Yuanquan Wang

Demonstration of 575-Mb/s downlink and 225-Mb/s uplink bi-directional SCM-WDM visible light communication using RGB LED and phosphor-based LED

We propose and experimentally demonstrate a novel full-duplex bi-directional subcarrier multiplexing (SCM)-wavelength division multiplexing (WDM) visible light communication (VLC) system based on commercially available red-green-blue (RGB) light emitting diode (LED) and phosphor-based LED (P-LED) with 575-Mb/s downstream and 225-Mb/s upstream transmission, employing various modulation orders of quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM). For the downlink, red and green colors/wavelengths are assigned to carry useful information, while blue chip is just kept lighting to maintain the white color illumination, and for the uplink, the low-cost P-LED is implemented. In this demonstration, pre-equalization and post-equalization are also adopted to compensate the severe frequency response of LEDs. Using this scheme, 4-user downlink and 1-user uplink transmission can be achieved. Furthermore, it can support more users by adjusting the bandwidth of each sub-channel. Bit error rates (BERs) of all links are below pre-forward-error-correction (pre-FEC) threshold of 3.8x 10(-3) after 66-cm free-space delivery. The results show that this scheme has great potential in the practical VLC system.

Enhanced performance of visible light communication employing 512-QAM N-SC-FDE and DD-LMS

In this paper, a novel hybrid time-frequency adaptive equalization algorithm based on a combination of frequency domain equalization (FDE) and decision-directed least mean square (DD-LMS) is proposed and experimentally demonstrated in a Nyquist single carrier visible light communication (VLC) system. Adopting this scheme, as well with 512-ary quadrature amplitude modulation (512-QAM) and wavelength multiplexing division (WDM), an aggregate data rate of 4.22-Gb/s is successfully achieved employing a single commercially available red-green-blue (RGB) light emitting diode (LED) with low bandwidth. The measured Q-factors for 3 wavelength channels are all above the Q-limit. To the best of our knowledge, this is the highest data rate ever achieved by employing a commercially available RGB-LED.

Network Architecture of a High-Speed Visible Light Communication Local Area Network

A novel ultrahigh-speed LED visible light communication (VLC) local area network to provide beyond 10-Gb/s optical wireless access based on star topology architecture is proposed and experimentally demonstrated for massive users. Fiber link is used as the backbone of the bidirectional VLC network. The hybrid access protocol is utilized: 1) frequency division multiplexing for downlink and uplink fiber transmission and 2) time division multiplexing for bidirectional VLC transmission. A full-duplex VLC network for eight VLC access points (VAPs) has been successfully demonstrated with the total throughput of 8 Gb/s. Each VAP is offered 500-Mb/s downstream and 500-Mb/s upstream. The measured bit error rates of downlink and uplink for all the VAPs are under 7% FEC limit of 3.8 × 10-3 over 25-km standard single mode fiber and 65-cm free space, clearly validating the promising potential of the proposed VLC network architecture for future 40- and 100-Gb/s wireless access.

Gigabit polarization division multiplexing in visible light communication

In this Letter, polarization division multiplexing is proposed and experimentally demonstrated for the first time that we know of, in visible light communication systems based on incoherent light emitting diodes and two orthogonal groups of linear polarizers. Spectrally efficient 16-ary quadrature amplitude modulation Nyquist single carrier frequency domain equalization is employed to obtain a maximum spectral efficiency. We achieve an aggregate data rate of 1  Gb/s, with bit error rate results for two polarization directions both below the 7% pre-forward-error-correction threshold of 3.8×10(-3) after 80 cm free-space transmission. Moreover, the cross talk between x and y polarization is also discussed and analyzed.

High-speed quasi-balanced detection OFDM in visible light communication.

In this paper, we proposed and experimentally demonstrated a novel quasi-balanced detection (QBD) technique in orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) system. By employing opposite signals to odd and even consecutive symbols, the nonlinearity distortion, and direct current can be eliminated efficiently. Additionally, the sensitivity of receiver can also be improved by 3dB, thus a longer transmission distance and high-order modulation formats can be received. We achieved physical data rate of 2.1-Gb/s enabled by wavelength-division-multiplexing (WDM), pre- and post-equalization, and the resulting bit error ratios (BERs) were below the FEC limit of 3.8x10(-3). The distance was above 2.5 meters that was long enough for indoor communication. Compared with conventional direct-detection optical (DDO-OFDM) and asymmetrically-clipped optical (ACO-OFDM), the BER can be enhanced by 22.2dB and 20.8dB, respectively, which shows great potential in short range and low cost access network.

