title: Blue Laser Diode Enables Underwater Communication at 12.4 Gbps.
abstract: To enable high-speed underwater wireless optical communication (UWOC) in tap-water and seawater environments over long distances, a 450-nm blue GaN laser diode (LD) directly modulated by pre-leveled 16-quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) data was employed to implement its maximal transmission capacity of up to 10 Gbps. The proposed UWOC in tap water provided a maximal allowable communication bit rate increase from 5.2 to 12.4 Gbps with the corresponding underwater transmission distance significantly reduced from 10.2 to 1.7 m, exhibiting a bit rate/distance decaying slope of -0.847 Gbps/m. When conducting the same type of UWOC in seawater, light scattering induced by impurities attenuated the blue laser power, thereby degrading the transmission with a slightly higher decay ratio of 0.941 Gbps/m. The blue LD based UWOC enables a 16-QAM OFDM bit rate of up to 7.2 Gbps for transmission in seawater more than 6.8 m.
authors.affiliation: Graduate Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan R.O.C.
authors.forename: Tsai-Chen
authors.initials: TC
authors.lastname: Wu
authors.affiliation: Graduate Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan R.O.C.
authors.forename: Yu-Chieh
authors.initials: YC
authors.lastname: Chi
authors.affiliation: Graduate Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan R.O.C.
authors.forename: Huai-Yung
authors.initials: HY
authors.lastname: Wang
authors.affiliation: Graduate Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan R.O.C.
authors.forename: Cheng-Ting
authors.initials: CT
authors.lastname: Tsai
authors.affiliation: Graduate Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan R.O.C.
authors.forename: Gong-Ru
authors.initials: GR
authors.lastname: Lin