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Telecommunications Essentials. CHAPTER 11 OPTICAL NETWORKING. Optical Cost Trends. Cost of fiber is declining Bit rate per wavelength is increasing WDM Repeater spacing is increasing Cost/bit = 0.006% of the cost in 1996. Nortel’s WDM System. Fiber Networks. Large Networks
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Telecommunications Essentials CHAPTER 11 OPTICAL NETWORKING
Optical Cost Trends • Cost of fiber is declining • Bit rate per wavelength is increasing • WDM • Repeater spacing is increasing • Cost/bit = 0.006% of the cost in 1996 Nortel’s WDM System
Fiber Networks • Large Networks • Dual Counter-rotating SONET Rings • 50 mSec switchover when cut
Fiber Optic Cable www.arcelect.com/
Optical Equipment • End-to-end optical (signal path) • EDFA – Erbium doped fiber amplifiers • DWDM • OADM – Optical add/drop multiplexers • Optical switches FTTH Terminal Box Fiber Optic Pigtails CATV Amplifier
Traditional Repeaters • OEO • Optical to electrical to optical • ~ ½ the cost of an optical network • Required to regenerate & retime the signals • Repeaters are needed ~ 200 miles
EDFA • All optical repeater • 50 – 100 km spacing • Uses erbium doped fiber • Operates at 1550 nm • Energy is pumped in at 980 nm • Supports DWDM • Encyclopedia of Laser Physics & Technology
WDM • Each wavelength 2.5 – 10 Gbps • OC-48 to OC-192 • Experimental systems at 40 Gbps • OC-768 • Each wavelength supports a separate service • CWDM< 16 wavelengths
DWDM • WDM by MRV • Cisco • OC-48 systems may carry 60 – 160 wavelengths • OC-192 systems may contain 8 – 32 wavelengths • Theoretically 15,000 wavelengths
DWDM Issues • Wavelength stability • Tunable lasers • Initially used in point-to-point links • Need to provision as rings • Need add/drop for MANs • 95% of fiber can not handle DWDM • Wavelength crosstalk • Routing • Interoperability standards
OADM • Optical add/drop multiplexer • Use filters to drop off a wavelength • Each wavelength is assigned • Specific protocol (ATM, IP, etc.) • Specific customer (essentially point-to point) Optical Filter
Optical Switch • Also called optics cross-connect or wavelength router • Connects the light from one fiber to another
Optical Switching Fabrics • MEMS – micro-electromechanical • Uses microscopic mirrors • Lucent Lambda router - 256 x 256 ports • Xros – 1024 x 1024 ports • DLPflash demo
Optical Switching Fabrics • Bubble Switch • Liquid filled cavities • Heated to a gas to switch
Optical Switching Fabrics • Thermo-optical switch • Refractive index is a function of temperature • The glass is heated or cooled
Optical Switching Fabrics • LCD • The LCD polarizes and rotates light • Tunable laser
Fiber Attenuation • Intrinsic Absorption • Due to the nature of glass • Extrinsic Absorption • Impurities • Rayleigh Scattering
Other Fiber Components • Lasers • Gratings • Filters • Dispersion Compensators • Variable attenuators • Passive splitters • Raman Amplifiers
IP Over Optical Standards • MPlS • IETF’s Multiprotocol Lambda Switching initiative • OIF • Optical Internetworking Forum
Managing Optical Networks • There are no network management standards • There are no error correcting protocols • Digital Wrappers • WaveWrapper by Lucent • Part of submarine cabling systems
Future Developments • Wavelength changer • ROADM • Nonzero Dispersion-Shifted Fiber
Optical Dispersion • Passive Optical Network
For More Information • Optoelectronics World • Photonics.com