Dual-core optical fiber could enhance data processing

2013-01-02 11:18:15

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Verizon completes fiber-optics installation in lower Manhattan as part of Hurricane Sandy restoration effort
Approximately seven weeks after Hurricane Sandy, Verizon says it has completed the installation of fiber-optic cables between the company's two critical central switching offices in lower Manhattan and buildings put out of service by the storm surge.The completion of the fiber-installation phase of the project is part of Verizon’s plan to modernize communications capabilities for customers as it restores services to the businesses and office buildings in lower Manhattan that were affected by the hurricane.Once Verizon completes the project, the area will have the nation's most advanced communications infrastructure, providing customers with the highest level of service and reliability, the company claims. Furthermore, the modernization project will make lower Manhattan "future-proof," enabling Verizon to easily update the communications infrastructure with new capabilities.During the restoration process, Verizon has provided alternate communications services to thousands of small businesses and residential customers in the area. The company has provided call-forwarding capabilities to approximately 7,000 telephone lines so that calls are automatically forwarded to a working landline or cellphone number. In addition, it has provided (at no charge to customers) more than 2,600 Verizon Wireless Home Phone Connect and Verizon 4G LTE Jetpack Mobile Hotspot devices.While Verizon has been installing the fiber-optic network, it is also working with landlords as they ready their properties for the return of tenants. The reconstruction of telecom rooms – frequently relocated to upper floors – power, and access to those rooms are important steps in the process. As building owners and managers complete these steps, Verizon is rapidly connecting the newly laid fiber to the new electronic systems and turning up service.The steps these building owners are taking, in conjunction with the new fiber infrastructure from Verizon, will provide additional protection for the communications infrastructure in lower Manhattan in the event of future large-scale weather events."The work Verizon is doing now will make us a smarter, faster, better-connected city and region," said Mitchell Moss, Henry Hart Rice Professor of Urban Policy and Planning at New York University. "These repairs will actually lay the groundwork for a new era of growth and higher efficiency, which will benefit everyone."The company estimates that more than 70 percent of the affected buildings served by its Broad Street switching office, where copper services were most significantly damaged, now have fiber-optic cables and facilities serving them, with many buildings downtown already receiving full service.Copper cables were destroyed that served businesses and residences in the area south of Worth Street, from the East River to the Hudson River. These cables were rendered inoperable as the result of the unprecedented flooding, the mixture of salt water and diesel fuel in some buildings from compromised tanks that were in place to fuel generators, and the loss of air pressurization systems that help protect copper cables from water infiltration.Verizon estimates that it has already installed more than 5,000 miles of fiber in the dense lower Manhattan area, and more than 100 tons of copper cables have been removed from the area – 30 percent more than all the copper in the Statue of Liberty. More is being removed each day. The copper is being collected and recycled in an environmentally sensitive way, Verizon says."We are doing years' worth of work in just a few weeks, and doing it round the clock," said Martin Burvill, senior vice president of global operations for Verizon Enterprise Solutions. "We are keenly focused on transforming the communications infrastructure of lower Manhattan with this new architecture in a way that fully benefits our residential and business customers."Although this work is being done away from the public's view – in basements, manholes and in still-darkened office towers – it will have a visible and lasting impact by providing a critical part of the city with a network that is world-class, and built for the communications needs of the 21st century," Burvill said.
Dual-core optical fiber could enhance data processing
Optical fibers carry movies, messages, and music at the speed of light, but switching, routing, and buffering of data mostly rely on the use of relatively slow electronic components. Hoping to do away with these information speed bumps, a team of researchers has developed an elegant dual-core optical fiber that can perform the same functions just by applying a miniscule amount of mechanical pressure.The new nanomechanical fibers could greatly enhance data processing and also serve as sensors in electronic devices, say researchers at the University of Southampton in the UK. The work is described in the Optical Society of America’s open-access journal Optics Express, Vol. 20, Issue 28, pp. 29386-29394 (2012).“Nanomechanical optical fibers do not just transmit light like previous optical fibers,” said Wei H. Loh, deputy director of the EPSRC Centre for Innovative Manufacturing in Photonics and researcher at the Optoelectronics Research Centre, both at the University of Southampton. “Their internal core structure is designed to be dynamic and capable of precise mechanical motion. This mechanical motion, created by applying a tiny bit of pressure, can harness some of the fundamental properties of light to give the fiber new functions and capabilities.”The cores in the optical fiber are close enough to each other (less than 1 micron) to be optically coupled – a photon traveling down one core is physically affected by the presence of the nearby second core. By shifting the position of one of the cores by just a few nanometers, the researchers changed how strongly the light responded to this coupling effect. If the coupling effect is strong enough, the light immediately jumps from one fiber to the other.