Optical Communication Engineering (4041) B.Eng.

Transcription

1 Optical Communication Engineering (4041) B.Eng. School of Electrical and Electronic Engineering The University of Adelaide, Australia Dr Bernd Fischer The Dream & The Reality Leadership is the ability to redefine reality Warren Bennis 1

2 Redefining Reality How to Pass this Course Come to all lectures Do all exercises Read the text book Work through text book examples Study an hour per day (on this subject) Focus and good study habits Do everything I say 2

3 The Big Secret High Distinction Best study habits Pass Poorest study habits Highest IQ Lowest IQ Lectures There are no homeworks There are two large tutorial sheets See the course website We have a double lecture on Thurs We have an extra single slot on Friday We will use Friday most of the time except this week. 3

4 COURSE NOTES or TEXTBOOKS Highly recommended course text: J.C. Palais, Fibre Optic Communications, Publ: Prentice-Hall. Texts for general reading: M. Born and E. Wolf, Principles of Optics, Publ: Cambridge University Press C.C. Davis, Lasers and Electro-Optics, Publ: Cambridge University Press Text Books Highly recommended course text: J.C. Palais, Fibre Optic Communications, Publ: Prentice-Hall. 4

5 General Reading M. Born and E. Wolf, Principles of Optics, Publ: Cambridge University Press C.C. Davis, Lasers and Electro-Optics, Publ: Cambridge University Press E. Rosencher and B. Vinter, Optoelectronics, Publ: Cambrideg University Press B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Publ: : John Wiley & Sons A. Yariv, Optical Electronics in Modern Communications, Publ: : Oxford University Press Dr Bernd Fischer bfischer@eleceng.adelaide.edu.au Phone: (+61 8) Room location: N234 5

6 Dr Bernd Fischer Wednesday,, 2pm-3pm Tuesday,, 29/07/2008 6

7 Outline of this course 1. Introduction 2.FundamentalsofOpticsandLightwarePropagation 3. Optical Waveguides 4. Light Sources 5. Light Detectors 6. Fibre Components 7. Modulation 8. System Design A historical view Early primitive origins: : Smoke signs, pope election,, etc 7

8 A historical view 1880 Bell's Photophone Modulating light by flexible mirror, detecting with cystalline selenium A historical view 1880 Bell's Photophone 1900s Signal Lamps 1960s Lasers 1970s Low-loss Optical Fibres 1980s Analogue and Digital Communications 1990s Fibre Networks 8

9 History Coaxial cables limtd to 100 Mbit / s for 1 km. Losses increase with frequency (bitrate) Increase in Bitrate-distance product BL during the period History (continued) Increase in Bitrate-distance product BL during the period

10 Visible Spectrum colour violet blue green yellow orange red wavelength nm nm 495nm nm 50nm nm 590nm nm nm 10

11 Optical spectrum Useful wavelengths for optical communications: µm m UV µm Visible µm m IR µm most widely used for fibre communications since losses are low in windows within this region. Why?? See page 93. Nature of Light Quantum Theory Light consists of small particles (photons) Wave Theory Light travels as a transverse electromagnetic wave Ray Theory Light travels along a straight line and obeys laws of geometrical optics. Ray theory is valid when the objects are much larger than the wavelength 11

12 Review of basic Optics Ray Theory: Rules for ray tracing based on Geometric Optics (GO). Velocity of ray v = c/n, where n is the index of refraction of the media in which the ray travels. 12

13 Review of basic optics Ray optics (continued) Rays travel in straight paths unless deflected by a change in the medium. Review of basic optics Ray optics (continued) At a plane boundary, rays are reflected at an angle θ equal to the angle of incidence θ i, ie. θ r = θ i 13

14 Basic optis Snells Law: 14

15 Information rate Pulse spread (τ/l) per unit length is given by material Dispersion M λn M= c, (τ/l) = -M λ Modulation frequency f limited by: 1 2 τ f Information rate (continued( continued) 3-dB optic frequency-length limit 1 2 (τ/l) f 3-dB x L = Asuming a Loss L f of 1.5 db we found f 1.5-dB (optic) = f 3-dB (electrical) = 0.71 f 3-dB (optic) 15

16 Information rate (continued( continued) Electrical frequency Length limit gven by: f 3-dB (elec) x L = 0.35 (τ/l) Example Question Find the amount of pulse spreading in pure silica for an LED operating at 0.82 µm m and having a 20 nm spectral width. The path is 10 km long. What are the corresponding frequency and data limits? 16

17 Example Question (continued) M = 110 ps/(nm m) for 0.82 µm. Thus (τ/l) = 110x20ps/km = 2.2 ns/km f 3dB = 23 MHz 3dB (elec)) = 16 MHz f 3dB Reflection coefficient (%) 17