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Project Tests Gas Lines as Conduit for Fiber Optic Cable

Photonics Spectra
Dec 2002
Brent D. Johnson

The problem of connecting homes and businesses to the local area network gateway has been aptly described in terms that suggest the final leg of a marathon. The symbolism is appropriate. The last mile is the hardest, there will be only one winner, and many will not finish the race.

The system would carry fiber "the last mile" via gas lines.

Although free-space optical networking has been one of the most promising strategies for resolving the last-mile issue, interference from atmospheric propagation and concerns about eye safety remain stumbling blocks. Companies that are taking a second look at the hard-wired approach may prevail.

Michael Clover, president of Sempra Fiber Links, a subsidiary of Sempra Energy, believes that free space will have its niche in point to point, but that fiber is the obvious choice for high data rates and secured transactions.

The company has invented a technology called Fiber-In-Gas that enables the installation of fiber optic cable in live natural gas lines, taking advantage of an existing infrastructure. A section of the main line is tapped with a special fitting that is electrofused or welded to the inside of the pipe, and a conduit of medium-density polyethylene material is inserted and pulled through the gas line. This fitting allows the insertion of equipment or apparatus while the main line is active and under pressure, and the conduit takes up only 10 percent of the cross-sectional area of the pipe. Once the conduit is installed, optical fiber of any variety -- up to bundles of 472 strands in 1500-foot sections -- can be installed, although 500 feet is more likely for the urban setting where this technology will find its greatest application.

The Fiber-In-Gas system is being installed in a section of Fort Worth adjacent to the Dallas/Fort Worth International Airport. The project is in partnership with Texas-based Oncor, the gas and electric delivery arm of TXU Gas.

According to Greg Pittillo of Frontier Energy, an affiliate of Sempra Fiber, the technique is safe and results in minimal gas leakage. The result is that fiber optics can be expanded into urban environments without trenching of streets and sidewalks, without disruption of utilities and, because the facilities are underground, without visible environmental impact. Clover estimates that a lateral connection for the Fiber-In-Gas system will cost $5000 or less, compared with $25,000 to $100,000 for a conventional lateral connection.


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