| dc.description.abstract | In this thesis, the microring resonators have been studied to propose the guidelines to design the high Q-factor microring resonators. First, by wrapping the curved waveguide around the microring to form the pulley coupler, the bending loss can be effectively decreased. The longer interaction length of coupling region such as the concentrically curved waveguides is helpful to decrease the radiation loss of microring to improve the Q-factor of resonator. Second, the large difference of propagation constant between the microring and the bus waveguide can maintain the propagating light in the microring. Third, the critical coupling can be optimized by adjusting the bus waveguide width to increase the Q-factor. The reasons mentioned above and the obtained results by comparing the performance of the different type ring resonators show that the pulley-type microring can provide higher Q-factor.
Besides, in order to define the coupling length of the pulley coupler, the conformal transformation method based on Helmholtz equation is employed to estimate the coupling length of the concentrically curved waveguides. The coupling length obtained by the method proposed in this thesis has a good agreement with the finite-difference time-domain method.
For demonstrating the performance of the designed high Q microring resonator, the pulley-microring resonator and the grating coupler are fabricated on the silicon-on-insulator substrate by using the E-beam lithography and the reactive-ion etching. The grating coupler is adopted to guide the light into the pulley-type microring resonator. The Q-factor can be obtained as high as 173000.
In the literature, the microring resonator with the radius of 20 um constructed by the pulley coupler, such that pulley-type microring resonator can provide the high Q-factor from 20000 to 600000 by using the reflow process or covering the cladding layer. However, the radius of microring resonator is too long. In this thesis, the pulley-type microring resonator with high Q-factor of 173000 and with the smaller radius of 4.43 um is proposed and demonstrated. The high Q-factor pulley-type microring resonator is obtained by adjusting the bus waveguide width. This indicates that the pulley-type microring resonator is suitable for the miniaturization of the optical integrated circuit. | en_US |