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The data rate of the zero-power-consumption visible light communication system is limited due to the solar cell bandwidth limit. A new method has been proposed to improve the data rate of communication systems. The predistortion circuit based on the nonlinear compensation principle of the communication system is added between the transmitter and the receiver to equalize the amplitude–frequency response of the solar cell. Based on the measurement of the original amplitude–frequency response of the system, the zero-pole of the predistortion circuit is calculated, and an accurate equalization circuit is designed by using separate components to expand the 3 dB bandwidth of the system. The test results show that the 3 dB bandwidth of the visible light self-powered communication system is increased from 85 kHz to 750 kHz, and the system bandwidth is expanded by nearly 10 times.

In this paper, we propose and experimentally demonstrate HyperSight, which is a precise image decoding algorithm for the mobile-phone camera based visible light communication (VLC) system. The conventional algorithms have to select an appropriate column matrix, and then decode the image according to the fitting curve. The selection of the column matrix and the fitting of the function are not only time-consuming but also error-prone, leading to low decoding efficiency and high bit error rate (BER). While HyperSight calculates characteristic grayscale matrix to avoid column matrix selection and uses critical grayscale to replace the function fitting to decode the image. As expected, our algorithm not only reduces the BER, but also improves the processing performance. The experimental results show that, the BER can be reduced by two orders of magnitude on average compared with the conventional scheme. For the $4.8\,$ kbps data rate, our algorithm can achieve the transmission distance of $50\,$ cm under the $7\%$ forward error correction (FEC) threshold with the low illuminance of $702\,$ lux.

In this article, a novel method for constructing a pre-equalizer by optimized filter synthesis with vector fitting is proposed to broaden the bandwidth of a visible light communication (VLC) system. By using the proposed method, an active-passive hybrid equalization circuit is constructed, and it is demonstrated that the 3-dB bandwidth of the VLC system with commercially available phosphorescent white LED is extended from 30 MHz to 600 MHz. A 1.35 Gb/s NRZ-OOK VLC transmission over 12 cm free space transmission distance is experimentally realized, achieving a bit error rate (BER) of $\text{8.8} \times \text{10}^{-\text{5}}$ . To the best of the authors knowledge, this is the largest reported 3-dB bandwidth and real-time data rate achieved in the VLC system with a single commercially phosphorescent white LED.

An overall bit rate of 625 Mb/s real-time multi-access VLC system is presented in this paper. In order to decrease the effect of ambient light and deal with the non-linearity of LED, we propose a new algorithm to get orthogonal codes which is suitable for OOK modulation. By employing a single white LED and three photo diodes, three users are provided access to the VLC system individually at the same time. A data frame and CRC32 are adopted to realize a reliable and continuous data interaction between Ethernet and VLC system. All the numerical calculations are implemented by FPGAs so as to provide a practical high-speed transmission.

In the paper, a mixed-interval multi-pulse position modulation (MI-MPPM) scheme for visible light communication (VLC) system is theoretical proposed and implemented on field programmable gate array (FPGA). It has better bandwidth efficiency than PPM and MPPM. And it has better anti-jamming than MPPM. A real-time VLC link based on phosphorescent white LED is also built to measure the performance of the proposed MI-MPPM scheme. The data rate of 104 Mbps in our VLC system under the distance of 60 cm could be achieved, and bit error rate is 3 . 81 × 1 0 − 5 . As far as we know, it is the highest data rate that can be achieved in continuous real-time VLC system with phosphorescent white LED based on PPM and its derivative modulation. The performance of VLC system under different distances, advantages and the possible application scenarios of MI-MPPM are also discussed.

Silicon photocell acts as the detector and energy convertor in the VLC system. The system model was set up and simulated in Matlab/Simulink environment. A 10 Hz square wave was modulated on LED and restored in voltage mode at the receiver. An energy gathering and signal detecting system was demonstrated at the baud rate of 19200, and the DC signal is about 2.77 V and AC signal is around 410 mV.

In order to ensure stable, correct and real-time high-speed transmission of indoor visible light communication (VLC), the key modulation and demodulation technologies of orthogonal frequency division multiplexing (OFDM) are studied in this paper. The time-domain synchronization, frequency synchronization and channel equalization of receiver are analyzed and optimized by utilizing short and long training preamble. Moreover, field programmable gate array (FPGA) development board (Xilinx Kintex-7) and Verilog hardware description language are used to realize the design of proposed OFDM-VLC system. Simulation and experiment both verify the feasibility of the hardware designs of this system. The proposed OFDM-based VLC system can process signal in real-time, which can be used in actual VLC application systems.

We propose and experimentally demonstrate a multi-channel uplink visible light communication (VLC) system for the first time, which is based on three commercially available white light emitting diodes (LED) and only one photo-diode (PD). By employing independent Xilinx field programmable gate arrays (FPGA), we realize the real-time data transmission. The on–off keying (OOK) modulation and time division multiple access (TDMA) techniques are combined together to offer a reliable multiple uplink access for three users. The electrical idle signal is designed to deal with serious inter-symbol interference (ISI) caused by the overlap of different LED signals at the receiver side, as well as to provide a stable illuminating environment. The experiment results indicate that our scheme has a great potential for the indoor practical VLC system implementation.

