Optical Mode Converter for Coupling Between Waveguides with Different Mode Size

An optical mode converter for coupling between photonic integrated circuit (PIC) and optical fiber of different mode sizes is illustrated. The optical mode converter includes a waveguide assembly including a Single waveguide structure, a Multi-layer waveguide structure, and a Transitional waveguide structure. The Single waveguide structure includes a single waveguide. The dimension and propagation constant of a first end, of the single waveguide, is similar to a waveguide of a photonic integrated circuit (PIC). Furthermore, the Multi-layer waveguide structure included a multi-layer waveguide. Further, the Transitional waveguide structure is formed at a transitional structure. The Transitional waveguide structure allows transition of an optical mode between the Single waveguide structure and Multi-layer waveguide structure. The Multi-layer waveguide structure is configured for coupling light between the Transitional waveguide structure and an optical fiber and the Single waveguide structure is configured for coupling the light between the PIC and the Transitional waveguide structure.