Plot of radiative quality factor as a function of wave vector for a photonic crystal slab. (via MIT)

Researchers at the Massachusetts Institute of Technology, MIT — who successfully developed materials that can trap light, and stop it dead in its tracks — are working to implement this material into a plethora of other physical systems, like small-scale particle accelerators. The findings have been reported in a paper published in the Physics Review Letters, which was co-authored by MIT physics professor Marin Soljačić and several postdocs.

The interesting thing about this material is that it can accomplish something that has never been done before. Normally, Light can only be confined by mirrors or photonic crystals, yet these two materials accomplish the same task via the simple process of reflection, however this new material blocks light by canceling out its own radiation field, which involves twisting the polarization direction of the light, (In other words, it is modeled around  a vortex.)

On top of this, the material is quite stable, and hard to disturb, even during trapped state.

“People think of this [trapped state] as very delicate,” Zhen says, “and almost impossible to realize. But it turns out it can exist in a robust way.”

The plane, or direction, of polarization can be thought of as the direction in which the light waves vibrate. This direction remains static for natural light. However, in the case of this material, light enters and becomes polarized in a manner akin to a vortex, with the plane of polarization changing depending on the direction of the light ray.

Vortices of bound states in the continuum. There are five bound states in the continuum on the left. The right panel shows the polarization vector field in the same region as the left panel, revealing five vortices at the locations of the bound states in the continuum (via MIT)

The product of this type of polarization is a singularity, or a topological defect, which is a point that traps light within the material.

Chia Wei Hsu claims the phenomenon could pave the way for the production of vector beams. A vector beam is a type of laser beam that could potentially create small-scale, table-top particle accelerators, which would be very useful — not to mention, cost effective — for high-energy experiments.

“The finding”, Soljačić says, “could also enable easy implementation of super-resolution imaging (using a method called stimulated emission depletion microscopy) and could allow the sending of far more channels of data through a single optical fiber.”

“This work is a great example of how supposedly well-studied physical systems can contain rich and undiscovered properties, which can be unearthed if you dig in the right spot,” comments Yidong Chong, the assistant professor of physics and applied physics at Nanyang Technological University (he took no active part in the research).

Chong says says that the process “deals with photonic crystal slabs of the sort that have been extensively analyzed, both theoretically and experimentally, since the 1990s. The fact that the system is so unexotic, together with the robustness associated with topological phenomena, should give us confidence that these modes will not simply be theoretical curiosities, but can be exploited in technologies such as microlasers.”

You can read the full press release here.


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