Undersea cables play a crucial role in enabling global communication and data transfer, significantly affecting Internet speeds. Without them, global communication would be severely limited. As technology advances and network demands increase, the number and variety of optical fibers within cables are constantly increasing. This growth results in more costly cable networks with the ability to transmit more data and enhances the speed and reliability of data transmission. The construction of an undersea cable system requires careful consideration of the appropriate bandwidth of the cable to meet network bandwidth requirements while minimizing costs. In this article, we formulate the undersea cable network optimization problem taking account of the bandwidth capacity of each cable edge on the cable network as a weighted edges Steiner minimum tree problem and describe a new algorithm called the weighted edges Steiner minimum tree (WE-SMT) algorithm. For the given locations of the terminal nodes and the bandwidth capacity requirement, the WE-SMT algorithm optimizes the position of Steiner nodes, the bandwidth capacity of each cable edge, and the cable path. We implement our algorithm in a real-world setting, evaluating the benefit gained against the outcomes obtained without accounting for bandwidth optimization, as well as studying the effect of data resolution on the quality of the path planning results. In addition, we assess the performance of our new algorithm in comparison with that of an operational real-world cable system.