Cable-TV show highlights 1550-nm optical amplifiers
GEORGE LAWTON
Since the approval of the Telecommunications Act of 1996, fiber-optic communications products and services are proving more important to cable-TV industry operators as they seek to implement voice and data communications and push video services over longer transmission distances. Traditionally, cable-TV systems have been built using 1310-nm transmission equipment. However, the continuing reduction in product costs and improving performance of 1550-nm optical amplifiers are receiving close scrutiny by many cable-TV operators.
These trends became apparent at the National Cable Television Association (Ncta) show held in Los Angeles last April, where cable-TV operators expressed high interest in migrating to 1550-nm optical amplifiers for their fiber-optic infra structures. Many indicated that they expect to push fiber-technology frontiers in the same way telephone companies have been doing. Also highlighted at the show were new laser transmitters and receivers that work with the 1550-nm optical amplifiers.
Traditionally, optical amplifiers have been limited to telephony networks because they work only with 1550-nm equipment. But because optical amplifier costs have dropped dramatically, the technology has now become cost-effective for the cable-TV industry.
Installed in a fiber-optic network distribution application, an optical amplifier strengthens lightwave signals so they can be split onto multiple fibers. Installed in a fiber-optic network transmission application, an optical amplifier enables lightwave signals to travel to 100 km without the need for intermediate regeneration.
Until recently, a technological obstacle for optical amplifiers dealt with the amount of power that could be sent down a fiber. Traditionally, 15 dBm has been the highest amplified power available without causing transmission problems. At the show, vendors displayed amplifiers that shattered that boundary.
Suppliers react
Until recently, Synchronous Networks in San Jose, CA, was the sole equipment supplier selling 1550-nm optical amplifiers and associated products to the cable-TV industry. But during the past two years, other companies have entered this product arena.
For example, Ortel Corp. in Alhambra, CA, has traditionally focused on the 1310-nm transmission equipment market. But at the Ncta show, the company unveiled several 1550-nm products for resellers and systems integrators that centered on the cable-TV market.
Wim Selders, Ortel`s chief executive, said, "Ortel has been known as a supplier of 1310-nm distributed-feedback lasers and photodiodes for hybrid/fiber coaxial-cable (HFC) networks. The new products mark our presence in the field of 1550-nm broadband transmission and underscore our determination to provide linear fiber-optic products for cable-TV operators and HFC networks worldwide."
Ortel`s 1550-nm product line includes an externally modulated transmitter that meets National Television Standards Committee and European Committee for Electro Technical Standardization frequency standards, and 40- and 80-mW optical amplifiers.
ATX Telecom Systems in Naperville, IL, introduced the Javelin 1550 series optical fiber amplifier as a low-power product for cable-TV applications. According to the company, this amplifier can deliver outputs to 15.5 dBm into a fiber. It complements the company`s existing high-power amplifier, which can deliver outputs to 22 dBm using an erbium yttrium-doped fiber technology. Because this high power cannot be entered into a single fiber without causing Brillouin scattering, cable operators could split a lightwave signal from one laser transmitter into numerous fibers.
For example, Santa Clara, CA-based Harmonic Lightwaves claims that its MAXLink 1550-nm transmission system uses an optical amplifier that can launch up to 17 dBm of power with no scattering effects. The system uses two fibers to split the transmitter signal and then recombines the signals at the receiver.
John Dahlquist, vice president of marketing at Harmonic, says, "MAXLink achieves high performance in 80-channel supertrunking applications and eliminates the need for split-band configurations. For example, on a 100-km link, users can achieve a high carrier-to-noise-ratio of 55 dB."
Another company that claims to have pushed the power of its optical amplifiers to new limits is Pirelli Cable Corp. in Lexington, SC. Its 1550-nm optical amplifier for cable TV meets the need for unrepeatered video between locations. This amplifier uses a phase-modulation technique that can push 17 dBm of power into a fiber without scattering effects.
Moreover, the company contends that the amplifier can push 80 channels of video 80 miles with a carrier-to-noise ratio of 52 dB. Although Pirelli is manufacturing optical amplifiers for telephony applications that can carry eight separate optical wavelengths, the new amplifier for the cable-TV industry handles only one wavelength.
ADC Video Systems Inc. in Meriden, CT, also introduced new 1550-nm transmitter and optical amplifier products that plug into ADC`s HomeWorx broadband system. When used with the amplifier, the broadband system can output up to 17 dBm of optical power into a single fiber. It also uses phase modulation to avoid scattering problems.
Furthermore, ADC has licensed optical-feed-forward technology from Photonic Applications Inc. in Bloomfield, CT. According to ADC, this technology gives its broadband transmission system an extra 3 dB of performance when carrying 80 channels of video at a carrier-to-noise ratio of 55 dB (see figure).
ADC also unveiled an optical node, the ISX-2, for scaling up cable-TV systems cost effectively with service demand. In this manner, cable operators can deploy only needed services and then gradually upgrade as demand increases.
John Holobinko, vice president of marketing at ADC Video Systems, explains, "In deploying broadband services, the ISX-2 enables network providers to safely invest in capital equipment and have the option to increase services based on future revenue streams." q
George Lawton writes from Brisbane, CA.