Study On Basic Functional Devices Of Silicon-Based Photonic Integration

The explosive growth in telecommunication capacity facilitates the development of silicon photonics.It has several outstanding advantages including low power consumption,high speed and very compact in size,which is regarded as one of the key technologies to break the bottlenecks of current information networks,such as power consumption,bandwidth and volume.To keep peace with this hot research area,in this thesis,we foucus on silicon-based on-chip fundamental functional devices,which can be utilized in signal channel capacity expanding,signal channel delay processing and high-performance wavelength monitoring for integrated optical system.Both detailed theoretical analysis and experimental demonstration are presented as follows:1.Signal channel capacity expanding:(1)A broadband,fabrication tolerant and easily extended mode-division multiplexer/Demultiplexers(MDM)based on contra-directional adiabatical coupler are proposed and experimentally demonstrated.Crosstalk(CT)is lower than-15dB in a wide wavelength range of 1 00nm.(2)To realize a flexible MDM transmission system,we designed and fabricated a novel reconfigurable optical mode-division multiplexer based on asymmetric Y-junction.Extinction ratios are 12dB-17dB over the C band for both states when switching the outputs by heating the narrow arm of Y-junction.The maximum insertion loss is?1.5 dB.(3)Switchable optical mode interleaver based on an asymmetric Y-junction to realize the switching and routing functionality for the future reconfigurable on-chip communication network.The odd and even modes of the input source can be classified into two groups by controlling the widths of the output arms.The outputs of the odd and even modes can be switched from one output arm to the other output arm by changing the effective index of the narrow output arm.A four-mode optical mode interleaver is designed as an example.The numerical simulation results show that a low CT of<-17.9dB for a wide wavelength range of 200nm before and after switching the outputs.2.Signal true-time delay processing:a "fish-bone" like one-dimensional(1D)grating waveguide based true-time delay(TTD)lines on SOI platform is proposed and experimentally demonstrated.It has advantages of high disperision parameters,low propagation loss and small footprint.Through optimizing the structural parameters,a large time delay of 94.93ps/mm and group index of 19.47 away from the band edge are experimentally obtained.(2)To further reduce the propagation loss,a symmetric cadding of silicon oxide(SiO2)is applied on the 1D garting waveguide.The structural slow light is enhanced by optimizing the parameters.To facilitate low loss coupling from strip waveguides to 1D grating waveguides and vice versa,a novel step taper is designed and shows a coupling efficiency of?80%· A highest measured group index of 38.4 of he fabricated optimized 1D grating waveguide,and the lowest propagation loss is about 0.48dB/mm.A time delay of 77.23 ps/mm can be readily achieved.A wide beam steering angle from-67.84° to 67.84° for the X-band 4 element phased array antenna(PAA)with an array pitch size of 1.25 cm is obtained.3.Wavelength real-time interrogating:(1)An asymmetric embedded microring resonant system is proposed and fabricated on a silicon-on-insulator(SOI)chip to achieve slope and central wavelength tunable Fano resonance.The Fano resonance can be well tuned to be ultra-high(40dB)by controlling the microheaters to adjust the phase condition.The slope can be tunned from-35dB/nm to-93dB/nm.These types of Fano resonance line shapes are relatively stable,which means not only that the Fano-resonance transmission spectrum shifts,but also that the Fano-resonance line shape remains unchanged when the bulk temperature changes.(2)Two asymmetric embedded microring Fano resonators are utilized to function as edge filters to obtain high-resolution wavelength monitor.Heaters are applied to tune the spectra to achieve the"X-type".An ultra-high resolution of 0.8pm in a 0.47nm wide wavelength range is experimentally demonstrated.(3)To solve the problem that the measureable wavelength range and resolution limit each other in a conventional ratiometric wavelength monitor(RMWM),we design and fabricated an integrated high-performance two-stage RMWM on silicon.The first stage is a coarse wavelength monitor with a wide working range based on two unbalanced Mach-Zehnder interferometers acting as edge filters.The second stage is a fine wavelength monitor with picometer wavelength resolution utilizing two tunable microrings acting as edgefilters.A highest wavelength resolution of 1.6 pm is achieved with a functional range of 55 nm.