fibre in a 3D world special report
using different wavelengths (or colours) of light. Using this coarse wavelength division multiplexing (CWDM) process, a single lightweight fibre optic cable can carry more high- bandwidth signals over a longer distance than thick bundles of copper cables weighing many times as much.
Cable considerations
Practically all fibre optic systems for broadcast applications will use one of two types of cable: tactical (or ‘mil- spec’) fibre optic cable, or the more specialised SMPTE hybrid cable. Tactical fibre optic cables are designed for repeated deployment and retrieval under harsh environmental conditions. The cables are non-metallic, crush resistant, reinforced with aramid (Kevlar) strength fibres, and covered with a tough polyurethane jacket. Since they have no copper in them, cameras cannot be powered from a remote location using tactical cable, and must be powered locally via batteries or some other local power supply. SMPTE hybrid cable is a specialised cable defined by the SMPTE (Society of Motion Picture and Television Engineers) 311M standard. It is designed specifically for direct
connection between HD/SDI video cameras or 3D rigs and the camera control unit (CCU). SMPTE cable comprises two single-mode optical fibres along with four copper conductors, a steel strength member, and shielding. The optical fibres carry the analogue and digital video, audio and data signals, while the copper conductors are used for powering the camera. The optical properties of the cable are the same as a two-strand (duplex) single-mode cable. However, SMPTE fibre is bulkier and significantly heavier than tactical fibre, and it is less robust.
For most of its 3D acquisition, 3ality Digital currently relies on TAC-6 (a single tactical cable carrying six individual fibre strands). “One disadvantage of TAC-6 is that it’s not part of the fibre infrastructures at a lot of venues so we have to bring it with us,” said Postley. “Also, as we do more live sports events we have an increased need to supply power to the camera via the cable - something tactical fibre isn’t designed for. Therefore, we’re relying more and more on transceivers and multiplexers that can multiplex more signals onto fewer strands of fibre, and that work with SMPTE cable.”
Tom Kinyon and Steve Boyce from Panavision: “We tried to work with copper coax on a couple of 3D jobs, and we kept ending up with a big, unwieldy mess of
cables...There had to be a better way, and fibre was it.”
The fibre factor in 3D productions
In many ways, the challenges of 3D production are similar to those of high-end HD broadcasting - the difference, of course, being the requirement to deliver a stereoscopic camera feed, which is twice the bandwidth of a single HD camera. This is because a 3D camera is essentially a custom rig with two full HD cameras mounted on it, one for each ‘eye’ of the stereographic signal. This poses unique challenges for live event production. The latest generation of compact, high-quality HD cameras
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