Transverse detuned loading for modulation bandwidth enhancement in VCSELs
Directly modulated vertical-cavity surface-emitting lasers (VCSELs) are central to short-reach optical interconnects, where modulation bandwidth and power efficiency are critical factors for increasing data transfer capacity. Conventional oxide VCSELs still require power-hungry signal processing to achieve high-speed data transmission above 100 Gb/s. Here we report an experimental implementation of detuned loading in a VCSEL to enhance the modulation bandwidth. The detuned loading is achieved by carrier-induced index variations that reshape an engineered transverse mode so its overlap with spatially selective optical losses decreases with increased carrier density. This produces a negative differential loss reminiscent of that in detuned-loaded DBR lasers lasing on the long-wavelength reflectivity flank. The resulting 850 nm single-mode VCSEL exhibits an enhanced carrier-photon relaxation frequency of 44 GHz, yielding a 3dB electrical modulation bandwidth exceeding 50 GHz. The enhancement persists from 25 °C to 75 °C showing the robustness of the mechanism introduced. The same device supports 106.25 Gb/s NRZ transmission without digital signal processing, transmitter pre-emphasis or receiver equalization. These results establish transverse detuned loading as a robust alternative approach for extending the modulation bandwidth of vertical-cavity surface-emitting lasers.