Light waves transmit data with much greater speed than do electrical signals, says Qiaoqiang Gan, a Ph.D. candidate at Lehigh University in Bethlehem, Pa. If they are guided with sufficient precision inside the tiny circuits of an electronic chip, they can bring about applications in spectroscopy, sensing and medical imaging. And they can hasten the advent of faster all-optical telecommunication networks, in which light signals transmit and route data without needing to be converted to electrical signals and back.
To enable light waves to store and transmit data with optimal efficiency, engineers must learn to slow or stop light waves across the various regions of the spectrum.
Gan and his adviser, Filbert J. Bartoli, department chair of electrical and computer engineering, made a major contribution to this effort last year when they developed a graded metal grating structure capable of slowing or stopping terahertz (THz) light waves. The achievement, said Bartoli, "opened a door to the control of light waves on a chip" that could help reduce the size of optical structures, enabling them to be integrated at the nanoscale with electronic devices.
Gan and Bartoli reported their results in June in Physical Review Letters (PRL). Their article was coauthored by Yujie J. Ding, professor of electrical and computer engineering, and Zhan Fu, a Ph.D. candidate advised by Ding. The researchers are affiliated with Lehigh's Center for Optical Technologies.
Recently, Bartoli's team recorded a second major advance. Working again with Ding, they demonstrated that their grating structure could be scaled down in size to a dimension compatible with light waves in the telecommunications portion of the spectrum.
THz waves measure several hundred microns in length (1 micron is one-millionth of a meter) and are suitable for security applications. Wavelengths in the telecommunications range of the spectrum measure 1330 to 1550 nanometers (1 nm is one-billionth of a meter) and are suitable for optical communications.
The three researchers reported their progress in a second PRL article, titled "Rainbow Trapping and Releasing at Telecommunication Wavelengths." The article was published in the journal's Feb. 6 issue.
In the current article, the researchers also address a phenomenon called loss in metals, in which the metal materials of a chip, instead of simply propagating light, also absorb it and dissipate it as heat. Metal loss occurs more strongly with telecommunications light waves than with THz light waves.
To use trapped light waves for telecommunications, says Gan, it is necessary to release them from the grating structure. Gan and his colleagues accomplished this by covering the structure with dielectric materials.
"By tuning the temperature of the dielectric materials, we were able to change the optical properties of the metal grating structure," he said. "This in turn enabled the trapped light waves to be released."
The Lehigh researchers describe their structure as a "metallic grating structure with graded depths, whose dispersion curves and cutoff frequencies are different at different locations." In appearance, the grating resembles the pipes of a pipe organ arranged side by side and decreasing gradually in length from one end of the assembly to the other. The degree of grade in the grating can be tuned by altering the temperature and modifying the physical features on the surface of the structure.
The structure arrests the progress of light waves at multiple locations on the surface and at different frequencies. Previous researchers, Gan says, had been able "to slow down one single wavelength within a narrow bandwidth, but not many wavelengths over a wide spectrum."
Most of the initial work on this project has been theoretical, using mathematical equations and computer simulation. Bartoli's group has now moved to the next stage, which includes fabricating and characterizing the structures.
"It will be challenging," Gan says, "to achieve a grade of grating depths which range from very shallow to as much as 50 nanometers on a 200-nm substrate. To do this, we are using the focused ion beam milling facilities in the materials science and engineering department. We have already fabricated many structures and will now try to characterize the graded gratings with near-field scanning optical microscopy in Prof. Volkmar Dierolf's lab in the physics department.
"We are pursuing promising applications based on these structures. These include biosensing and bioimaging."
An article in the Feb. 14 issue of the British journal New Scientist said the results obtained by Bartoli's team "suggest that one day we might be able to slow down light long enough to store it as a 'rainbow' or colors – an advance that would revolutionize computing and telecommunication networks."
Light is stored for a few pico-seconds in the grating structure, the New Scientist article notes. But this, according to physicist Ortwin Hess of the University of Surrey in the United Kingdom, "is quite significant for many applications."
Wednesday, March 4, 2009
Tuesday, March 3, 2009
Its Urgent to get to Iraq's oil
International companies have waited years to tap into Iraq's vast oil wealth and now Iraqi officials are working feverishly to make that happen soon.
