Low-Cost Optical Transmission Technology Based On Kramers-Kronig Receiver

High-speed and cost-efficient transmission is the main appeal of shortreach optical systems in the background of big data and broad connections.Among all the candidate transmission solutions,the low-cost single sideband(SSB)intense modulation direct detection(IMDD)transmission system is a preferred scheme due to its higher spectral efficiency and less severe chromatic dispersion(CD)-induced RF power fading.Despite of all the benefits,SSB signals still suffer from severe signal to signal beating interference(SSBI)induced by the square law detection of photodetector(PD).In 2016,A.Mecozzi etc.proposed the Kramers-Kronig(KK)receiver which can easily reconstruct complex field,eliminate SSBI and enable electrical dispersion compensation while the signal meet the minimum phase condition.Compared with other SSBI cancellation schemes,the adoption of KK Receiver can eliminate SSBI at relatively low carrier to signal power ratio(CSPR)with optimal performance.However,the natural logarithm in KK relation will degrade the system performance,due to nonlinear amplification of noise near 0 as well as the required digital upsampling.Besides,the cost of the transmission system is an important issue to be considered.In view of the above problems,this dissertation focuses on the key technologies to implement and improve KK receiver in low cost scenarios.First,we implemented low-cost dual-drive(DD)MZM instead of IQ modulator to transmit 56G-bps SSB PAM4 via 40 km standard single mode fiber(SSMF),with both electrical amplifier and optical amplifier omitted.Due to the Hilbert transform,the peak to average power ratio(PAPR)of SSB PAM4 is much higher than DSB PAM4,which challenges the dynamic range of digital-to-analog convertor(DAC).To realize the electrical amplifier-free system,clipping operation,which means clipping the peak of SSB signal,was implemented to expend the output electrical signal power of arbitrary waveform generator(AWG).Also,KK system and typical SSB IMDD transmission system were compared.Results showed that :1)KK system without Feed-forward equalization(FFE)could compensate CD electrically,but it could not compensate the inter-symbol interference(ISI)induced by imperfect channel response such as component-induced bandwidth limitation and in-band rippling;2)KK system with FFE showed almost the same performance with typical IMDD system with FFE in all cases.It indicated that in this low-cost transmission system,with DDMZM implemented to emulate IQ modulator and electrical amplifier omitted,the CSPR is relatively high and there is little SSBI,so the KK receiver could not improve the system performance.Second,this dissertation focuses on zero-by noise effect induced by the natural logarithm(ln)in KK relation,and the amplitude shifting and clipping(ASC)scheme is proposed to overcome it.The curve of y(28)ln(x)near 0 is very steep while the curve away from 0 is relatively flat thus the additive Gaussian white noise becomes extremely nonlinear near 0.It means that the noise near 0 is amplified by numerous times,resulting in devastating damage during KK reconstruction.In order to prohibit the small variation near 0 from stretching into enormous variation,we put both amplitude shifting operation and clipping operation into consideration,and got the best combination to achieve optimal system performance.Simulation results showed that with optimum ASC scheme implemented,the system performance can outperform typical KK receiver by 3d B in receiver sensitivity at 6-d B CSPR for 112-Gbps QAM16 signal after 80-km SSMF in C-band.And experimental results showed that ASC scheme could outperform typical KK receiver by ?0.5d B receiver sensitivity at 56 Gbps PAM4 signal after 40 km SSMF.