Abstract: An optical encoder disk comprising an opaque disk, an outer track adjacent a peripheral edge of the disk, an inner index track defined by a first pattern of radial light-blocking elements subtending an arc within an annular band interposed between the outbound track and an axis of the disk, and an opaque support pattern of non-radial elements located within the annular band outside of the arc in which the index track is located formed of substantially non-radial elements. The inner index track further includes pattern apertures formed through the disk between the light-blocking elements so that light emitted on one face of the disk passes through the pattern apertures and falls upon photodetectors located adjacent an opposite face of the disk.