Xi'an Institute of Optics and Fine Mechanics has made significant progress in the field of metasurface nonlinear photonics

Recently, the Research Group of Nonlinear Photonics Technology and Application in the Transient Optics Research Room of Xi'an Institute of Optics and Mechanics, Chinese Academy of Sciences has made important progress in the field of super surface nonlinear photonics. Relevant research results were published in Laser&Photonics Reviews (IF=9.8), the top journal of the first district of the Chinese Academy of Sciences. The first author of the paper is Shi Wenjuan, a 2020 doctoral student. The first completion unit and communication unit of the paper are Xi'an Institute of Optics and Mechanics.

Nonlinear optical technology is an important technology in cutting-edge fields such as all-optical signal processing, biomedical imaging, and quantum information. However, it is limited by the weak nonlinear optical effects of traditional materials, dependence on strong laser sources, and long interaction distances, making it difficult to meet the development needs of integrated and low-power nanophotonic devices. Epsilon near zero (ENZ) materials have ultrafast and ultra strong nonlinear optical effects, which are expected to solve this problem. Micro nano structures based on quasi continuous bound states in the continuum (Q-BIC) significantly enhance the interaction between light and matter through high-quality factor resonance, opening up new avenues for regulating nonlinear optical effects. However, the narrow bandwidth characteristics and extreme sensitivity to structural parameters of the Q-BIC system severely restrict its practical applications. How to break through the constraint relationship between high quality factor and working bandwidth at the micro nano scale, and achieve the design and preparation of high-performance photonic devices, has become a key scientific problem that urgently needs to be solved in the field of photonic integration.

In response to the above issues, the research team has proposed for the first time a non local metasurface structure design with strong coupling between quasi guided mode (Q-GM) and ENZ mode. By introducing periodic perturbations to achieve the folding of the first Brillouin zone, an angle adjustable high-quality factor Q-GM has been successfully constructed, breaking through the wave vector and wavelength limitations of traditional Q-BIC.

Figure 1. (a) Three dimensional structure (b) Linear transmission spectrum measured and simulated

Figure 2. (a) Band folding of ENZ free thin film (b) Relationship between resonance transmission peak and structural parameters

Figure 3. Measurement and simulation of (a) nonlinear refractive index coefficient and (b) nonlinear absorption coefficient under normal incidence

Figure 4. Linear optical properties of oblique incidence (a) Experimental and simulated linear transmission spectra at different incidence angles; (b) The relationship between electric field distribution, resonance transmission peak, and incident angle

This coupling mechanism has three breakthrough advantages: the strong field overlap effect between Q-GM and ENZ modes generates a 260 meV energy level anti crossover splitting, significantly enhancing nonlinear optical effects; Under normal incidence conditions, the nonlinear refractive index of the metasurface reaches In2I=3.8 × 10-13m2/W, which is three orders of magnitude higher than the nonlinear coefficient of the ENZ film and effectively reduces the power consumption of on-chip nonlinear photonic devices; Thanks to the high-quality factor of Q-GM in the wide wave vector, the experimental measurement of the nonlinear coefficient of the metasurface has robustness with increasing incident angle, achieving broadband tunable strong nonlinear optical effects.

The research results provide a new technological route for the development of nonlinear photonic devices with large angle and multi wavelength modulation, and demonstrate important application potential in fields such as integrated photonics, all-optical signal processing, and biosensing imaging.

Source: Opticsky