Research On Low Loss Double Strip Silicon Nitride Integrated Photonic Devices

Silicon photonic integration has been recognizing as one of the key technologies to solve the critical issues regarding high-power consumption and large loss in the information network due to its advantages of low loss,less power consumption and small footprint.In the silicon based optical integration platform,silicon nitride waveguide plays an important role in research areas of processing high optical power,performing nonlinear and linear optical functions by considering its favorable features of low loss,wide transparent window(transparent for wavelength from 0.4?m up to 2.35?m),no two-photon absorption and compatibility with complementary metal oxide semiconductor(CMOS)processes.Moreover,silicon nitride(Si₃N₄)materials can form complementary advantages with silicon-on-insulator(SOI)and III-V materials to support a variety of passive and active building blocks,which can pave the way for the system-on-chip implementations.At present,based on silicon nitride waveguide platform,researchers have developed a series of high-performance photonic integrated components,such as ultra-high Q resonators,optical filters,high coherent lasers,optical signal processing circuits,nonlinear optical devices,frequency comb generators and bio-photonic system-on-chip.In this thesis,based on the low loss silicon nitride waveguide,multimode interference coupler,dual-ring coupled Mach Zehnder interferometer,multimode microring,microdisk resonator and switching delay line are studied theoretically and experimentally.In addition,tunable microwave photonic filters based on several designed silicon nitride optical filters were also investigated.The main results of this thesis can be summarized as follows:1.The classifications and structures of the silicon nitride waveguides are illustrated in detail.The main characteristics of the double strip silicon nitride waveguide,including its single mode condition,the minimum bending radius,bending loss and polarization dependence were investigated numerically.Then the fabrication process of the double strip silicon nitride,including film deposition,lithography,etching,and cutting were given.The loss of fabricated double strip silicon nitride waveguide was measured and analyzed.Also the loss optimization methods are given.2.Based on the self-imaging principle,1×2 multimode interference coupler,2×2multimode interference coupler and waveguide crossing based on the double strip silicon nitride waveguide were optimal designed and fabricated.The measured results are in accordance with the design.In addition,the fabricated devices have the merits of low loss,low polarization dependence and broadband operation.3.The tunable integrated optical filters based on dual-ring coupled Mach-Zehnder interferometer,multimode microring resonator and microdisk resonator were proposed,and based on these tunable integrated optical filters,reconfigurable microwave photonic filters were constructed.Combined the silicon nitride microdisk resonator with dual-driven Mach-Zehnder modulator and 90°RF hybrid,the RF rejection ratio of the microwave photonic bandstop filter was enhanced to 51 d B,and the frequency tuning range is 2 GHz?25 GHz.Using the same modulation method,the microwave photonic bandstop filter with a bandwidth of 125 MHz can be implemented by taking the advantages of small mode coupling coefficient and low loss of the multimode microring cavity.A maximum RF rejection ratio of58 d B and a frequency tuning range of 2 GHz?18 GHz was obtained.In addition,a microwave photonic bandpass/bandstop filter was constructed based on the phase modulation and dual-ring coupled Mach-Zehnder interferometer.The frequency tuning range is 4 GHz?25 GHz,the bandwidth tuning ranges of microwave photonic bandstop filter and bandpass filter are 3.65 GHz?6.35 GHz and 5.76 GHz?9.72 GHz,respectively.Moreover,the microwave photonic filters constructed by three different optical filters can be easily switched between bandstop and bandpass responses without changing the link.4.A 6-bit optical switching delay line unit based on the silicon nitride waveguide was designed,fabricated and tested,which consists of seven silicon nitride thermo-optic switches and six waveguide delay lines with different lengths.The designed switching delay line can achieve 64 different delay values with delay step of 1.42 ps and maximum delay of 89.46 ps.The measured delay values are in good agreement with the design values.