We experimentally demonstrate a high-speed phosphorescent white light emitting diode (LED) visible light communication (VLC) system without utilizing an optical blue filter. Here, the white light response is equalized by using the proposed analog equalizers. The 3 dB bandwidth of the VLC link could be extended from 3 to 132 MHz, which allows 330 Mbit/s non-return-to-zero on–off keying (NRZ-OOK) data transmission with a bit error ratio (BER) of 7.2×10−10 and 672 Mbit/s 64-quadrature amplitude modulation (64-QAM) data transmission with a BER of 3.2×10−3. These resultant BERs are less than the forward error correction (FEC) limit of 3.8×10−3. The VLC link distance is 1 m using a single 1 W LED. The transmitter and receiver modules are integrated to a compact size. Furthermore, the relationships between the signal performance and illumination level or optical power are investigated and analyzed.

A research in extending bandwidth of the visible light communication (VLC) system that uses phosphorescent white LED has been reported in this letter. Slow response of the phosphorescent component limits the modulation bandwidth of white LED to the lower MHz range. In this letter, we present a post-equalization circuit that contains two passive equalizers and one active equalizer. With blue-filtering and the post-equalization circuit, a bandwidth of 151 MHz has been achieved in our VLC system, which allows OOK-NRZ data transmission up to 340 Mb/s. The VLC link operates at 43 cm using a single one Watt white LED, and the bit-error-ratio was below 2×10-3, which is within the forward error correction limit.

This paper investigates and compares the direct upconversion sensitization luminescence of ErYb co-doped oxyfluoride glass (ErYb:FOG) and vitroceramics (ErYb:FOV) when excited by a 966-nm diode laser. It is found that there are splendid upconversion luminescence phenomena which are studied and analyzed carefully. (1) It is found that the direct sensitization upconversion luminescence L of ErYb:FOV is generally 10 times greater than that of ErYb:FOG. It is also interesting that not only blue light but also red light increases more vigorously than green light when pumping laser power increases. It results from the Er 3+ –Yb 3+ ion's cluster effect. (2) For the ErYb:FOG, there is an obvious “characteristic” saturation phenomenon. That is, the F–P log–log curves of upconversion fluorescence vs. pumping laser power are basically rather good straight lines. The smaller the laser facula is, the smaller the slope of F–P log–log curves. This “characteristic” saturation phenomenon is mainly the result of strong energy diffusion among Yb 3+ ions caused by the long-range correlation. For the ErYb:FOV, because of the small and uniform micro-crystallites with a size of about 10 1 nm, the sensitization action of Yb 3+ ion to Er 3+ ion is greatly enhanced. The “typical” saturation caused by population exhaustion is also very much increased and has great effect. (3) The most interesting phenomenon is at about 474 nm of ErYb:FOG (or 476.5, 468.5 nm of ErYb:FOV) cooperative radiation upconversion fluorescence oriented from a couple state of two Yb 3+ ions' cluster! (4) Both ErYb:FOV and ErYb:FOG have a new kind of common “diffusion–transfer” upconversion mechanism, i.e., “energy diffusion” among Yb 3+ ions sequentially followed by energy transfer between Er 3+ and Yb 3+ ions. (5) The passage of cluster effect upconversion induced by couple state of two Yb 3+ ions' cluster could be described as { 2 F 7/2 ( Yb 3+ )+ 2 F 7/2 ( Yb 3+ )}→{ 2 F 5/2 ( Yb 3+ )+ 2 F 5/2 ( Yb 3+ )}→{ 2 F 5/2 2 F 5/2 ( Yb 3+ Yb 3+ )}→{ 2 F 7/2 2 F 7/2 ( Yb 3+ Yb 3+ )} . To the best of our knowledge, similar mechanism has not been reported up to now.

This article analyzes up-conversion physical processes under CW laser excitation. A qualitative `population branching ratio β ' model is proposed for the first time. The physical understanding of up-conversion explored from this model can be deduced as the following five aspects. (1) The spontaneous emission rate A is a very important variable in determining the up-conversion efficiency. When the spontaneous emission rate A is smaller than the non-radiative relaxation rate W n , i.e. A W n , the up-conversion efficiency increases with decrease of the phonon energy of host material. When A > W n , the up-conversion efficiency increases with the increase of phonon energy. Past research has only studied the case of A W n . The significance and value of the A > W n case has not been described previously. (3) A traditionally accepted concept, i.e. the up-conversion fluorescence of high cutoff phonon energy materials like quartz is about 10 000 times smaller than that of fluoride glass, is the result for case A W n . Therefore it is only partially description about the up-conversion process. (4) This paper also further proposes, for the first time, a phenomenological model `equivalent spontaneous emission A equivalent ' to explore the particular physical significance of indirect up-conversion sensitization. Spontaneous emission A , together with other factors, could be considered phenomenological as an equivalent spontaneous emission A equivalent . Generally A is small, however A equivalent is large. The range of up-conversion fluorescence increasing with the increase of phonon energy therefore could be expanded from W n A to W n A equivalent . So that under indirect up-conversion sensitization, it is possible to obtain high up-conversion efficiency for material with large phonon energy such as oxyfluoride glass and so on. (5) Further study indicates that the optimized cutoff phonon energy should be in a range about between 600 cm −1 and 900 cm −1 , and the host material should have large solubility for rare-earth ions in order to obtain a large indirect up-conversion sensitization fluorescence. This is of great significance for finding materials with both high up-conversion efficiency and advanced material properties to facilitate up-conversion development. As we know, the similar research has not been reported before.

This paper devoted to report the design and the achievement of an optical communication subsystem with 12 parallel channels in one chip. The system is capable of transmitting 10 Gbps bidirectional date over hundreds of meters. It can provide error detection and correction by using 8B/10B encoding and Cyclical Redundancy Checking (CRC) encoding when only single-channel fails. The design scheme has already passed the simulation in FPGA. This technique is useful to enhance the capability and the reliability of the very short reach (VSR) transmission systems.

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.