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orientation for optimal single-mode per- formance.


In contrast to the MT ferrule, ARINC 801 termini allow individual optical fibers to be installed or remo ved. The contacts are a standard technology within com- mercial aviation, but they are also find- ing wider use in military/aerospace, marine, and ground applications. Lik e MT ferrules, the ARINC 801 termini are a physical contact technology and may experience higher loss over time due to end-face abrasion.


Expanded Beam (EB) termini for extreme environments EB connectors are widely known for being extremely robust.


The EB insert, defined in VITA 66.3 and based on ball lens technology in MIL- DTL- 83526/20 and 21, is the most rugged interface and supports up to four fibers per module. The ball lens technology expands


the effective diameter of the channeled light and collimates the beam, projecting it across an air gap to the receiving ball lens, which reverses process and reintroduces the light to the awaiting fiber core. Where a speck of dust might completely block a 50 micron or smaller fiber core, the expanded beam minimizes the impact of dirt and debris on insertion loss. A small dirt parti- cle on the glass face of the expanded beam connector does not dramatically block the light as it can on the end-f ace of a typical ceramic-based ferrule.


The non-contacting EB interf ace elimi- nates potential abrasion induced by shock, vibration, or repeated mating/ unmating. The fiber ends are basically protected behind safety glass, allo wing very easy cleaning and inspection. The EB interface makes them suited to two- level maintenance or applications calling for frequent insertion/extraction, such as a secure storage device requiring removal after each flight operation.


Fibers/Module Fibers/Connector


Performance characteristics of VITA 66 optical termini MT ferrule ARINC 801 Expanded beam VITA 66.1 48 48


Standard


3U 6U


Durability (Mating cycles) Ruggedness


Individual fiber repair/Replacement Contacting Interface Weight


Fiber type


Insertion Loss (dB), typ SM MM


Return loss (dB)


SM MM


240


100* Low No


Yes Low


VITA 66.2 4 4


20 100


Moderate Yes Yes


Moderate


MM and SM MM and SM 0.25 0.2


0.15 0.1


>55 >20


>50 >20


Table 1 | Performance characteristics of VITA 66 optical termini. (*proposed) 20


>3,000 High Yes No


High


MM and SM 0.8 0.7


>34 14


Insertion losses—the loss of optical power as light passes through the connectors— for EB connectors are higher initially. But unlike MT and ARINC 801 termini, the losses remain constant over the life of the connector without degradation because its non-contacting optic interface does not become damaged. The EB interface is a better solution for applications with higher levels of vibration, dirt, and mating cycles. Where multiple mating cycles are expected, it only takes one mating of an MT or 801 terminus without adequate cleaning to per- manently damage the fiber endface. Table 1 summarizes the performance characteris - tics of the different optical styles.


While VITA 46.0 defines P5/J5 and P6/ J6 as user def ined locations in the 6U implementation, and P2/J2 in the 3U, the VITA 66 fiber-optic modules have been designed for installation in P2/J2 through P6/J6. The integrator could even mix the ferrule technologies along the same card edge if the situation w arrants doing so. Figure 1 illustrates the three module types on a notional 6U VPX card edge.


VITA 66.3 4 4


VITA 66: Flexibility in VPX optical interconnects VITA 66 is an important addition to the VPX family and further empowers the rugged embedded computer architec t. It supports a wide range of f iber-optic interconnection needs, from intrasystem board-to-board links to intersystem net - works spanning many kilometers. Because application requirements can vary greatly between airborne, shipboard, and ground defense needs, the standard offers a range of high-integrity choices. By using well- established termini, VITA 66 will also speed adoption of optical interconnections in VPX systems. Distance, weight, EMI, and bandwidth limitations are no longer insurmountable challenges for data trans - port in rugged embedded computing. CS


Gregory Powers serves as Market Development Manager for the Electronic Systems and Space segments within the Global Aerospace, Defense


& Marine business unit of Tyco Electronics. Mr. Powers received a BMSE from Syracuse University, has completed numerous graduate-level studies, and holds two patents relative to optic datacom devices. He can be contacted at gregory.powers@te.com.


Figure 1 | VITA 66 modules applied


Tyco Electronics 425-413-1910 www.te.com


VME and Critical Systems / Spring 2011 27


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