An easier transition to fiber using SFP modules By Chuck Meyer, Chief Technology Officer - Core Products, Grass Valley, a Belden Brand

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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 in-frastructures 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 elec-trical 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

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.

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.

Cost, space and weight issues

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.

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 ben-efits for production trucks/OB vans, which have to tightly manage space and weight issues.

Format Maximum Copper Cable Length

SD 275 to 350m

HD 100 to 150m

3D Level 75 to 100m

Bundle of 96 COAXMulti Core 96 FIBER

15 mm

75 mm

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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.

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.

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.

Fiber:

• Virtually no speed limits

• 18 video signals per fiber with CWDM multiplexing

Coax:

• 3G

• 1 video signal per cable

Densité card

SFP slot is part of rear module

Dual channel SFP module

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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.

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:

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.

Typical applications

Transmitter

Transmitteroutput

Link loss

Margin

Power

Receiversensitivity

FiberReceiver

Distance from transmitter

Connectors SpliceConnectors loss Splice loss

Production truck Production truck

Truck to truck

Stadium to broadcast station

Belden, Belden Sending All The Right Signals and the Belden logo are trademarks or registered trademarks of Belden Inc. or its affiliated companies in the United States and other jurisdictions. Grass Valley is trademark or registered trademark of Grass Valley. Belden Inc., Grass Valley and other parties may also have trademark rights in other terms used herein.

Copyright © 2014 Grass Valley. All rights reserved. Specifications subject to change without notice.

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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.