Nanoplasmonics: Towards efficient light harvesting

January 7, 2014

The control of light is vital to many applications, including imaging, communications, sensing, cancer treatment, and even welding processes for automobile parts. Transformation optics is an emerging field that has revolutionized our understanding of how to control light by constituting an effectively curved electromagnetic space. This revolutionary strategy not only revisits the fundamental physics of light-matter interactions, but also renders trivial the design of optical functions that may otherwise be difficult or virtually impossible, such as an "invisibility cloak," which could only previously be found in science fiction. When compared with ray optics, the new transformation optics technique provides a picture that is equally intuitive, but that is much more accurate in its description of the wave nature of light by using the electric and magnetic field lines as its basis.

Therefore, the validity of this method is not restricted to the macroscopic regime, but can also be extended to the subwavelength scale. In a recent review paper published by SCIENCE CHINA Information Sciences, Yu Luo and colleagues from Imperial College London illustrate how the general capabilities of the transformation optics technique can be used to treat the subwavelength fields that occur in plasmonic systems and review the latest developments in transformation optics as applied to nanophotonics.

In plasmonics, metallic structures with sharp corners can trap light into nanometric volumes, thus giving rise to strong near-field enhancements. This effect can be used to detect single molecules, generate high harmonic signals, and even improve absorption in photovoltaic devices. Further developments using these techniques need to be guided by accurate and versatile theoretical modeling. However, modeling of this type can be difficult, because various aspects associated with the sharp plasmonic structures can hinder provision of accurate and convenient solutions to the problem at hand. First, the size of the sharp metallic point structure is normally much smaller than that of the device overall, which makes it difficult to create meshes for numerical simulations. Second, the strong contrast in the dielectric functions at the metal-dielectric interfaces leads to slow convergence of the field expansions.

Yu Luo and colleagues deploy the theory of transformation optics to circumvent these problems. Their idea is to transform a complex plasmonic system with little intrinsic geometrical symmetry into a canonical structure with translational or rotational symmetry, which is then relatively easy to study using conventional theory. For example, two touching nanowires can be transformed into two flat metal surfaces that are separated by a gap, and a sharp metal edge can be related to a periodic array of metal slabs. Other structures that can be studied using transformation optics include pairs of metallic nanospheres, asymmetric core-shell structures and rough metal surfaces. In fact, using transformation optics techniques, we could reverse engineer the optical properties of complex plasmonic nanostructures and redesign these structures based on the requirements of the desired applications.

Practical issues with the realization of plasmonic devices, such as the effects of edge rounding at sharp boundaries on the local field enhancement and resonance properties, can also be considered theoretically using transformation optics and provide useful guidance for the fabrication of these devices. In particular, the necessary conditions are highlighted for both broadband light absorption effects and large field enhancements. Experimental evidence for phenomena that have been predicted by transformation optics has also been reviewed, indicating potential applications in biosensing and broadband solar photovoltaics. These studies demonstrate the accuracy and versatility of methods and are expected to encourage more researchers to enter this field.

Explore further: Harry Potter-style invisibility cloaks: A real possibility next Christmas?

More information: Luo Y, Zhao R K, Fernandez-Dominguez A I, et al. Harvesting light with transformation optics. Sci China Inf Sci, 2013, 56(12): 120401(13). … abstract512908.shtml

Related Stories

Transformation optics make a U-turn for the better

July 1, 2010

( -- Berkeley researchers have combined the scientific fields of transformation optics and plasmonics to demonstrate that with only moderate modifications of the dielectric component of a metamaterial, the physical ...

Researcher construct invisibility cloak for thermal flow

May 8, 2013

By means of special metamaterials, light and sound can be passed around objects. KIT researchers now succeeded in demonstrating that the same materials can also be used to specifically influence the propagation of heat. A ...

Recommended for you

Two teams independently test Tomonaga–Luttinger theory

October 20, 2017

(—Two teams of researchers working independently of one another have found ways to test aspects of the Tomonaga–Luttinger theory that describes interacting quantum particles in 1-D ensembles in a Tomonaga–Luttinger ...

Using optical chaos to control the momentum of light

October 19, 2017

Integrated photonic circuits, which rely on light rather than electrons to move information, promise to revolutionize communications, sensing and data processing. But controlling and moving light poses serious challenges. ...

Black butterfly wings offer a model for better solar cells

October 19, 2017

(—A team of researchers with California Institute of Technology and the Karlsruh Institute of Technology has improved the efficiency of thin film solar cells by mimicking the architecture of rose butterfly wings. ...

Terahertz spectroscopy goes nano

October 19, 2017

Brown University researchers have demonstrated a way to bring a powerful form of spectroscopy—a technique used to study a wide variety of materials—into the nano-world.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.