A filter based on a Mach-Zehnder interferometer (MZI) formed by cascading a pair of long period fiber gratings (LPFGs) written by CO 2 laser in a twisted single mode fiber is proposed. The transmis sion spectrum of the filter is tuned by modifying the bending curvature of the MZI, and thus wavelength tun ing is achieved. And a tunable erbium doped fiber (EDF) ring laser employing the filter as a wavelength selection component is experimentally demonstrated. The laser can be tuned continuously from 1573.05 to 1595.75 nm with a side mode suppression ration of ~50 dB over the total tuning range.

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 CO(2) laser pulses. Bandwidth tuning is achieved by applying torsion to the composite grating. Our experimental filter shows a bandwidth tuning of approximately 16.3 nm at a rejection level of approximately 15 dB and a polarization-dependent loss lower than approximately 0.9 dB.

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