To infinity and beyond: Light goes infinitely fast with new on-chip material

October 19, 2015
In this zero-index material -- made of silicon pillar arrays embedded in a polymer matrix and clad in gold film -- there is no phase advance. Instead zero-index material creates a constant phase, stretching out in infinitely long wavelengths. Credit: Peter Allen, Harvard SEAS

Electrons are so 20th century. In the 21st century, photonic devices, which use light to transport large amounts of information quickly, will enhance or even replace the electronic devices that are ubiquitous in our lives today. But there's a step needed before optical connections can be integrated into telecommunications systems and computers: researchers need to make it easier to manipulate light at the nanoscale.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have done just that, designing the first on-chip metamaterial with a refractive index of zero, meaning that the phase of can travel infinitely fast.

This new metamaterial was developed in the lab of Eric Mazur, the Balkanski Professor of Physics and Applied Physics and Area Dean for Applied Physics at SEAS, and is described in the journal Nature Photonics.

"Light doesn't typically like to be squeezed or manipulated but this metamaterial permits you to manipulate light from one chip to another, to squeeze, bend, twist and reduce diameter of a beam from the macroscale to the nanoscale," said Mazur. "It's a remarkable new way to manipulate light."

Although this infinitely high velocity sounds like it breaks the rule of relativity, it doesn't. Nothing in the universe travels faster than light carrying information—Einstein is still right about that. But light has another speed, measured by how fast the crests of a wavelength move, known as phase velocity. This speed of light increases or decreases depending on the material it's moving through.

When light passes through water, for example, its phase velocity is reduced as its wavelengths get squished together. Once it exits the water, its phase velocity increases again as its wavelength elongates. How much the crests of a light wave slow down in a material is expressed as a ratio called the refraction index—the higher the index, the more the material interferes with the propagation of the wave crests of light. Water, for example, has a refraction index of about 1.3.

When the refraction index is reduced to zero, really weird and interesting things start to happen.

In a zero-index material, there is no phase advance, meaning light no longer behaves as a moving wave, traveling through space in a series of crests and troughs. Instead, the zero-index material creates a constant phase—all crests or all troughs—stretching out in infinitely long wavelengths. The crests and troughs oscillate only as a variable of time, not space.

This uniform phase allows the light to be stretched or squished, twisted or turned, without losing energy. A zero-index material that fits on a chip could have exciting applications, especially in the world of quantum computing.

"Integrated photonic circuits are hampered by weak and inefficient optical energy confinement in standard silicon waveguides," said Yang Li, a postdoctoral fellow in the Mazur Group and first author on the paper. "This zero-index metamaterial offers a solution for the confinement of electromagnetic energy in different waveguide configurations because its high internal phase velocity produces full transmission, regardless of how the material is configured."

The metamaterial consists of silicon pillar arrays embedded in a polymer matrix and clad in gold film. It can couple to silicon waveguides to interface with standard integrated photonic components and chips.

"In quantum optics, the lack of phase advance would allow quantum emitters in a zero-index cavity or waveguide to emit photons which are always in phase with one another," said Philip Munoz, a graduate student in the Mazur lab and co-author on the paper. "It could also improve entanglement between quantum bits, as incoming waves of light are effectively spread out and infinitely long, enabling even distant particles to be entangled."

"This on-chip metamaterial opens the door to exploring the physics of zero index and its applications in integrated optics," said Mazur.

Explore further: In a major breakthrough, scientists control light propagation in photonic chips

More information: On-chip zero-index metamaterials, Nature Photonics, DOI: 10.1038/nphoton.2015.198

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2.1 / 5 (7) Oct 19, 2015
Doesn't a vacuum have a 0 index of refraction?
2.5 / 5 (6) Oct 19, 2015
That's what I was thinking. There's nothing material there, so it would almost have to 0 refraction.

Also, in a vacuum, light IS infinitely fast, from its own point of view, so the photon doesn't have time to react to anything, and the phase shouldn't have time to change. In normal materials, such as water, light travels slower than it does in a vacuum, so it "sees" the passage of both time and distance.

