Fiber connectivity
GEP100 - HEP100
Fiber
optic
connections:
an alternative
to coaxial
3Gb/s,
HD,
SD embedded
domain Dolby
E tocables
PCM
decoder with audio shuffler
A
A
®
® product
application
note
Quad speed
Upgradable to
3Gb/s
Embedded
Metadata
S2020
COPYRIGHT©2011 AXON DIGITAL DESIGN B.V.
ALL RIGHTS RESERVED
NO PART OF THIS DOCUMENT MAY BE REPRODUCED IN ANY FORM WITHOUT THE PERMISSION OF
AXON DIGITAL DESIGN B.V.
EMBEDDED
FIBER
CONNECTIVITY
AUDIO PROCESSING
Introduction
Traditionally video connection between devices has
been accomplished with co-axial cables and locking
connectors, most commonly BNC and more recently
the higher density DIN 1.0/2.3. These connectors,
together with smaller outside diameter co-axial
cables have allowed greater connector density to
be achieved on broadcast equipment.
Video cables are manufactured by several companies
in a variety of different sizes and constructed from
a range of materials however they can be broadly
grouped in three size ranges: miniature (less than
3.5mm OD), standard (between 4 and 4.75 mm
OD) and low-loss (OD greater than 5mm).
The table below gives typical distances over which
SD and HD signal can be successfully carried, cables
of different manufacturer may perform differently
and this table only gives general figures and is not
specific to any make or type of cable.
Typical co-axial cable usable distances (m)
Data Rate (Mb/s)
270 (SD)
540
1500 (HD)
3000 (3G)
35-50
20-30
Cable OD (mm)
<3.5 (used for short runs in OB
vehicles and within racks)
80-130
4 - 4.75 (“standard” cables
used in general installations)
240-260
170-190
80-110
50-90
5 – 10 (considered to be low loss
and used over longer distance)
330-435
240-305
90-155
65-130
Whilst the majority of video signals being carried
were standard definition (SD) coaxial technology
easily supported the distances normally found
between broadcast equipment machine rooms and
edit suites, studio floors and control rooms.
As the table shows, the distance a 3G or HDSDI signal can be carried on co-axial cable is
considerable shorter than for SDI.
Within a machine room or OB vehicle these
distances would not preclude the use of co-axial
cable however the distance from a Studio Wallbox,
Control Room or Edit Suite to the equipment room
may be beyond the capabilities of traditional cable.
Therefore a different transportation technology
needs to be considered when distances exceed
approximately 100m for HD-SDI and 80m for 3G.
An obvious solution would be to use fiber-optics
which can carry signals over many kilometers and
has successful used in the IT and telecommunications
industries for many years.
Fiber-Optic Technologies
Fiber-optics is a method of carrying information
from one point to another over relativity long
distances.
An optical fiber is a thin strand of glass or plastic
that carries light and it is the light that carries the
information encoded onto the light by changing the
intensity of the source of the light.
Optical fibers are made up of a Core, the inner
light-carrying medium, the Cladding which has a
different refractive index that allows total internal
reflection of light in the Core.
Light entering the fiber and striking the core/
cladding boundary at greater than the critical angle
reflects back into the core and continues to travel
along the length of the fiber zigzagging from side
to side.
Jacket
Strengthening
Coating
Cladding
Core
Light
Source
The Cladding is surrounded by the Coating,
Strengthening material and an outer Jacket
providing strength and protection to the cable.
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AUDIO PROCESSING
The size of the core and cladding of a fiber optic is
very small, smaller than the width of a human hair.
The diagrams below show the core and cladding
dimensions for three common fiber sizes, fibre
sizes are normally expressed by giving the core
size followed by the claddding size, thus 62.5/125
means a core size of 62.5µm with a cladding size
of 125µm.
9mm
125mm
125mm 62.5mm
125mm 50mm
There are basically two modes in which a fiber can
operate, if the size of the Core is large compared
to the wavelength of the light travelling along it the
light can take more than one path and is said to
be multi-modal (MMF). However as the wavelength
increases fewer and fewer different modes are
possible along the fiber, until at point is reached
when the wavelength appraches the Core diameter
and only one mode is possible. At this point the
fiber becomes single-mode (SMF).
Light
Source
Light
Source
Multi-mode Fiber (MMF) (Step-Index)
Multi-mode fibers and in particular the transmitting
and receiving devices used with them tend to be
available at a lower price than those for single
mode, however single mode fibre can carry higher
data rates for considerably longer distances than
multi-mode fiber.
Multi-mode fiber can typically carry 10Gb over
distances of between than 300m and 600m, single
mode can carry similar data-rates over in excess of
30Km. Single mode fiber can carry more than one
wavelength of light, often 16 or more, similtaniously
allowing much greater data carrying capacity.
Multi-mode fiber does not provide significant
advantages to the broadcaster in terms of the
ability to carry video signals over longer distances
than using larger diameter co-axial cable, therefore
most broadcast equipment manufacturers have,
typically, adopted single mode fiber as a method of
sending digital video over long distances.
