Bandpass filter with adjustable bandwidth based on a press-induced long-period twisted holey-fiber grating

A bandpass filter with adjustable bandwidth based on a press-induced long-period grating in a twisted holey fiber is presented. By twisting the holey fiber prior to the application of periodic pressure, each rejection band of the nontwisted induced long-period grating is split into two shifted rejection bands that move further apart as the twist ratio increases. This feature results in a wide bandpass filter with controllable bandwidth. A bandpass filter at 1523 nm with adjustable bandwidth from 15 to 65 nm with near-linear response and insertion loss lower than 0.7 dB is demonstrated. Additionally, the bandpass filter can be tuned over 100 nm.