Balanced Precoding Technique for Vector Signal Generation Based on OCS

The phase and amplitude precoding technique is essential in optical carrier suppression-based photonic constant-and multi-amplitude quadrature-amplitude-modulation vector signal generation at radio frequency bands. In this letter, a novel precoding scheme with constellations balanced distribution is proposed and investigated. We experimentally demonstrate 8-GBd quadrature-phase-shift-keying (QPSK) vector signal generation at 16 GHz enabled by a single Mach-Zehnder modulator-based oscilloscope modulation and the proposed precoding scheme. Compared with imbalanced precoding, this scheme can provide 2-dB receiver sensitivity improvement, and the obtained constellations at the receiver end is much more symmetrical, which represents the in-phase (I) and quadrature (Q) components have equal performance. The bit-error-ratio for 8-GBd QPSK vector signals can be under hard-decision forward-error-correction threshold of 3.8×10-3 after a 25-km standard single-mode fiber transmission.

High Speed WDM VLC System Based on Multi-Band CAP64 With Weighted Pre-Equalization and Modified CMMA Based Post-Equalization

Multi-user access is one of the key problems in the visible light communication (VLC). In this paper, we propose and experimentally demonstrate an approach for multi-user access based on multi-band CAP modulation over a wavelength division multiplexing (WDM) VLC system using a single RGB LED. In this scenario each wavelength will provide 3 sub-bands. Depending on the combination of the different wavelength and the sub-bands, a dynamic capacity can be achieved for up to 9 users access. At the transmitter a weighted pre-equalization method is proposed to overcome frequency attenuation of the LED, while at the receiver a post-equalizer based on modified cascaded multi-modulus algorithm (CMMA) is utilized. The experimental results show that the bit error rate (BER) for an over-all 1.35 Gb/s CAP64 signal over 30-cm transmission can be under the 7% forward error correction (FEC) limit of 3.8 × 10-3. The results clearly demonstrate the benefit and feasibility of the multi-band CAP modulation for the short range multi-user VLC systems.

Stable Optical Frequency-Locked Multicarriers Generation by Double Recirculating Frequency Shifter Loops for Tb/s Communication

We propose and experimentally demonstrate a novel scheme to generate optical frequency-locked multicarriers by using double recirculation frequency shifter loops based on different frequency shifting direction single-sideband modulation in I/Q modulators driven by RF clock signals. By changing the phase difference of I and Q RF drive signal, each loop generates long wavelength and short wavelength subcarriers, respectively. The tone-to-noise ratio (TNR) performance with amplified spontaneous emission noise and the effect of polarization state are theoretically analyzed and experimentally investigated for the first time. Experimental results are in good agreement with the theoretical analysis. Using this scheme, we successfully generate 104 frequency-locked subcarriers with TNR larger than 17 dB and carrier spacing at 12.5 GHz covering 10.21 nm from 1545.01 to 1555.22 nm which shows that this scheme has great potential in future Tb/s per channel communications. The feasibility of this scheme is demonstrated by the experimental results.

High-power polycrystalline Er:YAG ceramic laser at 1617 nm

We report on the efficient operation of a high-power erbium-doped polycrystalline Er:YAG ceramic laser at 1617 nm resonantly pumped by a high-power 1532 nm Er,Yb fiber laser. Lasing characteristics of Er:YAG ceramics with different Er3+ concentrations are evaluated and compared. With an output coupler of 15% transmission and 0.5 at. % Er3+-doped YAG ceramic as the gain media, the laser generates 14 W of output power at 1617 nm for 28.8 W of incident pump power at 1532 nm, corresponding to a slope efficiency with respect to incident pump power of 51.7%.

Integrated 10 Gb/s multilevel multiband passive optical network and 500 Mb/s indoor visible light communication system based on Nyquist single carrier frequency domain equalization modulation

We propose and experimentally demonstrate a novel integrated passive optical network (PON) and indoor visible light communication (VLC) system based on Nyquist single carrier frequency domain equalization (N-SC-FDE) modulation with direct detection. In this system, a directly modulated laser and a commercially available red light emitting diode are served as the transmitters of the PON and VLC, respectively. To enable high spectral efficiency, high-speed transmission, and flexible multiple access with simplified optical network unit-side digital signal processing, multilevel, multiband quadrature amplitude modulations 128/64/16 are implemented here. VLC N-SC-FDE signals are successfully delivered a further 30 cm indoor distance after transmitting over a span of 40 km single mode fiber (SMF) together with 3 sub-band PON signals. As a proof of concept, a 10 Gb/s PON and 500 Mb/s VLC integrated system for three wired users and one wireless user is successfully achieved, which shows the promising potential and feasibility of this proposal to extend multiple services from metropolitan to suburban areas.