High-refractive-index 2D photonic structures for robust low-threshold multiband lasing.

Abstract

High-refractive-index (HRI) dielectrics are gaining increasing attention as building blocks for compact lasers. Their ability to simultaneously support both electric and magnetic modes provides greater versatility as compared to plasmonic platforms. Moreover, their reduced absorption loss minimizes heat generation, further enhancing their performance. Here, we employ a scalable soft nanoimprinting lithography method to create a series of two-dimensional (2D) periodic square hole arrays in polymeric films (SU-8), which are coated with an HRI dielectric layer (TiO₂). These structures exhibit low-threshold lasing from an organic dye-doped SU-8 layer deposited on top. We study arrays with different lattice parameters and a sample with a random distribution of holes, finding that the optimal laser performance occurs when the optical resonances of the array align with the emission wavelength range of the dye. Furthermore, we observe that the anisotropy in the TiO₂ coating breaks the polarization degeneracy of the square arrays, leading to the emergence of new modes and enabling the simultaneous appearance of multiple lasing peaks. Our work shows that, despite the simplicity of their fabrication process, the HRI structures studied here exhibit a high degree of complexity, leading to a rich optical response and enabling multiband lasing. This offers an innovative approach to building robust HRI platforms for lasing with improved control over their emission properties.