New mirror reflects light differently than conventional mirrors

November 14, 2017 by Lisa Zyga feature
When a regular mirror reflects circularly polarized light, it reverses the spin state of the light. In contrast, the chiral meta-mirror preserves one of the two spin states when reflecting circularly polarized light, while absorbing the other spin state. Credit: Kang et al. ©2017 American Chemical Society

(Phys.org)—Researchers have designed a new type of mirror that reflects light in a completely different way than conventional mirrors do. The new mirror, called a chiral meta-mirror, has potential applications for information processing with light, next-generation 3-D movies, and other technologies that manipulate light in novel ways.

The researchers, led by Wenshan Cai at the Georgia Institute of Technology, have published a paper on the chiral meta- in a recent issue of Nano Letters.

The unconventional reflective properties of the new mirror arise from the way in which the mirror responds to that is circularly polarized. Light waves are composed of electric and magnetic fields, and when the electric field travels slightly behind the magnetic field or vice versa, the light wave moves along a helical path through time, and this is called circularly polarized light. Most of the light around us, such as light from the sun and lightbulbs, is unpolarized but can become polarized by passing through a polarization filter.

A circularly polarized light wave can travel in either a clockwise (right) or counterclockwise (left) fashion, which is determined by an intrinsic physical property of light called the and, consequently, is called the spin state of light. The main difference between the new mirror and conventional mirrors is how each responds to the spin states of circularly polarized light.

When a circularly polarized light beam reaches a conventional mirror, the mirror reverses the beam's spin state, so that the light it reflects back out has the opposite spin as the light that enters. For many applications, this property does not pose any problems, and in fact mirrors are one of the most important components of many optical devices. However, for certain new applications such as photonic information processing in which the spin states of light carry data, it is important to maintain and control the spin states when reflected by mirrors.

The new chiral meta-mirror does almost the opposite of a conventional mirror with respect to spin states. Instead of reflecting the opposite spin state, it reflects the same spin state of an incident circularly polarized beam, but only for one spin state. When a beam with the opposite spin state arrives at the mirror, the mirror completely absorbs that light. So the final result is that the mirror reflects only light with one spin state—either left or right circularly polarized beams, but not both.

Comparison of microscopic images of the chiral meta-mirror illuminated by right circularly polarized, linear, and left circularly polarized light waves. Credit: Kang et al. ©2017 American Chemical Society

"We offer the ability to preserve of an optical wave upon reflection from a chiral meta-mirror," Cai told Phys.org. "In sharp contrast to a regular reflective surface, the chiral meta-mirror operates by absorbing one spin state, while allowing the other to be reflected back with the same spin state as that of the incident wave."

While most conventional mirrors are made of common metals, such as a thin silver film covered by a thicker piece of glass, no known natural material has the chiroptical property exhibited by the new mirror. For this reason, the researchers fabricated the new mirror from an artificial material—a metamaterial with a nanoscale geometry designed specifically to exhibit this property. The meta-mirror consists of a thin film perforated by an array of asymmetric holes, and this asymmetry contributes to the unconventional chiroptical response.

"Metamaterials, which offer light manipulation on the nanoscale, can achieve polarization alteration in propagation lengths of just a couple hundred nanometers," Cai said.

The researchers note that the chiral meta-mirror is relatively easy to fabricate, and they expect that it will have applications in optical data transmission and other technologies that they plan to further investigate in the future.

"Some of the most common ways to send data via optical means is by time-division or wavelength multiplexing," Cai said. "However, as the demand for increasing data bandwidths grows, a higher degree of multiplexing is needed. In terms of optical communications, polarization control opens another paradigm for multiplexing and data handling. The ability of our meta-mirror to preserve an incident spin state will aid in the development of these polarization-sensitive systems.

"Chiral meta-mirrors can also be used for applications in chiroptical sensing, chiral signal analysis, and may even play a part in the next generation of 3-D movies. Most 3-D movies rely on the left and right handedness of the that passes through the glasses that we wear in the theaters. With this polarization distinction at hand, chiral meta-mirrors could even find utility in this industry."

Explore further: Breaking metamaterial symmetry with reflected light

More information: Lei Kang et al. "Preserving Spin States upon Reflection: Linear and Nonlinear Responses of a Chiral Meta-Mirror." Nano Letters. DOI: 10.1021/acs.nanolett.7b03882

Related Stories

Breaking metamaterial symmetry with reflected light

April 5, 2016

Optical activity—rotation of the polarization of light—is well known to occur within materials that differ from their mirror image. But what happens if this symmetry is broken by the direction of illumination rather than ...

Chiral crabs

September 22, 2017

Sander Wezenberg, and PhD students Thomas van Leeuwen and Kaja Sitkowska, from the University of Groningen in the Netherlands, spoke to us about their work in chirality and molecular motors, and the seaside scene on the cover ...

First circularly polarized light detector on a silicon chip

September 22, 2015

Invention of the first integrated circularly polarized light detector on a silicon chip opens the door for development of small, portable sensors that could expand the use of polarized light for drug screening, surveillance, ...

Recommended for you

The microscopic origin of efficiency droop in LEDs

November 21, 2017

Light-emitting diodes—or LEDs, as they are commonly known—have been slowly replacing incandescent light bulbs in applications ranging from car taillights to indicators on electronics since their invention in the 1960s.

Borophene shines alone as 2-D plasmonic material

November 20, 2017

An atom-thick film of boron could be the first pure two-dimensional material able to emit visible and near-infrared light by activating its plasmons, according to Rice University scientists.

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Whydening Gyre
3 / 5 (5) Nov 14, 2017
You call it "circularly polarized light.", I call it a gyre...:-)
dnatwork
5 / 5 (3) Nov 15, 2017
You call it "circularly polarized light.", I call it a gyre...:-)


That pun reflects poorly on you.
Whydening Gyre
5 / 5 (1) Nov 15, 2017
You call it "circularly polarized light.", I call it a gyre...:-)


That pun reflects poorly on you.

The fact that you see it as a pun, and not the metaphoric comparison it actually is, reflects poorly on your literary acumen....:-)

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.