If this has a refractive index of 0, then they have invented a material equivalent of a vacuum. I wonder how it would work for long distance fiber optics? No losses, so no need for amplifiers.
4.4 / 5 (14) Oct 19, 2015
No, in a vacuum, the index of refraction is 1 (n=c/v = c/c=1), not 0. Metamaterials have allowed us to create negative indices of refraction, and now a 0-index.

It's not really proper to talk about light being "infinitely fast" from it's own point of view. There is no physical reference frame for free-traveling photons. The limit as we approach c says that the distance between source and emission shrinks to 0, and thus, takes 0 time to cross. That's not precisely the same thing as "infinitely fast" since it doesn't actually "travel" anywhere in that time.
3.9 / 5 (7) Oct 19, 2015
The image is helpful for understanding what they're talking about, but it's not immediately obvious to a lay person how to interpret it, so here's my best attempt:

Look at the light on the right. This is, I think, the incoming light. I think the red and blue represent electric and magnetic fields (but they've rotated the magnetic field or are just displaying its magnitude in 'height').

If you go perpendicularly to the rows of red and blue, this is the direction of travel of the light.
If you look transversely (down a row), you'll see in the incoming light that it oscillates up and down. Thus, any part of the beam may be out of phase with its neighboring elements (one strong when the other is weak, and vice versa)

But if you look out the left and bottom beams, you see that transversely (down the row) the oscillations have smoothed out to a uniform crest. So, in a way, this converts incoherent light into a coherent beam (to some degree)
1 / 5 (3) Oct 19, 2015
Shavera: Thank you.

My "infinitely fast" was in reference to time dilation, which means that a photon experiences no time when traveling through vacuum. Thus, in its own reference frame, it arrives at the same instance it left, meaning it is infinitely fast. Of course, it actually travels at c, as always in vacuum, so it would be just as accurate to say that it appears to travel 0 distance, as you say, but the effect is the same. No time for anything to change.
1.7 / 5 (6) Oct 19, 2015
I am skeptical if this material will be useful. You cannot achieve a index of 0 over a set of frequencies. It will only be zero at a specific frequency point. Trying to manufacture this given fabrication tolerances would be difficult at best. They used electron beam lithography and still only managed to get a zero index at 1570nm when they designed for 1590nm.

As far as loss goes that claim of not loosing energy sounds unlikely. The equation for dielectric loss tangent is tand=e''/e' (permittivity=e'-i*e''). As e' approaches zeros losses go to infinity. I also see they used metal to truncate pillar size. Metal is unreasonably lossy at optical frequencies. Unless I missed something, this seem like a dead end to me.
2 / 5 (8) Oct 19, 2015
There isn't a spacial geometry that allows light to have infinite velocity in it's own frame.

If it did so:
Length contraction along that dimension of motion would hypothetically reduce the apparent width of the entire universe to zero, while the width of the universe in the other two dimensions would remain unchanged. This produces problems because the majority of photons in the universe are supposed to be moving in 2 or more dimensions (diagonal and triagonal) relative to the one you choose as a reference point, but because this dimension would be collapsed to zero, this means those photons net velocity would be observed to be something other than "c" fact, the other photons' velocities will be observed to be "greater than infinite", but they are supposed to appear to be "c" with respect to the chosen reference frame.

Time is not Zero in a photon's own reference frame, because doing so would violating the speed of light postulate with regards to the other photons.
1 / 5 (3) Oct 19, 2015
Makes me wonder if this metamaterial would allow entanglement at long distances, like across an ocean. Maybe the reflective material could be aluminum.
2.6 / 5 (5) Oct 19, 2015
@jimbo Quantum entanglement has already been observed over 143Km
Oct 19, 2015
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Oct 19, 2015
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Oct 19, 2015
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Oct 19, 2015
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not rated yet Oct 19, 2015
Most of the time I understand the practical implication of discoveries. This one eludes me, but I would imagine someday someone will explain how this will be of practical use.

