Research On High-performance Optical Switch Based On Silicon Photonic Crystal Cavity

With the explosive growth of global data traffic,higher demand is placed on the processing capabilities of current optical communication network nodes.Conventional method based on electrical signal processing consumes a large amount of energy due to the need for frequent optical/electrical and electrical/optical conversion,and there are problems of relatively low conversion efficiency and limited rate.The all-optical signal processing technology which can avoid the above conversion process by directly performing signal processing on the optical domain,has become the first choice for solving the problem above.As a basic unit of all-optical signal processing technology,optical switch has important applications in information processing of optical communication network nodes.In addition,optical switche is the cornerstone of optical computer and quantum computer,and its performances often determine the upper limit of overall system performances.Therefore,it is extremely important to realize a high-performance optical switch with high speed,low power consumption,high contrast,and small footprint.According to the switch function,the optical switch can be divided into two types: time domain all-optical switch and air-area optical switch.The former refers to the control of the "on/off" state of light in the time domain,and the control signal is light,which generally needs to be realized based on nonlinear effects.The latter refers to switching the transmission path of light in space.The control signal can be either light,electric,thermal,acoustic,magnetic,mechanical,etc.,but currently the most commonly used are based on electricity,heat and machinery.The two types of optical switches are basically the same in performance requirements.The difference is that the former has higher requirements on the switching rate,and usually requires switching time below nanoseconds,while the latter mainly focuses on fast switching of optical signals between different paths.At present,there are many platforms that can be used to realize these two types of optical switches,for example,silicon dioxide,indium phosphide,silicon,etc.However,the silicon-based photonic integration platform has become the first choice for realizing integrated optical switches due to its compatibility with CMOS technology,small size,and low loss.Among many silicon-based photonic integrated devices,silicon-based photonic crystal microcavity is one of the best choice for high-performance optical switches due to its high quality factor and small mode volume.In this thesis,we focus on how to use silicon-based photonic crystal microcavities to achieve high-performance optical switches with high speed,low power consumption,high contrast,small size,etc.The specific research results are summarized as follows:(1)The nonlinear effects in silicon-based photonic crystal microcavity are summarized,and the transfer function of the cavity-waveguide coupling system is derived.A nonlinear time-domain coupled mode theoretical model for describing the switching dynamics of silicon-based photonic crystal microcavities is established.In addition,the fabrication process and test method of silicon-based one-dimensional and two-dimensional photonic crystal microcavities are also introduced in detail.These lay a solid theoretical and experimental basis for realizing high performance optical switches based on silicon photonic crystal microcavities.(2)A multi-channel all-optical switch based on silicon photonic crystal microcavity is designed and fabricated.2.5-G/s signal extraction and signal blocking functions are realized by the free carrier effect in the microcavity.A blue-detuned filtering method is proposed to improve the switching dynamics of the device.The feasibility of the method is verified theoretically and experimentally,and the signal processing rate is increased to 10 Gbit/s by using this method.(3)On the basis of work(2),in order to further improve the performance of all-optical switch,an all-optical switch based on Fano resonance was designed and fabricated.Compared to all-optical switches based on Lorentzian resonance,it has lower switching power consumption,higher switching contrast and higher switching rate.(4)Aiming at the problem that the switching rate in work(2)and(3)is still limited by the free carrier lifetime in silicon,a scheme for realizing high-rate all-optical switch by using the Kerr effect in highly nonlinear polymer material is proposed.The simulation results show that the scheme can achieve a high-speed(40 Gb/s),low-power(83.3 fJ/bit),high-contrast(18 dB)and small-size(15 ?m)silicon-based all-optical switch.(5)A scheme for enhancing the FWM effect by using a silicon-based cascaded photonic crystal L3 cavity is proposed.The theoretical simulations show that the frequency spacing between adjacent modes is different,which is not conducive to improving the conversion efficiency of FWM effect.However,by adjusting the structure of the middle cavity to make its initial resonance frequency produce pre-detuning,a three-cavity coupling system with almost the same frequency interval is realized.Finally,the four-wave mixing effect with a conversion efficiency of-37 dB was achieved experimentally using the optimized device.(6)A high performance photonic crystal thermo-optic switch based on graphene electrode is proposed.The switching time is reduced by using a suspended ridge waveguide structure and Fano transmission line style.Simulation results show that the scheme can achieve 139ns/178 ns switching rise/fall time,3 nm/mW tuning efficiency,17 dB switching contrast,and the entire device is very compact.