Investigation Of All-optical Signal Processing Technology Based On Photonic Integrated Circuits

At present,human society is entering the era of Internet of Things,in which the huge mass of data needs to be transmitted and processed all the time.With the massive growth of data,a more effective capability of information processing,such as all-optical signal processing,is required for communication networks.All-optical signal processing technology can directly process the optical information in optical domain and be applied to ultra-high speed information processing because of no"electronics bottleneck".On the other hand,with the rapid development in micro fabrication technology,all-optical signal processing technology is combined with photonic integrated chips.The emergence of the integrated devices based on some materials,such as those of silicon,Si₃N₄,sulphide waveguides,have greatly promoted the applications of all-optical signal processing technology.In recent years,integrated Kerr comb devices have brought a revolution to all-optical signal processing technology from the practical point of view.In the field of optical communication,Kerr comb may act as an ideal new coherent source for wavelength-division-multiplexing?WDM?communication system,and can markedly relax the demand for traditional electronic digital signal processing?DSP?.This dissertation mainly investigates all-optical signal processing technology based on photonic integrated circuits and focuses on the applications of Si₃N₄ microring resonators and silicon waveguide in all-optical signal processing.A robust soliton generation shceme based on auxiliary laser heating approach is proposed,which is able to markedly reduce the complexity of soliton generation.On this basis,a Kerr comb based coherent optical communication experiment is conducted and the advantage of high mutual coherence among all comb lines is announced in the coherent transmission.Finally,the four wave mixing effect in optical chip waveguides is studied,and carrier recovery and multi-wavelength signal regeneration are experimentally illustrated in the high-Q microring cavity and the silicon waveguide,respectively.The main contents and innovations are summarized as follows:1.The generation and evolution of dissipative soliton in microcavity is studied,and the thermal compensation scheme based on auxiliary laser heating is proposed and verified by experiment.The corresponding theoretical model is built up.The main innovations are summarized as follows:?1?The auxiliary laser-assisted thermal compensation scheme for the generation of dissipative solitons is proposed to overcome the thermal instability in microring resonators.The feasibility of this thermal compensation scheme is verified by experiment.A dissipative soliton with 200 nm optical spectral span is generated.The coherence,noise and time-domain characteristics of the dissipative soliton generated in auxiliary laser-assisted thermal compensation scheme are measured in detail.The influence of the residual perturbation caused by backscattered auxiliary laser on the characteristics of the dissipative soliton is analyzed.?2?The theoretical model of the auxiliary-laser assisted thermal compensation scheme is established by modifying the standard Lugiato-Lefever equation?LLE?,in which the cross-phase modulation?XPM?and frequency detuning terms induced by the auxiliary laser are taken into account.The simulation results are in excellent agreement with the experimental data.?3?Several new physical properties of the dissipative solitons are observed in the auxiliary laser-assisted thermal compensation experiment.For example,a new soliton existence range characterized with a step-like and inverse-sloped comb power curve is observed in our experiment;In the frequency comb dynamics,there exists the deterministic transition from Turing-like comb patterns directly into the dissipative Kerr soliton state,bypassing the chaotic states;A new disspative solitons generation shceme with the red-detuned pump entrance route is proposed and dissipative soliton bursts is observed.?4?By using the auxiliary laser-assisted thermal compensation,a method of automatic soliton comb recovery against strong external perturbations is implemented and helpful for the practical applications of dissipative solitons.2.The advanced optical transmission technology based on Kerr comb is studied.Based on the high coherence between the comb lines for dissipative Kerr soliton,the experiment on seamless channel multiplexing in coherent communications is demonstrated.By utilizing two cloned soliton frequency microcombs as carriers and local oscillators?LOs?,the frequency offset and carrier phase estimation can be greatly simplified.The main innovations are summarized as follows:?1?The mutual coherence of the generated dissipative soliton comb is characterized.Through Nyquist pulse modulation,the flexible configuration of Kerr comb is realized.On this basis,the coherent communication with seamless channel multiplexing based on a dissipative Kerr soliton is demonstrated.?2?The regeneration scheme of cloned Kerr comb through transmitted pump light is proposed.By utilizing this shceme,the frequency locking and phase coherence of two soliton combs over the span of 50 km is experimentally demonstrated.?3?The coherent communication technology based on cloned soliton combs is investigated,and a new frequency-offset estimation algorithm simpler than the traditional DSP method is proposed by taking advantage of the high frequency stability of two cloned soliton combs.The complexity of carrier phase?CP?estimation can be reduced by the factor of more than 1000 and joint CP processing among multiple channel are demonstrated.3.Carrier recovery and optical signal regeneration are demonstrated based on microring integrated chips and silicon line waveguide,respectively.?1?The optical parameter amplification?OPA?in Si₃N₄-based micoring is experimentally studied.A narrowband OPA gain spectrum with a peak gain of 22.0 dB and a bandwidth as low as 15.2 MHz is obtained.Then this microring chip is used to implement carrier recovery from 16QAM optical orthogonal-frequency-division-multiplexing?OFDM?signal.The employment of the regenerated carrier is able to relax the requirement for DSP compensation in self-homodyne coherent detection?SHD?.?2?The Q-factor degradation induced by two-photon absorption?TPA?and free carrier absorption?FCA?in silicon-on-insulator?SOI?waveguide is analyzed by simulation.A three-wavelength amplitude regeneration experiment using the clock-pump FWM is conducted by optimizing the input powers.It is shown that the improvement of extinction ratio?ER?,signal to noise ratio?SNR?,and Q can be up to 3 dB,0.7 dB,and3.2 dB,respectively,and the time jitter is also reduced to 50%.