An underwater optical communication link provides high-speed data transfer between water surface buoys/ships and underwater vehicles for robotics applications. However, currently such optical links are severely limited by the coverage range due to the high attenuation of light in the water environment as well as by the scattering problem. A new optical transceiver structure is proposed in this work to significantly extend the coverage range by several folds, targeting to solve this coverage bottleneck problem for high-speed data transfer. The proposal is a new optical transceiver structure with hybrid nonlinear pulse position modulation and time-frequency spreading. This new scheme is able to boost the range coverage by several folds, and was verified via thorough computer simulations using realistic models tailored for the optical channel propagation environments. The proposed structure can be integrated into the existing underwater vehicles and robots to enable the next-generation range-extended and high-speed optical links for oceanic explorations.