Special
VPX/OpenVPX on the front lines
VITA 66 expands VPX with fiber-optic connectivity By Gregory Powers
As rugged embedded computing systems strive for higher operating speeds and densities, adding fiber-optic connectivity to the proliferating VITA 46 (VPX) market space brings benefits in higher bandwidth, longer transmission distances, and lower weight. VITA 66 defines fiber-optic connector modules for VPX using well-established and proven optical termini. Each style of termini offers different benefits in terms of density, ruggedness, repairability, and other characteristics.
The thirst for higher bandwidth and faster processing speeds in military and aero - space applications seems unquenchable. VITA 46 (VPX), with a backplane con - nector system supporting 6.25 Gbps in a switched-fabric architecture, is the latest generation of VMEbus and offers new lev- els of performance for embedded computer systems. VPX systems are designed for the flexible application of demanding high- speed protocols – such as 10 GbE Rapi - dIO, InfiniBand, and HyperTransport – in ground, aerospace, and marine applications. While the basic architec - ture of VPX is defined in VITA 46 and 65 (OpenVPX), ongoing efforts by the VITA Standards Organization (VSO) to enhance VPX capabilities include VITA 66 – “Optical Interconnect on VPX” – which adds fiber-optic interfaces to the connec- tor platform.
The issue at hand is one of elegant, high- volume data transport. As operating speeds increase, copper cables become increasingly limited in transmission dis - tance, besides becoming hea vier and more expensive to deploy. For example, Category 6 twisted-pair cable runs 100 m at 1 Gbps. As the I/O speed increases to 10 Gbps, the recommended cabling dis - tance reduces to 55 m in a benign elec - trical environment. Where high levels of alien crosstalk may exist – such as with high densities of closely packed cables – the distance is reduced to 37 m. Mili - tary and aerospace applications also can involve substantial levels of EMI, elevat- ing the need for cable shielding, which increases the size, weight, and complexity of the interconnection system.
Fiber-based I/O does not of fer the same trade-offs in bandwidth and distance. Among the well-known advantages of fiber-optic cables are: lighter weight, higher bandwidth, and longer transmis - sion distances. For instance, with single- mode fibers multikilometer transmission distances at multigigabit speeds are pos-
sible. In addition, fiber-optic cables are inherently EMI resistant and require no electromagnetic shielding.
The installed advantages are clear, too. In cutting-edge composite vehicles, fiber- optic lines minimize shielding and bond - ing challenges. Problematic installation of heavy metallic components is eliminated, saving weight and time and reducing risk. Vehicle designers achieve location- independent architecture. Boxes that are meters or kilometers apart communicate as though colocated. VITA 66, by defin- ing optical I/O capabilities, additionally provides improved density, ruggedness, and repairability via three termini styles.
Flexible options in optical connections The VITA 66.0 base specification defines the common mounting interface require- ments for the v arious fiber-optic inter- connects within 3U and 6U VPX appli- cations. This includes definition of the mounting provisions, permitted locations, and range of e ngagement. Additional “dot” specifications define requirements for the specific optic module interfaces. A fundamental goal of VITA 66 is to offer designers multiple existing and fielded mil/aero termini technologies, allo wing them to quickly and conf idently imple- ment the best solution for specif ic appli- cations. The three module v arieties are based upon proven optical termini:
■ MT ferrule (VITA 66.1) ■ ARINC 801 termini (VITA 66.2) ■ Expanded Beam (EB) insert (VITA 66.3)
Each style of termini of fers different benefits in terms of density, ruggedness, repairability, and other characteristics. In addition, the modules are designed to meet the requirements of VITA 47 (Environments, Design and Construction, Safety, and Quality for Plug-In Units), which covers environmental and mechan-
26 VME and Critical Systems / Spring 2011
ical ruggedness for VPX systems, includ- ing temperature cycling, vibration, shock, altitude, and more.
MT ferrule for high fiber counts VITA 66.1 modules use the MT ferrule, configured to enable up to 24 optical fibers per the standard. With two ferrules per module, this equates to 48 f ibers in a 3U system and up to 240 f ibers in a 6U system. Of all industry-standard optical connectors, the MT ferrule pro vides the highest-density interconnections for both multimode and single-mode f ibers in a ferrule with an end-face only 6.4 mm by 2.4 mm. The MT, with its history in rug- ged box-level applications, is ideal for switches and concentrators.
Application considerations for the MT ferrule are the inability to perform f ield terminations and to replace indi vidual fibers. In addition, the MT is a ph ysical contact style termini, meaning the glass end-faces are in direct contact. While this style of termini initially can provide very low loss, polish de gradation via end-face abrasion is possible.
The interconnect for MT ferrules is the first “dot” specification to be published, and will be VITA 66.1. The intention is to have it serve as a template, allowing the additional “dot” specifications to be cre- ated and ratified quickly. It is anticipated that VITA 66.0 and 66.1 will be submitted to ANSI in mid-2011, with VITA 66.2 and 66.3 following later in the year.
ARINC 801 termini for highest optical performance ARINC 801 termini, as used in VITA 66.2 modules, are based on industry-standard 1.25 mm ceramic ferrules, bringing all the advantages of discrete ceramic fer - rule connectivity. The ceramic ferrules offer high-performance features that include physical contact technology for very low insertion loss, angled polishes for minimal reflection loss, and k eyed
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