Adaptive 84.44-190 Mbit/s phosphor-LED wireless communication utilizing no blue filter at practical transmission distance

Mitigation of performance degradation due to dynamic display contents in visible light communication using TV backlight and CMOS image sensor

Here, we propose and demonstrate a performance degradation mitigation scheme in TV backlight and smart-phone-based visible light communication (VLC) system when the display content in the light-panel is dynamically changing. In order to evaluate the influence of the dynamic display contents to the VLC performance, we use a noise-ratio (NR) and noise-ratio standard deviation (NRSD) as the figure-of-merits for the bright-and-dark contrast of the display content; and the dispersal of the changing display content regarding the bright-and-dark contrast respectively. Performances of 4 dynamic display contents with different combinations of NR and NRSD are analyzed. They are: low NR and low NRSD (NR = 36.69%; NRSD = 0.0226); low NR and high NRSD (NR = 30.09%; NRSD = 0.2698); high NR and low NRSD (NR = 81.66%; NRSD = 0.0052); high NR and high NRSD (NR = 73.91%; and NRSD = 0.2717). The proposed scheme can work well; that is, even the transmission distance is up to 200 cm in both smart-phones. If the proposed scheme is not used, then high success rate can be observed only at the low NR and low NRSD display content when the transmission distance is < 100 cm.

Hydrogen Peroxide-Treated Carbon Dot Phosphor with a Bathochromic-Shifted, Aggregation-Enhanced Emission for Light-Emitting Devices and Visible Light Communication

It is demonstrated that treatment of blue-emissive carbon dots (CDs) with aqueous hydrogen peroxide (H2O2) results in the green emissive solid state CD phosphor with photoluminescence quantum yield of 25% and short luminescence lifetime of 6 ns. The bathochromic-shifted, enhanced green emission of H2O2-treated CDs in the powder is ascribed to surface state changes occurring in the aggregated material. Using the green emissive H2O2-treated CD phosphor, down-conversion white-light-emitting devices with cool, pure, and warm white light are fabricated. Moreover, using the green emissive CD phosphor as a color converter, a laser-based white-light source is realized, and visible light communication with a high modulation bandwidth of up to 285 MHz and data transmission rate of ≈435 Mbps is demonstrated.

Using advertisement light-panel and CMOS image sensor with frequency-shift-keying for visible light communication

A frequency-shift-keying (FSK) visible light communication (VLC) system is proposed and demonstrated using advertisement light-panel as transmitter and mobile-phone image sensor as receiver. The developed application program (APP) in mobile-phone can retrieve the rolling shutter effect (RSE) pattern produced by the FSK VLC signal effectively. Here, we also define noise-ratio value (NRV) to evaluate the contrast of different advertisements displayed on the light-panel. Both mobile-phones under test can achieve success rate > 96% even when the transmission distance is up to 200 cm and the NRVs are low.

0.52-11.86 Gbit/s OFDM modulation for power-sharing VLC transmission by using VCSEL laser

In this paper, we propose employing a 682 nm vertical-cavity surface-emitting laser (VCSEL) with 1 GHz bandwidth for high-speed and power-sharing wireless visible light communication (VLC) in the different transmission distances of 2 to 5 m. In the measurement, the data rate of 0.52 to 11.86 Gbit/s (0.44 to 10.8 Gbit/s in a net data rate) can be achieved by using spectral-efficient orthogonal frequency division multiplexing (OFDM) modulation with bit-loading algorithm. Therefore, 4- to 256-quadrature amplitude modulations (QAMs) are employed simultaneously in the modulation bandwidth for VCSEL-based VLC. The proposed power-sharing VLC system can be divided to four end-users, when three beam splitters (BSs) are used simultaneously. Moreover, all of the measured bit error rates (BERs) are below the forward error correction (FEC) threshold (BER = 3.8 × 10^-3).