Single Mode fiber is also commonly used to carry
other broadcast related digital signals such as
MPEG Transport Streams or digital control signals.
In multi-mode systems only a single wavelength
Single-mode Fiber (SMF)
of light is used, normally 850nm, whereas in
single-mode fiber cables, which can carry mulitple
wavelengths, 1310nm is the normal single
wavelength, but this can be joined by fifteen, or
more, other wavelengths between 1270nm and
1610nm in course-wave division multiplex (CWDM)
systems, and even more if dense-wave division
multiplexing (DWDM) is used.
It should be noted that all of these wavelengths
are in the Infra-Red (IR) part of the spectrum and
therefore are invisible to the human eye. Care
should be taken when handling active fiber-optic
equipment not to look directly into the transmitter
or at the end of a fiber cable as both could be
emitting high levels of IR energy which could cause
permanent eye damage.
Normally multi-mode fiber (MMF) is used with MMF
transmitters and receivers and single-mode fiber
(SMF) with single mode transmitters and receivers.
However because SMF transmitters and receivers
are design to work with a narrow fiber core they
may be used with MMF,having a wider core, over
short distances if SMF is unavailable.
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AUDIO PROCESSING
Fiber optics in broadcast equipment
Manufacturers have adopted the use of fiberoptic cable as a method of carrying video signals,
particularly HD, over long distances. Initially this
was achieved by the use of stand-alone transmitter
and receiver units which accepted a SDI signal from
co-axial cable, modulated it on to a light source and
sent it along a fiber cable. It was then converted
back to SDI and presented on a BNC connector at
the destination.
Often these converters were combined into modules
which could be accommodated along with other
products in a common enclosure.
Example 1 shows how Axon has packaged 8 fiberoptic to coaxial converters onto a Synapse module,
18 of these, housed in a 4RU frame, provide 144
copper/fiber interfaces in a very small space.
Example 1: Axon BFR80 8 Channel 3Gb/s fiber receiver rear module and 18 mounted in a SFR18R
frame providing 144 circuits in 4RU.
This method has the advantage that any broadcast
equipment can be connected to the fibers and all
the fiber connectivity is localized into one place.
However it does require additional hardware to be
purchased, consumes additional power and takes
up rack space.
An alternative space- and power-saving method
is to replace the coaxial connectors with fiber
transceivers directly on the processing modules or
video routers.
Axon produce a wide range of modules which
process digital video (frame synchonization, up-,
down-, cross-conversion, aspect ratio converters,
audio embedders and de-emebbders etc.), any of
these modules can utilize fiber-optic connectivity
simply by the choice of rear connector unit without
and modification being required to the actual
processing module.
Example 2 shows a Synapse rear module with a BNC
connector substituted by a copper/fiber interface
with a FC/PC fiber connector.
Manufacturers can also make use of the ability
of single-mode fiber to transport more than one
wavelength by providing devices which can mix
light from different sources, each having a different
wavelength, on to a single fiber allowing up to 16
x 3Gb HD video signals to be sent together on a
single optical line.
Fiber-optic cable can be packaged in multi-core
jackets, a 24-core cable has an overall diameter
of less than 9mm, if this were deployed so that
each fiber was carrying 16 HD signals the overall
multi-core cable would be capable of carrying 384
uncompressed video signals over distances in
excess of 30Km in a cable package similar in width
to a human finger.
Example 3 shows an Axon module designed to mix
together 8 wavelengths onto a single fiber, when
used in combination with another similar unit 16
different video signals can be sent over a single
fiber-optic cable.
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AUDIO PROCESSING
Example 2: Axon BPH01T-FC/PC rear connector
module showing electrical to optic transceiver.
Example 3: Axon BFM88 optical multiplexer.
A passive combiner or splitter for up to 8
wavelengths. Adding a BFM89 provides combining
or splitting of another 8 wavelengths.
Coaxial to fiber
converter
Fiber connector
Fiber optic cable in broadcast centers
The obvious answer to the distance limitations of
coaxial cable is to employ fiber optic technologies
which can carry video signals for many 10s of Km.
However there is a misconception that fiber-optics
are difficult to deploy in a broadcast environment
without specialist knowledge.
to connect the broadcast equipment to a local fiber
patch panel, normally in the same equipment rack,
and multi-core cable which runs from patch panel
to patch panel possibly over many Kilometers.
Fiber-optic cable is more susceptible to damage
than coaxial if poorly handled, it may need some
additional protection if installed under flooring
along with other cables and fiber termination is
more complex than coaxial, but broadcasters
should not be deterred by this.
Although fiber cables can be run along-side coaxial
cable under a raised floor it is normal practice to
separate the fiber cables by installing the fiber cables
in a dedicated containment or fiber basket. Because
of optical fiber’s insusceptibility to electrical noise
it is common to find fiber cables running adjacent
to electrical power feeds in basket or cable tray
installed above the equipment racks.
Fiber optic cables are generally robust and the
methods of termination are well understood.
