Transcript UNLEASHING the LIGHT - TS

Unleashing the Light around the CERN Accelerators
ST/EL/OF
Luit Koert de Jonge.
ST-EL-OF
Unleashing the light around the accelerators is may be a somewhat misleading title, but hundreds of laser light sources will transmit vital data for the
operation of LHC at 2/3 of the light speed (200’000 km/s) all across the CERN surface and underground sites.
More than a simple piece of glass.
Optical fibres play today a vital role in communications, machine controls, instrumentation and safety systems. CERN will count at LHC commissioning
over 25’000 installed fibre kilometres and more than 40’000 optical terminations. The optical fibre network for LHC must be extremely reliable and
redundant loops shall exist to avoid single points of failure. Laser power used at the transmitter rarely exceeds 1 mW and optical connections must
therefore have a high quality standard in order to keep optical reflections and attenuation within acceptable limits. The long distance surface optical
fibres (in ducts) may suffer from mechanical stress and will therefore be permanently monitored via an autonomous monitoring system using optical time
domain reflectometry. The optical fibres in the LHC tunnel will be subject to irradiation and will therefore darken, thus increasing their attenuation. This
process will be closely monitored as well, in order to set off a replacement of these fibres in time.
Optical glass fibre production can be considered as a
wonder of modern engineering.
A preform of ultra pure silica is produced, usually by
chemical vapour deposition technology and by
adding concentrations of dopants (germanium oxide)
to obtain the required refractive index profile across
the diameter.
Preform Feed
Preform
Furnace
Laser Micrometer
Coating Cup 1
UV Curing Oven 1
The optical fibre is drawn from the preform in a large tower
between 10 and 20m high, where the preform is heated to
form a got that drops by gravity. An operator picks it up at
the bottom of the tower.
The thickness of the fibre is adjusted to 125 µm, then it is
covered with several layers a of flexible polymer coating,
before it is being spooled on a drum at a speed of about 20
m/s.
One can produce today up to 1000 km of optical fibre in one
length, but normal production lengths are 80 to 200 km.
How are optical fibres terminated?
Optical fibres are usually terminated with an optical
connector. The connector mounting is a very precise job
and is usually done at the factory.
We buy so called “pigtails”. This is a 2m long buffered
fibre with the appropriate connector type.
The pigtail is then fusion spliced to the fibre.
The connectors must be very precisely polished to avoid
reflections as much as possible.
Optical connectors are always “male” connectors. They
connect to each other via an adapter.
Coating Cup 2
UV Curing Oven 2
Tractor & Drum
125 µm
Non
colored
fibre.
Coloring of fibre.
coating
cladding
d= 125 µm
Head office Geneva/CH
d= 250 µm
Basic structure of a fibre.
To reduce reflections we can use
Angled Polished Connectors with
end faces having an angle of 8°.
These connectors are only used
with single-mode fibres.
E2000-APC single-mode 9/125 µm
ST multimode 50/125 µm
E2000 adaptor & connector
A fibre has a diameter of 125 µm.
A hair measures 80 µm.
Laser light protection cover
Fibre
Fantasy
c

f
Wavelength versus frequency
The system is based on individual
guide tubes running through
protective ducts. In these guide
tubes small, but ”outside plant
resistant” mini optical cables can
be installed without any splice.
(C = speed of light)
Dense Wavelength Division Multiplexing
The CERN optical access
network is very dense and
can be compared with a
Metropolitan optical fibre
network.
For the LHC surface installations, the shafts and
underground machine areas, we intend to use a new cabling
concept called JETnet. It is based on tube technology and
was developed by the company Draka Comteq NKF. It is a
complete new solution for the laying of optical fibre access
networks with parallel and serial upgradeability. It requires
lower initial cost and the network can grow with demand.
Latest developments in optical transmission.
Optical
Redundant loops
can be realized all
over the network.
At the pictures we see the blowing of a 216 fibre
cable between PA8 and Bld. 513.
core
• Single-mode 9/125 µm (ITU G.652)
ITU = International Telecom Union
•Reflections reduce optical transmission performance
FC-PC single-mode 9/125 µm
d= 50 or 9 µm
At CERN we use mainly 2 fibre types:
•Defects on the endface and poor
polishing quality, as well as air
gaps between the fibres are
responsible for reflections
Today we blow the optical cables into the cable ducts
which lay along the HV cables between the CERN
sites. The laying speed varies from 40 to 100 m/min.
if all goes well. The air compressor must deliver
10m3/min. at a pressure of 10 bar.
In CERN’s optical access network
we use following 3 connectors.
The optical core alignment
must be optimal for low
attenuation.
Optical fibre splice.
Buffered optical fibre Ø 0.9 mm.
• Graded index 50/125 µm (ITU G.651)
Assembling of colored fibres
into a jelly filled loose tube.
9/50/62.5 µm
•Reflections occur on fibre surfaces
at the exit as well as entry
connector endfaces
Blowing of fibre cables is that possible?
Transmission
technology trends
Electrical
Optical
Blowing of guide tubes
with a Superjet.
Remote trouble shooting and monitoring.
Theoretical bandwidth of single-mode optical fibre is extremely high (75 THz) and
instead of installing many fibres, telecom operators prefer investing in DWDM.
DWDM technology is still very expensive but allows today typically 100 wavelengths
@ 10 Gb/s TDM channel rate on a single fibre. This equals 15.625.000 simultaneous
telephone conversations and still even many more wavelengths are possible………
OTDR
OTAU
to other
cables under
test
With so many channels on one single fibre, a network must be protected via redundant
automatically restoring loops and one must avoid single points of failure.
SNMP Agent
Optical Time Domain Reflecto meter
At CERN, with maximum distances not exceeding 15 km, one does not intend to use
DWDM at the moment. It seems more economical to install many fibres.
TDM
Optical Test Access Unit
RTU Remote Test Unit
NTE
The installation however, must have redundant loops for Safety and Reliability.
Cable under test
NTE
Network
terminal
WEB Client
Time Division Multiplexing
single mode Laser
multi mode Laser
wavelength nm
1800
Optical
Optical
fibres in a
LHC
Cryostat
CERN
Radar
range
1600
1400
Dense Wavelength Division Multiplexing
1200
1000
2x1014
800
600
400
200
3x1014
Laser
range
DWDM
1
2
3
Electrical
1st Optical window 850 nm
2nd Optical window 1300 nm
3rd Optical window 1550 nm
Infrared
range
System
Management
CERN intranet
Internet
1x1015
Frequency Hz
Visible
range
5x1014
Ultraviolet
range
A fibre monitoring system has been installed, for the surveillance of all main optical trunks and in the future the
optical network in the LHC tunnel, as the fibres will be subject to radiation damage.
The system has 24 optical ports. Each port can test an optical fibre link with a maximum length of 200 km.
The heart of the system is a powerful optical time domain reflecto meter at =1550 nm.
5th ST Workshop, 28 January 2002 Echenevex France