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Nanodevice Increases Optical Networks'Bandwidth

MIT scientists have developed a tiny device that promises to overcome a significant problem in photonics and yield less expensive, higher-performance, more useful optical networks.

The researchers' optical add/drop multiplexer (OADM) adjusts the different directional polarizations of the light waves that optical fibers deliver so that all of the waves have the same polarization. Optical networks could then use all the light and thus provide stronger signals and higher bandwidth.


Figure    Researchers have developed an optical add/drop multiplexer (OADM) that promises to yield less expensive, higher-performance optical networks. Wavelengths within a light beam passing through optical fiber typically become polarized horizontally in some cases and vertically in others, making it difficult for an optical system to use all the light. The OADM uses a splitter to divide the wavelengths into the two polarizations and a rotator to turn the vertically polarized beam to a horizontal orientation. It passes the two sets of beams through identical filters, picks off the wavelengths desired for transmission, and recombines them.

Different wavelengths within a light beam passing through optical fiber typically become polarized horizontally in some cases and vertically in others, depending on factors such as the temperature within the link, explained Rüdiger Paschotta, CEO of RP Photonics Consulting.

The inability to process the differently polarized light would prevent the optical systems from handling all of the signals with the full potential bandwidth. It could also make signal amplification or detection inefficient, causing transmission errors, fade, or interruptions, noted MIT professor Erich Ippen, who worked on the OADM project.

The approach commonly used to cope with this problem is to run the sets of laser beams through two devices, each processing light with a different polarization. However, this is costly, adds size and complexity to systems, and makes the manufacturing process more complicated, according to Ippen.

The MIT team's nanoscale OADM uses a splitter to divide all of the wavelengths into those with a horizontal and those with a vertical polarization. It then uses a rotator to turn the vertically polarized beam to a horizontal orientation.

The system passes the two sets of beams through identical filters and picks off the specific wavelength desired for transmission. It then recombines the two sets of wavelengths and sends them on their way.

Using all of the light passing through fiber, regardless of the polarization, would increase an optical system's bandwidth and performance and enable more network functionality.

The tiny OADM can be made of silicon. Manufacturers thus can build them as part of a processor via the standard silicon-chip-production process, rather having to assemble them by hand as part of a separate structure, which is more expensive and time-consuming.

Paschotta said, "The design and the fabrication of the relatively complex device is a significant achievement, demonstrating for the first time a polarization-independent photonic integrated circuit based on polarization-dependent components."

There hasn't been economic pressure in the past couple of years to improve optical networks' performance because they have had more than enough bandwidth for their applications, Ippen said. However, he noted, communications demands—specifically increased transmissions of large image and video files—are growing.

IBM Demonstrates Fast Memory-Chip Technology

Linda Dailey Paulson

IBM researchers have developed an embedded dynamic RAM technology that will enable manufacturers to put DRAM directly onto a chip and thereby increase single-core and multicore microprocessors' performance.

The development promises to help move large amounts of data quickly within chips to achieve faster performance, said Subu Iyer, IBM's director of 45-nanometer development.

Because multiple cores take up more space on a chip and leave less room for memory, multicore processors will particularly benefit from eDRAM, Iyer noted.

eDRAM is a simple, volatile, capacitor-based cache memory unit that improves overall performance by keeping data inside a microprocessor for quick access by the chip. This reduces the time the chip must wait for data to process.

The technology will reduce memory cycle times—which measure the speed at which a processor can access data from memory—to less than two nanoseconds, about 10 percent the amount yielded by the off-the-shelf DRAM that PCs use, according to Iyer.

Regular DRAM usually comes as an external module, which increases chips' data-access time and thus memory-cycle times.

Typically, on-chip memory has used fast, transistor-based static RAM. eDRAM can also be used on chips, but it offers more data density and is smaller, less expensive, and more power-efficient than SRAM.

With eDRAM, chip makers could place more memory on a chip than SRAM; provide the same amount of memory as SRAM but leave more space on the chip for another core; or make smaller, less expensive chips with the same capacity as those using SRAM.

"Processors have long had embedded RAM of some sort for use in high-speed caches," said Jonathan Eunice, president and principal analyst of market research firm Illuminata. "The advances here are that eDRAM enjoys DRAM's large capacity and lower power draw but also tight integration with the processor."

