Research on a carrier suppression analog optical transmission method based on directly modulated lasers

In conventional directly modulated analog fiber links, the conversion efficiency of RF signals to RF-over-fiber (RROF) signals is low due to the slope efficiency of semiconductor lasers. To reduce the transmission loss of the directly modulated analog fiber links, we propose a carrier suppression method. By analyzing the effect of drive current on the slope efficiency of the directly modulated laser (DML), we realized a carrier suppression modulation mode for the double sideband (DSB) via optimal drive current selection. Subsequently, the optical amplifier is cascaded to enhance the percentage of the RROF signal power under the premise of constant optical power input to the photodetector, thereby achieving the high-gain direct modulation. Experiments are conducted combining the performance of the actual commercial devices, and the results show that the carrier suppression method for modulation of 3 GHz RF signals exhibited 32.5 dB improvement in AM efficiency and a signal-to-noise ratio (SNR) enhancement of 5 dB compared with the conventional method.