title: Broadband focusing grating couplers for suspended-membrane waveguides.
abstract: We propose and demonstrate broadband focusing grating couplers for suspended-membrane waveguides on silicon-on-insulator both in near-infrared (near-IR) and in mid-IR wavelength range. Finite-difference time-domain simulation predicts ∼100  nm 3 dB bandwidth with -1.7  dB coupling efficiency for an apodized grating in near-IR. -3.5  dB maximum coupling efficiency and ∼90  nm 3 dB bandwidth are realized experimentally. In mid-IR, -5.5  dB maximum coupling efficiency from a uniform focusing grating is measured at 2.75 μm, and ∼500  nm 3 dB bandwidth is predicted theoretically.
authors.affiliation: Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong, China. zzcheng@ee.cuhk.edu.hk
authors.forename: Zhenzhou
authors.initials: Z
authors.lastname: Cheng
authors.forename: Xia
authors.initials: X
authors.lastname: Chen
authors.forename: Chi Yan
authors.initials: CY
authors.lastname: Wong
authors.forename: Ke
authors.initials: K
authors.lastname: Xu
authors.forename: Hon Ki
authors.initials: HK
authors.lastname: Tsang