High contrast ultrashort pulse written transmission filter based on Moiré fiber grating

We present narrowband and high contrast ultrashort pulse written phase shifted fiber Bragg gratings (FBG). The phase shift in the fiber was implemented by overlaying two spectrally slightly differing gratings, resulting in a Moiré grating. They were realized using the phase mask scanning technique, providing a reliable and reproducible inscription process. The different grating periods were implemented by controlling the applied strain on the fiber during inscription which was monitored spectrally. We present the results of single and multiple phase shift gratings with passband bandwidths as low as 4 pm and contrasts as high as 42 dB.