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 μm. The measured output coupling efficiency was 40%, whereas the theoretical prediction was 60%.
© 1999 Optical Society of America
(130.1750) Integrated optics : Components
(130.2790) Integrated optics : Guided waves
(230.1950) Optical devices : Diffraction gratings
(230.3120) Optical devices : Integrated optics devices
(230.7370) Optical devices : Waveguides
Shogo Ura, Takayoshi Fujii, Toshiaki Suhara, and Hiroshi Nishihara, "Efficiency-Enhanced Third-Order Grating Coupler," Appl. Opt. 38, 3003-3007 (1999)