| With the advent of information era,services and technologies such as virtual reality,Internet of Things and high-definition video live broadcasting are penetrating into people's daily life and work,leading to the huge bandwidth requirements of optical fiber communication systems.Researchers have used methods such as improving single-channel data rates,optimizing spectral efficiency,and developing new multiplexing dimensions to continuously increase system capacity.Summarizing the postdeadline articles at OFC conferences over the past 30 years,we can see that the system capacity in lab increases 10 times every four years on average.The capacity of transmission system can be greatly improved by combining various technologies,but the complexity of network nodes will also be greatly increased.Therefore,higher requirements for optical signal processing capability are put forward,such as generating high-quality optical signal sources,processing multiple channels simultaneously,transparent to signal wavelength and bandwidth,and reducing nodes complexity and so on.Optical signal processing technology,which can cope with complex network environment and has low cost,will be a key factor for the successful commercialization of super-large capacity systems.In this paper,supercontinuum generation in normal dispersion region,optical time division multiplexing(OTDM)add-drop multiplexer,all-optical wavelength conversion,width-tunable pulse generation and all-optical correlator are studied,and some useful conclusions and results are obtained.The highlights of this work are summarized as follow:(1)The spectral condensation in the evolution of supercontinuum in normal dispersion region of highly non-linear fiber(HNLF)is studied theoretically.In normal dispersion region,there exists a mechanism of energy transfer from both side wavelengths to the inside.This mechanism is mainly caused by the energy return in four wave mix(FWM)process and the spectral walk off caused by group velocity dispersion(GVD).After the optical wave breaking(OWB)phenomenon occurs,the propagation distance is inversely proportional to the peak power of the pulse and the fiber dispersion.This mechanism occurs after OWB and its propagation distance is inversely proportional to the peak power of the pulse and the dispersion of the fiber.In addition,simulated raman scattering(SRS)and cross-phase modulation(XPM)effect have different effects on the spectral shrinkage phenomenon.When the overlapping frequency components in the pulse reach the Raman bandwidth at the same time,the short wavelength part will transfer energy to the long wavelength part under the effect of Raman Scattering,resulting in the short wavelength part shrinking faster than the long wavelength part.XPM exhibits different characteristics in front and back edges of the pulse,which are red shift and blue shift,respectively,resulting in asynchronous spectral contraction on both sides.(2)The evolution of the non-frequency-shifted component in front and back!edges of pulses in the normal dispersion region of HNLF is studied theoretically.SRS accelerates the energy weakening process of the non-frequency-shifted component in front edge but slows down the energy weakening of the non-frequency-shifted component in back edge.Although the third-order dispersion and self-steepening effect can lead to the asymmetric broadening of the spectrum,it has little effect on the non-frequency-shifned component in front and back edges.The influence of cross-phase modulation on the non-frequency-shift component is that when the different frequency components of the pulse overlap at the front and back edges,the stronger one modulates the non-frequency-shift component with weaker energy.The phase modulation first occurs near the center of the pulse,the non-frequency-shifted part appears red-shift in front edge,and blue-shift appears in back edge.The non-frequency-shifted component o is always under control of cross-phase modulation.The red-shifited part and blue-shifted part keep red-shifting and blue-shifting,and their wavelengths are gradually approaching to the frequency-shift component.(3)Based on XPM and self?phase modulation(SPM)effects,all-optical add-drop multiplexing and wavelength conversion schemes by bidirectionally using of a HNLF are proposed.Compared with the existing schemes,the proposed scheme realizes simultaneous processing of two OTDM signals by using only one HNLF,which has the same processing capacity and reduces the use of devices.The experiments of 2*80 Gbit/s OTDM signal add-drop multiplexing and 50 Gbit/s and 20 Gbit/s signal simultaneous wavelength conversion are carried out.The experiment results show that the proposed structure achieves error-free signal reception and has good signal processing ability.(4)Width-tunable pulse generation schemes based on the polarization dependence and traveling wave characteristics of Mach-Zehnder modulator(MZM)are proposed,and these schemes are analyzed theoretically and verified experimentally.Compared with the existing scheme,the proposed schemes realize continuous adjustability of pulse duty cycle from 21%to 50%by using a single drive intensity modulator.Experiments of 40 Gb/s OTDM signal demultiplexing and 80 Gb/s OTDM signal over 100 km transmission demultiplexing are earried out by using the proposed width tunable pulse generation structures,respectively,and error-free reception are achieved.(5)An all-optical correlator based on mode dispersion in multimode fibers is proposed.Theoretical and experimental studies show that short pulses injected into multimode fibers from different positions at different angles can excite discrete mode groups.These mode groups will form a unique impulse response at the fiber output due to mode dispersion,and accordingly establish a one-to-one correspondence between space and time.The experimental structure of all-optical correlator based on mode dispersion is built,and the all-optical detection experiment of 8-bit code i5 completed.In addition,when the pulse response of the correlator is rectangular,it can be used to realize all-optical integration,and the experimental verification is carried out. |
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