Study On Tunable Microring Resonator Based On Silicon Nitride Waveguide

Nowadays, the optical network is developing toward higher speed, larger capacity, and higher integration. In order to enhance the flexibility and adaptability of optical network, many kinds of integrated optical devices with different functions and structures have appeared. As a typical integrated optical devices, the microring resonator has advantages of simple structure, compact size and high integrity. And it is widely used in different optical systems, such as in optical filtering, optical modulator, optical delay line, optical bio-sensors. This dissertation focuses on the related theories of tunable silicon nitride waveguide microring resonator as well as its fabrication techniques. Here the silicon nitride was chosen as the core material of waveguide. Compared to the polymer, silicon nitride has the following advantages, such as the large refractive index difference between core and cladding, compact size, environmental stable. And compared to the silicon-on-insulator, the silicon nitride waveguide has the advantages of easy fabrication and low cost.In this thesis, based on coupled mode theory, the transmission characteristics of microring resonators with different structures and parameters were analyzed by using Matlab. And an integrated silicon nitride waveguide microring resonator based on the thermo-optical effect was designed and fabricated. By employing the thermo-optic effect of polymeric materials, the tunability of the resonant wavelength and the extinction ratio of the microring resonator has been realized by adjusting the driving voltages on the microring and the tunable coupler based on the Mach-Zehnder interferometer(MZI). Besides, the waveguide size, bend radius, coupling gap size and other parameters were designed and optimized by using the optical waveguide device simulation software (Rsoft). The silicon nirtride waveguide microring resonator with single ring and cascaded double-ring were fabricated by the lithography, reactive ion etching (RIE) and other micro fabrication processes.The characteristics of the fabricated silicon nirtride waveguide microring resonators were measured. The results show that around the wavelength of 1550nm, for the microring resonator with radius of 2000?m and 2500?m, the free spectral ranges are 68pm and 59pm, the 3dB bandwidths are 16pm and 18pm, the Q factors are 9.68×104 and 8.61×104, the extinction ratios are 15dB and 13.2dB respectively. Through thermo-optical effect, the tunable extinction ratio of 17dB was achieved. And the extinction ratios of two cascaded microring resonators can be superposed by tuning the resonant wavelengths. The study of this tunable microring resonator is very promising for the optical communication and the microwave photonic filtering.