Vertical field enhancement of a spot-size converter using a nanopixel waveguide and window structure

Zan Hui Chen, Wenying Li, Yu Han, Leiyun Wang, Haisong Jiang, Kiichi Hamamoto

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


Spot-size converter (SSC) is an essential building block for integrated photonic circuits applied as a mode transformer between optical components. One typical issue for SSC is the difficulty of broadening the vertical field profile. Herein, we propose a nanopixel SSC (1 × 2 µm2) with changing hole size and density. Unlike a typical SSC, this configuration controls both the lateral and vertical field profiles relatively easily by enhancing the nanopixel density. A vertical field expansion of 1.21 µm was obtained by enhancing the nanopixel density. In addition, we designed the optical field in the lateral direction using deep neural network (DNN)-based learning to realize a perfect circular spot for high coupling efficiency that reached -3 dB at λ0 = 1.572 µm when the optical field aspect ratio was adjusted to 1 after training for 200 epochs. Furthermore, the vertical expansion was increased from 1.21 to 4.9 µm and the coupling efficiency from -3 to -0.41 dB by combining it a silicon dioxide window structure (5 × 15 × 10 µm3). The 1-dB operating bandwidth of the designed SSC structure is 100 nm (1.5–1.6 µm), while fabrication tolerance of the nanopixels and window structure length for the designed SSC structure are ±15 nm and ±250 nm when the coupling efficiency drops by 1 dB.

Original languageEnglish
Pages (from-to)2757-2768
Number of pages12
JournalOptics Express
Issue number2
Publication statusPublished - Jan 18 2021

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics


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