Optoelectronics
Meeting demand for reliable networking through expanded-beam fiber-optics T
he data carried by fiber-optic cable networks continues to grow in leaps and bounds, even with the difficulties involved with laying and operating cables in harsh environments. This raises the question of how manufacturers can satisfy the demands of network operators and assure them of robust operations across their service areas. Generally, fiber-optic cable is replacing copper, however the problem is it must operate safely across sustained and large temperature and humidity ranges. Fiber-optic connectors with expanded beam capabilities provide one possible solution, as they have proven to be reliable and efficient even under harsh operating conditions. Robust and reliable network connections
are a must in numerous industrial applications, as well as energy distribution, entertainment networks and the hospitality sector; the same applies to military networks. All these applications are now being served well by fiber connections, with great advantages including the reliability they offer under difficult environmental conditions. Fiber-optic communication networks need reliable interconnects to improve usability, so in order to be appropriate for the many possible use cases, an adequate connector system is required, developed to deliver the necessary levels of robustness and reliability. Of foremost concern is the physical layout, which must be able to guarantee a safe and durable connection between two fiber cable terminations. Direct contact connection is the traditional method used here. It involves a precise ceramic ferrule, which allows single- or multi-channel connectivity at a low insertion loss of about 0.25dB. The drawback of direct physical contact at the fiber ends is its known tendency to mechanical misalignment (axial run-out). Also, the mechanical contact is susceptible to contamination, which is of great concern when the quality of the connection must be maintained under a variety of difficult environmental conditions. It also brings up the issue of sufficient control over the long- term durability of the connectors. The solution to many, if not all of these adverse conditions is fiber-optic connectors based on the expanded beam approach. Expanded beam connectors have evolved quite successfully and proven to be a robust and valid alternative to their traditional physical-contact counterparts. The expanded beam concept uses two beams to collimate, expand and refocus the light input from the transmitting fiber to the receiving lens. Here, most often either graded-index (GRIN) rod lenses, or ball lenses are used.
Low-loss connections
Lowering the signal level is a major concern in all transmission and connection systems. Lower losses enhance the efficiency and practicability of all types of interconnect since this will reduce the inherent noise contamination of the usable signal. The fact
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that the connections are not physical, rather the light beam crosses an air gap, is very advantageous in regard to possible wear and tear of the connection, because there is no mechanical friction. Here, the precision ferrules used are proven to align the lenses, while connection shells are used to align the lenses. All in all, this contact-free connection method can achieve real low insertion losses in the neighborhood of <1.0dB. The relatively higher cost of the expanded beam connection method has been known to impede its general application – limiting it to high-end situations that are able to bear more demanding infrastructure outlays. Military applications are a case in point, however that only endorses expanded beam connections as being valid for general acceptance in industrial and commercial applications. The military sets and insists on its own standards regarding debris, dust, mud, oil and moisture for their network connections, to extend uptime and guarantee persistent operability for critical data transmissions. Furthermore, the cost landscape has changed dramatically recently, through the availability of a host of low-cost expanded beam connectors for use in multiple cost-conscious commercial applications, such as telecom and healthcare. Generally speaking, they are a viable choice for reliable, low-latency data connections in upcoming next-generation network services. There is, of course, no single solution to the multitude of network configurations that already exist and their need for reliable, affordable interconnect; each application will predefine the most suitable connector type. Network operations in harsh environments demand their own approach in selecting the appropriate connector system, since expanded beam connections tend to behave differently under changing environmental conditions and in the presence of contaminants. As always, moisture is a major challenge for electronic systems; a physical connection can potentially remove the majority of moisture present. On the other hand, the expanded beam method has its own problems caused by moisture forming on the lenses, which will degrade the signal transmission due to a scattering of the emitted light. This requires a detailed assessment of the operational conditions and the required performance levels of the connectors to be chosen. Experienced installers will make their choice based on the data and behavior of a range of connectors considered for their intended applications. Special consideration is also needed in the design of IoT systems developed for industrial or consumer applications. Here, appropriate connection systems are crucial as these IoT systems have structures that require a high degree of data purity, as well as demanding levels of speed and efficiency. Low latency is of a foremost concern in the industrial M2M communication space to ensure the functioning of the interconnected systems.
