Asymmetrically clipped optical orthogonal frequency division multiplexing(ACO-OFDM)has been a promising candidate in visible light communications(VLC)due to its improvement in power efficiency and reduction of nonlinearity based on previous simulation analysis.In this paper,for the first time as far as we know,we experimentally verify that ACO-OFDM would be an efficient scheme to improve the performance of a gigabit wavelength division multiplexing VLC system.Our theoretical investigations reveal that the advantages of ACO-OFDM can be attributed to the reduction of inter-carrier interference caused by signal–signal beating noise.An aggregate data rate of 1.05 Gb∕s is successfully achieved over 30 cm transmission below the 7%forwarderror-correction threshold of 3.8×10−3.The experimental results show that ACO-OFDM can outperform DC-biased optical OFDM by BER performance of 1.5 dB at the same data rate and 4 dB at the same bandwidth,which clearly demonstrates the benefit and feasibility of ACO-OFDM.
In this paper,we describe the generation,detection,and performance of frequency-shift keying (FSK) for high-speed optical transmission and label switching.A non-return-to-zero (NRZ) FSK signal is generated by using two continuous-wave (CW) lasers,one Mach-Zehnder modulator (MZM),and one Mach-Zehnder delay interferometer (MZDI).An RZ-FSK signal is generated by cascading a dual-arm MZM,which is driven by a sinusoidal voltage at half the bit rate.Demodulation can be achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection.We perform numerical simulation on two types of frequency modulation schemes using MZM or PM,and we determine the effect of frequency tone spacing (FTS) on the generated FSK signal.In the proposed scheme,a novel frequency modulation format has transmission advantages compared with traditional modulation formats such as RZ and differential phase-shift keying (DPSK),under varying dispersion management.The performance of an RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is discussed.We experiment on transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal.The feasibility of all-optical signal processing of a high-speed RZ-FSK signal is confirmed.We also determine the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF),under the post-compensation management scheme.Because the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying),it can be used in the context of the combined modulation format to decrease the data rate or enhance the symbol rate.It can also be used in orthogonal label-switching as the modulation format for the payload or the label.As an example,we propose a simple orthogonal optical label switching technique based on 4
We propose a novel scheme for optical frequency-locked multi-carrier generation based on a directly modulated laser(DML) and a phase modulator(PM) in cascade through synchronous sinusoidal radio frequency(RF) signal. The optimal operating zone for the cascaded DML and PM scheme is determined via theoretical analysis and numerical simulation. We demonstrate 16 optical subcarriers can be successfully generated based on the cascaded DML and PM scheme in the optimal zone. The generated 16 optical subcarries have frequency spacing of 12.5 GHz and power di?erence of less than 3 dB. These results agree well with those of the numerical simulation. We also demonstrate intensity modulation and direct detection(IM-DD) based on one of the 16 generated optical subcarriers. After 20-km single-mode fiber-28(SMF-28) transmission,the bit-error ratio(BER) of 1×10-9can be attained for both 3.125- and 12.5-Gb/s bit rates.
We propose a configuration of a wavelength division multiplexing(WDM)-visible light communication(VLC) system using orthogonal frequency division multiplexing(OFDM) modulation and an adaptive Nyquist windowing of the OFDM signal in the receiver.Based on this configuration,we demonstrate a 750-Mb/s WDM-VLC transmission based on RGB light-emitting diode(LED) with a distance of 70 cm.The measured bit error rate(BER) for all channels are under the pre-forward error correction limit of 3.8×10 3.The BER performances of all the channels of the proposed WDM-VLC system show considerable improvement compared with those of the system without Nyquist windowing.
