Silver film and distributed Bragg reflector microcavity: multilayered laser model threshold analysis

Abstract

The paper is devoted to the theoretical investigation of threshold conditions in layered microlaser structures combining a finite-thickness silver film and a dielectric distributed Bragg reflector (DBR). The research is motivated by the growing demand for compact and efficient coherent light sources that can be integrated into modern photonic and optoelectronic systems. Microlasers based on hybrid metal–dielectric cavities attract considerable attention because they offer reduced size, low power consumption, and the potential for precise spectral control. At the same time, their operation is strongly affected by the reflectivity of cavity boundaries, the thickness of the active medium, and the presence of parasitic resonances. In this context, the present work focuses on analyzing how these structural factors determine the lasing threshold and spectral characteristics of operating modes. The study employs the Lasing Eigenvalue Problem approach, which enables a rigorous description of cavity modes at the emission threshold, and the Transfer Matrix Method, which is widely used for multilayer optical systems. The numerical results demonstrate that increasing the silver film thickness can noticeably reduce the lasing threshold, while adjustment of the active layer thickness provides efficient wavelength tuning in the visible and near-infrared ranges. A specific example is given for Nd:YAG-based microlasers, where emission near 1064 nm can be accurately controlled by selecting appropriate cavity parameters.
A significant part of the analysis is dedicated to the role of the DBR. It is shown that the DBR not only forms photonic band gaps that suppress energy leakage, but also gives rise to a series of additional resonances. These parasitic modes originate from sub-cavities within the multilayer reflector and become more numerous as the number of dielectric pairs increases. However, they are characterized by much higher threshold gain values and weak overlap with the active region, which makes them less favorable for practical lasing. The comparison with a purely metallic cavity demonstrates that the inclusion of a sufficiently wide DBR can improve the performance of the primary mode, lowering its threshold while isolating it from parasitic resonances.

The obtained results highlight the potential of combining noble-metal films with DBR structures in the design of advanced microlasers. By carefully adjusting the reflector parameters, it is possible to optimize mode selection, suppress unwanted resonances, and achieve stable, efficient operation. Such approaches are expected to be valuable for the development of integrated photonic devices, optical communication systems, LiDAR sensors, and compact biosensing platforms. The paper provides useful theoretical guidelines for further research and practical implementation of layered microlasers with tunable properties.