New metallic grate may help integrate optical structures with electronic devices at nano-scale

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Washington, June 28 : Lehigh University researchers say that they have innovated a "metallic grating structure with graded depths" which has the unique ability to arrest the progress of terahertz (THz) light waves at multiple locations on its surface, and also at different frequencies (colours).

"Previous researchers have reported the ability to slow down one single wavelength at one narrow bandwidth. We've succeeded in actually stopping THz waves at different positions for different frequencies," says Qiaoqiang Gan, a Ph.D. candidate in electrical engineering.

"Our next goal is to develop structures that extend this capability to the near infrared and visible ranges of the spectrum, where optical communications signals are transferred," the researcher adds.

He has revealed that the metal grate his team has created 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.

He says that the degree of grade in the grate can be "tuned" by altering the temperature, and modifying the physical features on the surface of the structure.

Similarly, he adds, temperature and surface structure can also be adjusted to trigger the release of the light signals after they have been slowed or trapped.

"The separation between the adjacent localized frequencies can be tuned freely by changing the grade of the grating depths. And the propagation characteristics of the trapped surface modes can be controlled by the surface geometry," Gan says.

The researchers say that the significance of this work lies in the fact that the new grating structure may help scientists and engineers reduce the size of optical structures so that they can be integrated at the nano-scale with electronic devices, a task that has been unaccomplished thus far because light is more difficult to control at the nano-scale due to the natural limits on its diffraction.

"Our grating structure can also be scaled to telecommunications frequencies for future possible applications in integrated optical and nano-photonic circuits," says Professor Filbert Bartoli, Gan's advisor and chair of the department of electrical and computer engineering.

"This might even help us realize such novel applications as a spectrometer integrated on a chip for chemical diagnostics, spectroscopy and signal processing applications," Bartoli adds.

Gan, who has used computer modelling to develop and test the grating structure, says that physical experiments may begin soon.

A research article about the innovation of the new metallic grating structure has been published in Physical Review Letters (PRL), a publication of the American Physical Society.


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