frequency modulation of the carrier, but by varying the intensity of the optical power. two classes of transmission medium:
atmospheric channel:FSO(free space optical communication) guided-wave channel:planar waveguide、optical fiber

2013-7-11

The Sch. Of Information Engineering, WHUT

13

Optical spectrum ranges from about 50nm(ultraviolet) to about 100μm(far infrared)

visible region: 400-700nm
for optical communication system, the wavelength

band is 800-1600nm

2013-7-11

The Sch. Of Information Engineering, WHUT

14

1、During the 1960s
The invention of laser in 1960-carbuncle laser

Maiman(American)
LD(GaAs 870nm)-in 1962

It was suggested in 1966 that optical fiber may be the
best transmission medium to guide the light. C.K.Kao(British scientist) and C.A.Hockham Problem: high loss(in excess of 1000dB/km)

2013-7-11

The Sch. Of Information Engineering, WHUT

15

2、During the 1970s The fiber’s loss could be reduced to below 20dB/km

in 1970.(Corning Corp.)
GaAs semiconductor lasers, operating continuously

at room temperature.
So the year of 1970 is a milestone in the history of

fiber optical communication.

2013-7-11

The Sch. Of Information Engineering, WHUT

16

2013-7-11

The Sch. Of Information Engineering, WHUT

17

3、Four generations from 1975 to now

(1) The first generation of lightwave systems operated near 0.8μm and used GaAs semiconductor lasers. Such system operated at a bit rate of 45Mb/s and allowed repeater spacing up to 10km.

2013-7-11

The Sch. Of Information Engineering, WHUT

18

(2)The second generation operated near 1300nm and use MM or SM fiber.
InGaAsP semiconductor laser Fiber loss is below 1dB/km(0.5dB/km) Optical fiber exhibit the minimum dispersion in this wavelengh region.(G.652) It is available in the near 1980. The bit rate of early system was limited to below 100Mb/s because of dispersion in MM fiber. By 1987, the system operating at bit rates up to 1.7Gb/s with spacing of about 50km were commercially available.

2013-7-11

The Sch. Of Information Engineering, WHUT

19

2013-7-11

The Sch. Of Information Engineering, WHUT

20

(3)The third generation operated near 1550nm
Lower loss (0.2dB/km)

Large fiber dispersion near 1550nm. This problem could be overcome neither by using DSF(dispersion shift fiber) or by using SLM(single longitudinal mode) laser. Third-generation lightwave systems operating at 2.5 Gb/s became available commercially in 1990.
Drawback: the signal is regenerated periodically by using electronic repeaters spaced apart typically by 60–70 km. coherent lightwave system

2013-7-11

The Sch. Of Information Engineering, WHUT

21

(4) The fourth generation of lightwave systems makes use of optical amplification for increasing the repeater spacing and of wavelength-division multiplexing (WDM) for increasing the bit rate.
a.Optical Amplifier (OA) ? Advent in 1989 ? The first OA is GaAlAs-based solid-state OA ? The most successful and widely used devices are erbiumdoped fiber amplifiers (EDFA) operating at around 1550nm. praseodymium-doped fiber amplifier operate at 1310nm ? Semiconductor optical amplifier ? Distribute raman amplifier (DFA)

2013-7-11

The Sch. Of Information Engineering, WHUT

22

Potential of Optical Fiber: perhaps 250 waves x 100 Gb/s = 25,000 Gb/s = 25 Tb/s ?

Total ~ 200 nm: 500 ~ 1,000 waves ?
Raman Fiber Amplifier

RFA TDFA
Thulium Doped Flouride-Based Fiber Amplifier Erbium Doped Fiber Amplifier

EDTFA EDFA C Band
1,530nm

Tellurite-Based Erbium Doped Fiber Amplifier
Gain-Shifted Erbium Doped Fiber Amplifier

GS-EDFA

80 nm: ~ 200 waves ? S+ Band
1,450nm 1,490nm

S Band

L Band
1,580nm 1,610nm

L+ Band
1,650nm

1,550nm 1,570nm

40 nm

2013-7-11

The Sch. Of Information Engineering, WHUT

23

b.WDM technology

Basic principle: use multiple sources operating at slightly
different wavelengths to transmit several independent information streams over the same fiber. DWDM (Densen WDM) CWDM (Coarse WDM)

The fourth-generation systems have revolutionized the whole field of fiber-optic communications.

