Static Properties of 980 nm Vertical Cavity Surface Emitting Lasers With Different Monolithic High Refractive Index Contrast Grating Mirror Designs

Abstract

Vertical-cavity surface-emitting lasers (VCSELs) with monolithic high contrast gratings (MHCGs) as top coupling mirrors are highly attractive nanophotonic components with manyfold application prospects due to their small size footprint, energy efficiency, and wavelength flexibility. We report on the design, fabrication, and characterization of the static properties of 980 nm MHCG VCSELs and compare their performance to that of conventional double distributed Bragg reflector (DBR) VCSELs of comparable design. To increase the MHCG's optical power reflectance at 980 nm and the width of the optical stopband for single-mode behavior and improved energy efficiency, we add a 5.5-period p-doped DBR beneath the MHCG grating, thus forming a composite DBR plus MHCG top coupling mirror. With such a low number of supporting DBR mirror pairs, the MHCG characteristic dominates the output performance of the resulting devices. Our systematic study includes a variation of the grating period $P$, the grating fill factor $F$, and the oxide aperture diameter $\phi$. We report record static light output power-current-voltage (LIV) performance for our MHCG DBR VCSELs with threshold currents as low as 0.25 mA, wallplug efficiencies of 8%, optical output powers exceeding 1.6 mW, and stable linearly polarized emission with orthogonal polarization suppression ratios $>33$ dB. By varying the grating designs, record current-induced wavelength tuning ranges up to 13.4 nm and single mode emission with a side-mode suppression ratio of up to 46 dB, and $>40$ dB even beyond thermal rollover, are achieved. Moreover, the MHCG DBR VCSELs feature excellent thermal properties with thermal resistance of only 2.46 K/mW, and we observe grating design dependent side mode suppression behavior; from normal oxide aperture diameter dependent number of side modes up to oxide aperture diameter independent single mode emission up to 9 $\mu$m oxide aperture diameter. Overall, our study demonstrates that MHCGs, as a key source of optical power reflectance, can be strategically designed to tailor a VCSEL's output characteristics. By varying the MHCG geometry, we can produce side-by-side VCSELs (on the same epitaxial wafer) with vastly different emission and performance properties. By supporting a broader range of resonance wavelengths and enabling post-growth wavelength tuning, MHCG-based DBR VCSELs offer significant potential for applications in 2D VCSEL arrays, data transmission, sensing, and imaging.