Current developments in Telecommunications Philip Allen

Transcription

1 Current developments in Telecommunications Philip Allen

2 Contents Introduction Newer display technology for TV Optical Fibre Technology Satellite Technology The Future - Quantum communictions? Concluding Remarks

3 Introduction Telecommunications is pervasive and increasingly so! This talk focuses on a few of the topics covered in Information Systems (section 9.4 of the Senior Science Stage 6 Syllabus)

4 Beyond CRTs Colour Primer The eye has 3 kinds of cone cells with sensitivity peaks in: short (S, nm), middle (M, nm), and long (L, nm) wavelengths. The chromaticity diagram illustrates how the human eye will experience light with a given spectrum The CIE 1931 color space chromaticity diagram. Ref:

5 Beyond CRTs Plasma Displays A well known mechanism but how to make a high resolution display from it? Ref: &

6 Beyond CRTs Plasma Displays xenon and neon gas is contained in 100,000s of cells Address electrodes used to ionise individual cells or pixels The phosphors give off coloured light when excited by the UV Ref:

7 Beyond CRTs LCD Displays LCD cell controls the light through it but how to create an array of coloured pixels? Ref:

8 Beyond CRTs LCD Displays Passive-matrix LCDs again use a simple grid to address a particular pixel Active-matrix LCDs additionally use thin film transistors (TFT) Ref:

9 Optical Fibres - types Typical Bandwidths 20 MHz-km 500 MHz-km at 1300nm 160 MHz-km at 850 nm 100 GHz-km Pulse broadening decreases the Bandwidth Ref:

10 Optical Fibres Optical fibres have been in production since the early 70s. they can be categorised in two classes: Multimoded fibres: Used mainly for local area networks, they were the first type of fibre developed. Fundamental structure of an optical fibre consisting of a core and cladding. Single moded fibres (SMF): Now commonly used in all long-haul, high speed telecom networks. Single mode fibres have been research extensively during the 70s, 80s and 90s. This research effort has lead to subclasses targeting specific applications Dispersion shifted fibres Dispersion flattened fibres Polarisation maintaining fibres. Typical fundamental intensity distribution in single mode optical fibre (in µm).

11 Optical Fibres High speed optical network operate in two major transparency windows due to the very low attenuation of glass fibres. These windows are centred at 1.3 and 1.55 µm respectively Note: 0.2 db/km ~ 95% transmission after 1 km. Only needing 1% of power before regeneration means a link can be 100 km! NB: the rayleigh scattering has a wavelength dependence:

12 Optical Fibres - manufacture Pioneered by Bell Laboratories (now Lucent Technologies), the Modified Chemical Vapour Deposition (MCVD) process is probably the most widely used fibre fabrication technique. Optical fibres made by MCVD are produced in a preform. SiCl4 and GeCl4 reactants reacting with oxygen to produce SiO2 particles but P and B dopants can also be used

13 Optical Fibres at UNSW

14 Optical Fibres: Drawing Tower

15 Optical Fibres: Drawing Tower UNSW Tower height 7.6m Max Draw Speed: 200m/min Preform Diameter: <50mm Commercial towers can draw fibre at 125 km/hr using 3000 fiber-km preforms

16 Finished spool of optical fiber Photo courtesy Corning Optical Fibres Dimensions of single mode optical fiber. 1.- Core 8-10 µm 2.- Cladding 125 µm 3.- Buffer 250 µm 4.- Jacket 400 µm

17 Micro-structured polymer optical fibres (MPOF) also known as photonic crystal fibres (PCF) a topical research area. MPOF fabricated at the Optical Fibre Technology Centre at Sydney University using the drilling approach. This image represent the preform (diameter ~10 cm) before the drawing processs. Courtesy of Martijn van Eijkelenborg and Maryanne Large They can guide light through two mechanisms: Effective index: The presence of (air) holes in the glass structure results in an perceived average reduction of the refractive index. Hence by tailoring the hole patterns, both core and cladding regions can be defined and guidance is very similar to standard fibres. Bragg resonnance: In this case, guidance is achieved through a resonance mechanism due to the radial (quasi- )periodicity of the hole pattern. This is similar to multilayer coating on glasses or to the periodic electronic potential in semiconductor resulting of band gap or forbidden bands. A photonic band gap is created and light cannot travel radially.

