Spot-Size Conversion Optical Waveguide Design

The core portion is divided into a first core portion (with high refractive index difference for miniaturization) and a second core portion (with low refractive index difference for compatible spot size). This segmentation allows different regions to serve different functions: the first core enables compact waveguide design while the second core ensures efficient optical fiber coupling, thereby resolving the contradiction between device miniaturization and connection loss reduction.

Different regions of the waveguide are assigned different refractive index characteristics. The first core portion has a high relative refractive-index difference to enable down-sizing, while the second core portion has a low relative refractive-index difference to maintain a spot size compatible with optical fiber coupling. This local differentiation of material properties allows simultaneous achievement of miniaturization and reduced connection loss.

The invention merges the spot-size conversion function with the waveguide structure itself by incorporating a second core portion directly into the waveguide. Instead of using a separate conversion component, the waveguide's core is designed with two distinct portions that together achieve both waveguide functionality and spot size matching, thereby reducing overall device complexity while maintaining low connection loss.

The waveguide structure performs multiple functions simultaneously: the first core portion provides waveguide confinement and miniaturization, while the second core portion provides spot size conversion for optical fiber coupling. This multi-functionality eliminates the need for separate components, reducing device complexity while achieving effective connection loss reduction.