A rotary encoder and an optical wheel for the rotary encoder are provided. The rotary encoder further includes a light source module, a code plate and an optical sensor module. The light source module is coupled with the code plate. The optical wheel is rotary, and has imaging elements arranged annularly; at least one of the imaging elements is coupled with the code plate. The optical sensor module is coupled with at least one of the imaging elements. The light source module emits lights to the code plate, and the lights passing through the code plate forms an image which is then transmitted to the optical sensor module via the imaging element. When the optical wheel rotates, the image moves accordingly. The optical sensor module senses that the image moves. A method for generating a zeroing signal of a rotary encoder and a liner encoder are also provided.