Multimode Interference Coupler (MMI)

The Multimode Interferometer (MMI), also known as the Multimode Interference Coupler, is based on the principle of multimode interference self-imaging. It has advantages such as low insertion loss, compact structure, simple fabrication process, and insensitivity to structural variations.

1. Introduction to Principles

The MMI operates on the principle of self-imaging: when a single-mode waveguide enters a wide multimode waveguide, multiple guided modes are excited. These modes interfere with each other, and along the waveguide's direction, one or more replicated images appear at periodic intervals.

2. Key Performance Parameters of Silicon-Based MMIs

• Insertion Loss: The reduction in optical power at a specific output port relative to the total input optical power.
• Excess Loss: The total optical power reduction across all output ports relative to the total input optical power, expressed in decibels.
• Splitting Ratio: The percentage of power distributed to each output port relative to the total output power.
• Isolation: The ability of one optical path to isolate signals from other paths. Higher isolation implies less crosstalk between paths.

3. Structural Modeling

An MMI typically consists of three parts: input waveguides, a multimode waveguide, and output waveguides. The input and output waveguides usually consist of one or more single-mode waveguides.

4. Simulation Results

Field propagation distribution: