An easier transition to fiber using SFP modules
By Chuck Meyer, Chief Technology Officer - Core Products, Grass Valley, a Belden Brand
WHITE PAPER AN EASIER TRANSITION TO FIBER USING SFP MODULES
Many broadcasters are upgrading the video/audio backbone interconnections between their different facilities
such as studios and control rooms to support 3G, and this is creating an increased demand for fiber-based infrastructures to support the higher data rates. Fiber offers many substantial advantages over traditional coax,
including high performance over longer distances, virtually unlimited bandwidth and reduced sensitivity to electrical interference. It also offers greater space and weight efficiency. Fortunately, it has now become much more
affordable and easier to use, especially with the availability of Small Form-factor Pluggable (SFP) fiber modules,
and this has led to it becoming the de-facto standard for 3G signals.
High performance over long distances
Cost, space and weight issues
Optical fiber has virtually unlimited bandwidth compared to copper
coaxial cable (coax), which has an inherent bandwidth limit of
3G. This unlimited bandwidth, in combination with relatively low
attenuation, can produce some rather startling increases in capacity
and range. For instance, with some fiber optic product combinations
it is possible to establish a link length of more than 100 km (60 mi.). In
contrast, a copper cable can only handle 3G for up to 75m (246 ft.),
which represents an enormous performance disparity between fiber
and traditional coax.
Cost is another key advantage of fiber. At the moment, the typical
published price in the US for a single core PVC jacketed single
mode fiber is around $0.23/meter. In contrast, broadcast quality
coax cable, suitable for HD-SDI, costs about $1.75/meter. So,
coax is approximately seven and a half times more expensive than
comparable fiber! Considering how many thousands, if not tens of
thousands, of meters of cabling are typically used in a broadcast
facility, then the savings can be substantial. This advantage is
particularly evident in applications requiring the transmission of
disparate signal types, such as video with audio, or audio with data.
Fiber optic engineers can easily design affordable digital systems that
accommodate a mixing and matching of signal types, such as two
video signals with four channels of audio, all over a single fiber.
The virtually unlimited bandwidth of fiber also means that it can carry
multiple signals, and a wide range of signal formats, in a single cable.
It also allows fiber optic cables to be used bidirectionally, with one
wavelength in the forward direction, and a second wavelength in the
reverse direction.
Format
Maximum Copper Cable Length
SD
275 to 350m
HD
100 to 150m
3D Level
75 to 100m
Fiber optic cables are also significantly lighter, with 2.9 mm single
core fiber weighing about 9 grams/meter, and 1694A coax about 61
grams/meter. So, fiber is over six and a half times lighter than coax.
This greater space efficiency of fiber can be seen by comparing two
typical cable bundles (see below) with equivalent signal capacity:
These significant size and weight advantages of fiber are huge benefits for production trucks/OB vans, which have to tightly manage
space and weight issues.
15 mm
75 mm
Multi Core 96 FIBER
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Bundle of 96 COAX
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WHITE PAPER AN EASIER TRANSITION TO FIBER USING SFP MODULES
Bandwidth advantages of fiber
Simply put, bandwidth costs money, and fiber offers a way to minimize these costs. With single mode fiber, we can easily multiplex multiple
wavelengths of light onto one fiber core, even at very high data rates. For instance, just one 2.9 mm single mode fiber can be used to
communicate up to 18 uncompressed 3G/HD/SD-SDI signals, either within a broadcast facility or cross-town. Naturally, this can lead to
substantial, aggregate savings.
Fiber:
Coax:
• Virtually no speed limits
• 3G
• 18 video signals per fiber with CWDM multiplexing
• 1 video signal per cable
Small Form-factor Pluggable (SFP) fiber
To make it much easier for production facilities and broadcasters to take advantage of the many benefits of fiber, Grass Valley has designed
many of its products around Small Form-factor Pluggable (SFP) fiber modules. These are small, hot-pluggable devices used to provide fiber
connectivity to 3G/HD/SD devices. By using single-mode fiber instead of coaxial cables, these devices can be used over much longer distances
without degrading signal quality.
Densité card
Dual channel
SFP module
SFP slot is part
of rear module
Video SFP cartridges can directly slide into any product offering Video SFP connectivity. These cartridges offer either one or two fiber
connections, available as single Tx or Rx, dual Rx, dual Tx or as a bidirectional Rx/Tx. Efficiency can be increased by transporting two channels
on a single fiber, using WDM Series SFP cartridges. For more demanding applications, up to 18 channels can be multiplexed onto a single fiber
using SFP cartridges from the CWDM family (external CWDM Mux/Demux required), and this minimizes transmission costs related to the use
of metropolitan dark fiber.
A key advantage of this SFP approach is that it simplifies the migration to fiber. Equipment can be purchased with integrated fiber connectivity,
or fiber can be added easily in the field, without any disruption to existing coaxial services. This allows the building of future-proof infrastructures,
while minimizing initial roll-out costs.
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WHITE PAPER AN EASIER TRANSITION TO FIBER USING SFP MODULES
Using CWDM fiber
When there is a requirement to carry multiple and different signals across long distances, either building-to-building or truck-to-truck, the use of
Coarse Wavelength Division Multiplexing (CWDM) is ideal. For instance, Grass Valley’s CWDM mux unit combines up to 18 different-wavelength
signals from different optical fibers into a single optical fiber. Similarly, the CWDM demux unit separates up to 18 different-wavelength signals
coming from a single optical fiber to 18 separate optical fibers. These units are completely agnostic to the signal type, and this allows multiple
different signals, such as AES, MADI, DVB-ASI, 3G/HD/SD-SDI or Ethernet, to travel on the same fiber link.
Typical applications
Production truck
Production truck
Truck to truck
Stadium to broadcast station
Power budget calculation
Calculating the distance an optical signal will travel requires the determination of several key factors, namely: the optical output power, the
optical frequency of the transmitter, and the optical receive sensitivity or optical range of the receiver. It is also important to determine the length
of fiber, and the number of connection points, splice points and passive optical devices such as optical multiplexers and splitters. Here’s a
simple example to illustrate the concept:
Transmitter
Fiber
Receiver
Transmitter
output
Link loss
Power
Margin
Receiver
sensitivity
Distance from transmitter
Connectors
Connectors loss
Splice
Splice loss
Power budget = output power of 0 dBm – (Rx Sensitivity of -28 dBm) – Safety Margin of 3 dB = 25 dB.
Four connectors and one splice (at 0.5 dB each) consume 2.5 dB, leaving 22.5 dB available for fiber loss.
Distance when fiber loss is 0.4 dB/km = 22.5 dB / 0.4 dB/km = 56.25 km.
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WHITE PAPER AN EASIER TRANSITION TO FIBER USING SFP MODULES
Conclusion
In summation, it’s clear that there are multiple advantages to using fiber for signal distribution:
• Fiber cable costs less
• Fiber cable is physically smaller
• Fiber cable weighs less
• A single fiber can carry 18 full 3G signals, compared to only one for copper coax
• A fiber signal path can be 500 to 1000 times longer than a copper coax signal path
With the availability of SFP modules, the deployment of fiber is now a much simpler proposition, from a system design, installation and
maintenance perspective. Therefore, it’s highly likely that the uses of fiber optics are going to grow in all broadcast facilities, as well as at pay
TV operator networks. Simply put, fiber optics are here to stay.
GVB-1-0250A-EN-WP
WWW.GRASSVALLEY.COM
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