Research On Carrierless Amplitude Phase Modulation For Hybrid Fiber And Visible Laser Light Communications

With the rapid growth of bandwidth demands for data centers,supercomputing centers and other optical interconnect applications,using higher bandwidth optoelectronic devices can improve the transmission capacity.However,it is uneconomical.Considering the cost,advanced modulation formats and effective digital signal processing algorithms are used to meet the transmission rate requirements.Among them,Carrierless amplitude phase(CAP)modulation has gained increasing interest from research due to its low power consumption and high spectral efficiency.In this paper,the digital signal processing algorithms to improve system performance for CAP modulation are studied.Meanwhile,CAP signal are analyzed for fiber and visible laser light Communications(VLLC).The innovations of the work in the paper are as follows:1.An overlap frequency-domain equalization(OFDE)algorithm based on training sequence to compensate impairments from optical fiber channel and optoelectronic devices is proposed in intensity-modulation and direct-detection(IMDD)optical communication system with CAP modulation.The number of complex multiplications indicates that OFDE algorithm has lower computational complexity than time domain equalization.The experimental results show that the receiver sensitivities have been improved by 0.6 dB,0.4 dB and 0.5 dB for CAP32/64/128 system,respectively.In addition,the spectral efficiency of the CAP system with the OFDE scheme has been improved by 12.18%,compared with the traditional frequency domain equalization.2.A Low-cost bidirectional hybrid fiber-visible laser light communication system based on CAP modulation is proposed.At the indoor side,the received optical CAP signal from the central office is divided into two portions through an optical splitter.One part is used for downlink transmission.For another part,a Fabry Perot optical filter is employed to remove the CAP signal,and the optical carrier can be extracted for uplink transmission.Thus,the system complexity and cost can be reduced because the extra external cavity laser is not needed.Meanwhile,the cheap and easy integration 680nm vertical cavity surface emitting lasers are used as light source of VLLC.By optimizing the voltage and bias of the CAP signal and utilizing an effective decision feedback equalization algorithm,the simulation results show that the bit error rate(BER)of 3.8×10-3 can be achieved for 16-Gbps CAP signal after 30km standard single mode fiber(SSMF)and 8m VLLC transmission.3.A WDM-CAP-PON integration with VLLC system based on optical frequency comb is proposed.Five flat optical carriers are generated using one Mach-Zehnder Modulator(MZM).After channel estimation and equalization to eliminate inter-symbol interference(ISI),the experimental results show that each channel can offer 2 Gbps data rate and 10 Gbps indoor access rate can be achieved.The power penalty is-1 dB using negative chirp of MZM after 20km SSMF and 4.5m VLLC transmission at the BER of 3.8×10-3.