Research On The Applications Of Silicon-based Waveguide Gratings And Microrings In Microwave Photonic Systems

Microwave technology plays an important role in the development of human science and technology,and has been widely used in high-tech fields such as communication systems,automobile collision avoidance,radar system,electronic countermeasures,and satellite navigation.However,due to the bandwidth limitation of conventional electronic devices,there are a series of problems in the generation and processing of microwave signals by electronic devices,which can no longer meet the increasing communication requirements.At the same time,photonics have gradually become the first choice for information carriers thanks to the long-distance optical transmission system with the advantages of low loss,strong anti-electromagnetic interference ability and ultra-broadband.The combination of microwave technology and optical technology,called Microwave photonics,can take advantages of both,which is one of the important means to solve the problems of future wireless communications.However,building microwave systems with discrete optics is also faced with problems such as large system size,high power consumption,vulnerability to environmental influences,and low consistency and reliability.With the development of photonic integration technology,various integrated optical components have been fabricated using semiconductor processes.It has become a trend to realize complex microwave photonic system on integrated platform in current researches.Compared with various material systems,silicon-based microwave photonics integrated devices can be directly fabricated by etching,growing or bonding on an SOI platform using a mature CMOS process.It has many advantages such as low cost,low loss,compact size,etc.Based on the SOI platform,two types of integrated devices based on waveguide Bragg gratings and optical microring resonators are designed and fabricated.This thesis focuses on developing silicon-based photonic integrated circuits for microwave photonic applications.The main research contents are as follows:(1)The research background and significance of integrated microwave photonics are introduced in detail.Then the latest researches of integrated microwave photonics in recent years are introduced,covering important applications in microwave signal generation,processing and measurement,and some representative solutions are discussed and analyzed.(2)The basic theory and analysis methods of silicon-based microrings and gratings are introduced,as well as two commonly used tuning methods for silicon-based devices of thermal tuning and electrical tuning.The manufacturing process,test methods and packaging schemes of the device are summarized.(3)Based on the 220 nm and 250 nm SOI platforms,we propose and experimentally demonstrate tunable optical delay lines based on integrated grating-assisted contradirectional couplers.Based on the theoretical analysis and simulation design of 220nm SOI passive waveguide,the apodization type of grating delay device of 250 nm SOI devices is studied,and we choose an optimized apodization to suppress the ripples of the transmission spectrum and delay lines.A 744?m long device is fabricated on a 220 nm SOI platform,and the total delay is 28 ps within bandwidth of 10 nm.The spectral drifts at different temperatures are also studied using an external temperature control device.Then,devices with various parameters are fabricated on a 250 nm SOI platform,and the impact on device performance are analyzed.To solve the problem of large heater resistance caused by the long gratings,heaters with parallel circuits are designed to reduce the resistance and show better heating efficiency.Tunable group delay lines of 50 ps at different wavelengths within the bandwidth of 12 nm are realized with a grating length of 1.8 mm.Under thermal tuning mode,the actual delay tuning range is around 20 ps at 7.2 V voltage.We combine grating-assisted contradirectional couplers with an ultra-compact reflector for double delay in the same size,and the fabricated 6 mm device can achieve a large group delay of 400 ps and dispersion value of up to 5.5×10~6 ps?(nm×km)within the bandwidth of 12 nm.In order to further reduce the size of the device and the difficulty of fabrication,a spiral grating structure is proposed,and the parameter analysis and simulation are carried out.(4)We propose and experimentally demonstrate an all-optical integrator based on silicon photonic phaseshift Bragg grating.By introducing the phaseshift Bragg grating as the integrator,the bandwidth limitation of the finite FSR is broken.The proposed integrator shows a wide operation bandwidth of 750 GHz and high maximum theoretical energetic efficiency of about-12.4 dB.The integration time window of the integrator is 9 ps due to the low Q factor.(5)We propose a wideband microwave frequency identification system using an integrated silicon photonic scanning filter.The key component is a thermally tunable high-Q silicon microring resonator,which is used to implement frequency-to-time mapping.When driven by a periodic sawtooth voltage,the resonant wavelength of the MRR will experience a periodic redshift,exhibiting a periodic scanning filter.First,the relationship between the frequency to be measured and the pulse time is derived.Then we introduce the design method and measurement results of the thermally tunable high-Q silicon microring.The Q-factor,spectral drift characteristics and modulation rate of the thermally tunable microring are measured.The system exhibits a versatile capability to identify and quantify single frequency microwave signal and complex microwave signals,including multiple frequency,chirped frequency and frequency-hopping microwave signals as well as their combinations.The measurement speed is about 10 ms.The frequency measurement range is ultrawide,from 1 to 30 GHz,with a high resolution of 375 MHz and a low measurement error of 237.3 MHz.