PROBLEM TO BE SOLVED: To provide a grating coupler which when arranged in an array form can increase integration density and facilitate mutual connection, a grating coupler array, an imaging optical system, an optical scanner, and a laser radar device.;SOLUTION: The grating coupler comprises: an introduction waveguide 16 introducing light; a spot size conversion part 14 having a predetermined width end part connected to one end of the introduction waveguide 16, expanded in a substantially sector form from both ends of the end part, and expanding a spot size of light propagating through the introduction waveguide 16; a diffraction grating part 12 including a plurality of arc-like irregularities formed around a connection between the introduction waveguide 16 and the spot size conversion part 14 and concentrically along a circular arc part of the spot size conversion part 14. A substantially rectangular overall shape is provided by gradually increasing the length of the arc and then decreasing it.;SELECTED DRAWING: Figure 1;COPYRIGHT: (C)2017,JPO&INPIT
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