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.

InGaN/GaN Laser Diodes With High Order Notched Gratings

“…ASER Diodes based on Gallium Nitride (GaN) have found a wide range of applications ranging from atomic spectroscopy [1] to optical communications [2]. To fully exploit many of these application areas there is a requirement for a GaN laser diode with high spectral purity and wavelength selectivity.…”

Underwater optical wireless communications, networking, and localization: A survey

“…Subsequently, the authors in [33] demonstrated a UOWC system with the data rate of 4.8 Gbps using 16 quadrature amplitude modulationorthogonal frequency division multiplexing (QAM-OFDM). A UOWC system with the data rate of 4.88 Gbps was proposed in [34] by using 32 QAM-OFDM to get the transmission distance of 6 m. Recently, a 7.2 Gbps UOWC system has been proposed in [35] for 450 nm blue laser with the transmission distance of 6 m. Table I summarizes the comparison between three different kinds of underwater wireless communication systems.…”

Light based underwater wireless communications

“…4,8,9) Taking advantages of the low absorption window of seawater in visible portion of the electromagnetic (EM) spectrum, UWOC provides unprecedentedly high transmission data rate thanks to the large available bandwidth (THz). 10,11) Link distances up to hundreds of meters (≈ 300 m) are possible. Other advantages of UWOC include high security, low power requirements, and unlicensed spectrum.…”

“…9,11,[33][34][35][36] Notably, Wu et al have experimentally achieved a 12.4 Gbps 16-QAM OFDM data transmission over 1.7 m underwater link using a 450 nm LD. 10) Meanwhile, Xu has reported 2.0 m, 161 Mbps using 450 nm LED. 37) Such LED based UWOC systems can be more promising for applications that require medium bit rates, low cost, and simultaneous illumination and communication.…”

“…Table I gives a brief summary of data rates and link distances achieved in recent UWOC system level demonstrations. [9][10][11][32][33][34]38,42,43) Another aspect of recent UWOC research is the channel modeling taking into account the effects of optical turbulence using experimental measurements. The probability density functions of laser beam intensity fluctuations due to salty and bubbly underwater channels under various channel conditions were experimentally obtained by Jamali.…”