Fabrication of wide-bandpass filters based on phase-shifted long-period fiber gratings inscribed by focused pulses of CO/sub 2/ laser

We demonstrate the first fabrication of wide-bandpass filters based on phase-shifted long-period gratings inscribed by the mechanism of macro-deformation with focused pulses of CO₂ laser and a point-by-point technique. By introducing the π-phase shift in the middle of the grating with 500 μm of a period-length and with total number of 20 periods, the notch of resonance wavelength at 1318.55 nm of an initial long-period fiber grating is split into two symmetrical notches that are located at 1282.45 nm and 1349.75 nm, respectively, in the transmission spectrum. The passband bandwidth is as wide as 36.55 nm measured at -3 dB from maximum transmission between them, and the resonance strength of those two notches is almost the same as ~-12 dB. The temperature sensitivity is 8.8 pm/°C at a range of 23-190°C. Such fiber grating components could be used as an all-fiber filter in a laser cavity. Long-period gratings with different phase shifts are also investigated with different notches of resonance attenuations. All gratings fabricated are of a compactness to be packaged into fiber-optic based devices.