Vertical-Cavity Surface-Emitting Lasers with Monolithically Integrated Metasurfaces

Abstract

The vertical-cavity surface-emitting laser (VCSEL) is a ubiquitous optoelectronic device, for example, powering short-reach communication in data centers and facial recognition. Its claim to fame is its small cavity, which enables low threshold currents, lasing within a single longitudinal mode, and excellent high-speed modulation. However, the small cavity size also implies a significant beam divergence, which means that the VCSEL is typically butt-coupled to a fiber, integrated with microlenses, or packaged with bulky external optics. The latest paradigm of miniaturized beam-shaping optics is called metasurfaces, nanostructures with a thickness similar to the wavelength of light and capable of imparting arbitrary phase profiles and polarization states to an incident beam. By integrating a metasurface directly in the substrate of the VCSEL, its compactness is preserved, thereby eliminating bulky optics and delivering an on-chip, tailored beam.In this thesis, I present the design and fabrication of single-mode, single-polarization, bottom-emitting VCSELs monolithically integrated with GaAs metasurfaces. These devices are thereafter utilized for miniaturized biophotonic illumination modules. To overcome the aspect-ratio-dependent etching limits inherent to monolithic integration without an etch stop-layer. I demonstrate an unconventional metasurface design capable of shaping the VCSEL emission at exceptionally steep angles (>60°) with high efficiency (>90%). These metasurface-integrated VCSELs enable the realization of a combined dark-field and total-internal-reflection microscopy module, along with a surface plasmon resonance sensor with near state-of-the-art sensitivity, in a new integrable, flat format.