Fiber nanogratings induced by femtosecond pulse laser direct writing for in-line polarizer.

Self-organized fiber nanogratings (FNGs) induced by femtosecond pulse laser direct writing are demonstrated in optical silica fibers for the first time. Ge doping in the silica fiber core plays an important role in the formation of nanogratings. Negative changes in refractive index with sawtooth fluctuation and strong birefringence of FNGs were investigated by an optical fiber refractive index analyzer and a crossed polarization microscope, respectively. The polarization features of FNGs were characterized by the Mueller matrix analytical method and in-line polarizers based on FNGs were fabricated. FNGs are promising integrated components because of their prominent properties of polarization and salient compatibility with most fiber-optic systems.