Approximate visible light cloak simulated and practical device within reach


Silicon photonic crystal has holes of the right sizes and waveguides

In computer simulations, the researchers have demonstrated an approximate cloaking effect created by concentric rings of silicon photonic crystals. The mathematical proof brings scientists a step closer to a practical solution for optical cloaking.

“This is much more than a theoretical exercise,” said Harley Johnson, a Cannon Faculty Scholar and professor of mechanical science and engineering at Illinois. “An optical cloaking device is almost within reach.”

Axisymmetric photonic crystal structures may be designed to possess interesting optical properties, particularly when the photonic band structure of the material is highly anisotropic. We use finite element calculations to demonstrate an approximate electromagnetic cloaking effect imparted by a structure consisting of concentric silicon photonic crystal layers. The results show that it is possible to bend light around an object by simply using anisotropy. The calculations show that the cloaking mechanism is fundamentally different from Pendry’s approach. This design may work as a practical solution for optical cloaking.

D. Xiao and H. T. Johnson, “Approximate cloaking effect in an axisymmetric silicon photonic crystal structure,” Optics Letters, 33, 860-862 (2008).

In October 2006, an invisibility cloak operating in the microwave region of the electromagnetic spectrum was reported by researchers at Duke University, Imperial College in London, and Sensor Metrix in San Diego. In their experimental demonstration, microwave cloaking was achieved through a thin coating containing an array of tiny metallic structures called ring resonators.

To perform the same feat at much smaller wavelengths in the visible portion of the spectrum, however, would require ring resonators smaller than can be made with current technology, Johnson said. In addition, because metallic particles would absorb some of the incident light, the cloaking effect would be incomplete. Faintly outlined in the shape of the container, some of the background objects would appear dimmer than the rest.

To avoid these problems, postdoctoral research associate Dong Xiao came up with the idea of using a coating of concentric rings of silicon photonic crystals. The width and spacing of the rings can be tailored for specific wavelengths of light.

“When light of the correct wavelength strikes the coating, the light bends around the container and continues on its way, like water flowing around a rock,” Xiao said. “An observer sees what is behind the container, as though it isn’t there. Both the container and its contents are invisible.”

Currently simulated in two dimensions, the cloaking concept could be extended to three dimensions, Xiao said, by replacing the concentric rings with spherical shells of silicon, separated by air or some other dielectric.

The researchers’ optical cloaking technique is not perfect, however. “The wave fronts are slightly perturbed as they pass around the container,” said Johnson, who also is affiliated with the university’s Beckman Institute and the Frederick Seitz Materials Research Laboratory. “Because the wave fronts don’t match exactly, we refer to the technique as ‘approximate’ cloaking.”

FURTHER READING

Invisibility to sound for acoustic shields (hide nuclear deterrent submarines from sonar detection) and shaping sound and other waves (like earthquakes) is also coming soon

Researchers at the University of Illinois are the first to achieve optical waveguiding of near-infrared light through features embedded in self-assembled, three-dimensional photonic crystals. Applications for the optically active crystals include low-loss waveguides, low-threshold lasers and on-chip optical circuitry.

Harley Johnson site

Photonic crystal tutorial

Silicon photonic crystal

Scanning electron micrograph of a porous silicon photonic crystal

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10 comments

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1

How many pounds of cargo could this sucker fly to Luna, or Mars?

2

The new designs for gaseous rockets are still to use hydrogen fuel but they have to change the geometry and layout of the injection and flow system.

3

The 70's idea of using hydrogen fuel around the reacton chamber walls to keep the nuclear fuel from melting the chamber was said not be used now.
What are they planning to use now to accomplish this?


Bob Cark

4

All of these comments about people misjudging risk are spot on. The Harvard School of Public Health spends a lot of time wrestling with this problem. You can read more about it http://www.hsph.harvard.edu/review/review_fall_04/risk_perspective.html" REL="nofollow"> here. Unfortunately, in the nuclear case, the "natural vs artificial" bias comes into play: It's illogical, but common for someone to be comfortable with sunning themselves at the beach (melanoma kills 8000 per year in the US), but to be vehemently anti-nuclear (when basically, no one has died in a US nuclear power accident).

