Vertical-Cavity Surface-Emitting Laser with Facet-Etched Metasurfaces

Licentiate thesis, 2024

The vertical-cavity surface-emitting laser (VCSEL) is a ubiquitous device today. It is responsible for efficiently powering the short-reach fiber-optic links in data centers and registering your face every time you unlock your iPhone. The VCSEL's popularity comes from its micro-sized cavity, enabling the laser to lase with low threshold currents, inherent single longitudinal mode, and excellent high-speed modulation performance. However, the small cavity size implies that the emitted beam will have a significant divergence. Which means that the VCSEL needs to be packaged together with bulky external optics to perform even the simplest optical task. One of the more recent advancements in nanophotonics is called metasurfaces, a surface patterned with nanoparticles that can tailor the phase and polarization state for an incident beam. By carefully designing the geometry of the nanoparticles, it is possible to replicate and combine the output of essentially any classical refractive optical element, all in an optical component with a thickness that is of the same order as the wavelength of the beam.

The idea behind this work is to monolithically integrate metasurfaces directly in the facet of the VCSEL, removing the need for any beam shaping optics and delivering an arbitrary beam while maintaining the small footprint of the laser diode. In this thesis, I present how to design and fabricate a VCSEL with an integrated metasurface and how we have utilized them to construct miniaturized illumination modules for biophotonics. We have demonstrated an unconventional metasurface design that can very efficiently, >90%, deflect light to large angles, >60 degrees, and circumvents the inherent problem of aspect-ratio dependent etching associated with monolithic integration. The VCSELs with facet-etched metasurfaces have enabled a combined dark-field and total internal reflection microscope module, and a surface-plasmon resonance sensing module with comparable to the state-of-the-art resolution.