Researchers create bizarre optical phenomena, defying the laws of reflection and refraction

Sep 01, 2011
Top, clockwise from left: Patrice Genevet, Nanfang Yu, Federico Capasso, Zeno Gaburro, and Mikhail A. Kats. Bottom: A simulation of the image that would appear in a large mirror patterned with the team's new phase mirror technology. Credit: Photos by Eliza Grinnell and Nanfang Yu.

Exploiting a novel technique called phase discontinuity, researchers at the Harvard School of Engineering and Applied Sciences (SEAS) have induced light rays to behave in a way that defies the centuries-old laws of reflection and refraction.

The discovery, published this week in Science, has led to a reformulation of the mathematical laws that predict the path of a ray of bouncing off a surface or traveling from one medium into another—for example, from air into glass.

"Using designer surfaces, we've created the effects of a fun-house mirror on a flat plane," says co-principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS. "Our discovery carries optics into new territory and opens the door to exciting developments in photonics technology."

It has been recognized since ancient times that light travels at different speeds through different media. Reflection and occur whenever light encounters a material at an angle, because one side of the beam is able to race ahead of the other. As a result, the wavefront changes direction.

The conventional laws, taught in physics classrooms worldwide, predict the angles of reflection and refraction based only on the incident (incoming) angle and the properties of the two media.

While studying the behavior of light impinging on surfaces patterned with metallic nanostructures, the researchers realized that the usual equations were insufficient to describe the bizarre phenomena observed in the lab.

An array of nanoscale resonators, much thinner than a wavelength, creates a constant gradient across the surface of the silicon. In this visualization, the light ray hits the surface perpendicularly, from below. The resonators on the left hold the energy slightly longer than those on the right, so the wavefront (red line) propagates at an angle. Without the array, it would be parallel to the surface. Credit: Image courtesy of Nanfang Yu.

The new generalized laws, derived and experimentally demonstrated at Harvard, take into account the Capasso group's discovery that the boundary between two media, if specially patterned, can itself behave like a third medium.

"Ordinarily, a surface like the surface of a pond is simply a geometric boundary between two media, air and water," explains lead author Nanfang Yu (Ph.D. '09), a research associate in Capasso's lab at SEAS. "But now, in this special case, the boundary becomes an active interface that can bend the light by itself."

The key component is an array of tiny gold antennas etched into the surface of the silicon used in Capasso's lab. The array is structured on a scale much thinner than the wavelength of the light hitting it. This means that, unlike in a conventional optical system, the engineered boundary between the air and the silicon imparts an abrupt phase shift (dubbed "phase discontinuity") to the crests of the light wave crossing it.

Each antenna in the array is a tiny resonator that can trap the light, holding its energy for a given amount of time before releasing it. A gradient of different types of nanoscale resonators across the surface of the silicon can effectively bend the light before it even begins to propagate through the new medium.

Researchers create bizarre optical phenomena, defying the laws of reflection and refraction
Nanfang Yu, Zeno Gaburro, Federico Capasso, and colleagues at SEAS have created strange optical effects, including corkscrew-like vortex beams, by reflecting light off a flat, nanostructured surface. The images at the top are experimental photos; the images at the bottom are simulations. Credit: Image courtesy of Nanfang Yu.

The resulting phenomenon breaks the old rules, creating beams of light that reflect and refract in arbitrary ways, depending on the surface pattern.

In order to generalize the textbook laws of reflection and refraction, the Harvard researchers added a new term to the equations, representing the gradient of phase shifts imparted at the boundary. Importantly, in the absence of a surface gradient, the new laws reduce to the well-known ones.

"By incorporating a gradient of phase discontinuities across the interface, the laws of reflection and refraction become designer laws, and a panoply of new phenomena appear," says Zeno Gaburro, a visiting scholar in Capasso's group who was co-principal investigator for this work. "The reflected beam can bounce backward instead of forward. You can create negative refraction. There is a new angle of total internal ."