The HSPH researcher Ropeik's book "Risk: A Practical Guide..." is an excellent overview of the many ways people get risk evaluation wrong. The examples that comprise most of the book are overkill IMHO, but the book is definitely worth reading for the first 100 pages or so. Check your local library.

5

how about we go with a message of:

"using nukes for a better future"
lately i've been looking at the DoD's National Security Space Office SSPS (Space Solar Power study) concept over at http://spacesolarpower.wordpress.com/

And I keep thinking what could we do with "Fly dirty to get clean" use nuclear to get to space then use space power to do away with nuclear.

we could certainly do a lot more alot faster with nuclear engines, we could lift lage sections of completed componets with onorbit assembly. and/or go back to the moon with enough supplies to set up mining and electro-launch capabilities so that all equipment
is made through a few Heavey "dirty" flights with immediate realization of goals that would take convenitional HLLVs 10x-100x more flights.

6

bw,

I'm sure that this thing could be made safe. However, the fact that it is a rocket, with exhaust, that is launched from the surface of the Earth is enough for all of the greens and everyone else to come out of the woodwork to oppose it.

This is why I think that something like this could only be launched from China or, maybe, Japan. An ocean-based launch site makes sense, but this would also have to be done by a Chinese or Russian entity in the Western Pacific near China.

However, a rocket like this could certainly be used in deep space without the political controversy surrounding its use as a launch vehicle.

7

You would launch this from the middle of the Pacific Ocean

http://www.nuclearspace.com/a_liberty_ship9.htm

A nuclear rocket if this type would have in the range of 10 pounds of radioactive nuclides in it. The Ivy Mike nuclear bomb test which took place on November 1st, 1952. This is a real test, you can go look it up. Released 1023 pounds worth of radioactive nuclides. No one died or was injured.

The a gas cored reactor has several potential "scram" (emergency shutdown) modes, both fast and slow, and the speed of the reaction is easily "throttled" by adding and removing fuel or by manipulating the vortex. A 'scram' is an emergency shutdown, usually done in a very fast way. For example: a gas cored reactor can be fast scrammed by using a pressurized "shotgun" behind a weak window. If the core exceeds the design parameters of the window, which are to be slightly weaker than the silica "lightbulb," then the "shotgun" blasts 150 or so kilos of boron/cadmium pellets into the uranium gas, quenching the reaction immediately. A slightly slower scram which is implemented totally differently is to vary the gas jets in the core to instill a massive disturbance into the fuel vortex. This disturbance would drastically reduce criticality in the fission gas. A third scram mode, slightly slower still, is to implement a high-speed vacuum removal of the fuel mass into the storage system. Having three separate scram modes, one of which is passively triggered, should instill plenty of safety margin in the nuclear core of each thruster.


http://en.wikipedia.org/wiki/Space_disaster

As of 2007, in-flight accidents had killed 18 astronauts, training accidents had claimed 11 astronauts, and launchpad accidents had killed at least 70 ground personnel.

There have been 230+ ground crew and civilian casualties.

Driving cars kill 1.2 million each year.

http://en.wikipedia.org/wiki/Aviation_accidents_and_incidents#Safety

Trains have .04 deaths for every 100 million miles
Air travel has .01 deaths for every 100 million miles traveled.
Automobile has .94 deaths per 100 million miles

8

What happens when it goes wrong and the core gets blasted across Florida?

9

I had an article that Steve Howe was trying to get an orbit to the moon nuclear thermal stage done.

If that was used for a while, then maybe this could fly.

Or China flys it Or we have to wait for other high performance but public relations friendly tech like laser array launch.

==
Irrational ideas about risk cause us to give up 6-200 times the performance in rockets

10

This would never fly. The anti-nuclear hysterics people would ensure that this type of launch vehicle would never be allowed to fly. Or regulatory hurtles would be created that would make it impossible for anyone to get the necessary environmental permits for such a vehicle to fly.

If anything, the Europeans and Aussies would be even more psychotic about this than Americans.

My recommendation would be for the individuals or company developing this technology to do so either in Japan or China.