Researchers simulate novel metal-filtered VCSEL modal control

A study led by researchers from the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences revealed a novel metal-dielectric film mode filter structure that can flexibly regulate transverse modes in vertical-cavity surface-emitting lasers (VCSELs), which demonstrates the potential of metal apertures in enhancing mode control within VCSELs. The study was published in Sensors.

Traditional oxide-confined VCSELs often struggle with increased series resistances and low output power when operating in single mode. To overcome these limitations, researchers proposed an effective mode filtering technique using metal apertures.

Researchers developed a finite element simulation model of a metal mode-filtered VCSEL (MMF-VCSEL) using COMSOL software. The simulation results showed that the modal control performance of the MMF-VCSEL was significantly influenced by the number of P-Distributed Bragg Reflector (P-DBR) pairs, metal aperture size, and oxide aperture size.

Specifically, the transverse optical field was strongly confined within the metal aperture when the number of P-DBRs was low, but the confinement weakened as the number of P-DBRs increased.

When the metal aperture was smaller than the oxide aperture, the optical scattering effect was intensified as the distance between the two apertures decreased.

This resulted in increased mode discrimination and modal loss, facilitating better single-mode stability. When the metal aperture exceeds the oxide aperture, the optical mode in the VCSEL is primarily controlled by the oxide aperture. This highlighted the complex interplay between metal and oxide apertures in determining optical field confinement and mode discrimination.

Additionally, researchers introduced a new parameter, optical gain, which characterized the change in threshold gain of different transverse modes due to optical scattering by the structure. By balancing the optical gain difference between modes and the optical gain of the fundamental mode, they identified optimal structural parameters that enhanced both single-mode stability and slope efficiency of the MMF-VCSEL.

This metal mode-filtered VCSEL structure represents an advancement in optical mode control. By flexibly modulating the transverse mode, researchers have demonstrated the potential of high-power, single-mode VCSELs with improved performance characteristics.

This study underscores the critical role of metal apertures in enhancing mode control in VCSELs. It opens up new avenues for developing high-performance VCSELs with a wide range of applications.