Components in Electronics
Choosing the best suited connector type for this kind of application is not an easy task, but it is a critical precondition.
The expanded beam concept As mentioned above, mechanical direct- contact connections are often unreliable in harsh operating contexts. They derive from much older concepts, which served traditional applications such as data centers and old-line telephone exchanges. The transition to expanded beam technologies has gained momentum, as they are more flexible to use and offer robust functional parameters even in challenging installations. The design principle of expanded beam connectors enables them to reduce potential damage and increase the reliable data throughput. The reason for this is their design; the terminating cable is positioned behind a lens which acts as a protecting shield, while also generating a wider active area for the connection. These protective lenses don't come into physical contact, so the potential for mechanical damage caused by friction or direct impact is substantially reduced. This explains their suitability for operating in adverse conditions, their robustness in the presence of vibration and the low potential for damage, all of which makes expanded beam connectors an ideal choice for challenging applications.
In traditional connectors, dirt particles with diameters ranging from 5 to 40m could induce transmission problems, while a single dust particle of just 9m in diameter settling on a single-mode fiber core could block the entire signal transmission. Despite the cost-effectiveness of a physical connector it is not recommended under harsh environmental conditions; the potential for losses due to small dust particles is clearly pointing to the more reliable expanded beam connectors. The concept of expanded beam connectors involves several supporting technologies to achieve a robust and reliable connection between the cable terminals. Multi-channel expanded beam connector inserts are now available that have evolved as expanded beam connectors continue to mature. In multi- channel connectors the inserts typically form a stainless metal housing to hold from one to up to 16 spherical lenses. Being spring loaded, these inserts are configured to maintain the correct alignment of the lenses during the process of mating. This presents another major advantage, because if the terminals are damaged for some reason the termini can be changed without re-terminating the entire fiber cabling feed. Physical contacts still offer lower insertion losses than expanded beam connections, but their sensitivity to damage caused by harsh environments can over time lead to lower performance levels. They may also require regular cleaning and maintenance. Expanded beam, on the other hand, is a connection technology that has proven its merits. It is a low-maintenance solution for extreme conditions in regard to
temperature and moisture. It is the most appropriate solution for stable connectivity under adverse conditions.
Fiber-optic solutions The demand for reliable and efficient network interconnect is on the upswing worldwide. Cinch Connectivity Solutions (Bel Group) supplies the Fibreco fiber- optic connectors and cable assemblies, offering expanded-beam connection systems to meet the industry’s demanding requirements. The Fibreco Junior expanded-beam connectors offer up to four multi-mode or single-mode fiber-optic channels in conformance with MIL-DTL-83526. Conceived for use in harsh environments the Fibreco Junior offers a fully sealed hermaphroditic construction. It is field terminable and repairable with standard fiber-optic tools and equipment. The Fibreco expanded-beam insert deploys a unique, patented optical arrangement. All the critical interface elements between fiber and lens are permanently sealed in a controlled atmosphere during their manufacture to ensure that no dust, moisture or other contaminants will migrate into the optical path over the product’s lifetime. The Geo-Beam Series of connectors, such as Geo-Beam EX and BA, conform to the ATEX Directive and to IECEx 60079 for Zone 1 Hazardous Areas. The BA connector offers a special "force-only break apart" option if needed. The Fibreco Junior expanded-beam connector is compatible with all MIL-DTL-83526 connectors, such as the Tyco Pro-Beam Junior, the Stratos HMA/HsMA connectors and the QPC QMINI connector. The Fibreco design takes into consideration the range of application scenarios that cable users and system designers are confronted with as the demands on performance and durability continue to rise. It offers a range of options, regardless of the number of channels in use. Cable assemblies and field-splicing kits are also available. Worldwide expansion and the growing dependence on data services and network structures demand stability and reliability throughout. In light of these requirements, fiber-optic technology has shown itself to deliver, but advanced fiber-optic cable configurations require proper terminal connection technologies that are sufficiently suited for harsh environments. The expanded optical beam concept is the optimal solution for highly efficient connections at a level of reliability and durability that physical terminals won't provide.
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