There is growing apprehension about the cost of rebuilding the country with the price of crude, the nation's major source of revenue, nearing five year lows. Iraq must produce more oil and it is foreign oil majors that have the wherewithal to do that. Iraq recently sweetened the terms: increasing ownership percentages for foreign oil companies and making it easier to meet production targets. But the government wants production to begin quickly. The Associated Press reports that the country is now requiring any oil company that signs a contract to begin operating in the country within six months. Though low crude prices have not diminished interest in Iraqi oil, negotiations between the two sides have lingered over security concerns and the absence of a national law regulating Iraq's oil industry.
Prime Minister Al-Maliki said the government would form a committee to oversee development of the country's devastated oil industry and increase exports. He said Iraq must also work quickly to diversify its economy to cushion future spending from a drop in oil prices. But right now, the onus is on ramping up oil production, and fast. As violence has declined in Iraq, so to has the price of oil worldwide. The Iraqi government relies on oil sales for more than 90-percent of its revenue. Falling oil prices have reduced the projected 2009 budget from $79 billion to $64 billion and have forced Iraqi officials to slash rebuilding plans by 40-percent. U.S. officials have repeatedly warned any significant slowdown in reconstruction could imperil the security gains that have reduced violence in Iraq to a five-year low.
It remains to be seen how international firms will respond to Iraq's new carrot and stick approach. Iraq hopes the contracts-scheduled to be awarded in June-will boost oil production by 1.5 million barrels per day within four years. Iraq currently produces about 2.4 million barrels daily. The companies are bidding on long-term service agreements that would pay them fees depending on production levels.
There is growing apprehension about the cost of rebuilding the country with the price of crude, the nation's major source of revenue, nearing five year lows. Iraq must produce more oil and it is foreign oil majors that have the wherewithal to do that. Iraq recently sweetened the terms: increasing ownership percentages for foreign oil companies and making it easier to meet production targets. But the government wants production to begin quickly. The Associated Press reports that the country is now requiring any oil company that signs a contract to begin operating in the country within six months. Though low crude prices have not diminished interest in Iraqi oil, negotiations between the two sides have lingered over security concerns and the absence of a national law regulating Iraq's oil industry.
Prime Minister Al-Maliki said the government would form a committee to oversee development of the country's devastated oil industry and increase exports. He said Iraq must also work quickly to diversify its economy to cushion future spending from a drop in oil prices. But right now, the onus is on ramping up oil production, and fast. As violence has declined in Iraq, so to has the price of oil worldwide. The Iraqi government relies on oil sales for more than 90-percent of its revenue. Falling oil prices have reduced the projected 2009 budget from $79 billion to $64 billion and have forced Iraqi officials to slash rebuilding plans by 40-percent. U.S. officials have repeatedly warned any significant slowdown in reconstruction could imperil the security gains that have reduced violence in Iraq to a five-year low.
It remains to be seen how international firms will respond to Iraq's new carrot and stick approach. Iraq hopes the contracts-scheduled to be awarded in June-will boost oil production by 1.5 million barrels per day within four years. Iraq currently produces about 2.4 million barrels daily. The companies are bidding on long-term service agreements that would pay them fees depending on production levels.
Monday, March 2, 2009
Improved Solar Energy Performance with Plastic Solar Cells
The University of Alberta and the National Research Council's National Institute (NINT) for Nanotechnology have engineered an approach that is leading to improved performance of plastic solar cells (hybrid organic solar cells). The development of inexpensive, mass-produced plastic solar panels is a goal of intense interest for many of the world's scientists and engineers because of the high cost and shortage of the ultra-high purity silicon and other materials normally required.
Plastic solar cells are made up of layers of different materials, each with a specific function, called a sandwich structure. Jillian Buriak, a professor of chemistry at the U of A, NINT principal investigator and member of the research team, uses a simple analogy to describe the approach: "Consider a clubhouse sandwich, with many different layers. One layer absorbs the light, another helps to generate the electricity, and others help to draw the electricity out of the device. Normally, the layers don't stick well, and so the electricity ends up stuck and never gets out, leading to inefficient devices. We are working on the mayonnaise, the mustard, the butter and other 'special sauces' that bring the sandwich together, and make each of the layers work together. That makes a better sandwich, and makes a better solar cell, in our case".
After two years of research, these U of A and NINT scientists have, by only working on one part of the sandwich, seen improvements of about 30 per cent in the efficiency of the working model. Michael Brett, professor of electrical and computer engineering, NINT principal investigator and member of the research team is optimistic: "our team is so incredibly cross-disciplinary, with people from engineering, physics and chemistry backgrounds all working towards this common goal of cheap manufacturable solar cells. This collaboration is extremely productive because of the great team with such diverse backgrounds, [although] there is still so much more for us to do, which is exciting." This multidisciplinary approach, common at the National Institute for Nanotechnology, brings together the best of the NRC and the University of Alberta.
