The invention belongs to the technical field of optics, and provides a collimator. The collimator comprises a polarization-maintaining optical fiber and a multimode fiber or a core-free optical fiber welded to one end of the polarization-maintaining optical fiber, wherein the tail end of the multimode fiber or the core-free optical fiber is fused into a spherical micro lens; the center axis of the spherical micro lens is collinear with the center axis of the multimode fiber or the core-free optical fiber; the length from a vertex of the spherical micro lens to the melting point of the multimode fiber or the core-free optical fiber is equal to the focal length of the spherical micro lens. Compared with the conventional composition of an optical fiber head and a lens, the collimator disclosed by the invention is not required to be clamped or ground, and is not influenced by a clamping size, and even the size is smaller; in addition, the polarization-maintaining optical fiber is welded to the thicker multimode fiber or the core-free optical fiber, the output light beam can be expanded, the light spot on the spherical micro lens is greater than the diameter of the polarization-maintaining optical fiber, so that the collimator can bear the power higher than the power at the output end of the polarization-maintaining optical fiber, namely the power is higher than the bearing power of the conventional collimator, and the high-power resistance of an on-line polarizer can be improved.