Influence of optical coupling strength on the resonant oscillation frequency in multiaperture VCSELs

We investigate the ultrafast dynamic response of multi-aperture (MA) vertical-cavity surface-emitting lasers (VCSELs) using time-resolved streak camera measurements. Quasi-isolated 2×2 MA VCSELs emitting at 850 nm, 880 nm, 910 nm, and 940 nm are studied to assess relaxation oscillation dynamics across different wavelengths. These devices exhibit relaxation oscillation frequencies exceeding 25 GHz and reaching up to approximately 30–32 GHz, significantly surpassing the typical limits (≈20 GHz) of single-aperture VCSELs. For 850 nm MA VCSELs, the influence of the optical coupling strength on the resonant oscillation frequency is investigated in detail. Optically coupled 2×2 devices show a pronounced increase in oscillation frequency, reaching values up to approximately 70 GHz. Interestingly, the coupled apertures exhibit an inverse temporal chirp, with oscillation frequencies increasing during the transient response, indicating dynamically evolving selfinjection locking between the apertures. Strongly coupled 2×1 MA VCSELs processed with an antireflection coating demonstrate even higher resonant oscillation frequencies of up to approximately 86 GHz and additionally, some tighter aperiodic peak squeezing showcasing the possibility of 100-GHz modulation. In contrast to the 2×2 case, these devices exhibit a normal temporal chirp, with oscillation frequencies decreasing over time and forming a sequence of aperiodic oscillations. The results highlight the critical role of aperture geometry and coupling strength in enabling ultrafast collective dynamics in MA VCSELs and demonstrate the potential of coupled-aperture designs for future high-speed optical transmitters.