Patent ID: 8514309

Claim:
A solid state image sensor comprising: a pixel unit having a substrate including therein a photoelectric conversion section and an optical waveguide arranged on an incident side of the substrate so as to guide an incident light converted into a guided mode of the optical waveguide and being propagated through the optical waveguide to the photoelectric conversion section, wherein the optical waveguide has a mode conversion section for changing a propagation state of an incident light, and wherein the image sensor satisfies a requirement of V<p, wherein V is a normalized frequency of the mode conversion section for a wavelength of the incident light and p is the number pi, and also satisfies a requirement of formulas (1) and (2) or of formulas (1) and (3): |cos(β0 ·L )|−1.5|cos(β1 ·L )|≧0 (1) α·cos(β0 ·L )·cos(β2 ·L )≧0 and |cos(β0 ·L )|−9|cos(β2 ·L )|≧0 (2) α·cos(β0 ·L )·cos(β2 ·L )<0 and |cos(β0 ·L )|−1.5|cos(β2 ·L )|≧0 (3) where β0, β1 and β2 are propagation constants or zero-order, first-order and second-order guided modes, respectively, for propagation of the incident light through the optical waveguide at a cross section taken along a central axis of the optical waveguide, L is a distance between a substrate-side end of the mode conversion section and the substrate and a is a factor that is 1 when a refractive index of a portion at and near a central axis is higher than a refractive index of a portion at surrounding areas in the mode conversion section and is −1 when a refractive index of a portion at and near a central axis is lower than a refractive index of a portion at surrounding areas in the mode conversion section.