![]() ![]() ![]() The notion that you can stick a photonic crystal into a microring with this kind of strength and modulation, while retaining a high quality factor (low loss), has actually been rather surprising for a lot of people, myself included.” “But in general, when people put them together this didn’t happen – sometimes you could even get the worst of both worlds. “People have been saying for a long time that microrings and photonic crystals have complementary strengths, and so it would be great to put them together to get the best of both worlds,” Srinivasan says. Finally, the microgears confine just a few colors of light into tight bundles, while allowing other colors to circle around the microring freely. Moreover, to add a defect, the researchers simply modified the size of a few of the notches. It turned out that adding the gear notches inside the ring didn’t reduce the number of times the light would go around before leaking out-the ring trapped light just as well as before. To add a photonic crystal element, they cut notches into the inside wall of their ring, making it resemble a gear. The researchers created a regular microring out of silicon nitride, a hollow circle much like the gallery in St. The design of this hybrid is surprisingly simple. The new hybrid ring is easy to manufacture and guide light into like WGMs, but it also provides extra localization for particular colors, like photonic crystals. Moreover, photonic crystals that can trap multiple colors have been challenging to realize. Photonic crystals are unrivaled in comparison to WGMs in terms of the light intensity they can create per photon, but they require very detailed electromagnetic design and precise manufacturing to implement in practice. The regular grid reflects light of a very specific color, and a small, intentionally introduced imperfection in the grid-called a defect-accumulates the light within the surrounding reflecting grid, trapping it in a tiny space. They achieve this with a carefully crafted periodic structure made up of a grid of holes or posts in a chip. Photonic crystals can confine light to much smaller volumes-sometimes less than one wavelength across. Building a WGM microring that traps the desired color with minimal loss, as well as getting the light into the ring, is relatively straightforward for a wide range of colors. Light of the right color travels round and round the ring many thousands of times before leaking out, producing a high light intensity in a small volume. Similarly, optical WGMs trap light in a ring, typically about a tenth of a millimeter in diameter, made of silica or another material that is transparent to optical light. Whispers in the Cathedral can be heard anywhere within the gallery because the sound gets trapped by the round walls and reflected back inside. Paul’s Cathedral, a masterpiece of Baroque architecture that towers over London. Whispering gallery mode (WGM) microrings are named after the gallery inside St. The team introduced their device in a paper published in the journal Nature Photonics in 2021, and they showed off more of what it can do in a paper published recently in the journal Physical Review Letters. ![]() “But a part of it is also fun electromagnetism and fun optical phenomena in these devices.” ![]() (Credit: Kartik Srinivasan/JQI) Kartik Srinivasan, who is also a fellow of the National Institute of Standards and Technology (NIST). “There are potential applications, like single photon sources and quantum gates,” says Adjunct Professor Scanning electron microscope image of a novel photonic microring with micron-scale gears patterned inside a larger circle. This unique combination of features opens a route to new applications, as well as exciting possibilities for manipulating light in novel ways for basic research. This hybrid device, which they call a microgear photonic crystal ring, can trap many colors of light while also capturing particular colors in tightly confined, high-intensity bundles. Recently, a team of researchers at JQI struck upon a clever way to combine whispering gallery modes and photonic crystals in one easily manufacturable device. Of all the moonbeam-holding chip technologies out there, two stand the tallest: the evocatively named whispering gallery mode microrings, which are easy to manufacture and can trap light of many colors very efficiently, and photonic crystals, which are much trickier to make and inject light into but are unrivaled in their ability to confine light of a particular color into a tiny space-resulting in a very large intensity of light for each confined photon. ![]()
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