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To prove their concept, the researchers used a three-dimensional, microwave- scale photonic crystal constructed from layered alumina rods and containing a full bandgap - a wavelength range in which electromagnetic waves cannot transmit. Just as electronic bandgaps prevent electrons within a certain energy range from passing through a semiconductor, photonic crystals create photonic bandgaps that confine light of certain wavelengths.
The add-drop filter created by the Ames Laboratory team contains an entrance waveguide and an exit waveguide created by removing rod segments from the layered photonic crystal. A one-rod segment separates the two waveguides. (A waveguide is a system or material that can confine and direct electromagnetic waves.) A defect cavity is located one unit cell above the waveguide layer. The waveguides can communicate through the cavity, allowing a specific wavelength frequency to be selected from the input waveguide and transmitted to the output waveguide, excluding other input frequencies and resulting in near 100 percent efficiency for the drop frequencies.
The idea of using photonic crystals for add-drop filters is not new. Since the mid 1990s, many groups worldwide have been working to develop the technology with two-dimensional photonic crystals.
"It works," Biswas said, "but there is loss of some intensity to the end user because 2-D photonic crystals don't confine the light completely. For example, in a phone conversation, the voices would dim out. But with 3-D photonic crystal add-drop filters, the communication would be clear."
Although Biswas, Kohli, Tuttle and
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| Contact: Saren Johnston sarenj@ameslab.gov 515-294-3474 DOE/Ames Laboratory Source:Eurekalert |