Study On Optimization For High-speed Nonlinear Optics Fiber Communication Links Based On Time Lenses

With the development of many internet services such as VoIP and IPTV, the internet traffic in backbone communications network is increasing very fast. The optics fiber communication system's evolution to 40Gbit/s,100Gbit/s or even Tbit/s is necessary. How to overcome the effect of fiber dispersion and nonlinearity on the higher bit rate signal by upgrading the existing commercial fiber links and transceiver is becomingly the focus of the research field of optical fiber communication systems. This thesis analyzed not only the dispersion compensation schemes and optical orthogonal frequency multiplexing based on time lenses but also the optical wavelet de-noising applied in optical fiber communication systems by numerical simulation. The comparison of quality between the scheme proposed by this work and traditional systems showed the optimization by use of time lenses is effective and advantageous. The main points of this work were listed as below:The characristics of fiber dispersion and nonlinearity were briefly introduced. The relationship of the order of VSTF applied to study the optical pulse evolution in fiber and the parameters of optics fiber was derived, which showed the interaction between fiber dispersion and nonlinearity and their effects on signal.The analyzing of time lenses' basic structure showed its characteristic of all optical Fourier transform or inverse and the relationship of the dispersive part's dispersion and the phase curve of the phase modulator that is part of the time lenses. The method to enlarge the spectrum frequency range and its effect on the optical signal was discussed.By use of the time lenses as the all optical Fourier transformers and inverse Fourier transformers instead of IFFT/FFT and ADC/DAC, a coherent optical orthogonal frequency multiplexing system based on time lenses was proposed. The scheme proposed by this work can break the electronics computing speed bottlenecks restrain on higher speed optics fiber communications. The constellation maps of the signal transmitted in these two optical OFDM systems were compared. The results of comparison and the bit error rate vs. input optical power showed the advantages of the OFDM based on time lenses.Two fiber dispersion compensation schemes based on 4f time lenses was proposed as dispersion compensation with time lenses at receiver and with time lenses at transmitter and receiver. The signal frame length or guard interlude length's effect on the dipersion compensation results was studied in these two disperiosn compensation scheme based on time lenses mentioned above. At last with the synthesis of fiber dispersion, nonlinearity and EDFA's ASE noise, the relationship of the bit error rate vs. the input signal's optical power were curved in this two dispersion compensation schemes based on time lenses and DCF compensation fiber links within IM-DD,16-QAM and 100Gbit/s 4-QAM systems respectively. The results confirmed that the dispersion compensation system with 4f time lenses at receiver only was better than the other two schemes.Optical wavelet de-noising with several different types of wavelets such as db4, coif4 and dmey wavelet was applied at the end of the 40Gbit/s multi-span intensity-modulated fiber communication systems. The results of numerical simulations carried out show the effectiveness of the wavelet de-noising in the fiber-optic communication systems and wavelet de-noising with demy wavelet can achieve better result than with other type wavelet. To the point that the optical wavelet filter composed of cascaded MZM was complex, an optical wavelet decomposition filter by use of time lenses was proposed.All the above leads up to that, the optimization for optical communication system by use of time lenses was feasible and effectiveness. The application of time lenses can apply at transmitter and receiver only, which was better for the system upgrade and save the costs. The application of time lenses in optical fiber communication can improve the capability of overcoming the fiber dispersion and nonlinearity to guarantee the quality of higher bit rate optical fiber communication and make it adaptive to the demand on the backbone network caused of the increasing internet traffic.