The team estimates it will be five to seven years before plastic solar panels will be mass produced but Buriak adds that when it happens solar energy will be available to everyone. She says the next generation of solar technology belongs to plastic.
"Plastic solar cell material will be made cheaply and quickly and in massive quantities by ink jet-like printers."
Plastic solar cells are made up of layers of different materials, each with a specific function, called a sandwich structure. Jillian Buriak, a professor of chemistry at the U of A, NINT principal investigator and member of the research team, uses a simple analogy to describe the approach: "Consider a clubhouse sandwich, with many different layers. One layer absorbs the light, another helps to generate the electricity, and others help to draw the electricity out of the device. Normally, the layers don't stick well, and so the electricity ends up stuck and never gets out, leading to inefficient devices. We are working on the mayonnaise, the mustard, the butter and other 'special sauces' that bring the sandwich together, and make each of the layers work together. That makes a better sandwich, and makes a better solar cell, in our case".
After two years of research, these U of A and NINT scientists have, by only working on one part of the sandwich, seen improvements of about 30 per cent in the efficiency of the working model. Michael Brett, professor of electrical and computer engineering, NINT principal investigator and member of the research team is optimistic: "our team is so incredibly cross-disciplinary, with people from engineering, physics and chemistry backgrounds all working towards this common goal of cheap manufacturable solar cells. This collaboration is extremely productive because of the great team with such diverse backgrounds, [although] there is still so much more for us to do, which is exciting." This multidisciplinary approach, common at the National Institute for Nanotechnology, brings together the best of the NRC and the University of Alberta.
The team estimates it will be five to seven years before plastic solar panels will be mass produced but Buriak adds that when it happens solar energy will be available to everyone. She says the next generation of solar technology belongs to plastic.
"Plastic solar cell material will be made cheaply and quickly and in massive quantities by ink jet-like printers."
Sunday, March 1, 2009
Your Laser Printer is Dangerous!!! Beware of It
The identity and origin of tiny, potentially hazardous particles emitted from common laser printers have been revealed by a new study at Queensland University of Technology.
Professor Lidia Morawska from QUT's International Laboratory for Air Quality and Health led the study which aimed to answer questions raised by earlier findings that almost one third of popular laser printers emitted large numbers of ultrafine particles.
These tiny particles are potentially dangerous to human health because they can penetrate deep into the lungs.
Professor Morawska said the latest study found that the ultrafine particles formed from vapours which are produced when the printed image is fused to the paper.
"In the printing process, toner is melted and when it is hot, certain compounds evaporate and those vapours then nucleate or condense in the air, forming ultrafine particles," she said.
"The material is the result of the condensation of organic compounds which originate from both the paper and hot toner."
The study compared a high-emitting printer with a low-emitting printer and found that there were two ways in which printers contributed to the formation of these particles.
"The hotter the printer gets, the higher the likelihood of these particles forming, but the rate of change of the temperature also contributes," Professor Morawska said.
"The high emitting printer operated at a lower average temperature, but had rapid changes in temperature, which resulted in more condensable vapour being emitted from the printer.
"The printer with better temperature control emitted fewer particles."
Professor Morawska said this research provided information which would help consumers better understand the risks of laser printers and would help the printer industry to design low or no emission printers.
Professor Lidia Morawska from QUT's International Laboratory for Air Quality and Health led the study which aimed to answer questions raised by earlier findings that almost one third of popular laser printers emitted large numbers of ultrafine particles.
These tiny particles are potentially dangerous to human health because they can penetrate deep into the lungs.
Professor Morawska said the latest study found that the ultrafine particles formed from vapours which are produced when the printed image is fused to the paper.
"In the printing process, toner is melted and when it is hot, certain compounds evaporate and those vapours then nucleate or condense in the air, forming ultrafine particles," she said.
"The material is the result of the condensation of organic compounds which originate from both the paper and hot toner."
The study compared a high-emitting printer with a low-emitting printer and found that there were two ways in which printers contributed to the formation of these particles.
"The hotter the printer gets, the higher the likelihood of these particles forming, but the rate of change of the temperature also contributes," Professor Morawska said.
"The high emitting printer operated at a lower average temperature, but had rapid changes in temperature, which resulted in more condensable vapour being emitted from the printer.
"The printer with better temperature control emitted fewer particles."
Professor Morawska said this research provided information which would help consumers better understand the risks of laser printers and would help the printer industry to design low or no emission printers.
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