An optical imaging system includes a birefringent element, a light modulating element, and a polarizer element. The birefringent element is configured for decomposing un-polarized light into first linear polarized light and second linear polarized light under different refractive indexes to respectively form a first focal length and a second focal length in the optical imaging system. The light modulating element is configured for modulating a state of polarization of the first and second linear polarized light in response to control signals. The polarizer element is configured for filtering out one of the modulated first and second linear polarized light for creating a single image.