Modulation bandwidth enhancement via resonance detuning in coherently coupled vertical cavity laser arrays

Vertical cavity surface emitting lasers (VCSELs) are the dominant source for optical data communication links in computer server, data center, and super computer applications. These applications demand higher bandwidth (> 20 Gbps), longer fiber propagation length (> 1 km), and lower power operation. There have been several reports of VCSEL modulation bandwidth in excess of 50 Gbps [1, 2] although these experiments have been into a few 10s of meter of fiber and require very high current density. Modulation gain bandwidth x distance products of 25×1 [3], 20×2 [4], and 1×10 [5] Gbps/km have been achieved using single mode or quasi-single mode VCSELs. Note that longer propagation implies lower bandwidth presumably due to insufficient power. Recently transversely coupled VCSELs have been shown to operate at 36 Gbps, albeit in highly multi-mode operation [6]. We report significant bandwidth enhancement achieved from 1×2 coherently coupled photonic crystal VCSEL arrays. 25 GHz small signal bandwidth (receiver limited) is obtained under single mode operation and simultaneous increased output power, which is nearly a 3-fold improvement compared to incoherent array modulation.