VCSEL Multilayer Film Structure for High-Order Mode Suppression

The patent applies local quality by creating an asymmetric refractive index distribution in the multilayer film structure. The film stack includes alternating layers of materials with different refractive indices (e.g., AlGaAs and GaAs), where the refractive index varies locally through the thickness of the film. This local variation in optical properties creates a gradient that suppresses high-order transverse modes while maintaining fundamental mode oscillation, thereby resolving the contradiction between reliable single-mode operation and preventing harmful high-order mode oscillation at high injection levels.

The patent implements asymmetry by designing the multilayer film with an inclined side surface rather than a vertical one. The side surface forms a specific angle (e.g., 45 degrees) with respect to the substrate plane, creating an asymmetric geometry that selectively suppresses high-order transverse modes. This asymmetric configuration causes different effective optical path lengths for different modes, thereby suppressing high-order modes while maintaining manufacturability through standard semiconductor fabrication techniques such as angled etching.

The patent employs composite materials by constructing the multilayer film from alternating layers of semiconductor materials with different refractive indices, such as AlGaAs and GaAs. This composite structure creates a periodic variation in optical properties that enhances the suppression of high-order transverse modes through constructive and destructive interference effects. The multiple layers work together to create a more effective optical confinement and mode selection mechanism compared to a single-layer structure, thereby reducing harmful high-order mode oscillation.