In this paper, we proposed and experimentally verified a diffraction-based optical beam shaping technique for underwater optical communication (UWOC) applications. The proposed method aimed to address the key issue in UWOC links, i.e., the high propagation loss experienced by the launched optical beam. It enabled a significantly higher portion of the launched signal to be collected by the receiver. The optimal transmission distance could also be fine-tuned by the software configuration. In a proof-of-concept demonstration based on the off-the-shelf components, 100 Mbps transmission was achieved over 15-meter distance and a significant enhancement in the transmission quality was observed. There is a huge scope for further improvement in the transmission distance and data rate when the proposed technique was used with purpose-built optical components and advanced coding schemes.