The invention discloses an optical encoder comprising a mechanical rotation system and a photovoltaic conversion system. The mechanical rotation system consists of an optical grating code plate, a rotating shaft, and a shell. The photovoltaic conversion system includes a lead wire, a positioning column, a point light source, a lens, an array photocell, a wiring circuit board, and a frame. The optical grating code plate is fixed at the rotating shaft fixed inside the shell. The rotating shaft drives the optical grating code plate to cut light from the point light source; the light passes through the lens and then irradiates the array photocell and a voltage signal at a frequency is generated; and the voltage signal passes through the wiring circuit board and then a standard voltage signal is outputted by the lead wire. The photovoltaic conversion system and the frame form a fixed body; and the photovoltaic conversion system is fixed at the shell of the mechanical rotation system by the positioning column.