Ball lens is a short focal length glass ball that can obtain the desired focal length by selecting different material refractive index and spherical curvature. In the field of fiber communication,TO-CAN can be made by using a ball lens and a metal tube shell, which can be combined with a laser (LD) to couple the light into fiber. Ball lens is also used to collimate the divergent beam emitted by lasers into parallel beams or couple parallel beams into a detector (PD).