Resonance-based High Performance Silicon Optical Devices

Photonics integrated circuits have become one of the leading technology for many applications such as optical communications,high performance computing,optical sensors,and artificial intelligence.Over the last two decades,there have been many breakthroughs in the field of silicon photonics.For instances,hybrid silicon lasers,varies types of modulator,high-speed light detectors,and other basic building blocks.Photonics integrated circuits combine the unique properties of optical waveguides such as low propagation losses,absence of diffraction,high power confinement,low crosstalk,and immunity to electromagnetic interference with other highly desirable features such as small footprint,compactness,stability,reduced power consumption,and the possibility of low-cost manufactory.Therefore,integrated silicon photonics has garnered vast interest in the field due to its tremendous market potential.High-Q microcavities of various shapes are versatile functional elements for integrated optics.They could confine light in small volumes at resonant frequencies for extended periods and fundamentally alter the interaction of light with matter.The high ability of store light energy has great promise for many optical applications such as filtering,switching and sensing.Inverse design method can explore the full design parameter space of the linear passive optical components by using optimization algorithms.It has shown great potential in designing ultra-compact and high-performance integrated photonic devices.Natural and artificial resonators bring many useful applications,ranging from musical instruments to complex devices such as lasers.Resonances are the cornerstone of photonics,with the more familiar Fabry-Perot and Bragg resonators employed as building blocks for sophisticated optical devices with unique properties.For successful design of photonic devices,it is important to gain deep insight into different resonant phenomena and understand their connection.For instance,whispering gallery modes can be interpreted as electromagnetic waves that circulate and are strongly confined within ring resonators or spherical resonators.Fabry-Perot resonator is based on the fact that the light bounces back and forth between two end mirrors.For continuously circulating light,there are always counterpropagating waves,which interfere with each other to form a standing wave pattern.Some subwavelength structures can support strong optical resonances that can enhance and effectively control light absorption and scattering processes.In this thesis,we fabricated the high-Q silicon spherical microcavities on chip by laser heating and reshape the silicon mushroom structures.The mushroom structures are prepared by a two-step Bosch processes,and then melted and transferred into spherical microcavities by a short time green laser heating directly because of the surface tension.The shape and the surface roughness are characterized using SEM and AFM.The RMS roughness of the surface is about 0.6 nm.The tapered fiber coupling system was used to measure the optical resonance performance.The resonances loaded Q factors above 105 are realized from microcavities with diameter of about 15 ?m.Waveguide crossing is an important integrated photonic component that will be routinely used for high-density and large-scale photonic integrated circuits.By leveraging an inverse design concept,we successfully designed ultra-compact waveguide-crossing structures.Detailed numerical analysis shows that our device with etched lens-like structures has an insertion loss less than 0.175 dB,and crosstalk less than-37 dB within C-band.Despite the fabrication imperfection,our device is still robust with measured insertion losses less than 0.28 dB and crosstalk around-30 dB.The mechanism behind the high transmission of our device can be explained by the fact that the two lens-like structures in the transmission path act as two partial reflecting mirrors and form a Fabry-Perot(FP)cavity,the low insertion loss and high transmission of our device are enabled by the resonance tunneling from this FP cavity.We designed a broadband antireflective silicon structure based on resonances of nanostructures.Particle swarm optimization was then used to fine-tune and optimize the main parameters.With the FDTD simulation,the reflection effect can be considerably reduced across a very wide wavelength range.The reflectance spectrum from a coated array of the AR structure shows that reflectivity can be reduced down to<5%over the entire spectral range from 400nmto 1,100nm.In addition,under an ideal condition,the Short circuit current(Jsc)is about 28.6 mA/cm2 with a 53%increase when compared to a device without AR layer.