50 m/187.5 Mbit/s real-time underwater wireless optical communication based on optical superimposition

Abstract

In this paper, an optical pulse amplitude modulation with 4 levels (PAM-4) using a fiber combiner is proposed to enhance the data rate of a field-programmable gate-array-based long-distance real-time underwater wireless optical communication system. Two on-off keying signals with different amplitudes are used to modulate two pigtailed laser diodes, respectively, and the generated optical signals are superimposed into optical PAM-4 signals by a fiber combiner. The optical PAM-4 scheme can effectively alleviate the nonlinearity, although it reduces the peak-to-peak value of the emitting optical power by 25%. A real-time data rate of 187.5 Mbit/s is achieved by using the optical PAM-4 with a transmission distance of 50 m. The data rate is increased by about 25% compared with the conventional electrical PAM-4 in the same condition.

Improved Synchronization Scheme for the Photon- Counting-Based Underwater Optical Wireless Communication System

“…This is the author's version which has not been fully edited and content may change prior to final publication. To reduce the number of jointly estimated unknowns in problem (8), we first maximize F 1 (n, k, λ s , λ b , d) with respect to {λ s , λ b } for given (n, k) and d, yielding…”