IBM says its improved eDRAM technology should be ready for commercial release next year.

According to Iyer, the company will use the technology first in high-performance microprocessors for corporate computing applications, which stand to gain more from the greater performance, and then in processors for demanding consumer applications such as mobile computing and video games.

Eventually, he said, IBM will explore potential improvements such as stacking eDRAM on chips to further increase performance.

News Briefs written by Linda Dailey Paulson, a freelance technology writer based in Ventura, California. Contact her at

Company Develops Handheld with Flexible Screen

A Dutch display technology firm has developed what apparently is the first handheld device with a large, flexible, roll-out display that could be used like a PDA or even an electronic book.

Having a big screen that can roll up into a small device enables the viewing of content—such as complex Web pages—currently not practical for handhelds, said Thomas van der Zijden, vice president of marketing for Polymer Vision, which manufactures the device.

The flexible black-and-white display also consumes less energy than standard handheld-device screens and thus would enable batteries to last longer, he noted.

By the end of this year, Telecom Italia Mobile plans to sell the device, which is code-named Readius but which will be marketed in Italy as Librofonino. It will play podcasts; have Internet access via Wi-Fi; and display RSS (really simple syndication) feeds, e-books, e-mail, and PDF and text files.

The 100mm × 57mm × 22mm device's electrophoretic reflective display is 127 mm wide, said van der Zijden.

In an electrophoretic display, he explained, tiny black and white particles are contained in small capsules with clear liquid. This material is considered electrophoretic ink. Depending on the applied electric field, he said, either the black or white particles move to the front or back, thereby changing the display's appearance.

The display is very readable because its contrast is more like that of a sheet of paper than that of a typical black-and-white screen, noted van der Zijden.

Polymer Vision builds the display using a 25-micron-thick flexible, organic plastic substrate. The substrate uses thin-film-transistor technology, in which a transistor deposited on the substrate controls each visual element.


Figure    A Dutch company has developed a small device with a large, flexible, roll-out display that lets users look at content not easily viewable on most handhelds.

The display's electronics are also organic and flexible and can be deposited at the low temperatures necessary to keep the plastic substrate from melting. This creates a screen that can roll into or out of a host device.

"Once the picture is established with electrophoretic ink, no battery power is required to keep the image on the display, unlike LCD displays that require continuous refresh of even a still image," van der Zijden explained. This saves energy.

The display is thin and reflects incoming light back up through the screen and thus doesn't need backlighting. This also reduces power consumption.

Polymer Vision is working on future versions that could show color and video, noted van der Zijden.

"This is the first commercial rollout display of any kind. Any material on the Internet will be viewable. It is a significant technological event," said Barry Young, senior vice president of market research firm DisplaySearch. "However, the resolution is limited and the display response time is slow, so it won't be a very good device for reading a book."

And, he added, without an additional light source, it won't be easily readable in dark environments.

Startup Uses Sensors to Save Houseplants

There is a new consumer technology designed to help people who can't seem to keep their plants from dying.

PlantSense is a sensor in the form of a stake designed to monitor and report on microclimate data—such as light, humidity, and temperature—at locations indoors or outdoors.

Company founder and CEO Matt Glenn used his knowledge of sensors gained while working at Cisco Systems to develop PlantSense technology.

The PlantSense Microclimate Probe, which can be pushed up to four inches into soil, contains a microcontroller, as well as light, humidity, temperature, and soil-moisture sensors.

The microcontroller, with the stored information, can be connected to PC's USB port, said PlantSense vice president of engineering David Wilkins.

When attached, the controller launches a browser and links to PlantSense's Web site, which analyzes the data and recommends the types of plants best for the microclimate, the best way to care for plants in such conditions, the best places to move plants currently in the wrong microclimate, and possible owner mistakes such as overwatering.

This is very valuable for inexperienced growers, particularly those with challenging plants such as orchids, African violets, or tomatoes, according to Wilkins.

The PlantSense stake is reusable and has a button-cell-battery life of about a year, he said.

The company is finalizing the design specifications, as well as software components. It plans to begin beta testing later this year and to release the product in time for the 2007 winter holiday gift-buying season.

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