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Researchers create first supermode optical resonator

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Experimental realization of cascaded mode resonators in integrated photonics. a A SEM picture of a cascaded mode cavity shows two mode converters connected through a wide multimode waveguide. wwg and length L.wgMultimode waveguides placed before and after the cavity guide the telecom light into and out of the cavity.The mode converter is realized by laterally corrugating a silicon waveguide into the shape of a rectangular grating of period Λ and width wg. Scale bar = 5 μm and 2 μm (inset). The periodicity Λ is chosen such that the phase matching condition is met for coupling in opposite directions. The entire optical circuit ridge is embedded in a silica layer. b The device schematic shows three different sections.0 (above) or TE2 (bottom), 2. the cavity region consisting of a multimode waveguide surrounded by two mode converters, and 3. the output of the cavity, 2 spatially separated according to its transverse profile TE Two analyzer waveguides transmitting to one location0 (above) or TE2 (low).Probe 1 excites TE0 mode of the upper waveguide.Probe 2 excites TE0 in the waveguide below. This mode translates to TE.2 The effective refractive index of TE is0 The nanowaveguide modes correspond to the effective refractive index of the TE2 Modes of a multimode waveguide. Similarly, Analyzer 1 and Analyzer 2 measure TE.0 and TE2 mode, respectively. Spatially, the coupling occurs where the nanowaveguide is in close proximity to the multimode waveguide. c Full-wave simulations of the telecom field in a cascade-mode cavity show that two different transverse-mode TEs yield self-consistent solutions for the round-trip condition at the same input wavelength.0 (above) and TE2 (low). d Zooming in on the marked white region within the cavity reveals the hybrid nature of the cascade modes arising as superposition of counter-propagating TEs.0 or TE2 A mode with a characteristic beat length independent of the input probe field. credit: Nature Communications (2023). DOI: 10.1038/s41467-023-35956-9

What does it take for scientists to push the limits of current knowledge? Researchers in Federico Capasso’s group at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed an effective formula .

“Dream big, question everything we know, question the textbooks,” says Vincent Ginis, visiting professor at SEAS and lead author of the new paper.Nature Communications reports breakthroughs in optical cavity technology. “That’s how Federico asks our lab team to work with him. He asks us to make the device work better and in new ways.” I demand that we rethink all the classic rules to see if we can.”

That approach led to the team’s latest result, an optical cavity that can manipulate light in ways never before observed. This breakthrough has implications for how resonators are understood and may open the door to new capabilities.

“This is an advance that fundamentally changes the design of resonators by using reflectors that transform light from one pattern to another as it bounces back and forth,” said Robert L. of Applied Physics. said Capasso, Professor Wallace and Vinton Hayes Sr. Electrical engineering researcher at SEAS.

Optical cavities play an important role in many aspects of modern life.

“Resonators are central components in most applications in optics, lasers, microscopy and sensing. They appear as essential building blocks in all these technologies,” says Mathematics and Physics Ginis, who is also an assistant professor at “They bounce light back and forth, focus light in lasers, for example, or filter light frequencies. fiber optic and telecommunications. ”

Optical resonators are key to telecommunications transmission, encoding images and sound through the frequencies of light.

“Each message is encoded with its own specific frequency to distinguish it from other messages,” says Ginis. “Resonators allow you to ‘tape off’ precise, unique frequencies to transmit many different messages simultaneously. ”

So far, a cavity and two reflecting mirrors within it have controlled the intensity and frequency of light, but not the modes of light that determine the shape and way photons flow through spacetime. Although we often think of light as traveling in straight-line-like beams, beams of light can also travel in other modes, such as spirals. The new optical cavity developed by Capasso’s team is the first such device to give scientists. precise control More importantly, it allows multimode coupled light to exist within the cavity.

The team achieved this by etching a new type of pattern on the surface of the reflectors at each end of the resonator device.

“We realized that we could test new resonator concepts with an integrated photonics platform and chose silicon-on-insulator, which is used by many scientists and companies for applications such as sensing and communications.” EPFL Institute Associate and Assistant Professor of Microengineering in the Capasso Group of Electro and Microengineering, where he spearheaded the experimental portion of the research.

Etching, roughly 300–600 nanometers in size, allowed the team to control the shape of the light beam inside the cavity. By using different patterns of reflectors on either end of the cavity, the ability to change the shape of the traveling light was unlocked.

“These light modes can interact to create loops of different light modes moving through the same space, turning from one mode to another and back to the first mode,” says Ginis. says. “When we saw this, we realized that we were in an ‘unknown world’.”

Combining multiple modes of light creates what researchers called “supermodes.”

“In conventional cavities, light travels back and forth, so the mode is always the same. The properties of light are always symmetrical,” he says. “In our case, the modes are different when light goes from left to right or right to left. We found a way to break the symmetry inside the cavity.”

“Multimode control of light will have a significant impact on the bandwidth of information that can be transmitted using light,” he says. “It opens up a lot of infection channels that were previously inaccessible at the same time.”

capasso team optical resonator It provides new tools for performing basic physics experiments, including optomechanics, using light to move objects.

“By placing an object inside a resonator, we can manipulate matter such as small atoms, molecules, and DNA strands,” says Ginis. New devices with supermode capabilities may unlock new degrees of freedom for researchers to manipulate extremely small materials with light beams of different shapes.

“By questioning the grounds of textbooks, resonator Capasso said: These properties, including “mode-independent resonance and direction-dependent propagation,” unlock unexpected opportunities in photonics, acoustics and more, he adds. .

For more information:
Vincent Ginis et al, Cavities with Tuned Optical Paths by Cascading Mode Conversion,Nature Communications (2023). DOI: 10.1038/s41467-023-35956-9

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Quote: Researchers Create First Supermode Optical Cavity (Feb 2, 2023) from https://phys.org/news/2023-02-supermode-optical-resonator.html on Feb 2, 2023 acquisition

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