# Analysis and Investigation of Dual-Polarized Color LED Based Visible Light Communication System
###### Abstract  
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\({}^{\circ}\) 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. visible light communication (VLC); light-emitting diode (LED); polarization-division-multiplexing (PMD); dual-polarized; energy efficiency +
Footnote †: journal: Photonics  
0000-0001-7000-0001-7000][PERSON] 1,0000-0001-7000-0001-7000][PERSON] 2,0000-0001-7000-0001-7000-0001-7000-0001-70000-0001-70000-0001-70000-0001-700000-0001-700001-700001-700001-700001-70001-700001-70001-700001-700001-700001-700001-700001-70  
nonlinear equalization (VNE) method by using PIN PD for detection at the illuminance of 1000 Lux [19]. Here, the larger illuminance and complex VNE algorithm were required to decode PDM and WDM VLC signal, and the wireless VLC length was not indicated. As mentioned above, they required OFDM modulation format for a shorter VLC connection length (or at the greater illuminance) to achieve >1 Gbit/s data rate. In 2017, [PERSON] et al. presented a hybrid PDM and RGB-WDM VLC system to achieve a 2.16 Gbit/s OFDM rate through 3 m link length within 100 MHz available bandwidth [20]. However, the related locations of the VLC transmitter (Tx) and receiver (Rx) were both fixed to deliver and decode the VLC signal for indoor application. In this demonstration, we propose and investigate a PDM-based G- and B-LED VLC transmission system with an orthogonal-polarization state to double the data traffic. Here, to obtain the dual-polarized VLC signals, the two orthogonal polarizers (POLs) at the receiver (Rx) side can be controlled for rotation automatically to match the dual VLC signals from the transmitter (Tx) site. The presented dual-polarized VLC system can achieve the total modulation rate of 1200 and 1120 Mbps (VLC\({}_{\text{(Green+Blue)}}\)) passing through 3 and 4 m free-space transmission lengths, respectively when the detected corresponding illuminances of G- and B-LEDs are 2.4 and 0.5 lux and 5.4 and 2.3 lux. To make the presented LED VLC system more flexible, we also employed paired G-LEDs and B-LEDs acting as the optical transmitter (Tx) to produce dual-polarized VLC\({}_{\text{(Green)}}\) and VLC\({}_{\text{(Blue)}}\) signals for alternative indoor applications, respectively. Hence, the proposed 2 \(\times\) 2 PDM G- and B-LED VLC system does not need any color filter for decoding signals. When the VLC client is moving randomly, the two polarizers (POLs) of the Rx side are controlled to match the dual-polarized VLC signals and avoid missing received signals. In addition, we also perform and discuss the influence of different polarization offset at a fixed VLC rate through a wireless link length of 3 and 4 m, respectively. Based on the observed results, the largest offset angle of two POLs should be less than 50\({}^{\circ}\) to maintain the optimal VLC modulation rate below the forward error correction (FEC) level. The presented LED VLC system is for fully static scenarios in the investigation. The optical wireless signal indoors might also bring a possibility of occupying by unauthorized stealer. To reach the signal security in the VLC connection, applying the encryption algorithm in the upper layer is one of the methods [21; 22].