title: Efficiency-enhanced third-order grating coupler.
abstract: A third-order grating coupler with a grating period 3 times that of a first-order grating is discussed in terms of efficiency enhancement. A reflection film is integrated between the optical buffer layer and the substrate beneath the grating-guiding core. The power-distribution ratio for each diffracted wave depends on the optical buffer layer's thickness because of interference effects. The thickness is determined to suppress first- and second-order diffraction and to enhance the power distribution to the output air-radiation wave generated by third-order diffraction. A demonstrator was designed and examined at a wavelength of 0.82 microm. The measured output coupling efficiency was 40%, whereas the theoretical prediction was 60%.
authors.affiliation: Department of Electronic Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-Oka, Suita, Osaka 5650871, Japan. ura@ele.eng.osaka-u.ac.jp
authors.forename: S
authors.initials: S
authors.lastname: Ura
authors.forename: T
authors.initials: T
authors.lastname: Fujii
authors.forename: T
authors.initials: T
authors.lastname: Suhara
authors.forename: H
authors.initials: H
authors.lastname: Nishihara