Termination of the multi-core cables often causes
most concern when using fiber-optics.
The use of fiber optic cable does offer other
advantages in additional too increased signal
distances such as insusceptibility to electrical noise
and small cable size.
The fitting of connectors to the ends of fiber-optic
cables is a precise operation which needs careful
attention to detail to ensure the best possible
optical coupling between the connector and the
fiber and also between the patch-cable and the
inter-panel multi-core cable. Failure to achieve this
will result in a high loss of light at the junction and
subsequent poor signal carriage over the fiber link.
As signal technologies develop coaxial cable may
no longer be a suitable transmission medium,
however fiber-optic systems would simply require
exchanging the transmitting and receiving elements
to change between signal types and increased data
rates and thereby offer a future proofed installed
infrastructure.
Installing Fiber-Optic Cables
On the next page there are examples of preterminated patch-cables, an un-terminated multicore cable and a 19” rack-mount fiber patch panel
into which the multi-core cable could be terminated.
Fiber-optic installations routinely use two different
cable types; pre-made, usually 2-core, patch cables
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FIBER
CONNECTIVITY
AUDIO PROCESSING
Example 4: 2 Core Patch Cable with FC/PC
connectors fitted
Example 5: 8 Core Multi-core cable with the outer
jacket stripped back showing the un-terminated
cores and strengthening material.
Example 6: 1RU 24-way FC/PC fiber patch panel
There are three common methods of installing
connections on multi-core fiber cable, Fusion
Splicing, Mechanical Splicing and utilizing premade cables.
practice moderately skilled installation technicians
should be capable of successfully terminating fiberoptic cables. The use of pre-made cable removes
the requirement to terminate cables on site.
Both splicing methods are used in broadcast
environments and with suitable training and
The table below shows the advantages and disadvantages of each method.
Jointing method
Fusion splice
Pre-made ends, called pig-tails,
which consist of the connector and
1m of fiber already attached, are
joined to the multi-core fiber cable
using a laser fusion splicer which
welds the two fibers together.
Mechanical splice
The multi-core cable is carefully
cut (cleaved), inserted into the
connector, part of the jacket material
is crimped to the connector and the
fiber is held in place with epoxy glue.
Pre-made cables
Pre-made, multi-core cable can be
purchased; these are cut to length
and supplied with customer specified
connectors already in place.
Advantages
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Disadvantages
Very accurate alignment of fiber
to achieve low light loss.
Pre-fitting of connectors onto
short lengths of fiber can be
undertaken in ideal conditions.
Potential
of
easy
termination.
Requires simple tooling
field
No
connector
termination
required.
All cables supplied pre-tested
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High
cost
of
termination
equipment.
Long run of un-jacketed fiber
most be accommodated in the
patch panel.
Higher light loss than fusion
splicing.
Termination requires practice
to be efficient in terms of time
required and reliability.
Increased cost.
Cable length cannot be changed
by the customer.
Connections can be become
damaged if the cable is poorly
handled.
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FIBER
CONNECTIVITY
AUDIO PROCESSING
Because of the small size of the Core fiber-optic
cable is susceptible to dust on the connector surface.
Connectors are always supplied with dust caps and
these should be kept in place until the connector is
to be mated with another. Once the cap is removed
the connectors should be inspected for dust, if dust
is found a lint-free wipe or swab should be used to
gently clean the connectors mating surface, care
should be taken not to scratch the end of the fiber.
Fiber Optic Usage in Synapse Modules
All Synapse modules are formed of two elements,
the plug-in processing card and a rear-mounted
I/O panel. The choice of plug-in module determines
the nature of the signal processing, whereas the
selection of the rear panel defines how the signal
will be physically presented.
Within the range there is a wide selection of rear
panels which provide the option for every module
that has serial digital video connections to exploit
fiber-optic connectivity, this also extends to some
AES audio distribution modules.
For modules that are already in operation the
process to change a rear panel from one with
all coaxial connectors to a unit providing fiber
connections is as simple as temporarily removing
the module, unscrewing the existing rear panel and
replacing it with a new unit with fiber I/O. There is
no re-configuration of the module necessary and
fiber rear panels are the same size as coaxial units
which always allow them to fit in the space of the
existing unit.
The rear panels can be specified with either screw-
locking FC/PC fiber connectors or latching SC
connectors.
It has been common practice for IT equipment
manufactures to supply their products with a
standard interface port allowing users to select the
type of fiber connector and optical wavelength they
require. This, widely adopted, interface is called a
Small Format-Factor Plug-in (SFP) and is steadily
gaining acceptance within the broadcast field.
The Synapse fiber to optical modules (GFR80 and
GFT80) already use this interface allowing users to
select optical wavelengths other than the standard
1310nm, necessary when the signals are to be
multiplex together on a single fiber.
SFPs are also available with coaxial SDI connections
which mean that future products may allow the
user to change from coaxial to fiber connections
by simply swapping a small interface module. The
Synapse SynCross modular router system already
utilizes this design on its rear panels (BPH25 and
BPH 26).
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