Fiber connectivity GEP100 - HEP100 Fiber optic connections: an alternative to coaxial 3Gb/s, HD, SD embedded domain Dolby E tocables PCM decoder with audio shuffler A A product application note Quad speed Upgradable to 3Gb/s Embedded Metadata S2020 COPYRIGHT 2011 AXON DIGITAL DESIGN B.V. ALL RIGHTS RESERVED NO PART OF THIS DOCUMENT MAY BE REPRODUCED IN ANY FORM WITHOUT THE PERMISSION OF AXON DIGITAL DESIGN B.V.
Introduction Traditionally video connection between devices has been accomplished with co-axial cables and locking connectors, most commonly BNC and more recently the higher density DIN 1.0/2.3. These connectors, together with smaller outside diameter co-axial cables have allowed greater connector density to be achieved on broadcast equipment. Video cables are manufactured by several companies in a variety of different sizes and constructed from a range of materials however they can be broadly grouped in three size ranges: miniature (less than 3.5mm OD), standard (between 4 and 4.75 mm OD) and low-loss (OD greater than 5mm). The table below gives typical distances over which SD and HD signal can be successfully carried, cables of different manufacturer may perform differently and this table only gives general figures and is not specific to any make or type of cable. Typical co-axial cable usable distances (m) Data Rate (Mb/s) 270 (SD) 540 1500 (HD) 3000 (3G) 35-50 20-30 Cable OD (mm) <3.5 (used for short runs in OB vehicles and within racks) 80-130 4-4.75 ( standard cables used in general installations) 240-260 170-190 80-110 50-90 5 10 (considered to be low loss and used over longer distance) 330-435 240-305 90-155 65-130 Whilst the majority of video signals being carried were standard definition (SD) coaxial technology easily supported the distances normally found between broadcast equipment machine rooms and edit suites, studio floors and control rooms. As the table shows, the distance a 3G or HDSDI signal can be carried on co-axial cable is considerable shorter than for SDI. Within a machine room or OB vehicle these distances would not preclude the use of co-axial cable however the distance from a Studio Wallbox, Control Room or Edit Suite to the equipment room may be beyond the capabilities of traditional cable. Therefore a different transportation technology needs to be considered when distances exceed approximately 100m for HD-SDI and 80m for 3G. An obvious solution would be to use fiber-optics which can carry signals over many kilometers and has successful used in the IT and telecommunications industries for many years. Fiber-Optic Technologies Fiber-optics is a method of carrying information from one point to another over relativity long distances. An optical fiber is a thin strand of glass or plastic that carries light and it is the light that carries the information encoded onto the light by changing the intensity of the source of the light. Optical fibers are made up of a Core, the inner light-carrying medium, the Cladding which has a different refractive index that allows total internal reflection of light in the Core. Light entering the fiber and striking the core/ cladding boundary at greater than the critical angle reflects back into the core and continues to travel along the length of the fiber zigzagging from side to side. Jacket Strengthening Coating Cladding Core Light Source The Cladding is surrounded by the Coating, Strengthening material and an outer Jacket providing strength and protection to the cable. page 2
The size of the core and cladding of a fiber optic is very small, smaller than the width of a human hair. The diagrams below show the core and cladding dimensions for three common fiber sizes, fibre sizes are normally expressed by giving the core size followed by the claddding size, thus 62.5/125 means a core size of 62.5µm with a cladding size of 125µm. 9mm 125mm 125mm 62.5mm 125mm 50mm There are basically two modes in which a fiber can operate, if the size of the Core is large compared to the wavelength of the light travelling along it the light can take more than one path and is said to be multi-modal (MMF). However as the wavelength increases fewer and fewer different modes are possible along the fiber, until at point is reached when the wavelength appraches the Core diameter and only one mode is possible. At this point the fiber becomes single-mode (SMF). Light Source Light Source Multi-mode Fiber (MMF) (Step-Index) Multi-mode fibers and in particular the transmitting and receiving devices used with them tend to be available at a lower price than those for single mode, however single mode fibre can carry higher data rates for considerably longer distances than multi-mode fiber. Multi-mode fiber can typically carry 10Gb over distances of between than 300m and 600m, single mode can carry similar data-rates over in excess of 30Km. Single mode fiber can carry more than one wavelength of light, often 16 or more, similtaniously allowing much greater data carrying capacity. Multi-mode fiber does not provide significant advantages to the broadcaster in terms of the ability to carry video signals over longer distances than using larger diameter co-axial cable, therefore most broadcast equipment manufacturers have, typically, adopted single mode fiber as a method of sending digital video over long distances. Single Mode fiber is also commonly used to carry other broadcast related digital signals such as MPEG Transport Streams or digital control signals. In multi-mode systems only a single wavelength Single-mode Fiber (SMF) of light is