| Silicon,as the fundamental material for the microelectronics industry,exhibits its intriguing ability of quasi-lossless signal transmission at the optical communication wavelength.Light,serving as the messenger in the information era,shoulders the great mission to overcome the electronic bottleneck.Combination of them not only enables the monolithic integration of photonics and electronics,but also allows for the fabrication of the conventional discrete optical components with mature complementary metal-oxide semiconductor(CMOS)process.Monolithic electro-optical integration brings an increase in data transmission bandwidth by replacing the electrical interconnects with optical solutions.And CMOS-compatible fabrication process paves the way for the high-density device integration and low-cost mass production.In recent years,due to ongoing advancement of technology and gradual emergence of market demand,a significant progress has been achieved in the research on silicon photonics.Potential applications cover a wide range of areas such as optical communication transceivers,chip-level optical interconnects,optical biosensing,nonlinear optics and microwave photonics.The implementation of all these applications requires high-performance silicon micro/nano waveguide devices.In this thesis,targeting some of these applications,several novel types of silicon micro/nano waveguide devices are proposed and demonstrated,including:(1)Two types of coupled ring resonator structures on silicon-on-insulator(SOI)platform are proposed to enhance the four-wave mixing(FWM)-based wavelength conversion of a high-speed signal.Both device structures are capable of creating resonances with different field enhancement factors and resonance bandwidths for the pump,signal and idler waves in FWM process,which enables a release of the limitation between the allowed bandwidth and wavelength conversion efficiency.Theoretical results show that the wavelength conversion efficiencies in the proposed two devices are around 5 dB and 14 dB larger than that in the single ring resonator with the same bandwidth for the signal and idler waves.Additionally,both devices exhibit large self-filtering pump rejection of more than 17 dB at the drop ports.(2)A reflectivity-tunable single wavelength reflector on SOI platform is proposed.In the ideal case without loss,reflectivity ranging from 0 to 1 at the fixed peak reflection wavelength can be achieved by this device.Combining the proposed reflector with delay-tunable photonic elements,an on-chip reconfigurable optical correlator is suggested.This optical correlator can be used to perform packet header recognition,a core functionality in the optical packet switching networks.(3)An air-mode photonic crystal ring resonator(PhCRR)on SOI platform is proposed and demonstrated.PhCRR structure enables the enhancement of light-matter interaction through combining the whispering-gallery mode resonance of ring resonator with the slow-light effect in PhC waveguide.Besides,the optical field is strongly squeezed into the PhC holes by operating in air mode.A maximum group index of 27.3 and a highest quality factor of 14600 are experimentally obtained.The simulated mode profiles indicate that the ratio of the squared amplitude of the electric field in the PhC hole of the air-mode PhCRR is about 6.4 times larger than that of the dielectric-mode PhCRR.By integration with functional materials,the proposed device is expected to have potential applications in optical biosensing,on-chip light emitting and nonlinear optics.(4)A resonance spacing-tunable single ring resonator on SOI platform is proposed and demonstrated.By incorporating a reflectivity-tunable mirror into the single ring resonator,this device allows for the control of the coupling strength between two counter-propagating degenerate modes in the ring resonator and thus the tuning of resonance splitting.In experiment,tuning of resonance spacing from zero to the whole free spectral range of the resonator(1.17 nm)is demonstrated within 9.82 mW heating power dissipation.Additionally,the proposed single ring resonator can be configured to achieve a second-order filter response with flat stopband attenuation.With the ability to tailor the spectral response and tune the resonance spacing,this device has potential for applications in reconfigurable optical filtering and microwave photonics.(5)The reduction on optical nonlinearity of the silicon subwavelength grating(SWG)waveguide,compared to that of the silicon wire waveguide,is investigated theoretically and experimentally.The effective nonlinear coefficients of the waveguides are first computed from the simulated mode profiles of the waveguide cross sections,which indicates that the nonlinear coefficient of the SWG waveguide is more than one magnitude smaller than that of the wire waveguide.Then,by using the wavelength-division multiplexing(WDM)technology and advanced modulation format,data transmission performances of the waveguides for a 2.86 Tb/s optical signal composed of 75 WDM channels are experimentally evaluated.Compared to the silicon wire waveguide with identical length,the optimum launch power is increased by 8 dB in the silicon SWG waveguide,indicating higher tolerance to the nonlinear transmission impairments.(6)Two types of four-channel silicon nitride(de)multiplexers in the O-band are proposed and demonstrated.These(de)multiplexers consisting of cascaded Mach-Zehnder interferometers are capable of achieving flat transmission passbands and their channel wavelengths are designed in accordance with the local area network wavelength division multiplexing(LAN WDM)and coarse wavelength division multiplexing(CWDM)grids,respectively.For both devices,the insertion loss of the transmission channels is below 1.8 dB,the crosstalk from the suppressed channels is less than-15 dB,and the 1-dB passband width exceeds 59%of the channel spacing.Additionally,benefiting from the relatively low thermo-optical coefficient of silicon nitride,the thermal sensitivities of two(de)multiplexers are both as low as 18.5 pm/?,which is close to a quarter of that of the silicon-based device and less than twice as large as that of the PLC device.Due to the moderate index contrast provided by silicon nitride,the sizes of demonstrated(de)multiplexers are only about three to four times as large as that of the silicon-based device and almost three magnitudes smaller than that of the PLC device. |
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