A fiber optic polarizer is an in-line optical device specifically designed to work with fibers. It is used to polarize or separate linearly polarized light passing through a fiber optic line. These polarizers have several advantageous characteristics including low insertion loss, high stability, compactness and light weight. They usually come with one input port of single mode fiber and one output port for a polarization maintaining fiber. Typically they also contain input and output collimators with a plate polarizer in between. Fiber optic polarizers find applications in fiber amplifiers, integrated optics, interferometric sensors, optical fiber based test equipment, coherent detection systems, and more.