All-fiber bandwidth-tunable band-rejection filter based on a composite grating induced by CO2 laser pulses

We propose an all-fiber band-rejection filter with a tunable bandwidth, which is realized by putting a normal long-period fiber grating in series with a rotary long-period fiber grating written in a twisted single-mode fiber by CO2 laser pulses. Bandwidth tuning is achieved by applying torsion to the composite grating. Our experimental filter shows a bandwidth tuning of similar to 16.3 nm at a rejection level of similar to 15 dB and a polarization-dependent loss lower than similar to 0.9 dB. (C) 2009 Optical Society of America