High-Speed Inverted-Polarity Oxide-Confined Copper-Plated 850-nm Vertical-Cavity Lasers

Inverted-polarity (n-up), high-speed, oxide-confined, polyimide-planarized, copper-plated 850-nm vertical-cavity surface-emitting lasers with various aperture sizes were fabricated and characterized. The reported devices demonstrated intrinsic, parasitic, and thermal maximum bandwidth limitations of 39.3, 24.6, and 22.9 GHz, respectively. VCSELs with 7 μm active area diameter and 4 μm of plated copper exhibited a maximum -3 dB frequency modulation bandwidth (f_{-3 dB max}) of 18.8 GHz and a resonance frequency of 14.8 GHz at a bias current density (J_bias) of only 8.8 kA/cm², limited by thermal effects, with a high modulation current efficiency factor of 17.0 GHz/mA^1/2 for quantum well VCSELs. The presented VCSELs also demonstrated a record high f²_{-3 dB max}/J_bias ratio of 40.2 GHz²/kA/cm² which represents an 11% increase compared with the highest previously reported ratio. Rate-equation-based thermal VCSEL model and three-pole transfer function approximation were applied to extract several VCSELs´ parameters, which enabled the estimation of the VCSELs internal temperature and major bandwidth limitation. Particle swarm optimization was utilized in parameter extraction and optimization.