One of the exciting things about this research is that it proposes an on-demand controlled laser. By changing the position of the scatterer, you can change the working system of the laser pointer. This will open up the possibility of new functional devices based on lasers. This research further enhances our ability to use micro-ring lasers. Not only can the increased loss be used to increase the power, as we have achieved before, but also the direction of the laser can be precisely controlled.
The micro-resonators they use are a type of whispering gallery mode resonators (WGMRs), because they work in a similar way to the well-known whispering gallery, the dome of St. Paul’s Cathedral in London. People on one side can listen. What the person on the other side of the wall said. The working frequency of the WGMR device is similar to the frequency of light rather than the frequency of sound.
Light is injected and coupled from the WGMR through both sides of the tapered fiber waveguide. The nano-displacement platform controls the scattering and detects the chirality of WGM. In the case of scattering, when light is injected into the WGMR clockwise or counterclockwise, the resonance peak appears in the transmission spectrum, and no signal is obtained at the reflection end.
When the system achieves a special point with the aid of a scatterer, this state will change,” Ozdemir said. “When there is only one injection direction, the reflection spectrum shows a clear resonance peak. This asymmetrical reflection is a unique feature of chirality, that is, an inherent property of a mode. There can be many special points in a physical system.
The result of placing the system in different special points is only the appearance of reflection peaks showing other injection directions. Therefore, we can control the chirality of the pattern from one particular point of the system to another. The research team then established a correlation between the asymmetric reflection at a particular point location and the inherent chirality of the blue laser pointer mode. For this purpose, they use erbium-doped WGM micro-resonators. Erbium, as a dopant, increases laser activity at different wavelengths compared to the light used to excite the laser.
In the case of a special point, the emitted light from erbium to WGM can rotate clockwise and counterclockwise at the same time. This makes it inefficient to extract laser light from WGM micro-ring lasers. And at a particular point, the photon will move in a consistent manner, whether in a clockwise or counterclockwise direction.
We have now controlled the chiral behavior of the whispering gallery mode, so the laser emission direction is due to the existence of special points. Where we put the scatterers and the extent to which we let them change the working system, increasing the versatility of the technology.
We can adjust the whispering gallery mode to have a two-way (clockwise or counterclockwise) micro-ring laser or unidirectional laser, and emit lasers in a clockwise or counterclockwise direction. Through the transition from one special point of the system to another special point, we can completely reverse the launch direction.
As a result, WGMR provides a new function for laser, sensing, light and quantum electrodynamics. The team’s research results once again prove that if properly designed, special points, engineering losses and scattering provide a new technique in optical science to solve the problems that hinder technological development and limit the practicality of equipment. This research is further enhanced So that we can use the laser’s ability, not only can increase the power through loss, as we have achieved before, but also can accurately control the laser direction.
The researchers say that their findings will help develop new technologies for controlling optical flow, pave the way for chiral photonic chips, and may affect science fields outside of the optical field. They have already begun to use and demonstrate special points, other counterintuitive features of non-Hermitian photonics.