Patent ID: 9549093
Date: 2017-01-17
CPC Classifications: G02B,H04N

Claim:
1. A light guide for use in an image reading apparatus, the light guide extending in a predetermined direction and comprising: a reflecting surface being parallel to the predetermined direction; an emitting surface; and a prism configured to reflect light to the emitting surface, the prism including a plurality of asperities formed on the reflecting surface; wherein when the light guide is viewed from a first direction orthogonal to the reflecting surface, at least one of the plurality of asperities includes a portion parallel to a predetermined curve; when the light guide is viewed from the first direction orthogonal to the reflecting surface, the plurality of asperities include portions parallel to predetermined curves; and when the light guide is viewed from the first direction, the predetermined curves vary gradually in curvature as a distance from an end of the light guide in the predetermined direction increases and the distance from another end of the light guide in the predetermined direction decreases; when the light guide is viewed from the first direction, each of the predetermined curves is an arc having a center of curvature on a point toward a center of the light guide; and a curvature of the predetermined curve for a third asperity of the plurality of asperities is smaller than the curvature of the predetermined curve for a fourth asperity of the plurality of the asperities, the fourth asperity being adjacent to the third asperity and being farther from the center of the light guide than the third asperity.