Using Spectral Cloaking for Object Invisibility

An example of when science fiction becomes science fact. This advance could be used in many different ways, including in digital security, with out of sight possibly meaning out of mind.

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Researchers and engineers have long sought ways to conceal objects by manipulating how light interacts with them. A new study offers the first demonstration of invisibility cloaking based on the manipulation of the frequency (color) of light waves as they pass through an object, a fundamentally new approach that overcomes critical shortcomings of existing cloaking technologies.

The approach could be applicable to securing data transmitted over fiber optic lines and also help improve technologies for sensing, telecommunications and information processing, researchers say. The concept, theoretically, could be extended to make 3D objects invisible from all directions; a significant step in the development of practical invisibility cloaking technologies.

Most current cloaking devices can fully conceal the object of interest only when the object is illuminated with just one color of light. However, sunlight and most other light sources are broadband, meaning that they contain many colors. The new device, called a spectral invisibility cloak, is designed to completely hide arbitrary objects under broadband illumination.

The spectral cloak operates by selectively transferring energy from certain colors of the light wave to other colors. After the wave has passed through the object, the device restores the light to its original state. Researchers demonstrate the new approach in Optica, The Optical Society’s journal for high impact research.

“Our work represents a breakthrough in the quest for invisibility cloaking,” said José Azaña, National Institute of Scientific Research (INRS), Montréal, Canada. “We have made a target object fully invisible to observation under realistic broadband illumination by propagating the illumination wave through the object with no detectable distortion, exactly as if the object and cloak were not present.”

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While the new design would need further development before it could be translated into a Harry Potter-style, wearable invisibility cloak, the demonstrated spectral cloaking device could be useful for a range of security goals. For example, current telecommunication systems use broadband waves as data signals to transfer and process information. Spectral cloaking could be used to selectively determine which operations are applied to a light wave and which are “made invisible” to it over certain periods of time. This could prevent an eavesdropper from gathering information by probing a fiber optic network with broadband light.

The overall concept of reversible, user-defined spectral energy redistribution could also find applications beyond invisibility cloaking. For example, selectively removing and subsequently reinstating colors in the broadband waves that are used as telecommunication data signals could allow more data to be transmitted over a given link, helping to alleviate logjams as data demands continue to grow. Or, the technique could be used to minimize some key problems in today’s broadband telecommunication links, for example by reorganizing the signal energy spectrum to make it less vulnerable to dispersion, nonlinear phenomena and other undesired effects that impair data signals.

Too Much Time in Dimly Lit Rooms May Decrease Intelligence, Neuroscience Research Finds

There’s a lot that could be said about this and the structural effects from it.

Spending too much time in dimly lit rooms and offices may actually change the brain’s structure and hurt one’s ability to remember and learn, indicates groundbreaking research by Michigan State University neuroscientists.

The researchers studied the brains of Nile grass rats (which, like humans, are diurnal and sleep at night) after exposing them to dim and bright light for four weeks. The rodents exposed to dim light lost about 30 percent of capacity in the hippocampus, a critical brain region for learning and memory, and performed poorly on a spatial task they had trained on previously.

The rats exposed to bright light, on the other hand, showed significant improvement on the spatial task. Further, when the rodents that had been exposed to dim light were then exposed to bright light for four weeks (after a month-long break), their brain capacity — and performance on the task — recovered fully.

The study, funded by the National Institutes of Health, is the first to show that changes in environmental light, in a range normally experienced by humans, leads to structural changes in the brain. Americans, on average, spend about 90 percent of their time indoors, according to the Environmental Protection Agency.

“When we exposed the rats to dim light, mimicking the cloudy days of Midwestern winters or typical indoor lighting, the animals showed impairments in spatial learning,” said Antonio “Tony” Nunez, psychology professor and co-investigator on the study. “This is similar to when people can’t find their way back to their cars in a busy parking lot after spending a few hours in a shopping mall or movie theater.”

Nunez collaborated with Lily Yan, associate professor of psychology and principal investigator on the project, and Joel Soler, a doctoral graduate student in psychology. Soler is also lead author of a paper on the findings published in the journal Hippocampus.

Soler said sustained exposure to dim light led to significant reductions in a substance called brain derived neurotrophic factor — a peptide that helps maintain healthy connections and neurons in the hippocampus — and in dendritic spines, or the connections that allow neurons to “talk” to one another.

“Since there are fewer connections being made, this results in diminished learning and memory performance that is dependent upon the hippocampus,” Soler said.

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The project could have implications for the elderly and people with glaucoma, retinal degeneration or cognitive impairments.

“For people with eye disease who don’t receive much light, can we directly manipulate this group of neurons in the brain, bypassing the eye, and provide them with the same benefits of bright light exposure?” Yan said. “Another possibility is improving the cognitive function in the aging population and those with neurological disorders. Can we help them recover from the impairment or prevent further decline?”