Laser diode based free-space, underwater, and white-lighting visible light communication
Date Issued
2016
Date
2016
Author(s)
Wu, Tsai-Chen
Abstract
Since visible light (wavelength ranging from 350 to 750 nm) communication (VLC) can extend the global high-speed network to specific space, its development of connecting all communication networks in human society is necessary. Using blue laser diode (LD) with higher modulation bandwidth and lower divergence than light emitting diode (LED) can not only enhance the VLC transmission performance but also further perform underwater communication. By further adhering phosphorous glass upon blue LD or mixing the red/green/blue (RGB) LDs, white-lighting source can also be provided. In this thesis, laser diode based free-space, underwater, and white-lighting visible light communication is proposed. Firstly, a 450-nm blue LD is used to perform 10.8-Gbps/16-m point-to-point VLC. Furthermore, the white-lighting VLC is constructed by adhering Lu3Al5O12:Ce3+ and CaAlSiN3:Eu2+ co-doped phosphorous glass upon 450-nm blue LD. The correlated color temperature (CCT), Commission International de l’Eclairage (CIE) and maximal illuminance value of white light generated by 0.85-mm phosphorous glass is 7856 K, (0.29, 0.3) and 1337 lux, respectively. In addition, the blue light damage of human eye is discussed by measuring the exposure limit. In addition, the white-lighting VLC with transmission data rate of 2.8 Gbps and free-space distance of 1 m is demonstrated without endangering human eyes. Moreover, the blue LD is also used to demonstrate the tap and pure ocean water based underwater optical wireless communication (UOWC) systems. For the tap water based UOWC system, the maximal allowable transmission capacities with corresponding underwater distances of 12.4-Gbps/1.7-m, 12-Gbps/3.4-m, 9.6-Gbps/6.8-m and 5.2-Gbps/10.2-m are demonstrated, which exhibits a distance related decay rate on capacity of 0.847 Gbps/m. When using the pure ocean water to replace the tap water, it inside impurities induced scattering would attenuate the blue laser power during underwater transmission. Therefore, a slightly high decay rate of 0.941 Gbps/m is observed for the pure ocean water based UOWC system, which achieves 7.2 Gbps for 6.8-m and 4 Gbps for 10.2-m. Finally, RGB LDs based indoor white-lighting communication is demonstrated for wavelength-division multiplexing (WDM) transmission. Before mixing the RGB LDs, the individual RGB LDs carried 16-QAM OFDM data exhibit maximal transmission data rate of 10.8, 10.4 and 8 Gbps at 1-m free-space transmission distance, respectively. After mixing the RGB laser light, the generated white light with CIE coordinate of (0.2928, 0.2981) and CCT of 8382 K exhibits a maximal illuminance of 7540 lux. To reduce the blue light hazard of human eyes, a filter with 0.3 optical density (OD) is adhered on the blue LD, and the CIE coordinate and CCT of RGB LDs generated white light are (0.2938, 0.3513) and 7275 K, respectively. Moreover, the indoor white-lighting WDM system reveals a total allowable transmission data rate of 5.2 Gbps with transmission distance of 0.5 m.
Subjects
450-nm blue LD
point-to-point VLC
white-lighting VLC
underwater optical wireless communication
RGB LDs based indoor white-lighting communication
Type
thesis