Analysis and fabrication by electric-arc technique of high performance bandpass filters based on phase-shifted long period fiber gratings

摘要

Bandpass filters based on π—phase-shifted long-period fiber grating have been numerically simulated and experimentally fabricated by the electric-arc technique. Calculations and numerical simulations, based on coupled mode theory associated with the F-matrix method, have shown that the isolation of lateral rejected bands is maximum when the final length of the grating is optimised and the π-phase-shift is inserted when the transmission at the desired resonance wavelength is -6.9dB. Two π-phase-shifts are introduced at optimised positions to obtain a large bandwidth of the badpass filter. We have fabricated the first bandpass filters that have lateral rejected bands isolation > 20 dB and very large flat-top bandwidths (FWHM =19.5 nm) around 1538 nm peak. The fabricated filters are characterized by a very low insertion loss ( < 0.5 dB).