Extremely deep long-period fiber grating made with CO2 laser

We report on the realization and tuning of a long-period fiber grating-based filter, which is made in a standard telecom optical fiber, with a resonant attenuation of more than 60 dB. This is, to our knowledge, by far the highest published value. The realized filters satisfy requirements of applications which are extremely demanding in terms of the resonant depth or require an exact pi-phase shift at the resonance.