Linear cascade VCSEL arrays with high differential efficiency and low differential resistance

We have fabricated monolithic linear cascade vertical-cavity surface-emitting laser (VCSEL) arrays intended for low loss fiber-optic radio-frequency links. Arrays with up to four VCSELs connected in series, with a spacing of 250 mu m, were fabricated on. an insulating substrate. A thick layer of BCB was used to facilitate series connection through contact metallization and enable high frequency operation. The threshold current is 0.6 mA, independent of the number of VCSELs in the array. Differential efficiency, maximum output power, voltage, and differential resistance scale linearly with the number of VCSELs. For a four VCSEL array, we achieve a high differential efficiency of 160%, a maximum output power of 24 mW, and a low differential resistance of 220 Omega. Basic link measurements, using a series connected VCSEL array, a parallel fiber ribbon, and a parallel connected detector array revealed a differential current gain exceeding unity in the low frequency limit.