Design of a TM-mode apodized photonic crystal grating coupler

Abstract Transverse-magnetic (TM)-mode silicon waveguide devices have diverse on-chip applications in biochemical sensing, photodetection, and nonlinear optics, due to their unique light field distributions. The grating coupler technique provides a practical solution for coupling light into/out of TM-mode silicon waveguides. In this paper, we theoretically designed a TM-mode photonic crystal grating coupler. Moreover, an apodized grating structure was utilized to tailor the grating diffracted light as a Gaussian shape to improve the coupling efficiency. The minimum feature size of the grating coupler is ∼200 nm, which is compatible with deep ultraviolet photolithography processes. Our numerical results show that the grating coupler has a maximum coupling efficiency of −1.9 dB with a 3 dB bandwidth of ∼70 nm at a center wavelength of 1540 nm. The study is expected to provide a helpful technique of optical packaging for TM-mode silicon photonic integrated circuits.