Slide Chapter 1 UG

Optical Communications

Chapter 1: Introduction

Textbooks

[1] G. Keiser, Optical Fiber Communications, 3rd Edition, McGraw-Hill, 2000

[2] G. P. Agrawal, Fiber-Optic Communication Systems,

John Wiley & Sons, 1992

[3] R. Ramaswami and K. N. Sivarajan, Optical Networks –

A practical Perspective, 3rd Edition, Morgan Kaufmann

Publishers, 2010

[4] J. Powers, Introduction to Fiber Optic Systems, 2nd

Edition, McGraw-Hill, 1999

Content

�Why optical communications?

�Major Milestones in Optical Fiber

Communication

�Evolution of Optical Communication

Systems

�1st and 2nd generation optical networks

Why optical communications?

� Increasing Need for High-Capacity & Broadband Services

Cisco Forecasts of IP Traffic in 2012

Why optical communications?

� Increasing Need for High-Capacity & Broadband Services

Cisco Forecasts of Global Consumer Internet Traffic in 2012

Why optical communications?

� Increasing Need for High-Capacity & Broadband Services

�Transport of video on demand, Internet video streams and

downloads, and the exchange of video and other files through P2P.

� Optical Fibers with DWDM Systems Technologies can provide needed solutions

Why optical communications?

� Greater bandwidth

� Small size and weight

� Low attenuation

� Freedom from EMI and crosstalk

� Safety & Electrical Isolation

� Security (non-invasive tapping impossible)

Major Milestones in Optical Fiber Comm.

� 1960: T. Maiman demonstrated first laser at Hughes Research Laboratories.

� 1966: Kao and Hockham proposed the use of optical glass fibers as waveguide for laser light transmission.

� 1970: Corning developed single-mode fiber with loss of 17dB/km at 633nm. Bell Labs developed first room temperature semiconductor lasers.

� 1987: University of Southampton developed Erbium doped fiberamplifier operating at 1550nm.

� 1988: First Trans-Atlantic fiber-optic cable, TAT-8, in service.

� 1996: Fujitsu, NTT Labs, and Bell Labs all reported sending 1 Tb/s through single optical fiber.

� 2002: 2.65-Tb/s (Tyco), 3.2-Tb/s (Fitel), 4.27-Tb/s (Alcatel) transmission demonstrated in research laboratories

Evolution of Optical Communication Systems� 1960s

� Experiments demonstrated the capability of free-space transmission of light signals

� 1970s� Invention of low-loss optical fibre

� Deployment of systems using LEDs and multi-longitudinal mode (MLM) lasers over multi-mode (MM) fibres

� Repeater spacing is several km due to modal dispersion

� 1980s� MLM laser over single mode (SM) fibre in the 1.3 µm band is

used

� Regenerator spacing is about 40km and bit rate is several hundred Mb/s

� A later system using the 1.55 µm band for lower loss, and using SLM DFB laser to overcome chromatic dispersion limits to increase bit rate to > 1 Gb/s

� Emergence of 1st generation optical networks

Evolution of Optical Communication Systems

� 1990s

�Development and Deployment of WDM systems operating with 8-32 wavelengths at a bit rate of 2.5 Gb/s

�Replacement of regenerators with EDFAs

�Experiments demonstrating > 2 Tb/s transmission over a single fibre

� Experiments on 2nd generation optical networks

1st and 2nd generation optical networks

� 1st generation Optical networks� Optical fiber is used purely as a transmission medium

� Mainly serving as a replacement for copper cable

� All the switching and processing of the bits is handled by electronics

� Widely deployed today in all kinds of telecommunication networks, except in residential access networks� Examples: FDDI, SONET/SDH

� 2nd generation Optical networks� More than just a direct replacement of copper with fiber

� Perform some switching and routing functions optically

� Both OTDM and WDM approaches are being investigated

� WDM are expected to be deployed not only in interexchange networks but also in local exchange & access networks in the next few years

1st and 2nd generation optical networks

Optical transmission system capacity

Course content

� Optical fiber – chapter 2

� Source – chapter 3

� Receiver – chapter 4

� Point-to-Point link – chapter 5

� SONET/SDH (1st generation) – chapter 6

� WDM (2nd generation) – chapter 7

Block-diagram of an Optical System