2013-7-11

The Sch. Of Information Engineering, WHUT

24

2013-7-11

The Sch. Of Information Engineering, WHUT

25

1.1.3 Optical Network
A network may be defined as a collection of transmission links and other equipment which provides a means of information interchange within a group of end users.

2013-7-11

The Sch. Of Information Engineering, WHUT

26

1.The type of networks
A slightly more complex type is where there is only one connection allowed per user but users may make arbitrary connections at will with other end users. The telephone network is a good example here. More complex are so-called “packet switching” networks where information is carried between end users in the form of packets (a.k.a. frames or cells). In these networks a single end user is usually capable of communicating with a large number of other end users at the same time.

2013-7-11

The Sch. Of Information Engineering, WHUT

27

2.Network may be further characterised by their geographic extend

Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN)

2013-7-11

The Sch. Of Information Engineering, WHUT

28

3.Concept of optical network
The simplest type of network is where a single link is shared by many different communications between different end users. This is achieved in commercial operation today in Wavelength Division Multiplexing (WDM) systems. A simple extension of WDM allows for long links where channels are tapped off to Service individual end users along the way. Networks using this principle (add/drop multiplexing) are possible today and a number of very large networks are planned.

2013-7-11

The Sch. Of Information Engineering, WHUT

29

Build full optical network (FON)
Synchronous optical network (SONET) in North

America
Synchronous digital hierarchy (SDH) in other part of the world these standards define a synchronous frame structure for sending multiplexed digital traffic

over optical fiber trunk lines.

2013-7-11

The Sch. Of Information Engineering, WHUT

30

Commonly used SONET and SDH transmission rates

2013-7-11

The Sch. Of Information Engineering, WHUT

31

1.2 the character of optical fiber Communication Systems
1.2.1 the advantage of optical fiber communication 1、Weight and Size 2、Material cost(SiO2 is plentyful) 3、Information Capacity 4、No electromagnetic interference 5、No electrical connection 6、Distance between repeaters 7、Better security 8、Low crosstalk
2013-7-11 The Sch. Of Information Engineering, WHUT 32

1.2.2 the limitation of optical fiber communication

1、Joining cables
2、Bending cables

3、Slow standards development
4、Optics for transmission only

5、Gamma radiation

2013-7-11

The Sch. Of Information Engineering, WHUT

33

1.3 Optical Communication Systems

2013-7-11

The Sch. Of Information Engineering, WHUT

34

1.3.1 Optical fiber as a communication channel
Loss: determine the repeater or amplifier spacing of longhaul communication system Dispersion: lead to broadening of individual optical pulses with propagation Nonlinearity: generate new frequency

2013-7-11

The Sch. Of Information Engineering, WHUT

35

1.3.2 Optical transmitter
Convert the electrical signal into optical form and to launch the resulting optical signal into the optical fiber. Consist of optical source, a modulator, a channel coupler

2013-7-11

The Sch. Of Information Engineering, WHUT

36

Optical source: LD or LED Modulator: generate optical signal

the output of a semiconductor optical source can be
modulated directly by varying the injection current. Coupler: focus the optical signal onto the entrance plane of an optical fiber with the maximum possible efficiency. a typical coupler is a microlens

2013-7-11

The Sch. Of Information Engineering, WHUT

37

1.3.3 Optical receiver
Convert the optical signal received at the end of the optical fiber back into the original electrical signal.

Consist of a coupler, a demodulator, a photodetector

2013-7-11

The Sch. Of Information Engineering, WHUT

38

Coupler: focus the received optical signal onto the photodector

Photodetector: semiconductor photodiode
because of its compatibility with the whole system Demodulator: depend on the demodulation format most lightwave system employ the scheme referred to as “intensity modulation with direct detection”(IM/DD)

2013-7-11

The Sch. Of Information Engineering, WHUT

39


赞助商链接
相关文章:
更多相关文章: