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Designing different sources of loss provides new features for full light absorption

Researchers have created two WGM microcavities with different absorption losses and combined their optical fields by bringing them closer together. Each resonator is coupled to a fiber waveguide. By changing the gap between the resonator and the waveguide, they were able to adjust the coupling loss.Credits: University of Washington, St. Louis / Lanyan

All natural and man-made physical structures lose energy, and scientists work hard to eliminate or compensate for that loss. Optical and photonic devices lose energy due to light scattering, radiation, or material absorption. However, in some situations, deliberate and careful design of the loss of open optics and systems can lead to unprecedented physical phenomena and new methods of optical control and engineering.


Physics and Physics at Team Yale University, including Professor Edwin H. & Florence G. Skinner in Electrical and Systems Engineering, McKelby Engineering, Washington University in St. Louis, and A. Douglas Stone, Professor Karl A. Morse of Applications. , And his lab discovered a new approach to manipulating Light absorption of Optical resonator Due to various types of light loss. They have achieved two coherent full absorption mode degeneracy. Absorption spectrum Ability to switch between weak and strong absorption In a wide frequency band.The work was released on September 9, 2021 Chemistry..

Jan’s team uses an experimental platform called the Whispering Gallery Mode (WGM) MicroResonator, named after the famous Whispering Gallery in St. Paul’s Cathedral, London. gallery. Optical WGM devices work as well, but Light Frequency, not sound. These structures support resonance. That is, only light of a particular frequency can stay in such a system for an extended period of time. Light can be absorbed by the resonator as a result of material absorption loss. In addition, fiber waveguides are typically placed tangentially to the cavity rim to couple light inside and outside the cavity. The coupling between the resonator and the fiber creates an additional non-dissipative coupling loss channel. This allows the light trapped in the cavity to escape from the fiber.

Researchers have created two WGM microcavities with different absorption losses and combined their optical fields by bringing them closer together.each Resonator It is coupled to a fiber waveguide. By changing the gap between the resonator and the waveguide, they were able to adjust the coupling loss.

In their experiments, researchers achieved a situation called coherent full absorption (CPA), the complete absorption of incident light from a waveguide channel, by optimizing the ratio of two coupling losses to two absorption losses. Did. CPA is the reverse time of the lasing process. Instead of emitting light, the system completely absorbs the emitted light without causing emission or scattering.

“In general, lossy optics can absorb incident light, but full absorption does not occur unless loss parameters such as the ratio of absorption loss to coupling loss are carefully designed and controlled,” Yang said. I am. “In addition, the incoming laser beam must oscillate at the correct frequency and be injected through the two waveguide channels in a well-designed ratio of amplitude and phase for complete absorption to occur.”

In a system with two optical resonators, there are two types of waveforms that can be completely absorbed, and they occur at two different frequencies. Therefore, the system typically acts as two complete absorbers. However, optimizing the coupling between the resonators tuned by the gap can result in unconventional fusion of these two frequencies and waveforms. By adjusting the system up to that point, researchers were the first to observe a line shape with a wider output spectrum than the traditional Lorenz line shape.

“When the two CPA modes merge, the system reaches a special kind of degeneracy called a completely absorbed exception,” said Changqing Wang, a PhD student in Yang’s lab and lead author of the treatise. increase. “This is fundamentally different from the other traditional types of degeneracy seen in openwave systems. It seems that there are two absorbers that operate at the same frequency and completely absorb the same type of beam. However, the behavior of the system is very different from one. It is neither an absorber nor just the sum of two absorbers. ”

In the degenerate full absorption mode, a slight change in the relative delay of the two laser beams entering the two waveguides can dramatically change the absorption of the system from strong to weak. Compared to traditional absorbers, this modulation occurs over a wider frequency range due to the effects of non-trivial degeneracy at fully absorbed exceptions. This phenomenon does not occur in lossless systems or in systems where gain and loss are balanced.

“This work provides new insights into how to operate open physical systems with different types of losses,” says Yang. “So far, losses have enabled so many interesting physics in non-Hermitian optics, acoustics, and electronic systems, but there is great potential to take advantage of the different roles of different sources of loss. Absorption losses play a different role than non-dissipative coupling losses in adjusting the scattering properties of a system. Different types of losses give you more freedom in optics. “

According to Yang, the discovery of this non-trivial, degenerate, complete light absorption provides insights into a variety of applications in photonics, acoustics, electronics, and quantum systems. Taking advantage of the exceptional points of complete absorption, you can design ultra-sensitive optical sensors for nanoparticle detection, rotation speed measurements, and imagery of living tissue.

“Adding gain to the device is always much more cumbersome and results in additional noise that degrades system performance, so the pure need for gain-free loss makes the design simpler and more accessible. , More stable, “says Yang. Said. “Loss is ubiquitous in nature, and by better understanding it, we make it more useful.”


By adjusting the optical resonator, researchers can control the transparency.


For more information:
Changqing Wang et al, coherent complete absorption at exceptional points, Chemistry (2021). DOI: 10.1126 / science.abj1028

Quote: Full light absorption obtained on September 10, 2021 from https: //phys.org/news/2021-09-sources-loss-features-absorption.html by designing various loss sources ( 2021, September 10th) new features will be provided.

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