18 Components used in Optical Fibre Links Injection laser diode e.g. 622 Mbit/s (OC 12) Fibre link single-mode e.g. 50 km Transmitter secondary channel primary channel Electronics drive circuit Connector Splice Optical coupler or beam splitter Receiver O/E signal regenerator Optical amplifier Photodetector Amplifier and restorer

19 EDFA - erbium doped fibre amplifier Electronic Regenerator Basic Erbium Doped Fibre Amplifier Ref:

20 EDFAs the essentials Consists of 10 to 30 meter of silica fibre lightly doped with Erbium ions: Its optically pumped (980nm or 1480nm); The amplification region is typically limited to nm; Can provide gain as high as 30 db; Requires no opto-electronic conversion; Is readily compatible with standard telecom fibres!

21 EDFAs configurations EDFA can be configured in three ways codirectional, contradirectional and bidirectional configuration. Here are two examples. Codirectional Contradirectional 2

22 EDFAs energy-level diagram The three-level transition diagram corresponding to the Er 3+ ion embedded into silica glass 1. Pump photon absorption 4. Signal photon re-absorption 2. Non-radiative decay 5. Stimulated emission 3. Spontaneous emission 2

23 EDFAs applications EDFA can be used in three basic ways when building a point-to-point link. 2

24 Fibre Link Hero experiments 1.03-Exabit/s km Super-Nyquist-WDM Transmission over 7,326- km Seven-Core Fiber We demonstrate Tbit/s, 7,326-km transmission of channel 25-GHz-spaced Super-Nyquist-WDM 100-Gbit/s optical signals using seven-core fiber and full C-band seven-core EDFAs. The record capacity-distance product of 1.03 Exabit/s km is achieved. K Igarashi et. al. KDDI R&D Laboratories Inc., Japan & Furukawa Electric Co. Ltd, Japan 1 exabit = bits = bits = 1000 petabits Ref:

25 Satellites Satellites permeate our lives. We depend on them in almost everything we do: Communications: TV broadcasting, telephony, internet Navigation: GPS, Galileo, GLONASS & Remote sensing and earth observation: Environmental monitoring, mapping the earth for resources Meteorology: weather forecasting, natural disasters (e.g. cyclones) Science: astronomy, but also study of our home the Earth

26 Satellite can be launched into various orbits: Low Earth Orbit (LEO) Satellite Orbits Medium Earth Orbit (MEO) Geostationary Orbit (GEO) QB50 GPS satellite

27 Satellite Communications One of the first uses for satellites was to enable communications between vastly separated points on Earth NBN Cost Per Premise Comparison of Technologies %

28 GEO Satellites GEO satellites used for TV broadcasting, telephony, etc.. GEOs have many challenges: They are expensive to launch The signal experiences long delays: about 0.25s The signal is attenuated by the large distance They cannot see the poles! Optus D1 Inmarsat operate 3 constellations of 10 satellites in geo orbit to provide a global mobile satellite communications system

29 Satellite Communications with LEOs LEOs have been proposed for communications Small round-trip delay Small relative attenuation Cheaper to launch Constellation needed to cover entire earth They move rapidly with respect to an object on earth and so must be tracked More complicated protocols (handover ) Iridium

30 Satellites at UNSW Masters in Satellite Systems Engineering QB50 project BLUEsat stratospheric balloon launch GPS receivers Satellite research

31 The Next Communication Technology for the 21st Century Quantum Communications? Teleportation is Common Place in a Quantum Network Quantum Communications and Quantum Networks are anticipated to be the core networking technologies of the 21st century. Many major companies also think so! Such as Toshiba, Hewlett-Packard, IBM, Mitsubishi, NEC, & NTT, have all commenced large-scale research projects into quantum networks. The US, Japanese and European Governments are spending billions of research dollars in this area

32 The Next Communication Technology for the 21st Century Quantum Communications? The Race is on to Create a Space-Based Global Quantum Internet Intense research efforts related to these systems are being pursued by all leading industrial nations. A large global consortium has commenced tests for a space-based Global Quantum Internet And EE&T at UNSW has PhD studentships to carry out leading-edge research into the development of a large-scale global quantum internet

33 But what is Quantum Communications? Quantum physics applied to communications Creates new applications which are simply impossible to achieve using classical communications Examples of the weird effects found in quantum communications are: teleportation of quantum qubits, transfer of information at twice current theoretical limits, instantaneous change in quantum particles located at opposite ends of the planet, and other new effects Quantum communications also provide ultra secure communications. No hacker can penetrate these systems as security is based on the fundamental laws of nature.

34 Concluding Remarks The demand for higher data rates is increasing Different technologies are advancing to meet the growing demand

35 Thank you

36 Additional Reference Sources Francois Ladouceur Robert Malaney Elias Aboutanious (All academics from the School of Electrical Engineering and Telecommunications)