Spot alignment based on a five-photodiode receiver for a UWOC system

Abstract

In the traditional underwater wireless optical communication (UWOC) system, spot alignment and communication are divided into different paths. Moreover, the attenuated optical signal is easily submerged by underwater noise, affecting the accuracy of the spot alignment. In this paper, a novel, to the best of our knowledge, five-photodiode receiver (5-PDR) combining communication and spot alignment is proposed, which includes transimpedance amplifiers (TIAs), gain stages, and output buffers. Furthermore, a new denoising algorithm based on the hidden Markov model (HMM) is introduced. Through combining the 5-PDR and the HMM noising algorithm, spot alignment accuracy has been improved. Simulation results show that the root mean square error (RMSE) of our proposed method is reduced by 57.2%, compared with that of traditional four-quadrant detector (4-QD). The RMSE is controlled within 0.0108 mm, even under the worst conditions. The experimental results also confirm that 5-PDR has a good spot alignment ability in UWOC.