An optical device may include a first surface having a shape of a quadrangle; and a second surface disposed to be opposite to the first surface and comprising a convex curved surface. The optical device has an aspherical shape in a cross-section taken along a diagonal direction of the quadrangle and has a semicircular shape in a cross-section taken along a direction connecting a central portion of a first side of the quadrangle and a central portion of a second side opposite to the first side of the quadrangle. In a cross-sectional view of the optical device, the second surface is continuously varied between the semicircular shape of the cross-section and the aspherical shape of the cross-section.