“Think of having a train traveling down a two-track tunnel and jumping the tracks and continuing along its way at the same speed,” explained Loh. The flexible suspension system of the fiber easily responds to the slightest bit of pressure, the researchers assert, bringing the two cores closer together or moving them apart, thereby controlling when and how the signals hop from one core to the other. The result is reproducing, for the first time, the function of an optical switch inside the actual fiber.This same capability may also enable optical buffering, which has been very hard to achieve, according to the researchers. “With our nanomechanical fiber structure, we can control the propagation time of light through the fiber by moving the two cores closer together, thereby delaying, or buffering, the data as light,” said Loh. Buffers are essential when multiple data streams arrive at a router at the same time; they delay one stream so another can travel freely.To create the new fibers, the researchers heated and stretched a specially shaped tube of optical glass with a hollow center containing two cores suspended from the inside wall (see image, courtesy of the University of Southampton). The fibers maintain this delicate structure as they are drawn and stretched to the desired thickness.According to the researchers, this is the first time that nanomechanical dual-core fibers have been fabricated directly. Other types of multicore fibers have been fabricated previously, but their cores are encased in glass and therefore are mechanically locked.“An implication of our work is that we would integrate more of these functions within the fiber backbone,” says Loh, “through the introduction of MEMS [micro-electro-mechanical systems] functionality in the fibers.”Loh and his colleagues also expect this introduction of MEMS functionality into the optical fiber to have implications in other fields, such as sensing. “Nanomechanical fibers could one day take the place of silicon-based MEMS chips, which are used in automobile sensors, video game controllers, projection displays, and other every-day applications,” observes Loh. Because the fibers are so sensitive to pressure and can be readily drawn to very long lengths, they also could be integrated into bridges, dams, and other buildings to signal subtle changes that could indicate structural damage.The next step of their research is to test the fibers at longer lengths and to enhance the precision with which they perform switching and other functions. The researchers hope that nanomechanical fibers could reach the market within the next three to five years.
Combining 40G DP-QPSK with 10G OOK channels on metro/regional networks
The advantages of dual-polarization quadrature phase-shift keying (DP-QPSK) modulation with coherent detection for long-haul and submarine channels are well known. Improved sensitivity and elimination of optical dispersion compensation result in considerable cost savings, as the number of amplifiers can be reduced and network design simplified. As demand for capacity continues to increase, carriers are now considering deployment of coherent technology in metropolitan and regional networks, where 40-Gbps links today are predominantly based on direct-detection differential phase-shift keying (DPSK) or differential QPSK (DQPSK).Metro/regional mesh networks are characterized by a large number of relatively short (10-80 km) spans, interconnected by ROADM switches, with optical amplifiers and dispersion compensation incorporated to give essentially zero loss and zero dispersion between nodes. Compared to DPSK and DQPSK, DP-QPSK coherent technology has distinct advantages as network speeds increase from 10 Gbps to 40 Gbps. DP-QPSK uses a symbol rate half that of DQPSK and one-quarter that of DPSK, and consequently has a much narrower spectrum. Additionally, DPSK and DQPSK often use RZ instead of NRZ, further broadening their spectra. The narrower spectrum of DP-QPSK results in less distortion for metro/regional networks with cascaded ROADMs.Metro networks are also trending to “colorless networks,” that is, networks without specific wavelengths assigned to individual add/drop ports.1 For colorless networks, the narrow spectrum of DP-QPSK can eliminate the need for a transmit filter when using a simple combiner instead of a more costly WDM multiplexer to combine wavelengths. With coherent detection, dropping wavelengths in a colorless network can be accomplished simply by tuning a local oscillator laser, instead of requiring a wavelength-selective switch. Eliminating such lossy optical components reduces the need for optical amplification, resulting in further cost savings.For all of the advantages of 40G coherent DP-QPSK signals in metro/regional applications, there is one hurdle that must be overcome when deploying this technology on legacy networks. Cross-phase modulation (XPM) can impair DP-QPSK signals when combined with 10G on/off-keyed (OOK) channels on fully dispersion compensated WDM links.2 Possible mitigation techniques include skipping channels to reduce XPM or assigning 10G OOK signals and 40G DP-QPSK channels to different bands, separated by guardbands. However, such methods waste valuable spectrum and reduce flexibility of network deployment. Others have proposed the use of more costly coherent binary PSK (BPSK), with an associated doubling of the spectrum required.Fortunately, there is a relatively simple method to deal with the impairments caused by XPM. Powerful forward error correction (FEC) codes at 40 Gbps, originally developed for submarine channels, can drive very high pre-FEC error rates essentially to zero. The high overhead of these codes is not problematic with DP-QPSK because of its relatively narrow spectrum. In fact, the high overhead can actually help alleviate XPM as it increases the baud rate difference between the 10G and 40G channels.2 These codes are commercially available today in Optical Transport Network (OTN) mapper/framer chips that are already deployed in many existing telecom systems.
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