The distributed feedback laser is different from the Bragg Grating, which belongs to the side emitting semiconductor laser. At present, DFB lasers are mainly semiconducting materials, including GaSb, GaAs (GaAs), indium phosphide (InP), zinc sulfide (ZnS), etc. The largest feature of DFB laser is a very good monochromatic (i.e. spectral purity). Its line width can be generally within 1MHz and has a very high side mode rejection ratio (SMSR), and can be up to 40-50dB at present.