In the meantime, WOW.
2.3 / 5 (3) Oct 19, 2015
@docile: The phase (crests) can carry information, however the power that is used to transmit information still moves at sub-luminal speeds.

That is not a wave running backwards, it is power that is reflected from the engineered material. Those videos are a finite difference time domain simulation. The wave is directed at the material and when it hits most of the power is transmitted, but some is reflected. The most vibrant colors are were the wave is excited.

Check out videos for double negative metamaterials, that is actual backward wave-front with power traveling in the opposite direction. This one is alright: https://www.youtu...b4cY5ZX8
Oct 20, 2015
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Oct 20, 2015
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5 / 5 (2) Oct 20, 2015
The image is helpful for understanding what they're talking about, but it's not immediately obvious to a lay person how to interpret it, so here's my best attempt:

Thanks. I was having trouble with the image.

No time for anything to change.

Or just that all change from emission to absorption is simultaneous (from a photon's point of view. But then again talking about a photons point of view makes little sense.)

"Time is an illusion, Lunchtime doubly so."
--Douglas Adams

5 / 5 (1) Oct 20, 2015
PAN and RayInLv: the use one can imagine is converting incoherent light into (spatially) coherent light. If you know that all across the transverse distribution of the wave, the light is in phase, then you have kind-of/sort-of turned "regular" light into something like "laser" light. (**nb** not an expert, this is just my understanding of what the implication of this technology is)

This benefit is realised even if it's only a monochromatic effect (one given structure only supports one specific wavelength). I mean, we do an awful lot with monochromatic lasers already, don't we?
1 / 5 (2) Oct 20, 2015
@Shavera The phase at the input phase is identical to the phase at the output phase. Incoherent light passing through the material would be incoherent at the output.

I still hold the losses for this material will probably be so large that it is unusable. Every artificial material I have ever seen, the losses go through the roof at the zero crossing.

However, assuming it is usable here is a excerpt for a paper published in physical review E

There may be a variety of potential applications for
matched zero-index media beyond their already demon-
strated use for compact resonators and highly directive
sources. These include delay lines with no phase differences
between their inputs and outputs and wave front transform-
ers, i.e., a transformer that converts wave fronts with small
curvature into output beams with large curvature planar wave fronts.
1 / 5 (2) Oct 20, 2015
Good achievement.This may be helpfull to practicle applications of physics in quantum computations, entanglement. Even it may be applicable for application of cognative sciences and 'physics of consciousness'.
Best of luck.......

Siva Prasad Kodukula
1 / 5 (1) Oct 21, 2015
If you know that all across the transverse distribution of the wave, the light is in phase, then you have kind-of/sort-of turned "regular" light into something like "laser" light.

Since we're not talking about a superposition of many photons in the article it's not really a laser (but there's no reason not to use this to create a laser in other applications. It would be a laser with an infinitely low wavelength/infinitely long wavelength - which is a freaky concept in and of itself).

The system - as is - could be used for synchronization purposes accross regions of a photonic chip. (Which may sound like not much but is crucial in secure communications protocols)
2 / 5 (4) Oct 21, 2015
"It's not really proper to talk about light being "infinitely fast" from it's own point of view. There is no physical reference frame for free-traveling photons. "

Did you often ride the photons to know that? Or only the theory in which you have invested time, effort and money say so? How to abandon it after such an investment in case you are a materialist or/and careerist?
not rated yet Oct 26, 2015
I've always hated the way this is stated.
Or have I made a gross error of misunderstanding?

The speed of light is C. Period. Always. And certainly in water.
The space between atoms in water IS a vacuum.

I assume they really mean the APPARENT speed of light (in, for example, water).
I assume this appearance is caused because of one or both of two things:

Photons are deflected by atoms making their path a zig-zag which is LONGER and so which APPEARS to take more time when measured at macroscopic levels.

And, photons are repeatedly absorbed and then a new photon is emitted, but this must take some time. That time also causes light to APPEAR to take longer to traverse the medium.

Someone help me if I'm wrong, or confirm if I'm correct.

Regards, Greg
Oct 26, 2015
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