ENE623/EIE 696 Optical Networks

Lecture 1

Historical Development of Optical Communications 1790 – Claude Chappe invented ‘optical

telegraph’.

1880 – Graham Bell invented ‘photophone’.

1930 – Heinrich Lamm presented unclad-fibers, but it showed poor performance.

1954 – van Heel and Kapany reported about the 1st clad-fibers by covering a bare fiber with a transparent of lower refractive index.

Historical Development of Optical Communications 1960 – Maimen demonstrated the 1st laser for

communications.

1966 – Kuo and Hockham introduced fiber communications with low attenuation (< 20 dB/km).

1970 – Maurer, Keck, and Schultz made a single-mode fused silica fiber (very pure with high melting point and a low refractive index) for 633 nm wavelength of HeNe laser.

1977 – Fibers used at 850 nm from GaAlAs laser.

Historical Development of Optical Communications 1980’s – A 2nd generation of optical

communication at 1300 nm with 0.5 dB/km for fiber attenuation.

1990’s – A 3rd generation operates at 1550 nm with fiber loss of 0.2 dB/km with EDFA serving as an optical amplifier . Signals also could be sent via WDM.

Preview on Fiber Optic Communication Basic schematic diagram

Preview on Fiber Optic Communication The advantages of optical fiber

communication over electrical based system are Low attenuation High bandwidth Immune to electro-magnetic interference Short circuiting, Earthing, and Fire Free Low in weight and volume Data security

Preview on Fiber Optic Communication The transmission passbands for installed

fibers today are 0.85, 1.3, and 1.55 μm (near-infrared).

Wavelength of 1.6+ μm can be seen in some applications.

There are more than 25,000 GHz of capacity in each of the three wavelength bands.

Preview on Fiber Optic Communication Digital transmission – The sampling

theorem says that an analog signal can be accurately transmitted if sampling rate is twice the highest frequency contained in that signal. Let R be the required transmission rate. R can

be expressed by

where m = number of bits/sample

fs = sampling frequency = 2(f)

. sR m f

Preview on Fiber Optic Communication

Message Type Used bandwidth(B)

Voice (telephone) 4 kHz

Music -- AM 10 kHz

Music -- FM 200 kHz

TV (Video + Audio) 6 MHz

Preview on Fiber Optic CommunicationNumber of Voice

channelsTransmission

DesignationSignaling Designation Data Rate

1 - - 64 kb/s

24 T1 DS-1 1.544 Mb/s

48 (2-T1 systems) T1C DS-1C 3.152 Mb/s

96 (4-T1 systems) T2 DS-2 6.312 Mb/s

672 (7-T2 systems) T3 DS-3 44.735 Mb/s

1344 (2-T3 systems) T3C DS-3C 91.053 Mb/s

4032 (6-T3 systems) T4 DS-4 274.175 Mb/s

Example 1 A telephone system has m = 8 bits/sample.

Find R.

Soln

Preview on Fiber Optic Communication A transmission standard developed for optical

communication is called SONET (Synchronous Optical NETwork).

Transmission

(electrical)

Designation

(optical)SDH system Data Rate(Mb/s)

STS-1 OC-1 - 51.84

STS-3c OC-3 STM-1 155.52

STS-12 OC-12 STM-4 622.08

STS-24 OC-24 STM-8 1,244.16

STS-48 OC-48 STM-16 2,488.32

STS-96 OC-96 STM-32 4,976.64

STS-192 OC-192 STM-64 9,953.28

STS-768 OC - 768 STM-128 39,813.12

Preview on Fiber Optic Communication

Band Descriptor Range(nm)

O-band Original 1260 - 1360

E-band Extended 1360 -1460

S-band Short wavelength 1460 - 1530

C-band Conventional 1530 – 1565

L-band Long wavelength 1565 - 1625

U-band Ultra-long wavelength 1625 - 1675

Installations

Optical fiber installations: on poles in ducts undersea

Fiber Attenuation History

Preview on Fiber Optic Networks Fiber-To-The-Home (FTTH)

2.5 Gbps Mid 90’s

10 Gbps y2k

40 Gbps and beyond state of art

Preview on Fiber Optic Networks Now a number of channels per fiber is more

than 128.

This was increased from 32 channels/fiber in 2004.

The link attenuation is less than 0.2 dB/km at 1.55 μm wavelength.

BER can be achieved at 10-15 with a help of Er-doped fiber amplifier (EDFA).

Optical Fiber

Source: ARC Electronics http://www.arcelect.com/fibercable.htm

Fibers

Source: Optical Fiber Communications, G.Keiser, McGraw Hill.

Connectors

Source: ARC Electronics http://www.arcelect.com/fibercable.htm

Optical communication systems Multiplexing refers to transmission of multiple

channels over one fiber.

Channels can be data, voice, video, and so on.

We may classify the communication systems into 3 classes as: Point-to-point link Multipoint link Network

Example 2 A cable consists of 100 fibers. Each fiber can

carry signals of 5 Gbps. If audio message encoded with 8 bits/sample is being sent, how many conversations can be sent via one cable?

Soln

Example 3 By using the same cable as previous example,

how many TV channels could be sent via a cable.

Soln

Generations of Fiber Usage Bandwidth and error rate improved (fatter

links), but propagation delay not changed (same length).

Source: Fiber Optic Network Paul E. Green, Prentice Hall.

Generations of Fiber Usage

First generation: no fiber (copper link)

2nd generation: Fiber used for point-to-point link only. Multiplexing & switching carried out electronically.

3rd generation: Fiber used for multiplexing and switching as well

as point-to-point transmission.

Generations of Fiber Usage Copper links

Copper links are more vulnerable to outside influence since moving electrons influence each other.

It is also affected by electromagnetic wave (EM wave).

Fiber links Moving photons of light in a fiber do not interact

with other moving photons. EM wave has no effect on a fiber as well.

Fiber Bandwidth We all know that

where λ = free-space wavelength ν = optical frequency

c = speed of light at free-space

c

Fiber Bandwidth At = 1.5 µm, the attenuation is about 0.2

dB/km, and there is a window about = 200 nm wide between wavelengths having double that number of dB per kilometer.

The useful bandwidth is about 25,000 GHz.

2

c

Fiber Bandwidth This can applied to = 1.3 µm and 0.85 µm as

well.

For 0.85 µm, this band is not defined by an attenuation standpoint, but by the range which GaAs components can be easily made.

Fiber Bandwidth

λ (nm) ν (x1014Hz) Δν (x1013Hz)

Δν/ν

0.85 3.53 2.5 0.071.3 2.31 2.5 0.111.55 1.93 2.5 0.13

Multiplexing Space Division Multiplexing Frequency Division Multiplexing Time Division Multiplexing Wavelength Division Multiplexing

Wavelength-Division Multiplexing For example, 16 channel WDM using 1,300 nm

or 1,550 nm with 100 GHz channel spacing.

Therefore, bandwidth = 16 x 100 = 1,600 GHz.

LAN = Local Area Network (< 2 km) MAN = Metropolitan Area Network ( < 100

km) WAN = Wide Area Network (unlimited)