Current developments in Telecommunications
Philip Allen
• Introduction
• Newer display technology for TV
• Optical Fibre Technology
• Satellite Technology
• The Future - Quantum communictions?
• Concluding Remarks
Contents
Telecommunications is pervasive and increasingly so!
Introduction
This talk focuses on a
few of the topics
covered in Information
Systems (section 9.4 of
the Senior Science
Stage 6 Syllabus)
Beyond CRTs – Colour Primer
The eye has 3 kinds of cone cells with sensitivity peaks in:
short (S, 420–440 nm),
middle (M, 530–540 nm), and
long (L, 560–580 nm) wavelengths.
The chromaticity diagram illustrates how the human eye will experience light with a given spectrum
Ref: http://en.wikipedia.org/wiki/CIE_1931_color_space
The CIE 1931 color space chromaticity diagram.
Beyond CRTs – Plasma Displays
A well known mechanism but how to make a high resolution display from it?
Ref: http://electronics.howstuffworks.com/plasma-display2.htm
& http://en.wikipedia.org/
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: http://electronics.howstuffworks.com/plasma-display2.htm
Beyond CRTs – LCD Displays
• LCD cell controls the light through it but how to create an array of coloured pixels?
Ref: http://electronics.howstuffworks.com/lcd2.htm
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: http://electronics.howstuffworks.com/lcd2.htm
http://www.plasma.com/classroom/what_is_tft_lcd.htm
Optical Fibres - types
Pulse broadening decreases the Bandwidth
Ref: http://en.wikipedia.org/wiki/Optical_fiber
Typical Bandwidths
20 MHz-km
500 MHz-km at 1300nm
160 MHz-km at 850 nm
100 GHz-km
Optical Fibres
Typical fundamental intensity distribution in
single mode optical fibre (in µm).
Fundamental structure of an optical
fibre consisting of a core and cladding.
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.
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.
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:
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
Optical Fibres –at UNSW
Optical Fibres: Drawing Tower
UNSW Tower height 7.6m
Max Draw Speed: 200m/min
Preform Diameter: <50mm
Optical Fibres: Drawing Tower
Commercial towers can draw fibre at 125 km/hr using 3000 fiber-km preforms
Dimensions of single mode optical
fiber.
1.- Core 8-10 µm
2.- Cladding 125 µm
3.- Buffer 250 µm
4.- Jacket 400 µm
Optical Fibres Finished spool of optical fiber
Photo courtesy Corning
Micro-structured polymer optical fibres
(MPOF)
– also known as photonic crystal fibres (PCF) – a topical research area.
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.
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
Components used in Optical Fibre Links
Injection laser diode e.g.
622 Mbit/s (OC–12)
Transmitter
Electronics drive circuit
Fibre link – single-mode
e.g. 50 km
Connector Splice
secondary channel
primary channel
Optical coupler or
beam splitter
Receiver
Photodetector
Amplifier and restorer
Optical amplifier
O/E signal
regenerator
EDFA - erbium doped fibre amplifier
Electronic Regenerator
Basic Erbium Doped Fibre Amplifier Ref: http://www.thefoa.org/
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 1530 – 1550 nm;
– Can provide gain as high as 30 dB;
– Requires no opto-electronic conversion;
– Is readily compatible with standard telecom fibres!
EDFAs – the essentials
2
1
EDFA can be configured in three ways codirectional, contradirectional and bidirectional configuration. Here are two examples.
Codirectional
Contradirectional
EDFAs – configurations
2
2
The three-level transition diagram corresponding to the Er3+ ion embedded into silica glass
1. Pump photon absorption 4. Signal photon re-absorption
2. Non-radiative decay 5. Stimulated emission
3. Spontaneous emission
EDFAs – energy-level diagram
2
3
EDFA can be used in three basic ways when building a point-to-point link.
EDFAs – applications
Fibre Link – “Hero” experiments
We demonstrate 140 7-Tbit/s, 7,326-km transmission of 7×201-
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
1.03-Exabit/s·km Super-Nyquist-WDM Transmission over 7,326-
km Seven-Core Fiber
Ref: http://www.ecoc2013.org/
1 exabit = 1018bits = 1000000000000000000bits = 1000 petabits
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
Satellites
Satellite can be launched into various orbits:
– Low Earth Orbit (LEO)
– Medium Earth Orbit (MEO)
– Geostationary Orbit (GEO)
Satellite Orbits
QB50
GPS satellite
• One of the first uses for satellites was to enable
communications between vastly separated points on
Earth
• NBN Cost Per Premise – Comparison of Technologies
Satellite Communications
%
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!
GEO Satellites
Optus D1
Inmarsat operate 3 constellations of 10 satellites in
geo orbit to provide a global mobile satellite
communications system
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…)
Satellite Communications with LEOs
Iridium
Masters in Satellite Systems Engineering
QB50 project
BLUEsat – stratospheric balloon launch
GPS receivers
Satellite research
Satellites at UNSW
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
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
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.
• The demand for higher data rates is increasing
• Different technologies are advancing to meet the growing demand
Concluding Remarks
Thank you
Additional Reference Sources
• Francois Ladouceur
• Robert Malaney
• Elias Aboutanious
(All academics from the School of Electrical Engineering and Telecommunications)