used, normally 850nm, whereas in single-mode fiber cables, which can carry mulitple wavelengths, 1310nm is the normal single wavelength, but this can be joined by fifteen, or more, other wavelengths between 1270nm and 1610nm in course-wave division multiplex (CWDM) systems, and even more if dense-wave division multiplexing (DWDM) is used. It should be noted that all of these wavelengths are in the Infra-Red (IR) part of the spectrum and therefore are invisible to the human eye. Care should be taken when handling active fiber-optic equipment not to look directly into the transmitter or at the end of a fiber cable as both could be emitting high levels of IR energy which could cause permanent eye damage. Normally multi-mode fiber (MMF) is used with MMF transmitters and receivers and single-mode fiber (SMF) with single mode transmitters and receivers. However because SMF transmitters and receivers are design to work with a narrow fiber core they may be used with MMF,having a wider core, over short distances if SMF is unavailable. page 3
Fiber optics in broadcast equipment Manufacturers have adopted the use of fiberoptic cable as a method of carrying video signals, particularly HD, over long distances. Initially this was achieved by the use of stand-alone transmitter and receiver units which accepted a SDI signal from co-axial cable, modulated it on to a light source and sent it along a fiber cable. It was then converted back to SDI and presented on a BNC connector at the destination. Often these converters were combined into modules which could be accommodated along with other products in a common enclosure. Example 1 shows how Axon has packaged 8 fiberoptic to coaxial converters onto a Synapse module, 18 of these, housed in a 4RU frame, provide 144 copper/fiber interfaces in a very small space. Example 1: Axon BFR80 8 Channel 3Gb/s fiber receiver rear module and 18 mounted in a SFR18R frame providing 144 circuits in 4RU. This method has the advantage that any broadcast equipment can be connected to the fibers and all the fiber connectivity is localized into one place. However it does require additional hardware to be purchased, consumes additional power and takes up rack space. An alternative space- and power-saving method is to replace the coaxial connectors with fiber transceivers directly on the processing modules or video routers. Axon produce a wide range of modules which process digital video (frame synchonization, up-, down-, cross-conversion, aspect ratio converters, audio embedders and de-emebbders etc.), any of these modules can utilize fiber-optic connectivity simply by the choice of rear connector unit without and modification being required to the actual processing module. Example 2 shows a Synapse rear module with a BNC connector substituted by a copper/fiber interface with a FC/PC fiber connector. Manufacturers can also make use of the ability of single-mode fiber to transport more than one wavelength by providing devices which can mix light from different sources, each having a different wavelength, on to a single fiber allowing up to 16 x 3Gb HD video signals to be sent together on a single optical line. Fiber-optic cable can be packaged in multi-core jackets, a 24-core cable has an overall diameter of less than 9mm, if this were deployed so that each fiber was carrying 16 HD signals the overall multi-core cable would be capable of carrying 384 uncompressed video signals over distances in excess of 30Km in a cable package similar in width to a human finger. Example 3 shows an Axon module designed to mix together 8 wavelengths onto a single fiber, when used in combination with another similar unit 16 different video signals can be sent over a single fiber-optic cable. page 4
Example 2: Axon BPH01T-FC/PC rear connector module showing electrical to optic transceiver. Example 3: Axon BFM88 optical multiplexer. A passive combiner or splitter for up to 8 wavelengths. Adding a BFM89 provides combining or splitting of another 8 wavelengths. Coaxial to fiber converter Fiber connector Fiber optic cable in broadcast centers The obvious answer to the distance limitations of coaxial cable is to employ fiber optic technologies which can carry video signals for many 10s of Km. However there is a misconception that fiber-optics are difficult to deploy in a broadcast environment without specialist knowledge. to connect the broadcast equipment to a local fiber patch panel, normally in the same equipment rack, and multi-core cable which runs from patch panel to patch panel possibly over many Kilometers. Fiber-optic cable is more susceptible to damage than coaxial if poorly handled, it may need some additional protection if installed under flooring along with other cables and fiber termination is more complex than coaxial, but broadcasters should not be deterred by this. Although fiber cables can be run along-side coaxial cable under a raised floor it is normal practice to separate the fiber cables by installing the fiber cables in a dedicated containment or fiber basket. Because of optical fiber s insusceptibility to electrical noise it is common to find fiber cables running adjacent to electrical power feeds in basket or cable tray installed above the equipment racks. Fiber optic cables are generally robust and the methods of termination are well understood. Termination of the multi-core cables often causes most concern when using fiber-optics. The use of fiber optic cable does offer other advantages in additional too increased signal distances such as insusceptibility to