Multichannel dense WDM combines audio, video and data

Multichannel dense WDM combines audio, video and data

BEN HARRISON

To meet a need for more available channels and greater capacity per fiber, Artel Video Systems in Marlborough, MA, has added dense wavelength-division multiplexing (dwdm) capability to its multichannel fiber-optic video-, audio- and data-transmission systems.

Dwdm technology allows transmission of 48 noncompressed video channels and 288 CD-quality audio channels over distances to 40 km. If longer spans are required, erbium-doped fiber amplifiers may be employed to boost the optical signal without degradation. The video-transmission systems can carry 48 channels at an aggregate rate of 9.6 Gbits/sec. Networks hundreds of kilometers long can be constructed at reasonable costs using commercially available components.

As an overlay system, the combination of 12-bit digital encoding quality, channel capacity and distance capabilities makes this video-transmission system competitive with traditional network solutions, including codec-equipped OC-48 Synchronous Optical Network interoffice and intercity transport, which have the disadvantage of requiring compression technology. When employed, compression dramatically affects the quality of the video image and increases network costs.

Dwdm uses laser-based optical transmitters with closely-spaced output wavelengths--or colors--to send multiple independent signals over a single optical fiber. Although Artel has previously offered traditional WDM systems that carry two optical signals at widely spaced wavelengths, its dwdm technology allows the video-transmission system to transmit and receive as many as eight optical signals on each fiber.

Artel`s dwdm solution combines the company`s SL4000 video communications system and the DW4000 dwdm system. The SL4000 supports microwave and coaxial video links, corporate teleconferencing and training systems, supertrunking and distance-learning. DW4000 applications include cable-TV supertrunking, telecommunications infrastructure, switched-digital video networks and hybrid services. With 48 video, 288 audio and 64 noncompressed data channels, the system offers greater capacity and reliability (see figure).

Baseband signals are fed into SL4000 encoder units, where they are converted to optical digital data. The outputs from the SL4000 optical transmitters are combined and transported over the fiber plant. At the remote site, the optical outputs are separated and fed into the corresponding SL4000 decoders, where they are converted back to baseband signals.

According to the company`s president and chief executive, Harold E. Charnley, "Artel`s fiber multiplexing capabilities provide a solution for regional cable-TV systems, as well as applications within regional Bell operating companies and interexchange and independent carriers." He claims the company is among the first to offer 48-channel dwdm capacity and may be the only one to offer it with the performance of 12-bit digital encoding (see Lightwave, August 1996, page 1).

Tony Lapolito, Artel`s director of marketing, explains that the company`s product and dwdm offer the promise of mixed services on the same fiber. "This capability means that the optical signals from different Artel product lines, vertical suppliers or even competitors can be optically multiplexed onto a single fiber," he says. "For example, a customer might call the vendor and request that `product X` be configured for dwdm slot 3, which corresponds to a certain industry-standard wavelength." However, he cautions that industry-standard wavelengths have yet to be finalized.

Carriers are now building overlay networks to their existing telecommunications backbones to take advantage of dark fiber, says Lapolito. Artel uses its dwdm capability to capitalize on what the carriers are doing.

Additionally, Lapolito explains that it is cheaper to upgrade or put additional electronic equipment on the end of existing fiber to increase its capacity than it is to pull new fiber. "Thus, the existing infrastructure that was paid for years ago can now carry eight times what it was originally intended to, and consequently revenues can be increased by a factor of eight."

Dwdm suppliers are currently offering four- and eight-channel dwdm products. However, vendors are also talking about 16-, 20-, 32- and 48-channel products. Because dwdm is modular by nature, after an initial investment in the fiber, dwdm equipment and terminals allow a base deployment. The cost to grow the network as needed or to offer additional services requires only the purchase of more terminal equipment.

Commenting on what Artel is doing with this dwdm capability, Bob Paulson, president of Omnimedia Communication, a high-end network consulting firm based in Westborough, MA, calls the company`s technology "impressive and the next step" in fiber transmission. "Being first is not as important as [simply] the fact that Artel is providing this dwdm technology."

Outlook for dwdm

Whether for transmission of video, audio or data, dwdm appears to be a booming technology for 1996, according to market forecast studies from ElectroniCast Corp. in San Mateo, CA.

When dwdm components were introduced in 1995, they represented a global market of $101 million. This figure is expected to soar to $4.17 billion by the year 2000. Growth is then expected to continue at a more moderate pace to reach $12.1 billion by 2005.

Component consumption is paced by North America, with a 44% share in 2000 and a 47% share or $5.7 billion by the year 2005 (see table). According to Jeff D. Montgomery, chairman of the market forecasting firm, "Several different component technologies have advanced to the point that dwdm networks are now the clear economics-based solutions in some networks, such as undersea cable and `long haul` terrestrial networks involving spans of hundreds of kilometers. As WDM component technology continues to advance and per-gigabit-kilometer costs drop, WDM increasingly will be applied to shorter- distance links."

Montgomery explains that the surge in broadband transport capacity is being driven by economics. During the past decade, service providers worldwide have made major reductions in their overhead costs. New construction also is designed for minimum cost. He says there are three ways to reduce the cost of network interconnect cable-capacity expansion:

Deploy more fiber, with current-generation transmitters and receivers.

Trade-out the current transmitters and receivers for high-data-rate optoelectronics used with the current fiber.

Use dwdm components with existing fiber and current-generation optoelectronics.

ElectroniCast sees the optical amplifier as a key driver of dwdm evolution. The basic concepts of WDM were demonstrated early in the history of fiber optics commu nications. Improvements by Lucent Technologies, Bell Laboratories, IBM/Zurich, Hitachi and others have made use of the optical amplifier technically feasible for submarine cable systems.

However, ElectroniCast cautions that no major breakthrough in optical-fiber technology appears likely. Most laboratory efforts in this field now are applied to cost reduction and to developing amplifiers for other than 1550-nm bands, notably in the 1310-nm region. q

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