Ultra-thin mid-infrared silicon grating coupler

• Published in: Optics letters 2022-03, Vol.47 (5), p.1226-1229
• Main Authors: Guo, Rongxiang, Gao, Haoran, Liu, Tiegen, Cheng, Zhenzhou
• Format: Article
• Language: English
• Subjects: Couplers; Coupling; Infrared spectroscopy; Integrated circuits; Nonlinear optics; Optics; Photonics; Silicon devices; Silicon wafers; Thickness; Waveguides
• ISSN: 0146-9592; 1539-4794
• DOI: 10.1364/OL.449140

Mid-infrared (mid-IR) silicon photonics has been attracting great attention due to its tremendous potential applications in nonlinear optics, ranging, sensing, and spectroscopy. To date, mid-IR silicon devices have usually been developed based on silicon wafers with top-layer silicon thicknesses of hundreds of nanometers. Compared with the thick silicon devices, tens-of-nanometers thin silicon devices can provide giant evanescent-field energy proportions and optical mode areas, being significant for many biochemical sensing and nonlinear optics applications. However, ultra-thin mid-IR silicon devices have seldom been studied due to the difficulty of light coupling. Here, we demonstrated an ultra-thin focusing subwavelength-grating coupler for mid-IR ultra-thin suspended subwavelength-grating-cladding waveguide coupling. The results show that the grating has a maximum coupling efficiency of -7.1 dB at a center wavelength of 2200 nm with a 1-dB bandwidth of ∼115 nm and back reflection of -19.9 dB. We also measured the fiber alignment tolerance of 12 µm for 3-dB coupling efficiency reduction and bending optical loss of 0.25 dB/90°. Our results pave the way to developing mid-IR ultra-thin photonic integrated circuits.