  This paper proposes the trajectory tracking problem between an autonomous
underwater vehicle (AUV) and a mobile surface ship, both equipped with optical
communication transceivers. The challenging issue is to maintain stable
connectivity between the two autonomous vehicles within an optical
communication range. We define a directed optical line-of-sight (LoS) link
between the two-vehicle systems. The transmitter is mounted on the AUV while
the surface ship is equipped with an optical receiver. However, this optical
communication channel needs to preserve a stable transmitter-receiver position
to reinforce service quality, which typically includes a bit rate and bit error
rates. A cone-shaped beam region of the optical receiver is approximated based
on the channel model; then, a minimum bit rate is ensured if the AUV
transmitter remains inside of this region. Additionally, we design two control
algorithms for the transmitter to drive the AUV and maintain it in the
cone-shaped beam region under an uncertain oceanic environment. Lyapunov
function-based analysis that ensures asymptotic stability of the resulting
closed-loop tracking error is used to design the proposed NLPD controller.
Numerical simulations are performed using MATLAB/Simulink to show the
controllers' ability to achieve favorable tracking in the presence of the solar
background noise within competitive times. Finally, results demonstrate the
proposed NLPD controller improves the tracking error performance more than
$70\%$ under nominal conditions and $35\%$ with model uncertainties and
disturbances compared to the original PD strategy.
