Search
Menu
PI Physik Instrumente - Revolution In Photonics Align LW LB 3/24

Going Negative in the Visible

Facebook X LinkedIn Email
Several positives, including a superlens, could result from negative refraction in the visible.

Hank Hogan

Negative refraction — the recently realized opposite of positive refraction — is of interest because, among other applications, it promises a superlens that can image far below the diffraction limit. To date, negative refraction has been demonstrated for various wavelengths but not seen.

Now researchers from California Institute of Technology in Pasadena have achieved negative refraction that is readily visible, with a beam emerging from their structure at a negative angle. That direct visualization is appropriate, said Henri J. Lezec, a visiting research associate at Caltech and a research director at the Centre National de la Recherche Scientifique in Paris. “To me, refraction is really about bending light.”

PRNegative_Fig-1_Slide1.jpg

Using waveguides, researchers achieved negative refraction in the visible region. Light injected in one slot traveled through a prism-shaped waveguide, with only a single mode appearing on the other end (left). In the red, the result was positive refraction (top right). In the green, the result was negative refraction (bottom right). As seen in the schematic of the device (left), the negative refraction caused a negative angle of deflection, making a direct geometric visualization of the effect. Courtesy of Henri J. Lezec, California Institute of Technology and Centre National de la Recherche Scientifique.


Meadowlark Optics - Building system MR 7/23
The researchers used suitably designed and carefully constructed metal-insulator-metal waveguides in which the effect of surface plasmons — electron oscillations found at the metal-dielectric interface — makes some transmission modes behave as if the material had negative refraction.

Waveguide construction

For their demonstration, they fabricated waveguides with silicon nitride dielectric cores 50 to 150 nm thick, cladding the core with silver on one side and gold on the other. Prism-shaped segments of these waveguides, which were predicted to have negative refraction in the blue-green region of the visible, were embedded in a thick waveguide that consisted of a 500-nm silicon nitride core clad with silver and that was predicted to have positive refraction throughout the visible wavelength range.

Lezec noted that the waveguide construction was helped because the researchers used a focused ion beam system from FEI Corp. of Hillsboro, Ore., to mill the dielectric material. The device allowed them to work on freestanding dielectric membranes and enabled them to have a variety of prism core thicknesses on the same sample. “We did a matrix, and we found a window where it worked,” Lezec said.

Once the structure was complete, the investigators injected a beam into it through a subwavelength-width input slot on one side. They characterized the angle of refraction of the beam after it emerged, visualizing the projected spot with an optical microscope. At 685 nm, the refractive index was small and positive. At 514 and 476 nm, it was –5 and –1, respectively.

Science, April 20, 2007, pp. 430-432.

Published: June 2007
Glossary
nano
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
Microscopynanonegative refractionphotonicspositive refractionResearch & Technologywavelengths

We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.