Table 2 Comparisons of the two types of 3D photonic integrated circuit fabrication technologies

From: Heterogeneous 2D/3D photonic integrated microsystems

3D PIC technology Multilayer 3D waveguides Ultrafast laser inscription 3D waveguides
Pros Precise lithographic fabrication; wafer-scale process; based on mature technologies;
Dense waveguide layout;
High index contrast
Single-step fabrication process; low-loss waveguides
Flexible integration with 2D PICs
Cons Multiple step fabrication process; stresses induced by multiple layers;
Non-uniform performance
Low index contrast;
Large bending radius; difficult to scale fabrication
  1. Abbreviation: 3D, three dimensional; 2D PIC, two-dimensional photonic integrated circuits.