Four layer Y-branch coupled mode analysis

The characteristics of a branching waveguide composed of a four-layer structure are analyzed. Conventionally, a lightwave guiding structure is composed of three layers with the center region having a higher refractive index than the other regions. Thus, a lightwave can be confined in the center region for propagation. However, there exists another structure which has an extra region, and this structure is called a four-layer waveguide. This geometry has two layers of higher refractive index, and both layers or one layer only can be used for guiding waves. This structure has the advantage of desensitivity in temperature and pressure with the extra variables of waveguide width and refractive index. Propagation in this structure is discussed