New Ideas Emerge between micro-nano and micro-nano - A novel optoelectronic core based on micro-nano optoelectronics

The micro-nano structure breaks through the framework of traditional optoelectronic chips based on the interaction between bound electrons and light fields, making free electrons also play a new role in optoelectronic chips. Through nanostructures or metamaterials, a new mechanism of interaction among flying electrons on chips, bound electrons in crystals, and photons can be realized, opening up a new path for the development of future optoelectronic chips.

Professor Huang Yidong's team from the Micro-Nano Optoelectronics Laboratory of the Department of Electronic Engineering at Tsinghua University has successfully developed a series of new optoelectronic chips for different application fields, focusing on the new physics of the interaction between light and matter in various new structures at the micro-nano scale and the new functions that can be achieved.

Free electron radiation chip

Cherenkov radiation (CR) is the radiation produced when the speed of charged particles is greater than the phase speed of electromagnetic waves in a medium. Based on this physical phenomenon, scientists have made significant breakthroughs in the exploration of fundamental particles and physical laws, such as the discovery of antiprotons, J-particles, and neutrino oscillations.

To produce CR, charged particles need to be accelerated to an extremely high speed. For instance, the speed of electrons that produce CR in water needs to reach approximately 0.7 times the speed of light in a vacuum, corresponding to an electron energy of 300,000 electron volts. It was previously reported that the minimum electron energy required to generate CR in the optical frequency band still needs to be 20,000 electron volts. How to lower the electronic energy threshold for generating CR has been a major fundamental scientific issue that has remained unsolved for decades.

On the other hand, free electron laser light sources have significant application value in fields such as fundamental physics, ****, biomedicine, and information science. However, free electron light sources usually require huge (several meters to several thousand meters) electron accelerators to generate optical frequency radiation. How to integrate free electron light sources on chips is a major challenge in device physics.

In response to this issue, the team from Tsinghua University proposed to eliminate the electronic velocity threshold that generates CR by using micro-nano hyperbolic matematerials (HMM). Metamaterials are a new type of artificial electromagnetic materials with subwavelength micro-nano structures, which can break through the limitations of the electromagnetic properties of traditional materials and achieve rich regulatory functions for the propagation of electromagnetic waves.

A research team from Tsinghua University has shown that since HMM can support electromagnetic modes with very large wave vectors, when the electron energy is extremely small, the evective field of the large wave vectors around the free electron can still be coupled into the HMM to generate CR. The team further overcame the technical difficulties in the comprehensive integration of metamaterials, electron emission sources and scattering gratings on the chip, and for the first time achieved an integrated free electron light source on the chip and observed the thresholless Cherenkov radiation phenomenon. Figure 1 shows the schematic diagram of the device and the electron microscope images of the key functional units.

Based on this, the team further deepened the research on free electron radiation combined with micro-nano structures, achieving Smith-Purcell radiation in the deep ultraviolet band, and theoretically studied the excited Cherenkov radiation based on plasmonic microcavities. The experimental progress indicates that the interaction between free electrons and micro-nano structures can provide an effective approach for the miniaturization and chip integration of free electron light sources, and has broad development space.