Fiber-optic transport
Oct 1, 2008 12:00 PM, By Jim Jachetta
As the demand for the transport of high-resolution video at higher bandwidths increases, the use of fiber in facilities will be more and more prevalent.
I t's been almost 30 years since the first commercial use of fiber-optic cable for the transport of a broadcast television signal. In 1980, broadcasters of the Winter Olympics, in Lake Placid, New York, requested a fiber-optic video transmission system for backup video feeds. Because of its quality and reliability, the fiber-optic feed soon became the primary video feed, making the 1980 Winter Olympics the first use of fiber optics for a live television production in history.
Despite the long history of the use of fiber-optic cable as a means for transporting video and audio signals, it is amazing that resistance still exists. Production studios are often limited in size to support video transmission over traditional copper coax or twisted pair. The control room is designed to be as close as possible to the camera positions. In the short term, this approach reduces some of the system costs, but the strategy can prove to limit the future of a permanent installation. In the past few years, the proliferation of HD-SDI, 3G HD-SDI and DVI formats has exceeded the limits of copper coax and twisted pair.
There are many applications in electronic newsgathering and sports where fiber is unavoidable. Fiber cables for video transport are widely used in these venues. Many broadcasters and systems integrators will use fiber only when absolutely necessary, only to spend more money to upgrade a system later when a new higher-resolution video format arrives.
Benefits
There are many reasons to use fiber. Early adopters of fiber-optic transport are now enjoying increased bandwidths for the new 3Gb/s HD-SDI and DVI dual-link formats. Users are limited to less than 100m over coax for 3Gb/s HD and 10m over copper for DVI dual link. Broadcast facilities are requiring the transport of 1080p 3Gb/s HD, and DVI single- and dual-link are used in just about every control room with a multiviewer or monitoring.
Users who have installed fiber for their SDI and HD-SDI infrastructure are now ready for the transition to 3Gb/s HD. Those who installed fiber for their RGBHV infrastructure can now easily upgrade to DVI.
In addition, fiber offers better signal quality over longer distances and better noise and interference immunity. Single-mode fiber provides virtually infinite bandwidth to future-proof your system. With all its benefits, fiber is affordable. Explosive construction and expansion in Asia has skyrocketed the cost of copper, while the cost of fiber-optic cable and components has steadily decreased.
A misconception is that fiber is expensive to install and maintain. Fiber-optic cable is available preterminated with any connector type. Bulk fiber can be purchased and pulled through conduit. The connectors are then fusion-spliced with preterminated pigtails using inexpensive slicing gear. Field installations and repairs can be achieved using epoxy-less connectors. A technician with basic skills terminating coax with a BNC can terminate an epoxy-less fiber connector.
Fiber-optic cable is available in many configurations for most applications. Cables are available with multiple fibers from one strand to hundreds of strands. Fiber-optic cable is available in configurations that meet all building and installation codes, including plenum-rated fiber for installing fiber cable in a plenum space; riser-rated cable that supports its own weight for vertical runs through walls in tall buildings; and tactical and armor-rated fiber cable, which is available for outdoor and military environments.
There are many applications for fiber-optic communications. Any application that requires high-bandwidth or high bit-rate communications is ideally suited for fiber-optic transport. Television and video applications are perfect examples. Analog television has a relatively high-bandwidth signal of more than 5MHz. Digital television or HDTV has bit rates of more than 3Gb/s. High-resolution DVI computer graphics can have bit rates exceeding 10Gb/s. The following is an examination of fiber's applications.
Broadcast television transmission
Television production and broadcast engineers have always sought out the best technology for media events such as the Olympics. In the 1980s, fiber-optic transport was introduced to the television industry. Today, fiber optics are used in all aspects of production and distribution of video and audio signals.
With the introduction of digital video in the 1990s, fiber-optic transport continued to enjoy growth in the broadcast industry. Digital video was encoded into 144Mb/s to 360Mb/s. These high bit-rate video signals could only travel over copper up to about 300m. A transport distance beyond 300m required fiber.
The transition to HDTV has created a need to transport signals with a bit rate as high as 3Gb/s. HDTV or HD-SDI in its native or uncompressed form is 2.97Gb/s, which can only reach about 100m over coax. Once again, fiber is the only choice to reach distances beyond 100m.
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