electrical noise and small cable size. The fitting of connectors to the ends of fiber-optic cables is a precise operation which needs careful attention to detail to ensure the best possible optical coupling between the connector and the fiber and also between the patch-cable and the inter-panel multi-core cable. Failure to achieve this will result in a high loss of light at the junction and subsequent poor signal carriage over the fiber link. As signal technologies develop coaxial cable may no longer be a suitable transmission medium, however fiber-optic systems would simply require exchanging the transmitting and receiving elements to change between signal types and increased data rates and thereby offer a future proofed installed infrastructure. Installing Fiber-Optic Cables On the next page there are examples of preterminated patch-cables, an un-terminated multicore cable and a 19 rack-mount fiber patch panel into which the multi-core cable could be terminated. Fiber-optic installations routinely use two different cable types; pre-made, usually 2-core, patch cables page 5
Example 4: 2 Core Patch Cable with FC/PC connectors fitted Example 5: 8 Core Multi-core cable with the outer jacket stripped back showing the un-terminated cores and strengthening material. Example 6: 1RU 24-way FC/PC fiber patch panel There are three common methods of installing connections on multi-core fiber cable, Fusion Splicing, Mechanical Splicing and utilizing premade cables. practice moderately skilled installation technicians should be capable of successfully terminating fiberoptic cables. The use of pre-made cable removes the requirement to terminate cables on site. Both splicing methods are used in broadcast environments and with suitable training and The table below shows the advantages and disadvantages of each method. Jointing method Fusion splice Pre-made ends, called pig-tails, which consist of the connector and 1m of fiber already attached, are joined to the multi-core fiber cable using a laser fusion splicer which welds the two fibers together. Mechanical splice The multi-core cable is carefully cut (cleaved), inserted into the connector, part of the jacket material is crimped to the connector and the fiber is held in place with epoxy glue. Pre-made cables Pre-made, multi-core cable can be purchased; these are cut to length and supplied with customer specified connectors already in place. Advantages Disadvantages Very accurate alignment of fiber to achieve low light loss. Pre-fitting of connectors onto short lengths of fiber can be undertaken in ideal conditions. Potential of easy termination. Requires simple tooling field No connector termination required. All cables supplied pre-tested High cost of termination equipment. Long run of un-jacketed fiber most be accommodated in the patch panel. Higher light loss than fusion splicing. Termination requires practice to be efficient in terms of time required and reliability. Increased cost. Cable length cannot be changed by the customer. Connections can be become damaged if the cable is poorly handled. page 6
Because of the small size of the Core fiber-optic cable is susceptible to dust on the connector surface. Connectors are always supplied with dust caps and these should be kept in place until the connector is to be mated with another. Once the cap is removed the connectors should be inspected for dust, if dust is found a lint-free wipe or swab should be used to gently clean the connectors mating surface, care should be taken not to scratch the end of the fiber. Fiber Optic Usage in Synapse Modules All Synapse modules are formed of two elements, the plug-in processing card and a rear-mounted I/O panel. The choice of plug-in module determines the nature of the signal processing, whereas the selection of the rear panel defines how the signal will be physically presented. Within the range there is a wide selection of rear panels which provide the option for every module that has serial digital video connections to exploit fiber-optic connectivity, this also extends to some AES audio distribution modules. For modules that are already in operation the process to change a rear panel from one with all coaxial connectors to a unit providing fiber connections is as simple as temporarily removing the module, unscrewing the existing rear panel and replacing it with a new unit with fiber I/O. There is no re-configuration of the module necessary and fiber rear panels are the same size as coaxial units which always allow them to fit in the space of the existing unit. The rear panels can be specified with either screw- locking FC/PC fiber connectors or latching SC connectors. It has been common practice for IT equipment manufactures to supply their products with a standard interface port allowing users to select the type of fiber connector and optical wavelength they require. This, widely adopted, interface is called a Small Format-Factor Plug-in (SFP) and is steadily gaining acceptance within the broadcast field. The Synapse fiber to optical modules (GFR80 and GFT80) already use this interface allowing users to select optical wavelengths other than the standard 1310nm, necessary when the signals are to be multiplex together on a single fiber. SFPs are also available with coaxial SDI connections which mean that future products may allow the user to change from coaxial to fiber connections by simply swapping a small interface module. The Synapse SynCross modular router system already utilizes this design on its rear panels (BPH25 and BPH 26). page 7