Impact of Photon Lifetime on High-Speed VCSEL Performance
ABSTRACT We investigate the impact of reduced photon lifetime on the static and dynamic performance of high-speed, oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs). The photon lifetime is reduced by a shallow-surface etch that lowers the reflectivity of the top mirror. From an analysis of the dependence of slope efficiency on mirror loss (etch depth) and temperature, we deduce values for the internal quantum efficiency and the internal optical loss and their dependencies on temperature. From an analysis of the dependence of the small-signal-modulation response on photon lifetime (etch depth) and temperature, we deduce values for differential gain and gain compression, and their dependencies on photon lifetime and temperature. We find a tradeoff between high resonance frequency and low damping for speed enhancement, leading to an optimum photon lifetime close to 3 ps for this particular VCSEL design that enables a modulation bandwidth of 23 GHz and error-free transmission at 40 Gb/s.
Article: Impact of Device Parameters on Thermal Performance of High-Speed Oxide-Confined 850-nm VCSELs[show abstract] [hide abstract]
ABSTRACT: We study the impact of device parameters, such as inner-aperture diameter and cavity photon lifetime, on ther-mal rollover mechanisms in 850-nm, oxide-confined, vertical-cavity surface-emitting lasers (VCSELs) designed for high-speed operation. We perform measurements on four different VCSELs of different designs and use our empirical thermal model for calculating the power dissipated with increasing bias currents through various physical processes such as absorption within the cavity, carrier thermalization, carrier leakage, spontaneous carrier recombination, and Joule heating. When reducing the top mirror reflectivity to reduce internal optical absorption loss we find an increase of power dissipation due to carrier leakage. There is therefore a trade-off between the powers dissipated owing to optical absorption and carrier leakage in the sense that overcompensating for optical absorption enhances carrier leakage (and vice versa). We further find that carrier leakage places the ultimate limit on the thermal performance for this entire class of devices. Our analysis yields useful design optimization strategies for mitigating the impact of carrier leakage and should thereby prove useful for the performance enhancement of 850-nm, high-speed, oxide-confined VCSELs.IEEE JOURNAL OF QUANTUM ELECTRONICS. ; 48.