My TN Connection

While the need for network transmission speeds continues to grow, so does the importance put on a company’s fiber optic backbone cabling. As cabling standards have evolved from 10Mbps and 100Mbps to Gigabit and 10 Gigabit speeds, optical cabling has had to evolve as well. With the growth of internet traffic, video conferencing, VoIP and other bandwidth intensive applications – Network Managers have been forced to evaluate their cable infrastructure to see not only if it will meet their needs today, but also well into the future. These days, one term that seems to have become synonymous with future proofing is: “laser-optimized fiber”. In the course of my post I’d like to define what laser-optimized fiber is, how it differs from legacy fiber, and why you need to know about this latest development in optical communication.

Before defining what laser-optimized fiber is and how it compares to standard 62.5 and 50 micron multimode fiber, I’d like to go over some of the characteristics of these legacy fiber optic solutions. For 15 years or more, the use of 62.5µm was by far and away the most prevalent fiber type used in premise applications. These systems operated at 155Mbps or less and were able to utilize inexpensive light-emitting diodes (LED’s) to transmit light down the fiber. As backbone speeds increased to Gigabit Ethernet, it became evident that using LED’s would not be a viable solution for transmitting the signal. LED’s could not be turned on and off fast enough to support the higher bandwidth. At this point the industry turned to a low cost laser source called a vertical cavity surface emitting laser or VCSEL as the preferred signaling technology. VCSEL’s were able to provide higher power, smaller spot size, narrower spectral width, and faster data rates than LED’s. Since VCSEL’s do not perform as well with 62.5µm fiber as they do with 50µm, this caused the move away from 62.5 to 50µm for those chasing Gigabit speeds.

As the 10 Gigabit Ethernet standard developed, it became quite apparent that not even 50µm fiber would be able to employ the VCSEL to push 10Gbps over a 300 meter distance. The limiting factor was something called Differential Mode Delay (DMD). Basically the concept of DMD is that the VCSEL’s laser beam would be sent through the fiber’s core and split into many different modes of light. These modes travel down the core at different speeds and spread out over the transmission distance, which reduces the receivers ability to identify the signal at the other end. In a response to the limiting effects of DMD on VCSELs, fiber manufacturers created laser-optimized fiber offerings. With laser-optimized fiber, manufacturers have removed impurities within the core of the fiber that would cause the various modes of light to spread out and arrive at the receiver at different times. By preventing the VCSEL’s signal from spreading out and allowing the modes of light to travel at similar speeds, the receiver is able to detect the optical signal over longer distances. Thus maximizing bandwidth and the ability to support 10Gbps to the TIA specified minimum distance specification of 300m and beyond.

Since fiber optic cabling is backwards compatible, it is crucial to choose a fiber
optic solution that will support current and future bandwidth needs. When considering the total cost of ownership for a facility’s cable plant, laser-optimized fiber presents a very solid case for maximizing your investment. Since laser-optimized 50µm fiber is compatible with legacy LED signaling solutions - yet still enables migration to higher speeds, it becomes a logical choice for new enterprise backbone installations. It’s no wonder that some researchers are estimating that around 50% of new installs in the next 5 years will be with laser-optimized 50 µm fiber.

Keywords: 10 Gigabit Ethernet, 50µm fiber, Applications, bandwidth, cable infrastructure, cabling, connection, differential mode delay, Fiber, fiber optic, LAN, laser-optimized fiber, LEDs, Multimode Fiber, Network Manager, Port, Systems, Transmit, VCSEL, VOIP

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