Design, Fabrication And Nonlinear Research Of Silicon-based Microring Resonator

The 21 st century is a highly information-oriented era, unprecedented high volume and speed is demanded for signal transmission, processing and storage. The traditional electrical interconnect encounters "bottleneck" for signal delay, large power consumption, and heat dissipation. Due to the merits of no RC delay, high transmission speed, no electromagnetic crosstalk, large transmission bandwidth and low power consumption, optical interconnect is widely used in signal processing field.Silicon-on-insulator (SOI) is one of the most popular platform for low-cost and highly compact optical interconnect since its transparency in C-band, large refractive index difference and fully compatibility with the standard CMOS (Complementary-Metal-Oxide-Semiconductor) technology. Microring resonator is the most basic structure unit for silicon integrated optics regarding its resonance enhancement for specific wavelength, controllable of light transmission direction, compact footprint, design flexibility and ease of integration with other devices. It can be served as various functional silicon photonic integrated devices. Since the optical power density in microring resonator is larger than in the straight waveguide, the nonlinear effect will be much more significant.In this thesis, the theory, design approaches and fabrication processes of silicon-based microring resonator are comprehensive introduced; and microring based nonlinear applications are investigated theoretically and experimentally. The major achievements of this dissertation can be summarized as follows:(1) Explored the fabrication processes based on various materials (silicon, silicon dioxide, silicon nitride), including material deposition, electron beam lithography, UV lithography, inductively coupled plasma (ICP) dry etching, wet etching, evaporation and lift-off, etc. Optimized the electron beam lithography process for different photoresistes. Explored various etching processes (Bosch deep etching, synchronized shallow etching, isotropic etching) on different substrates and fabricated waveguide, grating and photonic crystals with high-performance.(2) Designed and demonstrated a single-etched high-Q, high ER SOI microring resonator integrated with efficient grating couplers.40% coupling efficiency and 40 nm 3-dB bandwidth are experimentally realized. An ER of 19 dB and Q factor of ?55,000 are achieved for a 40 ?m radius ring. Strong optical nonlinearity of FWM and optical bistability in the microring resonator were observed, which laid a solid foundation for low power integrated nonlinear devices. Also, we demonstrated a resonance spacing-tunable single ring resonator device by incorporating a MZI-loop mirrorby integrating metallic microheater, the tuning of resonance spacing in the range of the whole FSR (1.17 nm) is achieved within 9.82 mW heating power dissipation. The device has potential for applications in reconfigurable optical filtering and microwave photonics.(3) Designed and experimentally demonstrated the first compact high-efficiency grating coupler for thick silicon-nitride-on-insulator (SNOI). The coupler was compact, easy to fabricated, high efficient and provides an easy approach for device characterization. By combining focusing grating and inverse taper, a compact footprint of 70.2?m×19.7 ?m is achieved. The fabricated coupler has a coupling efficiency of-3.7 dB at C band and a 1-dB bandwidth of 54 nm.(4) Proposed an SU-8 covered end coupler with etched facet by using two opposite tapers. The coupling facet was defined by EBL, thus the quality of it was improved, and the coupling loss was reduced. The simulated converting loss for TE mode from silicon nitride waveguide to the SU-8 waveguide was 0.24 dB.(5) Investigated the principle of on-chip optical frequency comb generation based-on microring resonator, designed and fabricated Si3N4 microring resonators with flattened zero dispersion in C-band. Silicon nitride based microring resonators with different radii and different coupling gaps were fabricated by using LPCVD, EBL, lift-off and ICP dry etching process. Utilized the power enhancement in the Si3N4 microring resonators to generate the optical frequency combs by cascading four-wave mixing.