In the paper, we study a single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser with a switchable single-and dual-wavelength output in C-band scale simultaneously. When a 1×4 wavelength-division-multiplexing (WDM) multiplexer is placed inside the ring cavity, four tunable single wavelengths and five sets of dual-wavelength with several mode-spacing can be accomplished, respectively. To achieve the selective and stable output characteristic, the suitable adjustment of cavity and birefringent losses are operated. Additionally, the laser characteristics of output wavelength, detected power, and optical signal to noise ratio (OSNR) have also been discussed.

To increase the data capacity of a light-emitting diode (LED) based visible light communication (VLC) transmission, a polarization-division-multiplexing (PMD) green (G)- and blue (B)- light-based transmitter (Tx) module is demonstrated here. It was demonstrated that we can achieve 1200 and 1120 Mbps VLC capacities based on dual-polarized G- and a B-LED based light wave after 3 and 4 m free-space link lengths, respectively, at exceedingly low illuminance. Based on the presented VLC system, paired G-LEDs or B-LEDs with dual-polarization can also be applied on the VLC-Tx side for doubling and delivering VLC data. According to the obtained results, the largest polarization offset angle of 50° between two polarizers (POLs) can be allowed experimentally to provide optimal VLC traffic. Moreover, the relationships of polarization offset, the illuminance of LED and maximum achieved VLC capacity are also performed and analyzed.

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