The method of fabricating phase-shifted fiber Bragg grating (PSFBG) that does not need a phase mask by femtosecond laser (fs) post-processing is demonstrated. A central region of standard single mode fiber Bragg grating (FBG) is irradiated by fs laser. A rotating jig is designed to hold and rotate the fiber when the fiber is irradiated by laser. The bandwidth of transmission peak of PSFBG and the transmission loss is growing with increasing of laser energy. PSFBG produced by this method is simple, fast and reproducible.
Fabricating of phase-shifted fiber Bragg grating (PSFBG) by a femtosecond (fs) laser postprocessing of standard single mode fiber Bragg grating (FBG) without phase mask is demonstrated. A central region of grating is irradiated by an fs laser assisted with a rotating jig, which produces a π phase shift at the central region of the grating and forms a π phase-shifted FBG. The procedure is simple, fast, and has good reproductivity. The bandwidth of transmission peak of PSFBG grows with an increasing amount of laser energy or length of irradiation and decreasing of translation speed; the transmission loss decreases with increasing irradiation length. Additionally, the repeatability of fs postprocessing and temperature stability of PSFBG were investigated.
Magnetic sensors utilizing direct magneto-optic field coupling in an optical fiber Bragg grating (FBG) is proposed and demonstrated. The FBG’s cladding is micro-machined into micro-curvities aided by femtosecond laser, and coated with TbDyFe, magnetic sensing element. Number of micro-curvities and laser energy under a laser beam were optimized during FBG micromachining and dramatically improved sensor performance. Six-micro-groove sensor is four times more sensitive as compared to non-micro-grooved standard FBG sample. The effect of 18 mW laser pulse power impacted magnetic sensitivity of magnitude 0.6 pm/mT as compared to 0.14 pm/mT on non-microstructured standard FBG sensor. The depth of the deposited magnetostrictive film was measured as ~5 μm.
Fabricating microstructures into the cladding of fiber Bragg grating, the FBG sensors will have wider applications in magnetic field measurement or gas sensing. In present paper, we regulate the physical feature of FBG by ablating single or cross spiral micro-trench with femtosecond laser. The influences of different processing parameters on M-FBG (microstructured FBG) have been investigated. The waveform variations and its controlling method have been discussed. It is shown that, the central wavelength shift enlarged with increasing of the laser energy, or decreasing of scanning speed. Finally, a cross spiral type M-FBG magnetic field probe and a temperature probe are also demonstrated.