Design of high-efficiency InP/InGaAsP diluted waveguide for edge couplers

Abstract

To transition integrated optical communication devices from laboratory settings to practical applications, efficient coupling between optical fibers and chip waveguides remains pivotal. This paper presents a systematic design of a diluted waveguide, a key component in the edge couplers of photonic integrated circuits. To commence, we employ the transfer matrix and effective refractive index techniques to simplify the 3-dimensional diluted waveguide into 2-dimensional multi-layer slab waveguides. By computing the field distribution of the fundamental mode within the diluted waveguide, the fiber-to-waveguide coupling efficiency can be derived using a simplified overlap equation and optimized diluted waveguide structure through particle swarm optimization algorithms. Consequently, we achieve a remarkable fiber-to-waveguide coupling efficiency exceeding 95% for TEmode and 92% for TM-mode, with a polarization dependent loss (PDL) of merely 0.13 dB. Interestingly, the optimized diluted waveguide exhibits quasi-single mode behavior, as the fundamental mode containing 98% of the total energy propagates within it. Additionally, the diluted waveguide edge coupler demonstrates favorable
alignment tolerance, with 1-dB excess losses of ±2.3 µm and (-2.5, +3) µm along the horizontal and vertical directions, respectively. Notably, our approach offers a versatile methodology for designing multi-layer waveguides across various materials.
This method has the potential to be universally applied.The primary purpose of the diluted waveguide lies in facilitating superior edge
coupling with fiber waveguides, thereby seamlessly integrating external light sources into the waveguide structure.