Cable TV turns to 1550-nm technology

Cable TV turns to 1550-nm technology

Mitch shapiro

Although 1310-nm technology has long been the dominant optical platform in the U.S. cable-TV industry, 1550-nm products continue to gain popularity and market share. This growing interest was evidenced at the recent National Cable Television Association (ncta) show in New Orleans, where almost all major suppliers of optoelectronics for hybrid fiber/coaxial-cable (hfc) networks displayed a line of 1550-nm high-power transmitters and optical amplifiers.

Previously, San Jose-based Synchronous Communications stood virtually alone among vendors as a 1550-nm product advocate, as did Cablevision Systems among the industry`s multiple system operators. In the past few years, however, strong demand has emerged for 1550-nm products in the "supertrunk" market segment, particularly for links between headends and remote hubs serving 10,000 to 25,000 homes. As virtually all the major multiple system operators have embraced 1550-nm supertrunks, several suppliers of optoelectronics have moved to compete with Synchronous Communications in this growing market segment.

For some, acquisitions have led the way to a 1550-nm product line. In 1996, for example, Scientific Atlanta acquired ATx Telecom Systems (formerly Amoco Lasers), a supplier of 1550-nm transmitters and erbium-doped fiber amplifiers.

adc Telecommunications, Minneapolis, MN, which already held a strong position in the supertrunk market through its DV6000 digital product, has also embraced 1550-nm technology via acquisition. The firm purchased Photonic Applications Inc., a Connecticut-based company that had developed a unique approach to 1550-nm transmission. While other suppliers use predistortion techniques or linearized modulators to deal with 1550-nm distortion problems, Photonic developed a technique based on feed-forward linearization, which it claims provides superior performance.

General Instrument, another leading equipment vendor, uses transmitters supplied by Connecticut-based Uniphase Telecommunications Products in its 1550-nm solution. Others, including Harmonic Lightwaves and Ortel Corp., have developed their own core optical technologies for 1550-nm applications. Among those unveiling new 1550-nm products at the ncta show were Philips Broadband Networks and Integrated Photonic Technology--ipitek.

Working together

Although most of today`s demand for 1550-nm technology remains focused on supertrunk applications, there are signs that this technology may migrate deeper into hfc networks, perhaps to be used in conjunction with 1310-nm products to deliver a mix of video signals from headends or hubs out to neighborhood nodes serving 500 to 1000 homes. Such architectures would use 1550-nm technology to deliver a tier of broadcast services and rely on low-power 1310-nm lasers for narrowcast signals that are dedicated to only one or two optical nodes.

This potentially larger role for 1550-nm techniques is being driven by technology developments in both the 1550-nm and 1310-nm market segments, increased price competition as more vendors have introduced 1550-nm products, and changing operator service strategies.

For example, fiber dispersion and transmission nonlinearities have posed key technical challenges to the developers of 1550-nm products. While different vendors have developed a number of techniques to overcome such problems, these solutions have varied in effectiveness depending on their application and have tended to increase hardware complexity and cost. The cost of 1550-nm technology in general has also suffered in comparison to 1310-nm products due to the much larger volumes associated with the latter.

Today, however, the improved performances and declining prices of 1550-nm transmitters and fiber amplifiers indicate that these problems may be solved. Thus, operators are now taking another look at the technology for the delivery of broadcast services to a cable system`s entire subscriber base. Also, the increased availability of low-cost, low-power 1310-nm lasers and the planned introduction of cable modems and other services that require more dedicated bandwidth are making the economics of narrowcasting more attractive.

According to Synchronous Communications chairman Vince Borelli, this approach recently received a major boost with the introduction of very low-cost, uncooled, isolated 1310-nm distributed-feedback lasers from components suppliers such as Lucent Technologies, Mitsubishi, and Fujitsu.

adc is among the vendors joining Synchronous Communications in embracing this hybrid approach to delivering broadcast and narrowcast signals. Along with its supertrunk product, the company displayed a "superdistribution" product at the ncta show that allows operators to take 1550-nm signals all the way to the node.

According to Walter Glomb, adc`s director of marketing for AM optical products, the company`s current product uses a rack-mounted erbium-doped fiber amplifier at a hub to extend the reach of 1550-nm signals originated at a centralized headend. For operators who want to add 1310-nm narrowcast signals, the adc platform allows these to be added at the hub or at another location.

Synchronous Communications is pursuing a solution that uses wavelength-division multiplexing (wdm) technology to load both 1310-nm and 1550-nm signals on a single fiber for reception by a single receiver. While adc`s current superdistribution product uses separate fibers and receivers to deliver 1310-nm and 1550-nm signals from the hub to the node, Glomb points out that adc already offers wdm in its digital product line and is looking into a wdm approach for analog products. q

Mitch Shapiro writes on optical technology from Encinitas, CA. He recently joined Probe Research as senior vice president.