Moreover, the frequency (color), amplitude (brightness), and polarization of the light can also be controlled, meaning that the output is in essence a designer beam.

The researchers have already succeeded at producing a vortex beam (a helical, corkscrew-shaped stream of light) from a flat surface. They also envision flat lenses that could focus an image without aberrations.

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User comments : 26

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NotAsleep
4.3 / 5 (12) Sep 01, 2011
This seems less like "law defying" and more like advanced application of existing laws
tadchem
4 / 5 (14) Sep 01, 2011
This goes *beyond* existing law in the same way that General Relativity goes beyond Newton's Laws of Motion.
The ramifications are mind-boggling.
Stealth technology alone will make a quantum leap.
Optical microscopes could be made with reflecting lenses.
Short focal length lenses analogous to Fresnels could be made flat, without the rings of ridges and associated image degradation.
It just goes on and on...
Skultch
not rated yet Sep 01, 2011
More powerful fiber optic communication modulation?
marcin_szczurowski
not rated yet Sep 01, 2011
Optical frequency chirped metamaterial? Cool.
Jeddy_Mctedder
1 / 5 (2) Sep 01, 2011
this is SWWEEEEEET. VERY COOL. way to go science.
SemiNerd
2.5 / 5 (2) Sep 01, 2011
This looks like nothing more than super fancy Fresnel lenses by making the lenses out of nano materials.
plasticpower
3.7 / 5 (3) Sep 01, 2011
If you stare at the "nanoscale resonators" picture for a minute without blinking you see a 3D unicorn
PinkElephant
4 / 5 (4) Sep 01, 2011
Very nice research, but I feel like a guy with a last name of Capasso is misapplying his talents. He'd be better off working on capacitors.

(My apologies to everyone who reads this...)
Vendicar_Decarian
1 / 5 (3) Sep 02, 2011
This seems less like "law defying" and more like advanced application of existing laws" - NotAsleep

"Well the laws of refraction and reflection don't apply when you put optically active tinfoil in front of the optics. They were never intended to.
Vendicar_Decarian
1 / 5 (4) Sep 02, 2011
Isn't Dr. Capasso someone from the Marvel Comic universe?

Batman perhaps?
210
1 / 5 (6) Sep 02, 2011
This looks like nothing more than super fancy Fresnel lenses by making the lenses out of nano materials.

Oh, OKAY...and you sound like...well....a "SEMI-NERD"...!

word-to-ya-muthas
Guy_Underbridge
5 / 5 (2) Sep 02, 2011
This seems less like "law defying" and more like advanced application of existing laws


Agreed. Nonetheless (Irregardless?), it's some kickass application of some fine tech.
Deesky
4.7 / 5 (15) Sep 02, 2011
So if man can now realize that ", the laws of reflection and refraction become designer laws", what is there to stop him from realizing that it was all designed in the first place, by the MASTER designer?

The master designer must be pretty shoddy to have designed an individual like you. In fact, I'd say you're proof positive against the existence of a master designer.
LivaN
5 / 5 (6) Sep 02, 2011
kevinrtrs
So if man can now realize that ", the laws of reflection and refraction become designer laws", what is there to stop him from realizing that it was all designed in the first place, by the MASTER designer?


Moreover, the frequency (color), amplitude (brightness), and polarization of the light can also be controlled, meaning that the output is in essence a designer beam.


Not "designer's laws", but designer laws. That being laws which designers can use.

Again the great deceivers minion twists words and meanings for his MASTER! See how he judges?
kevinrtrs
Only his arrogance, pride and ultimate foolishness stands in his way of acknowledging the Creator.

As if it is his right. As if arrogance did not pour forth from his very words, and they reveal his foolishness.
hush1
1 / 5 (1) Sep 02, 2011
Is there a acoustical equivalent to this?

http://www.physor...mit.html
Ricochet
not rated yet Sep 02, 2011
So if man can now realize that ", the laws of reflection and refraction become designer laws", what is there to stop him from realizing that it was all designed in the first place, by the MASTER designer?

