45° tilted fiber grating based in-fiber linear polarizer and applications

In-fiber optical devices have low insertion loss, high reliability and compatibility with the fiber systems and transmission network. They are different from the in-line components that are typically produced by coupling the light in and out of the optical fiber to and from some bulk or integrated optical waveguide device, therefore, inducing high insertion loss. An in-fiber optical polarizer is a key component for integration of optical fiber system. The fiber grating technology has been vastly developed in the last two decades. It is a mature technique to achieve in-fiber optical components (reflection mirror, dispersion compensator, mode coupler et al.) with simple fabrication process, freely designed operating wavelength and no fiber type limitation. We have reported the 45° tilted fiber grating (45°-TFG) is an ideal in-fiber linear polarizer, which is based on Brewster's law. The polarization extinction ratio achieved by a 48mm long 45° TFG is exceeding 50 dB at the peak value and more than 40 dB over 50nm wavelength range. Compare with the otherin-fiber polarizers technique, such as anisotropic absorption, chiral fiber grating, and polarizing fiber based structures, the 45°-TFG based polarizers have many advantages, such as low cost, simply fabrication process, no limited by the fiber type, arbitrary operation wavelength, high polarization extinction ration, linear polarization state preservation and high handling power. Moreover, by using 45°-TFGs, we can achieved an all-fiberLyot filter (AFLF) — an in-fiber polarization interferometer, an all fiber mode locking fiber laser system, in-fiber power taping device and optical spectrometer.