The first time I ever pulled a telecommunications cable, it was across a warehouse ceiling where my employer needed a temporary office in the far corner. However, the company’s IT consultant had failed to explain to me things such as bend radius and pulling limitations. So as I ran the cable, I secured it by tying it into trusty Boy Scout knots around the tops of ceiling-high equipment racks, being sure to pull each of the knots good and tight. My knots were exemplary, but my signal never had a chance.
With that introduction to the world of low voltage, you can imagine my favorable reaction to new bend-improved, bend-tolerant and bend-insensitive fiber optic cables that could have withstood even the punishment I gave the cable that day.
These single-mode fiber optic products, which are hundreds of times more bendable than a standard single-mode fiber, solve a historic technical challenge for telecommunications carriers. Optical fibers are made of ultra-pure glass waveguides that transmit light through their central cores.
With traditional single-mode cables, tight bends allow leakage of light, resulting in signal loss (attenuation) or optical power degradation. In contrast, bend-insensitive fiber optic cables, with their minimum bend radii—as low as 5 mm (0.2 in)—allow unlimited bends around very tight corners with virtually no signal loss. The new International Telecommunications Union (ITU) 657 standard requires a 7.5-mm bend. Cables manufactured by Draka Cableteq, North Dighton, Ma.; OFS, Norcross, Ga.; and Corning Cable Systems, Hickory, N.C., comply with this standard. Although Corning asserted that its fiber was able to bend down to 5 mm, most of the other fiber optic cable producers felt that 5 mm was too high a risk. The cable Draka and OFS offer on the general market meets the ITU 7.5 mm bend-tolerant rating.
These cables allow telecommunications carriers to install optical fiber cables into complex environments, especially fiber-to-the-home (FTTH) networks in multiple-dwelling units (MDUs). The average MDU installation involves a dozen 90-degree bends, making it difficult and expensive to run fiber all the way to customers’ homes.
The first major bend-improved product was introduced in 2005 by Nippon Telegraph and Telephone Corp. (NTT), Tokyo, which dominates the telecommunication market in Japan. Its “hole-assisted” or “holey” fiber is manufactured with tunnels in the outer glass fiber that surrounds the thin central glass core. The tunnels relieve stress on the outer glass as the fiber is bent. But NTT’s fiber is expensive and requires special connectors to mate with other types of fiber.
Corning uses ClearCurve technology, which is based on its proprietary nanoStructures optical fiber design. This coats the cladding that surrounds the inner fiber with a mesh of tube-like nanometer-scale (one-billionth of a meter) pockets. They create channels that guide the light back into the core and prevent signal loss in tight bends, providing the benefits of extruded holes without the high cost.
Draka announced an advancement in connector cables through the combination of its BendBright-XST bend-insensitive fiber cable and Megladon’s hardened lens connector (HLC) ScratchGuard connector technology.
Draka and Megladon Manufacturing Group, Austin, Texas, have combined high-end technologies to deliver a high-performance, scratch-resistant, bend-insensitive fiber optic cable assembly to the market. The product offering is diverse and includes patchcords, riser, plenum and low-smoke zero halogen cables available with ultra or angle -polish-hardened lens connectors.
Introduced in 2006 as Draka’s second generation of bend-insensitive fiber, BendBright-XS is a widely accepted product for customers who want a solid-glass G.657 A&B-compliant fiber.
With the fiber optic connector being a critical component, damage to the connector due to handling and repeated use has been a concern and point of failure for network operators. Megladon’s HLC ScratchGuard technology has virtually eliminated this problem.
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Some of these cables meet the ITU-T (Telecommunication Standardization Sector of the International Telecommunications Union) recommendation G.657.A, which emphasizes backward compatibility, and some meet recommendation G.657.B, which emphasizes optimal bend performance.
Verizon Communications Inc.,0 New York, was one of the early proponents of the newest technology for its Fiber Optic Service (FiOS) Internet and TV products in high-rise apartment and condominium complexes.
Additional information was contributed to this article by Frank Bisbee of Communication Planning Corp.
MUNYAN is a freelance writer in the Kansas City, Kan., area, specializing in business writing and telecommunications. He can be reached at www.russwrites.com.
Correction: The first bend insensitive singlemode fiber was developed by Plasma BV in Einhoven, Netherlands in 2002. Plasma is now known as Draka.