All-optical switches line up for HD video transport
15 May 2006
As the broadcast industry shifts its emphasis towards high-definition video production, the huge bandwidth requirements for transporting these data-intense signals naturally drives the infrastructure towards fibre.
As the broadcast industry shifts its emphasis towards high-definition video production, the huge bandwidth requirements for transporting these data-intense signals naturally drives the infrastructure towards fibre. With this emerging market firmly in mind, the UK-US optical switch specialist Polatis has released the Trinity family of optical video routing switches.
Currently, the vast majority of audio and video signals are carried over copper and 99.9% of the $800m (€650m) video routing market comprises electrical switches. However, high-definition video formats such as 1080p (the upcoming standard for high-definition TV broadcast signals, with a frame resolution of 1920 × 1080 pixels) can only be transported 50-100 m over copper. There is a clear need for optical transport - and its ability to extend this reach to tens of kilometres.
This shift also leads to a growing market opportunity for optical routing platforms, for applications at live broadcast sites, post-production facilities and mobile production vans. "The Trinity platforms use the same core technology as our other switching products, but we've changed the interfaces and the control plane to match the needs of the broadcast industry," explained Aaron Bent, Polatis' vice-president of marketing and business development.
The core technology in question is Polatis' DirectLight beam steering. In contrast with MEMS-based optical switches, which bounce light off mirrors to route signals, Polatis simply points collimating lenses across free space. Piezoelectric actuators position the input and output collimators and route the beams across the required paths. Eliminating the micromirrors means that there is a very clean optical path, with less than 1 dB of loss across every connection.
Another benefit of this scheme is that the channels are locked into place using position sensing rather than optical feedback, so that the system is able to create and hold a connection with no signal present. "The thing that the broadcast industry likes about this particular switch is the fact that it is always in a ready and waiting state," Bent said. "This simplifies the management architecture a lot - they know that when they send a signal it gets there immediately with no latency."
The alternative way to route optical signals is to use electrical switches with optical interfaces and perform optical-electrical conversion. Bent says that many companies are starting to offer this type of product, but points out that this approach is more costly and can introduce jitter. He notes, however, that there are some trade-offs when using all-optical switches. "One thing you don't have is very fast microsecond switching, so you cannot necessarily provide live content protection," he explained. "That said, the benefits of optical switching are so clear in the broadcast industry."
As an all-optical platform, Trinity supports virtually all protocols and feed rates - a critical capability in the broadcast world, which uses a much larger number of different signal formats than the telecoms industry. "You can take any video or audio format - digital or analogue - and you can put them all through the one box," explained Bent. "That's a very unique selling point to the broadcast industry."
Another broadcast-specific feature is Trinity's support for the popular SMS-7000 control protocol, which allows the platform to work under a single control system alongside other media platforms. "This allows us to drop it into any of today's existing broadcast systems and use it straight away," Bent said.
The Trinity platforms - available in a 1RU frame (up to 16 × 16 crosspoints) or a 3RU frame (up to 32 × 32) - boast some impressive specifications. Besides an optical power loss of below 1 dB, the systems offer signal stability of less than 0.05 dB, channel crosstalk of below -70 dB, return loss of more than 55 dB and zero jitter or signal delay introduced.
Polatis is partnering with broadcast equipment suppliers to offer Trinity as part of a larger system. "We only really provide one piece - albeit a core piece, the optical switch - but you need the rest of the equipment around it as the broadcast companies typically purchase total end-to-end solutions," Bent said. The Trinity platforms are currently being trialled with firms including the "largest broadcast company in the world".
About the author
Tami Freeman is editor, FibreSystems Europe in association with LIGHTWAVE Europe.
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