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Meta-transmitarray offers unprecedented control of light on subwavelength scales

Posted on May 31, 2013
(a) (Left) A basic building block of the metasurface made of silicon and aluminum-doped zinc oxide, and (right) a meta-transmitarray made of three stacked metasurfaces. (b) Graph showing the degrees of freedom necessary to independently control the phase of the transmission coefficient while minimizing reflection. (c) Amplitude and (d) phase of the transmission coefficient variation, with the eight circles in (d) indicating eight different configurations used to cover almost 360° of phase shift. Credit: Monticone, et al. American Physical Society ©2013

(a) (Left) A basic building block of the metasurface made of silicon and aluminum-doped zinc oxide, and (right) a meta-transmitarray made of three stacked metasurfaces. (b) Graph showing the degrees of freedom necessary to independently control the phase of the transmission coefficient while minimizing reflection. (c) Amplitude and (d) phase of the transmission coefficient variation, with the eight circles in (d) indicating eight different configurations used to cover almost 360° of phase shift. Credit: Monticone, et al. American Physical Society ©2013

The ability to guide, bend and focus light at the nanoscale is a highly sought-after goal in the field of nano-optics. Precise and efficient light control has direct applications in solar cells, holography, nanoscale signal processing, CMOS cameras, and many other areas. In a recent study, a team of engineers has proposed a new technique for controlling light at deeply subwavelength scales using a thin stack of patterned surfaces that the engineers call a “meta-transmitarray.” The underlying physics of the new concept is very different from any conventional lens and offers greatly improved efficiency and flexibility for manipulating light transmission at the nanoscale.

 

The researchers, Francesco Monticone, Nasim Mohammadi Estakhri, and Assistant Professor Andrea Alù at The University of Texas at Austin, have published their paper on the meta-transmit-array concept in a recent issue of Physical Review Letters, and their work has been selected as an “Editor’s suggestion.”

On large scales, light can be controlled in a fairly straightforward way by using conventional dielectric lenses. But since a dielectric lens’ properties are dependent on its thickness, these lenses are generally too thick to work well for controlling light at subwavelength scales, preventing their integration into nanophotonic and optoelectronic systems. At radio frequencies, one alternative to dielectric lenses for achieving subwavelength wave control is represented by transmitarrays, which are made of ultrathin sheets called frequency selective surfaces. These surfaces can be locally modeled with circuit concepts, and can shift the phase of incoming waves at will when combined in transmitarrays. So far, transmitarrays have been demonstrated only at radio frequencies.

In the new study, the researchers have integrated the concepts of transmitarrays and metamaterials, or more precisely, metasurfaces, which are the two-dimensional version of metamaterials. While bulk metamaterials are intriguing for their exotic, engineered properties that are not found in nature, they are difficult to fabricate. On the other hand, metasurfaces are planarized versions of metamaterials, with equally intriguing properties, but much easier to fabricate. Previous research has suggested that metasurfaces may be used as planar lenses to extend the concept of frequency selective surfaces beyond radio frequencies to optical frequencies, but the proposed designs had limited efficiency and applicability.

Read more at: Phys.org

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