Television and video look to planar-lightwave circuitry

photonic switches using PLC ­technology are likely to be a main force in the delivery of high-quality video traffic in the future.

Oct 1st, 2004
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The television/video industry has always had a need for transporting large volumes of video traffic, and video transport has been satisfied, so far, by using copper (coaxial) cables. Now the industry is migrating to higher-quality imaging (such as HDTV or high-­definition television) that requires higher data rates and higher bandwidth, and copper is no longer up to the task. Transport of this increased traffic requires the use of fiber links, especially in cases where those links span distances exceeding 100 m (about 330 ft). High-bandwidth video is transported over long distances for a variety of ­reasons, including camera feeds into a broadcast van (at golf tournaments, car races, and marathons, for instance, where multiple cameras are spread out over considerable distances), transport from remote events to television studios, and video transport in a studio campus environment.

To meet these demands an industry transition to fiber links instead of copper cable is practically inevitable, because the fiber links can transport noncompressed HDTV signals at 1.5‑Gbit/s, or even digital cinema at 10‑Gbit/s, along with voice and data traffic. Studios and networks are likely to use all-optical (or photonic) systems such as optical routing switchers in conjunction with the new transport links. These systems eliminate the need for conversion from electrical signals to optical, and vice versa, thereby simplifying the network. Advantages of this simplified architecture include cost reduction, lower power consumption, reduced space requirements, and improved reliability.

photonic switches using PLC ­technology are likely to be a main force in the delivery of high-quality video traffic in the future.
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To further increase the bandwidth of a fiber link, many networks migrate to wavelength-division-­multiplexing (WDM) ­technology, in which multiple high-speed channels are carried over a single fiber strand. Transport of WDM links through electronic systems requires a large increase of line cards (one per each channel), while photonic systems can handle multiple channels without the need for additional equipment. Transparency to channel count offers a huge cost benefit.

Transparency to traffic rates and formats inherent in all photonic systems, makes them future-proof and reduces operational expenditures. Migration to new standards, often requiring forklift overhaul when electrical systems are used, is done smoothly and with no added cost once optical ­systems are deployed.

No discussion of the television industry’s migration to fiber can ignore the issue of multicasting-the simultaneous routing of video traffic to multiple points, such as recorders and transmitters. While this requirement is easily met when electronic switchers are used, most optical switching technologies do not support this function. To overcome this shortcoming, optical switchers utilize fixed optical splitters but fall short of the flexibility offered by electronic switches. This drawback, however, has been overcome by an advanced, new breed of photonic switches, based on planar-lightwave-circuit (PLC) technology, which can support multicasting on the chip, over many miles and without loss of signal quality. Advanced PLC systems offer weighted multicasting, allowing optical signals to be directed to any number of targets and at any desired power ratio. Systems can be programmed for any weighted multicast configuration to tune the shared signal according to distances being traveled and can be modified dynamically to meet changing needs.

Planar lightwave technology, often referred to as integrated optics, is a solid-state technology and has been validated in such widely deployed optical components as AWGs (arrayed waveguide gratings) and optical switches. As solid-state systems, PLC-based switches have no moving parts and are therefore ultra-reliable. Their high reliability makes them particularly suitable for protecting video links. When carrying high-visibility video traffic, it is very important that the network is highly reliable and highly available, and PLC-based switches provide the most comprehensive and effective way to protect these links.

Photonic switches using PLC technology are likely to be a main force in the delivery of high-quality video traffic in the networks of the future, enabling every video format, at any speed, to be economically transmitted, configured, reconfigured, switched, protected and monitored.

ABE QUELLER is vice president of applications engineering at Lynx Photonic Networks, Calabasas Hills, CA 91301; e-mail

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