Expanded Beam Fiber Optic Connectors for Medical Devices

Expanded Beam Fiber Optic Connectors for Medical Devices

10/14/2020

New choices in expanded beam connectors minimize the impact of harsh environments on medical fiber optics

Advantages and Challenges of Fiber Optic Cabling

Fiber optic cables are replacing copper wiring in many medical devices due to fiber’s greater bandwidth, resistance to electromagnetic interference, reduced ferromagnetic content and lower weight. Fiber optic cables are, however, constructed from materials that are more easily damaged than copper wire. Fiber optic cables for medical datacom are often subjected to harsh environmental conditions. Dust, biological fluids, microorganisms, and other contaminants are unavoidable in clinical settings. Enclosures designed to protect fiber optic cables also make these systems more difficult to repair when unwanted ingression occurs.

Radiall's EB-LuxCis expanded beam optical connector
Radiall's EB-LuxCis® expanded beam optical connector (Courtesy of Radiall.)

One of the most common causes of failure is physical contamination with dust. While EB connectors are most commonly used with Multimode fiber, newer connectors also encompass single-mode fiber as well. The core diameter for most single-mode fiber optic cables is only 8 micrometers. Unfortunately, dust particles are typically 2.5 – 10 microns in diameter – enough to completely occlude the core diameter of the fiber. Multimode fibers do have larger core diameters (usually 50 microns), but are similar enough in size that contamination is also a problem. While careful design of connectors, cables and enclosures can limit the potential for exposure, it is typically not economically feasible to keep the environment completely dust-free. In addition to unwanted ingression, contamination can occur when the cables are unplugged to facilitate upgrading or servicing instrumentation. Expanded beam connectors offer greater resistance to contamination from dust, other materials and liquids.

Clean and contaminated fiber face
Clean fiber face (left) and contaminated fiber face (right). (Courtesy of Radiall.)

How Expanded Beam Connectors Work

As their name suggests, Expanded Beam connectors (EB) work by enlarging the light beam carried by the core of the fiber. When the beam is enlarged, typically into the millimeter range, the size of the beam is now very large compared to most potential contaminants. While severe contamination can still compromise performance, the effect of small amounts of dust are greatly reduced. This is largely due to the size difference created by the beam expansion; In a typical expanded beam connector the core diameter effectively grows from area of ~ 2000 square micrometers (for multimode fiber) to 3.24 * 106 square micrometers– a factor of 1,620! Expanding the beam increases signal reflection and produces Etendue effects, which can decrease transmission slightly (a few % or ~ 1dB are typical). In many optical systems, however, transmission power is not limiting and the slight transmission loss added by the expanded beam connector is more than offset by the contaminant resistance. Expanded beam optical connectors are also slightly larger than their standard equivalents.

Radiall EB connector
A cross section of an Radiall’s EB technology, which is typical of EB connectors. (Courtesy of Radiall.)

Putting It All Together

There are a variety of expanded beam connectors available on the market – and in many cases, the style of expanded beam connector must be carefully chosen to match the fiber type and connector to provide optimal performance for the particular medical device. This exercise must also involve careful choice of jacketing materials and construction technique to balance requirements for ruggedization, cost, bend radius and serviceability. Timbercon’s component agnostic approach means that our expert fiber optic engineers will design a system to meet your requirements using while optimizing cost, performance and lead time. Since Timbercon does not manufacture fiber optic cable or connectors, we are free to choose from the best commercially available options for your project. Whether this is one of Radiall’s innovative expanded beam connectors or one from a variety of other manufacturers, Timbercon’s engineers will choose the best match for your application. Once the design is finalized, Timbercon’s Zero Defect manufacturing process will ensure that your cable works the first time, every time. And as your fiber optic cable needs grow, Timbercon’s scalable manufacturing can help ensure consistent quality while reducing costs. Contact us today for a no-cost design consultation or review to see how expanded beam connectors can improve the reliability and serviceability of your medical fiber optic cables.

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