Fiber optic technology, fiber optic products, and the range fiber optic applications have certainly grown over the past several years. My first development project using fiber optics took place when I was still listening to music on cassettes. Fast forward 10 years and we were on the brink of Gigabit Ethernet. Gigabit Ethernet along with Fiber Channel were the two technology drivers that pushed fiber optics into the mainstream. Add another 5 years and we were in the middle of what would become the internet bubble. In the shadow of this activity, fiber optics also migrated and thrived in environments where not too long ago fiber would never have been considered. So what enabled this migration to take place?

Expanded Beam Applications

Before discussing the technology, let’s look at some of the new applications for expanded beam connectors: avionics, military vehicles, shipboard systems, the petrochemical industries, and a host of other industrial applications. These applications all require solid performance in high shock and vibration environments. They all must also provide a robust solution against fiber’s historical foe: dirt/debris/contamination. The technology solution that addresses each of these requirements, and that has enabled fiber optics into harsh environments, is expanded beam connector technology. Not to discount the advances in cable strength and durability, but it still comes down to the basic fact that light must successfully propagate across the connector interface in order to have a successful link.

Connector Design and Technology

Let’s start with a brief overview of expanded beam technology. The illustration above shows the key elements included in the connector, namely the standard ferrules, ball lens, lens insert and connector face. As shown, the light path is enlarged by over an order of magnitude to mitigate the impact of dirt and debris on the interface. This is the key attribute of the expanded beam interface.

A simple summary and comparison of both physical contact and expanded beam technologies is provided below.

Expanded Beam Advantages

The key aspect of the expanded beam solution is the consistent, repeatable insertion loss performance over mating cyclesand environmental conditions. While the initial insertion loss may be fractionally higher than the physical contact solutions, over time this parameter remains constant versus the increase in IR seen with the physical contact. This is illustrated in the graph on page 24. In addition to this, the expanded beam connectors can easily be cleaned in the field with slightly more than a bottle of water and a shirt sleeve. A video demonstration of this cleaning process can be found on YouTube at: http://www.youtube.com/watch?v=O2t50WiL6m4

Stratos offers a complete line of expanded beam products to address these applications. Options include channel counts, fiber types, and supported wavelengths. To obtain information on these products call 877-347-0091.

Some examples of the Stratos HMA, HTC, and copper/fiber hybrid connectors are shown below.

Mode Conditioning Patch Cord

What is a Mode Conditioning Patch Cord? A mode conditioning patch cord is a duplex multimode cord that has a small length of singlemode fiber at the start of the transmission leg. The basic principle behind the cord is that you launch your laser into the small section of single mode fiber. The other end of the singlemode fiber is coupled to multimode section of the cable with the core offset from the center of the multimode fiber. The laser light thus misses the “dip” and this new launch condition more closely mimics a standard LED launch. The bonus is that you still retain the speed advantages of using a laser.

A Mode Conditioning Patchcord (MCP) creates an offset in the launch from the laser into the multimode fiber, avoiding the index dip in the center of the fiber and allowing the signal to propagate properly through the fiber.   Newer “Laser Enhanced” multimode fibers do not exhibit this phenomenon due to the engineering of the fiber without an index dip in the core.

In legacy fiber optic systems, multimode fibers were not designed to properly transmit a SM laser source without the creation of dispersion problems, where the original signal becomes spread out over distance (>300m in most systems) and pulses can combine with each other creating an unreadable signal at the receiving end.   This was caused by a small dip in the Index of Refraction profile of the fiber in the center of the core in which the laser transmission becomes “mode locked”.