Science

Stanford researchers control light using synthetic magnetism

Electrons bent into a circular path by moving through a magnetic field (Photo: Marcin Bialek)
Electrons bent into a circular path by moving through a magnetic field (Photo: Marcin Bialek)
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Electrons bent into a circular path by moving through a magnetic field (Photo: Marcin Bialek)
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Electrons bent into a circular path by moving through a magnetic field (Photo: Marcin Bialek)
Photon motion in an effective magnetic field, showing the change in photon path radius as control voltage is changed (Image: Stanford University)
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Photon motion in an effective magnetic field, showing the change in photon path radius as control voltage is changed (Image: Stanford University)

Left to its own ways, light will follow the same path through an optical system whether the system is being used as a camera lens or as a projector. This is called time-reversal symmetry, or reciprocity. As many new applications and methods would be enabled by access to a non-reciprocal optical system, it is unfortunate that they have been so difficult to come by. But now researchers at Stanford University have discovered how to make such non-reciprocal systems by generating an effective magnetic field for photons.

The motion of electrons through a magnetic field is the poster child for non-reciprocity. That motion produces a force acting perpendicular to the velocity of the electron, so that the electron travels in a circular path. Since the velocity has a direction, reversing the velocity of the electron reverses the direction of the force, causing the electron to follow a different path than it followed in approaching the reversal point.

Non-reciprocal optical systems exhibit a range of useful phenomena that could greatly advance photonic communications and computation. For example, photons in an effective magnetic field follow a circular path whose size depends on the strength of the effective magnetic field. This effect could be used as the basis for switching an optical signal to one of several outputs. Non-reciprocity can lead to surfaces with zero reflectivity, and could also eliminate signal loss in optical fibers. This in turn would be a big step toward practical implementation of single-photon quantum communication and computing.

The Stanford solution is based on a new type of dynamic photonic crystals. A photonic crystal is a material in which the local optical properties vary to give the overall material some desirable optical property. Correspondingly, in a dynamic photonic crystal the local optical properties change in response to an external influence which can be adjusted and altered, allowing the material to exhibit a much wider range of global optical properties.

Photon motion in an effective magnetic field, showing the change in photon path radius as control voltage is changed (Image: Stanford University)
Photon motion in an effective magnetic field, showing the change in photon path radius as control voltage is changed (Image: Stanford University)

The Stanford device was made from a silicon photonic crystal structured so that an electric current applied to the device tunes the photonic crystal to exert an effective magnetic force upon photons. The device sends photons in a circular motion around the synthetic magnetic field. As shown above, the researchers were able to alter the radius of a photon’s trajectory by varying the electrical current applied to the photonic crystal.

Breaking time-reversal symmetry, the researchers believe, will enable a wide range of applications in photonics. “Our system is a clear direction toward demonstrating on-chip applications of a new type of light-based communication device that solves a number of existing challenges,” said Zongfu Yu, a post-doctoral researcher in Prof. Fan’s lab and co-author of the paper. “We’re excited to see where it leads.”

Source: Stanford University

13 comments
StrangeHero
So what you're saying is that we can expect lightsabers really soon???
Clay Jones
But I still don't know if the light in my fridge actually goes off once the door's closed. And is it the door's closing that makes the light go out or does the inevitability of the closing and the resulting futility of it all force the lamp to extinguish? Sorry. The article is actually fascinating. It's just difficult to assign importance to this tech yet.
JAT
Photons being curved around by a magnetic field? No wonder we can see so far into the universe. We're actually looking at ourselves at the light is curved around and comes back to us.
Sonya B
@StrangeHero: Actually, the light would be curved, so there would be lightscimitars instead. lol
tflahive
Ok. So... Bend the light at two places a meter apart and make a "Light Chainsaw".
Bill Bennett
Clay, just take out all of the beer and shelves, climb inside and find out when you close the door, don't stay inside too long ;)Bill
pieman390
can someone please explain the article to me? it really confused me.. i think what the article was trying to say was that we wont need satelites anymore because we can send the information through the light (like a fiber optic but with out the fiber) and it will go around the earth to something on the other side of the world with out having to bounce off satelites is this what it means? because i have no clue lol
Gregg Eshelman
Another step towards Bob Shaw's "Slow Glass"? Look up his 1966 short story, "Light of Other Days".
hec031
Lets clarify something here. The first picture shows electrons flowing in a curve path through a magnetic field. The second picture which is an illustration, is of a similar effect for photons inside a solid crystalline material, but not in free air or vacuum like the first picture shows. The initial picture gives you the wrong impression.
Fretting Freddy the Ferret pressing the Fret
Many applications involving light involve signal loss - look at fiber optics that need to use a signal booster every so kilometres distance. One of the drawbacks of such a technology could be removed by removing the need for signal boosters.