Simultaneous noise and distortion reduction of a broadband optical feedforward transmitter for multi-service operation in radio-over-fiber systems.

The broadband optical feedforward transmitter with uncooled and unisolated distributed-feedback laser diodes (DFB LDs) is developed for a radio-over-fiber system. Although we use DFB LDs for digital communications, the feedforward compensation method can significantly suppress the intermodulation distortions and background noise. For the wide frequency range from 2.05 to 2.60 GHz (550 MHz), the third-order intermodulation distortion (IMD3) is suppressed by more than 10 dB. We also analyze the variation of IMD3 and noise for the bias current of LDs. With the linearization technique, the maximum IMD3 suppression and spurious-free dynamic range enhancement are 21.3 dB and 7.11 dB, respectively, at 2.3 GHz.