4-Gbit/s visible light communication link based on 16-QAM OFDM transmission over remote phosphor-film converted white light by using blue laser diode

Visible Light Communication (VLC) as a new technology for ultrahigh-speed communication is still limited when using slow modulation light-emitting diode (LED). Alternatively, we present a 4-Gbit/s VLC system using coherent blue-laser diode (LD) via 16-quadrature amplitude modulation orthogonal frequency division multiplexing. By changing the composition and the optical-configuration of a remote phosphor-film the generated white light is tuned from cool day to neutral, and the bit error rate is optimized from 1.9 × 10(-2) to 2.8 × 10(-5) in a blue filter-free link due to enhanced blue light transmission in forward direction. Briefly, blue-LD is an alternative to LED for generating white light and boosting the data rate of VLC.

Phosphorous Diffuser Diverged Blue Laser Diode for Indoor Lighting and Communication

An advanced light-fidelity (Li-Fi) system based on the blue Gallium nitride (GaN) laser diode (LD) with a compact white-light phosphorous diffuser is demonstrated for fusing the indoor white-lighting and visible light communication (VLC). The phosphorous diffuser adhered blue GaN LD broadens luminescent spectrum and diverges beam spot to provide ample functionality including the completeness of Li-Fi feature and the quality of white-lighting. The phosphorous diffuser diverged white-light spot covers a radiant angle up to 120^o with CIE coordinates of (0.34, 0.37). On the other hand, the degradation on throughput frequency response of the blue LD is mainly attributed to the self-feedback caused by the reflection from the phosphor-air interface. It represents the current state-of-the-art performance on carrying 5.2-Gbit/s orthogonal frequency-division multiplexed 16-quadrature-amplitude modulation (16-QAM OFDM) data with a bit error rate (BER) of 3.1 × 10⁻³ over a 60-cm free-space link. This work aims to explore the plausibility of the phosphorous diffuser diverged blue GaN LD for future hybrid white-lighting and VLC systems.

Visible light communication using mobile-phone camera with data rate higher than frame rate

Complementary Metal-Oxide-Semiconductor (CMOS) image sensors are widely used in mobile-phone and cameras. Hence, it is attractive if these image sensors can be used as the visible light communication (VLC) receivers (Rxs). However, using these CMOS image sensors are challenging. In this work, we propose and demonstrate a VLC link using mobile-phone camera with data rate higher than frame rate of the CMOS image sensor. We first discuss and analyze the features of using CMOS image sensor as VLC Rx, including the rolling shutter effect, overlapping of exposure time of each row of pixels, frame-to-frame processing time gap, and also the image sensor "blooming" effect. Then, we describe the procedure of synchronization and demodulation. This includes file format conversion, grayscale conversion, column matrix selection avoiding blooming, polynomial fitting for threshold location. Finally, the evaluation of bit-error-rate (BER) is performed satisfying the forward error correction (FEC) limit.

A 550 Mbit/s real-time visible light communication system based on phosphorescent white light LED for practical high-speed low-complexity application

In this paper, we first experimentally demonstrate a 550 Mbit/s real-time visible light communication (VLC) system based on nonreturn-to-zero on-off keying (NRZ-OOK) modulation of a commercial phosphorescent white light LED. The 3-dB modulation bandwidth of such devices is only a few megahertz. We proposed an analog pre-emphasis circuit based on NPN transistors and an active post-equalization circuit based on an amplifier to enhance the 3-dB bandwidth of VLC link. Utilizing our proposed pre-emphasis and post-equalization circuits, the 3-dB bandwidth of VLC link could be extended from 3 to 233 MHz with blue-filter, to the best of our knowledge, which is the highest ever achieved in VLC systems reported. The achieved data rate was 550 Mbit/s at the distance of 60 cm and the resultant bit-error-ratio (BER) was 2.6 × 10(-9). When the VLC link operated at 160 cm, the data rate was 480 Mbit/s with 2.3 × 10(-7) of BER. Our proposed VLC system is a good solution for high-speed low-complexity application.