Multi-filament triggering of PCSS for high current utilizing VCSEL triggers

Abstract

We are developing advanced optically-activated solid-state switch technology for Firing Sets. Advanced switch development at Sandia has demonstrated multi-kA/kV switching and the path for scalability to even higher current/power, resulting in good prospects for sprytron replacement and other even higher current pulsed power switching applications. Realization of this potential requires development of new optical sources/switches based on key Sandia photonic device technologies: vertical-cavity surface-emitting lasers (VCSELs) and photoconductive semiconductor switch (PCSS) devices. The key to increasing the switching capacity of PCSS devices to 5kV/5kA and higher has been to distribute the current in multiple parallel line filaments triggered by an array of high-brightness line-shaped illuminators [Mar, A., et al., 2001]. This was limited by commercial mechanically-stacked edge-emitting lasers, which are difficult to scale and manufacture with the required uniformity. In VCSEL arrays, adjacent lasers utilize identical semiconductor material and are lithographically patterned to the required aspect ratio. However, we have demonstrated that good optical uniformity in rectangular-aperture (e.g. 5-by-500 mum) VCSELs is difficult to achieve due to the lack of optical confinement in the long dimension. We have demonstrated line filament triggering using 1-D VCSEL arrays to approximate line generation. These arrays of uncoupled circular-aperture VCSELs have fill factors ranging from 2% to 50%. Using these arrays, we are developing a better understanding of the illumination requirements for stable triggering of multiple-filament PCSS devices. In particular, we are examining the dependence of filament formation versus the illumination fill factor and spatial brightness along the length of the filament. Ultimately, we will apply effective index techniques, pioneered at Sandia for leaky-mode VCSELs, to create a lateral photonic lattice that selects a single transverse mode with high brightness and uniformity for even higher fill factors and illumination unformity [Zhou, D., et al., 2000]. These sources will be developed and tested with complementary PCSS designs employing interdigitated multifilament contacts for high-power switching.