Title: Communication Engineering IIITitle: Communication Engineering III

Credit-Credit- 3 3

Reference Books: Reference Books:

Optical communications by Optical communications by John Senior **John Senior ** Optical fiber communications by Optical fiber communications by Gerd KeiserGerd Keiser Optical Communication by Optical Communication by M. J. N. Sibley **M. J. N. Sibley ** Fiber Optic communication Systems by Fiber Optic communication Systems by Govind P. Govind P. Agrawal (Agrawal (For Advanced levelFor Advanced level)) Optical communications, components and Systems, Optical communications, components and Systems, by by J. H. Franz and V. K. JainJ. H. Franz and V. K. Jain

Contents:Contents:

Introduction to OFCIntroduction to OFC Brief historyBrief history

Optical fiber communication systemOptical fiber communication systemAdvantage and Limitation of OFCAdvantage and Limitation of OFC

IntroductionIntroduction

Brief history of Optical Communication Technology:

Before 1792, fire beacons or smoke was used to send information In 1792, Claude Chappe was invented optical telegraphy He was succeeded to transmit information between Paris and Lille By 1830, the network was extended In Europe (Bit/s < 1)

Optical telegraphy system and its inventor Claude Chappe

Relay Station

The advent of electrical telegraphy in the 1830 replaced the use of optical telegraphy and began the era of electrical communication

The bit rate of electrical telegraphy was increased to ~ 10 bit/s by using Morse Code (dots and dashes)

The invention of telephone in 1876 enables to transmit electrical signals in analog form, which dominate comm. for a century or so.

The development of worldwide telephone networks led to many advances in the design of Electrical communication systems

Use of coaxial cable instead of wire pairs increased system capacity considerable

Brief history of Optical Comm. Technol.:

The first coaxial cable put into service in 1940 with 3 MHz system capacity (300 voice channels or a single television channel) The bandwidth was limited by frequency dependent cable losses(~10MHz) This limitation was led to develop Micro-Wave communication (1~10GHz) The first Microwave system was operated at 4 GHz Most advanced coaxial cable put into service in 1975 (274 Mb/s, ~1Km) Microwave communications generally allow larger repeater spacing, but bit rate is limited by the carrier frequency of such waves

Brief history of Optical Comm. Technol.:

Bit rate-distance

product, BL

BL product 100 Mb/s-Km was achieved by

1970 and limited due to carrier

frequency1970

108

During 1950 it was realized that BL product can be further increased if optical waves were used as the carrier During 1950 there was no coherent optical source nor a suitable transmission medium In 1960 first LASER was developed (coherent light source) After 1960 first idea was developed to use glass material as a transmission medium In 1966 first optical fiber was made by Kao and Hockham but loss was 1000 dB/km By reducing concentration of transition-metal ions and water ions (Fe, Cu, Cr, Ni, Mn, Cobalt and HO) In 1970 Kapron et al. at Corning made a fiber with α < 20 dB/km in the wavelength region near 1 m In the same time GaAs semiconductor lasers operating continuously at room temperature at 1 m were developed Simultaneous availability of compact light source and low loss fiber

led to a worldwide effort for developing FO Comm. systems

Brief history of Optical Communication Technology:

Electromagnetic SpectrumElectromagnetic Spectrum

108 1010 1012 1014 1016 1018106

1.7 µm

Red0.7 µm Violet 0.4 µm

0.8 µm

Optical fiber communication

Microwave Millimeterwave Far

IR UV

1020

Visible Spectrum

X-ray

Light sources used in OFC having wavelength:

0.85µm, 1.3µm, and 1.55µm

NIR

Increase in capacity of lightwave Increase in capacity of lightwave system after 1980system after 1980

Due to advent of WDM tech.

Purpose: Eliminate repeaters used in inter-office trunk lines Technology: 0.8 µm GaAs semiconductor lasers, Multimode silica fibers Repeater Spacing: 10 km Limitations: Fiber attenuation 3 dB/km, Intermodal dispersion, bit rate 45 Mb/s Deployed since 1974

First-generation Fiber optic Systems

Opportunity: Development of low-attenuation fiber (removal of H2O and other impurities), Eliminate repeaters in long-distance lines Technology: 1.3 µm semiconductor lasers, Muti-mode fiber, low- attenuation silica fibers, bit rate: < 100 Mb/s due to dispersion 1.3 µm semiconductor lasers, Single-mode fiber, low- attenuation silica fibers, bit rate: 1.7 Gb/s Limitation: Fiber attenuation 0.5 dB/km, repeater spacing ≈ 50 km Deployed since 1978

Second-generation Fiber optic Systems

Opportunity: Long-distance Communication Technology: 1.55 µm single-mode semiconductor lasers, Single-mode fiber, low- attenuation silica fibers, bit rate: 2.5 Gb/s Limitations: Fiber attenuation 0.2 dB/km, repeater spacing ≈ 60~70 km, Fiber dispersion, electronic repeaters Deployed since 1982

Third-generation Fiber Optic Systems

Opportunity: Development of erbium-doped fiber amplifiers and WDM technology

Technology (deployment began in 1994): 1.55 µm single-mode, narrow-band semiconductor lasers, Single-mode, low-attenuation dispersion-shifted silica fibers, Wavelength-division multiplexing, with bit rate 2.5 Gb/s over 21000 km and 5 Gb/s over 14300 km by 1996. Using WDM technology bit rate was possible to increase 2.56 Tb/s by 2002

Nonlinear effects limit the following system parameters: Signal launch power, Propagation distance without regeneration, WDM channel separation, Maximum number of WDM channels per fiber

Fourth-generation Fiber optic Systems

Fifth-Generation !!!!!! Opportunity: Development of Raman amplifiers and WDM technology, dry fiber

Technology (deployment began in 1994): Dry fiber with low loss over the wavelength region 1.3 to 1.65 µm lead to lightwave systems having 1000 WDM channels, Each channel 40 Gb/s, which can be extended to 160 Gb/s in future

BL product in several generations BL product in several generations of lightwave systemsof lightwave systems

Optical fiber communication systemOptical fiber communication system

Optical Transmitter

Comm. Channel (Optical fiber)

Optical Receiver

Input Output

Attenuation, Dispersion, crosstalk & noise

1 Greater bandwidth 2 Low attenuation 3 Electrical immunity (no RFI, EMI)4 Greater security6 Flexibility 8 Falling cost7 Long repeater spacing5 Smaller size and weight than copper cables

Advantages of OFC

Disadvantages of OFC Stimulated Raman Scattering (SRS): An interaction between light and vibrations of silica molecules, causes attenuation of short wavelength channels in WDM system Stimulated Brillouin Scattering (SBS): An interaction between light and sound waves in the fiber, causes frequency conversion and reversal of propagation direction of light Four Wave Mixing (FWM): Two or more optical waves at different wavelengths mix to produce new waves at other wavelengths Self Phase Modulation (SPM): Change in signal phase due to change in intensity of the signal due to group velocity dispersion Cross Phase Modulation (XPM): It is an interaction via the non-linear refractive index between the intensity of one light wave and optical phase of other light waves Some other limitations: Dispersion, laser phase noise, relative intensity noise etc.