An optical module includes an optical waveguide, at least one beam splitter and a light source. The optical waveguide has a first surface, a second surface and a light incidence surface. An interior angle between the light incidence surface and the first surface is θ. A distance between the first and the second surfaces is T. A refractive index of the optical waveguide is n. Each beam splitter and the first surface have a first intersection point on a reference plane perpendicular to the first surface, and the light incidence surface and the second surface have a second intersection point having a first orthogonal projection on the first surface. A distance between the first orthogonal projection and the first intersection point closest to the light incidence surface is H. An incidence angle of a beam at the light incidence surface is a, and a ≤ sin - 1 ⁢ { n × sin - 1 ⁡ [ 90 ⁢ ° - θ - tan - 1 ⁡ ( H T ) ] } .