The multimode interference (MMI) coupler based microring resonator is a versatile component for photonic signal processing applications. Based on this basic building block, many functional devices can be fabricated such as optical switches, filters, modulators, add-drop multiplexers, and true time delay devices. In the analysis and design of such structures it is usually assumed that the MMI coupler is described by a 2 × 2 transfer matrix similar to that of a directional coupler. However, such a simple approximation is inadequate for a detailed design. The purpose of this paper is to present a more appropriate method for the analysis and design of MMI coupler based microring resonators. In this paper, the modal propagation method is used to determine the fields of the combination of an MMI coupler and a ring resonator. This method has the advantages of good accuracy, and quick computation compared with numerical methods such as FDTD and BPM. It is shown how the structure parameters such as the width and positions of access waveguides, width and length of the MMI coupler, and the waveguide geometry, can be optimized to allow the designer to achieve a prescribed performance. This method can be applied to more complicated structures such as the double ring resonator structure, a 3 × 3 MMI coupler based microring resonator, and microring resonators in series or parallel. The accuracy of the method is checked by comparison with numerical techniques.
展开▼