The master designer must be pretty shoddy to have designed an individual like you. In fact, I'd say you're proof positive against the existence of a master designer.


Actually, it proves it's existence, on the principle that everyone needs somethung to laugh at, and there must be a baseline from which to measure intelligence.
Dug
1 / 5 (1) Sep 02, 2011
"The resulting phenomenon breaks the old rules, creating beams of light that reflect and refract in arbitrary ways, depending on the surface pattern." If it is surface pattern dependent - it isn't arbitrary.
Isaacsname
not rated yet Sep 02, 2011
I bet it will change PV.

Nice article
Ricochet
not rated yet Sep 02, 2011
Funhouses will never be the same
VOR
not rated yet Sep 03, 2011
it will be interesting to see how the limitations of resulting image quality improve over time or it they inherently have a harder limit. That would dictate what applications it can or can't replace of course. Kinda like how holographic photos still have limits and dont look realistic.
VOR
3 / 5 (2) Sep 03, 2011
what is there to stop him from realizing that it was all designed in the first place, by the MASTER designer?
Only his arrogance, pride and ultimate foolishness stands in his way of acknowledging the Creator.
Or it could be having a brain that happens to not exhibit the state necessary for irrational faith. This state is determined by certain factors including genetics. It can be
artificially created in a non-believing brain by applying a specific magnetic field to a specific area of the brain. (experimentally shown and reported). All the evidence and historical culture point to the existence of a creator only within the minds of a subset of humans throughout history. Citing 'designs' as evidence of a creator is most likely nothing more than a pseudoscientific expression of faith.
lengould100
1 / 5 (1) Sep 06, 2011
Just trying to see how this might affect photovoltaics. Seems it might be used for concentrating, but no great benefit over plastic or glass fresnel. I wonder if it might be used to overcome that bugboo of space-based reflectors, being that light from the sun doesn't all arrive at a given point on the reflector at the same time, eg. the sun has a distinct diameter? Result is that light reflected from a single point reflector at GEO orbit will, when reflected to earth, disperse over about a 300 KM diameter area.

eg. fom earth orbit, the sun subtends an angle of 0.52° (1/2 degree). If s surface could be printed onto reflective mylar which caused light arriving at exactly 45.00 degrees to reflect off at exactly 45.00 degrees, but light arriving at 45.26 degrees and at 44.74 degrees to ALSO reflect off at exactly 45.00 degrees.....

Fix that problem, and solar energy suddenly goes really cheap.
A_Paradox
not rated yet Sep 06, 2011
@hush1
Is there a acoustical equivalent to this?


Full marks to that chap! Bloody good question!
Ricochet
not rated yet Sep 06, 2011
what is there to stop him from realizing that it was all designed in the first place, by the MASTER designer?
Only his arrogance, pride and ultimate foolishness stands in his way of acknowledging the Creator.
Or it could be having a brain that happens to not exhibit the state necessary for irrational faith. This state is determined by certain factors including genetics. It can be
artificially created in a non-believing brain by applying a specific magnetic field to a specific area of the brain. (experimentally shown and reported). All the evidence and historical culture point to the existence of a creator only within the minds of a subset of humans throughout history. Citing 'designs' as evidence of a creator is most likely nothing more than a pseudoscientific expression of faith.


By definition, all faith is irrational, as its based upon unproven, and mostly unprovable, beliefs.
Isaacsname
not rated yet Sep 07, 2011
I know it's woowoo, but...the spiral.....it looks like the spiral they spotted over Norway
DavidMcC
not rated yet Sep 12, 2011
This seems less like "law defying" and more like advanced application of existing laws

Agreed. Maxwell's equations still stand! Only technology has changed, not physics.

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